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Editor’s note: This post is one of a series by Eric Whetzel about the design and construction of his house in Palatine, Illinois, a suburb of Chicago. A list of Eric’s previous posts appears below. For more details, see Eric’s blog, Kimchi & Kraut.
Building with Passive House principles in mind, we knew that in addition to maintaining a tight building envelope and installing substantial amounts of insulation, we also would need continuous mechanical ventilation.
Our system, using either a heat-recovery ventilator (HRV) or an energy-recovery ventilator (ERV), would have to be highly efficient. It would need to hold onto some of the heat in the conditioned air even as it introduced fresh and, oftentimes, cold air by means of heat exchange as the two streams of air (fresh and stale) passed by one another inside the main unit (without actually mixing together).
After researching the many options, we ended up going with Zehnder’s ERV, in our case the ComfoAir 350. We only considered two other brands, UltimateAire and Renewaire. In all the research I did, these three brands showed up the most.
Another interesting option would be the CERV system. Because it’s a smaller, newer company, we didn’t feel comfortable pursuing it, but it does look like a viable option worth considering if building a Passive House or Pretty Good House. (For more information on the CERV system, see “A Balanced Ventilation System With a Built-In Heat Pump.”)
I was also familiar with Panasonic units, but I had read that they weren’t efficient enough in terms of the heat exchange function (or heat recovery) to seriously consider using it in a Passive House or a Pretty Good House in a predominantly cold climate region like ours here in the Chicago area.
A high-efficiency system
Our Zehnder ComfoAir 350 is said to be 84% efficient in terms of heat recovery (the same principle applies in summer, only working in reverse, when you’re trying to hold onto cooled, conditioned air). Based on what I read, the consensus seems to be that while more expensive, the Zehnder has a strong track record of performance and durability.
The Zehnder also came with its own ductwork, which we knew would simplify installation and save us some money by allowing us to do it ourselves rather than hire someone else to run more conventional ductwork. Conventional ductwork would’ve taken up a lot more space as well.
As far as the ERV/HRV for northern states debate is concerned, we decided to opt for the ERV because it was supposed to help us hold onto some humidity in winter months — especially important when most structures in the Chicago area are exceedingly dry for most of the winter (and our winters are long). Although I read repeatedly during the design stage that ERVs can also help control summer outdoor humidity entering the house, this has not been our experience at all. In fact, the ERV seems pretty useless in this regard (more on this below).
The system quote we received was easy to understand, and Zehnder was nice enough to essentially design the system, both in terms of layout (i.e., where we should put all the supply and exhaust points) and recommendations about the quantity of air for each point. The system is designed to be balanced, meaning the unit should be bringing in as much fresh outdoor air as it is expelling stale indoor air.
Installation is not a DIY-friendly experience
As far as Zehnder units being DIY-friendly in terms of installation, in our opinion, this is highly debatable, since the installation manual is far from comprehensive. Our installation manual ended at physically installing the main unit on the wall. Not very helpful.
Without a detailed installation manual showing step-by-step how all the individual pieces fit together, you end up with a pile of what initially seems like random parts.
This was incredibly frustrating, especially since Zehnder units come at a premium price when compared to other brands. It never occurred to me to ask for an installation manual before purchasing the unit. It seemed a fair assumption that no one would sell a premium product without detailed instructions on how to put it together.
We were only able to proceed because of numerous online videos, Googling Zehnder unit photos, and by staring at and experimenting with the various parts to try to figure out how they were all supposed to come together. It was an unnecessary and torturous puzzle that shouldn’t have needed solving, and it wasted hours of my life that I’ll never get back. If you do an internet search and type in: “Google review Zehnder America,” the experience Sean Hoppes had with his installation wasn’t all that different from ours.
The videos we found were especially helpful but still leave out quite a bit of information necessary for any first-time installer.
The lack of a comprehensive installation manual makes no sense. I’m not sure how even a licensed and competent HVAC installer would fare much better without direct experience installing the units. My guess is they would be searching online for missing info, much like we did.
Start by mounting the main unit
After we got the main unit installed on the wall, figured out how all the parts fit together on top of the unit, and got to installing the 3-inch ComfoTubes and the large ComfoPipe, the process became much easier.
The ComfoPipe is for the main fresh air supply and the main exhaust, both of which pass through the wall-mounted assembly. We found it more effective to put individual sections together on the floor. Once they were fully connected, we marked the points at which the pipes met with a permanent marker. That ensured a tight fit later when the pieces were reassembled in place.
If you try to piece the tubes together one piece at a time in mid-air, it’s much harder to judge when the pieces are actually tightly assembled. With each connection point of pipe clearly marked with a Sharpie, it gives you an obvious goal to shoot for once you have the pipe almost in its final position. More to the point, it’s obvious when sections of pipe get out of alignment, or the connection isn’t nearly tight enough.
Using a piece of ComfoPipe, we outlined on the interior side of our Zip sheathing on one basement wall exactly where we wanted the pipe to end up. After a hole was cut with a 3-inch hole saw, we cut out the rest of the hole with a jigsaw.
Once we started using the Sharpie, it was relatively easy to get all the ComfoPipe installed and air sealed around the Zip sheathing. We added a Roflex gasket to make the air sealing easier.
Following the directions, we kept the ComfoPipe exit points for supply and exhaust more than 10 feet apart where they enter and exit the structure. This is so the two air streams won’t mix.
On the outside, we made sure to extend the ComfoPipe out farther than we needed, giving us some leeway once insulation and siding were installed over the Zip sheathing. We cut the ComfoPipe back to the proper length before installing the permanent covers supplied by Zehnder.
Mounting diffusers on walls, not the ceiling
During the design phase, and even after we brought the Zehnder unit to the job site, we had intended to place the diffusers for supply and exhaust points on the ceiling. But after really looking at all the cuts in our ceiling service chase that would be required to make this happen, we decided to place them on walls instead.
It proved to be one of the better decisions we made during construction. Not only did we avoid having to make many cuts in the ceiling, which would’ve meant a struggle to appropriately map them out around conduit, ceiling lights, and plumbing vents, it had the added benefit of making it much easier to do ongoing maintenance at the diffusers. Once we had moved in, that consisted mainly of checking on and cleaning filters.
During commissioning, our Zehnder rep told me they have issues with homeowners not keeping their exhaust diffuser filters properly cleaned, effectively undermining the efficiency and overall performance of the units. This is understandable if the diffusers are on ceilings. We were also told that placement of the diffusers is extremely flexible — almost anywhere can work. (Check with Zehnder directly just to make sure your proposed placement will work.)
By keeping the diffusers around 7 feet off the finished floor, it’s easy for me to check and clean the exhaust filters on a regular basis — once or twice a month. I keep two sets of filters, so it’s easy to remove the dirty ones, put in clean ones, and then rinse and dry out the dirty ones.
Once we decided to go through walls, it was just a matter of deciding where in each wall we wanted the diffusers to go, then cutting the corresponding hole through the bottom plate and the subfloor — being careful to check, and re-check, in the basement for any floor joists, plumbing, or electric conduit that might be in the way.
For bathrooms, we placed the diffusers between the shower and toilet, slightly cheating towards the shower to ensure maximum moisture removal.
Zehnder supplied us with blue (fresh air) and red (stale air) tags, to mark each ComfoTube as it leaves or returns to the main unit. This should make any potential maintenance or repair issues in the future easier to resolve. It also helped us avoid confusion as we set each pipe in place at a diffuser.
