HVAC, Humidity and ERV for 1000 sq ft tight house!

[pearlhomes]

Hi everyone, new to this forum. I joined cause Im racking my brain over all the info out there for cooling, dehumidifying and bringing in fresh air for tight built spray foamed houses.

I'm a general contractor in South Texas and building my first house. Its a small fancy camp house at 1032 sq ft, has 10 ft ceilings with vaulted in the great room/kitchen. The exterior walls are 2x6 and were using open cell foam on exterior walls and the ceiling of the roof for a conditioned attic space. The exterior is being sealed with bottom seal wrap and OSB sheathing taped and caulked for a tight house.

What I'm looking for is the best HVAC setup to remove humidity and whether I need an ERV to bring in fresh air. Ive read so much about over sizing your HVAC where it does not run long enough to remove humidity. Ive also read about whole home dehumidifiers but all seems to be massively overkill for this size of house. Ive learned about Carrier Infinity two stage for better humidity removal but smallest is 2 ton, I assume I need to be in 1 or 1.5 ton range.



So pros... how should I proceed?

[teddy bear]

Simple a/c ducted or mini-split. A small whole house dehumidifier like the Ultra-Aire 70H with fresh make air option when occupied. 1,000 sq.ft. with 3-4 occupants needs 50 cfm of fresh air when occupied to purge indoor pollutants and renew oxygen. When unoccupied, no fresh air is needed.
A/c off when unoccupied with dehu set at 50%RH will keep it dry for a few bucks a month when the outdoor dew points are high. Will not operate when the outdoor dew points are low. The fresh air needs a manual or electric damper to provide fresh air when occupied and windows closed. Electric switch will activate the damper and fan motor.
The idea of cooling to dehumidify only works when there is significant sensible cooling load, provided the a/c has minimum of 30^F split and a +30% duty cycle. As the cooling cycle declines, not enough moisture goes down the drain to keep it dry. Over-cooling for humidty control dramitically increases the amount of moisture that most be removed to maintain low indoor humidity. Cooling the structure below the outdoor dew point causes moisture condensation in the structure, as opposed to warming the space and removing moisture with a dehumidifier.
Simple, reliable, and fool proof.
I keep my FL. camp dry in this way. No cooling for 7 years when unoccupied and no musty odors.
Keep us posted.
Regards Teddy Bear

[pearlhomes]

Teddy, thanks for the response and info.

So basically the Ultra-Aire 70H with the fresh air option is a dehumidifier with ERV all in one? Is that correct? I would have to add an electric damper to the system. Is there a setup for this that includes a controller? Also do you know of anything smaller than the 70H? Still seems overkill but if its the smallest guess thats the option.

[teddy bear]

Teddy, thanks for the response and info.

So basically the Ultra-Aire 70H with the fresh air option is a dehumidifier with ERV all in one? Is that correct? I would have to add an electric damper to the system. Is there a setup for this that includes a controller? Also do you know of anything smaller than the 70H? Still seems overkill but if its the smallest guess thats the option.

The fresh air supply/filter is built into the Ultra-Aire 70H. There is a controller, DEH3000 that controls fresh air and dehumidification.
Yes it larger than needed but smallest I know of with all of the features. Over-sizing dehus is not as much of a problem as over-sized a/c. You could build a bigger camp??
ULtra-Aire.com is a site sponsor also.
Regards Teddy Bear

[pearlhomes]

Makes sense and thanks for the controller info.

Another HVAC expert here locally is telling me to get the 2 ton Carrier Infinity 21 system which is two stage. He states that this system will take care of all the dehumidifier needs instead of needing a standalone. I would just add an ERV like the smaller Panasonic to it. Whats your thoughts on this take?

[teddy bear]

Good, tell him you like the statement of 50%RH during wet cool weather or money back.
If you trust him go with him. We deal with this all of the time. A/c will control %RH during high cooling loads. During low/no cooling loads, any a/c will not control moisture.
Keep us posted on how this all works.
Regards Teddy Bear

[pearlhomes]

Thanks Teddy. Yeah it sounded too good to be true and I feel this contractor although trying to help does not fully understand the spray foam tight house situation. So now what Im looking at is a Goodman 1.5 ton with gas furnace tied to the Ultra Aire 70h with the make fresh air option with damper and DEH controller.

