Looking for HRV pointers/ learning curve shortcuts.

[Poindexter]

The Poindexters have relocated to a fairly modern apartment, 613 sqft with 10 foot ceilings, so 6130 cuft. The old place (19000 cuft) will be listed soon and I am prepared to make you a screaming hot deal on the big old house if you are a climate refugee looking for 5 bedrooms way up north.

The new (rental) place has a Fantech SHR1504 HRV system I am trying to figure out. The landlord wants the HRV system to run ' one hour per day' except in really cold weather - but he does not have a specific RH or CO2 target for the interior of the building. The landlord is a mostly retired plumbing contractor, and the place is well built. The concrete work is superb. The drywall is excellent. The framing appears to be top notch. The flooring is very good to excellent. The plumbing is mind bogglingly well executed. As a career tradesman himself he had a pretty good idea of who in each of the various trades was doing good work, and hired them for this build. I suspect the HVAC sub told the landlord the HRV needs to run one hour per day, and the landlord took that to the bank without fully understanding the complexity of the situation.

When I choose to run the HRV, I am looking at exterior v- interior temperature, RH, and particles. It is hot, humid, and wildfire season outdoors currently. The HRV inlet is on the south side of the house and well shaded in summer, so it is advantageous for me temperature wise to run the HRV anytime the house is a bit on the warm side.

I have a couple dew point calculators booked marked on my phone. It is rarely advantageous to me to run the HRV in bright summer sunshine, as the absolute humidity in the apartment is likely to increase. I am observing pretty much 55-62% RH indoors the last couple weeks, with the cooler surfaces of the tiled floors in the bath and kitchen usually damp.

There is an add on filter setup on the outdoor air intake that is fairly sophisticated. With outdoor particle counts in the 100-150 mcg/m3 (each) range for PM2.5 and PM10, I can expect to see about 50 and 50 mcg/m3 indoors after running the HRV for 20 minutes at 67 cfm, so 1340 cuft exchanged, about 20% of the air in the cuft of the apartment. A single MERV 13 filter on the intake side if a 20" box fan can take that down to donuts in half an hour or so in this space.

I do have a CO2 detector/monitor on the way from Amazon, should be here any day now, but no useful info today. The HRV I do have has no dehumidification ability. It is up to me to choose when to run the HRV, but I am old enough to not like stepping out of the shower onto a damp tiled floor.


I am planning to add stand alone dehu to my as built setup, but I am very curious to know what other parameters I should be monitoring.

Thanks in advance.

 

[EbS-P]

My thoughts… what are you needing ventilation for? Humans, cooking, off gassing stuff, PM?… did I miss anything?

Contaminants you need to dilute through ventilation, CO2, VOCs and formaldehyde, PM?…. Others?

It seems to me your filter boxes Handel the PM well enough, add activated charcoal and you get some VOC and formaldehyde reduction… So really you want ventilation for CO2 and VOCs. Most of which will be higher when you are present.

This is where some proximity/occupancy sensors would be helpful. ecobee may be the only all in one box solution to set different profiles for your equipment based on sensed occupancy. It’s not great. It’s just good enough.

All of the data can be logged from your ecobee. Temp humidity (in and out) vocs, derived CO2. And equipment state.

Again not perfect but good enough. Not sure if you could control the HRV with the ecobee. But it would be worth lookIng into.

 

[zrock]

those systems are designed to continually run.. Running for a hour a day is going to do absolutely nothing.. I was a little skeptical when i seen my first one thinking it would make things cooler/hoter depending on the season. Boy was i wrong everything balances nice and the air quality is actually really good and you get no lingering smells..

 

[Poindexter]

My math doesn't work above. If I turn over 20% of the air in the space, but reach 33% of the outdoor particle concentration, then either the air outside the intake is dirtier than average, or the fan is running at some other speed.

I can see the attraction of having a unit like this run 24/7, but I question why. I spent a bit over $7k on heating the big house last winter. That number includes the oil bill, 7 cords of green splits dropped on the driveway, and me working for free humping 7 cords of green splits from the driveway to the kilns out back, then into the house, up the stairs, carry the ashes out, blah blah.

