How much "Fresh" air?

[TConnors]

I have a Thermostor Sante Fe dehumidifier, with a 6" duct going into it from outdoors. I've decided to remove it from the Sante Fe and duct it straight into a room (right near the main AC return). I also have a small 5"x10" Hepa filter on the outside grill. I am going to put a fan in the 6" duct, but all I can find is 160 CFM models. Can I assume with a Hepa filter, this volume will be cut considerably?

I am doing this because I only run my Dehumidifier fan when its compressor runs, this cuts down compressor run time 75%. It also has real bad DSS if the fan is blowing after the compressor shuts off.

I think I can control the fresh air flow rate much better this way. I am concerned about 160 CFM, and also want to make sure that a fan inside a duct can tolerate the humidity that will be passing over it. Does this sound like a good idea?

[teddy bear]

Two possibilities. Choke the fan with a damper to get the flow you want. The other way is to place a tee inside the home with one side connected to the outside filter and the other side connected to the home. With dampers get the mixture of outside/inside air to avoid condensation in any of the ducts. The air output of the blower could discharge into the a/c ducts. Any cooling coil allowed to set wet for days has potiential for for growing biologicals. TB

[core]

Originally posted by TConnors

I think I can control the fresh air flow rate much better this way. I am concerned about 160 CFM, and also want to make sure that a fan inside a duct can tolerate the humidity that will be passing over it. Does this sound like a good idea?


Keep in mind that you will only get 160 CFM at a predetermined system pressure drop. Since you don’t know how restrictive your duct is there is no way of knowing what the final CFM value is. So basically as your filter loads up with particles the CFM output will change based on drop. The manufacturer will supply a fan performance chart based on resistance.

Also let me ask you this Why do you want ventilation? Many people are under the impression that ventilation is needed to prevent mold growth. If this where true then dry climates would need zero ventilation.

A superior ventilation system would be one that is operated with a control input from a CO2 sensor and not one that just has a outdoor air grill, the latter is a true waste of energy.

Core

[TConnors]

I keep reading (here and elsewhere) that outdoor ventilation of 50 cfm is good for IAQ on tight houses. I have DSS in both my humidifier and A/C coils, and it doesn't matter how well their cleaned it just comes back in less than a month. "Fresh air" seems to be the only thing that helps house odors - although on high pollen days outdoor odors prevail. I do have a Hepa filter on the outdoor vent, so I assume pollen/mold is not entering the house, and with positive pressure, that reduces any infiltration.

I do believe it's wasting energy on 100 degree, 95% humidity days, or 32 degree days... but not sure what the best balance of IAQ and energy cost is.... I would guess a 160 cfm fan with a Merv 14 HEPA filter, will probably suck less than 50 cfm, and I can always reduce the 5"x10", or add a "T".

[teddy bear]

Originally posted by core

Originally posted by TConnors

I think I can control the fresh air flow rate much better this way. I am concerned about 160 CFM, and also want to make sure that a fan inside a duct can tolerate the humidity that will be passing over it. Does this sound like a good idea?


Keep in mind that you will only get 160 CFM at a predetermined system pressure drop. Since you don’t know how restrictive your duct is there is no way of knowing what the final CFM value is. So basically as your filter loads up with particles the CFM output will change based on drop. The manufacturer will supply a fan performance chart based on resistance.

Also let me ask you this Why do you want ventilation? Many people are under the impression that ventilation is needed to prevent mold growth. If this where true then dry climates would need zero ventilation.

A superior ventilation system would be one that is operated with a control input from a CO2 sensor and not one that just has a outdoor air grill, the latter is a true waste of energy.

