[HN Gopher] Air-to-Air Heat Exchangers for Healthier Energy-Effi...
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Air-to-Air Heat Exchangers for Healthier Energy-Efficient Homes
Author : MengerSponge
Score : 241 points
Date : 2023-02-04 08:26 UTC (14 hours ago)
(HTM) web link (www.ndsu.edu)
(TXT) w3m dump (www.ndsu.edu)
| olivermuty wrote:
| This required building code in all homes in Norway since 2017.
|
| It is good when the building is designed to have the system
| easily serviced, bad when the unit is in a hard to get loft.
|
| You need to change filters at least once a year to keep your
| indoor climate good.
|
| I just bought an old house, sealing all the vents and installing
| balanced ventilation with one of these is on my list for summer
| of 2024. Adding 5cm of insulation (up to modern codes, from 10 to
| 5cm of glass wool) to keep the house even less energy demanding
| in winter.
| wojciii wrote:
| Same story in DK.
|
| I live in a house with this tech in. Also with a heat pump
| (ground version) and solar panels/battery to offset some of the
| running cost of this system.
|
| The house is uncomfortably warm during summer but ok during the
| rest of the year. The air is not humid enough for my tastes.
|
| The Danish company called Danfoss sells complete systems used
| to heat and ventilate houses. There are other systems perhaps
| better in terms of communication with others (control systems).
| My main problem with Danfoss is that I'm unable to control
| their products without mayor hacking. So I'm never going to buy
| from them again.
| jupp0r wrote:
| You are unable to regulate the temperature of the heating in
| your house?
| drjasonharrison wrote:
| Probably unable to enjoy as much cooling as possible given
| existing insulation, unit size, etc.
|
| Humans don't sense temperature or wetness. We sense thermal
| energy flow. Two materials at the same temperature, one
| highly heat conductive and another poor at conducting heat
| will feel like they are are different temperatures. Eg, at
| room temperature, water and wool.
| dv_dt wrote:
| People know if they step into a hot humid environment vs
| a hot dry environment. Perhaps they're just sensing some
| level of thermal energy flow at the skin and how fast
| sweat cools, but I think you sinuses, sense of taste, and
| lungs may also also add additional senses to
| differentiate.
| jannyfer wrote:
| > "Humans don't sense ... wetness"
|
| I read this elsewhere too and think it's worded
| incorrectly. Maybe our _bodies_ don't have sensory
| receptors for wetness, but humans can "sense" it by other
| means (e.g. by observing change in friction, stickiness,
| etc)
|
| Our bodies don't have receptors for our spouse's
| emotions, but I can "sense" when my spouse is in a bad
| mood.
|
| Or maybe my English is just bad and it's worded fine.
| wojciii wrote:
| The heatpump is not able to cool the house - per design. It
| would need air conditioning.. which would be expensive.
|
| The house is very well insolatated and therefore difficult
| to keep cool during the warm months. We installed film
| blocking some of the light on the HUGE windows which are
| part of the problem.
|
| So we are able to regulate the temperature but the house is
| warmed up during hot days and not always cooled down enough
| during the night.
| [deleted]
| spockz wrote:
| How are you going to run the new ventilation shaft for balanced
| ventilation? In most houses I know that would mean tearing
| down/up a lot of walls and ceilings/floors. Or you have to run
| them on the existing ceiling and those pipes are quite large.
| HdS84 wrote:
| We did this for our house built in 68.
|
| Obviously it depends on the architecture but we where able to
| place the central unit beneath the roof. All rooms on the
| first floor are connected through the roof space. A central
| column runs through the first floor and goes to the corridor
| on the ground floor. From there we where able to connect all
| rooms. The floor lost 15 cm height but it has 250 cm so it
| did not matter much.
|
| If you cannot do it you can run the pipes on the exterior
| walls and insulate them with ,20 cm Styropor.
| ericd wrote:
| Usually HVAC heat exchangers pretty close to an exterior
| wall, because the run to the exterior heat exchanger is
| ideally not too long, so you can tap into the return plenum
| there. But even if there's not, there's some flexibility in
| where you tap in (though some places might be more ideal than
| others).
|
| For us, it was just a couple 6"holes in the cinderblocks of a
| basement wall (at least 6 feet apart).
| lnsru wrote:
| Using old obsolete way oversized chimney. Enough place for
| pipes and cables.
| drjasonharrison wrote:
| Laundry chutes too
| kkfx wrote:
| Hum, IME the cleaning cycle of both my old and new one is three
| months, I generally try to flush them one time but no filter
| last more than 6 month. Did you have some other filters in the
| chain like an electrical one? No pine pollen etc around in
| spring?
| lnsru wrote:
| I also bought an old house and going for 12 cm of Expanded
| Polystyrene (EPS) insulation for outer walls in southern
| Germany. Plus simple combined heat pump for mild weather in
| living rooms and gas heating for real winter for whole house.
| With all this setup I am going to install central ventilation
| system for living rooms. It's really really nice to have fresh
| air during the night. The morning in previous rental apartment
| was always ugly with condensed moisture on all the windows.
| Freak_NL wrote:
| Why EPS and not PIR?
| lnsru wrote:
| EPS is like one third of PIR in EUR.
| Freak_NL wrote:
| But those costs are marginal in the bigger picture. With
| only 12cm not going for PIR while you have the chance
| seems just a waste of effort. It's not bad, but you're
| really limiting the options you have for heating.
| lnsru wrote:
| Thanks, I will redo my calculations. PIR 0,026 W/mK. EPS
| 0,035 W/mK. There is a nice difference.
| stuaxo wrote:
| I've been looking at spray cork.
|
| You can have it applied indoors and skimmed at only about a
| cm total or outdoors.
