Guest guest Posted September 21, 2004 Report Share Posted September 21, 2004 AC units could be oversized and short-cycling, but the problem may very well be caused by outside air infiltration via return duct leakage or negative pressurization. Many retrofit AC systems are installed in attic spaces. I just had a project where a unit owner thought it was a good idea to keep a window open for ventilation when air conditioning. RH was over 90% but came down pretty quickly after I shut the window. Working for the property manager, I tried to explain the concept of relative humidity and psychrometrics to the owner. His response was, "So it could have 'exasperated' the mold problem?". I said, "Yeah, you should keep the windows closed when you use the air conditioning". You could say that his problem was just psychrological. Steve Temes I have run across three homes this month with unusally high RH inside ( 70% & higher ) with fungal growth either around the registers or growth on the surface of the sheetrock. All three homes have had new HVAC systems installed in the last three years and are spec'd for the homes. Any suggestions? Quote Link to comment Share on other sites More sharing options...
Guest guest Posted September 21, 2004 Report Share Posted September 21, 2004 > I have run across three homes this month with unusally high RH inside > ( 70% & higher ) with fungal growth either around the registers or > growth on the surface of the sheetrock. All three homes have had new > HVAC systems installed in the last three years and are spec'd for > the homes. Any suggestions? , a very common problem here on teh eastern shore of MD. What I usually suggest to the owner is to make sure the HVAC system is balanced correctly. An influx of cold air from a unbalanced system is not going to help the problem. Then I also will recommend that the owner look into plastic diffusers vs the metal kind. They will not condensate (usually) I always use the old.....remember a cooler surface in a warm environment will condesate (cold beer mug in a warm room). I also suggest puting a plastic or non cellulose template spacer between the diffuser/s (all you need to do is get the diffuser away from the wallboard 1/8 " in. It then really is only a matter of the owner keeping the humidity levels in check <55%. Also always make sure you check the surrounding wallboard with your moisture meter to make sure moisture levels do not require that the wallboard be removed and replaced. Good Luck Dan, HES Quote Link to comment Share on other sites More sharing options...
Guest guest Posted September 21, 2004 Report Share Posted September 21, 2004 Dear , The problem you have described is really rather simple to to draw a conclusion as to causation yet can be a bit complicated to nail down why it is happening. There are those out there that will disagree and want publication sources cited, but in the real world this is what is happening. First let me tell you that I am a HVAC contractor that has encountered these problems many times and applied effective solutions. 1. What is actually happening? - The air from the HVAC system is reaching surfaces and indoor ambient air in which dew point is being reached causing condensation meeting the three requirements for mold to occur. Moisture, Food Source and the Spore. 2. Why is this happening? This is where things start getting complicated. There is usually more than one reason for the air being so supercooled that the problem is occuring. First let me question the statement designed to spec's. This is such a general statement that usually does not mean anything. The reason I say this is that when you pick up most blue prints there is a disclaimer of sort concerning the HVAC system. It usually says something to the effect " the HVAC contractor shall verify the HVAC specifications on this plan " . What this means is the monkey is on your back if it does not work properly even though it is designed on the plans. Let me clarify that I am referring to residential plans. So the underlying problem now is " why is the air so cold that it is reaching dew point at the registers (diffusers). These are the things I check to answer the question. 1. Temperature across the coil. (at the return air grill and the closest supply register or in the plenum) should be 16 degrees plus or minus one. Of course this is in the AC mode. 2. Return air grill is of proper size. 200 square inches per ton for a standard throwaway filter. 3. Duct system is sized to distribute the proper amount of air for the system size. 4. Fan speed is set properly. Is the air handler ECM technology which is reduced airflow. 5. Ducts and boots are properly insulated. Some states require R-4.3, some R-6. You find less problems with R-6. 6. Negative pressures in the home or unbalanced air flow. 7. Unusual moisture sources in the home. i.e. fish tanks, spa's etc. 8. Occupants living habits. These are typical things I find. 1. Doors closed yet touch the carpet not allowing return air path creating negative pressures. 2. Undersized return air grills with high efficiency filters (air chokers) slowing the air so much it becomes supercooled usually in the high 20's temp difference. 3. Duct systems undersized, in particular flex ducts ( a 6 " round pipe equates to a 7 " flex per ACCA ductulator). 4. Diffusers closed in certain rooms. 5. Kids close doors and open windows in their rooms. 6. Variable speed air handlers with high efficiency filters (even lower air flow). 7. Boots improperly insulated and holes in sheet rock cut to big for the boot (air gaps). 8. Fan motors in reverse rotation or blower wheeles filled with mold. 9 Clogged evaporator coils. 