Dehumification on the Texas Gulf Coast

[teddy bear]

Current conditions:

Apr 7, 8:52 pm CDT
Overcast 72 °F
Humidity: 91 %
Wind Speed: SE 15 MPH
Barometer: 29.85" (1010.8 mb)
Dewpoint: 69 °F (21 °C)
Visibility: 7.00 mi

Inside temp is 70^F. Inside humidity 70%.

I talked with my Trane dealer and his techie today. They want me to buy an Aprilaire 1770A -135 pint whole house dehumidifier connected to the HVAC return and supply with a humidistat/controller next to the HVAC thermostat. Pricey solution (about $ installed). I haven't pulled the trigger yet.

This is good stuff.
You do not need a large dehumidifier. I suggest an Ultra-Aire 90H which is small and much more efficient.

MFG: Aprilaire
MFG#: 1770A
Our#: 172492
Capacity @ AHAM: 150 Pints/Day
Capacity @ Saturation: 265 Pints/Day
Amp Draw: 14 Amps
CFM: 500 CFM
Operating Temp. Range: 40° - 150°F
Warranty: 5-Year Factory Warranty
Sound Level: 53 dBA Ducted, 67 dBA Non-ducted

Ultra-Aire 90H
Capacities and Performance
Part Number: 4029820
Blower: 240 CFM @ 0 WG
Supply Voltage: 110 -120 Volt, 60 Hz
Amps: 6.7
Energy Factor: 2.5 liters/kWh
Efficiency: 5.3 pints/kWh
Operating Temp.: 56°F Min, 100°F Max
Sized For: 2200 Sq. Ft. - Typical
Capacity: 90 Pints/Day (80°F, 60% RH)
UA-90H Duct
Connections: 6" Round Inlet
10" Round Inlet
10" Round Outlet
Filter Efficiency: Standard MERV-11
(65% ASHRAE Dust Spot)
Power Cord: 7.5', 115V With Ground
Drain Connection: 3/4" Threaded NPT

Oversized dehus are like oversized a/C. They are best sized to avoid short cycling for efficiency and long cycles during peak loads. Short cycling involves re-evaporation of moisture on the coil back to the space. Plus the top unit uses 14 amps verses 6.7 for UA 90H. Also the UA is much more efficient than the other. Your contractor can purchace the UA from a local wholesaler or from the factory. I have worked for UA +20 years, developing the concept of the ventilating dehu.
Any dehu is better than no dehu, but get the best you can. UA is the most efficient and durable.
Regards TB

[Mvanza]

Teddy,
I like the idea of the UA 90_H for efficiency. I'm leaning against using the outside air circulation feature on whichever unit I choose. I think with the bathroom vents, can lights, dryer vent etc, I;m getting plenty of fresh air. But I probably don't know what the recirculation feature does. Does it bring air from the outside through the dehumidifier or exhause air?

I'm gonna talk to my Trane Dealer about the 90-H but their experience has been limited to the April-Aire product and that experience is limited. The techie said yesterday that yu can't oversize dehus like you can AC's so I'm a little worried about his knowledge. Really humid this morning. House inside at 67% humidity and 70^F. You can see the outside conditions below. My trane runs at low speed for 6-7 minutes then shuts off, never hitting the high fan speeds. Can my dehu be wired to run at the same time as my AC or is that a bad idea? Thanks for all the advice.

Mike VanZandt
Crystal Beach, Texas


Apr 8, 6:52 am CDT
Fog/Mist
71 °F
(22 °C) Humidity: 94 %
Wind Speed: S 10 MPH
Barometer: 29.86" (1011.1 mb)
Dewpoint: 69 °F (21 °C)
Visibility: 2.00 mi.
More Local Wx: 3 Day History:

[Shophound]

With your diligent monitoring of outdoor air conditions, are you concurrently monitoring your indoor humidity levels as outdoor air conditions change? If you find that your indoor air dew point fluctuates pretty much in sync with outdoor air dew point, that indicates building air leakage. If you find your indoor air dew point does not show direct fluctuations with outdoor air dew point, that's a tight building that needs dedicated dehumidification if indoor dew points are consistently too high (> 55°F). Such a building requires ventilation regardless, and in your climate a ventilating dehumidifier is the way to go, IMO.