| mikeyouse wrote:
| No matter the substrate, there is almost no insulation
| benefit to 1cm of material. It looks like cork has an R
| value of ~4.0/inch so 1cm is roughly R-1.5? That's about
| equivalent or a single pane of glass.
| drjasonharrison wrote:
| Sometimes you can only economically and aesthetically add
| a bit until you get to the "tear it down and rebuild".
| ericd wrote:
| Spray... cork? Is that just glue+cork bits? Does it end up
| airtight?
|
| I've been pretty excited about steam expanded cork boards,
| they apparently make for excellent (albeit expensive)
| exterior cladding. Ditto granules for replacing attic
| fiberglass, though the additional weight of a thick layer
| seems like it might be a problem for ceiling drywall.
| skybrian wrote:
| Seems to be a paint/stucco alternative:
|
| https://www.buildwithrise.com/stories/spray-cork-what-is-
| it
| tinco wrote:
| EPS is a filler material for concrete structures and floating
| installations that easily catch fire and has mediocre thermal
| properties. Is it even allowed to use EPS on your walls?
|
| PIR is the typical economical material used for that kind of
| application. And 12cm is about the minimal thickness you'd
| want for decent insulation.
| lnsru wrote:
| EPS will be plastered afterwards. I don't see any problem
| having it between brick wall and plastered layer.
|
| 12 cm is ok for an old house. More is not economically
| viable.
| stinos wrote:
| Why do you choose a hybrid system and not just a heatpump? I
| have the impression that unless your energy demand is still
| fairly high or the heatpump rating is too low, houses are
| doing fine with a heatpump and the high COP in mild weather
| balances the lower COP in cold winters such that overall it's
| still worth it.
| pitaj wrote:
| Moreover, why gas instead of electric backup?
| letitbeirie wrote:
| Depending on where the furnace is located, it can be
| cheaper and have a lower carbon footprint.
|
| In my area of the US for example, gas costs 32/C/therm,
| which equates to 1.1/C/kWh.
|
| Electricity on the other hand costs 6.4/C-10.9/C/kWh
| (depending on time of day), and while a third of it comes
| from renewables, another third of it comes from coal, so
| it ends up being net worse for the environment than just
| burning the gas.
| jupp0r wrote:
| How long will you operate this? Coal will be gone in a
| few years.
| philwelch wrote:
| Even with gas it's more efficient to burn the gas for
| heat yourself than for the power plant to burn the gas to
| operate a turbine which you then use to generate
| resistive heat.
| kkfx wrote:
| > Moreover, why gas instead of electric backup?
|
| Hum, I do not know in you country but here in France the
| maximum you can get from the grid is 36kW, 12kW per
| phase, 3 phases. And while the electricity is still far
| cheaper than in Germany if you try to heat a classic
| badly insulated home (who have a typical 34-40kW gas
| heating) with electricity you final bill will be a bit
| astronomical....
| djbusby wrote:
| Maybe, like me, they've got existing gas heaters/boilers
| installed.
|
| When you get a heat-pump you need the backup for really
| cold (-20c). So you just leave the existing one in for
| that case.
| [deleted]
| hedora wrote:
| It sounds like they are putting in minisplits, which are
| great for retrofits. The cost of minisplits is roughly
| linear in number of rooms.
| davemp wrote:
| afaik in many climates/older homes heatpumps can't supply
| enough BTUs to heat a house in peak winter without being
| massively oversized for the cooling load (which could cause
| humidity problems).
| jaclaz wrote:
| >You need to change filters at least once a year to keep your
| indoor climate good.
|
| It really depends on the location and on the specific
| machine/install, usually there is no need to change the filters
| (they are normally washable) but they should be cleaned much
| more often, like every 6 (or even 3) months.
| mhb wrote:
| How old? You can't put insulation around knob and tube wires
| since they need air around them for cooling.
| Freak_NL wrote:
| If you are doing retrofit insulation, updating the electrical
| stuff to modern standards is pretty much something you'll
| have to do anyway.
| germinalphrase wrote:
| Presumably, you are entirely removing interior
| plaster&lathe/drywall to access wall cavity (and replace
| wires) rather than drill holes and blowing insulation?
| drjasonharrison wrote:
| You don't have to remove all of the lathe and plaster.
| Blown in insulation after upgrading the electrical. Fish
| poles and long cuts repaired afterwards.
| Freak_NL wrote:
| If you are upgrading the insulation from the inside
| you'll have whatever is the inner wall out anyway, it's
| pointless otherwise; if you're doing it from the outside
| (possible with some roofs) it doesn't matter; and filling
| the wall cavity is done from the outside too, unless you
| have a really weird house no wiring goes there.
| PaulDavisThe1st wrote:
| > If you are upgrading the insulation from the inside
| you'll have whatever is the inner wall out anyway
|
| In Philadelphia in 1996, I had a company blow in
| insulation to my wood-framed, plaster+wood-lathe covered
| cavity walls without removing the inner walls. They
| created a series of 4"/10cm holes at the top of each bay
| and blew the insulation in that way.
|
| ps. I later found out that this is a terrible idea for
| vapor control reasons.
| Freak_NL wrote:
| Yeah, that's basically why just putting up new walls is
| the long term solution. And as a bonus you can put in
| some sweet CAT6 cabling and enough electrical sockets
| while you're at it. :)
|
| Another benefit: when you take out the inner walls in an
| old house, you are going to find layers and layers of...
| stuff. Like 2cm of styrofoam (insulation in a nineties
| way) and a new layer of drywall on top of whatever
| chipboard/grout/newspapers where put in in a distant past
| (at least in my old house).
| germinalphrase wrote:
| Massive project though.
