Dehumidifier Question

[Ziocarl]

Not sure this is the best place to post, but these are mostly basic questions regarding compressors.

I like to run a standalone dehumidifier in my basement in conjunction with my central AC in order to reduce overall humidity. My old dehumidifier unit died, so I just purchased a Frigidaire FAD704DUD 70 pt unit. Even though the finished portion of the basement in only about 700 sq feet, I like to put the fan on the AC that services the bottom two floors of my house (1314 sq feet for first floor) on circulate. I have a separate AC system cooling the topmost floor.

3 questions:

1) The new dehumidifier puts out some serious heat and can warm up the basement pretty quickly. Is this due to it being over sized for the space?

2) Should I assume that if it's putting out that much heat, that the cold side of the coils (which I can't reach with my fingers) is getting equally as cold? Or is it possible for there to be an imbalance - ie the warm side of the coils being much warmer than the cold side is cold relatively speaking? It just seemed like the cold and warm sides of the old dehumidifier balanced each other out better and resulted in more moderate temperature exhaust.

3) Is it normal at 75F and 60% humidity (hvac fan running) for the unit to pull 2 gallons of water in 10 hours, if the thing is rated at 8.75 gallons in 24 hours? The humidity never seems to get below 50% in that time frame, btw so it's not like it has no moisture to work with.

I have until Friday night to return this unit and get a smaller capacity, different model, or just a replacement of the same model.

Thanks so much for your time

[teddy bear]

Dehus are rated at 80^F, 60%RH. Yours is 70 pint per day or +3 pints per hour. 10 hours should be 30 pints or +3 gals. 2 gals is a little lite. The heat comes from the electricity used and the moisture removed. Removing 3 gals per day should keep your home <50%RH. 24/7 operation should maintain <50%RH throughout your home. Will it maintain <50%RH 24/7/
Return??????
I like the heavy duty Santa Fe Dehu but they cost more but are more efficient. Less heat, less electricty used, and more moisture removed.
Keep us posted.
Regards TB

[Ziocarl]

Thanks for the concise reposponse. Yeah I've heard those Sante Fe's are great, but I can't justify $ right now. To many other bills to pay.

I've been turning the dehumidifier on only when I know the ac will have long runs (morning and afternoon based on my settings). It's more work for me, but at least the AC counteracts the heat and circulates the air in the house while the dehumidifier is running, and I still get close to 2 gallons a day.

What I don't get is how this unit is supposed to be more energy saving (energy star and all) than my 11 year old kenmore and yet is puts out so much more heat. Am I right in assuming that the heat is left over wasted energy after the cooling and heating sides of the coil cancel each other out? Still wondering if it's possible for a compressor to put out more heat than cold or if the two, by nature, (not incluing waste heat), should always cancel each other out. Like if you ran an AC unit inside a room with the exhaust in the room, other than the heat from simply using power, wouldn't the cold air cancel out the hot air exhaust?

Finally, one of the big problems with these cheaper units is that they have moved the humidistat inside the unit (used to be exposed and outside on the kenmore). So when the unit turns off, the evaporation off the wet coils raises the internal humidity by at least 10% within minutes. When the dehumidifier turns on, the RH drops rapidly. This makes the unit cycle on and off constantly. To address this, I run the unit on "constant on" in the morning and afternoon and then turn it off for the rest of the day. Some units fix this issue by having the fan run constantly. Not only would this be annoying to anyone in the room, it also seems like an energy waster.

Can you suggest an external humidistat solution that might work? I found this
DAYTON 1UHG2 Dehumidifier Control,Plug In 120 V
Links to direct purchase sites are not permitted.

Has great reviews, but one person says "The only con so far is that it does not have enough hysteresis (slop) in the humidity level that is set so it cycles off and on a little too frequently. But for a normal basement this unit will work well."

Thinking of maybe getting a lower capacity (50 pint) unit to spread out the heater effect and one of those humidistats to solve the cycling. What do you think?

[teddy bear]

I've been turning the dehumidifier on only when I know the ac will have long runs (morning and afternoon based on my settings). It's more work for me, but at least the AC counteracts the heat and circulates the air in the house while the dehumidifier is running, and I still get close to 2 gallons a day.

