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  1. #1

    Humidity problems in MN. Cannot get answers.

    Hello. I am new to the forum. We have a 2 1/2 yr old 1.5 story house. 2,000 sf on main floor with high vault in great room, full basement, 700 sq upstairs, and It is closed cell spray foamed on all walls, foundation, and roof. with triple pane windows. We have a 6 Ton GeoComfort open loop geothermal water to water system. We also have a RenewAire air exchanger. The control is set on %time run, not on humidity. We run it at a minimum to not at all because we feel this would worsen our humidity problems.

    This summer we have had high humidity in our home. (60-70%). We set our thermostat at 70^ and leave the fan running nonstop per our HVACs instruction. We have called them and the rep from our elec coop who have been working together to try to fix this. They lowered the temp of the water, but that has showed no results. We had a stretch of days in the mid nineties. I thought maybe then the RH would drop since the AC ran more, but it did not make a difference. They also wired an outlet to keep the pump running the cold water over the coils even when the ac wasn't running. They thought with the fan on, this would pull out some extra humidity. No results.

    An interesting note, In the winter we mainly heat our home with our wood burning fireplace. We do use the geo to heat garage floor to 40^, and put a little heat in our basement floor(60^) and under some tile on the main floor. We run our fan continuously to circulate the heat from the fireplace throughout the house. The fireplace is supposed to be an efficient unit with closed doors.(Kozy Heat masonry unit) We had problems last winter with low humidity. (15%), so at the end of the winter our HVAC guys installed a Honeywell Truesteam. 9gpd. We have not yet used this since it was at the end of the season. We attributed the low humidity to the fireplace use.

    We are in a rural area without a lot of HVAC options. Are not getting answers from our HVAC. We kind of get the feeling they don't know what else to try and want to forget about us. Not sure what to do. Does anything stick out or would any additional information be helpful? I appreciate any advice.

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by mimjo View Post
    Hello. I am new to the forum. We have a 2 1/2 yr old 1.5 story house. 2,000 sf on main floor with high vault in great room, full basement, 700 sq upstairs, and It is closed cell spray foamed on all walls, foundation, and roof. with triple pane windows. We have a 6 Ton GeoComfort open loop geothermal water to water system. We also have a RenewAire air exchanger. The control is set on %time run, not on humidity. We run it at a minimum to not at all because we feel this would worsen our humidity problems.

    This summer we have had high humidity in our home. (60-70%). We set our thermostat at 70^ and leave the fan running nonstop per our HVACs instruction. We have called them and the rep from our elec coop who have been working together to try to fix this. They lowered the temp of the water, but that has showed no results. We had a stretch of days in the mid nineties. I thought maybe then the RH would drop since the AC ran more, but it did not make a difference. They also wired an outlet to keep the pump running the cold water over the coils even when the ac wasn't running. They thought with the fan on, this would pull out some extra humidity. No results.

    An interesting note, In the winter we mainly heat our home with our wood burning fireplace. We do use the geo to heat garage floor to 40^, and put a little heat in our basement floor(60^) and under some tile on the main floor. We run our fan continuously to circulate the heat from the fireplace throughout the house. The fireplace is supposed to be an efficient unit with closed doors.(Kozy Heat masonry unit) We had problems last winter with low humidity. (15%), so at the end of the winter our HVAC guys installed a Honeywell Truesteam. 9gpd. We have not yet used this since it was at the end of the season. We attributed the low humidity to the fireplace use.

    We are in a rural area without a lot of HVAC options. Are not getting answers from our HVAC. We kind of get the feeling they don't know what else to try and want to forget about us. Not sure what to do. Does anything stick out or would any additional information be helpful? I appreciate any advice.
    6 tons of cooling for a foamed house with 2700 SQ feet is probably at least 3 tons to large and will give you short run times and high humidity

    Running the fan constant will also re-evaporate the moisture that was removed during the cooling cycle.

  3. #3
    Thank you for your reply, second opinion. It would actually be 4700 since the basement is conditioned. But probably still oversized. So we should shut off the fan? So what do we do if our system is oversized? It doesn't seem feasible to replace it??

  4. #4
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by mimjo View Post
    Thank you for your reply, second opinion. It would actually be 4700 since the basement is conditioned. But probably still oversized. So we should shut off the fan? So what do we do if our system is oversized? It doesn't seem feasible to replace it??
    The basement load is probably near nothing.

    Changing out the system would be rather expensive, but not doing something could also be bad. High moisture content can lead to all kinds of problems.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,337
    Where does the combustion air for the fireplace come from?
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,319
    Do NOT run the fan all the time, that can raise the RH 10 points in humid weather.