Core

The main role of fresh air ventilation is to purge indoor pollutants. One person in a large home may never trigger high co2 but require purging indoor pollutants. Maintaining <50%RH and avoiding moisture condensation on cool surfaces controls mold and dust mites. The tube fans are high pressure and flat curve devices. Check http://thermastor.com/pdf/continental.pdf for air flow at various pressures. You will need restriction or tee for 50-75 cfm. TB

[core]

Originally posted by TConnors

The main role of fresh air ventilation is to purge indoor pollutants. One person in a large home may never trigger high co2 but require purging indoor pollutants. Maintaining <50%RH and avoiding moisture condensation on cool surfaces controls mold and dust mites. The tube fans are high pressure and flat curve devices. Check http://thermastor.com/pdf/continental.pdf for air flow at various pressures. You will need restriction or tee for 50-75 cfm. TB


Unfortunately you are incorrect. Ventilation is not designed nor should be designed to purge anything. Ventilation is needed to replace what has been exhausted.

Proper ventilation rates or air changes can only be achieved when an equal amount of air is exhausted via mechanical fan or other means. The so called “tight house syndrome” is produced mainly by interior exhaust fans that remove more air then natural infiltration can replace.

Of course 1 person can’t and may never trigger a CO2 sensor trip point, but then again when was the last time one person was able to contaminate a house full of air? Wouldn’t you agree that opening and closing an outside door a couple times a day would provide enough air for one person?


Core

[teddy bear]

Originally posted by core

Unfortunately you are incorrect. Ventilation is not designed nor should be designed to purge anything. Ventilation is needed to replace what has been exhausted.

Proper ventilation rates or air changes can only be achieved when an equal amount of air is exhausted via mechanical fan or other means. The so called “tight house syndrome” is produced mainly by interior exhaust fans that remove more air then natural infiltration can replace.

Of course 1 person can’t and may never trigger a CO2 sensor trip point, but then again when was the last time one person was able to contaminate a house full of air? Wouldn’t you agree that opening and closing an outside door a couple times a day would provide enough air for one person?
Core

A fan introducing 50-75 cfm of fresh air will change the air in the home without any exhaust fan. There are plenty of small leaks in a tight home to provide exit paths. Also bath fans, kitchen hood, and clothes drier have needs and leakage for make-up air. The pollutants that need to be purged are not necessarily from the occupants but also from home materials/furnishings. Depending on opening doors for fresh air and wind provides an inconsistant level of ventilation. Consistant controled ventilation rates inexpensive and overcome the variables of weather and activities. Monitoring pollutants in a home proves the point. In the past, I shared most of you opinions. I also was called to task for many of your issues. Most homes leak enough and most people are not sensitive to some of these problems. But to provide the ideal indoor air quality, controled fresh, clean air ventilation, <50%RH, +Merv 11 air filter are basic. Best not left to chance. TB

[core]

Hello Teddy

When I spoke of “other means” of exhaust this was referring to bathroom, and kitchen exhaust fans.

What do you mean when you said this Consistant controled ventilation rates inexpensive and overcome the variables of weather and activities.??

Also it is my opinion, and perhaps others on this site that “constant ventilation air” is and outdated and old way of thinking, this is not to belittle anyone but just to show that there is a trend moving in a different direction.


Tconners Have you tried to get rid of the DSS?

Core

[pstu]

I am a homeowner and here is my perspective. Smells are one thing which I would think would be dissipated by constant ventilation (in my climate, supply preferred). Suppose one cooks up a pan full of bacon, and for whatever reason neglects to run the range hood enough to suck all the cooking odor out. People don't always do the right thing in the first place, this helps fix the problem. I do experience this in my own house and wonder how it would be if a fresh air system were in place.

Fart fans are good, but sometimes they don't get used. We have a couple of dogs, thank goodness they aren't farters but what if they were? Sometimes a dog carries a certain odor which is normal and natural, but it's not exactly the fresh smell of outdoors.

People burning candles. Is that hopeless? I know people would be healthier and cleaner not do do it, but perhaps a FA ventilation system could help clean up after their sins. And of course the chemical whatnot that exists when one buys a new piece of furniture -- I don't even know what's present when materials offgas, not how much of a health threat it is. But I am reaonably confident that a FA system would expend a little energy and make the air cleaner.

Are these valid reasons to have a FA system? Personally I really want one and am planning to install one as soon as I can figure out *what* to do. While I have considered an ERV which would address all the above needs, I have misgivings whether the initial cost would ever be offset by energy savings in a hot-humid climate. A supply only system seems attractive, perhaps with dewpoint sensors to boost airflow when psychrometrics (heat and humidity) are favorable. If such controls turned it off during the height of heat and humidity, would it be any worse than no system at all? I kinda think it might be satisfactory.

