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If you have a home with an air-tight system done extremely well then bringing in a small amount of outside air directly to the unit to be conditioned at the coils should be absolutely no problem at all, even on a "design day" of high heat and high RH. It's actually a MUCH better way to do it.
Consider these two scenarios:
1) A normal house that has appreciable leakage. No controlled, direct-outside air ventilation is needed because the inherent leakiness off the house provides enough infiltration
2) A house that is built as air tight as possible with minimal leakage. Fresh outdoor air (let's assume at the same rate as scenario #1) is taken in through a controlled outside air intake directly through a filter and into the AHU serving the house.
As an HVAC Engineer, I would take #2 every time.
Scenario #1 creates a lot of problems. If you're going to have fresh outside air in your house anyway, you would MUCH rather bring it directly into your AHU, filter it and condition it before it enters the living area of the home which is what Scenario #2 lets you do. Scenario #1 just lets it leak into your house wherever, causing extra condensation on building components in the summer, extra humidity in the space, drafts in the winter, increased chances of mold, more chance of rapid temperature swings in the space, and an actual possible increase in heating/cooling capacities of your units to keep the space comfortable and controlled. Additionally, a house with a lot of leakage is more subject to wind and external pressure changes in terms of comfort and drafts in the house.
Scenario #2, when combined with a low-leakage house and a properly sized HVAC system can reduce or improve all of those.
Yes, you need fresh air in any occupiable building. But, given the choice between natural leakage and controlled outside air ventilation, imo you always want to build an air-tight envelope and then mechanically or naturally bring outside air in to the building in a CONTROLLED manner that is both filtered and conditioned before entering the occupied space. Of course this is a little more expensive and requires a little more thought so most contractors and homeowners don't opt to do it.
If you have a home with an air-tight system done extremely well then bringing in a small amount of outside air directly to the unit to be conditioned at the coils should be absolutely no problem at all, even on a "design day" of high heat and high RH. It's actually a MUCH better way to do it.
Consider these two scenarios:
1) A normal house that has appreciable leakage. No controlled, direct-outside air ventilation is needed because the inherent leakiness off the house provides enough infiltration
2) A house that is built as air tight as possible with minimal leakage. Fresh outdoor air (let's assume at the same rate as scenario #1) is taken in through a controlled outside air intake directly through a filter and into the AHU serving the house.
As an HVAC Engineer, I would take #2 every time.
Scenario #1 creates a lot of problems. If you're going to have fresh outside air in your house anyway, you would MUCH rather bring it directly into your AHU, filter it and condition it before it enters the living area of the home which is what Scenario #2 lets you do. Scenario #1 just lets it leak into your house wherever, causing extra condensation on building components in the summer, extra humidity in the space, drafts in the winter, increased chances of mold, more chance of rapid temperature swings in the space, and an actual possible increase in heating/cooling capacities of your units to keep the space comfortable and controlled. Additionally, a house with a lot of leakage is more subject to wind and external pressure changes in terms of comfort and drafts in the house.
Scenario #2, when combined with a low-leakage house and a properly sized HVAC system can reduce or improve all of those.
Yes, you need fresh air in any occupiable building. But, given the choice between natural leakage and controlled outside air ventilation, imo you always want to build an air-tight envelope and then mechanically or naturally bring outside air in to the building in a CONTROLLED manner that is both filtered and conditioned before entering the occupied space. Of course this is a little more expensive and requires a little more thought so most contractors and homeowners don't opt to do it.
I just found this trail which begins back in 2012. I am having this problem too. You sound like you know what you're talking about from everything I've read and researched. I am so upset that I bought a house that I can't breath in. My son and I are constantly having asthma attacks inside, but as soon as we step outside we are fine.
This might be more appropriate in one of the Florida forums, but figured I'd ask here first. I just found out my HVAC systems (two zones - two air handlers) are closed off from the outside. There is no external venting or air intake connected to the system to bring fresh air inside the home. Only thing we have vented to the outside is our dryer vent and bathroom fans - but those aren't connected to our HVAC system.