If the HRV does not need to be running, mine won't be. In a new build, especially with a bunch of carpeting, I can see running the HRV more or less full time for the first year while the manufacturing chemicals in the building materials are offgassing. Once the building is mature, I am not seeing a good reason to carry on.

Control CO2 and associated products of inadequate ventilation, yes. Seasonal humidity control, yes. In wild fire season or other periods of unhealthy/hazardous air quality it makes sense, to me, to focus on cleaning up the indoor air with ongoing circulation/filtration, and minimize exchange between clean indoor air and polluted outdoor air (within the limits of controlling CO2 concentration and etcetera).

In the moment Mrs. P is running the HRV for 40 minutes during her morning bath routine, and I am running the HRV for another 20 minutes in the evening when I take a shower at the end of each work day. I look forward to quantifying how much CO2 is produced by a sleeping geriatric cat while we are both gone to work.

Also, at this location the HRV system is the default system for sucking cooking smoke and airborne bacon grease out of the kitchen. I don't like it. I don't want airborne bacon grease in my HRV ductwork, and I don't want it in my HRV heat exchanger. If there is a replaceable filter element that can go on the intake in the kitchen I will consider it, but I really would rather place the cookstove on an exterior wall and seal up a penetration for an actual direct exhaust fan.

 

[EbS-P]

My math doesn't work above. If I turn over 20% of the air in the space, but reach 33% of the outdoor particle concentration, then either the air outside the intake is dirtier than average, or the fan is running at some other speed.

I can see the attraction of having a unit like this run 24/7, but I question why. I spent a bit over $7k on heating the big house last winter. That number includes the oil bill, 7 cords of green splits dropped on the driveway, and me working for free humping 7 cords of green splits from the driveway to the kilns out back, then into the house, up the stairs, carry the ashes out, blah blah.

If the HRV does not need to be running, mine won't be. In a new build, especially with a bunch of carpeting, I can see running the HRV more or less full time for the first year while the manufacturing chemicals in the building materials are offgassing. Once the building is mature, I am not seeing a good reason to carry on.

Control CO2 and associated products of inadequate ventilation, yes. Seasonal humidity control, yes. In wild fire season or other periods of unhealthy/hazardous air quality it makes sense, to me, to focus on cleaning up the indoor air with ongoing circulation/filtration, and minimize exchange between clean indoor air and polluted outdoor air (within the limits of controlling CO2 concentration and etcetera).

In the moment Mrs. P is running the HRV for 40 minutes during her morning bath routine, and I am running the HRV for another 20 minutes in the evening when I take a shower at the end of each work day. I look forward to quantifying how much CO2 is produced by a sleeping geriatric cat while we are both gone to work.

Also, at this location the HRV system is the default system for sucking cooking smoke and airborne bacon grease out of the kitchen. I don't like it. I don't want airborne bacon grease in my HRV ductwork, and I don't want it in my HRV heat exchanger. If there is a replaceable filter element that can go on the intake in the kitchen I will consider it, but I really would rather place the cookstove on an exterior wall and seal up a penetration for an actual direct exhaust fan.

I won’t cook bacon inside. That makes for a short bacon season in your part of the world. Kitchen exhaust via dedicated HRV that’s possible. But why not just open a window? Cooking will be a major source of indoor air pollution. The small volume means this needs addressed. We had an old Jen air down draft range. I really liked it. Not sure they are built like they once were.

https://www.jennair.com/ranges/electric/downdraft-electric-ranges.html?plp=%253Arelevance%253Acategory%253ARangesElectricDowndraftElectricRanges&plpView=list

Code mandates fresh air intake for exhaust over xxx cfm. This is where a dedicated ventilating dehumidifier could be used. It’s filtered. Can be controlled via damper from 50-150 cfm. I really think a slight positive pressure ventilation regime makes sense.

I think the high performance building community is moving away from ERV/HRV. HRV has a place in cold climates. ERV for bathrooms I could see a case for. But for the cost they don’t dehumidify. So why not put that money towards a ventilating dehumidifier.