Hope this helps -- Pstu

[TConnors]

Core: Got a solution for getting rid of DSS?

Sometimes the "cure" for mold (ie: a good dehumidifier to keep the house at 50%rh), can lead to worse mold and worse odors. My Sante Fe looked like a petrie dish after 3 months operation, black and white mold all over the stainless steel inside it. So the Merv 11 filter on it does nothing, since the fan just blows all that internal mold all over the house!

And "fresh air"? You need fresh air outdoors to start with! Here in Austin the pollen/mold count is almost always "high", and I'm in a woodded area, so moldly odors (and passer by skunks) don't help with that "fresh air" getting sucked into the house. But I do believe it must be fresher than the air in a sealed house.

Doesn't seem to matter how well I clean my coil or my dehumidifier, DSS comes back in a few weeks (or less). I had DSS 2 weeks after they installed a new AC with new ductwork! I think it's just my location. In the woods surrounded by cedar trees, near a lake surrounded by humidity... the odors walking OUT of my house are actually worse than the ones inside!

Also doesn't help when temperatures here go from 45 to 85 to 35 to 85 in the same week. AC just goes from heating to cooling to heating to cooling... seems to be when DSS is worst.

I actually found that misting in front of the return (AC and dehumidifier) with "Oust" for a couple minutes a week helps DSS more than anything!

[core]

Maybe I missed something. Do you have a central A/C system?

Core

[TConnors]

The AC has central AH is on 1st floor, feeding 3 levels of a 2300' house (Carrier 3 ton 2 speed). The SanteFe dehumidifier is on the 1st floor, with an outdoor return and a second floor return, with supplies in 2 rooms on 1st floor, it does a good job keeping humidity at 50% or below.

Central AC (coils) is main source or DSS, has been for 15 years. I replaced original AC because it was old and full of mold, with a Carrier single speed 4 Ton. It grew mold in the coil and ducts, so after 6 years I replaced it (and ducts) with a 3 Ton 2 speed, which seems to be doing better, but still has DSS. Has Merv-11 5" filter. I've pretty much learned to live with it... just looking for that "ultimate" cure... I guess that would be to move.

[core]

http://www.cannonwater.com/Products/condensation_pan_pads.html

The product above is what I have been using in the commercial field for years.

Check it out and call the company to see if its a possible cure for you.

I can say it has done wonders for me on commercial equipment.

good luck.

ALSO check out the MSDS sheet on it first.

Core

[teddy bear]

Originally posted by TConnors
I have a Thermostor Sante Fe dehumidifier, with a 6" duct going into it from outdoors.
I would like to test a new unit through the summer in your home and examine for growth. Have modifications that may eliminate any biological growth in the cooling coil. Call or email for details. TB

[Carnak]

That's putting your money where your mouth is teddy. Who-Rahh!!!

[kmills]

on this thread i hear mold mold mold... and no one even brings up UV lights? or the cause in the first place? every really bad coil i come across is usually a restricted return. either the duct collapsed or a forgotten filter. fresh air just brings in more humidity for that mold to thrive on... unless you need make up air for gas fired appliances, or have too much neg. pressure (from exhaust), seal that house up and get an electronic air cleaner for "smells"

[pstu]

Kmills, can you lead us to any published papers which verify that UV lights are effective against mold? Unfortunately I have heard very severe criticism of them on Hvac-Talk and tend to believe it.

Here is what I have learned (or think I know): The basis for preventing mold growth is humidity, necessarily so. Here is why: To have mold you need mold spores, enough moisture for them to grow, and something to feed on. Since houses are made using wood and paper, there is always something to feed on. I am told there is ALWAYS mold spores present, there's nothing we can do to change that. So that leaves humidity which we can control, with some effort and the right tools.

Plus, every case study of mold catastrophe I have heard of, especially in Texas, involves excess moisture. Usually a water leak but occasionally humidity from the air.

