I’m looking at installing a ventilation system in my house. New construction, will have radiant floor heating (no heating ductwork), located in Upper Michigan (cold a lot). I thought my location called for use of an HRV… but I have a guy here that has a unit that he bought and never got to installing and is now willing to sell it to me pretty cheap. I believe the unit is an ERV however. What’s the difference and does it matter much what type is installed? (I’ve done a little research but figured I’d ask ya’ll).
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In a heating-dominated climate one of the primary functions of ventilation in a tight house is to remove humidity, so an HRV is appropriate. An ERV will recapture some of the humidity from the exhaust airflow.
In a cooling-dominated climate, an ERV will help reduce summertime humidity levels by moving some of the incoming moisture into the exhaust air stream.
Solar & Super-Insulated Healthy Homes
But... cold winter air is dry... wouldn't you want a bit of moisture added to the incoming air stream in winter? (assuming major humidity sources are exhausted appropriately with a separate exhaust system (baths and kitchens)).
In a "completely" sealed house there will be much more moisture introduced into the house from people breathing, bathing, and cooking than will diffuses out though the building materials.Of course no house is sealed perfectly and you get some air exchanges when people go through the doors, etc.But it is common in modern "tight" houses that the internal moisture levels are too high without replacing some of it with dryer outside air. And of course that is needed to also remove other contaiminates and bring in fresh air.I would get the model number and brand of the ERV and see if you can download the manual. See if it can be operated in a mode that does not humidify the incoming cold air..
William the Geezer, the sequel to Billy the Kid - Shoe
Edited 1/1/2009 2:06 pm by BillHartmann
I would get the model number and brand of the ERV and see if you can download the manual. See if it can be operated in a mode that does humidify the incoming cold air.
Now, you just explained why a tight house needs dry incoming air and then you seem to be recommending humidifying the incoming air?????
This is what an ERV does and why it's not recommended for a heating climate.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I have a problem of my mind (not comments <G>) being faster than my fingers.There was suppose to be a NOT in their. Since edited..
William the Geezer, the sequel to Billy the Kid - Shoe
But... cold winter air is dry... wouldn't you want a bit of moisture added to the incoming air stream in winter?
Leaky houses are dry in the winter because they exchange too much air, and when even moist cold air is heated it's relative humidity plunges.
Tight houses have the opposite problem, which is why ventilation (min. 0.35 ACH) is recommended (or required for programs like Energy Star).
In a heating-dominated climate, you need to dehumidify the house. The indoor RH should be between 30% and 40%.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
In a cooling-dominated climate, an ERV will help reduce summertime humidity levels by moving some of the incoming moisture into the exhaust air stream.
Robert, I take it back...you are not always a climatist.
"one of the primary functions of ventilation in a tight house is to remove humidity"
I disagree. The purpose of ventilation in all occupied spaces is provide fresh, relatively clean air and to remove contaminants via dilution and displacement. This not affected by the construction of the building. Very few houses are constructed tightly enough or occupied heavily enough to warrant winter dehumidification. Even in those cases, the removal of humidity is secondary to the removal of contaminants.
Very few houses are constructed tightly enough or occupied heavily enough to warrant winter dehumidification. Even in those cases, the removal of humidity is secondary to the removal of contaminants.
Any house built to the current IRC energy code should be sufficiently tight to prevent the lowering of RH by natural air exchange (which is why leaky houses are dry). In a house built (as they all should be) with relatively non-toxic materials, the primary "contaminant" in the indoor environment is water vapor. Excess humidity will cause damage to electronic equipment, rot, insect infestation, mold & mildew, dust mites and allergies and increased outgassing of formaldehyde from wood panels, cabinets and furniture.
In a cold climate, indoor RH should remain between 30% and 40%. The human body prefers a range of 30% to 70%, while houses prefer 20% to 40%. The compromise range, then, is 30% to 40%. To maintain this level, however, requires a minimum of 0.35 ACH, as few houses have the thermal envelope permeability to evacuate moisture by diffusion.
