[HN Gopher] US companies are producing heat pumps that work belo...
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US companies are producing heat pumps that work below -20F
Author : jbrins1
Score : 212 points
Date : 2022-12-28 13:19 UTC (9 hours ago)
(HTM) web link (electrek.co)
(TXT) w3m dump (electrek.co)
| sneezesForAttn wrote:
| We just installed a Solstice Inverter Extreme[0] before the the
| storm hit. The low in our area was -24F. The heat pump is
| advertised to work at -22F, but was still heating the house at
| the low. Efficiency and capacity are reduced with as the
| temperature drops. We have backup resistive heat in the buffer
| tank of our hydronic setup. It is early but we are happy with the
| performance during this first cold snap.
|
| [0] https://www.spacepak.com/solstice-inverter-extreme
| maxerickson wrote:
| What's the rough cost?
|
| (obviously there will be lots of variation based on the
| complexity of the install, but the ballpark is still
| interesting)
| sneezesForAttn wrote:
| About $10k for the heat pump. NPV is positive for 10 years
| compared to a propane boiler. This doesn't include
| installation, but it is doable for the advanced DIY
| homeowner.
|
| The entire system cost $25k + installation. Not cheap, but in
| our climate we heat 7+ months and it is worth it. The
| extended federal tax credits help, but our state does not do
| anything in terms of rebates.
| DIVx0 wrote:
| I recently bought some land in Minnesota on a lake. I really want
| to do a 'no compromise' off-grid setup. Water and septic wont be
| a problem but I am worried about the heat.
|
| I plan to install a huge solar array with a battery house. I'd
| like to run everything off electric, including the heat.
|
| I am in early days of thinking about this and I have time to
| plan. Anyone have insights on electric heat in ultra cold
| environments? I assume I can simply scale up a solar array and
| battery capacity to meet needs (dead of winter, with spans of
| cloudy days). The only fossil fuels I want on property are for
| equipment and if I must have it, a backup NG generator.
|
| I don't know anyone who runs heat pumps in MN, I'm sure there are
| some but most folks are burning NG or wood pellets. Electric heat
| seems relegated to secondary needs, like base boards or heated
| floors.
|
| *edit cloudy
| jupp0r wrote:
| If you do some back-of-the-envelope math on this, you'll notice
| that this will be cost prohibitive to implement using
| batteries.
| mrinterweb wrote:
| I have a Mitsubishi Hyper Heat, and it operates to -13f, which
| would be unheard of in Western Oregon (where I live). So long
| as your house is well insulated, you'd likely be fine with a
| heat pump. Pay attention to R-Value for insulation, but if you
| choose the right materials, that goes a long way for heat
| storage.
|
| I know there exceptions in Minnesota where it can get
| considerably colder than -13f, but I don't know how long those
| super low temps are sustained. You would definitely need some
| sort of emergency heating system. An outdoor propane tank (the
| larger variety) and a propane heater would likely do the trick
| as an emergency backup. Not great for air quality in your
| house, but plenty of people use that as their normal heating.
| inthepipe wrote:
| [dead]
| zamalek wrote:
| Look up ground-sourced heat pumps. You store your heat in soil
| during the summer, and draw it out in the winter.
| vitaflo wrote:
| I want this someday too (also live in MN). Wood pellets or just
| a wood burner are your best bets for secondary heat. I grew up
| in WI and we only had electric base boards and a wood burner
| (then pellet stove). Get the house up to 85 before bed and by
| morning it's in the high 50's and start the fire again. You
| need to be ok with fluctuating temps to really make it work.
|
| You mention cloudy days but the one positive about our brutally
| cold winters is that when it's below zero it tends to be sunny
| out. If you set up your solar to extract as much sun as
| possible during these times, as well as build your house with
| large south facing windows with stone or concrete flooring you
| will not need to heat the house much during even the coldest
| days (solar radiation will heat the house and the concrete
| flooring will release what heat it gained in the evening).
| Qwertious wrote:
| Keep in mind that you don't need a traditional electrical
| battery for heat - storing heat directly is _extremely_ cheap,
| you just need insulation and thermal mass (i.e. sand /rocks,
| any old crap will do). There are a fair few systems that use
| easy summer-solar to generate heat, store it for months at a
| time and then release the heat in winter.
|
| It scales up really well thanks to the cube-square law, which
| is a euphemistic way of saying it's hard to make a viable
| system that's really small. But if you're off-grid because
| you're in the middle of nowhere, then you can spare a few
| square meters anyway.
| [deleted]
| nashashmi wrote:
| Can they work in pair with co2 capture? Assuming neg 20 deg is
| co2 liquid point ?
| londons_explore wrote:
| The needs of the homeowner and the needs of the grid are at odds
| with one another here.
|
| The electricity grid wants the highest possible efficiency on the
| coldest days, so that they can serve as many users as possible
| without building more infrastructure.
|
| The homeowner wants the _average_ efficiency to be as high as
| possible over the whole season, to reduce heating /cooling costs.
| They don't care if one or two really cold days have bad
| efficiency, as long as the system has sufficient output to keep
| the house comfortable.
|
| Someone needs to use laws or incentives to align those two -
| because if every home owner used one of todays heat pump systems,
| then the electricity grid would fail on the coldest days of the
| year.
| itake wrote:
| If my power goes out (due to ice storms or hurricanes) and I
| need to rely on a local power supply (battery, solar panels,
| gas generator), I would like my AC to be as efficient as
| possible.
| londons_explore wrote:
| I didn't explain clearly... AC systems don't have a single
| efficiency number - they have different efficiencies
| depending on the indoor temperature, the outdoor temperature,
| and the number of kilowatts you want delivered.
|
| You can generally design any AC system to work efficiently at
| any specific combination of those variables - but if any
| variable deviates far from the optimum design point,
| efficiency will drop.
|
| So the real question is, not "I want an efficient system",
| but "I want an efficient system when it is 20F outdoors,
| because that's the temperature most of the year".
| jnsaff2 wrote:
| Are there even heat pumps where efficiency goes down when the
| delta-T decreases?
| londons_explore wrote:
| Yes. If the cold side gets too hot, the pressure on the
| compressor input gets too high, which means the compressor is
| doing far more work with every stroke - and input electrical
| power goes up massively. The motor overheats and the thermal
| cutout stops it. When the motor is cutting in and out
| efficiency goes way down.
|
| This is an issue with fridges. When you buy a new fridge and
| first turn it on, it's called a 'pulldown'. The compressor
| gets far hotter than it ever normally gets in normal
| operation. Most fridges are only rated for 3 pulldowns in
| their lifespan - and if you do more than that and the fridge
| fails, they'll claim it isn't in warranty anymore. And in
| modern fridges, the software keeps track of how often so they
| can deny the warranty claim too...
| the-alchemist wrote:
| If you want an (entertaining) deep dive into heat pumps, I can
| recommend Technology Connection's
| https://www.youtube.com/watch?v=43XKfuptnik and its followup,
| https://www.youtube.com/watch?v=MFEHFsO-XSI
| moffkalast wrote:
| Do we really need heat pumps that work that far into the
| negative? You can always turn on an internal resistive heater to
| compensate after all.
|
| Not quite something you can do on the other end though, when
| trying to cool with exceptionally high ambient temperature. It's
| such bullshit that the physics of this universe does not allow
| for resistive cooling.
| eppp wrote:
| Resistance heat is extremely expensive to operate. Burning
| something is cheaper.
| zdragnar wrote:
| The problem is that if everyone comes off of fossil fuel heat
| and switches to heat pumps, you need a grid that is capable of
| delivering enough eletricity to power simultaneous resistive
| heating to every house... because every house is going to need
| resistive heating at the most dangerous time to not have any
| heat at all.
|
| These cold snaps tend to also coincide with extreme winds and
| other weather events that can take out power lines, so a
| stressed grid just compounds the issue.
| jupp0r wrote:
| On top of that, it's also the time when you need the most
| energy for heating because it's the coldest.
| EVa5I7bHFq9mnYK wrote:
| My AC runs just fine at -15C (+5F), the problem is when
| temperature swings between zero and sub-zero, it causes formation
| of the ice in the outer unit which can break the fan.
| kwhitefoot wrote:
| Some heat pumps designed for low temperatures have heaters to
| avoid the freezing of condensation.
| lizknope wrote:
| I'd like to see an efficiency curve of this heat pump at -20F,
| 0F, +20F, +40F
|
| I have a heat pump that can be used for both cooling an heat
| along with a natural gas burner. The installer has set the system
| to use the heat pump at 40F and above and switch to natural gas
| at below 40F below based on the efficiency of the heat pump
| dropping at low temperature.
|
| My heat pump is a SEER 18 unit primarily for cooling in the US
| south so I'm sure a heat pump designed specifically for northern
| cold climates will be more efficient than mine at low temps but
| I'd like to see how much.
| newZWhoDis wrote:
| Well that installer cutoff was likely waaaaay too high. Your
| heat pump should be fine to 30F, maybe even 25F before needing
| gas.
|
| Modern systems are 24 SEER and good to -5, and these research
| units take that to the next level.
| bowow wrote:
| Unfortunately only the very top-of-the-line (very expensive)
| variable speed compressor units are rated for anything close
| to 24 SEER / -5F (unless that's what you meant by modern
| systems).
| rudedogg wrote:
| > Well that installer cutoff was likely waaaaay too high.
| Your heat pump should be fine to 30F, maybe even 25F before
| needing gas.
|
| The parent post was saying it's cheaper to use natural gas at
| those temps, so that's why the installer did the cutoff
| there.
|
| You can look at COP numbers for heat pumps here:
| https://ashp.neep.org/#!/product_list/
| Majromax wrote:
| > Well that installer cutoff was likely waaaaay too high.
| Your heat pump should be fine to 30F, maybe even 25F before
| needing gas
|
| One possibility might be that the unit lacks de-icing
| circuitry. If that were cut for cost optimization, the unit
| would still work fine for cooling and for moderate-
| temperature heating, but anywhere near 30F it would ice up
| and stop working.
| sokoloff wrote:
| > "additional efforts are needed to address common technical and
| market barriers to wider adoption by consumers - which include
| performance at temperatures of 5F and below, installation
| challenges, and electricity grid impacts during peak demand
| periods."
|
| There are definite market barriers at play. In my house in New
| England, I tried to replace my aged boiler with an air-to-water
| heat pump (after carefully verifying, via experiments during a
| cold week in February, that my heat distribution would indeed
| work fine at a supply of 130degF). Only one company was even
| willing to come out and provide a quote and their quote was
| around 2.5x the costs of "put another boiler in", such that the
| payback period would be "literally never".
|
| If, after doing the research to find out about them and
| specifically seeking one out, I couldn't manage to make an air-
| to-water heat pump make sense, I doubt that very many of them are
| being sold. I suspect it's one of those items that, if more were
| sold, more firms would sell/install them, bringing the costs into
| the realm of economically reasonable (and lowering the risk of
| having a difficult-to-support heating plant in the decades to
| come).
