How to ventillate: ERV, HRV or other?

[sibellc]

Hi,

We're building a 4 bedroom, 4300 square foot new modular home in southern NY (Long Island). 2 story colonial with full basement. All ductwork and mechanicals are done on-site, and I've been trying to understand ventilation options. We intend to use in-floor radiant heat throughout the heat, and install central air (variable speed air handler, 2 stage compressor) and provide for ventilation. One family member has recently developed severe and debilitating allergies, identified as tree pollen and dust mites, so IAQ is a big issue. Buildingscience.com identifies the climate as cold. It is cold and very dry in the winter, and hot and humid in the summer. AC will run from May to September, heat from October through April. Often in summer, the nights are cool and very humid, so it is important to be able to dehumidify without cooling. Building Science seems to advocate supply ventilation through the return of the air handler, but I don't see the logic in introducing very cold air in the winter (hydronic heat, so the air handler is not a furnace), and very humid air in the summer through this method. Plus, it doesn't seem like a good idea to induce exfiltration of humid air into the building structure. We don't mind paying a little extra for better efficiency and comfort. It seems to me the most complete option would be the use of an ERV year round for ASHRAE ventilation standards to prevent over-drying of the house in the winter, and introduction of very humid air in the summer, a whole house dehumidifier to control moisture when necessary, and a separate supply-air method with some sort of differential pressure control solely for powered make-up air (perhaps up to 1000CFM?) to keep the house pressurized to about 5 pa. The air handler would cycle periodically for proper air mixing and high efficiency filtration.

Questions:
Does my setup seem reasonable? Any suggestions?

How good is the Carrier infinity system at controlling Humidity with low cooling loads? The system seems very interesting, but probably not worth it since I'm wouldn't be using any compatible component other than the compressor and air handler, and probably need a separate de-humidifier anyway.

I am a bit confused as to whether to use an ERV or an HRV. Each manufacturer seems to have different propaganda. Some claim an ERV is appropriate everywhere except the extreme north. Some claim an ERV is only appropriate in the very south. It seems silly to me to us a product that can only operate in one season, and and HRV would be useless in the summer, since it would be pumping massive amounts of humidity in the house. And I'm afraid of it over-drying the house in the winter. The ERV seems better, but some manufactures claim they can't be used in weather that will drop bellow 25°. It happens some in my climate, but not much. The average low in the coldest month is 26°. Do differing methods of ERV manufacturing make this true for some and not for others?

This is a very complicated field, with lots of different and often conflicting approaches and suggestions. Thank you for your time and thought.

Cody

[Edited by sibellc on 04-23-2005 at 12:56 AM]

[teddy bear]

60-80 cubic feet per min.(CFM) is estimated to be adequate fresh air to purge pollutants, replace oxygen, and remove moisture for 4-5 people. Most 4,300 sqft. homes infiltrate/exfiltrate 60-80 CFM of air during the coldest windy weather because of stack effect and wind pressure. On a windless, warm day, even a leaky home does not breath. Your home has a clothes drier, kitchen hood, bath fans, water heater, space heater, central vac, and fireplace needing make-up air. A controlled amount of make-up air ventilation supports the functions of these appliances, like 60-80 CFM comes close. Operating an ERV/HRV typical homes during cold weather over ventilates . During neutral weather there is no heat transfer benefit. ERV/HRVs are great for large quantities of continuous fresh in very cold climates with expensive heat sources like electric resistance. Also ERVs in schools with high ventilation rates in humid climates have payback.

Your climate needs 135 pints of dehumidification per day to deal with the moisture from the occupants and exhaust appliances/make-up air ventilation during the wet times of the year, May-Sept. On the hot days, the a/c will remove the moisture. As you suggest, a whole house 135 pint dehumidifier would deal with the remaining moisture to maintain <50%RH to control mold/dust mites. A make-up air ventilating dehumidifier with a MERV 11 air filter will deal with the year around fresh/make-up air ventilation. Use good bath fans and a moderate sized kitchen hood. All combustion appliance except the kitchen stove should be sealed combustion including fireplaces.