For ERV/HRV I think both intakes need filters.

 

[Poindexter]

I started reading up on ERV and my head hurts. I am going to thoroughly understand what the HRV system I am using can do before I try that again.

I do agree about cooking meat indoors. One of my early commitments to IAQ (indoor air quality) at the old big house was to cook as much meat as possible outdoors. And boiling big pots of water indoors is/was a strictly winter time, dry air activity.

But the small patio at the new apartment has been adjudicated "not aesthetic" by Mrs. P, so I can set up outdoor cookers on a 10x12 concrete pad facing the street. And the landlord has already approved a dog house sized structure on that same pad to hold charcoal.

 

[Poindexter]

Interesting results, I got two CO2 detectors in the mail today.

I hooked the first one up and found 1660 ppm CO2 indoors, somewhat concerning. I set the HRV to high and opened the second detector. On the outdoor front porch my outdoor CO2 was 370ppm, back indoors the second CO2 detector was also showing 1660-1670 ppm in another area of the apartment.

Both of the new devices are in good agreement with my older particles counters for PM2.5 and PM10, so I will continue to use the older particle counters for now.

I turned the HRV off, opened all the windows, and used 2 twenty inch box fans to get the indoor CO2 down to 500ppm average. With the house closed back up and the HRV running full time for two hours, just me and the cat here this evening, average CO2 has crept up from 500 to 507ppm average. When Mrs. P gets here later this evening I suspect the mean CO2 to increase even faster, suggesting I might need a fan speed on the HRV higher than whatever it is now, and continuous operation when we are home.

The good news is the apartment is clearly very tight. The bad news is HRVs lose efficiency as fan speed/ throughput increases.

The manual for the counters I got in today (linked above) also mentions a similar product with an added sensor for formaldehyde and VOCs, using an AGS02MA aka DART-WZS sensor. I don't know that sensor from Adam's cat, but will read up on it.

I am curious to see what the CO2 reading is on the big old house when the wood stove is running, but I am not really concerned. I have been tired and grumpy since we moved into the new place. I have attributed that to working three 12 hour shifts each week (at 12-15k steps each) and then spending three of my days off each week carrying stuff around. I look forward to seeing how much better I feel after sleeping in CO2 <1000ppm for a few days, while still having something in my hands pretty much full time while walking around.

 

[Poindexter]

With the HRV off for an hour the cat and I ran the average CO2 from 507 up to 590 ppm. I have one sensor (on a drop cord) next to my reading chair in the living room where I am not, and then other next to my computer mouse on my desk in the bedroom. Moving the sensor in the LR/dining/kitchen area I am not seeing much variability. I shall get another drop cord from the big house tomorrow, but my next step before calling it a night is to open some windows, turn some air over, and set the HRV to continuous before Mrs. P gets home from sorting one of the guest bedroom closets.

 

[EbS-P]

I started reading up on ERV and my head hurts. I am going to thoroughly understand what the HRV system I am using can do before I try that again.

I do agree about cooking meat indoors. One of my early commitments to IAQ (indoor air quality) at the old big house was to cook as much meat as possible outdoors. And boiling big pots of water indoors is/was a strictly winter time, dry air activity.

But the small patio at the new apartment has been adjudicated "not aesthetic" by Mrs. P, so I can set up outdoor cookers on a 10x12 concrete pad facing the street. And the landlord has already approved a dog house sized structure on that same pad to hold charcoal.

The ERV tries to moderate humidity, but does it poorly. There are active ones not that actually runs a dehumidifier.

How are the Scandinavian countries doing hvac? That’s probably worth looking into.

I would say once you have a problem needing solved posting your question(s) to hvactalk.com could be useful. The user teddy bear over there was on ther ground floor of thermastor and involved in some of the first commercial dehu products. He big on indoor air quality now. Might be the kind of challenge he would be interested in. He’s got a recipe for the lower 48 green grass climates down.

Interesting results, I got two CO2 detectors in the mail today.