Thanks again for the advice. Do you know of any of the smart thermos that can connect to Ultra Aire for an all in one?

[pearlhomes]

Hey Teddy, another question. I was thinking 1.5 ton so it would run longer to assist in dehumidification. But since there is going to be the Ultra Aire 70 in there doing that job anyways should I move up to a 2 ton that will only cycle briefly? If theres little to no savings 1.5 to 2 ton, which would you choose?

1032 sq ft, spray foam envelope, water and vapor barriers on slab and caulking, etc

[chippert]

A 2 ton will cost you more money to operate for your cooling needs than a 1.5t.

Sent from my SM-N910V using Tapatalk

[teddy bear]

There is no benefit to using a larger unit. Longer runs will do a better job of helping to control the %RH.
Keep us posted on how this works out.
Regards Teddy Bear

[PercyWilliams]

HVAC systems are capable of regulating humidity. It has an evaporator coil that condenses water vapor from the air. Your air conditioner will be effective at controlling humidity only if it is correctly sized for the amount of work it needs to do. Your professional residential ac repair service NJ specialist will calculate the appropriate size needed for your HVAC system based on the size of your home.

[teddy bear]

HVAC systems are capable of regulating humidity. It has an evaporator coil that condenses water vapor from the air. Your air conditioner will be effective at controlling humidity only if it is correctly sized for the amount of work it needs to do. Your professional residential ac repair service NJ specialist will calculate the appropriate size needed for your HVAC system based on the size of your home.

Just to expand my horizons, help me understand how a correctly sized a/c will remove latent load without any sensible cooling load. Like during an extended rainy spell of 70^F, 90%RH outside and several occupants in the home with t-stat set at 75^F, I want 50%RH. The sensible cooling 0 btus and the latent is 4,000 btus per hour from fresh air infiltration and the occupants latent load.
Looking forward to the discussion.
Regards Teddy Bear

[dannyb]

I am about to build a home and have a similar situation as the OP. What about winter? How do you address moisture in TX in the winter? In TX a so-called winter can have a 30 or more degree swing. I’m familiar with some foamed homes having heavy window sweating during the winter season. Mine does.

Does an ERV remedy this? Does a heat-pump do anything for dehumidification in winter?

[teddy bear]

I am about to build a home and have a similar situation as the OP. What about winter? How do you address moisture in TX in the winter? In TX a so-called winter can have a 30 or more degree swing. I’m familiar with some foamed homes having heavy window sweating during the winter season. Mine does.

Does an ERV remedy this? Does a heat-pump do anything for dehumidification in winter?

First, you need a fresh air change in 4-5 hours to purge indoor pollutants and renew oxygen whenever the home is occupied. The dew point of the outdoor air plus moisture from the occupants determines the moisture level or dew point of the air in the home.
We have focused on the moisture level in the high moisture seasons and removing moisture with an a/c and a dehumidifier maintaining 50%RH.
Ok, next comes the cold time of the year when the outdoor temperatures are low enough to make windows condense moisture on the inside. This means the sweating surface is below the indoor air dew point.
First comes the problem that the tons of material inside the home is at summer moisture levels. The window surfaces suddenly goes to <45^F while the home is 68^F, 50%RH, a 48^F indoor dew point. The windows are covered with moisture.
Even with a fresh air change in 4-5 hours of dry outside air the home is slow to dry down. The occupants are adding 1-2 lbs. moisture per hour plus the home may be adding several lbs. of moisture per hour, resulting in air above many of the surface of the home.
Now, simply, cracking in a window or/and operating exhaust fans will quickly lower the indoor dew point, stopping the sweating in a couple hours. With low outdoor dew point air, increasing the ventilation rate is more practical than operating a dehumidifier which will have difficulty to get the indoor dew point down 40^F that may be needed to stop poor windows.
Moisture on winter windows is a sign of inadequate fresh air ventilation, very poor windows, excessive temperature setback, or drape covering.
Keep in mind after the home dries down in fall, the main moisture is from the occupants. One person adds <.5 lbs. per hour. 2-3 occupants in a small home with an air change in 4-5 hours may need slightly more fresh air change to keep the windows dry. A large home with an air change in an air change in 4-5 hours and the same number of occupants will need humidification to maintain 35%RH during the coldest low dew points of winter to be comfortable inside.
Generally, adequate air changes with a make-up air from a whole house ventilating dehumidifier will keep the home comfortable and good windows dry. Also the exhaust devices like the clothes drier, bath fans, and kitchen hood need the make-up air from the fresh air ventilation to exhaust indoor pollutants.
Long story for a simple problem.
Post any questions and how this all works.
Regards Teddy Bear