[Shophound]

Teddy,
I like the idea of the UA 90_H for efficiency. I'm leaning against using the outside air circulation feature on whichever unit I choose. I think with the bathroom vents, can lights, dryer vent etc, I;m getting plenty of fresh air. But I probably don't know what the recirculation feature does. Does it bring air from the outside through the dehumidifier or exhause air?

I'm gonna talk to my Trane Dealer about the 90-H but their experience has been limited to the April-Aire product and that experience is limited. The techie said yesterday that yu can't oversize dehus like you can AC's so I'm a little worried about his knowledge. Really humid this morning. House inside at 67% humidity and 70^F. You can see the outside conditions below. My trane runs at low speed for 6-7 minutes then shuts off, never hitting the high fan speeds. Can my dehu be wired to run at the same time as my AC or is that a bad idea? Thanks for all the advice.

Mike VanZandt
Crystal Beach, Texas


Apr 8, 6:52 am CDT
Fog/Mist
71 °F
(22 °C) Humidity: 94 %
Wind Speed: S 10 MPH
Barometer: 29.86" (1011.1 mb)
Dewpoint: 69 °F (21 °C)
Visibility: 2.00 mi.
More Local Wx: 3 Day History:

I'm confident Teddy can answer your questions adequately, but thought I'd chime in here concerning a few points you raised. To my knowledge a dehumidifier with a recirculation mode is recirculating indoor air without adding outdoor air to the mix. April Aire and Ultra Air units can be configured like this. They can modulate between recirculation and bringing in fresh air for ventilation and dehumidification.

Also, if your dehumidifier runs ONLY when the a/c runs, you're almost back to Square One during mild weather like you're having now. A ventilating central dehumidifier has its own blower and will pump dehumidified air into your a/c ducts when your a/c is not running. When your a/c is running, it is dehumidifying, so no need to run both simultaneously. If the a/c is running and you need fresh air to ventilate the house, it will be dehumidified by the a/c. The dehumidifier is there to remove moisture and ventilate the house with fresh air when the a/c can't because the house isn't warm enough to keep the a/c enabled.

[teddy bear]

Teddy,
I like the idea of the UA 90_H for efficiency. I'm leaning against using the outside air circulation feature on whichever unit I choose. I think with the bathroom vents, can lights, dryer vent etc, I;m getting plenty of fresh air. But I probably don't know what the recirculation feature does. Does it bring air from the outside through the dehumidifier or exhause air?

I'm gonna talk to my Trane Dealer about the 90-H but their experience has been limited to the April-Aire product and that experience is limited. The techie said yesterday that yu can't oversize dehus like you can AC's so I'm a little worried about his knowledge. Really humid this morning. House inside at 67% humidity and 70^F. You can see the outside conditions below. My trane runs at low speed for 6-7 minutes then shuts off, never hitting the high fan speeds. Can my dehu be wired to run at the same time as my AC or is that a bad idea? Thanks for all the advice.

Mike VanZandt
Crystal Beach, Texas


Apr 8, 6:52 am CDT
Fog/Mist
71 °F
(22 °C) Humidity: 94 %
Wind Speed: S 10 MPH
Barometer: 29.86" (1011.1 mb)
Dewpoint: 69 °F (21 °C)
Visibility: 2.00 mi.
More Local Wx: 3 Day History:

Thank you, Shophound for your comments.

Things I learned over and over. Oversized a/cs and dehumidifiers cost more to buy and waste energy. Certianly, adequate size for peak loads is desired, but oversized dehus can dramatically increase the cost of maintaining <50%RH. Give 5 minutes with a good tech and he will agree!