All of the diffuser boxes required at least two ComfoTubes, except for the laundry/utility room, which only required one. Using one of the supplied black plastic caps made it easy to block off one of the outlets in the diffuser box. These black caps are also handy when pulling the ComfoTubes around into position since they help to keep out any construction debris.
In the kitchen, we located the diffuser across the kitchen, basically on a diagonal, from the stove. So far we haven’t had any issues with cooking grease or odors, and our range hood (recirculating) seems to be doing its job just as well.
Using scrap lumber, we were able to give each diffuser its proper stability inside the wall cavities. Although the mounting hardware for each diffuser box seems rather fragile, we didn’t run into any problems.
Applying a bit of hand soap around each opening in a diffuser box made getting a solid fit between the ComfoTube, the black O-ring, and the diffuser box fairly straightforward.
Because they are so small (at least compared to traditional sheet-metal ductwork), the tubes are easy to manipulate and move around, whether over a basement beam, around plumbing, electrical wiring, or any other structural component that’s not easily relocated. As long as you don’t need to make a short 90° turn, the tubes are easy to work with, so I imagine they would be ideal for renovation work in older homes.
Once all the ComfoTubes were installed at all the diffusers and at the main unit in the basement, we were able to pull all the lines tighter for a less messy final installation.
Summer humidity is a problem
The commissioning of the unit, after drywall was complete, was fairly easy and straightforward, apart from a couple of wiring and electrical issues that had to be dealt with by phone with a Zehnder rep. And ordering filters from the Zehnder website has also been a straightforward and painless process so far. (They’re not cheap, but they do seem to be highly effective.)
The only issue we’ve really noticed with the unit is during the summer when outdoor humidity levels are high. Since the ERV is constantly running, there’s no way to avoid bringing in some humid air.
And, unfortunately, it’s enough so that our Mitsubishi heat pump set-up (a future Part 2 of 2 for HVAC details) can’t properly get rid of the excess humidity either, even as it keeps the interior more than adequately cooled. We tried setting the heads to “dehumidify,” but they just dropped the temperature (to almost 60°F) without budging the humidity in the house very much — the rooms were freezing and clammy. As noted earlier, an ERV just can’t handle elevated levels of humidity in the summer on its own.
By having meters in various areas of the house, it’s easy to see when humidity levels become a problem. (We’ve been happy with our AcuRite gauges). Last summer our solution was to buy a couple of small dehumidifiers, one for the first floor and one for the basement. They worked, but they also ate up a lot of energy. Setting the Zehnder fan speed to low seemed to help somewhat, but not enough to avoid using the dehumidifiers. This summer we’re going to try a stand-alone Ultra-Aire whole-house dehumidifier, which should use less electricity — and it should perform at least as well as, if not better than, our current equipment at removing excess humidity.
Having read that anything above 60% indoor humidity can be problematic, especially in tighter, high-performance homes, it was disheartening to see the numbers move towards 70% in early summer. This is what prompted the purchase of the dehumidifiers.
From everything I had read during the design phase regarding Passive House, I knew that indoor humidity in the summer could be a slight issue, but having experienced it firsthand, it now seems obvious that incorporating a dedicated dehumidifier in any structure that will see elevated levels of summer humidity, even if it’s only expected to last for just a few weeks, is a necessity. Based on what I’ve read recently, it sounds like Passive House designers, who were already doing this for southern states, are moving towards doing it in states much farther north. Presumably this would also hold true for anyone designing a Pretty Good House as well.
Granted, 60-70% indoor humidity (or even higher) for a couple of weeks probably won’t ruin any structure, but for us, at least, keeping it in the 50-60% range during the hottest days of summer not only gives us some added peace of mind, regardless of the hit we’ll take in terms of overall energy use, but it’s also an issue of comfort. (I grew up in a house without air conditioning and still have vivid memories —all of them bad — of enduring hot and humid summer days and, even worse, long summer nights.)
Much like the initial complaints of overheating due to excessive or improper placement of glazing, especially on southern facades, this issue with excessive humidity seems to be part of the evolution in understanding how Passive Houses, or high-performance homes generally, actually work in real-world conditions. Although the concept has been around since the 1990s, anyone building to or even just leaning toward the Passive House standard should know they are guinea pigs to some extent, no matter how well established the idea may be in building science terms.
Winter has not been a problem
In the winter, we’ve had no issues. When temperatures fall below 20°F, we set the Zehnder to low in the hopes that it will reduce demand on the heat pumps slightly. The system seems to retain humidity somewhat when the cold air being introduced would otherwise be excessively dry.
Indoor humidity levels have been pretty consistent: When it’s above freezing they typically stay around 40%, and when temperatures plummet towards zero or below they’ve still stayed in the 30-35% range. We’ve rarely seen indoor humidity drop below 30%, even on the coldest days, which definitely makes a difference on overall comfort levels. I’ve also noticed that wood flooring and wood trim doesn’t shrink nearly as much as it did in our last, conventionally built home.
Also, even when we experienced record low temperatures in January (hitting -24°F without windchill), the Zehnder kept on running without any issues. As far as we know, it never shut off to try and protect itself from the cold (our minisplit system did, but more on that later). The product literature is somewhat vague, only noting that low temperatures could cause a unit to shut off, but it’s unclear at exactly what temperatures or what combination of other environmental conditions might cause this to happen.
Most people either tape or use sealant on the gray ComfoPipe seams to block air leakage. During our blower-door test, no air leakage showed up, even with a smoke pen test. Nevertheless, during our recent cold snap, some frost was evident on the ComfoPipe seams, so I’ll eventually caulk these seams with Pro Clima’s HF Sealant. There must be some air leakage, be it ever so minor.
Using the boost function
When the boost function is turned on, the ERV pulls from all the exhaust diffusers, not just a particular bathroom or the kitchen. Again, for the kitchen, even if we’ve been roasting garlic or cooking something else that’s equally pungent, by the next morning any cooking smell is usually completely gone. There have never been any lingering smells emanating from the kitchen.
For the kitchen, when we want to utilize the boost function we just set the ComfoSense wall unit to high. The bathroom boost switches run on a timer (set at the main unit in the basement). But in the kitchen, when we’re done cooking we have to remember to lower the fan speed; otherwise it just stays on high.
The ComfoSense unit can display error functions or tell you when filters at the unit need to be cleaned. It also has an “away” setting, meaning you can have minimal fan speed to exchange air while you’re on vacation instead of just unplugging the unit altogether.
The boost switch in a bathroom is set to run for 30 minutes on the highest fan speed. So far, this seems to be plenty of time for it to work properly. Unlike a normal bath fan, which tends to be quite loud, even when the Zehnder is in boost mode it’s still incredibly quiet. Guests need to know they only need to press the switch once — it is indeed working.
The boost function has been working really well at removing moisture after showers. Nevertheless, in the winter, when temperatures are below 20°F and we decide against using the boost function after showers (again, hoping to hold onto some of the added humidity), the bathroom humidity levels still quickly drop from the 60s and 70s back to the mid-30s in less than an hour (and this is even when the Zehnder fan speed is set to low).
The diffusers are unobtrusive
We’ve also been happy with the diffusers, in terms of installing/removing them when necessary, but also in terms of their overall look. Whether on more neutral colored walls, or something bolder, they just look nice in our opinion.
They’re subtle enough to blend in to the background, but attractive enough so when they are noticed they don’t stand out in a negative way.
As far as changing filters at the unit, or even cleaning the core itself, so far it’s been a trouble-free experience.
