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Thread: Fresh air

  1. #1
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    Fresh air

    Is there a system that will draw fresh air into the HVAC system when humidity levels are low, ie. under 40-45%? I realize it if tied into the return system it would have to have it's own filter. Are there any moderately( ie. wife says I'm a tightwad ) priced systems out there? I have thought of a simple damper system but that would take too much monitering on my part as far as temps and humidity levels. What I was thinking is something thats automated and is a stand alone type setup. I know $$ can't be given but what kind of dollar range would I be looking at(email me). Not looking for a quote but a range to shoot for on saving some money up to get it done.

  2. #2
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    Energy recovery ventilator ,Lennox makes a great one, I love em.
    Those who restrain desire do so because theirs is weak enough to be restrained. (William Blake)

  3. #3
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    What you want is what we in the commercial HVAC sector call an "economizer" aka "free cooling". It is more or less a damper tied to an actuator that responds to favorable outdoor air conditions of temperature and humidity (known as "enthalpy control"). It is not commonly installed in residential applications due to expense and the partial run times of residential HVAC equipment. But it can be done. It just won't be bargain basement cheap.

    But, as another mentioned, ERV's are a viable choice for residential.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
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  4. #4
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    Quote Originally Posted by shophound View Post
    It just won't be bargain basement cheap.

    But, as another mentioned, ERV's are a viable choice for residential.
    Ok that's out. Suggestions in what to look for, brand sizing, etc, in an ERV system. What questions should I ask a contractor when shopping for a system? And is this a good idea for the SE US climate? Meanwhile I'm going to do some reading about ERV's. Thanks.

  5. #5
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    The more your willing to spend the better features you will get Enthalpy sensors, Multispeed fans, dehumidification, better filtration, etc.

    They can be attached to your existing system if room is available or separate ducts can be run. You will have 4 ducts return, 1 from living space to ERV, 1 from ERV exhausted to outside, 1 fresh air from outside to ERV, and 1 from ERV fresh introduced into the living space.

    Though these installs are not terribly difficult, they are not cheap. If you are seriously considering this install pay more get a higher quality system.

    Yes they work fine in this area I'm from N.C. just outside of Charlotte, Installed many and they work great.
    Those who restrain desire do so because theirs is weak enough to be restrained. (William Blake)

  6. #6
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    [QUOTE=jl1;1386514]Is there a system that will draw fresh air into the HVAC system when humidity levels are low, ie. under 40-45%? QUOTE]

    Low dew point is the measure of moisture content, not %RH. 85^F, 45%RH is +75% RH at >75^F. Besides you need fresh air when occupied or when exhaust devices operate. A better strategy is to bring in 50-75 cfm when the home is occupied. This will purge pollutants and renew oxygen only when needed. During cold weather, 75%RH will keep your home dry because of low dew point. During hot weather, you a/c will remove the excess moisture in the fresh air. In green grass climates, a good dehumidifier in needed to keep the home <50% RH during low/no cooling load conditions with high outdoor dew points. You also have the make-up air necessary to operate the clothes drier, bath fans, and kitchen hood. This is a simple method of maintaining a healthy, comfortabe indoor conditions. There are systems that put this all in one package. Honeywell, Ultra-Aire, Santa Fe, and Aprilaire some of the suppliers of ventilating dehumidifiers. Independent dehumidification also allows using t-stat temp setup when the home is unoccupied while maintaining low indoor %RH. Turning of the a/c when a home unoccupied for an extended time will save a lot of energy. The Dehu TB

  7. #7
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    low dew point = large difference between normally quoted temp which is dry bulb
    and the now additional quoted dew point temp= wet bulb.

    BUT, be sure that you have the spread | difference BEFORE you spend $$$. -- for most of the 24hours.

    read my thread on crawl vent <> here.
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  8. #8
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    Quote Originally Posted by teddy bear View Post
    Low dew point is the measure of moisture content, not &#37;RH. 85^F, 45%RH is +75% RH at >75^F. Besides you need fresh air when occupied or when exhaust devices operate. A better strategy is to bring in 50-75 cfm when the home is occupied. This will purge pollutants and renew oxygen only when needed.
    Thats kinda what I'm looking for. An automated window opener if you will . Right now winter time temps are up and down but humidity is relatively dry, around 25 to 35%. If I leave the house closed up. Inside humidity will stay between 50 and 60%. When it gets cold at night the windows will condensate. Now I don't understand some of this stuff but I know if I can drop the humidity some inside with some fresh air the problem will get somewhat better. I have checked out some of the ERV systems on the web and that's really not what I'm looking for. What I've been doing is turning on the system blower to circulate air , opening a few windows(nice outside today ) and running the 70cfm bathroom vent. Now this has helped a good bit with reducing the humidity but my kids are trained pretty good, they keep cutting it off . I guess what I want is a damper type setup with a dedicated filter that could open and close to draw fresh air into the system when weather outside is favorable. Something that monitor the outside humidity and open and close when necessary. Does something like this even exist or will I have to design it . Keep the ideas coming. Oh just looked on NOAA and temp here is 61F, humidity is 18% and dewpoint is 17F. Inside temp is 69f and humidity 38%, been running the redneck vent system most of the day.
    Last edited by jl1; 02-24-2007 at 03:18 PM. Reason: updated

  9. #9
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    I would like it if you would look over this product:
    http://www.smartvent.net/hiiq.htm

    It sounds like what the original poster asked for, I have collected literature on it but don't know how good it really is. If anyone has criticisms of this product I would like to hear it. Also if anyone knows of a better product to do the same thing, I need to hear that!

    Best wishes -- Pstu

  10. #10
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    That looks like it would do the job. Pretty close to what I'm looking for. Emailed them for more info. Not a lot of info on their website. Thanks pstu.

  11. #11
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    I did find this on the web-- http://www.aircycler.com/ . But there seems to be no monitoring of outside conditions other than temp. Doesn't keep a check on humidity. I suppose the way it's run the HVAC system would take care of some of the outside humidity. Just seems it would put an additional strain on the system.

  12. #12
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  13. #13
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    Hmm How the "House" works!

    Quote Originally Posted by jl1 View Post
    That looks like it would do the job. Pretty close to what I'm looking for. Emailed them for more info. Not a lot of info on their website. Thanks pstu.



    Jl1, I too have reviewed their site and could not find much data. When you get more information please post it or send it to me for my records.

    Question for all those one hose “intermittent” devices out there that I have read about for the past 25 years; I have never found a home that only requires outside air to enter “intermittently” so what does the house do when they are off?. Another concern I have with one hose systems is where and how does the additional outside air leave the home, because lately there have been more “experts” agreeing that positive pressure is not recommended in residential homes in all climates. Therefore, ‘in my expert opinion” if you use a one hose system, you will only get “part-time” control of your Indoor Air Quality & Quantity, and remember, an ERV/HRV do not add air to the building!

    Therefore, jl1 continue your research on the best way to balance the air demands in your home.

    Editorial: Lately there have been many more posters, city inspectors and experts agreeing with my understanding of how a home works (but some still won't admit it); perhaps the world is not flat after all and an open window may be a good thing!
    The quality of my performance, sometimes depends on the quality of my audience.
    Imitation (Plagiarism) is the best compliment one can get -- "Open A Window"

    To improve Indoor Air Quality: Control Indoor Air QUANTITY = "I.A.Q.Q."

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