Using a geothermal heat pump system during house or building construction

Discussion in 'General Discussions' started by blc2290, May 3, 2010.

  1. blc2290

    blc2290 New Member

    I have an issue on a new construction home and unit. I had hardwood floors brought in on sat while the unit was being turned on. The unit is an Envision 5 ton, dual capacity, 3 zones, closed loop. I set the temp on the comfort system t-32-p universal thermostat @ 63 because I want to get a jump on getting the moisture out of the house asap for a couple of days then I was going to turn the temp to 72 as it will be in a normal environment. Here’s the issue. While I was out there the electricity went off for a few minutes and then back on. The thermostat defaulted to program 2 so I reset them and then the unit came on and starting cooling great and the inside temp was 69 and humidity was 59% and lowering so I left for the evening to arrive the next morning. the inside temp was 73 and humidity was 65% outside temp was 74 and 60 % humidity..... The unit was running but small amount of cool air coming out. Why want the unit get closer to 63 and why want it pull the humidity out? I have a moisture meter to check subfloor and hardwood… they are pretty much like they were 36 hours. Any help would be appreciated.
    Last edited by a moderator: May 8, 2010
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    First of all, a couple double A batteries in the stat (or whatever it takes - I'm not familiar with that model) should cause the stat to preserve and resume where it left off.

    The low temperature setpoint (63), mild outside air temps, and your comment about low airflow suggests the evaporator iced up. That is really not good for the unit and should be avoided.

    I would avoid setpoints below 70 unless you are there to continuously monitor operation. If your goal is to dry wood consider adding some sensible heat by using electric space heaters or use portable dehumidifiers. Be sure to safely power those appliances - they use quite a bit of current.

    Over cooling the house when it is warm and humid outside raises my concern that condensation and mold could occur in exterior wall assemblies. If drywall or sheathing surfaces within wall cavities have a temperature below surrounding air dewpoint, condensation will occur, and you don't want that.
  3. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Rent a commercial dehumidifier it's cheaper than your heat pump.
    Make sure system is ducted and zoned properly (3 zones make me suspicious that it may not be).
  4. WF_Inc

    WF_Inc Member


    We have read your comments regarding the geothermal system. We understand your position; however, WaterFurnace does not recommend operating the unit during construction.

    In reference to the geothermal system performance and not reaching the desired temperature, we do not feel this would be a fair test, as the unit is not operating under the design conditions since construction is not complete. Our suggestion would be to not operate the WaterFurnace unit until construction has been completed.
  5. Forum Admin

    Forum Admin Administrator Staff Member Forum Leader

    Given the pervasive misuse of geothermal systems during the construction phase I have changed the title and stickied this thread.

    Note to end users:

    With very few exceptions, using your system for space conditioning during the construction phase of your project is asking for problems!

    @ industry members Please add your comments.
    Last edited: Aug 15, 2010
  6. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    As a contractor

    I offer a machine for construction, if needed.

    No new equipment for drywall or floor sanding.

  7. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I'm thinking of mounting a 4 ton package air to air unit (mobile home type) onto a small utility trailer. At jobsites I would commandeer the homeowner's clothes dryer circuit (they are, virtually without exception, electric down here - 240V 30A).

    My initial thinking is to use the trailer unit to condition attics during duct correction work. I can't ask a tech to spend much time in a 100+ degree attic, much less do methodical, quality work while up there. My business emphasis at the moment is to offer room-by-room analysis of load and actual airflows with an I toward offering corrective surgery to the duct system to get the unit closer to rated SEER in actual operation as well as to cure typical hot room / cold room / unit runs too long complaints.

