[stevehull]

I have a well insulated 1600 sf (~ 60 sq meters) guest house on the property that I don't use too often. Problem is non-use humidity build up.

Background: My Mom lived there until she died a couple years ago. For the years she was here, to keep her happy in winter, I put in a two stage 24K BTU "pump and dump" (open loop) GT heat pump (EER 35 or so, COP 5). This enabled me to keep it at the winter elderly "comfort zone" of 76 F without breaking the bank! Almost never ran on stage two, winter or summer. Summer relative humidity with cooking, showers, etc of about 35-38%. Very dry and healthy.

Anyway, while it is empty, I set the thermostat at 85F, as my Yankee heritage doesn't allow me to set the temp lower. But the humidity crawls up to 48-52% or so after a week or so of non-use. The house is tight and well insulated; R25 in the walls, R40 in the ceiling, R20 below the floor, low e double pane windows and is tight as a drum. I put a plastic liner on dirt crawl space and it is well ventilated. No interior water leaks as I can turn water off to house (except GT heat pump) with same results.

The average summer daytime high temp here in central Oklahoma is about 95F, night low of 75F (100% humidity at night) with a daily average of about 85 F, so the heat pump barely works in the daytime (less than 30 minutes) to offset the small ten degree temp difference (outside to inside).

Of course, this nighttime humidity eventually creeps in and permeates all the interior volume and mass (sheet rock, furnishings, furniture, wood trim, etc). When guests are there (like this past weekend), it takes a day or two of running the GT heat pump (74F) to wring this moisture out.

Is it worth getting a small dehumidifier to pull this water out or should I turn down the thermostat to the GT heat pump? I have an extra 50 pint dehumidifier, but it runs at about 250 watts - and of course gives off heat.

I sure wish some smart company would invent a small capacity (6 K BTU) GT heatpump unit with 40 EER. Then I could run that and be happy that I am dehumidifying, cooling and heating the hot water tank.

Ideas?

Thanks in advance.

Steve