Finally, one of the big problems with these cheaper units is that they have moved the humidistat inside the unit (used to be exposed and outside on the kenmore). So when the unit turns off, the evaporation off the wet coils raises the internal humidity by at least 10% within minutes. When the dehumidifier turns on, the RH drops rapidly. This makes the unit cycle on and off constantly. To address this, I run the unit on "constant on" in the morning and afternoon and then turn it off for the rest of the day. Some units fix this issue by having the fan run constantly. Not only would this be annoying to anyone in the room, it also seems like an energy waster.

Can you suggest an external humidistat solution that might work? I found this
DAYTON 1UHG2 Dehumidifier Control,Plug In 120 V
Links to direct purchase sites are not permitted.

Has great reviews, but one person says "The only con so far is that it does not have enough hysteresis (slop) in the humidity level that is set so it cycles off and on a little too frequently. But for a normal basement this unit will work well."

Thinking of maybe getting a lower capacity (50 pint) unit to spread out the heater effect and one of those humidistats to solve the cycling. What do you think?

Something wrong with the way this is working out for you.
When you a/c runs the most, the dehu should not be needed. Is your a/c doing its basic job of keeping your home dry and not needing the dehu. Make sure your a/c has a 45^F cooling coil temp to max moisture removal. I would expect that your dehu is best operate during the evening hours. A timer on your plug in could help this. 2 gals of moisture is 20,000 btus of heat plus the electricity used. More moisture removed, the more heat. Keep the larger dehu, you will need it. What about some fresh air to purge indoor pollutants and renew oxygen. The next dehu you buy should be a Santa Fe/Ultra-aire dehu. More efficient and durable.
Regards TB

[second opinion]

2 AC systems 1300 square feet, might be the problem

[Shophound]

2 AC systems 1300 square feet, might be the problem

OP stated first floor is 1,300, basement is ~700, upstairs area not defined.

OP should consider running a/c blower on "auto" vs. "on" to prevent evaporating moisture off the cooling coil when the compressor is not running.

[Ziocarl]

yes bottom two levels finished are 2000 sq ft. Top floor is 1300 sqft. The AC units are what they are. No plans to change them until they break.

I usually use auto on the fans, but for downstairs I set to "on" while dehumidifying just to circulate moist and dry air. Don't I WANT to evaporate moisture off the cooling cool to prevent mold in the AC unit?

Still wondering if a defect or design flaw in the dehumidifier could cause the cold coils to not get cold enough and the warm to get too warm. How cold should the cold get? Maybe I can slide a meat thermometer in there and touch them to check them out.

[teddy bear]

yes bottom two levels finished are 2000 sq ft. Top floor is 1300 sqft. The AC units are what they are. No plans to change them until they break.

I usually use auto on the fans, but for downstairs I set to "on" while dehumidifying just to circulate moist and dry air. Don't I WANT to evaporate moisture off the cooling cool to prevent mold in the AC unit?

Still wondering if a defect or design flaw in the dehumidifier could cause the cold coils to not get cold enough and the warm to get too warm. How cold should the cold get? Maybe I can slide a meat thermometer in there and touch them to check them out.

One more time, expect heat from the dehumidifier! If its removing moisture, it is working. During high cooling loads, your a/c should keep your home drier.
Wow.
Regards TB

[Shophound]

yes bottom two levels finished are 2000 sq ft. Top floor is 1300 sqft. The AC units are what they are. No plans to change them until they break.

I usually use auto on the fans, but for downstairs I set to "on" while dehumidifying just to circulate moist and dry air. Don't I WANT to evaporate moisture off the cooling cool to prevent mold in the AC unit?

No, you do not want moisture to re-evaporate into the air from the coil when the compressor is not running. This may be contributing to your humidity problem. As for mold, keeping your filters changed on a regular basis can go a long way toward minimizing that potential, along with having the system serviced when the blowers and coils get dirty.

Still wondering if a defect or design flaw in the dehumidifier could cause the cold coils to not get cold enough and the warm to get too warm. How cold should the cold get? Maybe I can slide a meat thermometer in there and touch them to check them out.

Nope...TB is right. There are few here on this board who know dehumidifiers better than him. A dehumidifier will always put more heat into a room as it operates. It is not only adding heat because of removing moisture, but heat from the compressor, fan motor, and heat of compression. That is a net heat gain over the cold temperature of the coil where the humidity condenses out.

[Ziocarl]

ok. Thanks for the help.

