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Air-to-Air Heat Exchangers for Healthier Energy-Efficient Homes
- walterbell 4y agoBionaire'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-Purifier/dp/B001L1BPKQ 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-7067964/7067964.pdf https://ia904509.us.archive.org/29/items/manualzilla-id-7067... Commercial ERV/HRV units start around $500, https://www.greenbuildingadvisor.com/question/inexpensive-efficient-hrv https://www.greenbuildingadvisor.com/question/inexpensive-ef... DIY counter-flow design with coroplast sheets, https://ecorenovator.org/forum/showthread.php?t=891&page=38#post27793 https://ecorenovator.org/forum/showthread.php?t=891&page=38#...
- Someone1234 4y agoThat 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.
- walterbell 4y ago> 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 4y agoBoth are too close to each other.
- walterbell 4y agoThe 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-heat-exchanger/ 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=26861&postcount=291 https://ecorenovator.org/forum/showpost.php?p=26861&postcoun...
- D13Fd 4y agoThis. Last quote I got was $5k to install a $700 unit.
- Bluestrike2 4y agoThe 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-recovery-unit https://www.bpcventilation.com/bsk-zephyr-single-room-heat-r...
- spxtr 4y agoThe 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 4y agoThey 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.
- hasbot 4y agoHere are detailed plans for a DIY HRV: https://www.aivc.org/sites/default/files/airbase_2413.pdf https://www.aivc.org/sites/default/files/airbase_2413.pdf
- walterbell 4y agoThanks. A coroplast design from 1985!
- amatix 4y agoThe 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.
- olivermuty 4y agoThis 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.
- lnsru 4y agoI 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.
- stuaxo 4y agoI've been looking at spray cork. You can have it applied indoors and skimmed at only about a cm total or outdoors.
- ericd 4y agoSpray… 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 4y agoSeems to be a paint/stucco alternative: https://www.buildwithrise.com/stories/spray-cork-what-is-it https://www.buildwithrise.com/stories/spray-cork-what-is-it
- leashless 4y agoI 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-buildings https://www.kitbuildings.com/products/insulated-steel-buildi... For a sense of prices.
- amelius 4y agoI guess cell phone reception would be an issue too.
- paranoidrobot 4y agoCell 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.
- amelius 4y agoThat sounds like a way to get locked in by a particular carrier.
- hedora 4y agoLies, 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.
- throwawaygo 4y ago[flagged]
- MengerSponge 4y agoEvery 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 4y agoLet 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 4y agoUh huh.
- _Microft 4y agoHa, 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! :)
- MengerSponge 4y agoIt was inspired by the existence of the CO2 monitor article and thread. It's a solved problem, but it's not well known in the US, unfortunately! ) Which makes it Not Particularly Interesting(TM)
- mnot 4y agoInstalled one of these last year during a Reno, love it - no more condensation, no mold, much fresher air.
- microtonal 4y agoSame, 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.
- ClumsyPilot 4y agoI recently moved into an apartment with sucha ventillation sustem, really pleased with it.
- throw0101c 4y agoThese 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 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 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-a1a2-32127fe9328a/Owners-Manual-ERV100S-ERV100SP.pdf?ext=.pdf 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-94fd-1388d9e66583/Spec-Sheet-B160H65.pdf?ext=.pdf https://www.broan-nutone.com/getmedia/3ec22979-19c4-4f1e-94f...
- h0l0cube 4y ago> 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.
- shkkmo 4y agoThose 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 4y agoGot 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.
- losvedir 4y agoThis 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
- vegasje 4y agoI empathize with you, as I am in the same boat.
- ganoushoreilly 4y agoA 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 4y agoI'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.
- hasbot 4y agoHere are detailed plans for a DIY HRV: https://www.aivc.org/sites/default/files/airbase_2413.pdf https://www.aivc.org/sites/default/files/airbase_2413.pdf
- hasbot 4y agoFrom 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.
- strife25 4y agoDoes 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 https://inspectapedia.com There's great stuff on YouTube too (e.g. Matt Risinger's channel), but soooo much conflicting information.
- losvedir 4y agoIn 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.
- eternauta3k 4y agohttps://constructionphysics.substack.com/ https://constructionphysics.substack.com/
- walterbell 4y agoDIY forum, https://ecorenovator.org/forum/ https://ecorenovator.org/forum/ HVAC blog, https://www.energyvanguard.com/blog/ https://www.energyvanguard.com/blog/ HVAC pro forum, https://hvac-talk.com/vbb/ https://hvac-talk.com/vbb/ Heating forum, https://forum.heatinghelp.com/ https://forum.heatinghelp.com/
- nerdbert 4y agohttps://www.greenbuildingadvisor.com/ https://www.greenbuildingadvisor.com/
- jmuhlich 4y agohttps://buildingscience.com/document-search https://buildingscience.com/document-search
- akozak 4y agoI'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)
- simonebrunozzi 4y agoI 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 4y agoAsk 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 4y agoI was asking more about the technical aspects. Regulation, etc I will need to deal with but it is pretty much sorted. Thanks.
- pvillano 4y agoI'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 4y agoThe 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 4y agoWhat first-world country has good weather and is easy to migrate to? Israel?
- LarryMullins 4y agoLarge 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.
- jrockway 4y agoWhat 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.)
- MengerSponge 4y agoReally depends on what country you live in. It's expensive, but Ephoca's AIO line is one of the best options I've seen in the US: https://ephoca.com/aio/ https://ephoca.com/aio/ But I'll admit I posted this in part to see if any other good units exist yet.
- kkfx 4y agoHere 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℃).
- bradwood 4y agoThe article confuses Nitrogen Monoxide (NO), Nitrogen Dioxide (NO2) and Nitrous Oxide (N2O). I know this as a few kids in chemistry class a few decades ago thought they'd sneak into the the lab and make laughing gas (N2O). The made Nitrogen Dioxide (NO2), inhaled it and hospitalised themselves! Not a laughing matter (at least not for them). Anyway, I digress, but if you're going to write an article about gases, at least get the names and formulae right...