During the summer, of course, they look much worse after a month, with so much more stuff floating around in the air (pollen, debris from landscaping, insects, etc.). Also unsurprisingly, the exhaust-side filter always takes much longer to get dirty as stale air makes its way out of the structure. (It probably helps that we don’t have any cats or dogs.)
Overall, then, we’ve been extremely happy with our Zehnder ERV unit.
Other posts by Eric Whetzel:
- Choosing Windows
- Attic Insulation
- Installing an Airtight Attic Hatch
- Air Sealing the Exterior Sheathing
- Installing a Solar Electric System
- Prepping for a Basement Slab
- Building a Service Core
- Air Sealing the Attic Floor
- Ventilation Baffles
- Up on the Roof
- A Light Down Below
- Kneewalls, Subfloor and Exterior Walls
- Let the Framing Begin
- Details for an Insulated Foundation
- The Cedar Siding is Here — Let’s Burn It
- An Introduction to a New Passive House Project
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49 Comments
Interesting that you specifically mention the Panasonic ERV as not being efficient enough for a Passive House. If you look on HVI's data sheet on all their certified ERVs, you'll see that the Panasonic Intelli-Balance 100 (FV10VEC1 Cold Climate model) has an SRE rating the same as your Zehnder CA350ERV at comparable airflows, and also has far superior Latent Recovery (moisture transfer):
Panasonic Intelli-Balance 100 FV10VEC1:
https://hvi-1491.quickbase.com/db/bh6688vwb?a=dr&ifv=1&rid=10059&dfid=12
Zehnder CA350ERV:
https://hvi-1491.quickbase.com/db/bh6688vwb?a=dr&ifv=1&rid=6368&dfid=12
Of course the CA350ERV is a larger unit that can push higher airflows than the Panasonic can, but the higher the flow rate the lower the efficiency. The Panasonic more directly compares to the Zehnder CA200ERV, which is slightly less efficient than the CA350ERV.
Zehnder seems to justify their high price with flashy marketing and their PH certifications, choosing not to make available their HVI testing results. Their brochures are chock full of detailed noise spectrum data for their fans (which nobody looks at), and only offer the PH certificate for their HRV units, not their ERVs. Their HRVs are quite good, but as many are finding out, ERVs work better in most climates and Zehnder's ERVs are nothing special from an efficiency standpoint.
Anyone curious should be looking up published data at HVI's website. There's no marketing there, just the data.
Also, you state,
"Although I read repeatedly during the design stage that ERVs can also help control summer outdoor humidity entering the house, this has not been our experience at all. In fact, the ERV seems pretty useless in this regard..."
Your CA350ERV has a Total Recovery Efficiency of 62%, meaning during hot humid summer weather it recovers 62% of the possible Enthalpy (sensible + latent) load difference between the outgoing and incoming airstreams. If you had an HRV instead of an ERV, your humidity during summer months would be much worse. To call the ERV "useless" is incorrect, it's actually helping you out immensely.
HVI explains the details here:
https://hvi.org/proddirectory/CPD%20Files/Sec3_cover.pdf
Well written article and a pleasure to read. Thanks as always for sharing your experiences.
I should've been more precise regarding the Panasonic units: I heard repeatedly that they freeze-up in colder climates --- I think Dana Dorsett makes reference to this more than once here on GBA, and I think it was a Matt Risinger video where I might've first heard this, but I can't be sure.
I was doing most of my research for HRV's and ERV's back in mid-2016 before settling on the Zehnder, so maybe this is no longer true for the Panasonic units?
I found a thread where I posted the Zehnder vs. Panasonic info, in case anyone following along is interested:
https://www.greenbuildingadvisor.com/question/erv-choice
The Zehnder CA200ERV and Panasonic Intelli-Balance 100 are pretty much dead even on efficiency. The HVI rates the Zehnder slightly lower (when sorted by SRE) but they're both neck-and-neck.
The Panasonic has a defrost strategy that gets more aggressive as temperatures drop, which actually seems much more advanced than most ERVs I've looked at; below -30 (-22F) it only operates in short 4 min blocks to sample outdoor air temp, below -27C (-17F) it's 20 min ON and 9 min recirc (69% ON), below -20C (-4F) it's 27 min ON and 9 min recirc (75% ON), below -15C (5F) it's 35 min ON and 9 min recirc (80% ON), below -10C (14F) it's 60 min ON and 9 min recirc (87% ON), and above -10C (14F) it operates normally.
I've searched quite a bit for information and reviews on the Panasonic and come up with relatively little, which is why I try to spread accurate info about the product. Note, this is not my experience with the product (I don't own it), just published information from Panasonic and the Home Ventilating Institute (HVI). I AM interested in using it in my build.
Correct on that defrost strategy. We have had -38°F on the worst night(REAL dry bulb temp, not with chill factor!) here in Minnesota and my Panasonic ERV FV10VEC1 defrosted just fine. Based on the sound increase the defrost cycle jacks up air flow to full flow. On nights above zero °F we are not much aware of this cycle happening, but it does without problem.
As to humidity control in winter I noted that our humidifier uses about 50% less water as a result of the ERV being in operation. We control humidity in our 2700 sq ft home to 35% with a simple $120 humidifier with closed loop controls. I am pretty happy so far with the Panasonic ERV. We will monitor this summer's response to humidity closely after hearing about the expensive Zehnder's summer performance. Speaking of cost: TOTAL was $1500, installed(self). I wonder what the Zehnder was?!
By the way, our home is not to PASSIVHAUS level, only blows 1.0 on blower door.
Thanks for your feedback, Brian! I'm slowly getting more and more owner feedback on the performance of the Panasonic, and so fer it looks pretty good.
When you say your humidifier uses 50% less water with the Panasonic in use, what are you comparing it to? Did you use an HRV before?
"Thanks for your feedback, Brian! I'm slowly getting more and more owner feedback on the performance of the Panasonic, and so fer it looks pretty good.
When you say your humidifier uses 50% less water with the Panasonic in use, what are you comparing it to? Did you use an HRV before?"
New home, lived in about 1.5 yrs before installing new ERV(never had any HRV or ERV prior). In mid-winter Minn. I had been filling it with 2 gallons per day at the height of coldest winter in many years. Then, almost immediately after ERV install, feed rate dropped to half that. ERV recovered moisture.
I was forced to buy a humidifier because the humidity was running in low 20's, high voltage shocks touching doorknobs, cats etc !Ha! I had been ventilating, per code, with 50 cfm IN & OUT continuous so lots of dry air coming in. I thought I may be able to get by on the cheap with my $150 mech vent plan and found out humidity had to be "handled", just too dang uncomfortable. So, the combination of ERV and humidifier allowed an optimal winter solution. If I had used an HRV the air moisture would have been pitched out with the exhaust air. I am concerned about summer though.
In the summer, during the most humid and hot 3 or 4 weeks, we will be running the Mitsubishi mini-splits for AC. The plan would be to continue using the ERV. However, it appears from your experience and the enthalpy recovery design of an ERV, I should be concerned for accumulation of humidity-- even with the mini-split heads drawing some out.
Now that we are seeing 30's and rain the humidifier shut itself down as the humidity has risen into the 40's. (Set point is 35%.) If what I am intuiting is correct, it seems a combo type ERV/ HRV unit with a core changing capability may be an optimum design for an air exchanger. Maybe someone else can wade in here and enlighten me!
(Per later discussion with Lance and my post #41, the concerns about building moisture in summer and "combo" unit are nixed. BES, 3/15/19)
An ERV will help keep moisture in the house when outside air is dry, and it will help to keep moisture out of the house when outside air is moist. This is in comparison to using an HRV. Any ventilation will affect interior humidity, but an ERV affects it less than an HRV since it can pass moisture through the core between the air streams.
