[HN Gopher] Homemade Heat Pump Manifesto (2009)
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Homemade Heat Pump Manifesto (2009)
Author : walterbell
Score : 416 points
Date : 2022-09-24 05:02 UTC (17 hours ago)
(HTM) web link (ecorenovator.org)
(TXT) w3m dump (ecorenovator.org)
| frankus wrote:
| Slightly unrelated, but there's a proposal to use a shared
| ownership/utility model for the borehole/trench component and
| install it in e.g. the street: https://heet.org/energy-
| shift/geomicrodistrict-feasibility-s...
| kortex wrote:
| Fascinating! I would have not expected that maintaining annual
| thermal balance would be as big of an issue as it is.
| sethammons wrote:
| HN loves heat pumps; I'll never have one again - utter shite.
|
| I lived in the mountains of Southern California. As part of an
| FHA loan in buying my childhood house from my dad, we had to
| "upgrade" from a swamp/evaporative cooler and wood burning stoves
| and went with a heat pump. The unit and ducting just couldn't
| keep up. It sighed out slightly warmer/cooler air and, when it
| kicked on, it pushed outside-temp air into the house that, in
| winter, would take the unit over an hour to bring the house back
| to its starting temp, let alone warm it. It really sucks to be
| cold and to have to get colder before a chance at warming up. It
| was similarly lame at cooling, though it would keep the house
| from sweltering if started before sunrise. Temp range outside:
| 20-40s in winter, up to 90s with a couple of days in the 100s in
| summer.
|
| We went back to the wood burning stove and swamp cooler.
| ricardobeat wrote:
| Wait, why would the unit pull fresh outside air in? Shouldn't
| the ratio of recirculation be adjustable?
| sethammons wrote:
| The venting was exterior to the house and was heavily
| influenced by outside temp
| timbit42 wrote:
| I'm starting to wonder if you were scammed. That's not how
| modern air-to-air heat pumps work.
| [deleted]
| Gravityloss wrote:
| Something doesn't sound correct now. In an air heat pump, the
| compressor and a heat exchanger are outside, only warm liquid
| flows through a hose into the building where its heat is spread
| out with a room unit. The system doesn't move air in or out.
| sethammons wrote:
| The heat pump we had installed did not have any liquid hosing
| that I was aware of (maybe something internally in the unit?)
| timbit42 wrote:
| Whatever you had, it seems it wasn't like what are on the
| market today. I don't think your experience is relevant
| here.
| xani_ wrote:
| Sounds like fucked up install - why on earth it would get
| colder when it activates ?
| post_break wrote:
| My new dryer is a heat pump. Uses less than half the energy my
| previous one did. It does take longer to dry clothes, but it's
| much gentler on the clothes so it's a perfect trade off for me.
| I'd love to do a heat pump like this for the house but there is
| so much oil pipeline around me and there's no way a truck with a
| pile driver can reach my back yard.
| dzhiurgis wrote:
| Hot water cylinders can have heatpumps too!
|
| Wish we found a solid way yo harvest heat from waste water. So
| much energy is wasted on showers - similar to EV driving at
| highway speeds.
| bombcar wrote:
| We do it. It's not yet economically worth it but I've seen
| installs. I can't find it but I saw one that was designed to
| let a massive shower run continuously with very little heat
| loss - the water coming out the end of the drain was as cold
| as the inlet water from the main.
|
| https://en.m.wikipedia.org/wiki/Water_heat_recycling
| throwaway4220 wrote:
| https://en.m.wikipedia.org/wiki/Countercurrent_exchange A lot
| of mammals do this including humans. Don't know if there's a
| drop in plumbing shower solution.
| theluketaylor wrote:
| drain water heat recovery is already a thing. It's code for
| new builds in British Columbia, Canada.
|
| It's only expensive due to the amount of copper. The actual
| install has no moving parts and is completely passive.
|
| https://www.nrcan.gc.ca/energy/products/categories/water-
| hea...
| dzhiurgis wrote:
| What efficiency are these? Brainstormed this a bit and
| feels like shower cabins (pretty popular over NE Europe)
| should have such system as standalone... As in - it
| collects waste, collects heat and stores it for next
| shower. Dunno how much energy a typical refrigerant can
| store tho. Also great fit for Japanese-style smart baths
| (press a button and water of desired temperature fills and
| stays warm), tho they seem rare outside Japan.
| theluketaylor wrote:
| I think they can recover up to 60-70% of the heat in the
| drain water. Not bad for totally passive. The installs I
| have seen are on the main drain for the whole house and
| located right next to the hot water heater. For it to
| really work you need a hot water tank, but I have seen
| some small tanks combined with tankless.
| xani_ wrote:
| If you already have water-water heat pump I'd imagine it
| would be a heat exchanger away from recovering at least
| _some_
| walterbell wrote:
| From the same forum, a 50+ page thread on DIY ventilation heat
| exchangers, e.g. 4"x4"x24" window unit that moves heat from
| exhaust airflow to fresh incoming airflow,
| https://ecorenovator.org/forum/showthread.php?t=891&page=38#...
| and a home-sized DIY HRV,
| https://ecorenovator.org/forum/showpost.php?p=26861&postcoun...
|
| _> outside temperature is 10,0 degrees Celcius, inside T is 21,1
| and incoming fresh breeze (top) at 19,0!!_
| walterbell wrote:
| More links via above thread.
|
| 2016 pipe design with 3" metal duct inside 4" PVC pipe,
| https://www.loudawson.com/17884/how-to-build-air-cross-flow-...
|
| 2012 box design with aluminum foil on wood frames,
| https://makezine.com/projects/heat-exchanger/
|
| Elegant $100 commercial window HRV, discontinued (why?),
| https://www.amazon.com/Bionaire-BAP336M-U-EverFresh-Exchange...
| & https://ia904509.us.archive.org/29/items/manualzilla-
| id-7067...
| dzhiurgis wrote:
| I keep thinking window air cons should integrate heat pump
| and HRV. Such a simple solution for ton of problems.
| sgc wrote:
| One thing I noticed when reading on diy hrvs in the past, is
| that many porjects are not taking into account air volume in
| the two ducts, and the amount of nominal flow for the size
| ducts compared to the ideal amount of air exchange. A 5 inch
| duct inside a 7 inch duct is more or less the correct size
| for many homes: about 50 cfm each direction. I do like the
| fact that there is a ton of dead space in most attics, where
| you can just drop a long, well insulated pipe hrv and be done
| with it for a relatively low cost.
| alexose wrote:
| Note that this thread is still active 13 years later! The most
| recent post is by the OP, and reads:
|
| > I want to take a moment to recognize that the Homemade Heat
| Pump Manifesto has gone beyond 2 million page views. I would like
| to thank Daox and any other people who may have worked behind the
| scene to make it possible.
|
| > My initial goal was to make available the knowledge and
| possibility that anybody with a few tools and gumption could
| convert discarded air conditioners, and dehumidifiers into very
| high efficiency heat ources, or cooling sources. Through the
| years, we have received reports of success from many people,
| living in many states, and countries.
|
| > Another goal was to make zero money from this project, to give
| it away and to encourage others to take it, share it, sell it.
|
| > In the beginning I thought that maybe 200 people would find
| this interesting. Obviously, I was wrong, gloriously wrong.
| layer8 wrote:
| And that is why traditional web forums and their
| discoverability are great. This wouldn't work on Reddit or
| Discord.
| HenriTEL wrote:
| What makes you think reddit is not discoverable?
