I'm a kid, living with my parents, and my bedroom stands alone as separate building from the main house.  It's new construction, very tight and well insulated, and of course since it's a small one-room building, the volume of air per occupant is way lower than in a normal house.  The result was that when I stayed shut up in the room for a long time, with all the windows closed due to the cold weather, the atmosphere became intolerable.  It was so bad I was worried I was depleting the oxygen in the room and what the health effects would be.

So I persuaded my parents to get me an HRV.  The problem was, I unfortunately live in the US, not the UK or Germany, and European models won't work even with a transformer, due to needing 50Hz motors.  It seemed like truly the only US option for an single-room system was the Panasonic FV-04VE1 "WhisperComfort".  And this is an ERV.  And I live in Massachusetts.

I was advised in a previous thread (http://www.greenbuildingtalk.com/Forums/tabid/53/aft/77484/afv/topic/aff/14/Default.aspx) in this forum (by Dana1) that this ERV would be okay to run in cold weather.  However Dana1 also accurately told me just how this ERV will operate when the outside temperature is 20°F or below (it somehow didn't sink in at the time).  I told Dana1 I was in the manual's "Zone B"; I probably should have mentioned I was near the top of that zone.  In December, January and February the average temperatures in my location are 28.9°F, 23.6°F and 26.0°F, that's got to mean it's below 20°F at night during these months, right?
So I'm not sure how to reconcile Dana1's two pieces of advice, because when outside temperature is 20°F or below, the unit will run in exhaust-only mode for 60 minutes, then in balanced mode for only 10 minutes to "test the outside temperature", then repeat.

I have 2 worries related to this:
-Air pressure:  This might be silly; obviously I'm no expert in the physics involved here.  As I said, this room is tight.  With a fan blowing out at 20 CFM all the time, is it possible that air pressure in the room would drop? I would not want to experience that in repeating 60 minute intervals.  I thought of using barometers to test for this, does this make sense?  The other possibility that occurred to me is that the fan would simply be unable to exhaust air as quickly due to the pressure.  So I'd be back to not having adequate ventilation.  If this fear is justified, then is there any way I could test for this effect, or measure how much air the exhaust fan is actually moving?
-Heat loss:  Let's assume the concern about pressure is groundless, and a 20 CFM exhaust fan will leave atmospheric pressure normal and cause 20 CFM of air intake through infiltration.  This still leaves me with zero heat-recovery benefit.  It's just blowing the room's heat out all the time.  Won't this be extremely wasteful of propane and my parents' money?  The ERV is supposed to be 66% effective at heat recovery; that doesn't actually mean that exhaust mode nearly doubles the heating bill, does it?  I'd appreciate it if someone could give me some guidance on whether this will be merely "unfortunately expensive" or "completely unacceptably and ludicrously expensive".  Is it really acceptable to have a fan exhausting the hot air at least 12 hours a day for the coldest 3 months of the year?

I really hope somebody here has advice for me, but I'd appreciate not getting any advice along the lines of "just turn it off when it's cold".  This strange little single-room building is not really livable without ventilation.  If this ERV is okay after all I'll be relieved.  If there's some other device we should have used instead of this ERV, I'll be disappointed: we already paid for this thing and did the work of installing it.  But I'll also be very grateful to anyone who could point it out to me, because this ERV was the only option we could find for the US.  Keep in mind that this is a single room, with no ventilation ducts, and only the US's 120V 60Hz AC power.

The really cold weather is not far off.  Please help!  Thanks.

Maybe you start a band and run away from home. That's what I did when I was your age. Just don't get anyone pregnant.

There are plenty of ways to preheat your intake air if you want to do that. Also it's good to remember that most houses don't have an ERV so they will either have infiltration that is NOT running through an ERV (so not very efficient) or they'll have no fresh air. I'm sure someone can explain this better than I but I do know that an ERV is a lot better than nothing.

Also, don't get hooked on drugs. Drugs are bad. Keep as many options open as you can until you are out of the teenage danger zone. (drugs, unplanned pregnancies, drunken car crashes, shootings, stabbings, fights because someone looked at someone else funny, fights because someone is different than someone else, excessive tattoos, expensive degrees in Comparative Literature from Ivy League Universities, tryouts on Reality TV shows, too much time on Facebook, and tractor accidents) Drama is the worst.

smk-

You are worrying way too much! The ERV running in exhaust mode should work fine for getting fresh air into the house without costing much money.

Pressure effect:
The pressure drop will be so low that it is hard to measure, and certainly has no bad health or other implications. For example, a blower door test is used to actually measure how tight a room is, and whether or not mechanical ventilation is required (like an ERV). One standard test with a blower door test is to measure the air flow through a fan that is exhausting air from a house (through a door that has been removed and sealed up around the fan) when the pressure drop is 50 Pa. For your one-room place, it might take 200 cfm of air flow, if it is tightly constructed, to achieve the 50 Pa pressure drop. Now 50 Pa compares to atmospheric pressure of about 100,000 Pa (100 kPa). So 50 parts out of 100,000 is 0.05%. A front blowing though will change the pressure more. You say your exhaust fan is providing 20 CFM instead of 200 CFM, so if we say the pressure drop is roughly linear with airflow, then the percentage change goes to 0.005%. Good luck measuring that.