| amluto wrote:
| Sure you can, even in code-heavy places like California:
|
| https://www.nachi.org/knob-and-tube.htm
|
| In any case, if you overheat Romex and destroy the
| insulation, you can create a line-to-ground-or-neutral arc or
| short. If you overheat knob and tube and destroy the
| insulation, you are quite unlikely to cause an actual problem
| -- there's nothing nearby for it to short to.
|
| Modern insulation tolerates rather higher temperature than
| old insulation, and knob and tube has plenty of other
| problems, but this isn't really one of them.
|
| (If GCFIs on branch circuits or feeders were widely deployed,
| even at higher thresholds than 5mA, and everyone used either
| grounded metallic conduit or bundles of wire with a bare
| ground in the middle (like Romex or NM-B), then insulation
| failures would be quickly detected.)
| mhb wrote:
| Thanks. Good to know. But probably worth mentioning that,
| even though you can insulate around knob and tube where
| local jurisdictions allow it:
|
| "K&T wiring is designed to dissipate heat into free air,
| and insulation will disturb this process. Insulation around
| K&T wires will cause heat to build up, and this creates a
| fire hazard. The 2008 National Electrical Code (NEC)
| requires that this wiring system not be covered by
| insulation."
| drjasonharrison wrote:
| I wonder how often this actually is a problem, in that
| the owner looks at knob and tube wiring and keeps it for
| the heritage value. My parents were ripping it out in the
| 1970s from a 1920s home. I know that heritage
| designations often require using the original
| construction techniques but do they prevent upgrades to
| the electrical system?
|
| "I'm sorry sir but your grandparents didn't have grounded
| outlets so you can't install have them either."
| mhb wrote:
| The problem, at least in my case, is that my 1930 house
| has k&t wiring and little/no insulation. The easiest way
| to add insulation would be to blow it in through drilled
| holes. This is a lot less involved than rewiring the
| house.
|
| I have no affection for the wiring - nostalgic or
| otherwise.
|
| And, yes, vapor issues.
| drjasonharrison wrote:
| Most home owners would either prioritize replacing/upgrading
| knob and tube wiring because we like to have more outlets and
| circuits than when knob and tube wiring was installed, or
| because the building code or local permitting office would
| require the upgrade. Same thing for aluminum wiring (1970s?),
| GCFI, replacing fuses with breakers, etc.
| oliwarner wrote:
| 100mm? Not sure what your climate is but the recommendation in
| the UK has been 270mm for two decades (based on 0.044W/m2K
| fluff). It's a relatively cheap and easy upgrade.
| lnsru wrote:
| 270 mm for roof or walls? For roof yes, for walls I don't
| know. I have no plan to create passive home from an old one.
| Freak_NL wrote:
| In an old house? Rarely. I've been able to fit 100mm of PIR
| (Polyisocyanurate) under my roof (1920s Dutch terraced brick
| house), and that is pushing it without eating too much into
| your living space.
|
| PIR is a great solution for space-constrained insulation
| though: 0.022W/m2K, so 100mm gives you a thermal resistance
| of 4.54m2K/W. It's the equivalent of 200mm of mineral wool
| with a thermal insulance of 0.044W/m2K.
| HyperSane wrote:
| I really like the fresh air system were air from these is piped
| to rooms in small diameter pipes.
| pvillano wrote:
| I've been meaning to do something like this for venting the fumes
| of my resin printer in the winter. Glad the work has been done
| for me
| LarryMullins wrote:
| The best method is to live someplace with a tolerable climate,
| dress appropriately for the season (that means warm clothes in
| winter!), and open your windows. I've run neither my furnace nor
| my AC in years.
| eternauta3k wrote:
| What first-world country has good weather and is easy to
| migrate to? Israel?
| LarryMullins wrote:
| Large swaths of America, and much of Europe. Most of the UK
| has a climate similar to the climate where I live (PNW). It
| sometimes drops below freezing where I live, but rarely much
| longer for a day or so. Not long enough to necessitate
| running the furnace to keep my pipes thawed.
|
| Dressing appropriately for the season is the key. Most people
| don't. From what I've seen, most people have a single set of
| clothing they use in every season and jackets they use in
| winter when outside. I wouldn't wear a jacket indoors either,
| that would be weird, but my winter clothes are warm enough
| that I don't need a jacket indoors in winter. That's what
| sweaters, thick long-sleeve shirts, etc are for.
|
| The payoffs for this lifestyle are two fold: I get to enjoy
| fresh air whenever I want, without needing some moldy filter.
| And my energy bill is virtually nil, which is good for the
| environment.
| _Microft wrote:
| Ha, this is inspired by our comments in the CO_2 monitor thread,
| right? I thought about finding something to post about heat
| exchangers as well but was tending more towards the high-
| power/industrial end of the spectrum but this one's a good one
| too! :)
| akozak wrote:
| I've wanted an HRV/ERV system for a long time, but have been
| wondering about best practices with the intakes. One in each
| room? In the ceiling, if our furnace outputs are in the floor?
| The new ducting network seems like the hardest part by far. (Plus
| the house is 100 years old and super leaky anyway)
| kkfx wrote:
| Here in Europe these machines are called simply double-flux VMC,
| mandatory in "new" home (where new vary since in some northern
| countries are mandatory since a decade or so, while in the south
| it's more a recent thing, depending on local climate).
|
| They are VERY cheap in industrial terms, not so cheap for what
| they are in end-buyers terms.
|
| BUT really new buildings start to propose something better,
| "thermodynamic VMC" who happen to be double flux ones as well but
| instead of passively recovery the heat/cool they are active,
| meaning a small heat pump between the two flux. It's far less
| cheap in electricity bill (mine consume 10+kWh/day for 350 m3/h,
| 12.360 ft3/h if this is the unit Imperial system use) but they
| de-humidify extremely well.