[energy_rater_La]

so what temp heat should dehumidifier put out?
does a whole house dehumidifier have less heat or more?
what are normal/average temp ranges for both?

I have a friend who runs her stand alone all the time.
to begin with...she had to empty it every couple of hours
..it remove that much humidity. now she empties it every
few days. humidity is now under control.
although I'm sure she has to empty it more yesterday with
all the rain!

just curious about temps of heat in stand alone vs whole house.
thanks.

[teddy bear]

Dehumidifiers all generate heat. The sum of the heat is 1050 btus per lb. of moisture removed from the air plus 3,414 btus per kw of electricity used. Usually the whole house dehus are more efficient than free standing dehus. Therefore they use less electricity per lbs. of moisture removed. The most inexpensive dehus remove 1-2 lbs. of moisture per kw. The best dehus remove 7-8 lbs. of moisture per kw.Most a/cs remove 2 lbs. of moisture per Kw.
We should always setup a/cs to remove enough moisture to maintain <50%RH during days of high cooling loads. No a/c is able to maintain <50%RH during low/no cooling loads. Supplemental dehumidification is always needed during the hours of low cooling loads and outdoor dew points of +50^F dew points. Most do not have supplemental dehumidification and therefore have many hours of +50%RH.
To make things more complicated, all homes need fresh make-up air to purge indoor pollutants and renew oxygen. Also occupants add moisture from breathing, presperiation, and activities.
Its difficult to understand that the best of cooling system need supplemental dehumidification during low/no cooling loads.
Regards TB

Regards TB

[Ziocarl]

So I kept the Frigidaire. I wasn't clear on one thing, though. Since the internal humidistat is so inaccurate and causes short, constant cycling of the compressor, do you think I should set the humidifier to constant on and use a normal timer or an external plug in humidistat (DAYTON 1UHG2 Dehumidifier Control,Plug In 120 V)? Which one?

If I were to use a timer, does it need to be a heavy duty one, or will a standard timer (type people use with lamps) be safe? What specs should I look for?

Thanks again!

[teddy bear]

So I kept the Frigidaire. I wasn't clear on one thing, though. Since the internal humidistat is so inaccurate and causes short, constant cycling of the compressor, do you think I should set the humidifier to constant on and use a normal timer or an external plug in humidistat (DAYTON 1UHG2 Dehumidifier Control,Plug In 120 V)? Which one?

If I were to use a timer, does it need to be a heavy duty one, or will a standard timer (type people use with lamps) be safe? What specs should I look for?

Thanks again!

The Dayton control is OK and offers control based on %RH. The timer will overrun the dehu during low %RH and may not operate enough during high %RH.
Keep us posted.
Regards TB

[Ziocarl]

Will do, and thanks again.

Oh! Just remembered something that has been plaguing me for years and is right up your alley. My house is sort of built into a hill, so the garage is actual attached to the basement and a part of the bottom level of the house. You have to walk up a set of outside steps to get into the main level of the house. The garage is cinder block and partially underground (side and back). Ceiling of garage is dry-walled and insulated, I believe, but main AC trunk runs through that ceiling and leads to 4 vents in my family room above....this might contribute to a little cooling in the garage (probably not much though). It gets VERY humid in the garage. So much so that by the end of the summer, most cardboard or fabric items have some mold on them. I've been trying to think about how to fix this. If I open the garage during the day, I let in a ton of hot water-logged air, which cools over night and results in even higher RH. Have thought about the following:

1) seal concrete floor and walls to prevent moisture penetration from ground
2) run a dehumidifier in garage (seems unrealistic and expensive)
3) install some sort of vent in the side, cinder block wall of the garage (facing outside) with a fan controlled by a plug in humidistat.

With #3 though, won't I just be pulling in more 70% + RH air from outside? Is that better than what's in the garage to begin with? How can I get the garage down to below 60% RH?

Thanks.

[energy_rater_La]

oh btw...my house is built into the side of a hill!!
LOL!

[teddy bear]

Will do, and thanks again.

