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11-06-2007, 08:22 AM #1Regular Guest
- Join Date
- Nov 2007
- New Orleans
Fresh air confusion- need your thoughts
I am having 2 new Carrier Performance heat pumps and VS air handlers installed in my 2 story home (one up and one down). I am confused about one issue....fresh air.
Our contractor is highly recommended and is supposed to do very careful installs. He has done all the right things to date...based on information that I have gleaned at this site.
Our house is 27 years old and not what I would describe as "tight"...just average for a house of this age.
Our contractor is going to install a fresh air intake that is about the size of a dryer vent in a soffet (I think he said it has a damper). He said that this improves the air quality in the house and keeps it from drawing air from less desireable areas.
On the surface this seems to make sense but...I am puzzled about a couple of issues.
1. We live in a humid climate. Won't adding some extra humidity outside air create some issues?
2. Doesn't this fly in the face of energy efficiency?
Please share your thoughts. Thank you
11-06-2007, 08:28 AM #2
Your house will allow infiltration - air enters through all the little holes.
Adding a fresh air intake to the return allows the system to condition the air before it enters the home. It will also provide a slight pressurization of the home which will minimize the infiltration.
Whether you bring air through intake or infiltration, it needs to be conditioned. It's more efficient to condition the air before it mixes with the air in the rest of your home.
I would recommend the fresh air intake only be open when the air conditioner is running. Your contractor can install an automatic damper to accomplish this. In heat mode or continuous fan mode, you likely wouldn't want to be introducing the fresh air into the return.Merry Christmas
11-07-2007, 09:38 AM #3Regular Guest
- Join Date
- Nov 2007
- New Orleans
Could you explain how this automatic damper works and is there one that is specifically made for this application?
Is it reliable? If it would fail in the amount of air that it lets in that could be a mess?
Concerned about adding more humidity into the house.
I follow the idea of not pulling in air through the cracks in the house but would think that this might compromise energy efficiency?
11-07-2007, 11:23 AM #4
I think Skuttle makes a damper that can be automatic. Where I come from we are required to have a minimum 4" fresh air with any gas appliance but it is against code to damper it in any way, even interlocked with the furnace.
I don't think you need to concern yourself to much with the humidity aspect of this. When we first started doing these the utilite company did a check on how many CFM a 4" fresh air actually brings in. It was like 12 CFM. If it was a huge pipe then you might have problems. Otherwise your bringing in the humidity through infiltration anyhow.Its a good Life!
11-07-2007, 12:28 PM #5
ASHRAE, Am Medical As, EPA, and AM Lung AS. recommend we should have minimum of 75-100 cubic feet per minute of fresh air in home to purge pollutants and renew oxygen. They also suggest maintaining <50%RH inside homes throughout the year to avoid mold/dust mites.
All homes leak air is response to the air pressure across the building's imperfections. Wind is the greatest force occuring throughout the year. The stack effect is the other force. Stack effect is caused by the air temperature difference between inside air and outside air. There is high pressure on the home during cold weather (wind and stack effect) and very little during warm weather (only wind). Devices like your clothes drier, bath fans, and air handlers also create pressures that cause fresh air to enter your home.
Most old homes leak excessively during cold, dry weather and not enough the cool, humid part of the year. You may benefit from fresh air during the "none heating", windless time of the year. You need fresh air especially, when your air handler is not operating and wind is not blowing. Using you large air handler to provide a small amount of fresh air is especially inefficient.
Using a small 100 watt fan to blend/filter a small amount of fresh air into a home when occupied is good idea. Devices like Filter-Vent are made to do this. In green grass climates, humidity in a non-ventilated home is high already during the cool damp time of the year. The necessary fresh air raises indoor humidity even higher. Many are finding the ventilating dehumidifier the ideal device to maintain low humidity with or without make-up fresh air. Honeywell, Therma-Stor, Aprilaire, and Lennox are distributing these devices. You get fresh air (very healthy) and <50%RH (very comfortable). By keeping a home drier, the t-stat can be set-up and be comfortable. The t-stat set-up off sets the cost of the benefical fresh air. (And here is way I got there) I work for T-S. Regards TBBear 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"