HRV defrost mode setting

[organometallics]

Hi,

I have Trane XL-824, LifeBreath HRV, and Aprilair humidifier running my HVAC. My HRV is controlled by the thermostat to run "at least 20 minutes every hour" and runs when the fan of the furnace runs, in addition to the timers in the bathrooms.

Does the HRV go into defrost mode by itself or can i do it with the thermostat? Or can I place the HRV in recirculate? With this cold snap, there is a block of ice in my HRV at the bottom of the hexcore on the vent side.

thanks

[Admin]

Is this the Ecobee you have?  I'm pretty sure when the HRV runs the Ecobee will start the furnace fan and eliminates the need for interlock wiring.  The HRV should not run anytime the furnace fan starts.

What model of HRV is it?

Was it balanced?

The newer Lifebreath no longer have the defrost electric heaters and use a recirculating damper defrost system.  Some models like the RNC 200 ship with the defrost mode disabled and you have adjust a dip switch to turn it on.

Are you sure the HRV isn't running 24/7 due to maybe a faulty control or wiring problem?

Check the insulated flex and make sure it's sealed to the exterior and the intake flex from outside is not torn or sucking in room air before it reaches the HRV.

Another common fault with Lifebreath is that the damper motor stops working.  You should power the unit on and off with the door open and make sure the recirculating defrost damper is working and closes completely.  During defrost this will stop the incoming cold air from entering the HRV and will allow the core time to defrost.

[organometallics]

thanks!

Its a Trane XL824 thermostat with the LifeBreath RNC155. I did what you recommend and the flap did open and shut. Honestly, I think its just too cold. Hit -40oC and it its been in the -30's for the highs in the last few days and perhaps the default defrost cycle is not long enough. The core is iced up on the bottom, and the outside of the HRV, on the left side, its sweating a bit. I lowered my humidity from 35 to 30%, my windows also have ice on them.

The HRV was installed by the home builder choice (Weiss-Johnson), I would think it has been professionally installed and balanced (I hope!)

You said that the "The HRV should not run anytime the furnace fan starts" . The way mine is currently set up is that the HRV runs a minimum of 20 min every hour and is set to auto-run when the furnace fan kicks in (and vice versa). Is this correct?

[Admin]

That sounds right.

Have you checked the defrost settings on page 23!

https://manualsbrain.com/en/manuals/1284966/pdf/4e4dd6f1758cb17dd3affa6b7b6266dac5b98b16fe75cb66d999048e6ceb3725/lifebreath-rnc155-user-manual.pdf

[organometallics]

I was thinking about this a bit more. Look at the diagram you provided, when the unit is on defrost mode and recirculates, the flap closes the fresh air intake. But what about the the stale air to outside port? This is still open. Does the air escape when in recirculate mode?

When I opened up my HRV, I noticed, even with the defrost flap closed and nothing is running, there is still cold air pouring into the unit from the stale air to outside output. The ice buildup is on the bottom left of the core, near the stale air to outside output port. Please see picture attached.

Now the question remains, we have been under an extreme cold alert for the last 5 days, temperature were in the -30's and in to the low -40's, so is this normal for an extreme cold condition or do I have an imbalance problem?

[Admin]

Did you check the vent outside?  The exhaust vent should have flaps that close.  Maybe they are frozen open or some are missing.  There should be something outside to prevent the entry of outside air.

[organometallics]

you're right. The flap was not closed all the way due to ice and the mechanical issue with spring of the flap, therefore, its always open about an inch or 2. I'll have to fix this!!