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Senior Contributor

calculating dew point/condensation/mold

I want to cool the floors in our house with our water to water geo.  Any easy way to get a computer or something to constantly caculate dew point so I don't end up with floors that are sweating?  Or anyone have suggestions on a safe temperature to run the floors in North East Indiana?

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Senior Contributor

Re: calculating dew point/condensation/mold

Can't you just swag it based on temperature and relative humidity?

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Senior Contributor

Re: calculating dew point/condensation/mold

Everything I read on the internet says cooling via radiant pex in the floor won't work except in the Southwest where humidity is low.  But I think most of them are assuming low mass/wood floors.  We have concrete slabs on all three levels of our house with super insulated ICF's for the external shell .   We aren't running below 70 degree water through the floors.  So far no condensation issues whatsoever.  We have one humidifier in the house and it keeps the humidity in the 50-58% in the house.  I was just wishing someone sold a computer program that I could incorporate some sensors into to control the temperature of my chilled water I'm running to my floors. 

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Veteran Advisor

Re: calculating dew point/condensation/mold

  The cooling that is derived from circulating the fluid in a closed loop system is so minimal that the energy used to circulate it offsets any measly gains. There's also the issue of condensation building under the vapor barrier under the slabs. If you're running a dehumidifier now, the high amount of energy needed to run that and still need cooling would be better spent running a slightly undersized a/c unit, that would cool and dehumidify, instead of short-cycling before removing more humidity. You should also have your climate controlled areas in the 40-45% humidity range, just to keep the poorly circulated areas from getting mildew/mold growth, like closets. 

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Senior Contributor

Re: calculating dew point/condensation/mold

So far, we aren't seeing any condensation issues by circulating 70 degree water through our floors.  We have suspended slabs on all the floors and are able to keep the temperature in the house comfortable by circulating chilled water from our Geo.  We have to consider that our "heat exchanger", ie the concrete slabs, while very inneficient at cooling, total about 1300 square feet 15" thick.  (three slabs, basement, mainfloor, and upstairs). 

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Veteran Advisor

Re: calculating dew point/condensation/mold

  You probably won't have any noticeable condensation unless maybe at the exterior doors if there is some air infiltration. The only problem that I know of is from the heat migration through the ceiling to the underside of the slab. If your floors are a wood subfloor with a vapor barrier over it, there could be some moisture buildup at the subfloor below the vapor barrier, but it isn't a problem if they used styro forms for the subfloor. I've read articles that have researched this potential problem and it seems to be minimal and located near the kitchen from cooking heat, and the negative effects are over a long period.

  I had thought of doing this in some of my properties, but because of excess humidity AND the need for cooling, I opted for a different solution. The ICF design acts as a thermal storage and helps to keep the house from drastic fluctuations, and it's pretty air-tight too. Can you notice a difference with the circulating pumps on?

  Do you have a HRV/ERV system also? I was wondering about moisture problems because with a family of 4 and daily occupancy with cooking and sleeping, the added vapor from the people and things like cooking can add up to 3-4 gallons of water a day in the form of humidity.

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Senior Contributor

Re: calculating dew point/condensation/mold

We don't have any styrofoam under any of the top two suspended slabs/floors.  We have two and a half inches of foam (2" pink board and 1/2 inch foil coated styrofoam) under the basement floor.  Yes, we have an HRV being fed by a 200 foot long seven foot deep earth tube.  The earth tube slopes back to its inlet.  The earth tube does a good job of bringing fresh (somewhat dehumidified in the summer) air into the house.  We have epoxied, painted, and stained concrete floors in our whole house.  No floor coverings.  No carpet, tile, hardwood, linoleum, etc. 

Yes, our geo will bring the temperature of the house down.  We have enough thermal mass in our concrete that it takes about 100,000 btu heat source (or cooling) to change the floor slabs one degree per hour.  We have a good enough thermal envelope that our house can be cooled with 70 degree water.   The upstairs floor doesn't work great to cool since we are cooling the floor rather than the ceiling but the rest of the house is very very comfortable. 

   We are heating our approximately 4000 square foot house with a three ton water to water geo.  Plus, we are preheating all of our dhw to about 90-95 degrees via a Taco 3-way zone valve.  Believe it or not, our house could be heated with about half of our geo.  15000 btu's will heat our house in North East Indiana with a week of zero's.  The very low heat loss (or gain) plus the relative massive amount of concrete floors compared to this heat gain is allowing us to cool our house with 70 degree water.   Our biggest cooling issue is our south facing windows on the upstairs floor.  We put a passive heating porch in the main floor windows that allow heat/sun in until about the 20th to the 25th of April.  The Upstairs needs something because at 300btu's per square foot per hour in good sunlight it adds up fast.

If I do the calculations we are moving a fair amount of btu's out of the house via the floors.  We run up to a 6 degree delta but average about four.  We are probably able to move 12 gallons a minute through the three floors.  12 times four times eight times 60 puts my rough calculations at about two ton of cooling.  That is enough for our house.  I think most of that cooling is to take care of the sun light coming in the upstairs windows which I should do something about.

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Frequent Contributor

Re: calculating dew point/condensation/mold

Instead of running a dehumidifier, why don't  you run some of the cold water through a radiator or a coil of copper pipe, before it gets to the floor.  I would think you could use that for a humidifier and not have to pay to run a humidifier.  Why can you not use a normal thermostat enclosed in a insulated box, but open on one side which is against the floor, or having a water pipe running through it.

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