| lizknope wrote:
| I watch the PBS show This Old House which takes place in the
| Boston area. The plumber / HVAC guy Richard Trethewey is a fan
| both ground ("geothermal") and air source heat pumps including
| the air source heat pumps that work at 0F and heat water for
| radiant floor heating. I'm surprised that more companies aren't
| doing it there.
| maxerickson wrote:
| The majority of their projects are pretty high end (and they
| tend to want to demonstrate new technology, because it's more
| interesting).
| throw0101c wrote:
| For the 'project homes', perhaps, but if you're going to go
| through the effort of building new or re-doing an entire
| structure, you might as well use the latest and greatest
| stuff/practices/code.
|
| They also have many segments of smaller DIY jobs for
| simpler fixes/maintenance, e.g.:
|
| * https://www.thisoldhouse.com/plumbing
| panzagl wrote:
| The 'cast' of 'This Old House' is mostly MIT MechE grads who
| figured out they could make more money doing renovations for
| Route 128 techies than burning themselves out working at
| their companies.
| [deleted]
| throw0101c wrote:
| Oh yeah, Richard Trethewey and Tom Silva are definitely MIT
| guys:
|
| * https://www.thisoldhouse.com/21071273/richard-trethewey
|
| * https://www.thisoldhouse.com/21071309/tom-silva
|
| * https://www.thisoldhouse.com/cast
| panzagl wrote:
| Well, they've done episodes like this:
| https://www.thisoldhouse.com/season-20-ask-
| toh/23197052/s20-...
| throw0101c wrote:
| Advanced technology being developed at advanced research
| labs: who would have thought?
|
| But that doesn't change the fact that hosts are mostly
| 'regular folks' in the trades that hook up a bunch of
| wiring and pipes (or glue/nail/screw together a bunch of
| wood).
| panzagl wrote:
| I had 'cast' in quotes for a reason- I was half thinking
| of Norm (though I don't think he went to MIT) and more of
| the various sub contractors that filter through the show
| (some of which seemed to be thinly disguised product
| reps). Still, you can't deny they were higher quality
| outfits than anything most of us are likely to run into.
| caycep wrote:
| I haven't watched since a kid w/ the Bob Villa days....
| ngetchell wrote:
| No they are mostly second and third generation trades
| people.
| laidoffamazon wrote:
| I mean that did describe Car Talk
| ableal wrote:
| > their quote was around 2.5x the costs of "put another boiler
| in", such that the payback period would be "literally never".
|
| Doesn't that depend on the costs of both energy sources?
|
| Last year I made a similar choice, albeit at smaller scale,
| just for one water heater. Picked an electric heater with heat
| pump, also cost 2.5x more than plain electric, but 1/3 the
| energy cost. It will take a few years to pay back ...
| sokoloff wrote:
| > Doesn't that depend on the costs of both energy sources?
|
| Yes, it depends on the costs and efficiencies of the
| competing energy sources, the difference in capex, the annual
| building heat load, the projected lifespan of each source,
| annual maintenance costs, and the interest rate.
| linuxftw wrote:
| I recently spoke to a well driller that also does geothermal
| well drilling. He was telling me that the systems are more or
| less obsolete at this point, as the air-to-air units have such
| a high SEER rating that the ground loops really will never pay
| off.
| benmanns wrote:
| Is geothermal any quieter? I was assuming the ground loop
| pump would be quieter than the air-to-air fan.
| sokoloff wrote:
| There's no outside noise in a ground-source system (for all
| practical values of noise: it's just flow in insulated
| pipes). The pumps are nearly inaudible inside the
| mechanical room as well.
|
| Inverter-based air-source outdoor units are nearly
| inaudible during any time when your neighbors are likely to
| have their windows open. When the weather is uncomfortable
| enough to have the units need to run at high-speeds, they
| are no longer inaudible, but the neighbors are likely to
| have their windows closed.
| zacharycohn wrote:
| I'm looking at a system now that is 45 decibels - 10db
| quieter than my robovacuum which is one of the quietest in
| the market.
| implements wrote:
| What attracted me to geothermal was the year round
| availability of 50F water - easier to extract winter heat at
| that temperature, and you could create a simple fan /
| radiator ducted air cooling system for the summer. The latter
| would actually store summer heat in the ground, and could be
| powered purely by solar.
| Bedon292 wrote:
| I have been doing a bunch of research into geothermal
| recently and this doesn't seem to match with what I have
| seen. But it probably also varies a lot by location and such.
|
| They appear to still be about twice as efficient as an air to
| air one, and have less parts and maintenance (no outside unit
| to deal with). Yes the initial install is a lot higher
| because of the drilling but that should last for decades. In
| the US there is also 30% rebate at tax time which helps cut
| the costs down a bunch too.
| linuxftw wrote:
| You're looking to spend at least $30k if you need a
| vertical system, probably a lot more. And from what I
| understand, they ground loops inevitably don't reach their
| expected lifespan, so you'll be drilling new holes sooner
| than later.
|
| If you live in a very cold climate, I suppose with tax
| credits it could make some sense. For most people, AC +
| Natural gas is the cheapest way to go.
| dashundchen wrote:
| Was it a company that also did gas boilers?
|
| If it's not a company that solely does heat pumps, I have heard
| a lot of contractors will give outrageous estimates because gas
| is simpler for them and they don't want to do it without the
| huge markup.
|
| I had ground source heat pump installed with vertical wells in
| a city by a dedicated geo installer. The cost with tax credits
| came out not much more than a high end gas furnace and water
| heater. Going airsource would have been even more cost
| competitive, especially with the federal tax credits in place
| starting in 2023.
| sokoloff wrote:
| They did. To (only partially) guard against that, I made it
| clear that I wouldn't be hiring them to hang a gas boiler.
| (That still allows them to prefer someone else's gas boiler
| job over my air-source job, but at least prevents me bidding
| against myself.)
|
| And there definitely would be more labor, more piping, and
| more electrical work to switch to an ASHP; that's part of the
| market forces problem that is hard to overcome with anything
| other than large price increases for gas or larger direct
| subsidies for switching.
| CoastalCoder wrote:
| My house uses a heat pump + oil-burning furnace. It gives a
| pretty good combination of efficiency, and ability to handle
| really cold weather.
| toomuchtodo wrote:
| I think this is most of the way to what the future looks
| like: a high efficiency heat pump with cogeneration, so you
| can still burn propane or natural gas for heat and limited
| power to drive the heating system in an emergency (and if you
| don't have gas service to the premises, you have either a
| propane tank [1] or an exterior outlet to hook up outside).
| You must have a solution for when utility power is down for
| substantial periods of time.
|
| During the winter storm that just passed, a friend in the
| Midwest called that their house had no power and was rapidly
| cooling. The utility could provide no ETA to resolution. I
| walked them through (over the phone) safely enough
| backfeeding enough power from a gasoline generator (outside,
| with the extension cord run through a basement escape window)
| into their furnace circuit to bootstrap the furnace (and run
| the blower fan) to keep the house warm so that the pipes
| didn't freeze and burst. If the HVAC system had had a small
| battery and some way to generate power from the heat it was
| burning, the gasoline generator would've been unnecessary.
| Perhaps an integrated thermoelectric generator [2]? A standby
| generator isn't financially practical for most folks ($6k +
| install).
|
| (EDIT: to the safety folks out there possibly concerned, the
| furnace breaker and main breaker were tripped, and the meter
| was pulled to prevent any chance of harm to electrical
| linemen from inadvertently energizing the utility line; take
| no chances with safety, do not attempt this at home)
|
| [1] https://www.amerigas.com/about-propane/propane-tank-sizes
|
| [2] https://patents.google.com/patent/US5427086A/en
| throw0101c wrote:
| > _A standby generator isn 't financially practical for
| most folks ($6k + install)._
|
| An Honda EU2200i generator costs US$ 1400 (and less
| expensive generators can probably be found):
|
| *
| https://powerequipment.honda.com/generators/models/eu2200i
|
| You also need an external plug, a cable going from that
| plug to a sub-panel, and a line going from the sub-panel to
| the main panel with an interlock device for safety, if you
| wish to avoid running extension cords.
|
| There are dual-fuel generators that can also use either
| gas/petrol or propane, and some tri-fuel generators that
| could also be connect to a natgas pipes (and conversion
| kits that can be added to propane-capable generators).
| phil21 wrote:
| The Honda EU2200i can be aftermarket modded to run tri-
| fuel. I did it to mine just in case, and currently have
| it set to run propane. A simple swap of a small part will
| let it burn natural gas instead.
|
| I also like that I don't have gasoline to deal with - I
| can stock up a 20lb propane tanks and generally forget
| about it. Rotating gas is a giant pain if you keep enough
| on-hand for an outage of any appreciable amount of time.
| toomuchtodo wrote:
| Would you mind sharing a link to the part you mentioned?
| sokoloff wrote:
| https://www.amazon.com/Grenergy-Gasoline-Conversion-
| Generato...
| phil21 wrote:
| https://www.hutchmountain.com/products/honda-
| eu2200i-propane...
|
| If you are at all handy this is probably a 30 minute job,
| it involves cutting a single hole for the propane tank
| connection and otherwise can be done with a screwdriver.
|
| It's been reliable for me going on 4 years now - although
| I only really have run the generator for maybe 100 total
| hours since then.
|
| I haven't looked for some time, but there are also other
| kits on the market. I those these guys due to reputation
| on forums, and how clean it is to install.
| mindslight wrote:
| The problem is that while all that electrical work is a
| weekend project for a DIYer, it's quite expensive to have
| a professional do it. So then you start bundling things
| (since I'm already paying thousands, maybe I'll just
| splurge for that Generac with the auto tranfer switch...)
|
| (FWIW, I believe there is an aftermarket propane
| conversion kit for the EU2200i. Converting a gasoline
| engine to run on propane is straightforward)
| sokoloff wrote:
| For others interested in preparing for a situation like
| this, here's a video laying out in reasonable detail what
| to do.*
|
| https://www.youtube.com/watch?v=1JNuovFpCpQ
|
| * I don't like that they skipped putting a bushing or an NM
| clamp on the back of the box into the furnace, but
| otherwise the video looked sound when I watched it a couple
| weeks ago.
| jchw wrote:
| I've been waiting to do this in the event of a power
| outage; that said, I'm really curious what the current
| draw of my furnace blower will wind up being. There is a
| label that suggests it has a peak draw of 8.5A, but that
| seems like a lot. Still, it seems like a nice backup plan
| in the event of an outage, even if I only have a couple
| kWh worth of battery storage.
| a9h74j wrote:
| Many furnaces use third-party controller boards with
| well-known suppliers. You might find in the furnace
| manual that there are different wire-to-board
| permutations to allow different fan (interior
| recirculating blower) speeds. From home testing a few
| years ago, I recall RMS currents 50%-80% of peak rated
| draw, but could be mistaken.