In the summer months when the outside air has more moisture (grains per pound, NOT relative humidity(RH)) than your air conditioned interior air, the air conditioned ERV exhaust will absorb some of the moisture from the incoming outside air, drying it slightly. An HRV doesn't do this, instead it brings 100% of the outside air's moisture into the house.
An ERV still brings moisture into the house during hot humid weather, it just brings in less than an HRV does for a given ventilation rate.
In winter the opposite happens. An ERV still dries the house when it's cold outside, it just dries the house less than an HRV would for a given ventilation rate. This is shown with the Latent Recovery (Moisture Transfer) specification. One of the most appealing specifications on the Panasonic is it's 80% Latent Recovery, higher than any other ERV I've seen specs for.
I'm 43 years old and have never lived in a house that wasn't dry in the winter. Our current home (Ottawa, Ontario) isn't dry, but that's because I use a humidifier to keep it above 30% RH. Without the humidifier our humidity will drop below 20%; nosebleeds, cracked skin on fingers, shocks... I'm sure you are familiar! In fact, our crummy 2004 townhouse is so leaky that our humidity will drop almost 10% from 35 to 25 during sunny afternoons because the furnace stays off for a few hours while the sun warms the back half of the house. When the furnace is off the humidifier doesn't run, and the leaky envelope allows dry cold air in way too fast.
So I take it you were using a bath fan (or similar) to ventilate your house prior to using the ERV? If so, I've been skeptical of that arrangement ever since I first started looking into home performance a few years ago in anticipation of our build, and for that very reason; dry winter conditions.
Just FYI, we just got through our first winter in our well-sealed house with the HRV running. I don't think it ever got below 25%, and it was uncommonly below 30%. the majority of the time it was 30-40%. I am curious as to how much higher it would have been with an ERV, but we were satisfied with that range. Summer might be a different story.
Good to know, Trevor. What are the details of your house (size, ACH50, ventilation rate, occupancy)? You're in Southern Ontario, correct?
The house is 2470ft^2, two story no basement. 0.22ACH50. I originally set the ventilation rate to around 120cfm, per the design (and what the building department is going to want to see, once I get around to the final inspection). I tweaked it over time so that the CO2 stays in the 550-650ppm range. My rough guess is 90+/-10 at full occupancy (two adults, small child, small dog). If there's only going to be one adult, I drop it down to low, which is probably 50-60cfm. When just the dog's home, it goes to near zero. She doesn't seem to mind. And yes, near London Ontario.
thanks Lance. I guess I forgot some of that info on the ERV re: actually taking NET moisture out of the fresh air EVEN in summer. (A few months ago, I KNOW I had good reasons for concluding that the ERV was the best of both worlds and the big reason I finally bought one! However, being 68 I kind of "lose it" sometimes-- old-timers disease!)
In order to intelligently respond to your post I went back to those good old Psychrometric charts to document absolute humidity for summer and winter, and again, re-learn my 40 yr old thermo 101! Just for edification and perhaps someone else is interested(!?) (see att. file. I converted RH to grains/lbm dry air.)
Minneapolis data: So, to correlate to your example: summer 61 gn/lbm vs winter only 8 gn/lbm; there is 8X less moisture available in each pound of air in winter.
(New Orleans data shown for folks interested down South.)
Like any "heat" exchanger, the ERV will transfer moisture (also) from HIGH level to LOW: in winter inside air goes out(HI) around 35 and moves the 8 grain incoming air up towards it, thus, increasing winter dry air in moisture. In summer, the ERV again will transfer from the HIGH level outside air of 61 grains to the lower level, exiting, inside air of 52, thus, as you point out, reducing absolute moisture level. BUT barely, since there is so little driving force differential-- less than 10 grn/lbm! Really, the ERV IS the best of both worlds; the HRV has zero driving force for it-- winter & summer!
However, an ERV's moisture removal efficiency has to be a lot lower in summer vs winter. Compare driving force (delta) of only ~9 in summer vs 27 grn/lbm in winter-- only 1/3rd! If there was 3X the surface area in the summer months the efficiencies would be pretty close!
OK, changed my mind, let's design a 3:1 core area change for the two seasons! Contact the ERV manufacturers, quick! Ha!
Did the authors have any issues with Zehnder's planned layout? IIRC Zehnder requires a copy of the plans inorder to provide a quote.
We were happy with Zehnder's planned layout, but once we decided to put diffusers on the walls rather than ceilings the supply/exhaust points did change. My Zehnder rep assured me the changes would be fine --- the range of options (ceilings, high or low on walls, presumably even up through floors, although I've never seen it done) for the placement of the diffusers is surprisingly versatile.
I've read mention that moisture from new construction materials can significantly raise humidity, but for how long I'm unsure.
It looks like you've been living there through 1 summer, I wonder if this following summer will be noticeably drier inside for you.
Building my own PGH, and I too, lament humid nights. But I don't have a dehumidifying plan beside the ASHPs.
I hope you're right. I guess I'll find out for sure this summer.
One advantage of incorporating a whole-house dehumidifier now, before or during your construction process, is that you could have the heat produced by the unit vented directly outside.
In our case, we're going to try and place the dehumidifier in our basement and point the outgoing heat from the unit near our exhaust diffuser, which will obviously send it through the Zehnder core first before making its way eventually outside.
Something worth considering.
I was not aware of whole-home dehumidifiers that allowed heat to be rejected outdoors? The only one I've seen is a split-system that has an outdoor condenser unit and the indoor unit acts like an air conditioning coil, just with a lower than normal temperature and airflow to improve moisture extraction.
Some units have fresh air intakes that draw in outside air, but the dried exhaust air contains the heat from the refrigeration cycle. In the scenario you propose, I would think aiming the output of your whole-home unit directly at a ventilation exhaust duct would just mean you are exhausting dried air (when you should be exhausting moist air).
Too bad nobody makes a small in-line (as in in-duct) split system dehumidifier that could dry the post-ERV fresh air and reject heat to the post-ERV exhaust air. The Minotair works somewhat that way but doesn't have an exchange core; it relies solely on the heat pump to transfer heat and to dehumidify.
Eric I would caution against close coupling the dehumidifier supply to the ERV exhaust as you will be sending your dehumidified air out of your house. This will increase the operating time of your dehumidifier and the cost to operate it while purging some of your "freshly dehumidified" air out of your house. It will be better to distribute the dehumidifer supply evenly throughout the house so you do not end up with a "hot" room when it is dehumidifying.
Tim,
I was hoping that by pointing the exhaust air from the dehumidifier towards a nearby Zehnder exhaust diffuser in the basement that as this dehumidified air entered the core of the ERV that it would pull some of the elevated humidity out of the supply stream before making its way outdoors.
To Lance's point below, my thought was that, because of the summer bypass function of the Zehnder, outgoing air in the core, if warmer than the incoming fresh air, wouldn't be able to pass its heat to this supply air.
Are these two assumptions wrong?
I didn't think about it before, but are they in conflict with one another, meaning: During summer bypass mode, if heat from the outgoing stale air is rejected by the core so it can't enter the incoming airstream, does this mean the outgoing airstream can't pull any humidity from the incoming fresh air either? Are heat and humidity both bypassed?
Maybe I'm better off just pointing the exhaust air from the dehumidifier towards the center of the room, allowing the air from the supply diffusers and the heated/dehumidified air to slowly mix before making its way to the exhaust diffuser?
