Tieing AC to a humidistat

[Jeff]

hello:

I live in the mountains of Western North Carolina and the while the temperature is exceptionally nice during the summer, nice enough to keep the house open all of the time, we exerience high humidity levels (I would say humidity averages 75% in our house for height of the summer season with peaks at 85%+ on rainy days). This leads to a fairly damp environment and introduces some mold & mildew problems.

Part of the remediation plan I wanted to put in place was to purchase new thermostat/humidistat and leverage both to control the AC unit. Optimally, I would set the humidity theshold via the humidistat and kick on the AC whenever it exceeded that level.

Is it fairly straight forward to do what I am proposing and is there anything I should be looking for in a thermostat/humidistat beyond a humidify sensor?

Also, I do not have a dehumidifier in conjuction with my AC unit, I was just going to leverage the heat pump process to remove humidity from the air. I know humidifiers are not the most efficient devices in the world, but how do they compare to typical heat pumps (I believe we are running a 12 SEER unit).

Also, I'm open to other thoughts/suggestions on mold/mildew remediation. The house isn't that old, but we do plan on having the duct system inspected. Another thought was to install a whole house fan and tie it to a humidistat. From a cost and ease of implementation perspective, the AC solution definitely appears to be on the easier side, but as noted, we are looking at other options.

Regards,

Jeff

[udarrell]

(Wire circuit in parallel so either control keeps unit on until satisfied.)

You will need a somewhat "undersized" A/C unit so there is adequate run-time without dropping the temperature too much before it reaches your humidity setting.

- udarrell - Darrell

[Richard J Kinch]

Most concerns about mold/mildew are neurotic fantasies.

Forget the humidistat. Relative humidity cannot be measured automatically, accurately, quickly, *and* reliably enough by any reasonably priced device; without all of these the control will be faulty and you will be worse off than doing nothing.

Buy a programmable thermostat and program it to run at least an hour every day. That should control humidity in any modern construction.

[nicksanspam]

Sure it can.

Nick

[nicksanspam]

NREL's long term Ashville averages are

daily min avg max w

May 50.9 63.0 75.0 0.0095 June 58.3 69.4 80.4 0.0125 July 62.7 72.8 83.0 0.0144 August 61.9 72.0 82.1 0.0142 September 55.5 66.2 76.9 0.0118

Lovely weather for "thermal sailing," with no heat or AC. Open and close some windows from time to time as the weather changes or use a whole house fan and smart controls to charge and discharge the inherent thermal mass and water absorbing materials of the house, and control the indoor temp and humidity naturally, vs leaving the house open all of the time, like a sailboat with nobody steering.

You might slow the blower motor in dehum mode by putting a choke in series and return it to normal speed when the output airstream drops below 40 F.

Nick

[Jeff]

Thanks for the pointers on the thermidistat. I was considering the following from Home Dept:

So do thermidistat's require a separate unit or are they easily connectable to a heat pump to faciliate dehumidification of the air?

I'll ping the sales rep at HomeDepot, but that's typically hit or miss. I expect I'll get a more knowledgable response from this group.

[Dr. Hardcrab]

They ARE pricey, but look at this:

[Stormin Mormon]

I've heard of that kind of thing. The problem is that if you run the AC enough to lower the humidity, it might get too cold in the house. Then, the heat will have to run.

I don't know of SEER standards for dehumdifiers, but most of the ones I've seen use piston compressors, and so would be less efficient.

Since it's humid in your area, should be at least a couple local HVAC technicians who know this process.

[Michael Baugh]