With the proper controls like the DEH 3000, a Ultra-Aire dehumidifier will dehumidify to a set point with or without fresh air ventilation. Also connecting the dehu to the ducts as recommended avoids the need to operate the air handler while dehumidifying. Fresh air is optional but recommended for any will built home. Most add fresh air when the home is normally occupied during the milder calm times of the seasons. Also a CO2 controller can be used to provide fresh air when the CO2 indicates occupancy and a lack of natural ventilation.

Outside
71^F (22 °C) Humidity: 94 %
Wind Speed: S 10 MPH
Barometer: 29.86" (1011.1 mb)
Dewpoint: 69 °F (21 °C)
Visibility: 2.00 mi.

House inside at 67% humidity and 70^F
This is 60^F dew point. The a/c must be removing some moisture and there is very minimal fresh air infiltrating the home. If large amounts of fresh air where entering the home, the dew point would as high as the outside dew point.

With a 10 MPH, you are getting some fresh air. You should be getting 80 cfm when occupied to purge indoor pollutants and renew oxygen.
80 cfm of 69^F dew point fresh outdoor air dried down to 70^F, 50%RH, is a 50^F dew point. Reducing the moisture 80 cfm, 16^F dew points is 2.5 lbs. per hour of dehumidification. Plus the moisture from the occupants must be removed. If you have dehu provide the 80 cfm fresh make-up air, wind driven infiltration will be almost eliminated. You will be impressed by the way this works. Do this right and you can have the best of indoor quality, ideal comfort, and minimal operating cost.

Do not forget, get the best dehu you can.

I would be glad to assist your contractor with this install.
Check my email address.
Regards TB

[Shophound]

I'm curious, TB, if the CO2 sensor for a setup such as you describe above can act independently to cycle open and closed the outside air damper (OAD), or would it somehow be interlocked with a/c and/or dehu operation? In other words, if the a/c is operating, and C02 is measured to be above the upper limit, will the OAD cycle open without any action required from the dehumidifier? Likewise, if indoor air humidity levels are to where the humidistat is satisfied, but fresh air is required, will the OAD cycle open yet the dehumidifier not operate (or the opposite...opening the OAD toggles on the dehu)?

Being that I'm constantly learning and reviewing what I think I already know, I understand better where ventilating dehumidifiers have a proper place in many particular residential applications. This makes me more curious about the particulars of dehu operation itself.

[teddy bear]

I'm curious, TB, if the CO2 sensor for a setup such as you describe above can act independently to cycle open and closed the outside air damper (OAD), or would it somehow be interlocked with a/c and/or dehu operation? In other words, if the a/c is operating, and C02 is measured to be above the upper limit, will the OAD cycle open without any action required from the dehumidifier? Likewise, if indoor air humidity levels are to where the humidistat is satisfied, but fresh air is required, will the OAD cycle open yet the dehumidifier not operate (or the opposite...opening the OAD toggles on the dehu)?

Being that I'm constantly learning and reviewing what I think I already know, I understand better where ventilating dehumidifiers have a proper place in many particular residential applications. This makes me more curious about the particulars of dehu operation itself.

Thanks for the question.
The dehu is setup to circulate air from the open part of the home and supply to the conditioning supply duct down stream of the cooling coil. The fresh air damper is in fresh make-up air return connected to the return to the dehu. The dehu has enough fan power to operate with or without the a/c supply fan. The is able to blend fresh air with house air, filter it, and supply the air into the a/c supply duct with or with the a/c supply fan operating. Fresh air/dehu fan is controlled by the CO2 controller independent of dehumidfication. The dehu will function based on the inside %RH. All of theses functions are independent of each other.
Hope this helps. You can se the install manual on ultraair.com
The CO2 controller is shown yet but available special order.
Regards TB