I hooked the first one up and found 1660 ppm CO2 indoors, somewhat concerning. I set the HRV to high and opened the second detector. On the outdoor front porch my outdoor CO2 was 370ppm, back indoors the second CO2 detector was also showing 1660-1670 ppm in another area of the apartment.

Both of the new devices are in good agreement with my older particles counters for PM2.5 and PM10, so I will continue to use the older particle counters for now.

I turned the HRV off, opened all the windows, and used 2 twenty inch box fans to get the indoor CO2 down to 500ppm average. With the house closed back up and the HRV running full time for two hours, just me and the cat here this evening, average CO2 has crept up from 500 to 507ppm average. When Mrs. P gets here later this evening I suspect the mean CO2 to increase even faster, suggesting I might need a fan speed on the HRV higher than whatever it is now, and continuous operation when we are home.

The good news is the apartment is clearly very tight. The bad news is HRVs lose efficiency as fan speed/ throughput increases.

The manual for the counters I got in today (linked above) also mentions a similar product with an added sensor for formaldehyde and VOCs, using an AGS02MA aka DART-WZS sensor. I don't know that sensor from Adam's cat, but will read up on it.

I am curious to see what the CO2 reading is on the big old house when the wood stove is running, but I am not really concerned. I have been tired and grumpy since we moved into the new place. I have attributed that to working three 12 hour shifts each week (at 12-15k steps each) and then spending three of my days off each week carrying stuff around. I look forward to seeing how much better I feel after sleeping in CO2 <1000ppm for a few days, while still having something in my hands pretty much full time while walking around.

I have not read much on ventilation for spaces less than 1000 sq ft. Recommendation is a full air exchange every 2-4 hours. (Rule of thumb is 50-100 cfm of fresh air) for small spaces it obviously needs to be higher but I don’t have a good sense of how much. 150-300cfm just based on size differences??

You might try a timer or a smart switch on the bathroom fan.

 

[Poindexter]

I feel better this morning than I have felt in weeks. I have the HRV running continuous at a speed that has kept indoor CO2 levels at or near 500ppm overnight. My 'symptoms' were all generalized sorts of things that could be attributed to being 'tired' like muscle aches, joint pain and mental fog. All are improved this morning, remarkably improved.

I found one article about CO2 toxicity at NIH that wasn't super helpful, a bunch of co-hits for carbon monoxide, and one at INTJEM (International Journal of Emergency Medicine) that mentions CO2 is 1.5x heavier than air and therefore often collects in low places like the holds of ships and water meter pits.

I think my next step is to accumulate some sensors to see what else builds up in the space with the ventilation off. I am pretty sure I am already registered at hvactalk, thanks for the reminder.

 

[Poindexter]

At the risk of talking to myself in an empty room, I have a couple observations.

1. I am not going to be able to measure the CO2 emissions of my 7 pound geriatric cat with the instrumentation I have available. She is alive, she is putting off some CO2, but in 6100 cuft with the instruments I have her CO2 emissions could be statistical noise.

2. With one adult (and the cat) at home, we can run the HRV 40 minutes per hour at low speed and keep CO2 at or under 700 ppm.

3. With both adults (and the cat) at home, we need the HRV running continuous on I think medium speed, to keep CO2 under 700 ppm.

4. The Dart WZ-S formaldehyde and VOC sensor does not meet my purchase criteria. I am not buying one. I think the detection methodology has a bright future, but the LCS (least common squares) calibration methodology is a weak point. If I were to buy one of these sensors it would be looking for the formaldehyde level in my home to be about the same as it was last time I powered up the sensor. If I were to start embalming corpses on my dining room table I would expect this sensor to be able to tell if I was making money or not, however if I replaced say 1000 sqft of wall to wall carpeting I am not confident this sensor could accurately track diminishing formaldehyde emissions over the course of a year or so, powered on once weekly.

 

[Poindexter]

So here is the problem with consumer grade hygrometers.

My top two issues are 1) Mrs. P is extremely sensitive to mold and 2) I have easily $1-3k just in irons or blades in my various chisels and planes in my wood shop. Never mind my adzes or scorps or travishers, Mrs. P does not need to know I have very likely $7-10k of edges out in the shop.