[sibellc]

Are you saying it's better to keep the house of average tightness so that induced exfiltration provides sufficient ventilation? I was planning on specifying gasket electrical boxes and light fixtures, caulking all wiring and other penetrations, exterior rigid foam insulation in addition to cavity insulation, etc.., generally erring more on the side of the Canadian R-2000 specification, but certainly going for above average tightness. Also, the radiant heat requires each floor be insullated. This led me to the ERV for providing the necessary air changes. Since the ventilation function of the Ultra-Aire responds only to on and off, and not pressure, it does not seem adequate as a make up air device for the purpose of keeping the house at slight positive pressure. It seems that it would often either over-pressurize the house, or not be able to keep up if one had the range hood and a bathroom fan on at the same time. So I was thinking of using some sort of inline fan with an ECM and perhaps a modulating damper and a pressure sensor that would adjust its speed to provide just enough air to keep the house at +5 pa pressure, and the ERV would provide any additional required ventilation. The whole house dehumidifier would then be used just for dehumidification. All appliances are going to be sealed combustion, direct venting, with the possible exception of one open Rumford fireplace.

I thought my scheme was fairly reasonable given an above average tightness house. Is it? Would it be better not to have a super tight house?

Thanks for your input!

[beenthere]

A erv, or hrv, does not always add fresh air to the house, it exchanges stale for fresh, so you can make your house tight.

[fat bob]

Some random thoughts:

For dust mites, the most important thing is to control humidity and keep the bed linens and bed clothing clean. Dust mites like humidity.

For outdoor pollen, obviously the most important thing is to contol unfiltered infiltration. It varies by species and season. Where I live (central Texas) the pollen is high for juniper in winter, oak in spring. No idea about your location. I question whether an ERV or HRV would do more harm than good if you run it when pollen is high. Staying inside a tight house may help more than anything. Laundering clothes that have been outside often (like jackets) and keeping them out of the bedroom may also help.

People with really bad allergies where I live are told to limit the amount of carpet. Some have tile and wood only in their homes.

Most pollen grains are relatively large, compared to say smoke or smog. So bear that in mind when picking filters for your AC or other equipment. High airflow through a relatively cheap filter might do more good than using a really fine and restrictive filter.

If the affected person spends a lot of time in a car, some cars have cabin air filters that can be changed while other cars have no filter.

[uktra]

I would recommend aircycler in conjunction with a Hoyme motorless HRV. For humidity control, i would rcommend a Sante-Fe stand alone by Thermastor. This combination is cost effective and will give a great comfort level.

[teddy bear]

Originally posted by sibellc
Are you saying it's better to keep the house of average tightness so that induced exfiltration provides sufficient ventilation? Since the ventilation function of the Ultra-Aire responds only to on and off, and not pressure, it does not seem adequate as a make up air device for the purpose of keeping the house at slight positive pressure. It seems that it would often either over-pressurize the house, or not be able to keep up if one had the range hood and a bathroom fan on at the same time. So I was thinking of using some sort of inline fan with an ECM and perhaps a modulating damper and a pressure sensor that would adjust its speed to provide just enough air to keep the house at +5 pa pressure, and the ERV would provide any additional required ventilation. The whole house dehumidifier would then be used just for dehumidification. All appliances are going to be sealed combustion, direct venting, with the possible exception of one open Rumford fireplace.

I thought my scheme was fairly reasonable given an above average tightness house. Is it? Would it be better not to have a super tight house?

Thanks for your input!

Positive pressure is a good plan but unrealistic. You would over-ventilate the home most of the time for a minimal benefit. The effect of wind turns areas a the house positive/negative randomly throughout the year. I'm including some pressure data logging of a custom built, extremely tight home in WI.
http://hvac-talk.com/vbb/showthread....6&pagenumber=2
The natural leakage of this home on an average winter day is .1 air changes per hour. Test is in Oct. with an Ultra-Aire time (green)cycling make-up air ventilation. Pressure on the different surfaces varies. Total control is difficult and not worth the effort. Simple air sealing with make-up air ventilation when occupied and <50%RH is better than most. I have tried this on several homes.

[teddy bear]

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