| kybernetyk wrote:
| sometimes whole subreddits get deleted because of $reasons.
| sometimes I get to a link and a message greets me: this
| subreddit has been deleted because of no moderation.
| ceejayoz wrote:
| Whole forums go missing, too.
| Scoundreller wrote:
| Or the image boards that have all of the instructional
| photos from 10y ago disappear, or go premium but the
| original poster is MIA/dead.
|
| Faaaack, I'm still maintaining this 17yo Toyota. I need
| those brake change pictures!
| layer8 wrote:
| It's straightforward to have them archived on archive.org
| though, because they are more akin to static web pages
| than to a web app.
| layer8 wrote:
| What I mean regarding Reddit is that you couldn't have a
| thread running for 13 years like that, which you could
| easily follow (track up to which comment you've already
| read) and conveniently browse like on a forum. Pagination
| is important for that.
|
| On web forums, a new comment on a thread automatically
| bumps that thread up to the top of the thread list, which
| means that even after a pause, existing threads gain
| traction like if they were new threads. (Possibly even more
| than new threads, due to the existing contents.) That way
| it's easy to have a focused discussion for
| weeks/months/years on a particular subtopic.
| hutrdvnj wrote:
| But the problem with that approach is that people tend to
| revive zombie threads. I would estimate that <1% of
| threads actually have any useful discussion after 10
| years, the rest is bumping zombie threads.
| layer8 wrote:
| I'm not sure what qualifies as a zombie thread. If the
| new comments are meaningful contributions to the topic,
| it's perfectly fine to revive an old thread. It's
| certainly better than to have new threads about the same
| topic every few days or weeks, ignoring the previous
| discussions.
|
| In any case, I've never experienced reviving old threads
| to be a significant issue, or to happen inappropriately
| to any significant degree.
| Tostino wrote:
| Not my experience at all. I spent a whole lot of time on
| the endless sphere forum (forum for building PEVs) when I
| was in my teens and early 20s, and in my 30s now some of
| the technical threads from back then are still relevant
| and going strong. The discussion on there is light-years
| better than Reddit and HN for anything related to power
| electronics or EVs in general.
| JeremyBanks wrote:
| "Necro" or "zombie" threads aren't actually bad
| cortic wrote:
| I would just like to estimate that >99% of threads older
| than 10 years have useful information and the potential
| for useful discussion.
|
| I realize that where i am enthusiastic about older
| things, cars/bikes/tech/languages, you probably like new
| stuff. I hope you realize that most of the zombie
| revivalists agree with me. Most of the time we are
| looking for a new solution to an old problem, which is
| the definition of progress. Locking threads after 6
| months (thanks Reddit) or berating someone who want to
| revive an old topic, cripples progress.
| soulofmischief wrote:
| A simple visual indicator of the age of a post such as a
| zombie emoji (or something less tacky) is all that is
| needed to quickly disregard zombie posts you aren't
| interested in. Forums are great but we definitely need a
| UX overhaul incorporating the last 15 years of web UX
| research.
| layer8 wrote:
| About UX, I agree insofar as web forums have worse
| usability than Usenet clients had before. However, I
| don't see how web UX has improved in the last 15 years,
| in particular on the desktop, and in particular regarding
| forum and messaging apps.
| soulofmischief wrote:
| Mainstream design has taken a total nosedive, but there's
| still great UX research being done across multiple
| domains, one big driver being games.
| layer8 wrote:
| It would be great to have a couple of blog posts about
| that.
| rsync wrote:
| The ability to revive zombie threads is a _feature_.
| sgt wrote:
| IMHO a bit of the problem with Reddit is that it's so
| extremely threaded. I can understand replying to an
| individual message within a discussion topic, but the tree
| growing to the right just makes it hard to find out what's
| the "latest".
|
| The great thing about old style forums is that you'll check
| it once in a while and just go looking for the "latest"
| message, almost like joining IRC after a few days. You can
| go look at earlier messages but it's not always necessary.
|
| Or am I wrong - can you make some sub-reddits work that way
| ?
| neither_color wrote:
| On a ten year old reddit thread you'll find the top voted
| answers and top voted replies to those answers but not a
| sequential discussion for page after page.
| slowmotiony wrote:
| It's discoverable but you can't post comments in old
| threads, after a few months they get "archived" and you
| can't reply any more.
| brazzy wrote:
| This has changed. I just replied to a 5 year old post of
| mine to confirm.
| BolexNOLA wrote:
| A Reddit thread is automatically archived due to
| inactivity, forgot the exact duration. So in theory as
| long as somebody is posting a comment on a thread every
| few weeks (months?) it never archives unless the mods
| manually do it. The problem with this is that adding
| comments to a thread does nothing to make it more
| visible. Traditional forms bump up all threads as long as
| they have recent activity, which Reddit doesn't do.
|
| The closest solution you could probably find would be for
| the mods to pin the post to the top, but in my experience
| most people just ignore pinned posts except in very
| specific cases.
| teraflop wrote:
| That's not correct. On Reddit, thread archiving (on
| subreddits that haven't opted to keep threads open
| forever) is based on time elapsed since the thread was
| posted, regardless of how much activity there's been.
| IIRC the interval is 6 months.
| BolexNOLA wrote:
| Hmm it appears you're right. What I described used to be
| the case but they changed it several years ago it looks
| like.
|
| https://www.reddit.com/r/changelog/comments/25kvjo/reddit
| _ch...
| ginja wrote:
| I think it depends on the subreddit. E.g. this is
| archived: https://old.reddit.com/r/Python/comments/hmoabi
| /ive_designed...
| xani_ wrote:
| The thread would disappear from front page after days so
| new people wouldn't come in and talk about it constantly
| dna_polymerase wrote:
| Reddit Threads are locked after a while aren't they?
|
| Even if all of this would be in a Reddit thread I'd argue
| the usability of their site has declined to a point where
| using it for longer reading is unpleasant. (Login-Wall,
| collapsed threads, slow JavaScript frontend)
|
| So yeah discoverable yes, but nobody would use it like
| that.
| brazzy wrote:
| > Reddit Threads are locked after a while aren't they?
|
| Not anymore.
| wholinator2 wrote:
| What? I've seen more recent threads getting "archived"
| (no one can comment or vote) earlier and earlier than
| ever. It used to be that every thread was guaranteed to
| stay communicable for at least a year, maybe 2. That was
| enough for most things but still represented a
| discontinuity in the transfer of knowledge as a new
| thread would need to be made and gain traction and votes
| and rarely (very rarely) the previous thread would be
| linked to avoid just recycling the same points and never
| making progress. That exceedingly rare linking now
| basically never happens and threads get archived as early
| as 6 months! I assume there's some variation as I believe
| I may have seen threads that don't get locked so early
| but it's a significant disruptor on the transfer of
| knowledge. And with how bad reddit's searching is, unless
| the previous thread is linked there's a tiny chance
| you'll ever find it let alone even know it existed.
|
| That format just promotes reposting and restating the
| exact points that were popular 6 months ago. There have
| been many times I have had something to contribute to a
| discussion and have been rebuffed by the "This thread has
| been archived" popup. Truly any thread more than a year
| could not survive most current social conglomerates, I
| understand the scaling issues but it does not make it
| untrue.
| brazzy wrote:
| Yeah, independant of the auto-locking (which is
| apparently opt-out per subreddit), old threads just don't
| have any visibility to stay alive.