If I have a condensation event in my shop space it could easily cost me a year of time just in rust abatement and resharpening, I have a very strong desire to keep the drybulb temp in my shop at least 10 degrees F above dewpoint, because I am not going to live long enough to spend a year recovering from a condensation event and make enough furniture before I die for all of the potential great grands to inherit something from me.

So I need to know with reasonable precision what my actual RH is, and what my dewpoint actually is - so I can proactively avoid condensation events.

According to NIH, CDC and PGH, I need to keep RH in the 40-60% range to minimize mold. My personal comfort zone, given my edged tools, is 35-45%RH; a bit on the dry side but with some wiggle room to act during humid weather.

Pic is two particle counters with identical temp/RH sensors on board, and two analog devices from Kroger around $10 each. If the readings were in my 35-45%RH comfort zone I could put up with this imprecision. Front to back I see 55.7, 60.9, 54 and 58% RH. The decimal points and tenths readings on the digital displays are clearly window dressing.

 

[Poindexter]

Thank you for listening to my TED talk.

 

[Poindexter]

Two new data items today.

I went to my local hardwood purveyor and found an American Beech plank in my truck bed when I was ready to drive away. It is 4/4, nominal one inch thick, 14 inches wide, and 8 feet long. I didn't have the heart to carry the plank back into the store, so I bought it. The plank is as flat as the earth used to be believed was.

I must never visit a dog pound, I will bring them all home with me.

Any road, American Beech is very sensitive to moisture, it moves even more than white oak with humidity swings. The apartment (613 sqft) and the attached shop space (+288 sqft) was at 70dF and 60-70 (ish) RH. The apartment was fairly sticky and uncomfortable compared to the hardwood showroom.

Rather than solve the word problem: Poindexter has 900 sqft living space, ~9000 cuft, at 70 dF and 70%RH. Outdoor ambient is approximately the same at 70dF/70RH. The forecast is for overnight lows of blah blah blah, the HRV system is 76.8 % efficient on medium speed continuous ventilation...

Instead I am running both the dehu to shoot for 45-50%RH and the HRV to keep interior CO2 at or under 800ppm.

The good news is I have about 300# of other lumber stacked on this lovely beech plank to keep the plank flat while I get my RH under control. The bad news is I will have to maintain indoor RH for at least two years after I build a piece of furniture out of this lovely plank.

First world problems perhaps.

 

[Poindexter]

I woke up this morning with three fans running.

The HRV was ticking over on continuous. The new dehu was kicking off and on right regular, but maintaining ~45% RH in the space. And the particle filter was running, with the particle counters showing me donuts, 0/0.

When we left for the day I turned the particle filter off, set the HRV to 20 minutes per hour on low, and left the dehu with a setpoint of 45%. With no one at home I can run the HRV 20min/hr and expect indoor CO2 to drift down to outdoor ambient in 4-6 hours.

My outdoor counts today were a fair bit of PM10, I am seeing mostly 0-2 mcgm3 for PM2.5 and 20-30 mcgm3 for PM10 in the data stack at the nearest AQ police station. But the indoor particle counters were showing me donuts, 0/0, so I didn't need to run that fan today, as the intake filter on the HRV handled those particles.

I am about to go find an image of an EMC table and make it the background image on my desktop. I don't want my furniture (or my lumber) doing yoga this winter when the air eventually dries out.

I did move the setpoint on the dehu down to 40%RH when we got home this evening. I have about 300# of construction lumber in the shop space at likely 18-20%MC three days ago, and the beech planks were probably near 8%(wet basis) when I bought them yesterday, so I gotta kinda walk the line, but if something is getting pretzeled up it will be the construction lumber.

 

[Poindexter]

I am going to sit at 70dF and 45%RH for a little while. That should keep my beech happy with an EMC around 8.5%. It is going to put a great deal of pressure on my construction lumber to move from 18ish%MC to 8ish% MC, but I can add a couple heavy things to the lumber stack. Like an anvil or two.