HRV in the summer?

mark · #1 05-09-2012, 12:37 PM

New to this HRV thing.

Just turned on the central air and since know from years past it keeps the houses humidity down, turned off the HRV. Now wondering if I should just keep the HRV on?

reefermadness · #2 05-09-2012, 12:49 PM

Not sure about Alberta but here in Ontario it gets so humid in the summer you would just be bringing humid air back in the house. Also HRV are meant to exchange deep cold air with house air...they dont work efficiently unless there is a big gap in the temps of the air being exchanged.

I rely on my AC and dehumidifier in the summer.

wingedfish · #3 05-09-2012, 12:51 PM

Generally no. Warm air holds more moisture than cool air ( do not confuse this with humidity) so bringing in outside air will add moisture to the house in summer, which will be in direct combat with the AC.

But just for the benefit of ventilation, some leave it on low all year. This will equate to some associated electrical costs and a/c inefficiencies but outweighed by the benefits.

daplatapus · #4 05-09-2012, 01:57 PM

As a journeyman HVAC guy I would say it depends...

I lived in Alberta for over 20 years, (Calgary, Canmore) and the last thing we EVER had to worry about was too much humidity. One of the ways HRV's are ducted (and in my opinion the most energy efficient) is by drawing all the home air from bathrooms and closets. This eliminates all bathroom fans in the house. So instead of running a bathroom fan and exhausting that air outside and running an HRV beside that, only one appliance is running (the HRV) and you re-capture the heat from the air being exhausted from the bathroom. In this instance you have to run your HRV all year long because it is your main source of fresh air and exhaust.
Another way of ducting HRV's is drawing from other areas, high ceiling area's, hallways etc and it runs independently of your bathroom exhaust fan. In this case an HRV can be run only part time.
If you have A/C, this will take care of your humidity issues on it's own. The warm moist air will be draw into your central air system through the return air ducting and when it passes over the refrigeration coils of the A/C unit the moisture will condensate and run out of the condensate drain of your system. The dry cool air then gets distributed throughout your home. In this case, wingedfish is correct, the A/C will be fighting your HRV as the HRV continually brings in the warm air from outside.
You can get programmable switches for your bathroom exhaust fans that you can program to come on at certain intervals. This is what I've done in my place in an attempt to get rid of some humidity before it passes through my A/C system. I have my bath fan come on for 15 min every hour.

So i guess as a summary:
If you have A/C - I wouldn't run my HRV in the summer (assuming you have bath fans)
If you just have a furnace (no A/C) - I would run the HRV as long as the outside temp is cooler than the temp you want it inside your home.

Hope that helps

rayjay · #5 05-09-2012, 03:13 PM

I run mine 24/7/365.
I want the fresh air coming into the house at all times but especially when I don't have windows and doors open.
It doesn't take much difference in the indoor/outdoor temperatures to remove water from the incoming humid air in summer, and if I have the A/C on there is going to be a big difference or I wouldn't have the A/C on at all.

Delphinus · #6 05-09-2012, 04:20 PM

I found I had to have it going in the warmer months still, if I didn't have the A/C on. My tank room isn't ventilated otherwise, and without windows it can get like a sauna in there.

With A/C on it doesn't seem to be needed though.

The troublesome times for me are when it's like right now - not warm enough to justify running the A/C, but too warm and humid outside that the HRV doesn't actually do anything to the humidity in the tank room and it can get pretty warm in there, and this affects the tank temperature. I'm tempted to add a bathroom fan to my tank room after all. I was hoping I wouldn't have to bother with bathroom fans what with the HRV but we'll see. The alternative of course staring me in the face is to one day lose the 3x400w's over the tank and go with some kind of LED based solution after all (I really like the halides still but the heat is definitely hard to ignore..).