Is this normal in high heat and humidity areas of the country? Our AC rep says the HVAC is closed off from the outside to prevent humidity, mold spores, dust etc. from getting into the house. I can see his point, but it doesn't make sense to me that we just keep recirculating the same air over and over again. Colds and fevers from one familiy member quickly make their way to others and we're constantly getting sick. I'd think recirculating the same air can't be any good. Anyone ever deal with this? How do you get fresh air while maintaining a clean, cool, low humidity house?
This post is very old, but I found it when I googled "do all homes have outside air intake" and your post came up. I am having the exact same problem. Just moved from NY to Florida into a "tight house" and I've been told my asthma is from my home being so air tight because as soon as I step outside, I am fine.
I was wondering how did it turn out for your situation. Was it resolved and what did you do? Maybe it will help me going forward.
I would get rid of the system described above ASAP...
Anything that cannot be cleaned / does not rely on a HEPA type stack of filters sounds like a disaster waiting to happen. Mineral glass won't support mold growth when new, but as layers of organic material are deposited on it (and flowing air creates an unstoppable static charge that will attract more and more pollen / spores / dust ) all you need is some moisture (even dry climates will have dew early in the day...) and this is going to be a breeding ground of every kind of airborne contamination.
Location: Central Atlantic Region, though consults worldwide
266 posts, read 450,103 times
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Quote:
Originally Posted by SXN
This might be more appropriate in one of the Florida forums, but figured I'd ask here first. I just found out my HVAC systems (two zones - two air handlers) are closed off from the outside. There is no external venting or air intake connected to the system to bring fresh air inside the home. Only thing we have vented to the outside is our dryer vent and bathroom fans - but those aren't connected to our HVAC system.
Is this normal in high heat and humidity areas of the country? Our AC rep says the HVAC is closed off from the outside to prevent humidity, mold spores, dust etc. from getting into the house. I can see his point, but it doesn't make sense to me that we just keep recirculating the same air over and over again. Colds and fevers from one familiy member quickly make their way to others and we're constantly getting sick. I'd think recirculating the same air can't be any good. Anyone ever deal with this? How do you get fresh air while maintaining a clean, cool, low humidity house?
Don't think your home is so tight that it does not leak air like a screen door. A bower door test will tell you the air volume exchange rate in terms of air volume/hour.
If you have a leaky house ot want fresh air I recommend Sterming's fresh air heat revocery ventilators (HRV).
And no, outduur air (intake or exhausr) are not common to home systems. Especially, not in Florida.
On the other hand, I do include such systems in my upscale configurations. HRVs & ERVs do a fantastic job of capturing otherwise lost heat caused by venting operations.
Your bath fans such air from the house to create a negative pressure inside. Small leaks throughout the home permit air pressure inside the house to normalize even pressure. The pressure difference is very small.
Location: Central Atlantic Region, though consults worldwide
266 posts, read 450,103 times
Reputation: 95
That's Sterling heat revocery ventilators. In Florida you should have the energy recovery ventilatior. The difference between the HRV and ERV is that the HRV does not revover latent heat. Latent deals with heat contained within moisture of tempered air.
The health concerns you describe are minor compared to the potential health problems that could occur with recovery air from the exterior of the home- or so they say.
I believe that exposure can be good in the sense that it keeps the immune system working vigorously. If we continuely remove "bugs" from our environment, we weaken our system and cater to the more resistant strains of "bugs".
But from the energy standpoint, I see no immediately viable alternative.
An architect friend of mine said at one time all federal office buildings were to be 100% fresh air supply for heating and cooling. Can you imagine what that would cost? It's almost as if they are not spending their own money. I hope the spec has changed.
You're missing a significant hazard from recirculating the same air... CO2 buildup. Without ventilation the level will just continuously rise.
The research indicates a drop in tests, be interesting to see how much. That is not a health hazard. CO2 becomes a health hazard at much higher concentrations than being discussed in that article. Thousands of times higher.
I can understand what you are saying but bringing fresh air into a building constantly is going to require enormous amounts of energy.
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I would get rid of the system described above ASAP...