|
| IME those last + low inertia heating result in LESS expensive
| heating/cooling than passive ones + same heating. At least in a
| not so cold/not too hot place (typical winter minima -25, -15
| this year, typical summer maxima +30-32).
| throw0101c wrote:
| These is more generally known as "heat recovery ventilation", HRV
| (the term is first used about half-way down the article):
|
| * https://en.wikipedia.org/wiki/Heat_recovery_ventilation
|
| There are also energy recovery ventilators, ERV, which in
| addition to tempering the temperature of incoming air, also
| temper the humidity:
|
| * https://en.wikipedia.org/wiki/Energy_recovery_ventilation
|
| In the past HRVs were mostly used in colder climates, as the
| humidity exchange would cause frosting of the exchange core, but
| modern core membrane materials have improved in recent years, and
| some units can operate frost-free down to -10C / 14F: colder than
| that and you may need a have pre-heater running on the intake, or
| the unit may have a defroster.
|
| * https://www.broan-nutone.com/getmedia/d7230185-8067-4256-a1a...
|
| Some units have defrost modes so that they can run even in -27C
| (though it will probably be defrosting a lot):
|
| * https://www.broan-nutone.com/getmedia/3ec22979-19c4-4f1e-94f...
| oaiey wrote:
| That defrosting feature is very expensive. Move triggered early
| December for like 5 days. It runs at 1000W permanently. In our
| lovely energy process this translate to 15EUR a day or 450EUR
| if run for a full month.
|
| Switched it off air exchange for dinner days until it got the
| one degree weather where the dentist is not needed
| Volundr wrote:
| That's odd. I've got a heat pump, and it defrosts a couple
| times an hour, but the defrost cycle only lasts a couple
| minutes. Are you sure it's not malfunctioning?
| h0l0cube wrote:
| > In the past HRVs were mostly used in colder climates
|
| Did you mean warmer climates? You went on to mention new
| membrane tech and pre-heaters that can handle colder
| temperatures.
| throw0101c wrote:
| >> _In the past HRVs were mostly used in colder climates_
|
| > _Did you mean warmer climates?_
|
| No: HRVs were in cold climates previously because HRV do not
| deal with moisture, and so there was less frosting / icing up
| of the membranes.
|
| ERVs were more focused in warmer climates, because warmer
| climates tend to have a lot of humidity, so if you had a
| dehumidifier in (e.g.) Texas or Florida, and you exhausted
| stale air, it would end up exhausting the conditioned drier
| air and intake the outside humid air, which you would then
| have to dehumidify again.
|
| Of course ERVs are _also desirable_ in cold climates because
| cold air is dry(er), so you 'd be drying out your house. So
| now that is technically more easy, ERVs are also being used
| in colder climates.
| h0l0cube wrote:
| Thank you for clarifying.
| shkkmo wrote:
| Those allow ERVs to operate at lower temperatures. HRVs don't
| need a membrane that passes moisture through, they just need
| a heat conductive surface.
| h0l0cube wrote:
| Got it, thanks! If I understand correctly, HRVs have always
| been suitable for both warm and cold climates. Modern ERVs
| are becoming more suitable for cold climates with frost
| protection.
| jaggederest wrote:
| Not quite, HRVs are much less useful in a hot-humid
| climate, because most of the energy actually goes to
| condensing and removing the humidity, rather than the
| temperature difference.
|
| e.g. 25c -> 20c is only 5 kelvins different, but it might
| have to go from 95% relative humidity to 50% relative
| humidity at the same time.
|
| So the bottom line for a long time has been, don't bother
| with HRV in hot-humid climates because they only return
| ~20% of the embodied energy of the conditioned air,
| whereas in cold climates, 90%+ of the energy goes into
| the e.g. 25 kelvins differential in the temperature of
| the air, and the humidity is already low on incoming air
| (desirable, since people produce humidity through sweat,
| showers, cooking, and cleaning)
|
| Now that ERVs are coping with much colder temperatures,
| expect to see HRVs phase out except in extreme climates
| like Alaska, Alberta and the upper midwest US.
|
| I wouldn't expect to see either in very temperate
| climates like San Diego - there's just not enough energy
| payoff for the cost of installation. Better off just
| opening the windows when it's only 2 kelvins different
| inside and outside!
|
| PS the other major difference between ERVs and HRVs is
| that HRVs are more-or-less maintenance free for life,
| since they're basically just stacked aluminum plates.
| ERVs degrade in performance over time, being things like
| moisture-permeable membranes, so that's a concern for
| people interested in long term installation in remote
| areas, for example, but most commercial/residential usage
| isn't that worried about that.
| throw0101c wrote:
| > _Better off just opening the windows when it 's only 2
| kelvins different inside and outside!_
|
| Except for all the pollen, dust, and pollution that doing
| so would also bring in. ERVs can cost as little as US$
| 1000 for the units themselves:
|
| * https://hvacdirect.com/residential-industrial-
| commercial-fan...
|
| If this is a retrofit, there can be challenges with
| installation, but plumbing into existing force air ducts
| is a common scenario.
| jaggederest wrote:
| Well, HRV/ERV have no built-in filtration in themselves,
| so they're exactly comparable to throwing open the
| window. If you run them before a filter, obviously
| they're better, but they have no inherent advantages to
| opening windows.
| ericd wrote:
| He's saying that you'd use an HRV instead of an ERV, because
| the moisture exchange of the ERV would start frosting up in a
| very cold climate. If that's not a concern, the humidity
| conditioning the ERV does on the incoming air makes it
| preferable.
| stuaxo wrote:
| Is this the same thing as MVHR ?