| mikeyouse wrote:
| What's the model number of your furnace / blower? I've
| been doing a ton of research in this area as I'm
| remodeling my place and have several furnaces and duct
| loops to deal with.
|
| From what I've seen so far, unless your unit is super
| old, the 8.5A is almost certainly just a 'peak' startup
| current that's overstated as well. Your blower should say
| something like "1/3 HP" and from there it's
| straightforward conversion of 1HP = ~750W so a 1/3HP
| would be 250W. On a 120v service, that's 2 Amp. With
| maybe 15% efficiency loss, at peak speed, the blower
| motor wouldn't be drawing more than 2.5A. It could/will
| draw more than that to start, but literally just for a
| second or two.
| jchw wrote:
| Thanks, that's useful! That was my thought w.r.t. startup
| current, since I assume it is an inductive load. The
| model is a Carrier 58STA090-14 and it is indeed 1/3 HP.
| Seems likely I could run that load off my car in a pinch,
| which is definitely a good option to have available.
| mikeyouse wrote:
| So per the spec sheet -- the "Full Load Amps" for that
| model could actually be up to 5.2A per the bottom portion
| of the 90-14 column second from the right on page 5:
|
| https://d1049ui2fjityy.cloudfront.net/userfiles/inriver/d
| ocu...
|
| That motor has a switch so it could be in 3 different
| settings -- As shipped, the blower motor speed is set to
| be faster for AC (more draw in the summer) to prevent the
| coils from icing over, and then it's shipped to be the
| slowest fan speed while in heating mode, but it is
| possible that your installer changed that. If indeed it
| is in the "slow" speed for heat, then 2.5A would be about
| right.
| mynameishere wrote:
| I don't know what's up with that, but the standard fix is
| to let the faucets trickle.
| toomuchtodo wrote:
| Challenging when you're on a well and your well pump
| requires power. Will your generator support 220V and the
| surge start a well pump requires? That surge is going to
| occur every X minutes to replenish the pressure tank as
| it depletes due to trickling. In this scenario, driving
| the 15A furnace circuit was a more simple fix.
|
| Something else to consider: electric pipe heat cable to
| keep pipes from freezing draws ~7 watts per foot, is
| quick to install, and easy to power if you've planned
| ahead.
| mynameishere wrote:
| I guess I must plead ignorance once again. Maybe flushing
| the pipes would be possible? I just know I would
| electrocute myself screwing with anything more powerful
| than a laptop battery.
| sbierwagen wrote:
| Houses designed to be vacant in freezing temperatures
| will have a drain port at the main shutoff valve so the
| pipes can be fully emptied.
|
| Unfortunately, this is not a universal feature in
| residential construction.
| sokoloff wrote:
| I happen to have valves that would allow me to drain
| almost all of my house to prevent freezing, but that's
| not universally the case (and even in my case, I couldn't
| drain the hot water tank fully without power without
| letting it just flood the basement).
|
| Freezing pipes is one concern, though having heat for the
| humans is another pretty desirable thing, so if I could
| spend effort on something that would result in drained
| pipes and no heat or on something that would result in
| enough heat in the house to make that unnecessary, I'm
| going for option #2 every time.
| [deleted]
| lizknope wrote:
| I was also without power last week for 6 hours.
|
| I have a SEER 18 heat pump for cooling which can reverse
| for heating in the winter but it also has a natural gas
| burner. Based on the installer's advice we set the system
| to use the heat pump if the outside air is 40F or above and
| switch to natural gas below 40F.
|
| The problem was that when the power was out the electronics
| in the system could not communicate with the thermostat in
| the house. My Nest thermostat literally said there was no
| system connected. I wish there was some kind of UPS to
| power those electronics and the blower fan.
| jacquesm wrote:
| Can't you just hook up a sizeable computer UPS for that
| purpose? That should run it for long enough to get you
| through most outages.
| sokoloff wrote:
| The heat pump will be a 240VAC load. Consumer-level
| computer UPSes in the US are 120VAC.
|
| The 24VAC transformer for the control circuitry will be
| on one of the 120VAC legs, but it's likely the installer
| didn't specifically wire it to allow partial powering of
| just the transformer and electronics board.
| jacquesm wrote:
| Hm... you might be able to get away with ordering a EU
| UPS then, those are 240V, you'll have to add a center tap
| transformer and maybe mess around a bit with it to get it
| to output 60 Hz (that will only improve efficiency).
| alpos wrote:
| There is, an inverter sized for the load with an auto
| transfer switch attached to a set of 100ah batteries will
| do what you're looking for. And that is what a UPS is on
| the inside. They just tend to use terribly small
| batteries.
|
| Such setups are easy to build if you want it and running
| a 100-200w blower doesn't require too many batteries
| either. However, if you need to run a compressor, the
| number of batteries required to power that for 6hours
| would start to get cost prohibitive.
|
| https://www.amazon.com/s?k=2000w+pure+sine+wave+inverter+
| aut...
|
| https://www.amazon.com/s?k=220v+automatic+transfer+switch
| +50...
|
| https://www.amazon.com/s?k=100ah+lifepo4+battery
|
| This guy has accumulated essentially everything you could
| want to know about such setups, at any voltage, any
| reasonable power range, in various applications: backup
| systems, full off-grid, mobile power.
|
| https://www.youtube.com/@WillProwse
|
| https://www.mobile-solarpower.com/
|
| For a 240v load, there are inverters that output 220v or
| you can use one inverter to power each hot line, just buy
| the batteries at the same time from the same manufacturer
| and ensure they will stay balanced. In your case you
| could also use a cheaper manual transfer switch if you
| don't mind going into the closet to flip it when the
| power goes out.
| illegalsmile wrote:
| What model do you have? I currently have a boiler for
| hydronic baseboards and would like to move to a more all
| in-one-solution for heating/cooling that is predominantly
| electric. My goal is to move all my gas appliances to
| electric with solar but it would be great to have gas
| backup and gas for those cooler days.
| jabart wrote:
| New homes should be built to better insulation standards.
| You have to solve so much and use so much energy to solve
| for a drafty house or lack of insulation on the outside
| walls. Newer homes are factoring in the R-value of 2x6s and
| finding ways to insulate those now.
|
| In this scenario, high efficiency heat pump with a backup
| gas fireplace. Those typically don't require any
| electricity to run as they can ignite off AA battery or a
| push button. My PC battery backups barely last 30 minutes
| on a wifi router because of conversion loss. Furnace fans
| also account for up to 1/3 of energy usage of a unit.
| Cogneration would add $5-10k to a home build versus a 50
| gallon propane tank with a single emergency gas fireplace
| unit.
| toomuchtodo wrote:
| Most of the heat from a fireplace goes up the flue
| unfortunately. It's one of the least efficient heating
| sources per the dept of energy (~15% efficient). A low
| tech solution is more thermal mass perhaps in high
| performance dwellings.
|
| Wood burning furnaces are a challenge because homeowners
| insurance providers don't want to insure dwellings that
| use them (but will if certain conditions are met, such as
| it not being the primary hearing source, professionally
| installed, etc).
| jaggederest wrote:
| Wood stoves are really efficient these days, hitting 70%
| plus, and it's Carbon Neutralish(tm) as a fuel source
| (obviously uses fossil fuels for harvest and transport
| and such, but that's only some percentage of the total)
|
| I'm always amazed at the ability of our questionable
| 1990s wood stove to happily heat the entire house. It's a
| great backup heat source on days when it gets proper cold
| out, which is thankfully rare here.
| throw0101c wrote:
| > _Most of the heat from a fireplace goes up the flue
| unfortunately._
|
| Depends on the fireplace. Direct-vent gas fireplaces take
| outside air for combustion and then exhaust it, with no
| inside air being used in the process. There are also
| direct-vent wood _stoves_ that can do the same.
|
| Wood stoves can get about 85% combustion efficiency, but
| that's not heat-delivered efficiency (often 10-20%
| lower):
|
| * https://www.epa.gov/burnwise/energy-efficiency-and-
| your-wood...
| masklinn wrote:
| If you've got wood available, you could also have a wood
| furnace as backup, and / or an actual fireplace (an
| efficient one ideally, possibly a masonry heater if you
| have the space and foundations to handle that load).
| patentatt wrote:
| This is a great solution too. I have a wood 'heatilator'
| (or fireplace insert) and during the recent cold snap in
| the Midwest I went through about 1/4 face cord of kiln-
| dried oak over 3 or 4 days (that's a lot by my
| standards). It kept the gas furnace mostly idling and the
| home warm (in the 80's by the fireplace actually, lol).
| Probably not exactly cost efficient with the cost of wood
| these days but I like being able to take some of the load
| off the gas furnace.
| Scoundreller wrote:
| Problem is high efficiency furnaces/boilers require a
| powered vent, so they need quite a bit of power to operate.
| And then you'd need to circulate "cold" air/water against
| the heat exchangers.
|
| This usually adds up to several hundred watts.
| alpos wrote:
| Up in the northeast power goes out every winter. It also
| gets restored a lot faster than the midwest, personal
| experience, but the reliability of it going out at some
| point during the winter means that everyone has a wood
| stove and a backup generator. Portable ones are practical
| enough and wiring a couple of circuits and a plug for the
| generator is not cost prohibitive for most.
|
| What I've found in traveling the whole country for a few
| years is that local power generation or storage always
| forces you to consider just how little power you actually
| need. You can pretty much never just power the whole house,
| or even a whole RV. Even 50amps is ALOT of power and trying
| to provide that from solar/generator/batteries is
| incredibly expensive.
|
| So your real question is pretty much never going to be,
| "how do I power my whole house in an outage?" but rather,
| "What is absolutely essential to spend up to 3000w on?" and
| even then knowing that a generator putting out 3000w burns
| 20lbs of propane in about 4hrs and 3000w for 4hr on
| batteries would require 10 to 12 100ah lithium batteries at
| $350+ each.
|
| I still agree with you that super efficient heat pumps are
| the future without fossil fuels but that probably also has
| to come with greatly improved insulation values in almost
| all homes regardless of region. Think double the current
| DOE recommendations. If you're running on electricity, you
| will feel the cost of every bit of heat you lose through
| the walls, roof, and windows. More insulation is a one time
| cost versus monthly, it always makes sense in the long run.
|
| However, we'll need regulation to force home builders to
| invest in that instead of just adding unnecessary sqft that
| people never use but have to heat and cool anyway. For some
| reason people don't want to pay extra for a house that is
| well built and well insulated, they'd rather go with bigger
| is better even when it's already absurd, and builders have
| noticed this.
| jcadam wrote:
| My house uses a NatGas boiler and in-floor radiant heat. It
| also has wood stoves for those -20F (or worse) nights when I
| need a little supplemental heat (or the power is out and the
| main heating system is offline).
|
| A heat pump would be a waste up here in Alaska esp given I
| don't need A/C. Just opening the windows and running some
| fans in the summer tends to do the trick for cooling.