I believe what you say about potential problems with restricted returns or defective ducts. You are right about fresh air adding humidity load, *except* when it is via ventilating dehumidifier then you pay a price in electricity to have it fresh and dry too. But humans require fresh air to breathe, ASHRAE 6.2 may not be the ultimate wisdom but our engineers have agreed on a minimum ventilation level. Smells may be killed by electronic gadgets but I don't believe that equals fresh air. Dilution via fresh air will eventually wash out toxins as well as smells. That's what I think is true, anyway.

That is the lesson that I have learned by my reading, if you can counter that then I will be a willing and respectful student.

Regards -- Pstu




[Edited by pstu on 03-07-2006 at 10:03 PM]

[kmills]

sorry no links to studies, but read up on it outside this website (CDC or EPA) and i think you'll find better advice than you can get here. when i first began to install them i was a sceptic and thought it was just another jar of snake oil to sell to people but doing research later i became a firm believer that while UV will never bring an indoor environment to a sterile condition, it can't help but improve the condition of the air. especially in a well sealed home, installed on the return side of a coil, the "kill zone" can get multiple passes and protect THE problem area the evap coil. the only reasons i can think of to bring fresh air into a residence is make up air for gas, or if you have too much neg. pressure from exhaust. other than that what is the reasoning? afraid of running out of oxygen? check the mail once a day and the front door opening will bring the "fresh air". the best thing you can do is seal those lil cracks in the home and ventilate the attic. this greatly reduces infiltration of latent heat/humidity and reduces load on the A/C saving you $$$

[TConnors]

The reason I see to bring in fresh air is to pressurize house so dust/mold/pollen doesn't get sucked into the house. If you have a wet coil producing 25,000 CFU/g of Cladosporium and aspergillus, and house occupants sneezing and coughing because of it, replacing that air will help a lot (as long as the fresh air goes through a Merv-11 or so filter).

I've been running my AC fan 24/7 for about 6 months now, and that helps a great deal. Running my dehumidifier 24/7 with 50 CFM fresh air also helps (as long as mold isn't growing in the dehumidifier). But I do see your logic, why bring in 95% humid air, just to have to dehumidify it, especially if it's 90 degrees or more outdoors!

I really can't say that anything works well when outdoor mold counts are in the high level 80% of the year. I'm on the fence on UV, but may try it out with the titanium strip to produce PCO. Killing what's on the coil will go a long way towards eliminating a mold growth source.

[kmills]

the topic of IAQ is a debate with so many variables from climate to climate, season to season, even person to person. but when you ask what you are trying to acheive, you can point a customer toward something that will fit a concern and a budget. in our battle for clean air, we have airborne dust, pollen, mold, fungus, viruses, bacteria and all the other things that can differ from house to house number of pets and occupants, carpets and furnishings that introduce airborne particles that contribute. what i tell my customers about IAQ is simple... get the best filtration system you can afford. which range from that cheapo throw away filter to electronic air cleaners. and as stated earlier it is practically IMPOSSIBLE to eliminate every single particle from your indoor air no matter what you do. but you can control it. fresh air doesnt remove or significantly displace airborne anything! in residential application unless you have a reason for it fresh air just doesn't make sense. i have two kids and they are in and out enough to bring in PLENTY of fresh air as it is... and then theres UV-C... will it make your home a completely mold/fungus/bacteria/virus free? nope but it sure will help. FACT: UV-C kills all of the above to some degree... dont let the skeptics give you the wrong idea about UV. IAQ is the problem that can ONLY be treated but NEVER completely "cured"

[core]

Originally posted by kmills
sorry no links to studies, but read up on it outside this website (CDC or EPA) and i think you'll find better advice than you can get here.

Just what exactly are you saying here?
Many people on this site have YEARS of field service work under there belt, and have tested the products under real conditions. Also many here are not selling a product.

Many websites that review a product also have a stake in selling it so they will make it sound great.

Your best advise WILL come from any of these forums.