| strife25 wrote:
| Does anyone know of good building science websites? I'd love to
| better understand best practices.
|
| The only one I've found is https://inspectapedia.com
|
| There's great stuff on YouTube too (e.g. Matt Risinger's
| channel), but soooo much conflicting information.
| losvedir wrote:
| In another comment I mention how overwhelmed I am by all this
| stuff, so maybe don't take it from me, but when I've been
| searching for answers about stuff like best practices for
| windows or replacing my furnace with a heat pump,
| greenbuildingadvisor.com seems to come up a lot and seems
| pretty good. That said, much of it is behind a paywall that's
| quite expensive, and I've been waiting to save my free trial
| for the optimal moment.
| nerdbert wrote:
| https://www.greenbuildingadvisor.com/
| eternauta3k wrote:
| https://constructionphysics.substack.com/
| walterbell wrote:
| DIY forum, https://ecorenovator.org/forum/
|
| HVAC blog, https://www.energyvanguard.com/blog/
|
| HVAC pro forum, https://hvac-talk.com/vbb/
|
| Heating forum, https://forum.heatinghelp.com/
| walterbell wrote:
| Bionaire's elegant $100 commercial window HRV was discontinued,
| there don't seem to be any alternatives at that price point,
| https://www.amazon.com/Bionaire-BAP336M-U-EverFresh-Exchange....
| Product manual might be useful for DIY:
| https://ia904509.us.archive.org/29/items/manualzilla-id-7067...
|
| Commercial ERV/HRV units start around $500,
| https://www.greenbuildingadvisor.com/question/inexpensive-ef...
|
| DIY counter-flow design with coroplast sheets,
| https://ecorenovator.org/forum/showthread.php?t=891&page=38#...
| Someone1234 wrote:
| That Bionaire appears to have the air inlet and outlet within a
| couple of inches of each other, that isn't going to do anything
| except waste electricity. You're just recirculating indoor air.
|
| Real ERV/HRVs have ducting ports in both sides, and installing
| all the ducting and electrical is far more expensive than the
| $500~1000 the unit itself costs. That's why they're uncommon:
| Install is expensive and painful.
| Bluestrike2 wrote:
| The window unit linked at the top doesn't appear to do heat
| recovery. Most of the decentralized single-room mechanical
| ventilation heat-recovery (MVHR) units reverse their fans
| every 60-70 seconds in order to operate their heat
| exchangers, such as this example.[0] That period _should_ be
| long enough for the exhausted air to disperse far enough away
| outside that it won 't just be sucked back into the house,
| unless the exterior exhaust is positioned in a really weird
| spot outside where wind is minimal and the air can't
| effectively disperse. Alternatively, they can also be paired
| with another unit so that one exhausts air at the same time
| the other brings in fresh air, allowing better airflow
| across/within the room.
|
| The problem with this approach is that once you start
| ventilating multiple rooms with these small units (figure
| $500 per room with a single unit, twice that if two), the
| cost _rapidly_ approaches that of a centralized unit with
| ducting. But if you 're just looking to ventilate a room or
| two, they're likely a very cost-effective solution. I could
| also see them being used on a first floor living room/kitchen
| in conjunction with a centralized unit ventilating upstairs
| bedrooms with the ducting run through an attic. That'd
| probably be cheaper overall than trying to run an
| intake/exhaust duct downstairs or installing units in each
| room. Plus, each exterior penetration increases the
| opportunity for uncontrolled air leakage and, most
| importantly, water.
|
| 0. https://www.bpcventilation.com/bsk-zephyr-single-room-
| heat-r...
| spxtr wrote:
| The other problem with this approach is that it is limited
| to 50% efficiency long-term. They claim "up to 90%", but it
| is only 90% efficient immediately after switching
| directions. The efficiency then drops to 0% before
| switching modes again.
| erikerikson wrote:
| They make vents that exhaust in a spiral from the center and
| intake from the sides so that the air flows are
| perpendicular. Might look funny on that unit but could help
| with that mixing problem.
| walterbell wrote:
| _> That Bionaire appears to have the air inlet and outlet
| within a couple of inches of each other, that isn 't going to
| do anything except waste electricity. You're just
| recirculating indoor air._
|
| Are you referring to the ports on the interior or exterior?
| Someone1234 wrote:
| Both are too close to each other.
| walterbell wrote:
| The unit is 26 in. wide for a use case (e.g. apartments)
| where the HRV avoids leaving a window open for
| simultaneous intake and exhaust. If the exterior wind
| direction doesn't locate the exterior outlet downwind of
| the intake, one could potentially install a short
| exterior duct to add separation, as in step 13 of this
| DIY HRV, https://www.loudawson.com/17884/how-to-build-
| air-cross-flow-.... For the interior ports, 45-degree
| angled vents can reduce overlap between the airflow
| directions. Without the HRV, air would be moving in and
| out of the same window anyway, without any structural
| separation.
|
| Amazon reviews for the Bionaire reported both energy
| savings and air quality improvement, so it worked for
| some people.
|
| For homes, there are DIY full-sized HRVs, with custom
| ducting, https://ecorenovator.org/forum/showpost.php?p=26
| 861&postcoun...
| D13Fd wrote:
| This. Last quote I got was $5k to install a $700 unit.
| amatix wrote:
| The BluMartin FreshAir 100 and the Fresh-R series are both MVHR
| units that fit into existing walls: there's a Fresh-R model
| that goes into a window frame too.
| hasbot wrote:
| Here are detailed plans for a DIY HRV:
| https://www.aivc.org/sites/default/files/airbase_2413.pdf
| walterbell wrote:
| Thanks. A coroplast design from 1985!