| unixbane wrote:
| Has anyone hacked furnaces yet? They have giant PCBs in them.
| bombcar wrote:
| Most furnaces are incredibly amazingly simple and the large PCB
| is just for reliability and to support the transformers.
|
| Many even now are (blower on/off) and (flame on/off). Only the
| high end ones have variable blowers and flame heights.
|
| I know this because before ours was replaced I had to jumper
| past a bunch of the board to keep it running.
| inferense wrote:
| > Where did you learn to invent stuff like this?
|
| Lots of reading, being willing to try something, welcoming
| failure as also a learning moment.
| voisin wrote:
| Is there any way to combine a ground source heat pump with a
| well?
| bombcar wrote:
| Some of them are basically multiple bidirectional wells (when
| installed vertically in a colder climate) so drilling one more
| for a wellhead is probably possible.
| voisin wrote:
| I've got wells on my property. Rather than drill more wells,
| I am wondering if there's something that could be put in the
| well to utilize the stable water temperature down below to
| heat exchange? Seems like there would be a big market - lots
| of people on wells are heating with oil or propane or
| electricity at massive costs.
| bombcar wrote:
| It would depend on the well and the "heat availability"
| (not a technical term) and how deep it was.
|
| I suspect it could work but it'd be marginal enough as not
| to be worth it compared to straight air heat pump or an
| actual field (similarity could a heat field and a septic
| field be installed at the same time ,,,)
| voisin wrote:
| I understood, perhaps incorrectly, that the ground below
| the frost line is stable year round and if air source
| heat pumps work more efficiently down to -10C, we know
| the water isn't that cold (otherwise it would be ice), so
| wondering if the efficiency threshold is the same for
| ground source heat pumps?
| bombcar wrote:
| That's why the ground ones are dug vertically sometimes,
| they can get to stable temperatures.
|
| However, a well may be "just poking" into that territory
| so you get the right temperature, but not enough surface
| area to do much heating/cooling.
| timbit42 wrote:
| Absolutely but typically two wells, one to pull water from and
| one to put the cooled water down. You also need a minimum
| amount of water flow, depending on the unit and how much heat
| your home needs.
|
| They're considered better than air-to-air heat pumps which
| become less efficient as the outside temperature goes down.
| Ground source units remain efficient in cold weather as the
| water in the well is below the frost line (only the top few
| feet of the soil freezes). They cost four or five times more
| than a typical air-to-air unit though so aren't as common.
| xani_ wrote:
| And technically also can be used for very efficient AC in
| summer
| usrusr wrote:
| Reminds me of a surprising armchair heat macguyvering idea I've
| had: if for some reason you are stuck with resistive heating, you
| could use an old fridge as your resistive converter, with the
| cold end _inside_ (cold end outside would be an actual heat pump,
| but probably not a good one and very limited in placement, likely
| losing more to the insulation downgrade from the placement): open
| the door just enough to get the inside walls below condensation
| of your current humidity level, collect the condensed water in a
| way that it doesn 't just evaporate again but can be carried to
| the sink.
|
| Why? Slightly less air replacement required to fend off mold,
| slightly more heat created, because the condensation is the
| inverse of evaporative cooling. Haven't done the math but I think
| it's safe to assume that the benefits would be tiny, but if, for
| some reason, you were limited to resistive heating, doing it this
| way would be slight ly less bad.
| fsh wrote:
| That's just a very ineffective dehumidifier.
| sgc wrote:
| Except you usually have a very dry environment when heating due
| to the lack of moisture in the colder environmental air, and
| need to add moisture to avoid falling out of healthy humidity
| levels for human beings.
| usrusr wrote:
| Dry air is less unhealthy than moldy air.
| sgc wrote:
| We are talking about large amounts of moisture that need to
| be added to the air when heating. There is 0 risk of mold
| in that situation. Ideal humidity: General recommended
| range: 40-60%; ideal/goldilocks humidity, 50%; mold
| conducive conditions: 60%+; air when heating: often ~30%.
| usrusr wrote:
| Perhaps if the house leaks air like a sieve and you just
| compensate by more heating watts (or if you use some
| fancy heat recovery ventilation), but in a properly
| closed shell, with considerable cold outside, your
| primary problem is getting rid of all the humidity human
| life produces without the water condensing on whatever
| surface is coldest. I suspect that we are talking about
| very different environments.
| Gare wrote:
| My humidifier uses about 3 liters of water per day for 40m2
| apartment during winter, to keep the humidity at acceptable
| 40%. Otherwise it's extremely dry inside.
| JoelMcCracken wrote:
| This is exactly why I keep coming back to this website
| 0x53 wrote:
| I have been doing a ton of research on building my own GSHP
| lately and so this is a great resource!
|
| However, what I have found in the process is that for well
| insulated homes GSHP probably doesn't make sense.
|
| Originally I was considering buying a kit from this site:
| https://www.123zeroenergy.com/pricing/geo-thermal.html
|
| But like it says on the page, because air source heat pumps have
| been getting a lot better they no longer sell the kits. There are
| a couple of individuals on YouTube who have used similar GSHP
| kits and had good success. The main challenge is that you need to
| dig 100ft of deep trenches per ton of cooling. Edit: should be
| 300ft not 100
| halbritt wrote:
| > air source heat pumps have been getting a lot better
|
| Mitsubishi, specifically, makes a heat pump with the marketing
| vernacular, "H2i" or "hyper heat" which has reasonable
| efficiency down to -13F/-25C.
| hedora wrote:
| That's not even the best one any more. Some other systems hit
| -30C.
| genewitch wrote:
| The part with the compressor in it costs $12000-$15000
| minimum just for the device, nevermind installation and the
| rest, and that's for an equivalent to 3-6 ton systems
| commonly installed.
|
| My mini-split system worked fine down to about 10F, then it
| was defrosting for 10 minutes after every 8 minutes of use
| or so. I just turned on crypto miners on a few computers to
| supplement. Laptop crypto mining is useful if you want to
| keep your hands and wrists warm, hats, blankets, sweaters,
| and some old 100+ watt light bulbs will also help.
|
| All this is to say "you can just get a -30 degree capable
| system" is out of reach for most people in the world. A
| large swath of people geographically close to my house
| still use window or wall HVAC units, rather than ducted
| systems. I was the _only_ split ductless system my HVAC
| installer had ever installed - they had to come fix their
| install 4 times (four!) and eventually i contacted the
| asurion purchase protection people and got refunded for the
| cost of the HVAC system.
|
| it works fine now, i told the HVAC installer to cut the
| threaded connectors off everything and sweat all the copper
| lines together, and it hasn't had an issue since.
|
| it was always breaking in the late fall and early spring,
| where it had to heat at night but cool during the day, it
| would always break around 11AM. The pressure differentials
| must have been an afterthought in the design, i guess.
| cycomanic wrote:
| We just build a house on the west coast of Sweden and we
| initially considered both a ground or air heat pump.
| Essentially our builder said with modern houses and heatpumps
| going for the ground heat pump was really not worth it. Their
| efficiency gain only becomes significant at outside
| temperatures below 10 deg C and there were just not enough days
| of such low temperature. Instead it is better to invest that
| money into a solar installation.
| dzhiurgis wrote:
| Similar in Lithuania, where buildings are required to be
| certified to A++ efficiency. Electric floor heating and air
| to air heat pump (aka split system) is enough. Solar panels
| are much better value. Cooling in summer is kinda becoming
| much bigger issue.