Or would pointing the exhaust air from the dehumidifier towards a corner of the room, the farthest point away from supply and exhaust diffusers be even better?
The link below discusses the summer bypass function, along with other useful info on living with a Zehnder:
https://elrondburrell.com/blog/passivhaus-residential-ventilation-system/
"I was hoping that by pointing the exhaust air from the dehumidifier towards a nearby Zehnder exhaust diffuser in the basement that as this dehumidified air entered the core of the ERV that it would pull some of the elevated humidity out of the supply stream before making its way outdoors."
This is true, but the effect of this will be less than just keeping that dry air in the house.
In bypass mode, the outgoing stream does not go through the core. So in that mode, neither heat nor moisture will be transferred. The enabling of bypass mode is not based simply on whether the inside air is warmer than outside air. There is a comfort temperature setting which plays a part in the decision tree. I'm not sure of the exact algorithm.
https://www.zehnder.co.uk/summer-bypass
Eric, I won't speak for the ERV function - you should check with Zehnder regarding the function of your model.
Your house has an unmet latent (moisture) load (water vapor in the air). An ERV can help reduce this load by transferring some of the moisture in the fresh air stream to the exhaust air stream when dew points are high outdoors. Your air conditioner can also reduce this load by condensing and removing water from the air it cools when it operates. The dehumidifier will remove the remaining moisture in the air to maintain the conditioned space within your house at your desired humidity level.
If you exhaust the air processed by your dehumidifier the ERV may transfer additional water vapor to the exhaust air stream, but I doubt you get a 1:1 (dehumidifier to ERV) ratio of water removal. It may be substantially less than 1:1. You would need to ask the ERV manufacturer how effective their core is at moisture transfer at the actual exhaust and fresh air conditions. This is why I stated that the dehumidifier would run more and cost more to operate.
We typically recommend you distribute the dehumidifier supply air throughout a house rather than into a single small space since the supply of the dehumidifier is warm/hot when it is dehumidifying and a small space will become overheated quickly causing comfort concerns. I have found success running the supply of a dehumidifier into a basement, but this is typically in a retrofit into an older house with poorly insulated or uninsulated basement walls and slab. This type of application typically brings the basement ambient temperature closer to the ambient temperature of the above-grade space. A well insulated basement which maintains a temperature similar to the above-grade space may get too warm with this configuration.
Another option (with a serious drawback) is to run the dehumidifier supply into the air conditioner return and interlock the air conditioner and dehumidifier to run together. The delivers comfortable temperature air, but costs more to operate as the air conditioner removes substantially less moisture in this configuration which the dehumidifier must handle. This means the dehumidifier operates more than it would if it was not feeding the air conditioner return.
If you have a space which is colder than desired during the cooling season, it is a good candidate to receive the dehumidifier supply. Otherwise distributing the warm dry dehumidifier supply air throughout the whole conditioned space will be preferred. If you must direct the dehumidifier supply air into your air conditioner return it should be able to maintain a reasonable space temperature, but it will operate for more hours and cost more to operate than the other configurations. If possible you could also direct your dehumidifier supply into the air conditioner supply to mix and reduce the temperature of the dehumidifier supply air stream to maintain a comfortable room.
Another thought along those lines, is the hot exhaust from your dehumidifier going through the ERV will just preheat the incoming air more at the efficiency of the core, so most of the heat ends up back in the house anyway.
" new construction materials can significantly raise humidity, but for how long I'm unsure."
. . . only for a few weeks, I would bet, for the most part and 90% of that is drying sheetrock mud.
My electrician installed our Zehnder hrv and found it pretty easy, although it was his first Zehnder installation. Having Zehnder design the system was a big help, as was having a rep. come out to commission it. After four years, it has worked without any issues at all.
I have a Zehnder system that I installed myself. I found it self explanatory, and barely even looked at the install manual. But I agree, it's a little on the sparse side, especially when it comes to programming functions. If you want to use the analogue inputs, all you have is a table with designations. There's no text to explain anything, you just have to figure it out.
For the kitchen boost, try using the party mode. Basically the same as the bathroom boost, but a separately set timer and I think it can only be activated from the main control. Still, one step above manually adjusting the fan.
I would suggest getting an air quality monitor, or particle counter, and seeing what the PM2.5 is like after cooking events. You might be shocked. I found that the HRV boost has almost no effect on bringing those numbers back down. They remain alarmingly high for several hours. I'm looking at two possible solutions to this problem. One is to duct the range range hood (remove the built in fan) directly to the HRV extract air via a wye fitting with a servo controlled valve. That way you could have an externally ducted range hood at about 250cfm with heat recovery. Zehnder actually makes such a device, however so far I haven't been able to figure out how to obtain it. Zehnder America doesn't sell it, and when I contacted Zehnder International they referred me to Zehnder Rittling in Buffalo, who referred me back to Zehnder America again. I'm not too keen on engineering my own valve, but I haven't ruled it out. The other option is to again remove the irritatingly loud range hood fan, install a custom HEPA filter just above the grease baffles, and duct it to a high efficiency ECM blower motor above the kitchen cabinets. I know this would be more effective than the recirculating range hood is now, because I have a home made air cleaner that is essentially the same thing. It can lower the PM2.5 to acceptable levels in a couple of hours, and so putting that system right above the cook top should exponentially improve that performance.
Trevor, I've been fantasizing about a heat recovery range hood for a while now. The only "practical" solution I've come up with is to use an actual HRV dedicated to the hood, probably one with a plastic core that can be washed. A HEPA filter would keep most of the nastiness out of the core, but it would still need washing.
A major hoop to jump through would be the requirement for a grease certified fan (which I believe most/all range hoods have). I doubt a city inspector would pass a system without a range hood rated fan, regardless of the filtration system.
OK. . . now, guys. . . Let's rationally consider what the real problem is. How long is the range hood on for? What is it's utilization factor ie hours per day in use and at what CFM level? How many BTU's are we really worried about. Once you do those calculations perhaps you will choose to pick other, LOWER hanging fruit.
My experience: While cooking a meal, the externally vented 700 CFM hood may be on 1/2 hr to one hr, max. When we cook with our propane gas cooktop we put the hood onto 200CFM for one burner, about 300 for two. If we are really cookin' up a storm it gets flipped all the way to 5 or 700-- always with the nearby window cracked open. Hey. In a "hot" kitchen there is nothing like fresh air. It KEEPS you cool, nicely. It is WELCOME. Consider that the outside air also makes a short traverse in the home: from the window, to the range above your head, and BACK out! Often we forget and leave the dang winder' open . . . and notice it an hour later. Only to find there is mostly no substantial effect cooling the home, much less the kitchen, in zero degree weather. Minnesota.
The bigger concern is the 6" hole in the wall that is leaking air 24/7/365. It would be nice if an air tight damper was something easily obtainable, but it's not. Then there is the issue of make-up air, which is a second 6" hole that will leak, or having to manually open and close a window every time the hood is used. If there was an off the shelf option for an air tight damper, I would seriously consider it. If I have to engineer something, I might as well go all the way to integrating it to the HRV.
During this past winter, I never once felt the desire to open a window to bring cool air into the kitchen. I recently burned some cheese in the oven while making pizza, and opened a couple of windows to clear the smoke (and opened the 550deg oven). That lasted less than 5 minutes before I had to close the windows due to cold complaints from the other occupants.