| mnot wrote:
| Installed one of these last year during a Reno, love it - no more
| condensation, no mold, much fresher air.
| danieldk wrote:
| Same, our apartment complex has high-volume ventilation with
| heat exchangers in every apartment (The Netherlands). Humidity
| and mold has never been a problem and it's like continuously
| ventilating your house without the cold air. We recently
| replaced the gas heating and heat exchanger by an air-to-air
| heat pump that also acts as the heat exchanger and regulates
| the ventilation. Is a nice upgrade, because now the heat is
| fully controlled by one unit.
| alliao wrote:
| wow, do you have any links on the product? sounds really good
| simooooo wrote:
| I still find my air feels cold for to it being moving air
| leashless wrote:
| I have an ambition to live in an insulated metal barn. They're
| incredibly cheap compared to regular construction. I would then
| construct smaller dwelling units inside of it, non load bearing,
| which could be played around with much like legos. (It may help
| to know I'm the designer of the hexayurt, a shelter technology
| popular at Burning Man and eventually bound for the world's
| refugee camps.)
|
| Key to this plan is handling humidity. Metal buildings don't
| breathe. Humidity condenses on the metal, turns into mould, then
| you have real problems.
|
| But with humidity sensors and A2A heat exchangers you wind up
| with the best of both worlds. I think.
|
| Let's say I'm not going to be building this before I've had real
| analysis from a good hvac engineer or two.
|
| https://www.kitbuildings.com/products/insulated-steel-buildi...
| For a sense of prices.
| amluto wrote:
| Buildings don't need to breathe. They need some way to dry out,
| because there is essentially no such thing as perfect
| waterproofing.
|
| I suspect the condensation problems in a barn like that are due
| to insufficient insulation or insufficient control of air
| movement. 50mm of polyisocyanurate is less than R10, which
| doesn't come close to even the code minimums, and is totally
| inadequate for a roof of a house anywhere remotely cold.
| Separately, if it's cold, then the interior surface of the
| metal will be cold, and any humid interior air making it to
| that surface will condense. A real house would do something to
| minimize that movement of warm interior air outward through the
| insulation.
| stuaxo wrote:
| Co2 build up and indoor pollution is a thing.
| newsclues wrote:
| The building doesn't need to breath.
|
| The building needs to have a supply of fresh air.
|
| Both are true.
| amluto wrote:
| Indeed. You want fresh air (possibly filtered, heated,
| cooled, humidified and/or dehumidified) to enter the
| living space. This is not the same thing as air flowing
| _through_ the walls, roof, etc.
| aaronax wrote:
| Put a vapor barrier inside of the insulation--this is very
| typical in any cold climate construction. Then humidity inside
| doesn't matter, because it never touches a cold surface.
| rsync wrote:
| ... but be careful when layering moisture barriers.
|
| If you stack two moisture barriers with any void space or
| (other material) in between, you can create a space that
| moisture can enter ... but never escape.
| throw0101c wrote:
| > _Metal buildings don't breathe. Humidity condenses on the
| metal, turns into mould, then you have real problems._
|
| Neither do modern homes made out of timber and wood sheathing.
| This is a good thing.
|
| Humans need to breathe, not buildings. Buildings need to be
| able to dry:
|
| * https://www.energyvanguard.com/book-house-needs-breathe-
| or-d...
|
| * https://www.energyvanguard.com/blog/myth-a-house-needs-to-
| br...
|
| * https://www.greenbuildingadvisor.com/article/buildings-
| dont-...
|
| * https://www.youtube.com/watch?v=CIcrXut_EFA
| PaulDavisThe1st wrote:
| What lets them dry is mostly air movement, which some people
| would calling "breathing".
|
| The main difference between the "new" and the "old"
| approaches to this is that the new one calls for much more
| organized and controlled air movement, while the old one
| tended to just rely on leakage, well, pretty much everywhere.
| amelius wrote:
| I guess cell phone reception would be an issue too.
| paranoidrobot wrote:
| Cell phone repeater tech isnt hugely expensive if you want to
| do it.
|
| More expensive the bigger the installation. Some carriers
| offer basic units.
|
| If your carrier supports wifi-calling then that can do most
| of it if you have decent internet.
| hedora wrote:
| Lies, all lies!
|
| We have metal siding, and get bitten by RF issues over and
| over again. The back of the house is in a cell phone
| shadow. The WiFi access point on the roof has all sorts of
| unpredictable deadspots outside. The 900MHz weather station
| display has to be placed within a 2" square spot indoors.
| Also, the solar panels and batteries drop into "call
| installer" mode a few times a week when their mesh network
| collapses.
|
| And so on. The internet of things will only make this worse
| over time.
| rsync wrote:
| People who understand wireless technology use wires.
| amelius wrote:
| That sounds like a way to get locked in by a particular
| carrier.
| Retric wrote:
| What makes barns cheap is the lack of glass windows,
| insulation, plumbing, carpets, climate control, decks, etc.
|
| Add that stuff back in and you are just building a house.
| lnsru wrote:
| I don't know where are you located. But I worked in insulated
| containers in south Germany. The office was being built. It was
| like sauna in summer and unpleasantly cold in winter. I guess
| you would need 10 inches of insulation to have acceptable
| result here.
| stuaxo wrote:
| There's a some research into thin internal wall insulation in
| the UK, because our housing stock is old and small.
|
| Spray cork seems to come out the winner.
|
| https://www.gov.uk/government/publications/thin-internal-
| wal...
| PaulDavisThe1st wrote:
| and for a very recent (last week) US perspective on cork
| insulation (and siding), here's Matt Risinger (Build):
|
| https://www.youtube.com/watch?v=iXY_f-bJDyA
| fvdessen wrote:
| You will live in the dark :/
| defrost wrote:
| There's a _lot_ of variations of prefab sheds, metal roofs, etc
| in Australia. The vapour permeable sarking,
| separated from the roof sheet by a drainage batten provides
| drainage of any moisture or condensate forming below the roof
| sheet.