|
| For older building even replacing wood furnace with air to
| water system is enough.
| patd wrote:
| Ground heat pumps provide free cooling in the summer for a
| very limited amount of electricity as the ground will be at
| 10-15C (depending on where you live) so you don't need to
| use the compressor and just make the liquid flow to cool
| down your house.
|
| It also has the extra benefit of heating up your ground for
| the winter period.
| cycomanic wrote:
| While that is in principle true, in practice there are
| quite a few issues. Many heatpumps here are made to heat
| the water for floor heating but don't transfer heat to
| air indoors. So you would cool using your floor which
| isn't very comfortable usually. More importantly because
| of the above the heat pumps are build for only one
| directional transfer. If one builds their own system it
| might make sense to plan for it, but even then it's
| unlikely that Sweden will become so hot that opening
| windows will not cool off the house enough. If it comes
| so far we likely have more pressing problems.
| vel0city wrote:
| It would be cool to have a valve to change between a
| floor heat loop and an air heat exchanger for the inside
| side of the system.
|
| Of course this makes the system more complicated. More
| complicated means more chances for failure and higher
| costs for designing and installing.
| patd wrote:
| Some do wall heating or ceiling heating instead of floor
| heating. Wall heating/cooling would probably not require
| two systems.
| patd wrote:
| The ground heat pumps are not used in the opposite
| direction, it doesn't cool down water to the floor but it
| flows water at 10-15C into your floor. According to the
| installers I've talked to here in Belgium, all the ground
| heat pumps devices are capable of doing that.
|
| While this might not be needed in Sweden, it's more
| interesting further south. I live in Belgium and we had a
| long heatwave this summer and they predict more of those
| in the coming years. So cheap efficient cooling might
| turn out useful here (even if nobody had AC systems 20
| years ago)
| froh wrote:
| Goteborg is below 10degC November to March, five months
|
| https://weatherspark.com/y/71566/Average-Weather-
| in-G%C3%B6t...
|
| in contrast sunshine duration and angle in Winter is frickin
| low.
|
| sure that guy wasn't trying to sell sth?
| Scoundreller wrote:
| Ground source is also just a lot more work, and often has a
| large part of the job contracted out from your average HVAC
| tech.
| hedora wrote:
| I assume they made a typo, and meant to write "under 10degC
| below zero", Modern air source heat pumps are good to
| -30degC; the old ones were OK to 0degC:
|
| https://www.heatpumps.ca/articles/best-low-temperature-
| heat-...
| cassepipe wrote:
| Not to say you were wrong since in making that choice but
| with climate change days of extreme temperatures in both
| directions will become ever more common so so you may have
| considered it an investment into the future. Of course you
| may have other problems by then (a reliable source of food
| for example)
| arinlen wrote:
| > _(...) with climate change days of extreme temperatures
| in both directions (...)_
|
| This sort of take is unwise. It makes zero sense to invest
| today in domestic systems with the expectation that at some
| point in the future there will be extreme events a hand
| full of times throughout the year. The benefit of shaving a
| fraction of a percent from the baseline outweighs
| multipercent gains of hypothetical extreme events that
| happen a few times a year.
| bombcar wrote:
| And you can always add supplemental later.
|
| When building spend as much as you can on the building
| envelope (preventing air, vapor, water movement) and
| insulation.
|
| Those cannot be easily changed at all, but you can
| relatively easily add another heating or cooling device.
|
| And if you build above code minimums (you should!) be
| sure to have someone knowledgeable calculate the actual
| heating/cooling load. If you don't, the HVAC contractor
| may assume code minimums and oversize the system.
|
| Or get systems that are entirely variable.
|
| And get every step inspected! Mid build blower door tests
| are a great thing to do (right after the air seal
| envelope is up).
| arinlen wrote:
| > _And you can always add supplemental later._
|
| Great point.
|
| Investments are made based on expected returns on
| investment, and we're free to postpone them until they
| make sense.
|
| Spending money hoping to bank on the occurrence of
| unexpected outcomes simply can't be justified.
| hedora wrote:
| > _Spending money hoping to bank on the occurrence of
| unexpected outcomes simply can 't be justified._
|
| I would have agreed a decade ago, but in the one year our
| house has been standing, it has endured two 100 year
| events (a heat wave and a rain/windstorm).
|
| We overpaid about $1000 to go one size up on the
| (variable) heat pump / AC and $10-20k to oversize +
| harden the solar / battery.
|
| It has been worth every penny at this point; the solar
| kept the fridge, freezer and AC happy in > 100F heat
| during a power outage. That's $500-1000 of food just for
| the one event, and outages are increasing in frequency.
| (Air conditioning was mostly unheard of in this area 20
| years ago, since it didn't get hot enough to ever run
| it.)
|
| My big concern is that we're already eating into the
| engineeeing tolerances for the wind rating on the house
| itself.
|
| I do agree that you should consider what can be upgraded
| later, and put money towards things that are hard to
| change (insulation, wind ratings, etc.)
| genewitch wrote:
| the "it doesn't get hot enough to need air conditioning"
| argument was used to build out tons of apartment
| complexes in the pacific northwest, say, around Tacoma
| and Seattle. I lived in Tacoma in the mid-2000s for a
| summer and it was miserable. And everyone i spoke to
| about it said "yeah, that's the joke."
| jagged-chisel wrote:
| The same can be said for most insurance products. Whether
| it's Worth it is subjective.
| arinlen wrote:
| > _The same can be said for most insurance products._
|
| That's a terribly silly thing to say. Think about it for
| a second, particularly how insurance premiums compare to
| the cost of buying/rebuilding a new item.
| hedora wrote:
| Marge: I'm sure your insurance will cover the house.
|
| Maude: Uh, well, no. Neddy doesn't believe in insurance.
| He considers it a form of gambling.
| fest wrote:
| While I do agree that it was true a year ago, I wonder if it
| holds true for current electricity prices?
|
| My considerations for going with ground source heat pump
| were:
|
| * the maximum amount of solar that I could install is enough
| for ground source heat pump, but is a bit short for air
| source,
|
| * what if the seasonal electricity prices get so extreme,
| that the grid can't maintain 1:1 ratio for the net billing
| system anymore?
|
| * what if the global temperature swings become more extreme?
| ianbooker wrote:
| To aid the discussion: There are multiple kinds of heat pumps
| used for homes, mainly air-to-water and water-to-water. Since the
| post is 12 years old, the availability of air-to-water solutions
| may be understated. At least in Europe it is now quite common to
| find them in front of new homes. Placed and looks like an AC
| unit, sounds like a laptop from 2005.
| nicoburns wrote:
| > sounds like a laptop from 2005
|
| As someone who's never lived in a house with AC, is that
| loud(er) or quiet(er) (than an AC unit)
| bombcar wrote:
| Quieter than a window air conditioner, a bit louder than
| whole-home I suspect.
| jhallenworld wrote:
| The US Senate just approved an HFC ban. So which refrigerant
| should be used in the heat pumps? Can we get HFC-free heat pumps
| today?
|
| See https://www.danby.com/blog/danbys-commitment-to-
| remain-100-h...
|
| http://hvacrfundamentals.blogspot.com/2019/06/appliances-wit...
|
| Looks like r600a, iso-butane is already in use.
| AvocadoPanic wrote:
| r744
| wongarsu wrote:
| I would assume any refrigerant in use in air conditioning works
| just fine, based on heat pumps being air conditioners ruining
| in reverse
| VLM wrote:
| Does anyone have any financials on this?