Oh! Just remembered something that has been plaguing me for years and is right up your alley. My house is sort of built into a hill, so the garage is actual attached to the basement and a part of the bottom level of the house. You have to walk up a set of outside steps to get into the main level of the house. The garage is cinder block and partially underground (side and back). Ceiling of garage is dry-walled and insulated, I believe, but main AC trunk runs through that ceiling and leads to 4 vents in my family room above....this might contribute to a little cooling in the garage (probably not much though). It gets VERY humid in the garage. So much so that by the end of the summer, most cardboard or fabric items have some mold on them. I've been trying to think about how to fix this. If I open the garage during the day, I let in a ton of hot water-logged air, which cools over night and results in even higher RH. Have thought about the following:

1) seal concrete floor and walls to prevent moisture penetration from ground
2) run a dehumidifier in garage (seems unrealistic and expensive)
3) install some sort of vent in the side, cinder block wall of the garage (facing outside) with a fan controlled by a plug in humidistat.

With #3 though, won't I just be pulling in more 70% + RH air from outside? Is that better than what's in the garage to begin with? How can I get the garage down to below 60% RH?

Thanks.

Controlling mold requires several hours of <50%RH daily. Of course, a timer controlled dehumidifier would be a fix. The more air tight/moisture proof the space is, the smaller the dehu could be. A small dehu operating for several hours each evening could be a solution.
Another fix could be several hours of enough dry air from the home to the space during times of the year when the garage was damp.
A small duct fan on a timer sounds simple. This assumes that you have a little extra drying ability in your home to deal with the outside air that will pass through the home to the garage. If you had (or after you have) a whole house dehu you could route a 4" supply of dry air to the space. 30-50 cfm of dry air for 6-8 hour per evening would be enough.
I would wary about this problem any more this year, next spring remove anything that can get moldy or??
By the way, overheating from a dehumidifier indicates a too low of a setting.
Regards TB

[Ziocarl]

I had always figured that running a dehumidifier in the garage would make me NEVER want to open the big double wide garage door because it would mean dehumidifying the outdoors, but it sounds like from what you are saying I could just set the dehumidifier to run at night, while the door is closed. Sealing the floor and walls would reduce run-time further...got it.

Regarding the vent, I was thinking that it would be on the OUTSIDE wall venting out to the outside, along with an intake also on an outside wall...the idea was to bring outside air in, but then there is the issue of outside air during the summer being way over 50%RH. I see what you are saying about bringing in dry living space air, but how would that air be replaced in the home? I don't like the idea of pulling air into the living space through cracks and crevices, so would I have to create an outside air intake (crack a window)? Guess that would solve the "removing pollutants from the living space" issue, but otherwise, isn't that a less efficient route to the same results that you would get from simply putting a dehumidifier in the garage?

"By the way, overheating from a dehumidifier indicates a too low of a setting." - please explain.

Thanks.

[teddy bear]

I see what you are saying about bringing in dry living space air, but how would that air be replaced in the home? I don't like the idea of pulling air into the living space through cracks and crevices, so would I have to create an outside air intake (crack a window)? Guess that would solve the "removing pollutants from the living space" issue, but otherwise, isn't that a less efficient route to the same results that you would get from simply putting a dehumidifier in the garage?

"By the way, overheating from a dehumidifier indicates a too low of a setting." - please explain.

Thanks.

A small amount of outside infiltrates your home. An equal amount exfiltrates. The amount depends on the wind, stack effect, and exhaust fans. The most of the air moves through the cracks. 40 cfm into the garage means little. If you had a whole house dehu, you would bring in a small amount of air to assure correct air change during the mild calm seasons. The dehu could also provide dry air to the garage. The WH dehu has a timer to provide this during evening hours. When your clothes drier, bath fans, kitchen hood operate, the make-up air infiltrates through the cracks.

Regarding dehu settings. As the dehu warms the air, the %RH declines, -2%RH per degree rise. As you lower the setting of the dehu, the amount moisture removed decreases/KW used increases and the temperture rise increases. Make the %RH setting as high as acceptable. This will minimized the heat gain, as opposed to setting is lower which may require the dehu to run none stop.
Regards TB

[Ziocarl]

This might be crazy, but I always crack a window (even in winter) when I run any type of exhaust fan. I don't like the idea of air filtering through dirty crevices making it's way into my house. I also feel like it allows the exhaust fans, especially the bathroom ones that are a little undersized, move more air out of the house.

How would I bring air into the garage? a hole in the wall between garage and living space with a louvered fan on a timer? How do I ensure that the exhaust from the garage makes it outside instead of circulating back into the living space?

Thanks for the explanation on the dehu settings.