Suggestions for New Construction in High Humidithy Area?

[unc99]

Hi, I'm building a new home in the Carolinas (ie, high humidity roughly half the year) and am looking for suggestions for a "whole house product" to improve air quality. This website has been a great find, but I still need a bit of guidance (I'm a layperson in this field). Here is what I was considering, but thanks to some information on this website, I've realized that solutions may not be as easy as they appear on the surface:

First, considered the IQ Air Perfect 16, but it doesn't pull in fresh air from outside. Then, considered a Venmar HEPA Air exchanger. I like this option (pulls in fresh air and cleans it with HEPA filters), but am concerned about running this in a high humidity area. In other words, I don't want to pull in more humid air in the spring and summer months and risk mold issues. Does anyone have any thoughts or suggestions? Is there a product that pulls in fresh air AND cleans it with Hepa AND either heats the new air (in the winter) or dehumidifies the new air (in the summer)? I'm probably asking too much, but thought that there must be others in the south (U.S.) with this issue. By my estimation, air exchangers seem to be great options in cold weather climates but not so good with humidity. thanks!

[pwg11386]

a 2 stage a/c with a variable speed blower is a popular set-up used by us here in nc. I suggest trane's xl20i because it has two compressors which lets you run 50% airflow in the first stage of cooling. this is great for dehumidification. Combo that with a vs airhandler and a t-stat with a dehumidifying cooling-droop program like the honeywell 8000 = dry comfortable living. An ERV is a great addition to swap out air with clean outside air, but there are less expensive options as well. Of course all of this is based on having a competent installation contractor. What part of NC?

[teddy bear]

Hi, I'm building a new home in the Carolinas (ie, high humidity roughly half therisk mold issues. Does anyone have any thoughts or suggestions? Is there a product that pulls in fresh air AND cleans it with Hepa AND either heats the new air (in the winter) or dehumidifies the new air (in the summer)? I'm probably asking too much, but thought that there must be others in the south (U.S.) with this issue. By my estimation, air exchangers seem to be great options in cold weather climates but not so good with humidity. thanks!

Did you ever hear of a whole house ventilating dehumidifier? Some provide fresh air ventilation when needed and maintain <50%RH whenever tha a/c is not running enough to keep the home dry.
They start by blending fresh air with house air, filter the blended air with upto Merv 14 air filters. The blended filtered air circulated throughout the home via the a//c ducts. The dehumidifier part will remove moisture from the air whenever the %RH in the home is above your set point. The Ultra-Aire is unit I am most familar with and is granddaddy of this type of unit. The UA is also the most efficient dehu made.
Regards TB

[unc99]

Thanks for the replies. I'm in western NC (near Charlotte).

Would it be best to tie in the dehumidifier/ventaliator to the HVAC systems or have it stand alone? If I was building a 3800 sq foot home with two stories (downstairs is bigger and there is a two story ceiling in foyer), would I need one for each floor (there will be HVAC on each floor) or just one on the main floor. Would, of course, prefer to just get one, but there are bedroom upstairs that I would want to benefit. Thanks!

[teddy bear]

Thanks for the replies. I'm in western NC (near Charlotte).

Would it be best to tie in the dehumidifier/ventaliator to the HVAC systems or have it stand alone? If I was building a 3800 sq foot home with two stories (downstairs is bigger and there is a two story ceiling in foyer), would I need one for each floor (there will be HVAC on each floor) or just one on the main floor. Would, of course, prefer to just get one, but there are bedroom upstairs that I would want to benefit. Thanks!

If you want total control of all space, use a vent dehu on both a/cs. A dehu on the upper unit and a medium unit on the lower a/c. If on a budget, use an UA xt150H on lower unit with a supply connected to the upstairs a/c unit.

Stand alone units are less expensive but most intrusive.
Appreciate your consideration.
Regards TB

[TalkingHead]

TB: Where do you connect the discharge duct from the ventilating dehumidifier: before or after the evaporator coil? Doesn't Honeywell say before and Thermastor say after? Second question: Where should the return to the dehumidifier come from: a separate return opening or simply attach to the existing return duct to the A/C unit?

[momoformula70]

http://www.buildingscience.com/docum...ventilate/view

PDF file from Building Science web site about ventilation in all types of climates.

