Staging AC units for humidity control.

[rumn8r]

The HVAC system in my ~40 year old house consists of a large air handler and two 5 ton outdoor units that can be staged to work at different temperatures. This provides humidity control similar to the modern 2 stage systems. I am replacing the air handler with 2 variable speed air handlers and was considering two stage outdoor units (e.g. Trane 19i) for each. However, I would like to explore the possibility of using two single stage outdoor units plumbed together with a cooling coil in each air handler and staged to provide long run times for humidity control. This would be much less expensive than two 2 stage outdoor units. Is this even possible?

[BaldLoonie]

If you have 1 large duct system, you may end up with big problems "twinning" 2 variable speed air handlers. Instructions say don't! There's a thread around here somewhere where a member found this done and having trouble.

If you are indeed twinning, stay with single speed blowers and yes, you certainly can put a single stage unit on each one and stage them. I did a setup on a large house with twin air handlers, twin heat pumps. They are staged, even the 2 strip heaters are on a timer so both don't come on at once.

[rumn8r]

I forgot to say that the 2 air handlers are for 2 different duct systems.

[rumn8r]

I thought I would get a quick yes or no answer to this.

[BaldLoonie]

You would need a dual circuit indoor coil in the air handler. Trane sells one. By the time you bought it and 2 outdoor units plus did the creative wiring to run it, I would think you could buy a 16i or 19i and be done with it. If you need 5 tons, you actual efficiency would be much lower than the model # would have you expect however.

I may have typed too soon. Looks like the new VS air handler line doesn't have the 2 circuit coil. The old TWE-062E may be the last chance. With it, you could put 2 1.5 to 3 ton outdoor units on it.

[rumn8r]

Let me word this more precisely: Is there any way to use 2 outside units with 2 dual coil inside units in different air handlers (and duct systems) and have them staged so that one is set to 72°F and the other 74°F?

[coolguysfl]

I'd like to suggest when you consider for every dollar you spend for operating your A/C that .80 is sensible & .20 latent (moisture removal) that your A/C is only 20% efficient as a dehumidifier.

I'd take a look at high SEER product & add on a dedicated central de-humidification system bundeled w/ a Honeywell 9000. You'll find supporting information @ http://www.buildingscience.com/resources/mold/default.htm

[beenthere]

Originally posted by rumn8r
Let me word this more precisely: Is there any way to use 2 outside units with 2 dual coil inside units in different air handlers (and duct systems) and have them staged so that one is set to 72°F and the other 74°F?

Yes, but the possible headaches getting everything set up right isn't worth it, when 2 stage condensers are so readily availible.

[rumn8r]

coolguysfl, Good idea. I'll think about that.



Originally posted by coolguysfl
I'd like to suggest when you consider for every dollar you spend for operating your A/C that .80 is sensible & .20 latent (moisture removal) that your A/C is only 20% efficient as a dehumidifier.

I'd take a look at high SEER product & add on a dedicated central de-humidification system bundeled w/ a Honeywell 9000. You'll find supporting information @ http://www.buildingscience.com/resources/mold/default.htm