[Greenbuilding] HRV's

[JAY WALSH]

Hi Lawrence,

While I’m not from Canada (my wife’s Canadian does that count) I do have
some experience with cold climates as I designed and built super insulated
houses and community buildings throughout Alaska in the 80’s. Also, in the
early 80’s I worked on some of the earliest versions of HRV’s (then
referred to as air-to-air heat exchangers) in a lab where we could bring down
the temperature to minus 30 degrees F. 

In my current work as an Energy Star rater as well as a rater for the USGBC
LEED for Homes green building program I have been involved in the installation
and testing of many HRV’s from various manufacturers. Most designs are very
similar. Here are some of the highlights of what I have seen, tested and
feedback from others.
The comments refer only to independently ducted systems and not those
installed as part of the homes HVAC ducted system. 
1. While the ECM motors are very efficient and use less electricity (my
preference) they are noisier and produce a hum similar to a refrigerator.
Locate these and duct them in a way to avoid the transmission of this noise.
2. When choosing the exterior supply and return locations avoid these
locations: Asphalt or composite type roofs, or south or west facing walls if
vinyl sided, when heated by the sun they off-gas and this will be drawn into
the home. Also avoid locations where cars maybe parked and idling. Don’t
laugh, I’ll seen all these things.
3. Do not locate the HRV in a cold attic or similar location, and in very cold
climates be sure to provide for a connection of the HRV to the homes drain
system. This will be necessary for when the system needs to defrost (which it
will need if the outside temp falls below -10 F). 
4. Locate the HRV in an accessible place so you can remove and clean (or
replace) the filters and inspect the condensate trays.
5. The filters in these devices are only designed to keep out large particles
from contamination of the exchanger. There are better filters which fit these
devices and even MERV filters. Should you plan to use another type of filter
for the system it will add air flow restriction and will affect the air
exchange rate of the device. Consider the size of the HRV if you plan to add
additional filtration.
6. Flow restriction from ducts. Consider carefully the location of the HRV to
provide the shortest run of duct work.  The longer the ducts, the greater the
number of bends, and the type of duct used will all play into the performance
of the system.  Keep the runs short as possible, use rigid ducts over flex
ducts where ever you can. If you have very uneven lengths of runs on the
exhaust side, consider some method of balancing damper in the system to adjust
for equal exhaust from bathrooms.
7. Have the system tested to insure a balanced supply and exhaust so you do
not create a positive or negative pressure in the house.
8. Sizing formula for continuous home ventilation from ASHARE Standard 62.2.
(Number of bedrooms +1) x 7.5 + (Homes conditioned square footage / 100).
Example (3 BR +1) x 7.5 + (2400 SF/100) = 54 CFM of continuous ventilation.

I hope this is some help.

Sincerely,
Jay Walsh



> Lawrence Lile wrote:
> > A friend of mine is working on manufactured housing that will be sold in
> > Canada.  Apparently Energy Recovery Ventilators are required.  Any of
> > you Canadians have any recommendations - experiences good and bad -
> > caveats?  
> > 
> > Thanks!
> > 
> > 
> > 
> > Lawrence Lile, PE, LEED AP
> > Project Solutions Engineering
> >