|
| I get that if your heart is set on having a heat pump you need a
| heat pump, and that's the end of all financial consideration.
|
| But how does, say, $10K of heat pump compare to $10K of
| insulation and better windows/doors/roof, or $10K of solar panels
| and cheap ultra-low-tech repairable all-electric HVAC, or $10K of
| some other form of physical investment I'm not aware of?
| hedora wrote:
| Insulation almost always wins during initial construction.
|
| Solar panels probably come in second because they create waste
| energy that unlocks free EV charging, etc, etc (but you will
| pay more than $10K for the system), so, thanks to sunk costs,
| other stuff becomes "free".
|
| Heat pumps are probably the cheapest big bang for the buck
| upgrade for existing construction (especially if you have to
| replace your HVAC anyway). Minisplits are often a big win for
| retrofits of buildings without central air.
|
| All of these things are dominated by labor costs, and we are in
| the middle of a labor shortage. You are unlikely to find
| realistic financials unless you get bids and compare with your
| personal energy rates.
|
| We didn't do any of that.
|
| We just assumed energy prices would continue to explode over
| time (we were right), and jumped off the inflation carousel by
| putting in solar and all electric appliances.
|
| Also, we can't get natural gas service, and propane costs 4x
| per BTU more than natural gas around here. Most electrical
| appliance upgrades are subsided by the government to make them
| competitive with natural gas.
|
| That made it a no brainer.
|
| Since then, a bunch of indoor air pollution research showed
| that natural gas causes asthma, etc, etc. Also, the war in
| Ukraine started.
|
| So, what are your health, future financial predictability, and
| engineering economics braincells worth? For us, the answer was
| "less than the installation cost of the system".
|
| Also, after all they put us through, seeing a -$120 bill from
| PG&E each month makes me irrationally unhappy. ;-)
| ajross wrote:
| A heat pump is 3x more efficient at heating than a resistive
| electric heater, making it just about a wash with a gas furnace
| in most markets in terms of sustained cost. The hardware is
| more expensive, but not THAT much more expensive. When you
| include installation costs and amortize over a 20 year system
| life, the overhead is non-zero but quite low (10% or so). If
| you guess that gas is going to be more expensive in the coming
| decades where electricity is futureproof, it seems like a good
| bet to me. Ask me in 20 years.
| xani_ wrote:
| I wonder how's the failure rate compared to oldchool types of
| heating. The longest warranty I can find on the market is 10
| years
| fest wrote:
| It really depends on your starting point.
|
| If you have a perfectly serviceable means of heating that you
| are happy with, then it's a straightforward cost analysis (cost
| of consumables for the current heating method vs cost of
| electricity for the heat pump).
|
| I can only give an example that applies to my situation:
| previously I burned ~2300l of diesel which cost around 2300EUR
| for the previous heating season. So the yearly energy
| consumption is about 24MWh (combustion heat of fuel multiplied
| by efficiency of the furnace of ~94%). If I were to install air
| source heat pump, it would require about 8-9.6MWh (COP =2.5-3)
| of electricity per year (4000-4800EUR at the current fixed
| price offering from my electricity supplier of ~500EUR/MWh).
|
| If I were to install a ground source heat pump (COP of
| 4.5-5.5), expected electricity consumption is between 4.3-5.3
| MWh or ~2200-2600EUR/yr.
|
| If I were to power the ground source heat pump using the
| electricity generated by my solar panels (Latvia currently has
| 1:1 net billing system, but there is a grid cost of ~50EUR/MWh)
| the expected yearly heating cost is ~210-260EUR.
|
| At the previous electricity cost of ~100EUR/MWh, air source
| heat pumps for not-so-well insulated houses might be attractive
| option- but not at the current prices in Europe.
|
| When I did the calculations this spring, the break even time
| for heat pump + solar installation was ~8 years (based on fuel
| and electricity costs at that time).
|
| Right now it's around 4 years (and I might even get ~40% of the
| investment from a government clean energy incentive programme).
| However, I have to operate under assumption that a crazy
| dictator of a neighboring country doesn't decide to invade and
| wipe my house off the Earth...
| Slava_Propanei wrote:
| nqzero wrote:
| tangent: for a small air-to-air heat pump, what's the best
| commercially available coefficient of performance (COP) for a
| zero-delta-T ?
|
| all the common ratings that i've found online refer to COP at a
| non-zero delta-t over a ranges of conditions. to illustrate my
| question, if you needed to pump heat from 70degF indoor air to
| 70degF outdoor air with a 1-ton unit, what would be the best COP
| you could achieve in 2022 ?
| Roark66 wrote:
| It is a very interesting thread, but reading 100+ pages of a
| forum thread to find the details of the project is _hard_.
|
| I would definitely like to read a detailed description of his
| pump unit.
| VBprogrammer wrote:
| I've read it before and it's got some cracking info in there.
| One of my favourite bits was him using propane as a purge gas
| to get better quality brazed joints, though interestingly he
| baulks at the idea of using propane as a refrigerant gas!
| bagels wrote:
| Sounds dangerous.
| implements wrote:
| It's a standard refrigerant gas for some settings:
|
| https://www.agas.com/uk/products-and-
| services/refrigerants/r...
| theelous3 wrote:
| No the brazing sounds dangerous. How does it not ignite??
| Brazing is done with high heat open flame. Unless it's
| just for back purging? But that sounds even more
| dangerous - intentionally building up a propane resivoir
| behind the braze.
| bluGill wrote:
| It would only ignite where you already want a flame so
| who cares?
| bagels wrote:
| Where is the propane going when used as a purge? If it
| stays in the pipe, you may create an explosive mixture.
| If it doesn't stay in the pipe, you might create a
| fireball in your face.
| sidewndr46 wrote:
| Propane is not an explosive. Environmental concerns
| aside, millions of people burn propane each day all over
| the world relatively safely, explosion isn't really the
| leading concern.
|
| You may be thinking of acetylene. But that isn't really
| that dangerous in modern usage either.
| bagels wrote:
| Propane air mixtures can be explosive in the right
| measure. Less energetic than acetylene of course.
|
| It doesn't have to explode to burn you though. Where is
| the purge gas escaping when used this way?
| jonititan wrote:
| Probably because you need sufficient oxygen for
| combustion. The propane would only ignite where it comes
| out and mixes. Once the flame travels into the purged
| pipe it will probably die out for lack of oxygen.
|
| Ticklish though I'm sure to do it properly and safely.
| cyber_kinetist wrote:
| Ah, the vive of people on the Internet talking for over a decade
| on an old phpBB forum thread...
|
| A bit off topic, but I really think the existing forum sites
| aren't really that incompatible with "younger" people, and might
| have a renaissance later on (looking at how they are using
| Discord in a similar manner!) It's just that these old forum
| sites have lots of UI clunkiness that deter people from browsing
| or joining the site (older people who kind up grew up with phpBB
| might be accustomed to these sorts of jank, but you shouldn't
| expect someone who weren't in that era to be accustomed to it.)
| VBprogrammer wrote:
| I still use a couple of them for niche interests. The one thing
| that annoys me is that they still make uploading photos a
| chore. Usually you have to resize the image your self to get
| under some pathetic size limit. It's enough that people tend
| towards text when a picture or a drawing would be much better.
| betwixthewires wrote:
| When you're a guy running a long lived online community on a
| $100 a year VPS you avoid storing media as mush as possible.
| There's a reason photo bucket sites used to be so popular.