| throw0101c wrote:
| > _Just opening the windows and running some fans in the
| summer tends to do the trick for cooling._
|
| The problem with 'natural' ventilation is you also get
| things humidity, pollen, dust, _etc_ coming in as well.
|
| One of the major advantages of mechanical ventilation (like
| HRV/ERVs, which cycle the air) is that things are tempered
| and filtered beforehand. Sometimes you also want to deal
| with individual variables: the temperature is fine, but the
| humidity is off.
| a9h74j wrote:
| Is filtering incoming air (for a mix) necessarily the
| norm, though? Even in the rare high-performance homes
| built on spec[ulation], my sense is that filtering
| incoming air might be omitted, in favor of a single
| filter acting on recirculation.
| sbierwagen wrote:
| It wasn't the norm, but now that more people have pollen
| allergies and widespread summer fires are common again,
| it's become more important.
| jcadam wrote:
| And forced air can be quite dirty (dust/pollen/etc.) if
| you don't clean your ducts regularly.
| jcadam wrote:
| There's the expense of maintaining a central A/C,
| ductwork, etc., that I'd rather not deal with (not to
| mention electricity is expensive here). Yes, if the air
| outside is dirty (forest fires, volcanic eruption, etc.)
| you've got a point. HEPA filters can help some with this,
| I suppose.
|
| Humidity isn't usually a big issue here most days. If
| anything, it can be a bit dry (but not as dry as running
| an A/C would make it). Though, I do have a portable
| dehumidifier I use when I need to :)
| wmeredith wrote:
| Mine is the same with a gas furnace/heat pump combo. It's
| great.
| euroderf wrote:
| My use case is similar. The oil furnace feeds hot water into
| a network of radiators. My design goal is to maximize the
| electricity outage that we can make it thru without frozen
| pipes, and it has to be on a budget (so no generator or giant
| UPS).
|
| The house is mostly unoccupied (a second home). Operation in
| an outage has to be fully automatic - it needs an automatic
| transfer switch I guess. The typical indoor temperature is
| just 5.5C (42F) - this does not leave much margin for the
| house to cool down during an outage when outside is like -5C
| (or -10 or -20).
|
| But it turn out that an oil pump and a water circulation pump
| do not draw THAT much power, so if I can run them off backup
| power (say, a new car battery plus an inverter), it should
| last for some time before ice has any chance to form.
| ethagknight wrote:
| Anyone know how these pumps manage to squeeze enough heat out of
| ambient air to make it worth the while? -20 is down there! I
| understand how heat pumps work, but what's the differentiator?
| contravariant wrote:
| It helps if you look at it as temperatures in Kelvin, to bring
| something from 250K to 300K requires a 20% increase, which can
| be done by an ideal engine at an efficiency of 300/(300-250) =
| 6. Sure you can't ever reach that ideal but the upper limit is
| high enough to make it worthwhile.
|
| I'm not fully sure at what point it stops being worth it, but
| anything above 150K can get an efficiency of more than 200%, in
| theory at least, and 150K is way above any reasonable ambient
| temperature. As far as I know the ideal is not even that hard
| to approach it's just how to do it in small scale and quickly
| that is the problem.
| fallingknife wrote:
| What does an efficiency above 100% mean?
| Qwertious wrote:
| It's a multiplier for the electrical input - if your heat
| pump is 400% efficient, then it means the electricity is
| being 100% turned into heat, plus 3x as much heat is being
| sucked in from outside.
| supertrope wrote:
| Instead of burning fuel to generate e.g. 1500W of heat, a
| heat pump uses 500W of electricity to transfer heat inside
| generating the same 1500W heating effect.
| contravariant wrote:
| It means you transfer more heat than work put into the
| system.
| yosito wrote:
| > -20 is down there!
|
| That's 244 Kelvin. It may not seem like a lot of heat to the
| human body, or judging by the state of everyday elements like
| water. But in terms of energy, there's actually still quite a
| bit there.
| ape4 wrote:
| -29C for non-Americans. Its a prototype.
| Ottolay wrote:
| The issue with heat pumps is that most of the ones currently
| being installed in South East of the US don't work well below
| +20F let alone 0F or -20F. Most of them are being installed with
| an electrical resistive backup heat, which is incredibly
| inefficient.
|
| The problem is when a cold spell like Christmas 2022, with
| temperatures down towards 0F. All the heat pump users switch to
| resistive backup heat and it overloads the electric grid and we
| get rolling blackouts.
|
| In my opinion, heat pumps are amazingly efficient at moderate
| cold temps, but they really need propane or wood heat backup for
| the really cold temperatures instead of resistive heaters.
| newZWhoDis wrote:
| We've had heat pumps that work down to -5F for years. If you're
| installing one that can only go to 20F in 2022(3?) something is
| very wrong.
|
| Backup heat methods increase the complexity and cost.
| Ottolay wrote:
| I am just saying what the typical install is in the South
| East US. The heat pumps installed may produce some heat at 5F
| but they can't keep the temperature to the set value, so
| there are resistive elements (Aux heat) to make up the
| shortfall.
|
| It's pretty common for people with heat pumps to have Aux
| Heat kick in during cold spells, which cause power grid
| overload issues.
|
| I realize you can insulate a house well enough and have a
| good enough heat pump to avoid backup heat, but 5F or 0F days
| are rare enough that the codes do not enforce this.
| bowow wrote:
| When I researched this year on replacing my A/C / Propane
| Furnace system with a heat pump, I found that companies
| didn't seem to want to advertise what temperatures their heat
| pumps can operate effectively at. If I look at some marketing
| materials from Google it seems companies like Carrier and
| Trane are only willing to talk about their heat pumps working
| in low temperatures if it's regarding their top-of-the-line
| (very expensive) variable speed compressor units. No one
| talks about what temps the mid range units can handle, and
| I'm guessing it's because they don't work well below 20F.
| mrinterweb wrote:
| My heat pump is advertised to operate as low as -13F. One
| thing to note is the efficiency of heat pumps is not optimal
| when they are operating close to their extremes.
| haberman wrote:
| What is inefficient about resistive heat? Isn't
| electricity->heat basically 100% efficient?
|
| Maybe you are saying that heat->electricity->heat is
| inefficient, since most electricity is produced from heat
| inefficiently.
|
| I always get tripped up by this, since I live in an area where
| almost all electricity is hydro. In that case resistive heating
| seems fine.
| zdragnar wrote:
| Electricity offers resistive heating, and heat pumps. Heat
| pumps are much more efficient than resistive heating.
|
| Otherwise, you have chemical fuel which burns, and a bit of
| electricity to pump it around (either by forced air or water
| pumps).
|
| In terms of electrical input, resistive heating is the worst
| of the lot, even if it can be sourced in a carbon neutral way
| (unlike nat gas or fuel oil).
| 1123581321 wrote:
| In the US, anyway, when people say electric resistance heat
| is inefficient they are comparing it to natural gas heat.
| It's the same story in water heaters; if you install a HPWH
| you are betting on not needing to resort to resistance heat
| because if you do that too much, you probably should've
| installed a cheaper gas unit instead. (I'm a happy HPWH owner
| weighing the timing of adding a heat pump for central heat.)
| thatcherc wrote:
| That 100% efficient figure is correct - you get one Watt of
| heat for one Watt of electricity. It's just that heat pumps
| can deliver 3 or 4 Watts of heat for each Watt of electricity
| (usually quoted at around 300% or 400% efficiency!). Compared
| to that, resistance heaters aren't as efficient.
|
| The explanation that made the most intuitive sense to me is
| that it takes less energy to move heat from one place to
| another (air at 273 Kelvin to air at 300 Kelvin, like a heat
| pump does) than it does to create heat from nothing (like a
| resistor does). That's why the heat pumps can get deliver
| more heat to you from the same amount of electricity.
| haberman wrote:
| That makes sense, but GP was calling resistive heating
| inefficient compared with propane or wood heat, which
| doesn't make sense to me.
| bluGill wrote:
| The best natural gas power plants are 64% efficient. A
| modern furnace is around 95%. Sure electric restive heat
| is 100% efficient in your house, but the whole system us
| much worse.
|
| Of course electric can come from many sources, if your is
| renewable at the time resistive is good. However you
| might also be using some old 1920s coal generator that is
| 10% efficient (these still exist, but are only used in
| the worst emergencies)
| anikom15 wrote:
| Natural gas (not sure about wood; in most areas it's
| abundant) is about 1/3 of the cost of electricity in
| America, so it's economically less efficient.
| ARandumGuy wrote:
| Resistive heat is 100% efficient, but heat pumps can operate
| at greater then 100% efficiency. That's because a heat pump
| doesn't actually generate heat, but just moves it around.
| Even when it's cold outside, there's still a lot of heat
| energy in the air, which can be moved inside to warm your
| home.
|
| Due to the increased efficiency, heat pumps are better then
| electric resistive heat (when temperatures outside are within
| the heat pump's operating range, that is). This is regardless
| of the method of power generation.
| gibspaulding wrote:
| Since heat pumps are moving heat around rather than actually
| producing it, they can be effectively better than 100%
| efficient so it's not so much that resistive heat is
| inefficient, but that it's less efficient than a heat pump.
| brilee wrote:
| I wrote up a brief discussion here on the boiling points of
| refrigerants https://www.moderndescartes.com/essays/refrigerants/
|
| The long and short of it is that if the heat pump works below
| -20F, then the boiling point of the refrigerant must be below
| -20F. This, in turn, implies a higher pressurization (as per the
| Clausius-Clapeyron eq) required in order to achieve a T_hot of
| 80F (or whatever output temperature you want. The higher
| pressurizations require more expensive components and
| compressors.
| Scoundreller wrote:
| Maybe I'm dumb, but aren't compressors pressure-agnostic? They
| just add pressure, right?
|
| Other than needing to be a bit stronger to keep from bursting
| against the higher delta with the ambient atmospheric pressure
| like the rest of the components.
| zip1234 wrote:
| Even if you do need to make thicker pipes, strength in a
| metal generally increases with the square of the thickness,
| so it doesn't cost twice as much in materials to double the
| strength.
| londons_explore wrote:
| This isn't true. For pipes, double the pressure requires
| double the wall thickness, which requires double the
| material.
|
| However, I don't think raw material cost is a big part of
| the cost of refrigeration systems anyway.
| dragonwriter wrote:
| > For pipes, double the pressure requires double the wall
| thickness, which requires double the material.
|
| Double the wall thickness requires more than double the
| material.
| samtho wrote:
| The "soft" copper tubing they use in refrigerant lines is
| not only very cheap (it's not 100% copper) but is very
| much over built for pressure it is likely going to be
| subject to. It's way cheaper, in this instance, to simply
| sell a line set that works with 99% of systems instead of
| having dedicated factory lines and consumer confusion
| from having different grades of registrant tubing.
| SnowHill9902 wrote:
| Power for compressible fluids is approximately proportional
| to the relation of pressures not difference.
