It's been a while since I posted here...

Anyone have experience with HRV's (or any air exchange system).  I realize they're required when the home is built with SIPs.  But whenever I run mine (there's a setting where it runs 20 mins, then is off 40 mins.  This wreaked havoc on my A/C this summer, and now is causing my radiant heat to kick in way more often. 

I'm in Iowa, it was 10 degrees this morning, and I keep the thermostat at 68.

Any insight would be appreciated.

Ben Miller

Ben;

20 min sounds like too much

I had similar problems with my ERV in Florida my 1st. summer, it's kind of something you will need to experiment to get the desired results,

Normally, my ERV is set to come on just 5 min every hour, when the outside temp and humidity is similar to the interior space , I run is longer

Chris,

There's only 3 settings on my HRV. Minimum speed continuous on, Maximum speed continuous on, and Intermittent 20 mins on 40 mins off.

My wife stays home with our 3 kids, so I guess I could have her turn it on for a few minutes every so often...

How often should it run? (We're getting 1" of condensation around the bottom of our windows, the interior humidity is around 50% now, it's 68 inside and 18 outside.

That condensation is not good, usually units are available with a percentage timer switch, see if there is one available for you particular unit and change it out so you will have better controll over your HRV

what they said+ i would also question the duct size and were is it hooked up to the return on the hvac?

we never use these in our homes. we put as small of a duct as possible 4" i think it is. with a damper running to the return ducting of the hvac as far awy from the blower unit as possible. this will give good mixing of the air before being heated or cooled depending on time of year. also the other purpose is when you turn on a oven vent or bathroom vent it will allow the preasure in the house to stay constant.

what do you do in the case of radiant heat?  My house is all radiant heat, but with ductwork for the A/C.  So my HRV in dumped into the return air in the basement, but my air handler is in the attic.  We set the air handler to run whenever the HRV runs so as to not simply dump the fresh air out the return air intake grille in the basement.  (follow that?)  (The air handler runs and pulls the fresh air up 2 stories to the attic, (but there's no furnace to pass it through and heat it up, just the fan) and then distributes it throughout the house.)  I can see where it'd be nice to run it past a good hot propane flame, dry it out and heat it up.  But I really like the feel of radiant heat, just don't like the condensation.  I may just have to run a dehumidifier in my basement for a few months in early winter?

The duct size is 4" expanding to 6" as it goes to the exhaust and picks up the kitchen and bath on the main floor.  I don't have a range vent or any bathroom fans.  When my wife cooks or we shower, we run the HRV to get the wet air out. 

I talked to the installer tonight and he suggested running a dehumidifier, not running the 20 min off/40 min on option, and finding a balance of interior humidity vs window condensation that we're comfortable with.  Interior humidity is 44% now (though it's low 60% in my finished attic with closed cell spray foam on the roof deck... that's got me a little concerned, maybe the dehumidifier should be up there?)

Thanks for posting a response.

Ben

CFL-IF,

This is helpful info on where to place the HRV for mixing however I was wondering how being placed at the far end of the return helps equalize pressure from a bathroom vent.  I didn't think you put return plenums in a bathroom.

Thanks,
 
Chuck

I think he was saying he doesn't use an HRV; he just uses a plain outside air intake.  This will pressurize the whole house (very slightly) when the air handler fan runs and brings in air through that intake.  When the air handler fan does not run, no air comes in.  Outside air will come into bathrooms via the supply registers in the bathrooms (which are connected to the return via the air handler, and the intake via the return), or else through undercut doors or jump ducts or whatever, and if the bathroom is depressurized enough it will even suck air through that intake (via supply ducts) when the air handler fan is not running.  Ditto for kitchen exhaust fans.

The problem with this setup is that the amount of outside air you get is proportional to the amount of heating or cooling you're doing, because you only get outside air when you heat or cool.  (Unless you run the fan continuously.)  But in fact, the times when you're not doing a lot of heating or cooling is exactly when you want the most outside air, because that's when the weather outside is nice.  The best thing in this case is to get an air handler with an ECM blower, which can run continuously at very low speed efficiently, so that you get a little bit of ventilation and circulation all the time.  (A standard non-ECM blower will consume a fair amount of power if you run it continuously, plus it will be moving air faster than you probably want it to.)

I'm not sure why he thinks it needs to be at the far end of the return duct system.  I've usually seen it done right before the return air enters the air handler, and just before the central air filter if one is installed.  (And central filters are a very good idea, so long as the homeowner remembers to change them before they clog up and burn out your blower motor.)

in florida the return ducting is usualy not very long. so we just try to keep it from being right under the air handler. but ya you have the right idea.

A lot depends on the HVAC unit you have. I live in Fl and in the spring and Fall when the HVAC is not needed, my unit has an automatic circulation setting built in. This means that for what ever reason the heat or AC doesn't kick on for more than 4 or five hours the fan kicks on to circulate the air anyway and runs for about 20 minutes. This keeps moisture from building up and keeps air moving throughout the house. This is a must here in central FL. and keeps bringing in out side air although tat is not needed as this is the time of the year that i open the windows adn air out the house.

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