|
| https://dctech.com.au/products/dct-r01-1c/
|
| is a common housing solution - that's a "runoff sheet"
| immediately under the metal that allows vapor up to the metal
| and then catches condensed water and runs it down to the sides
| and out.
|
| In a hot climate big wide roofs with a good pitch (and a
| venting cap gap at the ridge line) can heat air under the metal
| and use the rise of hot air (and out the ridge cap) to draw in
| air through (say) watered hedges.
|
| You might get some ideas browsing Aussie prefab shed solutions,
| etc.
|
| https://www.theshedcompany.com.au/barns/american-barns/
|
| https://ams-group.com.au/
| PaulDavisThe1st wrote:
| > The vapour permeable sarking
|
| I would have hoped that with fairly good knowledge of both UK
| and US english construction terminology, AU english would
| have nothing left to confuse me with. But ... no. "Sarking" ?
| bitschubser_ wrote:
| Actually, I'm wondering why not more houses are build out of a
| metal-insulation sandwich contruction, one downside, no nails
| on the outside walls (but this can also be solved with a
| regular installation zone out of plywood, here is an example
| from one who built his own home out of a metal sandwich
| contruction: https://www.youtube.com/watch?v=brcGQZWbeLI
| according to him it was really cheap (don't know how it
| compares to wood framing with insulation)
|
| wondering how prefacb metal sandwich construction compares to
| prefab wood framing (which is quite common here in germany)
| Retric wrote:
| Wood beam construction is really fast, cheap, and easy to
| insulate or modify.
|
| People argue for all kinds of alternatives but the cost to
| construct a wood frame is only around 5% the cost of the
| home. Swapping to something else just doesn't buy you much
| and most alternatives have significant downsides.
| infecto wrote:
| Barndominiums are really popular depending on where you live.
| I see them all the time in the United States, really popular
| for new construction custom home.
| skeeter2020 wrote:
| You wouldn't need to have exterior load bearing construction
| inside, but I don't think that absolves all structural
| concerns. What about services (HVAC, electricity, plumbing)?
| What about interfacing with the outside world, i.e. windows?
| infecto wrote:
| With how popular barndominiums are these days I don't think
| handling humidity is going to be that much of an issue. I have
| even seen some more like you described where they build the
| actual home on the interior of the metal structure instead of
| adopting the metal structure as the homes walls.
| dalbasal wrote:
| Interesting, but I don't see the massive cost advantage.
|
| $150k for a 150 m2 kit. That's before you have constructed the
| outer shell _or_ the internal dwelling(s). What am I missing?
| gog wrote:
| The most expensive kit on the site (for me) is 50x15x7,3m
| which comes out to 750 m2 and it is 2 stories high, so that
| comes out to 1500 m2.
| ilostmyshoes wrote:
| Flexibility to change things without massive costs maybe?
| lnsru wrote:
| A drywall is then a solution. It can be build almost
| anywhere and removed within hours again.
| saalweachter wrote:
| You basically want balloon framing, in spirit if not in
| execution.
|
| In old balloon framed houses you'll often find all the
| interior walls are not structural -- they were often
| built _after_ the sheet rock was put in on the exterior
| walls and ceiling. That leaves you free to shift them
| however you please without compromising the stability of
| the house.
| hasbot wrote:
| From the article regarding maintenance:
|
| - Clean or change the filters every one to three months
|
| - At least once a year clean the heat exchanger core.
|
| - In addition to the core, the fans should be cleaned at least
| once a year.
|
| There is a home efficiency YouTuber that mentioned recently that
| his new home has 17 filters!
|
| There's always plenty of house maintenance to do anyway, this is
| just adding to it. I think Henry David Thoreau was onto
| something.
| losvedir wrote:
| This makes me so overwhelmed. I own a house built in the 1950s
| and I want to make it more energy efficient, but where do I
| begin, and how do I change parts of it without causing other
| problems.
|
| Can I improve insulation without causing moisture and mold at the
| boundary? Can I upgrade my furnace to a heatpump without first
| improving insulation and air tightness? Which of the several ways
| I've read about is the best to condition my crawl space? And now
| I'm reading that I shouldn't seal up the drafts in my home
| without one of these air exchangers? Etc etc
| robohoe wrote:
| Dealing with the same but a 1960s house. Make sure to air seal
| and insulate it well. Most insulation contractors skip the air
| sealing but that's very important!
| hasbot wrote:
| See if you can get an energy audit from your electric or gas
| company.
|
| You can definitely upgrade your furnace without first improving
| insulation and air tightness. There are other conceptually
| simple changes that will improve efficiency with low risk of
| causing other problems (e.g. attic insulation, blown in wall
| insulation, replacement windows). The energy audit will include
| an analysis.
|
| Home efficiency is pretty complex. Read up a lot before paying
| for any changes. Even today, many new homes aren't built to be
| airtight. There are air gaps everywhere. An HRV/ERV may help
| reduce energy costs because air has to enter the house from
| somewhere, but in older homes I'm not sure the slight benefits
| one will gains will be worth the cost and extra complexity (an
| HRV/ERV needs to be cleaned twice a year).
| maxerickson wrote:
| The audit should have some information about what is going to
| be the most beneficial cost wise. Additional insulation is
| often a pretty safe win (especially if it doesn't change the
| moisture barrier).
