What's the best way to hook an HRV to a Geo forced-air HP? Should the incoming fresh air (cold in winter) from the HRV be ducted to the return air plenum of the furnace or will the cold temp throw the HP into stage 2 or aux? Thanks DC PS Thanks TechGromit for your input on my last question

Ok I give up whats a HRV?

Heat Recovery Ventilator

Oh! a HRV is a Heat Recovery Ventilator..... a what? So what's it do?

I'll attach a diagram I found of an HRV (Heat Recovery Ventilator) ...similar to a ERV - Energy Recovery Ventilator) ...DC

The most efficient we've found in our climate is to not use HRVs, ERVs, or anything like that. We're dry.

However, if I were required to put one in my home, it would replace my bath fans. I'd duct it to draw air from the bathrooms, and dump it into the basement, not the duct--not that it's necessarily bad to dump it into the duct. Oh, and that would be into the return air. I'd have it controlled by fan timers in each bathroom, only. No humidistat (in my dry area).

Where I live, it is a code requirement that any [new] residence which is connected to the electrical supply grid must have a HRV that runs during the heating season. Building here are built airtight and, if you build tight, you must ventilate right. It's not just about removing humidity, it's about removing VOCs and other interior sources of pollution - but doing so without throwing heat out of the window (as it were).  Drawing air out of the bathrooms and dumping into the basement is very bad practice - if someone is "having a bad day" in the bathroom you're just going to distribute all those noxious gases throughout the house!!! In a new house we built, none of the bathrooms have fans -  they are all connected into the HRV and the pre-warmed incoming fresh air that comes out of the HRV is directed into the return ducts of the GSHP. In a well insulated house, airleakage is one of the largest sources of heat loss and so building airtight and using an HRV will save a lot of energy costs as well as providing fresh air.

Paul.

I didn't mean that you'd draw from the bathrooms and dump that air to the basement. Obviously, that would be bad.

What I said, is with use of an HRV as the bath fans, it exhausts that air outside, and the incoming fresh air dumps into the basement.

On the necessity of an HRV, talk to blower door test companies. See if they find any houses with an infiltration rate lower than 10%. With a 10% infiltration rate, every 10 hours, the house NATURALLY changed its volume of air, without opening any doors or windows. If someone opens a door once during that 10 hours, then it ventilates faster. 10% is hard to achieve, and lower than 10% is even harder.

OK, that makes sense - I thought it sounded odd! All that said, in the winter, I don't run the bathroom fans for moisture removal as it's nice to get some extra humidity into the house. Of course, if there's a toxic gas situation, then humidity be damned ;)

Paul.

I've never seen infiltration expressed in percentage terms before. If you have a blower door test done, the usual units are air changes per hour at a pressure differential of 50 Pascals - so you will see something like 2ACH@50Pa. The rate at normal pressure is nominally 1/20th of the 50Pa rate. So your figure of 0.1ACH@normal pressure would be equivalent to a blower door test of 2ACH@50Pa. Up here in Canada, that figure is not considered particularly remarkable. The R2000 energy efficient housing program here requires less than 1.5ACH@50Pa - in other words, one air change every 13 hours or so. There are many houses being built here at around the 1ACH@50Pa level-  which is about 1 air change per day. The ASHRAE has recommended continuous fresh air supply rates that would be hard to meet with natural infiltration without the use of an ERV or HRV.  And the nice thing with an HRV is that you can achieve a much higher effective ACH rate without throwing energy away. Of course, if you don't build airtight, then it's a moot point.

Paul.

For dry climates look into an ERV that uses an enthalpy wheel.
It returns the heat and moisture from the exhausted air to the entering air.
The main problem installing an ERV or HRV to the return air is the building may not
get the required ventilation if the air handler does not run for a sufficient time each day.
Better to draw air from the bathrooms and kitchen or other moist areas and supply fresh
air to the living space. That will distribute the moisture and fresh air throughout the building and remove
foul air.

Try to introduce fresh air in as far upstream (on the return) as possible, make sure it isn't back blown through the openings. Make sure to factor the additional load in when selecting your heat pump.
J

to answer the question
either way you could force it into 2nd stage most systems are staged by differential at the thermostat or / and time delay
cooler air entering the stream at either end would cause the system to run longer hence unducing upstage prematurly
That being said allowing air to enter the return has 2 pluses over the alternitave
cooler return air allows more heat to be absorbed by the air ( greater diff. between air and coil )
will not require a fan to push air in
That being said I would be very weary
There have been several posts complaining of extreme energy bills the turned out to be asc. with an HRV
Your are adding a significant load to the system Make sure your system is sized to handle
I think allmost all codes are in our best interest and should be fallowed to the letter ( with the exception here with putting condensation into a indirect drain ) but in this case I would size it to the bare min.

Half the inspectors out there don't know what an ERV, HRV or a geo heat pump are so no worries on that code thing ;)
Incidentally the International Mechanical code requires a hydrostatic test on loop systems. How's that working on your systems Tuffluck?
J

Ha Ha. Not a chance. Good thing the industry gives ear to this DX technology, NOT.

You might want to check out how this guy has his ERV set up with geothermal:

http://www.ourcoolhouse.com/hvac.htm

Joe,

Can you post the info from International Mechanical code about the hydrostatic test on loop systems?

Sorry Dewayne,
Just noticed your question (and i'm certainly checking my books a lot lately:)....
I need to qualify this as likely in your book; in MI we work with a slightly altered IMC referred to as the MMC (due to modest local revisions).
In chapter 12 Hydronic piping of the 2006 code....1208.1.1 "Ground source heat pump loop systems. Before connection (header trenches are backfilled) the assembled loop system shall be pressure tested with water at 100psi (689 kPa) for 30 minutes with no observed leaks. Flow and pressure loss testing shall be performed and the actual flow rates and pressure drops shall be compared to the calculated desigh values. If actual flow rate or pressure drop values differ from calculated design values by more than 10 percent, the problem shall be identified and corrected."
In every case so far local guys have accepted air tests instead.
Incidently in some (more informed) departments, this also means loop reports provided to the inspector.
Less inspectors know of this than contractors so it does not always come up, but it would be better for us reputable contractors to educate our local inspectors before the next wave of new geo installers. Educated inspectors will help keep fly by nights from doing the work incorrectly and giving us more black eyes. If new guys at least had to hire IGSHPA certified loop installers to do their digging and write reports, it might keep some of them out of trouble (it certainly did for me once upon a time).
Joe

Joe, thanks....no big deal

I was mostly curious about what others do. The hydrostatic test that they make us do on commercial projects is more involved.