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Community and Q&A

GSHP Vs whole-home dehumidifier

Venkat Y | Posted in Energy Efficiency and Durability on

Hello,

I am looking at retrofitting my home with a GSHP (please see the below thread for details):

https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/24978/geothermal-how-specify-and-verify-performance

I am also planning to have an HRV and a whole home dehumidifier (Lennox 65-pint) installed as part of the new setup. My question is:

1. The contractor has quoted a 3-ton system (please see the above thread for details) because a higher 4-ton unit will not run long enough to do dehumidification in Summer. Now what I am wondering about is which is more efficient at dehumidification: a longer running 3-ton Geothermal unit or the Lennox 65-pint whole home dehumidifier?

2. In winter, does the GSHP do any dehumidification at all? I am hoping the HRV will help in reducing the humidity levels so the Lennox dehumidifier doesn’t need to kick in often (I have high humidity inside in winters).

I am planning to have the setup such that the Lennox will stop whenever the Geo starts. I am also planning to have my thermostat at a constant 72 in winter and 79 in summer (as opposed to going down to 69 and 81 respectively at night time).

Thanks,

venkat

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Venkat,
    I notice from another thread that your home is in Illinois (climate zone 5).

    You wrote, "I have high humidity inside in winters." The first question you should address (before choosing new HVAC equipment) is, "why?"

    Most heated homes are dry during the winter. If your home has high indoor humidity during the winter, something may be wrong. You need to identify the source of the moisture and correct that problem.

    It is far simpler and cheaper to correct high humidity during the winter with ventilation than with a dehumidifier.

  2. Venkat Y | | #2

    Hi Martin,

    Initially, we thought the moisture was coming from the curing of the exterior concrete walls (this home uses ICF with EIFS siding), but the home was already one year old before we moved in about 9 years back. I later heard concrete will cure within the first year. We have come to believe that the unbreathable nature of the concrete walls coupled with the fact we do a lot of Asian Indian steam cooking plus some indoor plants are causing humidity buildup. I doubt the bath exhausts are able to get much humidity out due to lack of immediate makeup air. But we haven't had a professional verify that there isn't an unusual source outside of those mentioned. If we want to get such a verification done, who would that professional be? Would it be the HVAC contractor or some other professional?

    As you suggested, we are hoping the HRV will take care of the bulk of the humidity problems in winter.

    But in summer, I am wondering which is more efficient? A lower-tonnage, longer running GSHP/Air Conditioner that will run long enough to cool (and thus as a side-effect also handle the humidity) or a most efficient (higher tonnage?), short running cooling cycle coupled with a whole home dehumidifier that will pick up where the AC left off?

    Thanks,

    venkat

  3. User avatar GBA Editor
    Martin Holladay | | #3

    Venkat,
    Your analysis makes sense. It sounds like you have a relatively tight home and several interior moisture sources. I agree that your house probably needs an HRV. That should take care of the high indoor humidity during the winter. (Running an HRV during the winter requires much less electricity than running a dehumidifier.)

    Q. "Which is more efficient? A lower-tonnage, longer running GSHP/Air Conditioner that will run long enough to cool (and thus as a side-effect also handle the humidity) or a most efficient (higher tonnage?)"

    A. I don't think your question concerns efficiency. The most important issue is sizing your air conditioner properly. Most HVAC contractors aren't very good at performing cooling load calculations -- they either use a rule of thumb or they don't provide accurate inputs when using load calculation software. As a result, the vast majority of residential air conditioners are oversized. (For more information on this issue, see Calculating Cooling Loads.)

    You may want to hire a home energy rater certified by RESNET or BPI to perform a cooling load calculation for you.

    To answer your question, a properly sized (small) air conditioner does a better job of humidity control than an oversized air conditioner. In your climate, you probably don't need a separate dehumidifier, as long as your house has a properly sized air conditioner.

  4. Tim O'Brien | | #4

    Venkat,

    Martin is correct in (most of) his points above. I would like to offer a slightly different view regarding the relationship between the dehumidifier and the heat pump. If you want a very comfortable house with a reasonable cost to condition I suggest you install an efficient heat pump and an efficient whole house dehumidifier. The heat pump will remove some moisture from your house when it operates, but it responds to a temperature set point on your thermostat - it does not control the moisture content inside your house. You will get as much dehumidification as the heat pump provides while lowering the temperature of your house. Some days the heat pump may provide adequate dehumidification and other days it may not. The whole-house dehumidifier will control the moisture content inside your house every day (without over-cooling your house). Spring and fall are dehumidification seasons for your zone - there may not be much need for heating or cooling, but there will be some need for dehumidification.

    In the winter it is typically less expensive to ventilate (bring cool dry outdoor air into your house and heat it) to dehumidify than it is to operate a dehumidifier as long as the outdoor air is dry. The best thing you can do all year is to remove moisture as close to the source as possible (bath fans, kitchen hood) to prevent the moisture from remaining inside your house. These articulated kitchen hoods are an interesting twist on kitchen hoods that may help you if you cook and create a large amount of steam/moisture in your kitchen.

    http://www.thekitchn.com/steampunk-articulated-vent-hoods-from-minicciolaeurocucina-2012-169807

    I am a dehumidifier guy and I will let you know that there are more efficient dehumidifiers than the Lennox unit listed by Energy Star

    http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=DE

    including the Ultra-Aire units that my company manufactures.

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