|
| Of course there can be other goals. I don't expect that
| upgrading my 80% AFUE furnace would save me any money. High
| efficiency furnaces cost more, break faster and it would
| require more work to install one vs just replacing with an
| 83% unit. But it would change how air moves in the house,
| instead of drawing combustion air from the conditioned space,
| a high efficiency furnace would pull it from outside, so it
| would be easier to humidify the house to a more comfortable
| level (a medium size wick humidifier doesn't keep the house
| above 20% on colder days).
| PaulDavisThe1st wrote:
| Blown-in wall insulation is terrible in cold climates. With
| no vapor barrier, any moisture from the living space will
| condense once it hits the "cold zone", which is likely inside
| the wall, and thus lead to rot (and mold) over time.
| vegasje wrote:
| I empathize with you, as I am in the same boat.
| ganoushoreilly wrote:
| A lot of the improvements would be built around any renovations
| / remodels you want to undertake. One of our previous homes was
| built in the 1900's. One of the things we did that were
| immediately noticed were upgrading windows to double pane.
| Again not feasible if you don't need the upgrade, but for us it
| was a worthwhile investment. We also found that leaving doors
| closed in various rooms was important to retaining heat. The
| hallways would be cooler but it made it much easier to _spot_
| warm parts of the home with a heater if absolutely necessary.
|
| There may be a local company that can give you advice on things
| you can do in a cost efficient, least headache manner. Whatever
| you undertake though is probably going to be an expense, so
| check with your local state / county and see if they have any
| energy efficiency improvement programs. I just used one to
| improve windows and attic / crawl space insulation in my
| mother's home.
|
| Good luck
| hasbot wrote:
| I've lived in two 50's houses where the windows were replaced
| with double pane. Both window replacements were mediocre at
| best. Replacement windows are a bit smaller than the original
| windows so there is a gap between the house framing and the
| window frame. In neither house did the installer do an
| adequate job of sealing that gap. On one window, I could even
| see daylight through the gap. I had to remove the inside trim
| and spray in foam.
| ganoushoreilly wrote:
| That sucks, a poorly installed window definitely defeats
| the benefits.
| throw0101c wrote:
| In a perfect world, you'd be able to build the perfect wall:
|
| *
| https://buildingscience.com/documents/insights/bsi-001-the-p...
|
| What you should worry about in renovations may depend on which
| climate zone you are in:
|
| * https://www.ecohome.net/guides/3521/climate-zones-map-usa-
| ca...
|
| * https://basc.pnnl.gov/images/iecc-climate-zone-map
|
| > _Can I improve insulation without causing moisture and mold
| at the boundary? Can I upgrade my furnace to a heatpump without
| first improving insulation and air tightness? Which of the
| several ways I 've read about is the best to condition my crawl
| space? And now I'm reading that I shouldn't seal up the drafts
| in my home without one of these air exchangers? Etc etc_
|
| If you're serious about this, then hiring a consultant /
| company who specializes in this would be a first good step:
|
| * https://www.youtube.com/@HomePerformance/videos
|
| * https://www.youtube.com/watch?v=t-GIzX6bLeU
|
| The money you pay upfront for a plan may save you cash down the
| road to make sure you don't do things in the 'wrong' order or
| buy incorrect equipment (type or size). The above two
| presenters are a good start (and do remote consulting AFAICT),
| but looking at ResNet-certified folks (in your area?) is a
| broad good start.
|
| Generally, for indoor air quality (IAQ), you want to go air
| tightness (even without extra insulation) and then get a
| ERV/HRV. If your current furnace/AC is working fine then
| letting it run for a few more years won't harm anything, and
| changing it won't help IAQ or comfort. For crawl spaces, making
| it conditioned is a good start: insulation and a 10+ _mille_ (
| "mill") poly tarp so stop moisture drive would be a good start.
|
| P.S. If you think you have problems, I grew up a house from the
| 1890s.
| hasbot wrote:
| Here are detailed plans for a DIY HRV:
| https://www.aivc.org/sites/default/files/airbase_2413.pdf
| simonebrunozzi wrote:
| I am involved in a complex restoration project in Venice, Italy
| (a side hobby); and I am trying to figure out what would be the
| best option in regards to heat pump, potentially using geothermal
| energy from underground.
|
| In Venice you have the option to do air/water heat exchange,
| using the water from the canals.
|
| Any of you have any experience with something like that?
| pifm_guy wrote:
| Ask someone local.
|
| What's available and rules vary really widely city to city.
|
| What makes sense financially also depends on your building
| construction, climate and fuel prices, which also depends a lot
| on location.
| simonebrunozzi wrote:
| I was asking more about the technical aspects. Regulation,
| etc I will need to deal with but it is pretty much sorted.
| Thanks.
| ClumsyPilot wrote:
| I recently moved into an apartment with sucha ventillation
| sustem, really pleased with it.
| throwawaygo wrote:
| [flagged]
| MengerSponge wrote:
| Every story on HN is also posted somewhere on Reddit, but the
| discussion here is different.
|
| I posted this because its germane to HN readers. Air quality
| has major health and cognitive effects, and there are
| substantial opportunities for technological innovations that
| would dramatically improve our quality of life and work.
| antisceptic wrote:
| Let us not forget that it is squarely in the hacker spirit to
| share heat with tech savvy, instead of scaling up a bad
| solution!
| throwawaygo wrote:
| Uh huh.
| jrockway wrote:
| What kind of options do apartment dwellers have in this space?
| I've been thinking of DIY-ing something like this (suck in air
| from the window, heat it resistively in the rare event it's too
| cold inside, pass it through a HEPA filter, pass it through a
| humidifier, enjoy), but that is clunky and I'm wondering if
| products actually exist that I could just buy instead.
|
| (I own my apartment, but no HVAC system. Through-the-wall AC,
| steam radiator heating.)
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