My husband and I built our house about 4 years ago. We had a geothermal unit installed and we haven't really had any issues with it until summer. In the summer our house has a very damp feeling- the air feels damp, our furniture feels damp, our beds feel damp, clothes, pretty much everything in the house. Mold has been growing on our walls, doors, toys(kids toys) clothes, well you get the point. Anyways, I contacted the business who installed it and they said geothermal units do that because they aren't running long enough in the summer and to either turn up my heat extremely high for a few hours while we are out of the house or to buy dehumidifiers.. I'm a little erked by this because we spent a pretty penny on this unit. I feel like this shouldn't be an issue. Anyways, I was wondering if anyone had any suggestions or related issues with this that could give me some advice. Thanks in advance!
Sounds like you're having a problem with high humidity. The run time, or lack thereof, is not specific to geothermal systems. It has to do with the size of the HVAC equipment with respect to the heating and cooling loads of the house. For the equipment to to properly remove moisture/humidity from the air, it needs to run long enough to do so. If your system is short cycling, that probably would explain it. The fact that you've had several cooling seasons without this problem raises the possibility of something else influencing your situation this year. Just a homeowner here... I'm sure the pro's will be by soon
Thanks for the quick reply! What would you suggest we do? Call them again and ask them to come out? We have had this problem every summer since having it installed. I guess I should have made that a little more clear in my original post. But what you are saying makes sense.
Can you share anymore info? Size and type of unit? Calculated cooling load of the home? Maybe some pictures if you don't know what I'm asking? Dose the fan run all the time or only when cooling? Any duct work in unconditioned space that's not sealed? Have you noticed that the unit doesn't run very long/or often? The first thing that springs to mind is your unit maybe oversized. But it could be other things also. You may need professional boots on the ground for this one. I would question how good the contractor is if they respond like you poseted above.
More info is needed. Where do you live? Size and model of the unit? Also, it is not necessarily the unit's fault when you dealing with mold issues.
Mold needs three things to grow. Spores. Food. Dry wall glue and paper are perfect things to feed mold. Water. I am not a well know member here, but I am published on indoor air quality. What do you have for an indoor RH number while cooling? Mark
Fungal spores are everywhere, sometimes more, sometimes less, both indoor and outdoor. Us humans inhale an average of 6 million spores every day. Once they have the right living conditions, they can multiply rapidly. They don't need specific food, any organic substance will do, even kids tools. It comes down to temperature (that is why refrigerators were invented), the warmer the better, and especially humidity levels. Molds need humidity (RH) levels over 65%.
Dehumidifiers are the 16th item on our 15 point humidity control checklist: Some of these may not be able to applied since system sizing and selection train has already left the station. Bottom line - I regard a dehu, whether portable or central, as a noisy, crude pricey band-aid for crappy buildings and sloppy HVAC. We advocate a 15 point strategy to stave off the need for supplemental dehu under nearly all circumstances: 1) Minimize enclosure air infiltration - outdoor air is MORE humid, not less all summer in nearly all US climate zones. The home needn't be anywhere near as tight as a Passive House, 2-3 ACH50 will do fine. 2) Properly size HVAC system to minimize short cycling - endeavor to install the smallest feasible system. Use the Manual J safety factor to err on the side of smaller, not larger. Tonnage cools a home, but run time is crucial for drying. 3) Ensure ductwork is configured to provide individual room design air flows - stave off thermostat wars, zone where appropriate. Properly sized and configured ductwork supports smaller HVAC systems, as does zoning - provides ability for system to direct its capacity to where needed, whether occasioned by the sun's daily movement or intermittent concentrated loads such as intense cooking or gatherings in the public areas of a home. Zoning makes a system smarter and allows it to be smaller. Smaller dehumidifies better. 4) Ensure ductwork is entirely within conditioned space or at least minimize duct leaks to / from unconditioned space. Provide large filter cabinets that maintain good airflow over longer media change intervals. 5) Avoid single stage HVAC systems - they short cycle during part load conditions. 6) Include controls that modulate system airflow (reduced CFM per ton) in response to humidity excursions. 7) Manage point sources of humidity with ventilation - encourage use of bath vent fans by installing quiet models controlled by timers, spot humidity and / or motion. Ensure range hood is quiet, properly sized, selected, positioned, and ducted so that it both works well and is reasonably likely to be actually used. Position kitchen supply registers so that their discharge does NOT interfere with rising cooking fumes entering hood. (It is amazing how often this small but crucial mistake is made) 8) Discourage use of continuous fan in cooling mode - it re-evaporates water off coil while compressor is off. 9) Discourage use of natural gas or propane for cooking - a scant 20% of the fuel's heat goes into the cookware, and a byproduct of gas combustion is water vapor. Granted a properly configured hood will evacuate the water vapor, but why subject a southern kitchen to all that extra heat and humidity when viable alternatives exist - consider an induction range. 10) Evict panting dogs, sweaty children, and thirsty houseplants to the extent possible during summer months. 11) Endeavour to include a heat pump water heater, or at least its thermodynamic / psychrometric effect within the conditioned envelope of a home. The free cooling and drying are significant, though the noise and appearance are concerns to be managed. 12) Resist with every fiber of one's being Pecksniffian demands to arbitrarily over-ventilate in response to an arbitrary and capricious(A&C) standard. Failing that, provide the "required" A&C ventilation system with an OFF switch! 13 Thermal mass - Flattens and delays sensible load, providing repeated opportunities to meet latent load after dark and during early morning hours 14) Decrease CPH (cycles per hour, or similar parameter) for longer runtimes, better dehu 15) Select AHU profiles for improved dehu during short runtimes
