New Construction IAQ Suggestions
Let me start by saying that this is one of the best forums on the web. I lost my house due to a VERY bad mold problem about a year and a half ago. My family's health was suffering a great deal, and now most of us have MCS. I'm not complaining though, it could be much worse. Anyway, this forum was the first place that lead me to think that my problem could be mold related, and so I thank you all for your suggestions as they probably helped me get my family out of that home sooner than I would have otherwise. With that said, I also learned a great deal about HVAC in that time and the information has been invaluable. Thank You!
We are finally at a point where we're ready to build a new HEALTHY home. Needless to say, IAQ is the top priority. We're in a decent rental right now and it is suffering from classic DSS (Dirty Sock Syndrome). I took it upon myself to clean the blower coils and the drain pan (since I wanted to use a less toxic degreaser on the coils due to our MCS). Of course, there was a bunch of mold in the pans when I went to clean them out. Sigh, these are 3 year old Lennox units. They were cleaned in the Spring but not the Fall. Anyway, I read the massive DSS post and it left me a bit disheartened. Since I have the luxury of building our next home from scratch, what would be your reccomendations for an HVAC system? Details below:
1) We live outside of Asheville, NC so we're in a Mixed Humid climate at about 2500 ft elevation.
2) The house will be a WNC certified healthy home. It will be a very tight house with spray foam throughout. Water is our top priority so we will be grading very well, using Superior Wall foundations, and insulating under the basement slab.
3) It will be a 1600 sqft home with an 800 sqft Conditioned, unfinished basement.
4) No ductwork will be in unconditioned space. There will be an air handler in the basement utility room that will use a mechanical chase to go up and feed the other floors.
5) There will be a return in each bedroom to help equalize pressure.
6) I will insist on either an Ultra-Aire 100V or a Honeywell DR90 ventilation/dehumidification system.
I'm not looking for a load calculation or anything, just suggestions on the brand of equipment to use, and steps I can take to mitigate DSS going forward. For example, should I install UV lights at the coils? Should I go with a furnace instead of a heat pump (this has it's own problems as we don't want gas in the house)? If we go with a heat pump should the coils be coated? The DSS forum seemed to single out Trane, Amana, Lennox and a few others. Are there any brands that don't have DSS problems? What kind of preventative measures should I take to keep the system mold free?
I appreciate your time, and I'm really looking forward to your answers!
Mike on the DSS issues many of the manufactures are going to all aluminum coils on the evap. This should minimize the bacterial growth that causes the DSS. As a manufacture I can't recommend brands for the IAQ in this forum. But I would say this you need at least 4 to 6 inch Merv 13 filtration and I would avoid UV lamps on the coils in residential. The plastic drain pans can't handle the UV light. And you receive very little IAQ biologic reductions and 500 fpm in an airstream. There simple isn't enough residence time to permanently disable a biologic with just UVGI when it is moving. Depending on what part of the world you are in a HRV or ERV system would give you many benefits also.
The premise of ventilation is that the OA is clean or of sufficient quality to be used for dilution. Traditional ventilation is somewhat being threatened by the fact that the EPA is changing the requirements for outdoor air quality which is creating non-attainment zones in what is now becoming a significant portion of the country. That means that buildings in those areas will need to clean up the OA before they bring it into the building.
Genesis Air Inc.
All systems can have DSS. It's a function of biological dust, germs and humidity. High end air filtration is a good preventative measure -- don't give bacteria and mold anything to grow on. I am very skeptical about UV lights. Biological hoods in research labs use them and it takes hours of high intensity UV to disinfect a hood. The hood is sealed, the furnace continually brings more contaminants; think about it.
-If you won't turn it on then nothing else matters.
You are on the right track and thank you for consideration.
Many suggest that operating the a/c fan in "on" mode minimizes the possibility of growing any biologicals on the coil or in the a/c ducts. This eliminates the long hours of extreme humidity in the cooling equipment. It does increase the dehumidification load but may be a small price to pay for a mold/bacteria free system.
Simple high SEER cooling equipment with a thermostat that is easily use wide dead band to minimize on/off short cycling and varible speed blower will allow you to set up the a/c to max the moisture removed by the a/c when used.
Your selection of the whole house ventilating dehu is spot on. Setup the ventilation on the WHVD for an air change every 5-6 hours when occupied at a minimum.
Regarding outside air, the air in your home is outside air plus the pollutants you add to the air as the air passes through your home. You also remove the oxygen and add CO2 to the air. Filter out the dust and add or remove moisture as needed to be comfortable and healthy. The Ultra-Aire has a premium filter package to includes a merv 13 filter option that filters the fresh air and air in the home.
<50%RH is comfortable and prevents mold/dust mites growth in the home. <35%RH is uncomfortable to some. The dehumidifier is important and in some situations a humidifier may also be needed for comfort.
Keep us posted on your progress.
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"
Could you tell me what the source of the mold was in your first home?
Thanks for the input guys!
TB, does the placement of the ventilating dehumidifier make a difference (i.e. should we put it in the conditioned attic space, or should it go in the conditioned basement)?
energy_star, we had a home that was built in the late 70's in South Carolina. It had a ventilated crawl and attic space. There was a hole in the foundation wall. At some point in the past, a homeowner poked a hole in the wall to run a gas line to the back patio. Unfortunately, it was a crude job and it wasn't properly patched. That location happened to be poorly graded and in an area prone to water (gutter leak, and at the bottom of a slope). The gas line had almost rusted out. Our first two years in the home were during drought conditions. One month, it rained for 3 weeks straight. Water continued to flow into the crawl (as it obviously had in years past) and ran down a channel right to the blower in the crawl. The blower was part of a 25 year old Trane system. It was installed in the mud and it was full of mold (Asperigillus). To top it off, our gas water heater was also located in the crawlspace and was improperly vented so combustion products were floating around. We ran our whole house fan a good bit to bring fresh air into the house, but it was distributing spores throughout the house. I guess it was just a perfect storm.
One night while bathing my daughter I started to get a metallic taste in my mouth. My wife had the same thing, which we both thought was odd and chaulked it up to our meal, when it continued the next few days, we left the house and we never went back. We had it remediated and we replaced the units and the ductwork, but we still couldn't stand being in the house. It's been a long year and a half, but we're getting better and we're over the worst. It's a shame it took an event like this to open our eyes to the importance of building a healthy home. The science has been around for a while now and it's hard for me to believe that people are still allowed to build these efficient, tight houses without bringing in fresh air.
Hopefully the policy makers wake up and update the building codes ...
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