| Cerium wrote:
| In this case there is a higher delta between the system and
| the atmosphere as well as a higher delta between the hot and
| the cold side, which is what requires a stronger compressor.
| Gibbon1 wrote:
| I had a HVAC guy mention that seals are problematic always
| with non hermetic compressors. Everything larger than a
| fractional HP system has a shaft seal between the
| compressor and the motor. Small systems being a pain
| because there is less refrigerant and no way to monitor the
| amount.
| warmwaffles wrote:
| There is a way to monitor it, but you'd need to put in
| T-Junctions and add a pressure sensor on the high and low
| pressure sides. You'd then need to rig up some system to
| read those pressures. But _you_ would be unfortunately
| the one that has to do it because I don't think there are
| any off the shelf solutions.
| mindslight wrote:
| The ideal model of everything is everything-agnostic.
|
| Refrigeration stuff is generally soft copper, and modern
| refrigerants are already working up in the hundreds of PSI.
| So I can see that getting expensive or requiring a sea change
| in materials.
| eloff wrote:
| If they're using copper, changing materials would probably
| save money. Copper is comparatively expensive. I suspect
| your premise that they are using mostly copper is
| incorrect, but then I write software for a living, what do
| I know.
| loeg wrote:
| Copper is (very) effective for conducting heat. Aluminum
| is also pretty effective but obviously has different
| material properties than copper. It might be a good fit
| here; I don't work in the space.
| bluGill wrote:
| Aluminum generally has fatigue limits that mean it will
| fail eventually, releasing refrigerant (which is normally
| an environmental disaster)
| dylan604 wrote:
| what qualifies as a disaster? the amount of refrigerant
| in a consumer unit just doesn't seem like a lot even if
| 100% of it was released. if it was a continuous supply,
| then maybe it could get disaster level, but these are
| closed systems with a finite amount. at these levels, it
| seems to me that just driving one's car would qualify as
| an environmental disaster.
| adonovan wrote:
| If a typical large split system has about 10Kg of R410A
| (GWP = 2000x CO2) that's about 20 metric tonnes of CO2.
| Compare to 5 tonnes for an average passenger car per
| year. So a leak is like four years of driving a car.
|
| Is it a disaster when an invisible odorless gas escapes
| and no-one notices? Or when a tree falls in forest? Not
| on its own, but our entire crisis is a pile of sand
| grains each too small to count.
| dylan604 wrote:
| My real point was accident vs disaster. Whether anyone
| knows about it or not (someone will know when the AC
| doesn't work and the repair tech sees it being empty). If
| one house looses coolant, then I'd call it an accident.
| If a vendor has a major problem during manufacturing so
| that the majority of units fail, then maybe we can use
| bigger words.
| Retric wrote:
| The issue isn't just the 1st one that breaks the issue is
| the other 100,000+ that do.
| dashundchen wrote:
| The newer refrigeratants that require higher pressures
| are much better for ozone and have a lower global warming
| potential.
|
| Pentane and isopentane, R601 being one of them (of course
| flammability is a problem) and R744 which is just CO2.
| kazen44 wrote:
| aluminium also has the problem that it is a dissimaler
| enough metal from most other plumbing hardware (being
| either made of brass, copper or steel) that it will
| result in the buildup of a lot of gunk because the
| aluminium disolves.
| eloff wrote:
| That's galvanic corrosion, but it's usually an issue in
| water. I don't know that it would be a problem with
| refrigerants, likely not.
| pjc50 wrote:
| Copper has long been the choice for piping because it's
| soft enough to bend without cracking. The obvious #2
| choice, stainless steel, is often even more expensive.
|
| (I don't like the standard HN analysis technique of
| assuming that another field has made a really basic error
| that can be spotted by an autodidact from outside)
| etrautmann wrote:
| While I generally agree with your response to the
| perceived arrogance - shouldn't we all ask if we can do
| better than assuming someone else is an expert and has
| fully optimized a solution? As long as we approach new
| domains with a sense of humility and respect I think it's
| desirable to always be looking for better solutions.
| mindslight wrote:
| > _assuming someone else is an expert and has fully
| optimized a solution?_
|
| I wasn't offering my own singular expert [0] opinion, but
| rather pointing out what I've observed the entire
| industry has seemingly converged on. Despite being
| subject to the hyper-cost-optimization of the consumer
| market, every refrigeration appliance I've seen still
| uses copper heat exchanger tubes and copper piping.
|
| I would welcome someone chiming in saying something like
| "actually I work in HVAC and things are moving towards
| aluminum heat exchanger tubes and stainless piping" or
| "that's already the case for most new building-scale
| systems", because I'd learn something new. But "just
| asking questions" based on one single material property
| isn't particularly helpful.
|
| And yeah, copper has gotten expensive. That has helped
| some new technologies displace it (eg PEX), but copper is
| also still used where it's needed (eg PEX and PEX
| fittings over 1" nominal (which is equivalent to 3/4
| copper) are prohibitively expensive for some reason).
|
| [0] In fact, I'm not a refrigeration professional, and
| have yet to pretend to be one. I just tend to look at how
| things are built.
| eloff wrote:
| First off, I was upfront about my ignorance. Secondly,
| copper is way more expensive than stainless steel, unless
| I'm missing something. More than 8x according to random
| websites on Google.
|
| I'm sure there is a reason copper is used, but if the
| industry has to find an alternative, it would likely be
| cheaper.
| mindslight wrote:
| Stainless sucks at heat transfer, and has to be welded.
| Copper can be soldered (low temperature), or I believe
| refrigeration lines are commonly brazed (higher
| temperature).
|
| Material cost doesn't tell the whole story. Stainless is
| harder to work with, therefore costs more to manufacture.
| And even if it ended up being less expensive in the long
| run, there would a lot of capital equipment to recover.
| [deleted]
| jasonwatkinspdx wrote:
| FWIW there does seem to be a certain blind spot about PEX
| as an alternative in the US.
|
| A friend redid his whole house with it himself to great
| success. He mentioned one of the contractors he got a bid
| from while deciding his plan, when asked about PEX, said
| "Well that just saves you time and money" in tone of
| dismissal.
|
| I think there's something similar going on with ductless
| heat pumps in the US. They're a fantastic option in my
| area but still uncommon. Part of that seems to be the
| installers make more from other options.
|
| I very much agree with you about the tendency of HN's
| community to assume other industries are simply obvious
| idiots, rather than realizing they're just ignorant of
| that industry's reality.
| FuriouslyAdrift wrote:
| Scroll compressors have come down in cost a bunch in the last
| few years. There's really very few reasons not to get a heat
| pump, now, for new construction.
| nightski wrote:
| The main reason in my area is that a.) these fancy new
| efficient ones aren't available easily and b.) no contractors
| in the area to install/service them. I just got a new gas
| furnace and really wanted to add a heat pump to the mix but
| after several quotes all of them either said no or strongly
| avoided the question. I couldn't get a straight answer.
| bityard wrote:
| Even in areas where natural gas is much cheaper than
| electricity?
| FriedPickles wrote:
| Id love to see a combined heat and power system that burns
| natural gas to drive a heat pump compressor, and recovers
| the combustion heat. I wonder what multiplier it would get
| on a therm.
| mindslight wrote:
| There are refrigerators that run directly off of propane.
| https://www.ferrellgas.com/tank-talk/blog-articles/how-
| propa...
|
| The working temperatures of ammonia are probably wrong
| for a heat pump, but perhaps something similar could be
| devised.
| nanomonkey wrote:
| I've been contemplating the same thing. Something like
| the WhisperGen stirling engine hot water heater should be
| available to everyone. Hell even a water cooled honda
| generator that runs off natural gas, and pumps the
| radiator fluid into your home for heating purposes would
| be nice. It seems weird that we aren't producing
| electricity when ever you burn natural gas for heating.
| icedistilled wrote:
| yes. Because Global warming/climate change is real and
| installing new furnaces bakes in decades of additional
| natural gas usage. Also, that natural gas price may change.
| dgacmu wrote:
| A heat pump is likely to have an average efficiency of near
| 300% - call it 250 if you want to hedge. A high efficiency
| condensing gas furnace gets about 95%. So on a per-watt-
| hour basis (equiv., BTUs), your gas must cost less than
| roughly 1/3 what your electric costs.
|
| There are additional savings if your gas furnace is the
| only gas appliance in your house and you can remove gas
| service entirely, saving the monthly customer fee.
| pandaman wrote:
| And to get to 250% COP in heating on average you'd expect
| to have, at least, 8.5 HSPF2 rating on your heat pump
| (it's still just the heating performance w/o de-frosting
| cycles as far as I understand so the real world COP of a
| 8.5 HSPF2 will be lower than 2.5)
| raverbashing wrote:
| > The higher pressurizations require more expensive components
| and compressors
|
| Sure, that sounds like an acceptable compromise for those who
| need the lower operating temperatures
|
| And maybe technology can get those compressors at the same
| price point of current compressors
| jacquesm wrote:
| But then current compressors would end up cheaper and a
| difference would still exist.
| szundi wrote:
| Or not produced anymore and prices go up for legacy system
| maintenance. Like try to buy 4MB of EDO RAM
| jacquesm wrote:
| I don't think that will happen. The price difference will
| be substantial due to the changes required and volume
| will probably not be enough to offset those.
| abracadaniel wrote:
| Your point should stand, but it did make me discover that
| people make new 30pin 4MB simms, which were very
| difficult to get for years because they were commonly
| used in ATMs and only available used.
| londons_explore wrote:
| > then the boiling point of the refrigerant must be below -20F
|
| This isn't the limiting factor for choice of refrigerant...
| There is _always_ a low enough pressure that anything boils.
|
| The problem is that at very low pressures (think a few
| millibars), gasses need huge diameter pipes and huge pumps to
| move even a small number of kilowatts of heat.
| brilee wrote:
| Another issue is that at pressures below one atmosphere, the
| system will suck in ambient air, causing condensation to
| collect inside your refrigeration circuit, which creates ice
| crystals, etc... nobody does that.
| londons_explore wrote:
| Plenty of systems work below atmospheric pressure. For
| example, Fridge freezers most commonly use isobutane
| (R600a), and when operating with the freezer at -20C, the
| pressure will be half an atmosphere (ie. -0.5 bar below
| atmospheric).
|
| The systems are filled using a vacuum pump to ensure there
| is very little atmospheric air in them, and they also use a
| 'filter dryer', which is a chemical compound chosen to trap
| any remaining water and various other common contaminants.
| a_square_peg wrote:
| We need heat pump that work below -20F like we need an electric
| car that can go 1000 miles in a single charge - which is we
| really don't for the 99% of the use case. What's needed is a heat
| pump that's cheaper to install than gas furnace or oil boiler for
| the 80% of the population. On few days of the year when it's -20F
| or below, it's ok to use resistive heater as a back up.
| loloquwowndueo wrote:
| Millions of Canadians would disagree with that assessment.
| a_square_peg wrote:
| I'm Canadian myself. Heat Pump is actually very popular in
| the eastern maritime provinces and is gaining in popularity
| elsewhere also.