10. Dirty, clogged filters. Beware of the new filter because it was probably changed just before you got there. And the list goes on! Remember. A HVAC system is not a dehumidifier. Dehumidification is a by product of conditioning the sensible temperature for human comfort. A thermostat can care less what the RH is. If there is a need for additional dehumidification with no underlying problem, suggest they buy a stand alone dehumidifier. Also, I do not recommend real high efficiency filters. They can cause more problems than there was before. If there is a need to clean the air more than a standard throwaway, suggest a stand alone air cleaner. But not one that generates ozone. i.e. Ionic Breeze or Oreck. I suggest a hepa filtered air cleaner. I am sure there are people who disagree with some of my suggestions, but this is what I have found to be most effective and logical. Hope I have helped in some way. Best Wishes, Asbill excessive RH > I have run across three homes this month with unusally high RH inside > ( 70% & higher ) with fungal growth either around the registers or > growth on the surface of the sheetrock. All three homes have had new > HVAC systems installed in the last three years and are spec'd for > the homes. Any suggestions? > > > > > > FAIR USE NOTICE: > > This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available in our efforts to advance understanding of environmental, political, human rights, economic, democracy, scientific, and social justice issues, etc. We believe this constitutes a 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit to those who have expressed a prior interest in receiving the included information for research and educational purposes. For more information go to: http://www.law.cornell.edu/uscode/17/107.shtml. If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner. > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted September 22, 2004 Report Share Posted September 22, 2004 A possibility I haven't seen specifically mentioned yet is leaking supply ducts. When supply ducts leak more air is being pulled in through the return thatn is being blown back in through the supply ducts. Thus the house is put under significant negative pressure and pulls in large amounts of unconditioned outside air. I assume you are located in VA and that outside air air is at very high humidity levels. Negative pressurization can be checked for fairly easily with an accurate manometer. There are contractors who can measure the exact amount of leakage in the ducts and locate and seal the leaks. Tim Toburen Re: excessive RH AC units could be oversized and short-cycling, but the problem may very well be caused by outside air infiltration via return duct leakage or negative pressurization. Many retrofit AC systems are installed in attic spaces.I just had a project where a unit owner thought it was a good idea to keep a window open for ventilation when air conditioning. RH was over 90% but came down pretty quickly after I shut the window. Working for the property manager, I tried to explain the concept of relative humidity and psychrometrics to the owner. His response was, "So it could have 'exasperated' the mold problem?". I said, "Yeah, you should keep the windows closed when you use the air conditioning".You could say that his problem was just psychrological.Steve Temes I have run across three homes this month with unusally high RH inside( 70% & higher ) with fungal growth either around the registers or growth on the surface of the sheetrock. All three homes have had new HVAC systems installed in the last three years and are spec'd for the homes. Any suggestions?FAIR USE NOTICE:This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available in our efforts to advance understanding of environmental, political, human rights, economic, democracy, scientific, and social justice issues, etc. We believe this constitutes a 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit to those who have expressed a prior interest in receiving the included information for research and educational purposes. For more information go to: http://www.law.cornell.edu/uscode/17/107.shtml. If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner. Quote Link to comment Share on other sites More sharing options...
Guest guest Posted September 22, 2004 Report Share Posted September 22, 2004 My " sick house " had RH 10% higher than similar houses. Turns out the moisture was coming up through the slab, from improper drainage. Based on bad assumption about where the problem was coming from, we had the ductwork sealed. By diluting less, this made the problem which was coming into the house along with that moisture worse. HVAC was depressurizing the gravel under the slab, through cracks under the house's massive cabinetry near the hallway return. Note that the system was balanced overall, this was a local effect. Separately and in a different house, about 3 years ago we replaced our HVAC. The new system was put in by professionals and sized properly. However, to optimize SEER the A/C was tuned to remove *no* moisture from the air, by the well known U.S. manufacturer and installed according to the manufacturer's instructions. Only after I told the contractor the unit wasn't satisfactory and to " bring a truck " to get it off my property was he willing to work with me to reduce the fan speed to a level at which adequate dehumidification occurs. I wonder if your customers ended up with these intended-for-California units, which would be a disaster in your climate? Steve Chalmers stevec@... -------------------------------------- Message: 8 Date: Tue, 21 Sep 2004 20:24:08 -0000 Subject: excessive RH I have run across three homes this month with unusally high RH inside ( 70% & higher ) with fungal growth either around the registers or growth on the surface of the sheetrock. All three homes have had new HVAC systems installed in the last three years and are spec'd for the homes. Any suggestions? Quote Link to comment Share on other sites More sharing options...
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