We don't have to guess on the heat loss, it's pretty easy to calculate. Someone can check my math, but at 300cfm and a temperature differential of 70degF, my back of the napkin calculation gives me ~40,000BTU/h, more than three times the heating load of my entire house.
-- 1st please see attached image: showing the spring loaded damper INSIDE my Whirlpool range hood. Duct sealed ENTIRELY. Not to mention the gravity damper on the exhaust port. Ain't no flow when the thing is OFF.
a motorized 6" damper is about $70. IF you REQUIRE airtight closing during the operation of cheap range hood, tying that into the hood is simple electrical work. No "real" engineering required.
-- For the sake of argument, which both of us apparently enjoy, let us say the air tight damper I DO have does not exist. OK. Well, if the home is tight and mech ventilation system is "balanced" where is the forcing momentum coming from to push the air out at 300 cfm 24 / 7 when the fan is OFF? I am not planning on placing a 6" hole in my wife's kitchen wall to allow continuous ventilation and then place a propane re-heater to bring it up to Room temp! To make obvious and VERY verbose(sorry) I cannot help but reference you to this link: https://structuretech1.com/how-to-determine-if-makeup-air-is-required/
Make up air is a BS trope thrown out by a lot of people who really do not want to do the real calculation per the link above.
I did not bother to do the Heat loss calculation for Cp, m dot, delta T but will figure you did it correctly. I trust you. OK, I leave the window open and out it goes within seconds from the window to the exhaust hood 10 ft away. Yes, some of the precious room air which I HAVE heated to room temp goes with it, what?, 10, 20%. Let's be harsh and say 25%. For my home the daily heat loss on a really cold day is about 35,000 Btu/hr or about 840,000 that day. But for an hour of that day, while cooking, I lose 25% x 40,000 Btu-- 10,000 Btu. So, rather than being so extreme as a continuous 40K Btu/hr, it equates to about 1.2% of daily heat looses.
If you consider the complications raised by the engineering, design, unique requirements for makeup air and an HRV integrated to boot, it just seems WAY out there. Ask a homeowner: "Would you rather open a window occasionally when using your range hood or spend $5000 for this highly engineered neato air supply system so you can "Cook"?!
I've never seen a motorized damper that is air tight. People have inquired about it on here, and have been told there isn't one on the market.
I didn't mean to imply that the 300cfm was happening 24/7. The 300cfm is when it's in operation, which for my house would probably average 1 hour a day. The leakage is 24/7, but I don't have any guess as to what that might be in cfm. Certainly it would be the most significant leak in the house.
When it comes to what percentage of air going up the range the range hood is coming from the nearby open window, you've got a problem. If, as you suggest, it's between 75-90%, then your range hood isn't capturing nearly as much of the smoke particles that you might think, and definitely a lot less than you want. In order for the hood to actually do the intended job, it has to create a pressure differential all around it, which keeps the smoke from drifting away. If the majority of the air is coming from a nearby source, that is not happening. This is a well documented problem when it comes to makeup air provision for range hoods. It's really a trade off. Unless you enclose the cooking area, the air that goes up the the hood and out of the house has to come from the general ambient air of the house in order for the hood to do its job. If it comes directly from a nearby window, it has short circuited the range hood and it's not going to effectively remove the smoke. In practice, having a nearby window probably isn't going to act as a short circuit, because the range hood isn't going to preferentially draw air from that direction (unless it's really close). What is going to happen is that air will be drawn in from all directions, so the percentage of air that goes up the hood that was not conditioned is rather smaller than you suggested. Even the air coming from the direction of the window is going to get mixed with conditioned air on the way. I think the percentage of unconditioned air going into the hood will be a lot closer to the reciprocal of the number range you suggested.
I looked at the table at the link you provided. It's clearly meant to apply to a code built house, in terms of air tightness. It has only one variable, square footage. That means they've made an assumption on the air tightness and just plugged it in to get a multiplication factor. If we work backwards, we can determine what assumption they made for leakage. Let's take a house with a square footage of 2470, the same size as mine. If we plug that into the table, we get a predicted infiltration value of 370cfm. A house that size is about 21,000 cubic feet. 370cfm= 22,200cfh, which is pretty close to 1ACH. But at what pressure? I'm going to assume they're not going to expect you to depressurize your house to a vacuum of 50Pa to run your range hood, so surely not ACH50. It's a fair guess that their target air tightness they used to come up with this table is 3ACH50. So I'm looking at a table that presumes that my house infiltration is 370cfm, but I know it's actually below 50cfm at any reasonable static pressure. What it tells me is that if I lived in that jurisdiction, I would not be legally required to provide makeup air for a range hood up to 250cfm or so. It doesn't mean it's a good idea.
Our different houses and different assumptions are obviously going to lead us to different conclusions. My peak heating load is about 12kBTU/hr. The average over an entire day is more like 6kBTU/hr, so say 150kBTU/day. The average heat loss to the range hood will be below the worst case too, but even if it's 10kBTU/day, that's 6% of the total heat loss for the house. Again, I might consider it an option if there was an easy way to install and use an airtight gate on the hood and the makeup air intake, as it's the air leakage in the house I'm more concerned about. I think replying on someone opening the window is not a good idea, unless you're the only one living in the house.
Do you cook or bake enough to make it worthwhile? I don't like throwing away conditioned air, either, though energy recovery from cooking seems like chasing diminishing returns.
I burned green beans on the stove and logged PM2.5 in a few places of a test house when I was working on a smart home IAQ product. And I was shocked. With the AHU running the PM was distributed throughout the house in short order, and it would have taken hours for it to dissipate. Still took a while with open windows. Source control (range hood) is essential.
Jeremy, I am amazed that IAQ pros are using particle counters. I am well versed in their use for industrial clean rooms. My experience tells me that their use outside of a clean room is. . . likely overwhelming! (Your counter must go bonkers in the outside air, right? ) The level one sees in an ULTRA clean room are low enough one can track minute sources of particles without the counter going off the charts. Particles are generated by hand movements; shuffling along a floor can cause huge blooms of particles that take 3 or more minutes of absolute stillness to level out! Although your head is completely covered, if Uncovered, and you rustle your hair it is like shaking a dust rag in front of the sensor, off the charts. Pretty crazy.
In a NON-clean room environment you must be using counters that are an order of at least a 1000 lower in sensitivity. Just the same, I would think after using one for an hour or so you quickly conclude that almost anything generates particles and trying to make sense out of the counts is very confusing. To me, not versed in this protocol for air quality, measuring the level of all particles smaller than 2.5 µm seems . . . crazy! Besides, you cannot tell WHAT the particles are. Most of them are likely dust mites and skin cells in a house environment. So, you just have to vacuum more often and STOP shedding those dang skin cells. Good luck with that.
Dust mites are two orders of magnitude bigger than PM2.5. Skin cells are smaller, but still not close to PM2.5. I guess some debris from those is likely to be below 2.5um.
As far as I am aware, it all counts. It doesn't matter what the PM2.5 is made of, the health risk is the same. Vacuuming is counterproductive in most cases. Everyone should be using a vacuum cleaner with a HEPA filter, but most aren't.
The particle counter I have provides useful readings. I've checked it in different locations under different conditions, and it responds in an appropriate manner. I can't say it's accurate in absolute terms (and it only detects down to 500nm), but it gives reliable relative measurements. And you're right, walking around in a room raises the reading, bouncing up and down on the bed and flapping the comforter around (I have a three-year-old daughter) raises it a lot. I know most of that is "household dust". Should I not be concerned about it? I don't know. I would love to hear that I needn't worry. Running a good air cleaner brings the readings back down so that at least while we sleep they are fairly low. Without the air cleaner, they stay high for a very long time. Even if the particles from household dust should not be counted, it is actually a trivial matter to differentiate the source most of the time. If the reading is X before you start cooking, then it's 100X half an hour later, it's pretty clear it's smoke. If there was no cooking happening and it goes up to 100x, it was something else (and usually you can deduce the event).