| 2OEH8eoCRo0 wrote:
| I think a cheap heat pump and a cheap wood stove for
| emergencies would be ideal. Depending on resistive heat can be
| dangerous if power goes out.
| scojomodena wrote:
| Sort of, but really we need both. Yes cheaper for most people.
| But as someone who lives in Minnesota, we definitely get below
| those temps. By code we require full backup resistive heaters
| for a heat pump at such a rating which increases the full cost
| and installation cost. Plus, it is much less efficient than a
| heat pump (though efficiency lowers as the temp gets colder due
| to defrost cycles).
| mindslight wrote:
| AFAICT one of the main difficulties with heat pumps is that
| they want to use low temperature heat emitters, similar to
| condensing boilers. This is a general thermodynamic rule, but
| hits sources aiming for high efficiency extra hard, since
| they've been designed around exploiting it.
|
| So you can't just take a decades old system with oil/gas using
| finned radiators, just replace the boiler, and have it supply
| enough heat on the coldest day ("design day"). Rather you'd at
| least need to add some additional emitters, greatly increasing
| the scope of the project for a professional installer.
|
| What I haven't been able to find an answer to is that everybody
| says hydronic heat pumps need low delta T of 5-10 degree F
| (implying high flow rate for given heat transfer). But I would
| think the real constraint would be just on their leaving water
| temperature, and a heat pump (load side) that took in 100F and
| put out 120F (at say 5GPM) would be happier and more efficient
| than one that took in 110F and put out 120F (at 10GPM). But
| I've yet to find anything that confirms this.
| sokoloff wrote:
| Your intuition is correct on the last point. Where the
| "everybody says" side is coming from is the _average water
| temperature_ in the emitters (and therefore heat flux from
| emitters to the building) will be higher if the flow (supply)
| is 120degF and return is 110degF than if the flow is 120degF
| and return is 100degF.
|
| That's why designers are often specifying lower delta-Ts for
| low-temperature emitters: to allow the flow temperatures to
| remain as low as possible [for efficiency] at a given average
| water temperature [for effective heating].
| mindslight wrote:
| It's definitely in line with general thermodynamics. One
| would expect lower entering water temperature to be more
| efficient (especially with the condenser being
| counterflow). I'm just not sure if there's something
| specific about the design of real world heat pumps that
| makes it so that higher delta T across the pump is
| problematic. I thought I would have come across some
| hydronic professional explaining this a bit more in depth
| while focusing on each variable, but so far I have not.
|
| Maybe it never comes up in practice because heat pump
| systems inevitably need some kind of buffer tank. If you're
| designing a system from scratch then you design for lower
| delta-T in the emitters to keep the max water temperature
| down. And if you're using existing emitters then you just
| live with the inefficiency due to higher max water temp,
| but still keep the flow from the heat pump to buffer tank
| high regardless (to keep the max water temp from being even
| higher).
| a9h74j wrote:
| There is a YT video with Matt Risinger
| discussing/promoting "Thermafloor"(IIRC) which uses 25mil
| aluminum over the full surface of the flooring panels.
| They discuss some of the benefits of lower water
| temperature, but not all of the variables.
| amluto wrote:
| > What I haven't been able to find an answer to is that
| everybody says heat pumps need low delta T of 5-10 degree F
| (implying high flow rate for given heat transfer)
|
| I don't see why this would matter at all. Maybe the heat
| exchanger would need to be sized differently for a different
| flow rate, but in general a lower entering water temperature
| on the hot side seems preferable.
| [deleted]
| sigmar wrote:
| I'm not an expert on the topic, but I imagine that a heat pump
| that can handle -20F is also much more energy efficient when
| the temp is 0F (in comparison to a heat pump that was rated
| only for -5F, operating at 0F).
| Someone1234 wrote:
| Isn't the primary issue not the cost of installation, but
| rather the cost of the fuel? Natural gas in most of the US is
| far cheaper than electricity, and even if heat pumps are
| theoretically more efficient than natural gas (energy in:heat
| out), if the fuel is two or three times cheaper none of that
| matters.
| onlyrealcuzzo wrote:
| In most places in the US, in normal working conditions, Heat
| Pumps are 30%+ cheaper than a gas furnace to run.
|
| However, in some really cold places like Chicago,
| Minneapolis, etc - the days where current heat pumps are
| inefficient might be enough to make it cheaper to always run
| gas.
|
| OP is proposing to have both systems and only run the gas
| furnace on extreme days - which would lead to a ~30%
| reduction in running costs.
|
| I suspect the CapEx of having two heaters wouldn't make
| sense, though.
|
| It'd be better to just have a hear pump that can run
| efficiently at colder temps.
| mrep wrote:
| You generally have an air conditioner though as well as a
| furnace and you can get those that can also work as a heat
| pump. Mine supposedly works as both but they only set it up
| for cooling and my gas furnace does all the heating :(
| [deleted]
| Scoundreller wrote:
| I think it's the opex of 2 grid connections that messes
| with the numbers.
|
| Depends on how your utility charges, but I feel like
| many/most sell you the gas roughly "at cost" and then some
| fixed monthly delivery/connection charge that covers their
| regulated rate of return on their network equity.
|
| Oil or propane supplemental heat might be cheaper than
| Natgas supplemental heat. My money is on wood pellet stoves
| for supp heat for those that don't require full automation.
| Or maybe even dirty coal...
| BobbyJo wrote:
| Also, the capex of gas delivery. Not needing infra to
| deliver gas to each and every house would likely be a
| pretty big win.
| Epa095 wrote:
| Unless gas is subsidised I don't really understand how gas
| can be cheaper. A modern heat pump can give 3-5 kWh of heat
| using 1 kWh of electricity. And a modern gas generator is
| roughly 50% effecient at creating electricity (according to
| the Internet). So by using electric and a heat pump you
| should be able to get 1.5-2.5 times more heat from the same
| gas by making electricity of it first compared to burning it
| directly.
| SoftTalker wrote:
| Modern residential gas furnace is 90% or more efficient.
| Epa095 wrote:
| Makes sense (I would have guessed closer to 99%
| actually). But 99% is still less than both 150% and
| 250%:-P
| happyopossum wrote:
| You seem to assume that energy cost is the same no matter
| how it's delivered. Here in California, electricity is
| much more expensive than natural gas for the same amount
| of potential energy.
| Epa095 wrote:
| Yeah delivery cost might be a factor, maybe it costs more
| to deliver 1 kWh of electricity through a wire than (the
| equivalent of) 1 kWh of gas with a truck (that's what you
| use right?). Gas, if its stored in a big tank under your
| house, also had the advantage of beeing "locally cached",
| so you don't have to dimension the system for the max
| load in the same way.
| maxerickson wrote:
| Many urbanized areas in the US have natural gas
| distribution pipelines.
|
| Rural areas rely on propane delivery, which is roughly 2x
| the cost of the piped natural gas (per unit of energy).
| bluGill wrote:
| What is the efficiency of the power generation system?
| The whole system costs matter not just the individual
| HVAC unit
| chordalkeyboard wrote:
| > A modern heat pump can give 3-5 kWh of heat using 1 kWh
| of electricity.
|
| At lower temperatures the modern heat pumps cannot attain
| this COP, which is why they are working on heat pumps that
| work at lower temperatures.
| njarboe wrote:
| At least in the US, electricity rates and natural gas
| prices are highly regulated for retail customers. Thus the
| wholesale price of gas does not generally correlate to the
| retail price of electricity. In places like California
| electricity prices are very high due to renewable
| generation requirements. You would definitely want to have
| your own solar installation before converting over to all
| electricity in that state.
| DoneWithAllThat wrote:
| We're being forced to. After 2030 no more gas water
| heaters or furnaces can be sold. The cost of heating your
| house and water here is going to probably triple or more,
| and will fail every time there's a blackout.
| Scoundreller wrote:
| Maybe the gas is cheap, but the monthly and up-front
| connection costs mess with the economics.
|
| And that cost will only go up as people cut the gas cord.
|
| Depends on how your utility bills out it's infrastructure:
| some charge minimal monthly connection fees, others a lot.
|
| I honestly wouldn't want to own a residential-focussed gas
| distribution company unless someone revolutionizes stirling
| engines or micro cogen systems and people start cutting their
| electric cord.
| lizknope wrote:
| I live in a pretty standard suburban subdivision in the US.
| All the houses are 25 years old. I have about 60 coworkers
| in very similar situations. I think everyone of us has
| natural gas that was installed when the original company
| built all the homes in the subdivision over the course of a
| year. Stuff gets a lot cheaper when everything is put into
| the ground at the same time. My monthly gas connection fee
| is $10 so that in the summer my bill is around $19 which is
| $9 for the water heater and $10 for the connection fee.
| kube-system wrote:
| The thing with heat pumps is that they can be as much as 300%
| efficient (effectively) or more. This is because they can get
| "free" heat from the environment.
|
| So even if per unit of energy gas is way cheaper, heat pumps
| can _still_ come out ahead.
| anikom15 wrote:
| This is true when it's warm enough outside that you don't
| need the heat pump anyway. When the temperature becomes
| cold, it's a different story.
|
| Heat pumps might make sense when you have a well-insulated
| house, like the kinds in Northern Europe, to trap heat and
| reduce the power required to heat the room. American houses
| in most places are far too drafty.
| dragonwriter wrote:
| > Heat pumps might make sense when you have a well-
| insulated house, like the kinds in Northern Europe, to
| trap heat and reduce the power required to heat the room.
| American houses in most places are far too drafty.
|
| If you need significant heating _or_ cooling in a home,
| the first thing you need is to deal with is insulation,
| otherwise nothing you do is going to work well.
| anikom15 wrote:
| That's true, but unless you are doing some kind of
| industrial work (including running very hot computers),
| you shouldn't need significant heating or cooling in most
| of America.
|
| The idea that indoors needs to be between 72deg (F) and
| 75deg at all times is unsustainable.
|
| The other problem is that if you _do_ decide to insulate
| the house, then you may end up needing to use A /C
| because the house can no longer be wind-cooled to an
| acceptable temperature, and you will need to update the
| heating system as traditional methods of heating
| (fireplace, stove, simple furnaces) depend on external
| air circulation.
| dragonwriter wrote:
| > That's true, but unless you are doing some kind of
| industrial work (including running very hot computers),
| you shouldn't need significant heating or cooling in most
| of America.
|
| > The idea that indoors needs to be between 72deg (F) and
| 75deg at all times is unsustainable.
|
| The WHO recommends a general minimum household
| temperature of 64degF for all populations for health
| reasons, with a higher minimum for sensitive groups
| including children and the elderly; maximums are more
| regionally variant because acclimitization (which takes
| years) plays more of a factor in high-heat health risks,
| but even in extreme regions seems to top out at about
| 90degF for the general population.
|
| Lots of the US spends lots of time significantly out of
| at least one end of that range (and, especially given
| that the top gets lower in colder regions, lots of the US
| spends lots of time significantly out on both ends of the
| scale.)
