[crossdw]

I am researching dehumidifier installations and need some help please. I live in southeast Texas where it's humid most of the time. I recently built an ICF home and have noticed that the humidity runs between 60% and 75% most of the time. I do have an ERV but due to the outside temps and humidity levels it doesn't get much use. I have an energy efficient central AC unit (Trane XL20i 5-ton 2 stage) but with the concrete walls the temp stays around 70F so it hardly runs, and when it does, it doesn't run long enough to remove the humidity.

So now I am looking at installing a dehumidifier (Aprilaire 1870) and in reviewing the installation manual I see that their preferred method is to install the intake for the dh to the air return, pass through the dh, then return the air on the other side of the AC unit to the main supply plenum for distribution to the whole house.

The AC contractor wants to make this a standalone system and basically cut two new ducts (intake and exhaust). This is an alternative installation in the Aprilaire manual but not the recommended one.

My question is this - which is the better installation and why? It seems that by pulling the air from the main return duct and then returning the dehumidified air to the supply which is sent all through the house as opposed to a more localized distribution. I'm not an AC expert but I would like to be informed when talking with him so I can feel comfortable it's done right if he is recommending something different than the manufacturer.

Thanks

 

[SeniorSitizen]

After reading this lengthy article it looks as if a stand alone dehumidifier may be in order for your situation.

http://www.greenbuildingadvisor.com/blogs/dept/musings/hrv-or-erv

 

[beenthere]

5 tons on an ICF home? 5,000 sq ft home is my guess then.

The preferred method of installation is to pull from the return, and supply back to the return. So that air flow through the dehumidifier is not reduced, and so that the whole home is dehumidified at the same time.

 

[Bret86844]

How recently did you build your home? It's not even close to peak summer temps. Once your central AC runs more it's going to dehumidify much more(seems like you already know this). I'd hate to see you install a dehumidifier only to find out it's only useful a few weeks every year.

 

[beenthere]

How recently did you build your home? It's not even close to peak summer temps. Once your central AC runs more it's going to dehumidify much more(seems like you already know this). I'd hate to see you install a dehumidifier only to find out it's only useful a few weeks every year.

Only takes few weeks to develop a severe mold problem.

 

[crossdw]

How recently did you build your home? It's not even close to peak summer temps. Once your central AC runs more it's going to dehumidify much more(seems like you already know this). I'd hate to see you install a dehumidifier only to find out it's only useful a few weeks every year.

The house is 4 years old (built in 2012). You are correct about the temps not being hot yet. But, with the ICF walls, even during the middle of summer the house maintains about 72F so the AC hardly runs, and certainly does not run enough to remove the humidity. Obviously with hot temps and high humidity outside we don't open the windows to ventilate the house, and the ERV is pretty much useless unless the conditions outside are just right (mild temps, humidity below 60%).

My concern is that the installer wants to cut two new holes and install vents when I'm not sure it is the optimal method so I'm asking for some input from those who may have them in their homes or from installers.

The manufacturer suggests installing it in-line with the AC unit and can run either with or without the AC unit running. My local installer's recommendation, however, is to make it totally standalone which the manufacturer says it more of a localized installation to address humidity issues in a particular room.

Thanks

 

[beenthere]

Tap it into the return like I said, and let the air handler distribute the air through out the house. Much better performance that way, then stand alone.

How many sq ft is your house.

 

[crossdw]

3500 sq ft

 

[roughneck]

Without a doubt the unit will perform better tied into the air handler.

 

[beenthere]

3500 sq ft

Even in Texas, a 5 ton A/C is over sized for a 3500 sq ft ICF house. So you'll be using the dehumidifier a fair amount of the summer.

Installed as a stand alone, you would find some areas not as low in RH as others.

 

[SeniorSitizen]

This is beginning to answer some of my questions about the actual utility savings and the climatic areas where ICF built homes may or may not be advantageous.

Running a de-humidifier and air handler 24/7 certainly isn't contributing to operational cost savings.

 

[crossdw]

This is beginning to answer some of my questions about the actual utility savings and the climatic areas where ICF built homes may or may not be advantageous.

Running a de-humidifier and air handler 24/7 certainly isn't contributing to operational cost savings.

I'm not sure I agree. The ICF serves multiple purposes for me - first, it is much more thermally efficient than comparable stick frame homes around me but it's more than just the ICF. I also have closed cell foam spray insulation on the underside of the roof and radiant heat material on the top under the shingles, both of which help contribute to that efficiency. Even on the 100F days we have during the summer my attic space only gets about 10 degrees above the air conditioned space below. This helps because the air ducts are run through the attic and the AC doesn't have to work nearly as hard to maintain the temp. Secondly, we have hurricanes here so the house is built to withstand up to 225mph winds. Hopefully I never have to prove that, but it sure helps with windstorm and homeowner's insurance costs.

Strictly from an energy savings standpoint though, my electric costs average $110/month. In talking with neighbors, theirs are double that or more. Going back to your comment about the ERV and dehumidifier, I can't run the ERV 24/7 simply because of the outside temps and humidity levels. It only passes fresh air into the house, it doesn't "condition" it. Yes there is some humidity transfer at the core but when there's 90% humidity outside it's not enough to justify running the unit so we very rarely use it.

As for the dehumidifier, I won't know until it's installed but I suspect once we get the humidity level down to the proper levels it should only cycle occasionally to maintain that level and not run 24/7. It's also an Energy Star unit for whatever that's worth.

 

[roughneck]

This is why it's very important to find the right contractor to do a house like that. Many contractors still size based solely on sq ft, which is wrong and causes things like you are experiencing. Your energy usage would likely be lower with properly sized equipment.

 

[crossdw]

This is why it's very important to find the right contractor to do a house like that. Many contractors still size based solely on sq ft, which is wrong and causes things like you are experiencing. Your energy usage would likely be lower with properly sized equipment.

Absolutely. We won't get into the contractor part as I had to fire him less than halfway through. The bigger issue is finding someone who knows anything about ICF in this area. It's almost unheard of and you get funny looks when you tell someone your house is made of concrete.

I'll be interested to see, once the humidity is down, if my electricity bills go down any or if I'm just trading it for the energy usage to run the dehumidifier.

 

[beenthere]

This is beginning to answer some of my questions about the actual utility savings and the climatic areas where ICF built homes may or may not be advantageous.

Running a de-humidifier and air handler 24/7 certainly isn't contributing to operational cost savings.

The dehumidifier and air handler won't have to run 24/7. But his air handler has a VS ECM blower, so running it 24/7 cost very little.

Once the dehumidifier has the humidity down, it will shut off untill it builds back up.

With lower humidity, many people find they don't need to set the temp as low. And save on their cooling cost.