Fresh air

[jl1]

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:D ) 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.

[trey r]

Energy recovery ventilator ,Lennox makes a great one, I love em.

[Shophound]

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.

[jl1]

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.

[trey r]

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.

[teddy bear]

[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

[cem-bsee]

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.

[jl1]

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:confused: :D . 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:D ) 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 :D . 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:confused: . 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.

[pstu]

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

[jl1]

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 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.

[AIR PRO]

http://www.hvac-talk.com/vbb/showthread.php?threadid=34033

[Xavier]

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! :) :)

[teddy bear]

Real indoor air quality is about providing fresh air when the home is occupied. IAQ has nothing to do limiting fresh air to when outside air is dry. Wet for a week or a month so we don't ventilate?

Single hose ventilation- Homes have exfiltration and infiltration. Cold weather causes the stack effect = exf/inf. Wind causes = exf/inf. These vary due to conditions and location of leaks in the home. The extremes are from 200-0 cfm. Add the use of a clothes drier, bath fans, gas water heater, and kitchen hood exhausting 50-100 cfm. Any hint of condensation when the stack effect is strongest indicates a lack of fresh air. Remember most of the moisture is exiting the home through the exfiltration leaks. The exfiltrating dew point is high with danger of condensing in the structure. Introducing an additional 50-75 cfm of make-up fresh air increases the exflitration and decreases the infiltration. The moisture content (dew point) decreases, eliminating the danger of condensation in the structure. The "single hose" effect of introducing enough fresh air to purge all indoor pollutants including the moisture should be maintain when the home is occupied throughout the year. For the periods of time when the inside moisture levels exceed 50%RH, supplemental dehumidification is a logical solution. Over the last fifteen years, neat equipment has been developed that introduces specific amounts of fresh air when the home is occupied, blends, filters, and dries the home when damp. They are called "ventilating dehumidifiers". This is about health, comfort, and not about ventilating when the weather is acceptable. The Dehu TB

[jl1]

So would it be an acceptable idea of adding an automated small damper(4" maybe 6") to the return side and have some kind of control setup that would allow it to be open when the system runs? Providing the temps aren't too high or low outside or the humidity too high. My house isn't real tight despite my best efforts to make it that way so I feel the infiltration will get out without too much difficulty.

[teddy bear]

So would it be an acceptable idea of adding an automated small damper(4" maybe 6") to the return side and have some kind of control setup that would allow it to be open when the system runs? Providing the temps aren't too high or low outside or the humidity too high. My house isn't real tight despite my best efforts to make it that way so I feel the infiltration will get out without too much difficulty.
Using a damper in the make-up air duct connected to the return is OK. If your windows sweat during cold weather, you need 50-75cfm fresh air when the home occupied. The penalty of ventilating when hot, cold, or damp is $100-$200 per year. You will end up needing supplemental dehumidification. But fresh air is a start. The dehu TB

[propmanage]

:) http://www.venmarces.com/

[pstu]

:) http://www.venmarces.com/
The Venmar sounds like a quality product but I question how much good it can do in a South Carolina environment, or a more hot-humid one like my own. If your goal is the ne plus ultra of energy efficiency and cost is no object, then of course you would want one. AND a ventilating dehumidifier. AND an economizer system which manipulates indoor humidity and temperature based on outdoor dewpoint and temperature. But nobody can really afford all, they must pick what gives the best payoff for the money.

The duct from outdoors to return plenum is probably the cheapest thing to consider, and automation could consist of only a mechanized damper -- not even a sensor if you want to go cheap. In some rare cool dry days, you can improve inside conditions with it. If you don't mind watching outside dewpoint (or relative humidity with some temperature calculations) I suggest a simple timer could keep it open for your desired period of time.

But most of the summer, it seems clear to me that duct will add humidity to your house if open. It may be worth it on the basis of fresh air intake, but I do believe your humidity will rise a bit inside. Unless your house is really tight, you probably will not get enough CFM intake to significantly affect your house pressurization, or your infiltration.

A ventilating dehumidifier is the more certain solution to provide both fresh air and humidity control. While the above duct would pass outside air through your AC and provide that level of conditioning and humidity control... the ventilating dehu will lessen the load on your AC, not increase it. Of course it will consume some energy itself, that is your price to pay. But it *will* deliver the results I think you want.

An ERV I submit is a lot of money for not much results, in a hot-humid climate. It will lessen the load on the AC compared to just a duct, but it will still be increased compared to nothing. It will do only a partial job of transferring humidity between the incoming and outgoing air streams. There is the sweet idea of "neutral house pressure" which I believe is a deceptive illusion in a cooling climate. One: you normally will be better off with a positive pressure (not forgetting in a loose house this will be insignifigant). Two: with wind effects and stack effect, I submit your overall infiltration will not be anywhere close to zero. So the goal of "balanced ventilation" I think is inferior for SC summer at least, to the goal of "supply only ventilation".

For this reason I think the ERV may not be cost effective in a hot-humid climate.

Hope this helps -- Pstu

[jl1]

The unit prices I've seen on ERV's are enough to know my cheap rear doesn't want it :D . I believe in the KISS principle(keep it simple stupid):D . I have looked at the Honeywell automated damper systems. Cheap and simple. Would take a little monioring on my part but so does opening a window. Still not sure about the ventilating dehu. But there again is cost. Seems almost as much as an ERV setup. SC winters are fairly cold(to me) and dry for the most part. Summers are a yoyo. Temps ranging from mid 80's to 100 and humidity from 50% to 90%. Strange thing is though late in the day when temps are around 95ish I have seen humidity levels as low as 40%. Never know one year to the next. I always figured the kids ventilated the house enough in summer as many doors as they open. I will continue to research. Thanks.

[pstu]

>>...when temps are around 95ish I have seen humidity levels as low as 40&#37;

That is probably not as dry as you think. You certainly would not want that much humidity inside your home. When that air is cooled to room temperature the RH% will be way too high for comfort.

My own summer goal is 77F and 50% inside. That is dewpoint of 57 degrees. If you pull in 95F air at 28% RH, that will become 50% RH when cooled to 77F -- the dewpoint is the same at 57 degrees. Watch the dewpoint to know when air is too humid or dry, not the RH% if it is at a different temperature.

Here is a chart I made using a psychrometric calculator from this link:
http://www.envirochex.com/psychro.htm

60F, 90% RH is 57 dewpoint.
70F, 63% RH is 57 dewpoint.
77F, 50% RH is 57 dewpoint.
85F, 39% RH is 57 dewpoint.
95F, 28% RH is 57 dewpoint.

Any higher RH for a given temperature, and I know that opening a window will give me higher indoor humidity than I want. Only rarely does the air in S.Texas meet my humidity requirement when it is above 70F.

Hope this helps -- Pstu