Whole-house dehumidifier?

[hihum]

We have a split-system HVAC in our townhouse, with a 15-yr old gas furnace (Lennox Diplomat) and a new Trane XL15i 2-ton A/C for our 500 sqft walk-out level and the 800 sqft main level; in the attic we have a 15-yo gas furnace and a new 1.5-ton XL15i, for the 800 sqft upper level.

We had the A/Cs replaced because they were 15 yrs old and not dehumidifying properly, and the one in the attic was rusted and leaking. The new A/Cs do no better. They cool fine--just don't dehumidify as they should. I asked our HVAC tech to decrease the speed on the blower (it does blow very hard) but he said it is not a variable speed blower, therefore, he could not do it.

Should we get a whole-house dehumidifier? The walk-out level stays at 65% without a dehumidifier. Even when we run the air for a few hours to get the temp to 73 degrees, the humidity does not decrease by more than 2%. On the main and upper levels the humidity is 55-60%, and running the A/C doesn't do much good there, either. (We live in NoVA, moderate-high humidity.)

I don't even know if a whole-house dehumidifier would fit in the closet off our garage that holds the HVAC equipment. If we can't do that, how do we decrease the humidity? Is there some device we could add to decrease the blower speed on a single-speed blower, or to make it variable speed without having to replace the two furnaces which could last another 10 years?

(We're on our third portable dehumidifier in 1.5 years. Soleus is good for crap, I discovered after spending $400 on two of them. We'll see how the Frigidaire I purchased today for $200 works.)

Thanks for your opinions.

[beenthere]

Call your installing company back up.
And ask them what speed they have the blower set for. Or what CFM its moving.
Your blower speed/CFM is most likely adjustable.

Sounds like they just replaced like size. Instead of doing a load calc.

[BobbyBJr]

Yes, the blower speed is most likely adjustable. There are also after market variable speed motors available, so there is some options.

[Shophound]

Have your contractor check the ducts in the attic for any leaks, especially on the supply air side of that attic furnace. Supply air duct leaks in an attic can make controlling humidity within the house very difficult. Same holds true for the return air side.

You may also have air leaking into your house from various areas. An option available to you is to have your house leak tested via using a "blower door". The person who does this will best serve you if he/she can tell you where the worst leakage areas are, and how to remedy them.

[teddy bear]

We have a split-system HVAC in our townhouse, with a 15-yr old gas furnace (Lennox Diplomat) and a new Trane XL15i 2-ton A/C for our 500 sqft walk-out level and the 800 sqft main level; in the attic we have a 15-yo gas furnace and a new 1.5-ton XL15i, for the 800 sqft upper level.

We had the A/Cs replaced because they were 15 yrs old and not dehumidifying properly, and the one in the attic was rusted and leaking. The new A/Cs do no better. They cool fine--just don't dehumidify as they should. I asked our HVAC tech to decrease the speed on the blower (it does blow very hard) but he said it is not a variable speed blower, therefore, he could not do it.

Should we get a whole-house dehumidifier? The walk-out level stays at 65% without a dehumidifier. Even when we run the air for a few hours to get the temp to 73 degrees, the humidity does not decrease by more than 2%. On the main and upper levels the humidity is 55-60%, and running the A/C doesn't do much good there, either. (We live in NoVA, moderate-high humidity.)

I don't even know if a whole-house dehumidifier would fit in the closet off our garage that holds the HVAC equipment. If we can't do that, how do we decrease the humidity? Is there some device we could add to decrease the blower speed on a single-speed blower, or to make it variable speed without having to replace the two furnaces which could last another 10 years?

(We're on our third portable dehumidifier in 1.5 years. Soleus is good for crap, I discovered after spending $400 on two of them. We'll see how the Frigidaire I purchased today for $200 works.)

Thanks for your opinions.
Its all about cold a/c coils, fresh air infiltration, and how many hours your a/c runs per day. An a/c running for an hour with 45-50^F cooling coil should remove 3 lbs. of moisture per ton. A 3 ton a/c removes 9 lbs. of water per hour of operation if the coil is cold enough. Slow the fan motor or a better air filter are methods of slowing air flow. During partial cooling loads, the a/c cycles on/off. Short cooling cycles reduce moisture removal to the point where no moisture is removed. Adequate fresh damp air infiltration and moisture from the occupants is about 4 lbs. per hour. During low cooling loads, a dehumidifier removing 4 lbs. per hour provides <50%RH.

Getting a good whole house dehu takes care of low/no cooling moisture load, but an a/c with a high cooling load does not need supplemental dehumidification and should be set-up correctly.
P.S. Get a good w.h. dehu, I work for Santa Fe/Ultra-Aire, the oldest/most eff. w.h. dehu.
Regards TB

[fincomber569]

We have a split-system HVAC in our townhouse, with a 15-yr old gas furnace (Lennox Diplomat) and a new Trane XL15i 2-ton A/C for our 500 sqft walk-out level and the 800 sqft main level; in the attic we have a 15-yo gas furnace and a new 1.5-ton XL15i, for the 800 sqft upper level.

We had the A/Cs replaced because they were 15 yrs old and not dehumidifying properly, and the one in the attic was rusted and leaking. The new A/Cs do no better. They cool fine--just don't dehumidify as they should. I asked our HVAC tech to decrease the speed on the blower (it does blow very hard) but he said it is not a variable speed blower, therefore, he could not do it.

Should we get a whole-house dehumidifier? The walk-out level stays at 65% without a dehumidifier. Even when we run the air for a few hours to get the temp to 73 degrees, the humidity does not decrease by more than 2%. On the main and upper levels the humidity is 55-60%, and running the A/C doesn't do much good there, either. (We live in NoVA, moderate-high humidity.)

