Air-to-Air Heat Exchangers for Healthier Energy-Efficient Homes
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* 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...
Did you mean warmer climates? You went on to mention new membrane tech and pre-heaters that can handle colder temperatures.
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.
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.
Open the linked PDFs for the Broan units and do a text search for "filter": you will find that they do.
Further: even if they didn't, the RVs will have ducting for the intake, where you can put a box for a filter, which certainly take up space, but not a lot of money:
* https://acinfinity.com/air-filter-boxes/
How do you install a MERV ≥8 filter into a window?
> 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.
Switched it off air exchange for dinner days until it got the one degree weather where the dentist is not needed
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.
You can have it applied indoors and skimmed at only about a cm total or outdoors.
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.
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.
In my area of the US for example, gas costs 32￠/therm, which equates to 1.1￠/kWh.
Electricity on the other hand costs 6.4￠-10.9￠/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.
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....
So 48-96kw, technically.
Installing a pump without installing insulation (if you need it) is silly.
Classic homes here are built with rocks and mortar, laid down on grownd, often stitched together in villages to spare a wall or two. As a result they are essentially impossible to insulate: insulating from the outside means agree with others for a job often as expensive al living the home for a new one. From the inside it's even more costly and not always doable since old homes tend to be irregular and with low ceiling resulting a too much internal space loss, not counting the effect of having loss much thermal mass. Toll buildings from just after WWII to the sixties are in even worse shapes, at that time almost no one care about insulation or thermal design because heating was veeeeeery cheap. The old rule in winter was "if it's too hot just open a window, it's cheaper than a thermostat".
These buildings are the MAJORITY of the buildings and their own tend to be not so rich so they'll reach both natural and economical EOL soon and non one have a viable idea of what to do. Rebuilding anything is possible in mere theoretical terms, but in 30+ years, not tomorrow, and only with a public hand keeping costs low and plan with a bit of design instead of building a new real estate rush with similar results of those of the recent past in few decades. In practice though it's next to impossible because vast majority do not want to relocate. In south EU most home owners are middle class or even some low incomes, not just few rich and all other rent from big society.
That's the real point. For EVs and p.v. it's essentially the same: those who live in modern homes have both in mean or can have at least. Almost all others can't. Those who lives in cities have already big parking issues since cities was build far before cars, so with not much room for them, and as well no room for reasonable domestic p.v. systems. Classic homes tend to be badly oriented and many still have no garages. As a result most can only recharge cars from public stations who are spread enough not too few but most are 22kW 3-phase as homes, so you need to find one, occupy it for maybe 4+ hours, move the car thereafter to live the place for another and find a parking for yours now charged. Something stressful enough that most who do not have a private garage simply do not buy EVs.
Evolving civil infrastructures is not such a quick and easy things, especially in dense areas and during economic/social crisis of various kind.
Also, opening a window if it's too hot (in winter) was never a rule here, we must save a penny wherever we can ;)
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.
12 cm is ok for an old house. More is not economically viable.
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.
For us, it was just a couple 6”holes in the cinderblocks of a basement wall (at least 6 feet apart).
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.
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.
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.
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).
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.)
"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."
"I'm sorry sir but your grandparents didn't have grounded outlets so you can't install have them either."
I have no affection for the wiring - nostalgic or otherwise.
And, yes, vapor issues.
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.
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.
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.
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.
Why can’t your heat pump run both ways? It’s not that much more expensive!
But a heat pump has an internal and external part. The internal part needs to be where it cools and it's ugly too look at.
There are Aircon devices where everything is hidden away but they are expensive.
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.
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.
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.
Spray cork seems to come out the winner.
https://www.gov.uk/government/publications/thin-internal-wal...
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.
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.
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" ?
The word sarking is further used as part of the term scrim and sarking, a method of interior construction widely used in Australia and New Zealand in the late 19th and early 20th centuries.
In modern usage of the term in Australia, sarking refers to a laminated aluminium foil layer, or reflective foil laminate (RFL), that is installed on the roof trusses, beneath the battens, supporting a tile or metal deck roof. It acts as additional radiative (radiant barrier) and convective insulation and provides a condensation barrier.
https://www.bradfordinsulation.com.au/home-insulation/roof-s...
wondering how prefacb metal sandwich construction compares to prefab wood framing (which is quite common here in germany)
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.
$150k for a 150 m2 kit. That's before you have constructed the outer shell or the internal dwelling(s). What am I missing?
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.
Add that stuff back in and you are just building a house.
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.
The building needs to have a supply of fresh air.
Both are true.
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.
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-...
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.
I don't think they've had a mold issue, but it's only been a couple years. (I think with a lot of insulation there won't be condensation on the metal, but suppose bridging could still cause a way around this.)
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#...
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.
Are you referring to the ports on the interior or exterior?
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&postcoun...
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...
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
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
* 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.
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).
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).
) Which makes it Not Particularly Interesting(TM)
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.
HVAC blog, https://www.energyvanguard.com/blog/
HVAC pro forum, https://hvac-talk.com/vbb/
Heating forum, https://forum.heatinghelp.com/
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?
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.
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.
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...
(I own my apartment, but no HVAC system. Through-the-wall AC, steam radiator heating.)
But I'll admit I posted this in part to see if any other good units exist yet.
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℃).
- 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.