Author Topic: Ventilation and damper control  (Read 1463 times)

Offline radguyjames

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Ventilation and damper control
« on: May 02, 2019, 11:22:45 AM »
Hey Everyone!

Long time lurker, first time poster. I'm trying to improve my ventilation system using a series of mechanical dampers. I'm realizing my house is being over ventilated in winter and summer months where inside humidity is on two drastic sides of the spectrum (too humid in summer, too dry in winter). To remedy this I have decided to place a mechanical damper on the air intake on the hrv. I noticed even when the hrv is off, air is still being pulled in from outside via the vacuum from the cold air return. This results in dry air in the winter and high heating costs (although the hrv warms some air; bringing in air that is -40 C cannot be good for the furnace or the home). I installed a better HRV control unit that allows me to time when the HRV turns on (20 minutes out of an hour, etc.. ) which should give me greater control on how much ventilation occurs.  The HRV conveniently has a 24V interlock relay. I don't really need to have it connected to the furnace board because I have the fan running all the time to circulate air throughout the house. Instead I want to connect the mechanical damper to the duotrol interlock relay on the hrv so that it opens when the the hrv turns on. Is this feasible? Is there current running through the duotrol interlock or do I need to connect it to an external 24V relay and just use the interlock as a 'switch'.

Secondly I would ideally like to add a second mechanical damper connecting the air outtake on the hrv to the cold air return. The theory is that when the HRV turns on, this mechanical damper closes and the other opens, pushing out air from the house and drawing in fresh air from outside. When the hrv turns off, the damper on the outside air closes and the damper connecting the return ducts that normally push air outside will instead recirculate air into the cold air return.

Can I have two 24V mechanical dampers connected in parallel running through the duotrol interlock relay? Will I fry the board on the HRV? I think this would be kick ass system if I can get it working properly. Any thoughts or suggestions? I can provide a diagram if isn't clear what I'm trying to do :)


Offline Hgye

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Re: Ventilation and damper control
« Reply #1 on: May 02, 2019, 06:34:32 PM »
Can you tell us more about your house construction?  Year, etc.

Offline Admin

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Re: Ventilation and damper control
« Reply #2 on: May 02, 2019, 07:48:14 PM »
What kind of HRV exhaust hood is installed outside?  It should have a damper or louvres that close when the HRV stops running.  In high wind areas using a hooded style exhaust vent outside can help prevent air from entering the home.  There should already be a motorized damper on the fresh air from outdoors port.  Maybe it’s not closing properly.

The interlock relay on the HRV is likely a set of dry contacts.  It gets 24V from the furnace R terminal and sends it back to the G terminal.  You may need to use a separate transformer to power your dampers.

I’m not sure if I would want close any damper when the HRV is running.  One duct sucks stale air out of the return air, furthest from the furnace.  The duct closest to the furnace introduces fresh air into the return air.  You can just keep running the furnace fan continuously for inside circulation when the HRV is off. 

You may just need to use a humidifier on the heating system during the winter.  The AC should remove humidity in the summer but I would only use the HRV during the night when it’s cooler and less humid.