Heat in attic causing air from air handler not to be cool enough?

Discussion in 'Maintenance and Troubleshooting' started by rscott, Jun 25, 2013.

  1. rscott

    rscott New Member

    Hi all,

    I had a geothermal system installed last October. The main unit (water to water) is in the basement, along with one air handler in the basement (one zone) and one in the attic (two zones). All went smoothly over the winter (although the electric usage was a bit higher than expected).

    Now that summer is here, using an infrared thermometer, I'm seeing the air temp coming from the basement at roughly 55 degrees, which seems good. But from the attic it is around 68 degrees (after the system was running for a while). When I checked, the ambient temperature in the attic was around 120-130 degrees.

    If we're trying to get the house temperature to, say, 70 degrees, logic would suggest that the ~68 degree air from the attic is going to be much, much less efficient than the ~55 degree air from the basement (meaning the air handler in the attic would have to run a *lot* longer than the one in the basement).

    All the air ducts are insulated (some R6.0 and some R9.6/8.0), with the two ends of the air handler insulated as well (but not the middle section; I don't know if it is insulated inside).

    I had read that insulating the attic/roof could keep temperatures in the attic much closer to in the house. Does that sound like the best solution to the problem?
  2. When you say from the attic , is that open returned air from the attic (same? input "from the basement"?)
  3. If your unit is sealed off and ducts properly connected there should not be too much energy loss. The outlet temperature has more to do with water flow and air flow over the chilled water coil, so maybe water balancing is your issue. Slow air flow, or increase water, and outlet temp should drop. 68 degree outlet temp in cooling mode is not correct.
  4. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I suspect that the system with the attic air handler is experiencing a problem such as low refrigerant charge, or, more likely, a return air duct leak such that the system is attempting to cool some 120*F air pulled in from the attic.

    Another clue that this might be happening is a pronounced outflow of air from indoors to outdoors observable when a window or door is an inch or two open. A significant return duct air leak from an unconditioned exterior space such as the attic throws system airflow out of balance, resulting in the conditioned envelope (the part of the house you live in) becoming slightly overpressurized.
  5. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    With a single water to water unit and adequate supply temp in the basement unit, this sounds highly suspect for a lack of chilled water flow to the attic air handler. Water balance issues; possibly stuck valves; air in the lines. WHat is elevation of the attic relative to the unit and what pumps are you using for chilled water circulation.
  6. rscott

    rscott New Member

    Thanks to all who have responded.

    A few other notes here:

    An inspector came after the ductwork was installed to test it (e.g. they covered all the returns with plastic and such). So I'm guessing that if there was a big leak when it was installed last October, it would have been detected.

    I just checked this morning, with the attic at a balmy 80 degees (95 at the peak), and the air temperature coming of the ducts was about 58 degrees (about the same as what is coming from the basement).

    There is one geo unit, a GeoComfort Compass Two-Stage Water-to-Water Series (GWT060B11AAACSS), installed in the basement. The air temperature coming from the ducts in the basement seems pretty constant at about 58 degrees.

    I'm not sure of the terminology, but I'm referring to the air coming from the air handler (the air that is entering the room from the ducts).

    I just checked, and didn't notice any outflow. I had the system on, all doors/windows shut except for one window open slightly, and I didn't feel any air going in or out.

    The attic air handler is located about 25 feet higher than the geo unit. The pipes also go about 80 feet horizontally (about 50' one way, 30' the other) on their way from the basement to the attic.

    I believe the pumps are Grundfos circulation pumps, one (presumably for the basement air handler, about 40' away from the geo unit) is set to medium, the other set to high.
  7. ChrisJ

    ChrisJ Active Member Forum Leader

    "The pipes also go about 80 feet horizontally (about 50' one way, 30' the other) on their way from the basement to the attic."

    How well are those pipes insulated? that's a lot of ft of pipe. Any way to check water temp entering air handler?

    Spray foam insulation on underside of roof may be a solution, but an expensive one.
  8. Bergy

    Bergy Member Industry Professional Forum Leader

    What size is the pipe going to the attic? What type of pipe is it? (Copper... Pex...}

  9. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Did everyone miss Trent's point.

    If the attic system is full of water without ANYair then the only issue with pumping the chilled water is the friction in the piping and the air handler coil.

    Air can stop flow better than a ball valve.

  10. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I'm confused - is the supply air from attic system 58*F or 68*F? The difference is huge from the point of view of trying to maintain 75*F or so in the conditioned space.

    If the supply air is 58*F when attic conditions are mild and 68*F during hot afternoons, then I suspect a return air leak. It doesn't take much 120*F attic air leaking into a return to elevate supply air temperatures to where the system becomes ineffective.
  11. Because of the original question asked, I have another thought (from a different direction). Most of us have insulated attics, walls and floors in traditional ways: find the right width bat with a high R number, push it in hold it up, blow in some extra insulation, to fill gaps etc. That works. But I have also seen Floridians use THICK Styrofoam blocks (coffee cup) very successfully to get phenominal R values above usual numbers. It is thinking outside of the box. // While visiting my sister in Zepherhills, recently, she showed me what she and her husband had had done. She has lived in @ 1200 sq ft house for many years with the equivalent of 1940's insulation. Energy cost was high. The insulators she hired (after cleaning out the bat and rat crap in the long attic) SPRAYED a hot liquid foam on the UPPER part of the areas between spaced rafters supporting the roof. I forget the name of the material. It resembles "good stuff" that is used to fill cracks and spaces. So the thick foam when dried and cured is on the UPPER section, NOT the flat floor section. The sprayers must have had to use space suits to do it. Anyway the results are great and the attic is now very close to the same temperature as the house itself; a different way of thinking about a problem
    Last edited: Jul 1, 2013
  12. rscott

    rscott New Member

    Thanks again for all the help. Here is some more information:

    The piping that I took pictures of at installation was black, appeared to be plastic. Wording on the piping included "1-1/4" IPS OIL CREEK AQUA-JET (O.D.) PE3408/3", "ASTM D3035 NSF-PW DR-11 160 PSI @73'F".

    The air supply from the basement has been ~58 degrees each time I have checked. The air supply from the attic seems to be ~58 degrees when it is not hot in the attic, and has been up to ~68 degrees when it has been very hot in the attic (perhaps around 120 degrees by the air handler).

    I believe that the air supply from both zones handled by the attic is about the same, but I need to double-check that on a hot day. On the next hot day, I'm going to go in the attic and see if I can feel any cool air escaping from the ductwork.
  13. rscott

    rscott New Member

    This is what I am considering doing. It also would have the added benefit of providing semi-conditioned space I could use for storing things that cannot go in an unconditioned attic.

    Of course, it doesn't solve directly the problem (e.g. if there is a leak in the ducts), but would likely minimize the issue.
  14. Calladrilling

    Calladrilling Member Industry Professional Forum Leader

    Just thinking outside the box here.....
    To me this may seem like the easiest solution to the problem here. Install a window unit air conditioner into your attic vent and have it run all day to keep the attic air temps cooler than 120 degrees.
    Lets not over engineer this simple problem.....KISS!!!
    Last edited: Jul 1, 2013

Share This Page