A typical American family of four will put at least 3 gallons of moisture per day into the indoor environment. In a 2000 sf 2-storey home at 68° 35% interior and 30° 75% exterior conditions, even a house with a perm-5 envelope will diffuse only 0.67 gallons per day. Air exchange at 0.35 will remove 2.69 gallons per day. Without this controlled air exchange, the indoor humidity would quickly rise to very unhealthy levels.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/5/2009 2:06 pm ET by Riversong
"the primary "contaminant" in the indoor environment is water vapor"
I have to disagree again. While the relative humidity numbers you post are not too far off, the extremes seem "manufactured". Where did you get "The human body prefers a range of 30% to 70%, while houses prefer 20% to 40%"?
I agree that 30 to 50% rh is a commonly used acceptable range.
The primary contaminant in closed, unventilated indoor spaces is carbon dioxide. The secondary contaminants are primarily odors. Respiration, perspiration, off-gassing (by the building AND the occupants) cooking odors, smoke, mold spores and excess moisture all constitue indoor air quality challenges. All spaces contain mold spores and all mold produce gases. All fauna produce CO2 as a result of respiration and all emit various odors, dander, perspiration, etc. This is the reason that demand controlled ventilation is based on CO2, not humidity.
"Excess humidity will cause damage to electronic equipment, rot, insect infestation, mold & mildew, dust mites and allergies and increased outgassing of formaldehyde from wood panels, cabinets and furniture."
I have never heard such claims. Do you have a source for this data? Wood panels will "outgas" more in a higher humidity environment? - no. Damage to electronic equipment?-no. Mold and mildew (are the same thing, BTW) and they are affected by humidity. Growth is usually tied to the presence of liquid water, not vapor.
Apparently, you want me to do all your research.
While the relative humidity numbers you post are not too far off, the extremes seem "manufactured". Where did you get "The human body prefers a range of 30% to 70%, while houses prefer 20% to 40%"? I agree that 30 to 50% rh is a commonly used acceptable range.
The human comfort range comes from years of research and the safe range for the house depends on climate. In a cold climate, building scientists recommend no more than 40%, as any higher levels can result in visible condensation on even efficient windows and hidden condensation in the thermal envelope. Additionally 50% is the threshold level for dust mite activity.
The primary contaminant in closed, unventilated indoor spaces is carbon dioxide... This is the reason that demand controlled ventilation is based on CO2, not humidity.
While CO2 contamination is a primary determinant for air exchange in office buildings, it is not so in the home.
From Health Canada (emphasis added) http://www.hc-sc.gc.ca/ewh-semt/pubs/air/exposure-exposition/non-carcino-eng.php:
Indoor levels tend to be higher than outdoor levels. Gas stoves and unvented kerosene heaters are major sources of carbon dioxide indoors, but, in poorly ventilated rooms, levels may exceed 5400 mg/m3 (3000 ppm) from human metabolism alone. <!----><!----><!---->
<!----> <!---->
The lowest concentration at which adverse health effects have been observed in humans is 12 600 mg/m3 (7000 ppm), at which level increased blood acidity has been observed after several weeks of continuous exposure. A maximum exposure level of 6300 mg/m3 (3500 ppm) should provide a sufficient margin to protect against undesirable changes in the acid-base balance and subsequent adaptive changes such as the release of calcium from the bones. This level should also provide an adequate safety margin for sensitive groups. At such a level, the effect of carbon dioxide as a ventilatory stimulant is likely to be small and so would not greatly increase the dose received of other pollutants present in the air.<!----><!---->
"Excess humidity will cause damage to electronic equipment, rot, insect infestation, mold & mildew, dust mites and allergies and increased outgassing of formaldehyde from wood panels, cabinets and furniture."
I have never heard such claims. Do you have a source for this data? Wood panels will "outgas" more in a higher humidity environment? - no. Damage to electronic equipment?-no. Mold and mildew (are the same thing, BTW) and they are affected by humidity. Growth is usually tied to the presence of liquid water, not vapor.