[momoformula70]

another good one.

http://www.buildingscience.com/docum...w-case-studies

[momoformula70]

http://www.buildingscience.com/docum...humid-climates

[teddy bear]

TB: Where do you connect the discharge duct from the ventilating dehumidifier: before or after the evaporator coil? Doesn't Honeywell say before and Thermastor say after? Second question: Where should the return to the dehumidifier come from: a separate return opening or simply attach to the existing return duct to the A/C unit?

Ideally, connect the dehumidifier to the supply duct down stream of the fan/a/c coil. This connection maximizes the amount of moisture removed by the a/c. If the supply duct has +.4" of positive pressure, avoid the supply side or interlock the avoid dehu operation when the a/c is operating. When connecting a dehu to two a/cs, split the supply of the dehu to both of the a/c supplies.
There various methods of getting distribution of the dry air throughout the home and not require the a/c blow to operate when the dehu is operating.
A properly setup a/c will maintain <50%RH during lengthly operation. The dehu should only need to operate during low/no cooling loads. I am open to other suggestions.
Regards TB

[pmeunier]

...
I am open to other suggestions.
Regards TB

After years of trial and error, I found that what worked best for my house was to have a tight-band dehumidistat on the main floor, with the dehu's output directly in the open basement with a long stretch of straight flex duct to absorb noise, and drawing air from the return ducts. A relay cuts off the dehu when the A/C runs. The dehumidistat is a "Columbus Electric", which has internal Honeywell parts essentially identical to the Honeywell dehumidistat, but set at the factory to operate with a much narrower deadband.

Fresh air is fed with a "T" junction to the dehumidifier's intake, after being filtered with a HEPA filter running at a low speed. An autotransformer (variac) controls the HEPA filter speed, and a pressure switch at the HEPA filter's intake turns on a light if the HEPA is unable to maintain enough suction on the fresh air intake. When this happens and the variac has no more power to give to the HEPA filter, or it's too noisy, it's time to change the HEPA filters. Outside air is surprisingly dirty...

I think that the dehu configuration that works best is a function of the house's design and dehumidification needs. There isn't a single configuration that's the optimal one for all houses. Discharging the dehu in the basement has evened the temperatures between floors in my house, besides the desired effects on mold and insects.

[unc99]

Thanks to all for the responses. I'm leaning towards going with a venting dehumidifier on the first floor, and two air cleaners (such as either the Perfect 16 or the Lennox Hepa model) on each floor. Although perhaps this is too over the top.

A couple of questions:

1. Is there any issue with putting an air cleaner along with a venting dehumidifier? If I understand them correctly the air cleaners are just boxes with filters, so I'm guessing not but am not sure.

2. Does the venting dehumidifier expel indoor air, or just bring in out door air? In other words, does it work like an air exchanger? If not, is it problematic to having air forced in the house and not having indoor air mechanically expelled?

3. Is anyone aware of an EVR which also dehumifidies? If so, it seems this would erase if any issues I noted in point # 2 above.

Thanks very much in advance....this site has been a wealth of information...much appreciated.

[teddy bear]

Thanks to all for the responses. I'm leaning towards going with a venting dehumidifier on the first floor, and two air cleaners (such as either the Perfect 16 or the Lennox Hepa model) on each floor. Although perhaps this is too over the top.

A couple of questions:

1. Is there any issue with putting an air cleaner along with a venting dehumidifier? If I understand them correctly the air cleaners are just boxes with filters, so I'm guessing not but am not sure.

2. Does the venting dehumidifier expel indoor air, or just bring in out door air? In other words, does it work like an air exchanger? If not, is it problematic to having air forced in the house and not having indoor air mechanically expelled?

3. Is anyone aware of an EVR which also dehumifidies? If so, it seems this would erase if any issues I noted in point # 2 above.

Thanks very much in advance....this site has been a wealth of information...much appreciated.