"As far as I am aware, it all counts. It doesn't matter what the PM2.5 is made of, the health risk is the same."
I get from this that you are saying the constituents' ID of particles sensed are not relevant to the health risk. That is hard to rationalize! Now, I am just kidding here but, what if they are particles "known to the state of California to be of potential risk for causing cancer"?! Really though, the health risk is not the same-- asbestos particles vs skin cells! I do GET what you are saying, in essence. Used as a relative reading, yep, the counter goes up when you put it near the frying pan. Ergo, airborne canola! Will that kill ya' though? People have been fryin' over bacon grease, lard, hog fat, olive oil for millennia. Has there ever been a study indicating(uh, outside of California!) that bacon grease vapors are dealers in death? My heart goes out to all short-order chefs.
Regardless, so what? What are you going to do about it? Have you ever gone camping, sat around a camp fire, been in a high wind blowing debris at you, crawled on a forest floor stalking deer or turkey, used a push broom to clean up dust in a messy garage? How about the folks who lived through the dust bowl days?(1935-1938) How did they survive?!
This discussion leads me to believe there's folks out there who want to live in a bubble to protect themselves from nasty particles, microbes, and chemicals. Let's keep in mind that the body is less inclined to make anti-bodies if not exposed to threats on occasion. If you sequester yourself in an ultra-clean, particle free, microbe free room the body's lowered resistance will likely offer heightened susceptibility when you step out of the bubble.
I am reminded(by your subsequent response) of the need to drink 100,000 gallons of water in order to consume enough "carcinogen" to be at a health hazard level!
Anecdotes don't mean anything. When dealing with risk, it's about probabilities. Even if something has a 99.999% chance of killing you instantly, finding someone who survived is still compatible with those stats.
Smoke (including smoke from Canola oil, and bacon "vapors") is a known carcinogen. If you doubt that any of this is a concern, then I have to ask, why do you have a range hood at all? Yes, humans have been cooking for millennia, but for most of that time the average lifespan was around 30, so things like cancer weren't really much of a concern. Also for most of that time, humans didn't cook where they slept, and until very recently they didn't live in well sealed homes. So you can't really compare someone cooking outdoors four thousand years ago to cooking in a modern home today.
Short order cooks have commercial range hoods and ventilation, specifically because we know smoke is a problem. And they don't curl up to watch tv, then go to sleep right beside where they've been cooking all day.
Yes, I've gone camping and used a broom. Surely you must understand that exposure time is important (or maybe not, as I otherwise can't understand why you'd bring up examples like this).
No one is talking about living in a bubble. I'm not a germaphobe. But I should point out, antibodies are produced in response to pathogens, not airborne particulates. Exposing yourself to airborne particulates will absolutely NOT strengthen your immune system. People with repeated low dose exposure to silica dust don't get stronger immune systems. What they get is silicosis. Even that aside, the idea that taxing your immune system by constant exposure to a variety of threats will strengthen it, as if you're taking it to the immune system gym, is kind of a dangerous over-generalization of how a small aspect of it actually works. But this discussion has gone far enough off the rails, and no longer has anything to do with building science or green building, so I am going to bow out.
There are clean rooms, then there are CLEAN rooms. I work in ISO Class 8 clean rooms. They're not very clean by clean room standards, but are a heck of a lot cleaner than houses. Good enough for the work we do.
We have OEMs come in to certify our equipment and they're amazed at how clean everything stays compared to the same equipment elsewhere. They rarely need to clean anything.
My predecessors did particle count studies to determine the impact of proper lab dress vs. wearing ordinary clothes, and they claim the benefit wasn't worth the effort at this level.
A Class 5 or better clean room is a pretty clean environment, not exactly something to compare with a residential kitchen. We're making toast, not semiconductors. ;-) To my knowledge, Class 5 requires filtered unidirectional ceiling-to-floor airflow with floor mounted exhausts and a very high exchange rate. If this is implemented properly, scuffing your shoes along the floor should not increase particle counts at working level?
My understanding is, PM 2.5 are regarded as particles at risk for deep lung tissue penetration and are more likely to cause problems due to being absorbed into the body. As far as I know, our understanding of exactly which chemical compounds are responsible for certain conditions is not very good, so a "best practice" is to make an effort to limit the concentrations of PM 2.5 in general. Proper use of range hoods is recommended as studies have shown huge household increases of PM 2.5 during cooking events without proper range hood use.
Experience I had was responsibility for a class 2(100 count) clean room. A REAL "clean" room. Laser inspection / detection of INDIVIDUAL particles.
Lance, I have a scruffy neighbor who cooks in a pretty closed up home, no mech. ventilation, no range hood and his house always smells. He also closes himself up in an tiny ice house a couple days a week all winter long with a propane heater . . . unvented-- products of combustion all around him, except for Exfiltration.
He is still alive. Hard to believe. Kidding here. . .
When I hear things like PM2.5 related to deep tissue damage in lungs etc I am just shaking my head, incredulous.
Please. Tell me you do NOT live in California!
Reply to Brian Post #35 (for some reason I'm not getting the option to reply to your messages?)
Ottawa, Ontario. Almost as far away from California as you can get on the continent.
Everybody seems to have a story about someone who smoked, drank, and ate fast food until they died peacefully in their sleep at age 95. For some strange reason I feel those people are the exception, not the rule. Personally, I think I'd rather give myself the best chance possible of living a healthy life. I'm building a new home and think I'll spend a little effort trying to do the best job I can to plan things properly, since changes afterwards can be much harder to implement. That's my perspective, anyway. To each their own! :-)
Back to the range hood and makeup air thing. Regardless of how advanced or cool I'd like to make something, I fully admit there's likely to be no financial payback, at least in some sort of practical time period anyway. I'm a tweaker, and I understand that Engineering consumer grade products and systems is all about compromise. I tend to study things, discover and understand the compromises, then see where I think improvements can be made. Sometimes the "one-size-fits-all" approach is fine, other times it bugs me.
My wife is from India and cooks fantastic fresh meals most days of the week. And when we have people for dinner her preparation is often a 3-4 day affair. Our range hood gets a pretty good workout as some of the foods require frying spices in oil, and are generally dishes with a great smell. However, when you come in our house it doesn't smell like Indian cooking, which is a feat accomplished by opening windows and running the hood. A lot.
The energy penalty of having a 6" diameter hole in an otherwise highly effective building envelope is real, and it's two holes if you need makeup air. As Trevor said, it's a thermal/moisture/IAQ leak that's active 24/7/365. If we have to have it, well, I want mine to be as good as possible. I'm building a very high performance house and holes are to be avoided.
I'll admit that theory is fun, but there's a very good chance I'll end up with a normal range hood with a hole in the wall just like everyone else. Or maybe not. We'll see. It's fun to discuss possibilities, but reality is never far away.
Thanks for the article. I've faced similar challenges with humidity in a Panasonic ERV in a scandalously airy house by comparison to yours (6 ACH50). My conventional A/C has a dehumidification mode (runs fan at 50%) that does keep RH at about 55%. There have only been a few rainy, cool (70º) summer days where we felt a little chilly. The energy penalty is non-trivial. I'm still trying to figure out if I can change the ERV's distribution to keep CO2 in check and shorten the runtime a bit.