    Yea, I was thinking you are grossly oversized too. You really are conditioning 2700 sq ft as the basement needs almost no cooling and little heating. Seems they sized the geo for heating not cooling and this is the result. Simplest thing likely would be a whole house dehumidifier. The ventilator won't dry the house out in warm weather. The dehum can be tied into the duct system or put in the basement with a supply and return to the first floor which will also dry out the whole house.

  7. #7
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,538
    The fan should be in the "auto" mode! A small whole house dehumidifier like the Ultra-Aire 70H is needed for low/no cooling loads and outdoor dew points of +60^F. Under these conditions, you need 2-3 lbs. of dehumidification per hours to maintain 75^F, <50%RH, 55^F dew point. Also critical is <45^F cooling coil while the a/c is operating. Foam homes need a fresh air change in 4-5 hours. when occupied.
    Check the a/c supply temp/%RH at the grill while the a/c is operating.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  8. #8
    Join Date
    Sep 2010
    Location
    LA
    Posts
    198
    Quote Originally Posted by mimjo View Post
    . The control is set on %time run, not on humidity .
    Why not run it on humidity control? Wouldn't that be better for dehumidification?

  9. #9
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
    Posts
    1,781
    This is a water-water unit, so the unit is just making cold water, not directly controlling the way it is used, correct? What is(are) the fancoil(s) that is(are) used for the cooling? Is there a storage tank on the load side of the heat pump?

  10. #10
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    Water to water geo? Too bad the controls approach was probably typical DX bang on/bang off. You can do some really sweet dehumidification with chilled water if you set the controls up correctly.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,538
    DX is better than chilled water. With DX coil, the cooling occurs at the evaporating temperature. Chilled water starts cooling at the chiller temp. Every btu of cooling raises the chilled water temp. Cold water into a coil, water warms immediately as water moves through the coil. DX coil maintains the evap temp until all of the refrigerant is evaporated. Temp only in the super heat area of the coil. Results in much more moisture removed per ton of cooling. How does this stuff get started?
    Another issue, how much outside air infiltration is occurring? Measure the dew point outside, measure the amount of moisture removed by the a/c, calculated the number of occupants in the home, calculate the indoor dew point.
    An occupant add about .5 lbs. of moisture per hour. 100 cfm of infiltration 70^F dew point air entering a home and being dehumidified to a 55 ^F dew point before it exfiltrates is about 4 lbs. of condesate. So home with 4 occupants and 100 cfm of infiltration or controlled fresh air ventilation is about 6 lbs. per hour.
    The other way of estimating the amount of outside air entering a home is measure the CO2 levels in the home and counting the number of occupants. The CO2 increase in the mixed house air with the number of occupants extimates the amount of outside air entering the home.
    An example is 800 ppm of CO2 in a home with outside air being 450 ppm, estimates 30 cfm of fresh air per occupant. A basic CO2 from CO2meter.com is $100.
    Blower doors only estimate infiltration at average wind/winter temps. During calm weather and moderate temps, the amount of fresh air infiltrating is much less. Most homes do not get enough fresh air during calm weather.
    All of this because a/c is unable to maintain <50%RH during low/cooling loads with out supplemental dehumidification. Sad..

    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
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    1,781
    Teddy, that is a lot of wrong information based on the assumption that the chilled water coil is the same size as the comparable evaporator coil. ( which, is probably true in this case, looking at geocomfort's product offerings...) However, to say that dx dehumidifiers work better than chilled water shows a lack of familiarity with advanced chilled water schemes. A properly designed chilled water system can perfectly match dehumidification and cooling loads, while never adding any excess heat to the space. What is unfortunate, is that these control schemes have not made it to the residential market, which is still basically in it's infancy as far as chilled water goes.

  13. #13
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,538
    Quote Originally Posted by CraziFuzzy View Post
    Teddy, that is a lot of wrong information based on the assumption that the chilled water coil is the same size as the comparable evaporator coil. ( which, is probably true in this case, looking at geocomfort's product offerings...) However, to say that dx dehumidifiers work better than chilled water shows a lack of familiarity with advanced chilled water schemes. A properly designed chilled water system can perfectly match dehumidification and cooling loads, while never adding any excess heat to the space. What is unfortunate, is that these control schemes have not made it to the residential market, which is still basically in it's infancy as far as chilled water goes.
    Sorry about raising an issue that has nothing to do with this discussion, oversized chillers with plenty of reheat are needed to provide <50%RH in green grass climates. If the chilled water is not <40^F with a return temp <46^F, how will you provide <50^F dew point during light cooling loads, high outdoor dew points and reheat to occupied space?
    I understand chillers, in that I am involved in design for other applications that we manufacture. It would be nice to have real residiential application for chillers, but they are too expensive and do not deliver high btus per watt with good dehumidification, sorry. Prove me wrong and we would like to design chillers for residential applications.

    We currently supply the dairy and craft brewing with small custiom chillers.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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