You also have some options on the filtering of the fresh air/house air blend flowing through the dehumidifier. There is a Merv 14 option option available with the Ultra-Aire. Suggest a minimum of a Merv 11 for the air handler.
Regarding the make-up air issue, the ventilating whole house dehumidifier blends fresh air with the house air, filters, and circulates the filtered blend throughout the home. The amount of air should be enough to change the air in the home in 4-5 hours. There is no exhaust of stale air. You have several appliances that need make-up air to function. The clothes drier, kitchen hood, and bath fans exhaust air and benefit from the make-up air. Also, make-up air reduces untreated air from naturally infiltrating the home which is benefical. See no need to ventilate when the home is unoccupied for extened periods of time, but maintaining <50%RH is important to avoid mold, mildew, and dust mites. The DEH 3000 controller has a good occupancy schedule provide fresh air when you are in the home on a routine basis.
Being able to control fresh air on a routine basis that matches occupancy schedules also reduce cost of conditioning the make-up air.
Keep us posted.
Regards TB

[unc99]

Thank you very much Teddy Bear. If you don't mind, I have a couple more questions:

1. From the Ultra-Aire website, it appears that the ventilated/fresh air is added to the supply side of the HVAC. Doesn't the mean the air will enter the home uncooled/unheated? Maybe it doesn't make enough difference to affect the whole house temp, but seemed odd to me that the ventilated air would not be added to the return side so that the HVAC would then cool/heat it.

2. If I also add a Perfect 16 (or other air cleaner/filter) to the return side, I suppose the issue in 1 above would mean that the air supplied by the ventilator would not be cleaned until it circulated through the home and back into the return. Again, maybe this isn't too worrisome since you mentioned the Ultra Aire offers Merv 14 filtration.

3. If I use a ventilating dehumidifier for ventilation instead of an air exchanger, should I be concerned that I probably won't get any fresh air in the winter months as there will be no need for dehumidification? If you live in a climiate with hot/cold months is a air exchange with a separate dehumidifier a better option?


Thanks!

[teddy bear]

Thank you very much Teddy Bear. If you don't mind, I have a couple more questions:

1. From the Ultra-Aire website, it appears that the ventilated/fresh air is added to the supply side of the HVAC. Doesn't the mean the air will enter the home uncooled/unheated? Maybe it doesn't make enough difference to affect the whole house temp, but seemed odd to me that the ventilated air would not be added to the return side so that the HVAC would then cool/heat it.

2. If I also add a Perfect 16 (or other air cleaner/filter) to the return side, I suppose the issue in 1 above would mean that the air supplied by the ventilator would not be cleaned until it circulated through the home and back into the return. Again, maybe this isn't too worrisome since you mentioned the Ultra Aire offers Merv 14 filtration.

3. If I use a ventilating dehumidifier for ventilation instead of an air exchanger, should I be concerned that I probably won't get any fresh air in the winter months as there will be no need for dehumidification? If you live in a climiate with hot/cold months is a air exchange with a separate dehumidifier a better option?


Thanks!

1. 80 cfm of fresh air blended into a 600-800 cfm of cold air steam means little to the temp of air entering the rooms. The a/c runs a small percentage of time compared to the fresh air ventilation. All of our units have a merv 11 minimum air filter. Most pollutants enter the home on clothes and through structural cracks.
2. Merv 11 is very good filtering. The Merv 14 is an optional filter that can be added to any dehumidifier.
3. Fresh air ventilation is independent of the dehumidifying of the air in the home. They can a occur at the same time indenpendently. Fresh is dependent on occupancy while dehumdification is dependent on the %RH setting which usually <50%RH.
During the windy coldest weather, most homes get enough fresh air naturally. But you can have fresh air whenever you want it. Diffenitly, less fresh air is need during cold windy weather. Also your clothes dry and exhaust fans need make-up air when operating.

Hope this answers your questions, if not, repost.
Regards TB

[pmeunier]

Does the venting dehumidifier expel indoor air, or just bring in out door air? In other words, does it work like an air exchanger? If not, is it problematic to having air forced in the house and not having indoor air mechanically expelled?

Having air "forced into the house" is what you want when it's more hot and humid outside than inside. It causes a very small positive pressure that reduces the infiltration of humidity and dust. There are plenty of leaks for the air to go out, it doesn't cause problems. However, when it's much colder outside, positive pressure can cause condensation in the walls and then it's not a great idea.

[teddy bear]

Having air "forced into the house" is what you want when it's more hot and humid outside than inside. It causes a very small positive pressure that reduces the infiltration of humidity and dust. There are plenty of leaks for the air to go out, it doesn't cause problems. However, when it's much colder outside, positive pressure can cause condensation in the walls and then it's not a great idea.

