Question regarding ventilation system in Portland, NEW HOME...
I have been reading and searching on this forum as much as I possibly can, I am a total HVAC noob lol. My wife and I just bought our first house and it is the first house in our lives weve had that have a ventilation controller system. Its the AprilAire 8126. We have a gas furnace rated at 90 FMEU's or whatever the rating is. The 8126 is integrated into that.
It is a 2 story house, with crawlspace. It is roughly 1600 sq ft home,3 bedrooms, gas stove and gas fireplace. Brand new construction completed 9.21.09. It also has central AC. Its an energy effecient home.
My wife and I have never had gas furnace nor a ventilation controller. The builders supposedly configured it for defaults of our home.
I look and the dial that sets the ventilation time is set to 45mins! I sure hope the cycle time is every 3 hours or something cuz according to the manual 20mins every 1 hr is standard.
I have read the controllers manual and understand for the most part how it operates and whats conditions in operation are, but dont have any idea how that plays into our environment and indoor house conditions.
I am confused tho, and winter is fast coming up. If this thing ventilates air while we are trying to keep the house warm in winter, wont all that heat energy go to waste because this thing is letting in cold fresh air??
Or does the controller take into account the heater running and considers that "ventilation time" and therefore will not ventilate?
I am also confused about RH and dewpoint and all that stuff when it comes to indoors vs outdoor air mixture and how that all changes with the ventilator.
I know the ventilator reads indoor RH and somehow compares that with outdoor temperatures...but in the case above? would bringing in the cold air cause indoor RH to go above 55%?(the controllers indoor RH cutoff) and therefore not run anyways? Or, does the outdoor temp really not matter and it has to do with dewpoint, therefore the controller only looking at outdoor temp...doesnt really know what will happen? It decides to run anyways and causes our house to get bad humidity, etc...
I just dont know what the best setting is for this device and whether it will waste our energy during the winter...or cause mold / mildew problems...
So, Im asking if anyone would be willing to maybe educate me a bit and suggest best settings for this ventilator?
I would guess the 45 min setting is excessive.
Keep in mind, the purpose is to allow enough fresh air to maintain indoor air quality. On a leaky house this happens by natural infiltration. Some current homes are built tight enough that they require fresh air, as may be your case. Therefore, you should not be concerned about wasting energy because of letting in cold air. If set correctly, the damper will only allow as much as required. This quantity is determined by ASHRAE and explained in your manual.
The timer controls how long and how often the damper will open. If the blower happens to be running when it is time for fresh air, the damper simply opens to let it in. If the blower is not running, it will start when the damper opens. If the blower needs to continue running longer than the damper timer thinks is necessary, then the damper will close and cut off the fresh air even though the blower is still operating.
Depending on how your system is set up, the damper may not operate if the outside temperature is too cold or too humid. In Portland (Or?) you are lucky that it is rarely either of these things. Especially in winter. Cold air holds less moisture than warm air. So cold air coming in will tend to dry a house out when it gets warmed up, the opposite of what would cause mold.
I've had some questions about this product as well (search for my posts), and this site seems to have little feedback on it. From my experience, I would recommend setting the timer to be frequent (1 hour) and short (10 minutes).
Here is why:
1. If it is just the two of you, you'll need a bit less air than the ASHRAE says.
2. You probably have enough natural leakage to account for a significant portion of the required air.
3. If you run fresh air frequently you are more likely to have the damper open while you have an exhaust fan or clothes dryer running which will pull more air than the chart shows in the manual.
4. Running short periods of time will ensure that you're not overventilating. You can easily increase if you notice discomfort (I promise you will not suffocate).
Most important for controlling moisture is to run bath fans properly. Your new ones should be 80 cfm (notice this is more than the whole house needs). I'd say if you see condensation happening it is because of innadequate exhausting. Your bath fans should have timers so you can let them run after you leave, although I've seen lots of builders not using them. If this is the case I'd ask him to put them in: cite Oregon Residential Specialty Code M1507.4.
Homes breath at varible rates depending on the inside/outside temperture differentials, wind velocity, and the size/location of building imperfections. During the cooling season, your home needs an air change of fresh air every 4-6 hours when the home is occupied. During the coldest windy weather, you may not need any fresh air because of the extra natural infiltration. The time on off means little without the volume of the home and the volume of the mechanical/natural fresh air movement. Typically 70 cfm of fresh when the home is occupied is ok. Monitoring the CO2 levels in a home when occpied will provide information on the real air change rate of the home. Ventilating a home when it is unoccupied mechanical fresh air venitlation is not needed. Dry inside during cold weather is a sign of ample fresh air. Wet inside during high dew point outside weather is a sign of ample fresh air. Supplemental dehumidification is needed in green grass climates during high outdoor dew points and low/no cooling load. There is a lot of misinformation about fresh air ventilation. Keep us posted. Regards TB
Originally Posted by GenTarkin
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"
Pay close attention to what TB said about when to ventilate. Try to find a way to connect your ventilation system to your programmable thermostat so that the damper controller only operates during the time you are active in the home. Using mechanical ventilation while you are sleeping should be a personal comfort setting. Your home will have more natural infiltration with a greater difference between indoor and outdoor temperatures. There is no reason to ventilate while you are away and then have to pay to heat, cool or dehumidify the fresh air. Of course that is subject to any hobbies you may have that uses high VOC paint or adhesives that will be curing during your away time needing some fresh air to dilute things before you come back home.