[teddy bear]

Sorry about the long previous post.
The short answer is that during high outdoor dew points with low sensible cooling loads, a small whole house dehumidifier like the Ultra-Aire 70H with fresh air ventilation option keeps the home <50%RH.
During the cold times of the year, the adequate fresh air ventilation will keep the home dry. If any inside surface including windows sweat, increase the fresh air ventilation rate.
Much better right?
Regards Teddy Bear

[dannyb]

I think I have a better understanding. I kind of think some of these local HVAC guys are doing the "same old same old" with their system configurations.

I appreciate the feedback!!!!!

[niamishra]

I am going to manufacture home and have a comparable circumstance as the Operation. Shouldn't something be said about winter? How would you address dampness in TX in the winter? In TX a purported winter can have a 30 or more degree swing. I know about some frothed homes having overwhelming window perspiring amid the winter season. Mine does.

Does an ERV cure this? Does a warmth siphon do anything for dehumidification in winter?

[teddy bear]

The short answer is that during high outdoor dew points with low sensible cooling loads, a small whole house dehumidifier like the Ultra-Aire 70H with fresh air ventilation option keeps the home <50%RH.
During the cold times of the year, the adequate fresh air ventilation will keep the home dry. If any inside surface including windows sweat, increase the fresh air ventilation rate.
Much better right?
Regards Teddy Bear
This is a previous post.
When windows sweat on the inside, you are not getting enough fresh dry outside air change in the home.
Start by operating bath fans 24/7 until the windows clear. Kitchen hood also works. The dry outside air passing through your home will remove enough moisture control condensation on the windows. A the home is dried out, mush less fan operating is needed to control moisture.
As with the previous poster, a small whole house dehumidifier will keep the home dry during wet weather. You need fresh air year around. You need supplemental dehumidification during evenings and rainy weather.
Yes an ERV will help but only during cold dry weather, but you will also need a small dehumidfier during evenings and rainy weather.
If your home needs much more fresh air than typical, an ERV may have some pay back, but not typically.
Keep us posted.
Regards Teddy Bear

[AdrienneGC]

I recommend doing a load calculation and use ASHRAE 62.2 to determine the OA volume (7.5 cfm/ person + 0.01 cfm/sf). This will determine if you need additional equipment for dehumidification.

I live in Florida, another hot humid climate, and love a whole-house dehumidifier.

[teddy bear]

I recommend doing a load calculation and use ASHRAE 62.2 to determine the OA volume (7.5 cfm/ person + 0.01 cfm/sf). This will determine if you need additional equipment for dehumidification.

I live in Florida, another hot humid climate, and love a whole-house dehumidifier.

A couple of additional facts to consider before you make anymore recommendations.
Blower door test negatively pressurizes the home to match the stack effect from inside/outside pressure on the walls and ceilings plus average winter winds.That is great for that condition but when winds are calm and temperatures mild, the pressures causing infiltration/exfiltration drop to nothing.
Latest ASHRAE suggest a fresh air change in 3 hours when occpied. So your home blower tests shows a fresh air change in 3 hours. YOu will good air change on an average winter day. During calm winds and mild temperature even with a leaky home you may get a fresh air change in +12 hours. When I started measuring the CO2 levels in occupied homes, I was shocked.
Few homes in cold climates worst weather need mechanical ventilation. Leaky homes need mechanical fresh, filtered air when occupied at a minimum of an air change in 3-5 hours when occupied.
For me, make-up air ventilation is preferred to provide the exhaust devices necessary air scource to function.

I also suggest controlling fresh air ventilation with a CO2 controller to avoid unnecessary ventilation.

OF course the dehumidifier is needed to assist a properly setup a/c during times of low/no sensible cooling and high outdoor dew points.
I like the grand daddy of the whole house dehumidifiers, the Ultra-Aire line, US made and the highest efficiency dehu in the world.
Your thoughts??
Regards Teddy Bear