|
| > The other problem is that if you do decide to insulate
| the house, then you may end up needing to use A/C because
| the house can no longer be wind-cooled to an acceptable
| temperature
|
| If you have a house that is insulated well _and also_
| lacks doors and windows that can be opened, sure.
|
| But... that presents other problems, too.
| Epa095 wrote:
| Modern heat pumps can be up to 500% efficient (using 1kWh
| of energy gives 5 kWh of heat) at optimal temperature.
| kube-system wrote:
| Yes, I went with "300 or more" because that's a more
| typical number for a run-of-the-mill unit.
| a9h74j wrote:
| And even the low-temperature-capable heat pumps reduce
| toward 100% at the low temperature end, IIRC.
| mikeyouse wrote:
| Yep, here's a spec sheet for a unit I'm looking at as a
| drop-in ducted replacement for my existing system -- it
| has all of the models listed, but I'm looking at the
| 4-ton unit (12k btu per ton, so 4-ton = 48k BTU, hence
| the MDU180 _48_ ): https://mrcool.com/wp-
| content/dox_repo/mc-uni-perf-ss-en-01....
|
| It takes 7kw at 17oF to provide 48k BTU. There are
| 0.293W/hr per BTU so 7,000W = 25k BTU "in" and 48k BTU
| "out" or a COP of 1.9. At -15oF, it's using 5.9KW but can
| only produce 28,500. So a COP of ~1.4. Still better than
| electric resistive heating but not by much. At 40oF, the
| COP is more like 3.3 which is in line with the very
| efficient numbers.
|
| Fortunately my 99% design temp is ~8oF and my area only
| sees 20hrs below zero per year, so this will work just
| fine for me.
| a_square_peg wrote:
| Interesting thing here is that natural gas is about 1/3 the
| cost of electricity per energy unit, so when the COP is above
| 3, it's cheaper to heat home using heat pump.
|
| The reason why natural gas is about 1/3 of the cost of
| electriciy is because most natural gas power plants run at
| thermal efficiency of about 30%.
| pfdietz wrote:
| Combined cycle natural gas plants have an efficiency of
| about 60% (lower heating value). Even simple cycle NG
| plants are about 40% efficient (again LHV).
| doikor wrote:
| Yup. And at least here in Finland the pumps come with the
| resistive heater included so it automatically switches over to
| it once it gets too cold.
|
| Which where most people live here averages to less then 1 day
| per year so not a big deal.
|
| Way bigger issue here is some fall storm destroying the power
| lines and being without electricity for multiple days when it
| already is cold enough they one needs heating.
| kube-system wrote:
| That's an issue even with gas furnaces here in the US, as
| they won't run without electricity.
| dahfizz wrote:
| True, but furnaces have a much lower power draw. They are
| easy to run off a generator, which are common in areas that
| frequently lose power.
| jacamera wrote:
| Yes but it only requires a couple hundred watts to power
| the blower motor and electronics of a gas furnace. They're
| easy to power off of a small portable generator or even a
| cheap inverter hooked up to your car. The same cannot be
| said of a heat pump or resistive heater.
| kube-system wrote:
| They are, and I have a contingency plan for this myself,
| but few people have the tools and knowledge required to
| accomplish this.
| AuryGlenz wrote:
| Eh, for the first time I got an alert message on my cell phone
| asking people to reduce their electricity usage during a
| blizzard here in rural Minnesota.
|
| If everyone is suddenly using electric heat when it's -20 in an
| area there might be load issues.
| mirrorlake wrote:
| The number of electric devices added to the grid is likely a
| predictable percent increase every day/month/year, and
| likewise, the acceleration of that change is probably
| somewhat predictable, too.
|
| This is not to say we shouldn't be concerned, but denying
| yourself the most energy efficient technologies available
| (EVs, heat pumps, etc) because you're afraid of power outages
| 5-10 years from now seems like overkill.
| bowow wrote:
| If everyone uses resistive heat during that 1% of the time that
| it's -20F or below, the electric grid goes down and then no one
| gets heat. Consider what just happened in the southeast with
| TVA and rolling blackouts. That was precisely because it was
| too cold for heat pumps and so everyone's resistive heat
| engaged at the same time. I don't think your EV range
| comparison is a particularly good one. You can control your
| stops on a road trip, you can't control when it's colder than
| -20F outside.
| ledauphin wrote:
| If they can manage the grid granularly enough and isolate
| critical environments like hospitals, nursing homes, etc., I
| really don't see a good reason for us to overbuild to handle
| the third standard deviation of electricity demand. It makes
| a lot more sense to set the expectation that on the coldest
| days of the year, your house may spend a few hours
| disconnected from the grid in order to shed load. Not only
| does the avoid overbuilding, but it also contributes to less
| overall fragility in society, because black swan events that
| happen once every 50 or 100 years are the sorts of things we
| can't build for anyway, so it's better if people are prepared
| to endure the unexpected from time to time anyway.
| yosito wrote:
| Meanwhile, most people in the US don't even know what a "heat
| pump" is, and think that "air conditioners" are inherently
| wasteful and bad for the environment.
| Scoundreller wrote:
| It is kinda a concern with heat pump rollouts in Europe: now
| that people that didn't have air conditioning before will have
| it and will adopt it.
|
| Having said that, too much of my EU family still thinks air
| conditioning makes you sick... and a lot of the latest germ
| theory (aerosol transmission or respiratory viruses) is
| confirming they might be right. Ugh. At least the rental cars
| usually have AC nowadays.
| newZWhoDis wrote:
| That's absurd, AC doesn't "make you sick". What basis could
| anyone have for such a claim?
| SoftTalker wrote:
| AC evaporators and condensate pans can breed bacteria and
| mold. At best this can be smelly, at worst it can make you
| seriously sick. See the history of Legionnaires disease.
| nottorp wrote:
| If you have individual room split units you just clean
| them yearly or so. Just open the interior unit and spray
| it with the cleaning solution. Smells nice too :)
|
| Whole house a/c systems like the US has are an entirely
| different matter... don't know how you clean all those
| ducts.
| anikom15 wrote:
| I've never seen anyone clean their A/C system.
| nottorp wrote:
| Put "air conditioning cleaning spray" in Amazon. You open
| the plastic cover of the indoor part and spray the
| internal radiator.
|
| There's stuff for cars too.
| jupp0r wrote:
| You need to maintain these systems. Otherwise
| refrigerators, sinks and toilets also make you sick.
| Scoundreller wrote:
| There are hazards to recirculating air (instead of opening
| a window), e.g. aerosol viruses, off-gasing and some of
| these people smoke like chimneys.
| pitaj wrote:
| It was down to -8F (not including wind chill) a couple days ago
| here. I have a small, old house but I'm considering replacing the
| old system I have now with a heat pump.
|
| My concern is two-fold:
|
| - my house is not well air sealed
|
| - my house is not well insulated
|
| So I worry that I'll need an extremely oversized heat pump in
| order to have enough capacacity for the coldest days.
|
| I suppose having a backup heating source would prevent needing
| such a large unit. Plus it would provide some amount of
| redundancy of the heat pump were to fail in the winter.
|
| The question then is, should I use electric backup heat, or stick
| with my existing gas connection? Electric is simpler and there's
| no exhaust fumes or CO risk to worry about, but gas is still
| cheaper here I think.
| Scoundreller wrote:
| What are your no-use natural gas costs like? Might make a wood
| stove, oil, wood pellets or maybe even propane cheaper. And
| then you're not depending on two grids for standby/supplemental
| heat.
| coryrc wrote:
| The best ROI is to insulate and air seal.
| hn_go_brrrrr wrote:
| And if you can only do one, air sealing is almost always
| preferable.
| jebarker wrote:
| We live in the Colorado Front Range in a 50 year old house that
| isn't particularly well insulated. We have a Mitsubishi high-
| efficiency air source heat pump distributing air through our
| existing duct work. We have electric backup inside the air
| handler. Last week it got down to -15F overnight. The heat pump
| ran throughout and there was only really activity from the
| electric backup during the occasional defrost cycle. We keep
| our house pretty warm too as we have a baby.
|
| In winter the heat pump seems to have no issues meeting our
| heating needs albeit at quite a bit higher overall utility cost
| compared to our old gas furnace. In summer the heat pump is
| much more efficient than our old AC unit and our solar panels
| cover >100% of our usage from ~April-Oct.
|
| Prior to installing the heat pump we did as much insulating as
| we could (mostly attic) and I think that was important for
| enabling the heat pump to keep up in the cold. The nature of
| the heating is lower level and continuous compared to the
| occasional blasting from a gas furnace, so you do want to
| prevent rapid leakage of heat from the house.
| sokoloff wrote:
| My 2 cents: Find your local "design heating temperature" and
| then determine your tolerance for the house falling a few
| degrees below the setpoint during the 1% of hours that the
| outside temperature will be below that. Most people would be
| fine if their house fell to 67degF or 68degF for a few hours,
| especially since some of those hours are bound to be at night
| (where other people are setting their stats back to those
| levels anyway and you might well be asleep and never notice).
|
| If you have no other gas appliances and generally reliable
| electric supply, I'd be inclined towards going with electric
| backup. That avoids the $10-15/month gas meter charge, which
| pays for a fair amount of the more costly electric heat. If you
| have other gas appliances and cheap [at least for now] natural
| gas supply, going with a natural gas backup allows you to use
| the cheaper source of heat for both backup and/or in case
| electricity rates go up substantially versus gas.
|
| CO risk is minimal and you should have a line-powered CO meter
| in the mechanical room and some CO meter on each level of the
| house anyway.
| Scoundreller wrote:
| > have a line-powered CO meter
|
| Thank you for stating this. If your furnace requires
| electricity to run, you don't need a battery-powered or
| battery backup CO meter. Unless you have a wood stove or
| light fires indoors when it gets chilly. Otherwise you're
| just wasting batteries.
| r0m4n0 wrote:
| I'm in a very similar predicament but the temperature where I'm
| at only go down to the 30s-40s mostly during the winter. I get
| some rebates where I'm at to replace a furnace so that brings
| replacement costs to be about equal between furnace and heat
| pump. I don't have solar, kw per hour costs are around 13
| cents. My AC is non op needing to be replaced (it regularly
| gets into the 100s for months on end) and my furnace is
| functioning at 25 years old and no problems, although when it
| turns on it sounds like a small bomb exploding in my ducts. I
| have 50% of my house with extremely drafty single pane windows,
| the other 50% have been replaced. House was made in the 1930s
| out of brick and appears to be well insulated otherwise though.
|
| I am afraid that my overall utility expenses will go up
| drastically with a heat pump though. Can a heat pump even keep
| up with a house that loses heat like crazy out of the windows?
| I seem to get contradicting information from the salespeople,
| the internet, etc. if anyone has any anecdotal info it would be
| greatly appreciated
| Qwertious wrote:
| If your main heat problem is the single-pane windows, perhaps
| you could use the bubble-wrap trick?
