Replies

1. 
   jameshowison | Sep 14, 2020 03:51pm | #1

   UltraAire makes two kinds, a single box or a split system. The single box ones (e.g., 98H) do blow out hot air when dehumidifying (ie they convert latent heat to sensible heat). The split system (e.g., SD12 https://www.santa-fe-products.com/product/ultra-aire-sd12/) pushes it's heat outside.

   Not quite sure why foam insulation would matter, perhaps you are seeing elevated humidity levels in your attic? https://www.energyvanguard.com/blog/high-humidity-in-a-spray-foam-attic-part-2

1. 
   Deleted | Sep 14, 2020 05:14pm | #2

   Deleted

2. 
   suect | Sep 14, 2020 05:21pm | #3

   We purchased this unit to maintain the humidity on the main level as well as the foamed attic.

   The humidity in the attic increases with temperature increases and is the reason for this question. Should the split system be used in a Texas attic?

   We use the AprilAire ventilation system. Could this be a big part of the problem? I try to keep the humidity between 43- 50% with the a/c and fresh air.

2. 
   jameshowison | Sep 15, 2020 10:30am | #4

   Well, I'm no real expert, but the operation of the dehu should increase temperate but decrease water in the air. Since relative humidity drops as temp rises (even with the same amount of water in the air), the dehu operating correctly can't cause both to rise. So extra water must be coming from somewhere.

   Not sure if the unit also has ventilation with outside air; might it be that it does and that it is also pulling in outside air. Assuming that air has plenty of moisture in it (which it will in Texas this time of year) that could cause a rise in relative humidity. Check that the control for the vent is set to "Auto" (and that there is a backdraft damper in the outside air duct?) and that vent is set to 10-50 (ie 10 minutes open in each hour) or similar.

   Or you should check that the drain on the dehu is draining properly. Might need to be cleaned out with compressed air? If the water isn't making it outside then operating the dehu would cause temp to rise (but water would stay the same; hmmm, so relative humidity would decrease).

   Try not running the dehu for a while and see what happens? You might need a good sensor for both temp and humidity, like the wirelesstag.net ones: https://store.wirelesstag.net/products/wireless-tag-13-bit-temperature-and-humidity

   If, with the dehu off, the relative humidity rises (with temp stable) (or dewpoint rises) then the water is coming from elsewhere (and rising to the attic). In that case tackling water sources elsewhere matters (and the dehu is helping).