I will say 1) comfort with the dehumidification mode is greatly improved over the old A/C unit, and 2) our IAQ is both quantitatively and qualitatively improved with the ERV, especially in the warm-humid months when the windows are mostly closed.
I would suggest that efforts to air seal your house will go a long way to helping you control your indoor humidity levels. You likely have so much moisture coming in through the envelope that the difference between an ERV and an HRV would be hard to detect.
Would you say you are pleased overall with your Panasonic ERV? Which model do you have?
Hello Lance, I too cannot find a REPLY link to reply in line directly to your post #37. SO, replying under your #24. . .
-- I see you live just 5 miles north of me, but about 900 east! Similar weather maybe. Glad you are not in California.
I am confused though. What is different, mine vs yours? On my hood, as pointed out above and image to show, there is a spring loaded damper inside it, closes tight. NOT open 24/7. Additionally, the 6" duct outlet on the sidewall has a gravity damper on it. Infiltration air has to first get by the check valve-like gravity damper then through the insulated 20 ft long duct then through the spring loaded tight damper, then past the blower, then past the filter. How is that "open"?
Secondly, like you I have trained my wife to open the window when the range is ON. Trevor apparently does not agree that the air flow from the window to the hood only entrains about 25%, thinks its more like 75% ??! But, you have the same hood situation as I. What do YOU think on entrainment? On ours the window is probably only 7 or 8 ft away and you can FEEL the flow from the window coming into the home. . . where else will it go? sit around and NOT proceed to the hood? Don't think so. THEN, when the window is closed, there is no opening in the envelope. So, no 2nd 6" hole.
It's an obvious tough situation having to account for our gourmet cook spouses wild use of precious conditioned air, I understand. But, I like to tinker too. SO, what is the next level of embellishment here for us tinkerer's? hmmm.
How about running an insulated duct from outside to the back surface of your range into a long narrow SUPPLY hood. Place a motorized damper just inside the inlet -- closes when hood is off. "Re-engineer" the closure flap with expensive foam tape to make a "good" seal -- thus passing Trevor's spec. If you are familiar with Jennaire ranges they EXHAUST level with the countertop between the burners. a 3" by 20" slot. Some European systems offer, again EXHAUST, "hoods" that pop up out of the countertop along the rear of the range-- another slot arrangement 36 x 3". What I am suggesting is to use the same concept to FEED air to a similar slot very NEAR the back of the range at countertop level. Build an L-shaped "hood" to direct air from the slot horizontally over the range.
Advantage: Virtually zero entrained room air;
its insulated to just below the range and no air flow past the motorized damper, so near zero heat loss from natural convection to the air flow in the duct; and
best of all: NO makeup air heating! The whole idea is to use the "free" cold air to entrain the fuel combustion products and food smells then, send it back outside. Don't heat something you aren't using to keep you warm!
By the way, that chicken curry smells good even in Minnesota. My wife likes to cook too.
Just getting back to this now.
The damper on range hoods stops air flow but is sill an un-insulated hole in the wall. And "stopping" airflow is not really done effectively. The springs in those dampers are very weak as to allow the damper to open fully with fan flow and be negligible restrictions to flow, which also allows them to be sucked open on windy days (I can hear ours flapping open and closed all the time, YMMV). They also don't close all that tight. It's definitely better than nothing, but when you're making a considerable effort to keep everything else in the house airtight those dampers are a bit out of place as something to rely on.
Supplying makeup air to the range area is a great solution in my opinion. The trick, as you've pointed out, is to supply it with some sort of cosmetically acceptable solution that still functions well. I saw an interesting approach in a tiny house on wheels where they elevated the cooktop from the counter and had makeup air flowing all around it. Not exactly good looking, but interesting.
https://www.youtube.com/watch?v=Xy4OvjEd3IE
That was a REALLY interesting video. thanks Lance!
noticed a couple of things:
-- neat $12 smoke pen he used to prove out flow streams. Gotta' get one!
-- neat mech. damper he uses to relieve pressure from exhaust fan. If you look REALLY CLOSE you can see he has made it air tight by using some foam tape on each side of the damper face so the circular damper contacts it when close. AIRTIGHT, or dang close. This is exactly what I would recommend IF you used one. For mine, I still contend it is doubtful more than about 1 or 2 cfm reverse air flow is seen backwards through my range vent system. I will use my new smoke pen and check it though.
-- For FRESH air range hood supply: the Google pointer below shows an EXHAUST system that pops up along the backside of the range. My suggestion would be to buy one of these, gut the blower, replace feed with a mech. damper near outside wall while feeding with 6" insulated duct. When you flip the switch to actuate, the damper opens(instead of blower exhausting) allowing fresh air entry to backside of range. To see just google "GE Profile Series PVB98DTBB"
-- one more tiny point: When doing my blower door test I had the operator record flow with all three(3) of my DeltBrez fan ports taped SHUT on the outside wall vs NO tape over the exhaust.
NO difference in blower pressure sensed..
These are cheap $50 fans with a 50 cent, plastic gravity dampers. So, with TWO dampers-- one spring closed in the hood + a standard gravity damper on the exhaust port(outside wall), I feel PRETTY confident that there is no back flow when MY hood fan is off.
Once again, I can't reply directly, this is to post #47.
Sounds like you've done above average homework on your range hood duct. Sounds like it works pretty well!
Regarding the downdraft hood as a fresh air supply, I'm having one of those "why didn't I think of that" moments. Brilliant idea! I thought about incorporating vents into the backsplash behind the range, but somehow I knew better than to even propose that idea to the Mrs. I think that's called "survival instinct".
I'm going to look into that one further. Thanks for the idea!
"It also has an 'away' setting, meaning you can have minimal fan speed to exchange air while you’re on vacation..."
Why would you want to exchange air while the house is unoccupied? That is, after the first year of operation when the building materials have reached equilibrium moisture content?
It's probably beneficial to maintain a minimum amount of airflow to prevent back flow which could push dirt out of the filters and into the ducts. You can program the setting to be 0% if you choose.
Why not paint a few more white circles on the wall (and around that white rectangular plate) so the diffuser blends in even more?
The wall mural is based on Eddie Van Halen's Frankenstrat, so any additional circles would've ruined the look. 🙂
The details on the guitar, especially the replica, are impressive. If homes were built with this much love and attention to detail, no one would ever want to move.
https://youtu.be/9LnXW5cQKug
I see, so it is. Perhaps paint the diffuser and the wall plate to match the background?
More complete installation instructions are available on the Zehnder America website. The instructions inside the carton (shipped from Europe) definitely leave you "hanging" (pun intended), but complete system installation instructions have been provided for North American installers. Included is an overview of all the Zehnder air distribution components. Here's a link to the Zehnder America General Installation Manual...
https://zehnderamerica.com/wp-content/uploads/2019/09/Zehnder-Installation-Manual-9.20.19.pdf
Not sure when you did your install, Eric, but this has actually been available on the website since early 2018. I started with Zehnder America in 2017 after completing a couple of my own DIY Zehnder installs, and one of the first projects I undertook was to put together this comprehensive system installation guide.
Our European parent company builds a fantastic product, but the literature is clearly geared towards a distinct and established European construction environment. At Zehnder America our time is split between helping educate and mature the building community and picking away at adapting our literature for the North American market. We're making progress! We appreciate customer feedback and we're available by phone to help ensure your success when you select Zehnder Comfosystems.
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