| OJFord wrote:
| Making it not 'a chore' though could mean a nice frontend
| to upload to some such photobucket site and embed the
| result.
|
| Then you also avoid the annoying 'you must create an
| account to view attachments'.
| bombcar wrote:
| Some of the forums have features to do that on upload -
| you just have to configure it.
|
| Sadly most of the admins for these type of fora are just
| learning as they go.
| lifeisstillgood wrote:
| I understand that in a few years every new build in the UK must
| have a GSHP (no gas boilers) and the goal is for every house to
| have something like it.
|
| I think this manifesto is a piece of genius - I think I shall be
| studying :-)
| Gordonjcp wrote:
| I wonder if whoever thought that up has ever been to the UK?
| helsinkiandrew wrote:
| Its a UK government plan so yes, why do you ask?
| Gordonjcp wrote:
| Well, it doesn't sound like they know much about the
| geography or geology of the UK, quite frankly.
|
| How is every house builder going to afford a million quid
| borehole?
| helsinkiandrew wrote:
| I think the UK is effectively banning gas boilers and its
| upto the developer/consumer to choose an alternative - a
| combination of CHP (local heating), GSHP, but most likely
| air source heat pumps.
| thombat wrote:
| Ground source boreholes are mostly 10-15 metres deep, so
| not wildly expensive, especially when part of a new
| construction. You may be thinking of classic geothermal
| bores? Drilling down to proper hot-rocks would be a much
| costlier scheme in most of the UK.
| dzhiurgis wrote:
| Wonder if you could drill centralised borehole and then
| use retrofit old gas lines to move compressed
| refrigerant...
| voisin wrote:
| > Drilling down to proper hot-rocks would be a much
| costlier scheme in most of the UK.
|
| Is this something people do?
| bombcar wrote:
| Big buildings do. They often have to go down that deep
| for foundation pillars anyway.
| shh_labs wrote:
| You don't need a borehole at all. Ours uses coils of pipe
| that are about 1m deep.
| Gordonjcp wrote:
| So, not really suitable for most of the north-west then.
| dabeeeenster wrote:
| Almost all heat pumps in the UK being installed these
| days are air-source.
| Gordonjcp wrote:
| Those work in hot dry countries. Lots of the UK - in
| particular the north-west - is neither hot nor dry.
|
| Up here you end up with the outdoor part freezing into a
| block of ice.
| diordiderot wrote:
| Canadians have air source heat pumps with backups that
| get used ~5-10 days a year...
| d110af5ccf wrote:
| I live in a similar climate and have never once had this
| problem in the winter. Something is wrong if this is
| happening to you.
| g8oz wrote:
| Incorrect. Try a quality brand like Mitsubishi or
| Thermia.
| [deleted]
| n4r9 wrote:
| I don't think the original claim is quite right. The UK
| govt is banning new gas boiler installations after 2025,
| but I believe there's a range of alternatives such as an
| air or ground source heat pump, or a hydrogen boiler.
|
| From what I've read through, replacing my boiler with a
| gshp would cost in the tens of thousands, not a million
| pounds.
| bombcar wrote:
| How would a hydrogen boiler work? Hydrogen trucks
| deliverying? Is the UK piped for hydrogen? Electrolizing
| water on site?
| karottenreibe wrote:
| I skimmed the plan and didn't find any requirement to use
| a ground to water heat pump. Air to water devices are
| mentioned several times as viable heat pumps for this
| plan. These do not require boreholes.
| [deleted]
| PartyOperator wrote:
| GSHPs are rare in the UK and likely to remain so. In practice
| building regs will require most new homes to have heat pumps
| but they'll almost all be air-source units. UK winters rarely
| get very cold (typical minimum design temperatures are above
| -5C in most of the country) so ASHPs work well all year.
| tomatocracy wrote:
| Even better would be to build out (in new build housing
| estates at least) district heating. This is common in quite a
| few other countries and it should work pretty well in the UK
| too - it's always seemed odd to me that it isn't more common
| here.
| OJFord wrote:
| I used to have it; it's a technically nice system when
| working, but the problem is having no choice of provider,
| no control when it goes wrong, etc.
|
| Makes sense for flats (or dense area of many leasehold
| houses, if that happens) where there's a management company
| holding your throat anyway, but otherwise I can't see how
| it works unless perhaps it was provided by the council
| (similar disadvantages, just more trust/better outcomes
| from complaints).
| GordonS wrote:
| Plus, don't GSHPs need quite a lot of land for the piping?
| Houses in the UK are built on the smallest possible plots of
| land :(
|
| It's normal for temperatures in Scotland to dip below -5C
| over winter - do ASHPs not work at those temps?
| fest wrote:
| For horizontal designs yes- the rule of thumb is the brine
| coil area should be around 3x the heated area. However, the
| vertical bores don't need much area, just expensive
| drilling work.
| lifeisstillgood wrote:
| I think I can call myself fully corrected. I mistook GSHP for
| all heat pumps and got confused
| verisimi wrote:
| I'd love to see the source for this info - do you have a link?
| e2le wrote:
| https://www.gov.uk/government/publications/heat-and-
| building...
| verisimi wrote:
| Thank you!
| baybal2 wrote:
| melonrusk wrote:
| New UK houses would all be cavity-wall so is there a reason the
| inside of the exterior wall isn't being used as the source ?
| ArchitectAnon wrote:
| One note of caution, he describes removing the lath and plaster
| and inserting eps insulation. It didn't mention if he did this,
| he might have done, but it's important to have a continuous taped
| vapour barrier on the warm side of the insulation to prevent
| water vapour from passing through, condensing on the timber
| structure and causing it to rot. Also ventilate the cold side of
| the insulation or a least have a gap to form a capillary break
| with the cold outside wall. I've seen a few badly done insulation
| jobs in timber buildings that have needed floor joists and studs
| cut out and replaced. It only takes about 15-20 years.
| OJFord wrote:
| Lath & plaster does not form a vapour barrier; deliberately not
| in most cases (there was perhaps some crossover when more
| moderm building techniques were still using lath and plaster) -
| old houses need to 'breathe' as they say, moisture needs to be
| allowed to move between inside and out. They can be warm & dry,
| but the way to achieve it is (paradoxically) porous materials.
| ArchitectAnon wrote:
| Yes of course, but I was thinking more in terms of DIYers
| jamming a lot of non-breathable eps into old houses. Probably
| better to say consult someone who knows what they're talking
| about before you internally insulate your old house.
| bombcar wrote:
| Yeah insulation that is a vapor barrier shouldn't replace
| insulation that wasn't without considering the effects.
|
| You can use something like rock wool (in batts or panels)
| to get insulation that is still vapor permeable and water
| resistant.
| forgetfreeman wrote:
| I'm glad someone addressed this as I cringed visibly when I got
| to this part of the post. I'm very much hoping someone with
| actual experience with controlling moisture stopped this person
| before they completed this installation. If not, that house is
| the residential equivalent of a dead man walking.
| bombcar wrote:
| Be careful with an impermeable vapor barrier especially if
| adding one. It may work perfectly for keeping water out of the
| wall cavity in winter, but become the condensation layer in
| summer - on the wall side!
|
| You can use smart vapor control layers (such as Intello) to
| counteract this - but be sure you've discussed how the wall can
| dry out if it gets wet.
|
| And the worst of all is if you end up with two vapor barriers -
| one on the inside and one on the outside - you'll end up with a
| "dirty diaper" effect.
