connecting my HRV such that when the humidistat engages it starts the blower

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Old 10-18-14, 04:16 PM
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connecting my HRV such that when the humidistat engages it starts the blower

Hi I have a trane tam7 air handler and xl15i heat pump. I would like to connect my HRV so that when the humidistat engages it starts the air handler blower. I plan on connecting the HRV system to the green and red wires from the air handler through a relay. I found the following relay at a local store.

Relay - coil - 24VAC - 15A 240VAC / 30VDC - S.P.D.T

Would this relay be okay for HVAC operation? Could I mess up the air handler operation or would it be the same as the thermostat putting the fan on?

Thanks for any help in advance?
 
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Old 10-18-14, 04:22 PM
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HRV= heat recovery unit.

I'm not seeing why you'd have that turn the blower on. Doesn't the furnace usually turn the HRV on or am I missing something ?
 
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Old 10-18-14, 06:04 PM
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It's more a ventlator. It's actually an old air exchanger with heat recovery. It's a vanEE. You can only control the dampers there is no built in fan. Thanks to your help in a previous thread I have it hooked up such that when the air handler gives a heat demand it opens the damper. I'd like to do the reverse as well, use the humidistat to cause the damper to open and start the fan blower at the same time. Reason is to bring fresh air into the house or to exchange the air when there is a smell in the home for example.
 
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Old 10-18-14, 06:04 PM
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^Post the schematic of your setup if you have it. (model number?)

I never heard of an hrv without a fan; sounds like it's more trouble than it's worth.

A unit with a fan doesn't need the blower running to ventilate if ducted in an optimal way.
 
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Old 10-18-14, 06:39 PM
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The current setup is attached. What I would like to do is to pigtail the wire going to a air/heat exchanger also to a relay input, and the pigtail the white wire going to the heat exchanger to the other relay input. The relay outputs would be connected to the red and green terminals of the air furnace.
 
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Old 10-18-14, 10:12 PM
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Reason is to bring fresh air into the house or to exchange the air when there is a smell in the home for example
I understand that part but how will the humidistat know when the air needs freshening ?
 
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Old 10-19-14, 05:10 AM
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The humidistat that controls the air exchanger is mounted on top of the thermostat. Automatically it would be based on the humidity level in the house. Manually, I would turn the dial past the humidity setting to trigger it. The humidity level could be a good indicator in the winter if the house is too stuffy and air needs to be exchanged. But mostly I would activate it manually by turning the dial of the humidistat. I agree that there is no good automatic way of determining that the air is stale.
 

Last edited by Angelo Cuffaro; 10-19-14 at 07:10 AM.
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Old 10-19-14, 08:42 AM
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Presumably the HRV is being controlled by a relay.

There's a way to do it if the air handler transformer can handler it - i'll give more details later.
 
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Old 10-19-14, 09:30 AM
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Okay, this should work.

Leave the other wires on the terminal strip in the air handler alone.

The call for fan may backfeed and turn on the a/c if you have a mechanical t-stat.

The transformer in the air handler may not be able to handle the extra load, but it's protected by a fuse. If the fuse blows, you'll have to use a separate transformer and relay.
 
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Old 10-19-14, 05:47 PM
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Thanks Muggie but I'd rather use a relay and external transformer. The external transformer is already being used with the air exchanger. It uses about .25 amps at 24v. I'm clear on how to hook that up. My questions are the following:

1) is the relay I sent in a link ok for this?
2) could turning on the blower at the same time as the thermostat mess anything up? I don't think so but want to make sure. I have a programmable t-stat. White-Rodgers

Thanks
 
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Old 10-19-14, 06:42 PM
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The relay you linked to will work fine for your application.
The W/R t'stat should use separate relays for A/C and blower so you should be ok there too.
 
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Old 10-20-14, 11:33 AM
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Thanks PJmax for confirming. Attached is my proposed layout where the Air exchanger gets controlled by the relay. If you see any issues let me know.

Thanks again!
 
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Old 10-20-14, 11:39 PM
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Sorry Angelo.... I can't see it clearly.
 
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Old 10-22-14, 08:47 AM
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Sorry PJmax, hope this is clearer.

Angelo
 
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Old 10-22-14, 09:43 PM
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The wiring looks correct......
Your HRV control will activate the relay which will turn the blower on.
 
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Old 10-26-14, 11:14 AM
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Thanks PjMax. One question regarding surge filters or snubbers across the relay. Is one required for my application? My intuition tells me no because of the small currents used but wanted to confirm.

Also I'm thinking it might be simpler to power the HRV circuit from the thermostat through "fan on" switch. I.e. The green wire on the air handler (blower) would be connected to the relay as an input together with the common. I.e. This way whenever there is a heat, cool, or "fan on" switch is on the HrV would also turn on if the thermostat engages.

Thanks in advance/Angelo
 
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Old 10-31-14, 07:28 PM
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I hooked it up as per my last post and everything works fine. Thanks again
 
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Old 10-31-14, 07:49 PM
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Cool.... good news. For some reason I missed that post.
 
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