From the US CPSC http://www.cpsc.gov/cpscpub/pubs/725.pdf:
As the temperature rises, more formaldehyde is emitted from the product. The reverse is also true; less formaldehyde is emitted at lower temperature. Humidity also affects the release of formaldehyde from the product. As humidity rises more formaldehyde is released. The formaldehyde levels in a residence change with the season and from day-to-day and day-to-night. Levels may be high on a hot and humid day and low on a cool, dry day.
From Wikipedia http://en.wikipedia.org/wiki/Humidity:
Many electronic devices have humidity specifications, for example, 5 to 95%. At the top end of the range, moisture may increase the conductivity of permeable insulators leading to malfunction. A particular danger to electronic items, regardless of the stated operating humidity range, is condensation…leading to short circuit inside the equipment…Excessively high humidity causes corrosion in electronics.
<!----><!----> <!---->
From the US FS Forest Products Lab http://www.fpl.fs.fed.us/ahrc/mold/moldqa.html: <!----><!----><!---->
<!----><!---->
<!---->Mold growth requires ample moisture in the form of liquid or high humidity. While there is not universal agreement on the lower threshold of humidity required for mold growth, most literature indicates that the relative humidity needs to be at least 70% to 90% to support mold growth…a relative humidity of at least an average of 80% for a month's duration will provide sufficient moisture for substantial mold growth.<!---->
<!----><!---->
<!---->Next time, do your own homework before challenging accepted building science. <!---->
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
You specifics are still lacking. I expect no one to research for me. I do expect that opinions stated as fact be prefaced as such.
"Years of research", "building scientists recommend", "Additionally 50% is the threshold level for dust mite activity." Your typing it does not make it so. These are your stated opinions and/or your interpretations of data you were unable to document in your extensive research.
You stated "in the indoor environment", which includes offices as wells as houses, at least I define offices as indoor environments. Now, your example excludes all but poorly ventilated houses with unvented appliances. You should continue with your research. If you need help interpreting the facts, just ask.
Your example, and Wikipedia is far from definitive, on electronics states the obvious, that condensation is the main culprit. For your review, condensation is liquid water, not vapor, and as such does not fall under the category of "excessive humidity". Weak at best.
Again in your example, one sentence in the Consumer Product Safety report on Formaldehyde from 1997 is a very weak statement for humidity affecting release of formaldehyde.
Overall, an incomplete argument.
You're a piece of work, Tim.
You offered only personal disagreement and negations.
I have to disagree again.
I have never heard such claims.
Wood panels will "outgas" more in a higher humidity environment? - no.
Damage to electronic equipment?-no.
Mold and mildew and they are affected by humidity. Growth is usually tied to the presence of liquid water, not vapor.
Not a bit of substantiation beyond your own admitted lack of knowledge.
I refuted, with reliable sources, every one of your statements - all of which are demonstably false.
Perhaps if you took my upcoming class on Hygro-Thermal Engineering, you would understand these issues.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/6/2009 8:29 pm ET by Riversong
Edited 1/6/2009 8:41 pm ET by Riversong
now boys, remember we're all god's creaturesMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
A PLACE IN THE CHOIR<!----><!----><!---->
Bill Staines
Chorus:<!----><!---->
All God's creatures have a place in the choir, <!----><!---->
some sing low, some sing higher,<!----><!---->
Some sing out loud on the telephone wire,<!----><!---->
Some just clap their hands, or paws, or anything they’ve got now!<!----><!---->
<!----><!---->
Listen to the bass it's the one on the bottom<!----><!---->
Where the bullfrog croaks, the hippopotamus<!----><!---->
Moans and groans with a big to-do,<!----><!---->
The old cow just goes "Moo!"<!----><!---->
<!----><!---->
The dogs and the cats they take up the middle<!----><!---->
As the honey bee hums, the cricket fiddles<!----><!---->
The donkey brays and the pony neighs<!----><!---->
The old grey badger sighs<!----><!---->
<!----><!---->
Chorus:<!----><!---->
<!----><!---->
Listen to the top and the little birds singing <!----><!---->
The melody with the high notes ringin'<!----><!---->
The good owl sighs over everything,<!----><!---->
The blackbird disagrees.<!----><!---->
<!----><!---->
singin' in the night time, singin' in the day<!----><!---->
Little duck quacks and he's on his way<!----><!---->
And the otter hasn’t got that much to say<!----><!---->The porqupine talks to himself. <!----><!---->Chorus: <!----><!---->It’s a simple song a living song everywhereBy the ox the fox and the grizzly bearThe grumpy alligator and the hawk aboveThe sly old weasel and turtle dove
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
i'll see if our chorus director wants to include it in the spring concertMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
HRV, ERV? These apparently have to do with HVAC, but would you mind explaining for those of us in coastal SoCal what these terms mean? We have to run our furnace maybe 20 times a year when nighttime temps plummet all the way below 45°F and we dig out the floor fan in the summer for those 5 or 6 days over 90°F and humidity all the way up to maybe 70%.