Heat requirement:
It would be an interesting calculation to see how much fuel would be required to heat 20 CFM continuously. But basically, it would cost me more time to compute it than the few bucks a year to heat the air. I did a quick interpolation from data for my house which is a colder climate, and I get 3.8 Million Btu, or 38 therms, or 39 CCF (hundreds of feet of natural gas), and the cost of gas is variable, but let's say $0.70 per CCF, so yearly cost of $27 for my colder climate, less for you. You are on propane, so it might be slightly more, but it will be on that order. These costs assume that you were always exhausting, and never heat recovering, which will not be the case, so your cost will be MUCH lower.

Oxygen depletion:
This will not be a problem. From a health standpoint, the buildup of carbon dioxide is more of a problem than oxygen depletion, but I don't think that will be a problem.

When you say, "the atmosphere became intolerable" when the room was sealed up, I don't know if you mean that the humidity was building up, or the smells. The ERV should help in either case, although a dehumidifier would help if it was due to buildup of humidity.

Lee

Concerning the pressure balance, I should have asked what the heating system is for your stand-alone room. If there is a furnace and it is not a sealed combustion system (fresh air comes from outside in sealed combustion system), then the pressure balance is of more interest to make sure that the flame is not backdrafted. Still with only 20 CFM, that would be unlikely.

Lee

Lee Dodge -

Thanks for your reassuring reply.  I know I was probably worrying too much - but after all, this whole thing was my idea and I feel a certain amount of pressure to make sure it works right and justify it.

Glad to know the worries about air pressure were groundless, I had a feeling they would be.  It is a sealed combustion system.

What you wrote about the heating cost is also reassuring, but at the same time kind of disturbing.  Are you saying that if instead of buying this ERV at all, I just had a regular fan (like a bathroom fan for instance) that I ran at 20 cfm all the time, it would cost less than about $27 per year?  And the ERV's energy recovery just saves some portion of that already small cost?  It'll take a long time for this thing to pay for itself if that's true!  And if the benefit is really so small, I'm sort of confused about what this whole "single room ERV or HRV" thing is all about.  Why then do single-room ERVs/HRVs seem to be popular in the UK and elsewhere in Europe, if they only save so little a year?  Why aren't people just buying simple exhaust fans, the equivalent of a cheap bathroom fan over here?

Finally, about carbon dioxide buildup: maybe putting it in those terms was somewhat exaggerated and melodramatic.  I'm really just concerned about getting good air quality that's good for health and productivity.  I've been googling around, trying to get a handle on what level of air changes per hour is desirable.  Bits of info I've picked up (feel free to correct any of them): 0.35 ach - 0.45 ach are required by various building codes in various countries, and emerging evidence suggests that people at work and in school perform better around 0.5 ach or 0.6 ach.

Aren't the odds good that in this new building, with care given to making it as tight as possible using normal methods (my dad built it), infiltration would be below 0.5 ach, and therefore mechanical ventilation is a good idea?  What are the odds it would be below even 0.35 ach?

Of course, a single person in a single bedroom probably has more air per person than a bunch of students in a classroom - but probably less than an average-sized family in an average-sized house.  So it's all very confusing.

What would you recommend I do to get the equivalent benefit of that 0.6 ach, when I am a single person in a single room?  The room is (very roughly) 2668 cubic feet, so with the 20 cfm from the ERV I get 0.45 ach from the ERV alone, but I don't know how that interacts with infiltration (adds to it or replaces it or some of each?).  Is this too much ventilation, not enough, or just right?

smk-

The total air exchange is the natural ventilation (infiltration) plus the mechancial ventilation. You sound like you have studied ventilation recommendations fairly extensively, and you may have a better background in that area than I do. I think that the most current standard in the U.S. is ASHRAE 62.2, which is for a house, not a single room, but the formula is ([number of bedrooms +1] x 7.5 cfm + [0.01 cfm/ft^2 of conditioned space]). For my house this works out to 55 cfm or 0.16 air changes per hour (ACH). An older ASHRAE (I think) standard was the 0.35 ACH that you mention. I do not know the complete background for the development of those standards, but I think a significant part of the ventilation requirement is based on getting rid of cooking odors, bathroom odors, and humidity from showers and cooking. Your room should have relatively low ventilation requirements based on the lack of some or all of these sources.

Yes, payoff times for HRVs and ERVs is typically long, and as you scale down in size, the price probably does not scale down in proportion to the size. Therefore, payoff times for smaller units is probably much longer. I do not know the reason for the popularity of single room HRVs. Energy costs are higher in Europe than in the U.S., and higher with electric heat than natural gas, so the payoff period for an HRV in an electrically heated house in Europe should be much shorter than a natural gas heated house in the U.S.

It is very hard to guess what the natural infiltation rate is for your room. If your dad is not an experienced builder, then it might be difficult to construct a very tight structure, but who knows? That is why blower-door tests are used to quantify the leakage rates. However, since you already have an ERV, I would skip the blower door tests, and just set the ERV up to provide approximately 0.2 ACH (or whatever you calculate), and figure that will meet the minimum ventilation requirements, with natural ventilation simply add more fresh air. If the room smells stuffy at that ventilation rate, I would check for water leaks or improper vapor seals that might be making mold, and if none are found, increase the ventilation rate to see if things improve.

Lee

Okay. Thanks for all your help.