Core

[kmills]

my response is actually another question... how many service techs and owners here have tested fresh air vs. no fresh air (res. application) in a controlled (laboratory) environment? how can years experience give you any clue at all whether a UV is killing airborne particles or fresh air is needed in a typical home? i never meant to imply that this is not a great site for information!

[teddy bear]

Originally posted by kmills
my response is actually another question... how many service techs and owners here have tested fresh air vs. no fresh air (res. application) in a controlled (laboratory) environment? how can years experience give you any clue at all whether a UV is killing airborne particles or fresh air is needed in a typical home? i never meant to imply that this is not a great site for information!
My expierence supports the idea that fresh is not the most critical issue. We had a client with 1,700 sqft. home with 9 occupants. The HMO reported a visit to the emergency room by a family member with a severe asthma attack every month. Testing showed heavy mold in the carpet on the slab and dust mites throughout the home. Air testing showed high humidity during wet weather. The carpet was removed, house thoroughly cleaned, fresh air ventilation added, and 100 pints of dehumidification was added. The %RH was monitored & maintained <50%. No asthma attacks the following year. The home was tested for mold and dust mites every quarter. On a visit the following year during routine testing, an air blockage in the fresh air inlet was found. No mold or dust mites or health problems were found. But the fresh air ventilation was restored. To me, this confirmed that maintaining <50%RH was the single most important point providing IAQ. Fresh air and air filtering are secondary.

I have used UV in some tuff applications. The most impressive was aging prime beef. It's a high humidity, cool temperature room with hanging beef for 2-4 weeks. Any area within 2 ft. of direct uv light was free of mold. The rest of space grew mold and needed regular cleaning. Research at Purdue showed the same type of results. To control mold growth in a duct/coil beyond direct light, high ozone was required. All positive, but regarding IAQ. Humidity control, fresh air, and good air filtering are my favorites. Keeping ducts/coils clean and dry are next. A good cold coil should wash itself flushing the spores down the drain. Duct/coils need a daily drying to prevent mold growth or UV? Maybe of benefit but way down the list, not the first thing to do. Oxidizing VOC to co2 and h2o is a dream. TB

[core]

Originally posted by kmills
my response is actually another question... how many service techs and owners here have tested fresh air vs. no fresh air (res. application) in a controlled (laboratory) environment? how can years experience give you any clue at all whether a UV is killing airborne particles or fresh air is needed in a typical home? i never meant to imply that this is not a great site for information!

Please read my first Post, I have also posted many times how constant fresh air in a home is not practicle.

Core

[kmills]

Originally posted by teddy bear

Originally posted by kmills
my response is actually another question... how many service techs and owners here have tested fresh air vs. no fresh air (res. application) in a controlled (laboratory) environment? how can years experience give you any clue at all whether a UV is killing airborne particles or fresh air is needed in a typical home? i never meant to imply that this is not a great site for information!
My expierence supports the idea that fresh is not the most critical issue. We had a client with 1,700 sqft. home with 9 occupants. The HMO reported a visit to the emergency room by a family member with a severe asthma attack every month. Testing showed heavy mold in the carpet on the slab and dust mites throughout the home. Air testing showed high humidity during wet weather. The carpet was removed, house thoroughly cleaned, fresh air ventilation added, and 100 pints of dehumidification was added. The %RH was monitored & maintained <50%. No asthma attacks the following year. The home was tested for mold and dust mites every quarter. On a visit the following year during routine testing, an air blockage in the fresh air inlet was found. No mold or dust mites or health problems were found. But the fresh air ventilation was restored. To me, this confirmed that maintaining <50%RH was the single most important point providing IAQ. Fresh air and air filtering are secondary.