|
| https://www.buildingscience.com/documents/digests/bsd-106-un...
| ArchitectAnon wrote:
| Good point, in a hot climate with air conditioning,
| everything works in reverse in summer. My perspective is
| Northern Europe; consult a local expert.
| Freestyler_3 wrote:
| What about one way barriers?
| __turbobrew__ wrote:
| I don't think the underwriter on my house insurance would be
| happy with me hacking together a bunch of parts to create a
| bootleg HVAC system.
|
| The project is cool, but if the project caused a water leak or
| fire you are probably screwed and wont get anything from the
| house insurance.
| diordiderot wrote:
| I'm relatively young but this link feels like what hackernews is
| supposed to be. An ugly forum post of someone hacking something
| together
| aaron695 wrote:
| naasking wrote:
| You could try: https://hackaday.com/
| fest wrote:
| I am currently installing a Thermia Calibra ground source heat
| pump (installers are apparently too busy).
|
| When I looked at the insides of the pump, the simplicity of
| construction was surprising- I could readily understand whats
| going on, as it consisted of off-the shelf parts made by other
| companies- compressor, circulation pumps, VFD and heat
| exchangers.
| aivisol wrote:
| I second to that. Just got same model installed few weeks ago
| and was having exact same thoughts. However, now I start to
| think that devil is in the details (as always). And it has ton
| of details, which probably have cost thousands on people hours
| to design, test and implement. Most are related to how to make
| it work with maximum efficiency while consuming as little power
| as possible, some are safety related, etc etc. And the build
| quality is outstanding, it works flawlessly so far, no
| complaints. Despite the steep price, one of the best
| investments I have made recently.
| fest wrote:
| Yeah, I have travelled that road too often (hmm, looks
| simple, I bet I can make it for half the cost- and a year
| later I have spent way more even disregarding the cost of my
| time and still only have a barely working thing) to know how
| that would turn out :)
| aivisol wrote:
| I'm still catching myself doing that sometimes :)
| fest wrote:
| "That's OK, I learned a ton while doing this" :)
| Nition wrote:
| This is a wonderful thread, thanks for sharing it here.
|
| > "The kicker is, that the smallest I have been able to find is
| four ton (48,000 BTU/hr). So this means that in order to proceed
| with the project, I'll have to build my own heat pump. In HVAC,
| bigger is not better... just slightly smaller than big enough is
| best, economically speaking."
|
| Is he saying here that a heat pump that's too large for a space
| is less efficient at heating, or is he just saying that a bigger
| one costs more to buy?
|
| If it's the former, can anyone here tell me why that is? It's
| hard to Google since it gets mixed up with other info like "heat
| pumps are less efficient at very low temperatures" etc.
|
| I would have thought they'd end up the same. The only reason I
| can think of is that a bigger one will maybe turn on and off more
| often to maintain temperature than a small one that's on all the
| time struggling to keep up.
|
| Edit: Thanks all for the excellent responses.
| moepstar wrote:
| Not sure what the right terminology is, however, it's due to it
| turning off, on, off, on again and again...
|
| When it is slightly undersized, it'll run continously and also
| prolonging compressor life...
|
| Compare this to being able to drive continously at the same
| speed vs. having to stop/start every 500m or so...
| genewitch wrote:
| duty cycle, i think.
| zeckalpha wrote:
| GSHP don't have as much issue with low temps as the below
| ground temp is fairly stable year round.
| fest wrote:
| Brine temperature varies over the heating season by up to 10
| deg C.
|
| I really tried to verify the horizontal coil length and
| installation depth recommended by installers from the first
| principles, but I had to give up, as there were just too many
| unknown inputs: the type of soil (thus, specific heat and
| heat conduction), water content (which varies over the year),
| received solar energy (shady/sunny).
| boulos wrote:
| The term of art is "short cycle". There's also the related
| "turndown ratio" which is just minimum_output/maximum_output.
| The discussion at [1] isn't bad, but [2] has a little diagram
| showing the cycling (in this case as a benefit of variable-rate
| inverters, but also as a warning).
|
| [1] https://www.greenbuildingadvisor.com/question/what-is-
| minisp...
|
| [2] https://carbonswitch.com/heat-pump-sizing-guide/
| ArchitectAnon wrote:
| I think it takes a while for the juices to equalise and reach
| equilibrium before it's running at max efficiency. You don't
| want a duty cycle of say 15mins. You want say 1.5hrs. Something
| like that. (Numbers very hand wavy this is not my field
| directly) With an over designed system it stops and starts too
| quickly and this invalidates the warranty on commercial
| systems.
| lazide wrote:
| It also makes the environment itself uncomfortable in many
| cases - excessively drying the air, or causing weird
| moisture/condensation issues (as it won't fully cycle the air
| in the house before stopping).
|
| Essentially, you want your HVAC system to run for long enough
| it's a gradual transition in temperatures inside and the
| equipment can run for awhile each time it needs to run to
| avoid the start/stop problems and let it 'settle in'.
| fest wrote:
| Modern heat pumps drive the VFD and circulation pumps as
| needed (i.e. the pumps run slower when the heat demand is
| low).
|
| The main factor for good efficiency is low output
| temperature- underfloor heating works at ~35 deg C, radiators
| work at ~55 degC (because of smaller surface area).
|
| I sized my heat pump based on historical data of heating oil
| /diesel consumption- since I had the data of past two
| winters, I could reliably determine the maximum continuous
| heat requirements for my house.
| rickboyce wrote:
| I agree it's hard to find reliable information in this - ASHPs
| and GSHPs are very hyped right now so a lot of the information
| that comes up in searches is quite low level or low quality.
| For example I've been told that a heat pump is at peak
| efficiency when it is sized for a duty cycle of 50% but asking
| why exactly this figure hasn't yielded good answers.
|
| As I understand it, it comes down to a couple of things.
|
| Heat pumps are much more efficient when providing lower
| temperature flows, their efficiency drops off significantly
| where the delta between the heat source (air or ground) and
| their flow temperate is higher.
|
| When an oversized heat pump cycles it is going to quickly reach
| a higher temperate and shut off where as a correctly sized unit
| will cycle for longer. So I guess simply it comes down to
| having the heat pump operate in the most efficient range for
| that property for longer vs. short spikes at temperature where
| it is less efficient.
|
| Most heat pumps have a variable speed motors so they can
| modulate their output to match a desired flow temperature but
| this only operates within a range relative to the size of the
| unit. So if the unit isn't correctly sized for the required
| heat output to be in its range then it has no choice but to
| cycle inefficiently.
|
| A couple of sources I found helpful:
|
| https://assets.publishing.service.gov.uk/government/uploads/...
|
| Most of the consumer advice is very low level - this Heat Geeks
| site seems better that most, but it still lacks enough detail
| for me to get into the numbers:
| https://www.heatgeek.com/3-steps-to-maximise-your-heat-pump-...
| d110af5ccf wrote:
| I don't think it's the temperature delta in this case, at
| least not between the room and outside. I suspect internal
| equilibration of the unit when power cycled and also energy
| transfer design capacity on the indoor side of the unit are
| to blame.
|
| > Most of the consumer advice is very low level - this Heat
| Geeks site seems better that most, but it still lacks enough
| detail for me to get into the numbers
|
| You'll probably want an undergraduate physical chemistry
| textbook for this.
| Nition wrote:
| Thanks. Yeah, especially difficult when you read multiple
| different claims and none have a source. They probably heard
| it themselves from someone else.