I don't even know if a whole-house dehumidifier would fit in the closet off our garage that holds the HVAC equipment. If we can't do that, how do we decrease the humidity? Is there some device we could add to decrease the blower speed on a single-speed blower, or to make it variable speed without having to replace the two furnaces which could last another 10 years?

(We're on our third portable dehumidifier in 1.5 years. Soleus is good for crap, I discovered after spending $400 on two of them. We'll see how the Frigidaire I purchased today for $200 works.)

Thanks for your opinions.

I live in NVA also and I put a cc750 on my builder grade cheepie systems in my house. I love it, it makes any psc motor work like var speed and really gets the humidity out. I installed a few honeywell tru dry WH dehumidifiers around here also. Your systems could be oversized but I betya anything the cc750 will make a huge difference. Watch my buddy Dr zarkloff's video about the cc750.

http://www.youtube.com/watch?v=f2Hd9PBqEBE&feature=channel_page


There are quite a few contractors in northern VA that sell these things.

[beenthere]

No it doesn't.

It can speed up a PSC motor to maintain CFM.
If the motor is 1075 RPM, thats all the faster the motor can spin.

It has its purpose. But it is not the same as having a VS blower.

[hihum]

During partial cooling loads, the a/c cycles on/off. Short cooling cycles reduce moisture removal to the point where no moisture is removed.

Today our main level A/C was cycling on and off every 7-10 minutes when we had the thermostat set at 75 degrees, and the humidity was around 50 when it was 60-65% outdoors.

Now, upstairs I had to set the thermostat to 73% (too cold for us) because the humidity is reading 60% (outdoors it's 95%). And now the upstairs one is cycling every 7-10 minutes.

Are those considered short cycles?

Thanks for all the posts here. I guess what I need to do is see if we can replace the motors with variable speed motors. I'll also check to see if I can find someone who will check for leaks. Around here all the A/C guys are too busy and they don't want to bother it seems. I asked about it when our new A/Cs were installed last year and the guy said the ducts last forever; didn't think they would cause a problem. They're buried in insulation in the attic or locked behind drywall on the main and lower level--too much trouble, I guess. IS there a way to check without digging them out and cutting the drywall?

I don't know why, when they charge like an M.D., they are not willing to find and resolve HVAC problems like an M.D. attends to health problems.

[beenthere]

Depends how hot it was outside.

[hihum]

Depends how hot it was outside.

It was around 83 in the afternoon. Now it is 70 degrees.

[beenthere]

At 83, 7 minutes is a little short.

Atleast, for around here it is.

[teddy bear]

During partial cooling loads, the a/c cycles on/off. Short cooling cycles reduce moisture removal to the point where no moisture is removed.

Today our main level A/C was cycling on and off every 7-10 minutes when we had the thermostat set at 75 degrees, and the humidity was around 50 when it was 60-65% outdoors.

Now, upstairs I had to set the thermostat to 73% (too cold for us) because the humidity is reading 60% (outdoors it's 95%). And now the upstairs one is cycling every 7-10 minutes.

Are those considered short cycles?

.
You may find this graph of my WI home interesting. I use a whole house dehumidifier as a fresh make-up air ventilating device.
A fresh air change every 4-5 hours removes internally generated moisture and maintains 50%RH in the home when the outdoor dew point is less than 45^F. Purging indoor pollutants is the primary objective. As the outdoor dew point rose to +65^F, the indoor %RH approached 60%RH on the maintain floor of the home. A basement graph will follow showing extremely high %RH requiring immedeate dehumidification to avoid musty odors. As the outdoor dew point decreased, the dehumidifier turned off. I will post the basement graph later. You have many days per year when there is little or a/c cooling loads making supplemental dehumidification a must for maintaining <50%RH even without fresh air ventilation. Notice that outdoor temps are + 80^F for several days. Recirculating the basement air throughout the home avoids any a/c operation until the basement warms up.
Regards TB

[teddy bear]

Here is the cool basement's %RH Graph. A little complicated showing the the ^F dew point of the outside, mainfloor, and basement. Interesting point is that the basement has a lower dew point than outside and mainfloor.
Cool Basement's humidity is controlled with 60-80 cfm of fresh make-up air ventilation with <40-45^F outside Dew point. +50^F outside dew point needs dehumidification to maintain <55%RH. The air inside the home is recirculated by a VS fan on "slow" 24/7. The basement is gradually warming making humidity control easier. The basement's dew point is below the occupied area. This indicates that the main source of moisture is most likely from the occupants. The basement moisture follows the outdoor air's moisture up and down or what??.
This basement is cooling the home until the basement warms-up.
Regards TB

[beachtech]

XL15i should be running with a V/S indoor motor. the mismatch is quite a challange on it's own!!!

more equipment and make up air may help matters, but i would rather install furnace that is correct match for the AC...

[hihum]

XL15i should be running with a V/S indoor motor. the mismatch is quite a challange on it's own!!!

more equipment and make up air may help matters, but i would rather install furnace that is correct match for the AC...

If this were a new home, I'd agree with you, but I'm recycler and as long as the furnaces are working well, it's hard for me to justify scrapping them. Anyone know how hard it is, and what it costs to switch the motor to a VS one?

[beenthere]

If this were a new home, I'd agree with you, but I'm recycler and as long as the furnaces are working well, it's hard for me to justify scrapping them. Anyone know how hard it is, and what it costs to switch the motor to a VS one?

We don't talk price here.

Ask your contractor.