Some more recent thoughts about positive pressure ventilation in cold climates.
We build a state of the art air tight 2,500 sqft. home in cold climate. A blower door test shows that the home leaks and air change in 10 hours. This is 40 cfm of air leakage out the top of the home and down wind. Put the home in WI with the average outside temp at 17^F and 7.5 mph wind. If we have 3 occupants putting 1.5 lbs. per hour of moisture into the home from breathing and activities. As the 40 cfm of fresh air passes through the home, the air is warmed to 68^F and humidified to 67%RH which is a dew point of 57^F. As the damp exfiltrates the home, the dreaded condensation occurs in the attic and exterior cold surfaces. We know from past history that homes with more air leakage do not have any condensate problems exfiltrating the moisture from the occupants as long as the dew point of the exfiltrating air is low.
I have fixed many air tight homes with condensation problems in attics/walls by supplementing natural fresh air infiltration/exfiltration by introducing enough additional dry cold fresh mak-up air to get the lower the inside dew point to more normal inside conditions. Generally, <32^F dew point exfiltrating air typically will not cause condensation problems northern US.
This is a good strategy for homes that need make-up air to function.
Also consider that this same house on the coldest windy day, gets twice as much fresh air while the occupants are in and out of the home. The indoor moisture drops rapidily to point of needing humidification at the extreme.
Homes with bathfans, clothes drier and kitchen hood also add to the complexity.
Most homes leak more air and only need occasional supplemental fresh air during cold weather, which makes supplemental make-up fresh air a suitable choice when we are able to control the when and how much is added to the home.
I was amazed when called to a home with 6 occupants with condensation from the attic roof deck was leaking out of the siding during a warm thawing spell in the middle of winter in WI. To make things worse, the clothes drier was back drafting the ng furnace during some wind/temp conditions. The home owner was out of money and desperate. A duct fan mixing 100 cfm of fresh air into the home fixed everything. The attic dried and the furnace functioned. The heating bill went up <$100 for the year. That was 20 years ago and I have heard nothing. Since, all WI homes are required to a fresh air inlet as a minimum.
Enough for a holiday eve.
Lets start preparing for the feast tomorrow. I must beark away and plug the address for Mel's Diner into my GPS so I don't miss diner tomorrow.
Regards TB

[kaleun]

the first thing (energy efficiency wise) to dehumidify would be to use an energy recovery ventilator to ventilate. this dries some of the fresh air. Seal the house to avoid infiltration.

a 2-stage or variable speed AC helps too since that cycles less and dehumdifies more than an oversized single-stage AC.

this should take care of all issues, if not you have a building and not an HVAC problem.

All the dehumidifier does is dry the air and reheat it with its own condenser. So in summer you actually heat up your building with electricity. the only difference to an AC is, that the AC has the condenser outside and rejects the heat to outside. I only would use that as last resort if humidity really is an issue. If humidity goes up for some days in the shoulder season, so be it. On a rainy day humidity is high. unless it rains for months, this won't grow mold.

The only critical space is the basement if yo have cold basement walls in summer. thsi might justify its own standalone de-humdifier to stay below 60% RH. ASHRAE recommends 60% is the cutoff for mold grow. No need to de-humdify to 40%. when you look at the psychrometric chart you see that in a 60°F basement it with virtually impossible to de-humidy to 45% with regular refrigeration. all the de-humidifiers are rated to operate at 75-80°F. why people think they can set them to the same setting in a cold basement is beyond me. Every dehumdifier i see is set to t30% or whatever the lowest setting is. then they run all day. More moist air from the houise goes into the basement and people see the buckets of water and see that as evidence how moist their basement is. humidity is one of the things 99.999999% of the population don't understand. Many engineers don't understand it either.

Many people have the furnace in the basement. It always creates some negative pressure and draws (moister) air from the rest of the house. Same with dryers in basements. It is a losing battle to attempt to de-humdify the basement to 50% or less. All it does is use electricity and heat up the house, creating even more AC load. the AC is much better suited to dry the entire house.

i used to have a de-humdifier in my tri-level house basement. I now finished the lwoer level and condition it. teh need for dehumidification ithe basement went away becasue the neighboring space is dry enough to keep the basement below 60% RH.

[teddy bear]

the first thing (energy efficiency wise) to dehumidify would be to use an energy recovery ventilator to ventilate. this dries some of the fresh air. Seal the house to avoid infiltration.

a 2-stage or variable speed AC helps too since that cycles less and dehumdifies more than an oversized single-stage AC.

this should take care of all issues, if not you have a building and not an HVAC problem.

% RH.