|
| I'm quite curious because I _have_ an old-ish heat pump that
| 's a little small for the space and I've been thinking of
| getting a larger one. But if it'll be less efficient then
| maybe I won't. The one I have does perfectly fine except on a
| few of the coldest winter mornings.
| TheSpiceIsLife wrote:
| My 7kw unit can only possibly draw 900ish watt.
|
| 800 watt for the refrigerant pump, and about 100 watt
| combined for the two fans.
|
| This means even when I'd like it a little warmer on the
| coldest days, making the heat pump use more power isn't an
| option.
|
| A larger unit would have a bigger refrigerant pump and
| larger fans. This would result in us inadvertently leaving
| the unit on a higher heat setting more often.
|
| Also, a larger unit will be turning a larger pump and
| larger fans even when smaller would achieve the same
| outcomes. Mechanic losses.
|
| These two factors, human habit & mechanical losses, are, as
| I understand it, why you're generally better off having
| more small systems than one big system.
|
| We have three split systems, in addition to the 7kW unit at
| one end of the house, there are two 2.4kW units, one I'm
| each of the bedrooms we use. When one or more units aren't
| required they can be turned off. Another advantage of this
| setup is that it's extremely unlikely all three systems
| will breakdown simultaneously.
|
| Another issue with the larger units is they tend to be
| ducted, where the ducting is in a poorly insulated roof
| space, so there's additional heat losses there, and
| additional losses due to energy required to push air
| through the ducts.
| IgorPartola wrote:
| Your first point is a bit silly: get a smart thermostat
| and it'll take care of that for you.
|
| Your second argument is silly: a larger pump will surely
| take more energy to run but will run for less time. It'll
| also wear out slower as it doesn't have to work as hard
| unless you have drafts and it has to cycle on and off all
| the time. Generally having more capacity is always a good
| thing for mechanical things.
| emj wrote:
| It is explained like this in the thread.
|
| > if you have a large compressor, you pay more for it
| with every revolution the trick is to figure the maximum
| BTUs or watts you will need, and design a little bit
| smaller. Plan to use a supplimental energy source to fill
| in during extreme conditions.
|
| Worth noting the AC_Hacker paid $25 for the AC he used
| for this.
| taneq wrote:
| Are you sure? Every ~7kW unit I've seen pulls about 2.6kW
| electrical.
|
| Agree that multiple smaller split systems is the way to
| go though.
| omgwtfbyobbq wrote:
| Ecorenovator's great. Ecomodder has some pretty good stuff too.
| namuol wrote:
| I've heard that air source heat pumps can be very effective too,
| and far simpler to install. I wonder if there's any discussion
| about converting ordinary AC units into reversible units, which
| supposedly is basically all an air source heat pump is.
| ajross wrote:
| Exterior heat pumps used in humid or below-freezing
| environments need some kind of defrost mechanism, just like a
| refrigerator. Otherwise your coils end up clogged with ice and
| the system stops working. The compression cycle is indeed
| symmetric, but the second order design constraints are quite
| different.
| theluketaylor wrote:
| Modern setups are really good about managing frost buildup
| and can be more efficient than resistive heat down to -20C.
| Waste heat from the compressor is often used for the defrost.
| haunter wrote:
| I have zero knowledge about the topic but I wonder how NA
| specific is this thing? As far as I'm aware houses built with
| thin wood walls are more prevalent there, like in the original
| example. I live in a similar aged house (maybe a bit older) in
| Europe but we have 1 meter thick stone walls. We don't have AC or
| ceiling fan but house always keeps cold in the summer and warm in
| the winter. I like the topic but curious how would that work with
| stone wall houses, especially like my example old style ones with
| thick walls
| bagels wrote:
| One meter! Those are quite thick walls. Is it solid?
| haunter wrote:
| Yes of course. There is an outside insulation layer applied
| some years ago but otherwise it is as built in the 19th
| century
| phinnaeus wrote:
| Indeed, that seems absolutely insane. Like a castle that
| would need to survive some sort of siege. Land is expensive
| where I am and I cannot imagine wasting that much on such
| insanely thick walls.
|
| I want a picture. Walking through the front door must feel
| like going through a tunnel.
| ComodoHacker wrote:
| It's not insane. I currently live in a house where some
| older rooms have 0.9 meter adobe brick walls. These were
| built in mid-XX century, when this was normal. Now we have
| better materials and don't need that much width.
| xani_ wrote:
| My family house was expanded so it had a thick wall like
| that between kitchen and the new part of the house. It was
| so thick it barely got wifi thru
| bombcar wrote:
| I've seen some that are basically build as two concrete
| block or brick walls, and the center are was filled with
| rubble stone and dirt.
|
| This is similar to an "earth house" and is very comfortable
| where the average (or basement) temperature is comfortable.
| The walls make an insane amount of thermal mass and the
| temperature inside changes very slowly.
| dzhiurgis wrote:
| When you are building your most expensive purchase of lifetime
| everyone needs to pragmatic and cheap. Each area have their own
| climate, cost of materials, cost of labour, building code
| (safety, efficiency, style) and tradition.
|
| Europe spans 40 degrees of latitude - not listing yours is
| dishonest.
| mijamo wrote:
| Stone walls are terrible for heat insolation. They have inertia
| but no insolation. So they are good in the Mediterranean coast
| where you want inertia in summer as some sort of natural
| climate control to keep it cool during the day. But they are
| terrible in winter when what you want is insolation to keep the
| heat in during months. A 1m stone wall doesn't even insolate as
| good than 5cm of dedicated insolation panels. It happens very
| frequently now that old houses are renovated by adding
| insolation to those old stone walls, but of course you lose the
| charm of stone on one side of the wall. This is why you have
| basically no stone houses in Scandinavia, because in winter it
| would just be impossible to heat.
| nawitus wrote:
| Stone houses (in the modern times they're made from concrete
| or brick, sometimes with insulation) exist in Scandinavia and
| they have good insulating properties. A modern stone house is
| even better than stick built houses when it comes to
| insulation.
| astrostl wrote:
| I know two major things about heat pumps:
|
| 1) their owners insist they are the greatest thing ever and
|
| 2) nobody in the midwest seems to sell them (at any price)
|
| I don't quite know how to reconcile those two things.
| timbit42 wrote:
| They are great if you are looking to use electricity to heat
| because they are 3 to 4 times more efficient than resistive
| heaters. It depends on the price of electricity and other heat
| sources in your area.
|
| If you live in the north where temperatures go below -15
| Celsius, air-to-air units aren't as great because they lose
| efficiency as it gets colder outside. My heat pump has a COP of
| 3, meaning it can generate as much heat as a resistive heater
| using 1/3 the electricity, but it shuts off at -15 Celsius
| because below that point it is less efficient than resistive
| heat. If your heat pump has a COP of 4, you might get to -25
| Celsius before it is less efficient than a resistive heater.
|
| Better, but more costly, heat pumps use in-ground water, either
| from a pair of wells, or from a deep pond that won't freeze to
| the bottom, or from many meters of water pipe buried deep
| enough beneath your lawn to not freeze in the winter. Because
| of the depth, they always have access to the earth's heat so
| they don't lose efficiency in the winter.
|
| The Technology Connections YT channel has a couple of good
| videos about how them:
|
| 1. https://www.youtube.com/watch?v=7J52mDjZzto
|
| 2. https://www.youtube.com/watch?v=7zrx-b2sLUs
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