|
| https://www.builditsolar.com/Projects/Conservation/bubblewra.
| ..
| cbrozefsky wrote:
| Others have said it, but it bears repeating. Do the air sealing
| and then insulation ASAP. It increases comfort and the ROI is
| way higher than moving to a heat pump.
|
| I started with my old Vermont home with minimal insulation,
| single pane metal frame windows that would ice up, and drafts
| everywhere. After our first winter, we had the local efficiency
| program recommend a contractor who came out and measured air
| exchange and identified the order of work. New windows, sealing
| attic, re-insulating attic. We got a considerable tax credit
| for the work, and the comfort improvement was astounding.
|
| Just this last summer we made the jump to mini-split heat
| pumps. They are working well, but I doubt that would be the
| case without the air sealing. We keep them set at their lowest,
| 61F, and supplement with a wood stove in the living room, maybe
| burning 2 cords a year.
|
| As an aside, this is our first winter, and our bill for
| December was 300 dollars, at $0.18/kWh. That's about 25% lower
| than our estimated oil charges last year for the same period.
| However, this year oil is ~$4.6, almost 50% higher, so that
| hedge against fossil fuel price is really paying off. Add in
| the AC comfort that is largely offset by our solar array, and
| they are a worthy investment (oh, and 0% financing).
|
| None of this would be working without that critical investment
| in air sealing and insulation.
| pinkorchid wrote:
| It may be worth insulating it first. It cost me just about
| $1500 to go from effectively no attic insulation to R60 for a
| thousand sq ft, and besides making a massive difference in
| comfort it reduced energy usage by about 50%.
| hooverd wrote:
| How expensive would it be to run source water to an entire
| neighborhood for heating and cooling? Have one heating/cooling
| plant and per building heat pumps.
| projectazorian wrote:
| This is called district heating and is not uncommon, some
| cities in the US have it (it's used in Manhattan for example)
| but it's more popular in Europe and Asia, especially in
| Scandinavia and former socialist countries.
|
| https://en.wikipedia.org/wiki/District_heating
| hooverd wrote:
| Lots of colleges have steam tunnels too. With individual heat
| pumps you probably lose some efficiency but the source
| doesn't have to get as hot or as cold. Doing a residential
| retrofit sounds like herding cats but in somewhere like
| Phoenix or Tucson the efficiency gains might be worth it.
| mlsu wrote:
| This is frequently done when you have a (very hot) boiler in a
| power plant or chemical process nearby. A natural gas turbine
| can't generate electricity very efficiently on even 212f steam,
| so instead of building some gigantic turbine to get that last
| bit out, you route the waste heat into a nearby neighborhood.
| PreInternet01 wrote:
| Having heat pumps that can operate during arctic freezes is of
| course, and pardon my pun, pretty cool, but I wonder which
| percentage of the consumer market actually requires this?
| Especially keeping in mind that your pump not actively heating
| its internal storage for a few hours every day is not a huge
| issue: it only becomes problematic when the external heat
| exchange is unavailable for 6-8 hours or so.
|
| Another comment in the article, regarding electricity grid
| impacts during peak demand periods, is more interesting to me.
| Currently, there is no mechanism whatsoever for heat pumps to
| automatically shift their grid draw (or re-delivery) to certain
| time slots, and/or to coordinate those slots with other units
| nearby. Both of these would greatly help to balance the grid, but
| won't be available until standardization gets off the ground and
| expensive retrofits are done. That's a shame, really...
| eternityforest wrote:
| It's usually about 35F to 22F daytime when I turn on the
| heater, so efficiency at low temperatures would be the main
| thing that matters. It doesn't get to -20F that often most
| years, but it does hover around -5F for days at a time on
| occasion.
|
| Current generation heat pumps are probably still worth it but
| ultra low temp performance would be nice.
| therealcamino wrote:
| There may be no existing, comprehensive central management of
| electrical demand from heat pumps but that doesn't mean there
| are no mechanisms whatsoever, because there are systems already
| for regulating AC demand. In our region of the US, residential
| customers can opt in to a system where the electric utility can
| remotely disable their air conditioning compressor during times
| of peak load, in exchange for discounts. There are agreements
| on how long that can remain in effect, which would probably
| have to be stricter for heating systems, and probably have
| other safeguards added. There are also non-centralized AC
| mechanisms through Nest thermostats, where they can pre-cool
| buildings early in the morning to spread load out more evenly
| during the day.
| rainsford wrote:
| Maybe just as important, whether or not there is a
| centralized mechanism for dealing with it, utilities already
| have exactly the same load problem with AC in the summer and
| have more or less figured out how to deal with that. It may
| be different in places where AC is less widespread, but in
| most of the US I wouldn't expect heat pump load issues to be
| much of a problem in the winter.
| bluGill wrote:
| Winter is worse than summer, because Delta-t is much
| bigger. 130f to 70f is 60 degree difference, while -30f to
| 70f is 100 degrees difference.
| altacc wrote:
| There's quite a big market for this, such as a lot of the
| Nordics, where -15C for a few days is common enough that not
| having heating then would rapidly become an issue as homes
| freeze quickly. At those temperatures you have heating on 24/7
| to keep the cold at bay. Electricity costs on those cold days
| are indeed high due to the constant demand of heating.
| rektide wrote:
| House heating tends to have controls from thermostats or other
| devices; I'd tend to look to them for grid-related time-
| shifting.
|
| I did run across a release on a new generation of a heat-pump
| hot-water heater, which does seem to have some kind of grid-
| shifting built in. A. O. Smith's Voltex AL,
| https://cleantechnica.com/2022/12/21/all-i-want-for-christma...
| PreInternet01 wrote:
| > House heating tends to have controls from thermostats or
| other devices; I'd tend to look to them for grid-related
| time-shifting
|
| Not for heat pumps. In a typical configuration (large heat
| reservoirs combined with under-floor heating in a well-
| insulated house), temperature-setpoint changes take 12-24
| hours to propagate.
|
| So, governing the (in-room) target temperature settings is
| unreliable/unpredictable. Whereas the in-pump storage
| temperature is a whole lot more manageable.
|
| The old advice "turn your thermostat down at night" therefore
| also doesn't apply to most heat pump installations -- in
| fact, it might be disadvantageous. "Select the average
| temperature you need and don't touch it" is much better
| advice. Need localized heat/cold? Use another solution for
| that...
| a9h74j wrote:
| > don't touch it" is much better advice
|
| Saw one heat pump controller discussed which had a curve
| set for demand vs outside temperature, and the "thermostat"
| was to set a delta relative to this.
| mindslight wrote:
| The standard large buffer tank is 120 gallons, which stores
| about 20kBTU at 20F dT. So to last 4 hours you'd need your
| design heating load to be 5kBTU/hr, which I think is out of the
| realm of even new construction.
|
| You could raise the max water temp and install a few tanks to
| get in the ballpark, but that's an assumption that most systems
| won't have. Also I wouldn't be surprised if "operates down to
| -20F" includes reduced efficiency/output that already relies on
| the buffer/storage to compensate for.
| agentwiggles wrote:
| My Senville mini split claims to work at temps down to -22F.
| During this recent winter storm, temps got down to about -10
| where I am, and it managed to keep my garage around 50F. Nowhere
| near comfortable, but pretty damn impressive to be able to keep
| my relatively poorly insulated garage 60 degrees above the
| weather.
|
| I was quite happy that this storm occurred while I was in
| Christmas PTO, since my garage is my office. I could have made it
| workable with a supplemental space heater but it was nice not to
| have to!
| therusskiy wrote:
| I am lost.
|
| Are heat pumps the same thing as split air conditioners that can
| heat air?
| zip1234 wrote:
| A mini split is usually a heat pump system although some of
| them use resistive heating. They have been getting much better
| in recent years.
| Qwertious wrote:
| Heat pumps are also known as "reverse cycle air-conditioners".
| downvotetruth wrote:
| outside source(d) heater
| [deleted]
| ARandumGuy wrote:
| Air conditioners are heat pumps. They move thermal energy from
| the inside to the outside to cool a space.
|
| In this context, a heat pump refers to the same type of system,
| but in reverse. Instead of moving thermal energy from inside to
| outside, you're moving that energy from outside to inside. This
| can work even when it's cold out, because cold outside air
| still has a lot of thermal energy that can be moved.
|
| The main benefits of heat pumps for heating are twofold:
|
| 1) It's significantly more efficient then electric resistive
| heat, because heat isn't being generated, simply moved around.
| 2) Heat pump systems can be configured to work to both heat and
| cool a space. There are very few changes needed to make this
| happen, meaning that if you need AC, you might as well get a
| heat pump to do both jobs.
| throw0101c wrote:
| -22F / -30C capable heat pumps already exist, e.g.:
|
| * https://www.spacepak.com/solstice-inverter-extreme
| Scoundreller wrote:
| I think the ultimate combo will be heat pumps + wood pellet stove
| as supplemental heat.
|
| Then you can cutoff the gas grid connection and its associated
| standby/account/blah blah charges. It's a big sunk cost in a lot
| of places that messes with the economics of switching to heat
| pump as primary heat.
|
| Pellet stoves are semi-automated. Around 90% efficient. If you
| already have central heat pumps, you can install one and let your
| HVAC circulate the heat around. Can stockpile as much fuel as you
| want. Cheaper than oil or propane and not much more expensive
| than firewood once accounting for improved burn efficiency. Just
| need to empty the ash gray once a week or so, and dump a nice
| smelling bag in for every ~24h of operation.
|
| Relatively straightforward install: just need a wall to punch
| through and a standard power outlet. Minimal clearance
| requirements. Fun to watch the fire tornado.
|
| Big downside is they need some electricity (mainly for for the
| powered vent). Hit or miss when it comes to insurance companies
| that think explosive gas systems or high current electric devices
| are safer.
| 2OEH8eoCRo0 wrote:
| Pellet stoves require electricity to run the auger. Also-
| nobody gives away free pellets but it's pretty easy to come by
| free wood people are giving away.
| inthepipe wrote:
| Gas heaters also have around 90% efficiency, I think. It seems
| like gas is strictly better?
| Scoundreller wrote:
| Depends on your constraints. The CO2 round trip is a lot
| longer for gas.
| sandworm101 wrote:
| Cool. But it hit -39c in my area a couple weeks ago. They still
| have some way to go.
| Qwertious wrote:
| If you run copper tubing underneath the frost line, a heat pump
| can still run at that temperature. Problem is, that's a whole
| lot of expensive construction for relatively minor energy
| savings. I hear they're doing it in Alaska, where it's used
| much more frequently once it's installed.
| svdr wrote:
| A nice explanation of the working of heat pumps from Technology
| Connections: https://www.youtube.com/watch?v=7J52mDjZzto
| a9h74j wrote:
| Great channel. Doesn't he lament that US installers are still
| charging "don't bother me" enormous premiums on heat-pump
| installs?
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