    Such a rig would also be suitable for temporary / construction cooling. My first thought is to slow the blower and not return air from the space under construction, avoiding issues of drywall or floor dust entirely - 100% makeup air from outdoors.
  8. portableac7

    portableac7 New Member

    Keep monitoring..... I have the similar case :D
  9. Drying out space

    A portable dehumidifier like the ones used by the water restoration people can suck the air so dry you can't believe it. Easiest way to keep flooring dry.
  10. gabby

    gabby Member Industry Professional Forum Leader

    The suggestions supplied are dead on center. You are in a mixed climate, meaning cold, hot and humid variables. You can use propane heaters outside under a plastic tarp for stucco when temps are below 40 degrees, but don't use them inside for drying unless up north where the humidity drops as it gets colder. Another option but more expensive is radiant gas heaters like they use in barns. Although nature gas gives off moisture, they pull more than they give off. I have used wood fireplaces to dry out rooms, as well as electric element heaters providing the room is sealed from outside or adjoining unconditioned spaces. If you have had a lot of soaking rain in the construction phase it may take 10 years to dry out the wall units unless you become proactive with humidity units as mentioned above. The cost will offset the agony of trying to repair warped, separated wood products that were still too wet to properly install. Remember, wood moves....let it.
  11. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    WB Gabby

    Are you TX or OH? Happy New Year BTW. Call me and I will tell you how the spring job went.
  12. gabby

    gabby Member Industry Professional Forum Leader

    Got in from Texas last night............second floor trusses are to arrive Monday.

    I'll give you a call tonight or tomorrow afternoon....wouldn't want to interrupt your beauty sleep...LOL.
  13. OBS

    OBS New Member

    The drying rate of the wood depends on relative humidity. By cooling the air, your system will remove moisture, but ironically, this may actually increase RH, since cooler air has less capacity to hold moisture (that's why it's called '*relative* humidity). Depending on house leakage rate and outside air humidity, trying to reduce RH by turning down the stat is usually a losing battle.

    Also, as other have noted, you are attempting to operate your heat pump well beyond it's intended design, and second, running any forced air system during construction is a bad idea. Be sure to check your filters!

    Dew point is a good proxy for absolute moisture content of air (see for easy dp calculation). If outside dew point is lower than inside dew point and outside air is warmer than, say 70F, then opening windows would reduce indoor RH. If outside dew point is higher than inside dew point, running a dehumidifier would be a waste of energy since infiltration will just replace the moisture. In that case, heating the air is your best option, as someone else suggested. Warmer air has a higher capacity to hold moisture, so warming the air will always lower the RH (unless you use a combustion type heater, which produces a lot of water vapor).
  14. Tony Scarpelli

    Tony Scarpelli New Member

    We used cheap used dehumidifier, window air and ceramic space heaters during our drywall, sanding, paint stage of construction. Drywall dust can get into motors and ruin them so I wouldn't allow even the circulation of air with the air handler until all dusty construction stopped.
  15. It just drives me nuts that builders expect the HVAC guys to provide ac and heat as soon as power gets on. If the job is clean enough sometimes I reluctantly agree. They want units fired up the day the electricians get them hot. And then demand filter changes and coil cleanings to clean up the mess. Portable AC units are now sold for $400 for a 1 ton. That is the way to go. If you let them vent into space, instead of running the condenser air flex out the window, they act as dehumidifiers.

    Another note, We have to keep in mind that heat does not remove moisture from the air, but just increases the capacity for the air to hold moisture. Only a dehumidifier or AC will remove moisture content. We have this problem in South Texas where builders are trying to install ceramic floors, paint, drywall etc. at this time of year, when we are 50-60 outdoor temp, and nothing dries. Last week I had a builder running the geo unit on heat, but the window frames were sweating badly. He blamed system design, but I made him rent dehumidifiers for a week. Humidity went from 87% to 50% without heat or ac. After work is finished, the humidity will stay down.
  16. GoHuskers

    GoHuskers New Member

    DO NOT use your HVAC system DURING construction, learned from my personal experience.

    My system was turned on about 1 month before the completion to make sure everything is working properly (also contractors wanted to be cool in hot Aug/Sep temps). The original filter was PACKED dirty and 3 days before the signed off on the house the motherboard was FRIED. HVAC contractor overnighted a new board and I asked why? He said it was overheated.

    It has been a year now and the system is great (knock on woods).
  17. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Back in the day when I did new construction. I had a few loaner units. I would not install real equipment until the finish paint and flooring was installed. I would bill the GC for duct cleaning.

    Those were the good old days. My body still worked well. The bankers thought I was crazy.


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