Yes ERVs do transfer 40-50% of the moisture from the wet air to the dry air provide the you are exhausting dry air. During wet, cool weather and evenings, 50%-60% of the moisture goes into the home. At an air change in 4-5 hours after a couple days, the air inside the home is as wet as the outside air. Mold only needs a couple days of high humidity to grow. Under a carpet or behind the insulation of basement old floor or cold wall, the humidty may be near 80-90%RH.
Two stage a/c without any cooling load in a home with proper ventilation and active occupants will have months of 65-80% RH at the cool surfaces. Yes dehumidifiers should be set at 50%RH not any lower. Good high efficiency dehus will maintain 50%RH throughout the home when the a/c is operating enough. Get a good %RH meter and place it in the cool corners. If the %RH is <60% occasionally, do nothing. If the %RH is +70%RH, get the %RH down to 50%RH. Not "so be it" or in a couple years your basement will smell like a basement.
Air tight home without fresh air ventilation and low occupancy may not have big trouble during dry hot weather like some years. The wet cool weather with an air change of fresh air in 4-5 hour and 3-5 occupants require 30-60 lbs. of moisture removed every day to maintain <50%RH.

theAll the dehumidifier does is dry the air and reheat it with its own condenser. So in summer you actually heat up your building with electricity. the only difference to an AC is, that the AC has the condenser outside and rejects the heat to outside. I only would use that as last resort if humidity really is an issue. If humidity goes up for some days in the shoulder season, so be it. On a rainy day humidity is high. unless it rains for months, this won't grow mold.

The only critical space is the basement if yo have cold basement walls in summer. thsi might justify its own standalone de-humdifier to stay below 60% RH. ASHRAE recommends 60% is the cutoff for mold grow. No need to de-humdify to 40%. when you look at the psychrometric chart you see that in a 60°F basement it with virtually impossible to de-humidy to 45% with regular refrigeration. all the de-humidifiers are rated to operate at 75-80°F. why people think they can set them to the same setting in a cold basement is beyond me. Every dehumdifier i see is set to t30% or whatever the lowest setting is. then they run all day. More moist air from the houise goes into the basement and people see the buckets of water and see that as evidence how moist their basement is. humidity is one of the things 99.999999% of the population don't understand. Many engineers don't understand it either.

i used to have a de-humdifier in my tri-level house basement. I now finished the lwoer level and condition it. teh need for dehumidification ithe basement went away becasue the neighboring space is dry enough to keep the basement below 60% RH.

A well designed dehu like a Santa Fe/Ultra-Aire/Honeywell etc will not operate as long as the a/c runs enough to maintain your desired %RH. All of monitoring I have shows 5-6 hours of running in the wettest cool weather.

The inside moisture levels are the dew point of outside infiltration/ventilation plus the moisture from the occupants and their activities. Ultimately the occupants are responsible for the indoor air quality in their homes. Indoor air quality is fresh air change to purge indoor pollutants and <50%RH to avoid mold and dust mites. Comfort is also an issue. Lower %RH allows a high indoor temperature. With moving indoor air 77^F-78^F, 50%RH is very comfortable. During rainy cool weather, not much cooling load.
The debate goes on. As my a/c salesman answered my question, will this system keep my house <50%RH, Yep pretty much.
After a rainy week, I called and ask the question. Well, its been raining for a week, what do you expect.
So be it!
Regards TB

[pmeunier]

...
I have fixed many air tight homes with condensation problems in attics/walls by supplementing natural fresh air infiltration/exfiltration by introducing enough additional dry cold fresh mak-up air to get the lower the inside dew point to more normal inside conditions. Generally, <32^F dew point exfiltrating air typically will not cause condensation problems northern US.
...

Thanks TB, but I believe that this approach is incompatible with the well-being of the occupants. It's been found that low absolute humidity (dew point) increases virus transmission (not relative humidity). Below about 15 mbar of water vapor pressure, the influenza virus greatly increases its survivability and infection rates (see "Absolute humidity modulates influenza survival, transmission, and seasonality", Shaman and Kohn 2009, Proceedings of the National Academy of Sciences, http://www.pnas.org/content/early/20....full.pdf+html). That's a dew point of about 55^F. Air with less than a 50^F dew point is a health issue, besides causing discomfort. Recommending increased ventilation to reduce the dew point down below 32^F dew point or less in winter is risky for human health.