I have used UV in some tuff applications. The most impressive was aging prime beef. It's a high humidity, cool temperature room with hanging beef for 2-4 weeks. Any area within 2 ft. of direct uv light was free of mold. The rest of space grew mold and needed regular cleaning. Research at Purdue showed the same type of results. To control mold growth in a duct/coil beyond direct light, high ozone was required. All positive, but regarding IAQ. Humidity control, fresh air, and good air filtering are my favorites. Keeping ducts/coils clean and dry are next. A good cold coil should wash itself flushing the spores down the drain. Duct/coils need a daily drying to prevent mold growth or UV? Maybe of benefit but way down the list, not the first thing to do. Oxidizing VOC to co2 and h2o is a dream. TB

BINGO! the response to the problem BECOMING THE PROBLEM! re: blockage in fresh air with dehumidifier= bigger problems and ask any service guy out there... you can barely get the average homeowner to change filters and maintain equipment as it is... this makes the SOLUTION part of the PROBLEM! on top of the added cost of fresh air/latent load... it all points away from fresh air..(in hot and humid environment)

[TConnors]

I was "surfing" today and came across this page:

http://eetd.lbl.gov/iep/2.html#2.5

Some interesting reading on many subjects talked about here. Much a bit technical, but a few good bits of info here and there. Especially getting into the bi-products of the PCO process... "food" for thought.

[kmills]

Originally posted by TConnors
I was "surfing" today and came across this page:

http://eetd.lbl.gov/iep/2.html#2.5

Some interesting reading on many subjects talked about here. Much a bit technical, but a few good bits of info here and there. Especially getting into the bi-products of the PCO process... "food" for thought.

the typical home is not a commercial building... applying them to residential is not a good idea unless you weigh the pros and cons..

[pstu]

A couple of times you have stated that evidence toward commercial buildings, is not useful toward residential buildings. I would think that info would be at least partially applicable. Or perhaps it would help a lot if you would point out some of the rules which are different for residential.

We are left with the impression that having rejected commercial guidelines, one is left with no rules for residential. I am sure your position is not that negative.

BTW I would accept simple "tradition" as a valid reason, with qualifications. There is a good logic to upholding traditions, at least they have been observed and the results proven over a long time. But when building tight structures, that is one way we have broken with tradition already and most people consider that a good thing.

Best wishes -- Pstu

[kmills]

Originally posted by pstu
A couple of times you have stated that evidence toward commercial buildings, is not useful toward residential buildings. I would think that info would be at least partially applicable. Or perhaps it would help a lot if you would point out some of the rules which are different for residential.

We are left with the impression that having rejected commercial guidelines, one is left with no rules for residential. I am sure your position is not that negative.

BTW I would accept simple "tradition" as a valid reason, with qualifications. There is a good logic to upholding traditions, at least they have been observed and the results proven over a long time. But when building tight structures, that is one way we have broken with tradition already and most people consider that a good thing.

Best wishes -- Pstu

i would say that all the basic principles apply to both and most if not all the advances in residential were borrowed from commercial practices. the main differences between the two are
1) commercial buildings are much tighter construction... fewer entrances and windows with greater indoor area... generally less natural ventilation
2) occupancy levels are much higher in commercial
3) commercial systems tend to be more complex and require more maintenance from the trained professional while residential systems are more basic and simple maintenance is usually handled by the homeowner

typically very different needs especially in the area of occupancy and tight construction... residential ventilation needs are addressed primarily by natural means but also from the things commonly found in a home... bath exhaust, kitchen exhaust, dryer exhaust, fresh air required for gas fired appliances etc. even tight residential construction is still providing places for infiltration that the average large building does not..

[teddy bear]

Originally posted by kmills

typically very different needs especially in the area of occupancy and tight construction... residential ventilation needs are addressed primarily by natural means but also from the things commonly found in a home... bath exhaust, kitchen exhaust, dryer exhaust, fresh air required for gas fired appliances etc. even tight residential construction is still providing places for infiltration that the average large building does not.. [/B]
In the past,typical homes had an air change every 1-2 hours during cold winter weather. The ventilation rate droped to and air change every 3-6 hours when the stack effect decline during summer. These leakers will do ok with natural ventilation. The heating/cooling cost were comparable.
To save 20-30% of conditioning cost, insulation and air tightning is occuring. The resulting homes are averaging to an ach every 3-10 hours during cold weather and almost nothing without the stack effect. The market place will settle the issue. Most home owners understand the problem and are willing to have a tight home with just enough fresh dry air througout the year. It's your option to explain that they do not need this or here's how I take of this. Thanks for the discussion. TB