Thanks,
All well-built houses that meet the IRC Energy Code standards or better will be too tight for natural air exchange and are required by many codes and efficiency programs to have mechanical ventilation systems to guarantee a minimum of 0.34 air changes per hour.
In a very energy-efficient house in a cold environment, this air exchange becomes a major heat loss vector. So many builders install Heat Recovery Ventilators or Energy Recovery Ventilators which use a cross-flow or counter-flow or rotary-wheel apparatus to transfer heat (and also water with ERVs) from the exhaust air to the intake air.
In the summer, if it's an air-conditioned house, an HRV will transfer the excess heat of the incoming air back to the outgoing air.
They tend to run at about 70% heat-transfer efficiency.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Thanks.BruceT
If you are not running your heating or cooling unit for a large percentage of the year I assume that means you have windows open in your house most of the time? If that is the case, you have little need for a HRV or ERV, or, at least purchasing one would pretty much be a waste of money.
Just curious: are whole house fans popular in your climante?
Edited 1/2/2009 5:24 am ET by Matt
Very popular. It's common for it to be in the 70's in the morning until 12 or so, then the temp spikes up into the 90's, with areas getting into the 100's with direct sun exposure. But when dusk comes, the temp drops like a stone again. late in the day, our house has heated up from 68 to 80 degrees - a stuffy 80. At this point, pulling in drier slightly warmer air feels better than the air in the house. So we open the doors and windows on the N, S, and E sides of the house in the late afternoon (the west side is BAKING still) and run the big fan to pull air in and get a chimeny effect going up our stairs.
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
All the more reason not to use an HRV/ERV.
Well, yes and no. If I was running AC, I might see a use for it.
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
I'm glad you mentioned that you have a whole house fan. Someone asked me the other day about putting one in. Can you recommend a source for them? I'm guessing that they aren't hard to install, right?BruceT
I just put in a big cheap one myself from a big box store, but there is a nice one advertized in FHB that has an automatic insulated door.
The key to those beasts is making sure you have enough of an opening in your attic to get rid of the 3000CFM those monsters can pump into your attic! I didn't, and I can't run mine on high... I can actually feel a wind blowing out through the outlets! A simple dormer vent above it would likely be all you need.
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
Sucks to be us, doesn't it? ;)
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
"Sucks to be us, doesn't it? ;)"
Doesn't it though? :) When I would tell my daughter in New Haven or her sister in Cambridge, MA that it's a cold day here in Huntington Beach, they would just Harrumpf and tell me I have no idea what cold IS. BruceT
HRV is Herve' (a Spanish guy)
ERV is Irving (a Jewish guy)
Forrest
Here is a very cool online HRV/ERY system builder tool.
http://www.hvacquick.com/sysbuilder/hrvbuild.php
Ok. So I will have an HRV located in the basement of a two-story structure. Bedrooms will be on the upper floor. They will need fresh air supply ducts. To get fresh air to each location will require a fair amount of ductwork (primary heat is RFH). Some runs will end up being much longer than others. So.. how does one go about balancing the system? Is it complicated?