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.
>> 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.
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.
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.
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.
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.
> Well, HRV/ERV have no built-in filtration in themselves
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:
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 15€ a day or 450€ 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
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?
The defrost on the linked Broane units apparently works by recirculating the inside air through the unit, not by a 1000W heating element. It sounds like you have a pre-heater?
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.
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.
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.
Tons of air to water heat pumps can run the cycle in reverse (cool your house) these days. I'd double check if it's a recent installation, it almost certainly does. If so, the question is what your heaters look like. Not every likes cold feet for instance.
Danfoss which is the maker of this (ground heat) pump doesn't support this. This is per design. You can buy an add-on with a separate loop which I find silly.
Thanks for sharing. Do you mean the air-conditioning would be expensive in terms of upfront cost? As I imagine, with the solar, panels, it would be an ideal combination during the summer.
I could install a heat pump which can be run in reverse and cool the house. That would probably be cheap enough to install and use generated energy mostly.
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.
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.
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.
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.
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.
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.
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).
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￠/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.
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.
If this does not happen in the next 15 years in developed countries then we have a giant problem. I understand that installing a gas heater right now might be a reasonable personal decision, but I don't understand how one could argue it's the right thing to do from a climate protection angle.
It's the right thing to do from a climate protection angle if a significant proportion of your electricity is generated by natural gas, which is what I said to begin with.
It is, but only temporarily. Will you switch it over to a heat pump immediately after the cut off point is reached or will you operate till the end of its life before you replace it? If you keep operating it, will it really emit less over its lifetime than switching to a heat pump right now? Making the assumption that today's electricity mix is a steady state is flawed.
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....
The first thing you do when looking a heat pumps is discover how overdimensioned gas heaters are. My house has a 20kW unit, and I'm replacing it with a 6-7kW heatpump, based on a calculation of historical use. Note that heat pump are usually placed in houses that are well insulated and thus never cool down; it's designed to run 24/7, not regularly heat up from eg 15C.
Installing a pump without installing insulation (if you need it) is silly.
I have new home and designer specified 8kW of heating, but I thought it's ridiculously low for such a big home, so I've bought 24kW pellet furnace. Guess what, it averages about 6kW.
I know, I've build a new home, electrically heated and well insulated. An water-water heat pump + and air-air in the VMC, for a total of ~1kW suffice for mild climate (like -2/-5℃ at night) it climb to 3kW for -10/12 and to 4kW to -15/18 outside. Never seen more than 6kW for -25. BUT it's a new home.
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.
It depends a bit on how houses are built and how the culture of keeping them maintained is. Here it's feasible for most home owners to renovate. My house is from the 80ies, so some work is required, but not much, to get things compatible with a heat pump. Adding false walls in older houses is common though. The beauty is that these things pay for themselves.
Also, opening a window if it's too hot (in winter) was never a rule here, we must save a penny wherever we can ;)
US new construction is typically 200 amp (though some go up to 400 amp) 240v ‘split phase’ (so most branch circuits will be 120v). It’s technically single phase though.
So it's more than here for private homes (you can get much more, but only for business) BUT even with enough amps how much it cost per kWh in mean? Here we are from 9.7 cent/kWh for the cheapest hours, 15 cent/kWh for the mean, 67.12 for the most expensive hours of most expensive days (22 days per year in winter, the coldest essentially) i.e. https://www.fournisseurs-electricite.com/edf/tarifs/tempo for business in the "cheap" segment (not more than 36kW) it's from 21 to 25 cent per kWh.
CAlifornia is stupid expensive - averaging over $.50/kwh. Other areas are cheaper - Washington and Oregon have a lot of hydro power, and it is usually $.12/kwh or less there.
This is changing. Peak cost during summer afternoons is definitely $0.50+/kWh, but most other times are in the $0.20-0.30/kWh range, due to the broad deployment of solar and lower nighttime demand.
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.
EPS is not allowed for new builds here in NL, it doesnt meet fire safety codes. To me, that means Im not using it for renovation either. PIR can be had for good prices and is superior in every metric.
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.
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.
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.
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.
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.
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).
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.)
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."
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."
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.
Presumably, you are entirely removing interior plaster&lathe/drywall to access wall cavity (and replace wires) rather than drill holes and blowing insulation?
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.
> 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.
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).
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.
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.
>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.
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?
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.
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.
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.
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.
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.
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 UK has a lot of dialects and the north (Scotland) has a lot of Danish hybrids unique to the region - curiously a bunch of those words survived better in the colonies (Australia, New Zealand, Canada, backwards parts of the US) than perhaps they did on UK soil.
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.
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.
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?
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)
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.
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.
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.
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.
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.
In-laws have gone this route. I helped them install dense-pack-cellulose in the walls (like 8" of it or so). They have plenty of windows and tall ceilings. Doesn't feel dark or dank. I'm not sure what they have done in terms of indoor air quality but I'd definitely recommend an ERV.
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.)
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.
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.
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.
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.
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.
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.
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.
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.
> 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?
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.
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.
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
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).
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).
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.
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.
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.
> 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:
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.
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!
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! :)
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.
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?
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.
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.
The 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...
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.)
Really 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/
But I'll admit I posted this in part to see if any other good units exist yet.
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℃).
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.
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)
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.
* 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...