I’m in climate zone 4A.  1600 sq ft house, 1.5 stories, 2 ACH 50.  R40 ceiling insulation, R26 walls, and R12.5 crawl space (conditioned).

 

The HVAC is a split system.  2 stage 17 SEER.  2 zones (master suite and rest of house, Honeywell, normally closed dampers).  Aprilaire 1830 70 pint dehum (supports fresh air) and Aprilaire fresh air controller.

 

 

Currently, everything (vent controller, dehum, and HVAC) is all sharing the same ducts.  The dehumidifier is not wired to anything.  The vent controller is wired to the air handler (and the outputs of the zone controller).  See attachment Current for a diagram.

 

Normally, fresh air ventilation happens when HVAC is running, which is fine.  The issue is that if the required time is not met, then the vent controller will call for the system fan to open.  The zone controller is not aware of this, so it doesn’t open any zone dampers.  The air just sits and spins through the bypass.

 

Also, based on the duct drawing, I don’t see how the dehumidifier would ever be effective, since it’s pulling air from the bypass instead of the return and blowing it back into the return.  Also a problem here, the dehumidifier wouldn’t call to open any zone dampers or even the system fan.

 

I don’t see any way to get the zone dampers to open with this setup.

 

 

I’m thinking the easiest fix is to disconnect everything.

 

– Remove the vent controller

– Install a dedicated return for the dehumidifier

– Rewire the dehumidifier to control the vent damper

– Dump the fresh air into the supply of zone 1 and 2 past the zone dampers with back flow dampers and a balancing damper

 

See attachment Considering for a diagram.

 

Are there any downsides to this other than the serious amount of work modifying the duct work and installing a new return?  Or any alternative solutions?

I’ve also considered dumping the dehum and fresh air only into the rest of the house zone, and putting a Panasonic WhisperComfort ERV in the master suite for fresh air.  That’s a bit more expensive though (and substantially more work).