Comments on: An Energy Recovery Ventilator Is NOT a Dehumidifier

By: George Reynolds

George Reynolds — Sat, 25 Oct 2014 21:38:11 +0000

The CDC has a lengthy
The CDC has a lengthy discussion about ebola and AGP (aerosol generating procedures) for patients. I am well aware that many pathogens cannot exist in air. However, an aerosol is not air, it is an airborne solution.

By: David Butler

David Butler — Thu, 25 Sep 2014 14:30:12 +0000

@Ryan, sorry I missed your
@Ryan, sorry I missed your intent to use SD12 for ventilation. According to the specs, the ventilation feature is just an option, not a primary function. The ventilation rate would be determined by the static of the outside air duct, fine tuned with a balancing damper. In REM, it would be modeled like any other supply-only ventilation system (in addition to the AC function).

In order to satisfy 62.2 with a supply-only system, the blower must be set to operate off-cycle to ensure a consistent ventilation rate. In this case, you're operating what's essentially a one ton blower between cooling and DH calls to draw in a much smaller volume of OA necessary to meet your design ventilation CFM. The penalty can be substantial, depending on blower watts and typical operating cycle, which for this product, may be 0 for much of the year.

According to the specs, the SD12 blower consumes 160 watts (348 to 406 CFM depending on static). That's a LOT if it has to operate 8760 hrs/yr!

The blower penalty can be reduced somewhat by using a cycle timer (as opposed to continuous fan) and increasing the OA volume accordingly to achieve the desired effective rate (see cycle-timer ventilation option in REM, and refer to the 62.2 table on duty cycle adjustments). Note that running the SD12 blower off-cycle with a high OA ratio can cause comfort issues in cold weather. You might be better off bringing in your ventilation air separately with a 30 or 40 watt ERV, allowing it to mix with house air, then let the SD12 handle the diversified DH and first stage cooling load.

By: Ryan Moore

Ryan Moore — Wed, 24 Sep 2014 07:16:36 +0000

Tim & David,
Tim & David,

The dehumidification side makes sense to set that up as a custom A/C in REM/Rate, but the ventilation is more difficult. It's obviously supply only, but what CFM? What wattage? What is the duty cycle? In short, how am I meeting ASHRAE 62.2 with this unit? All the literature I can find online is mum on the subject. I'm going to call the manufacturer tomorrow and see if I get anywhere.

By: David Butler

David Butler — Tue, 23 Sep 2014 21:43:03 +0000

In REM, you can set up a
In REM, you can set up a custom AC and set the total (sensible + latent) capacity and the SHR according to the mfr specs. Depending on how the specifications are given, you may have to back into total capacity.

By: Tim O'Brien

Tim O'Brien — Tue, 23 Sep 2014 19:59:31 +0000

Reply to Debbie -
Reply to Debbie -

The Ultra-Aire dehumidifier creates a warm and dry supply air stream when dehumidifying. It sounds like most of the dehumidifier supply air is exiting thru your kitchen supply grille. I will assume the following constraints exist:

Dehumidifier will not be relocated
Supply ducting will not be modified

The dehumidifier processes less air than your air handler so the supply ducting is oversized for the dehumidifier air flow (alone). This allows the dehumidifier process air to be "lazy" and find the shortest path from the supply to the return. This is typically not a problem unless you occupy a spot near the supply in the short path (which sounds like the case in your house). You can check this theory by reviewing the air flow from other supply grilles (while the dehumidifier is operating)in your house and comparing to your kitchen supply. If your kitchen supply seems to be getting all/most of the warm dry air, than it is the short path.

There are some options to address this comfort issue. These options may increase the time of operation and cost to operate your HVAC equipment, but should improve your comfort in your kitchen.

If the Ultra-Aire supply duct directly opposes your kitchen supply drop, the dehumidifier supply air velocity may be carrying most of the dehumidifier supply air to that drop. Modifying the dehumidifier supply duct connection to direct the dehumidifier supply away from the kitchen supply drop is a passive solution which will reduce the amount of warm dry air emanating from your kitchen supply.

Have you tried interlocking your air handler fan with the Ultra-Aire dehumidifier when it runs? The Ultra-Aire DEH3000 controller can be configured to do this. This will help in two ways:

1 - by adding more air to the supply and pressurizing the supply plenum air will better distribute to all of the supply grilles in your house

2 - mixing the warm dry dehumidifier supply air with cooler return air from the air handler will reduce the temperature of the mixed supply air making the warming effect of the dehumidifier less noticeable when it reaches you

Since you have a variable speed AC you could also operate the AC on low speed when the dehumidifier runs if you want cooling in addition to dehumidification, but I suggest you try running just the air handler fan first.

Feel free to contact me if you wish to discuss these options.

By: Tim O'Brien

Tim O'Brien — Tue, 23 Sep 2014 18:25:05 +0000

Reply to Ryan Moore -&
Reply to Ryan Moore -

I am not familiar with and have not used REM/Rate, but I would describe the SD-12 as Curt above - a one ton air conditioner with an unusually low sensible heat ratio (SHR). I'm not sure if the unusually low SHR value will cause problems with the REM/Rate software calculations.

Feel free to contact me if you wish to discuss in more detail.

By: Debbie

Debbie — Tue, 23 Sep 2014 18:10:25 +0000

David,

David,
moving the dehumidifier isn't an option. with limited space in closet & on the supply plenum...this is the only location that fits.
as I will be adding fresh air intake...again part of the whole plan...redesign isn't going to happen.

what saves me, unlike most homeowners, is that the vs ahu handles most of the humidity. as it is, I'm only using dehumidifier in the shoulder seasons. where as normally unit wouldn't run & RH inside would rise, the dehumdifier takes care of the humidity.
not ideal...but workable.
its ok with me, I figured all of this out before the install, just didn't expect to feel the dehumdifier heat.

Roy, cooler air while cooking isn't a bad deal for me.

I'm not really looking for a 'fix', just sharing what I've learned.

I've been in the efficiency business for 15+ years & each step of making my house more efficient was well planned. the afterthought was the dehumdifier, too good of a deal to pass up.

in a different configuration the heat from dehumidifier wouldn't be as noticeable. but putting equipment & ducts in conditioned space is the big savings for me.

By: Ryan Moore

Ryan Moore — Tue, 23 Sep 2014 09:04:28 +0000
Does anyone have advice on
Does anyone have advice on how to model the SD-12 in REM/Rate?

By: David Butler

David Butler — Tue, 23 Sep 2014 01:40:35 +0000
+1 to what Tim said.
+1 to what Tim said.

@Ted, I get your comment about homeowner confusion, but we need to cast aside the notion that dehumidifiers must have compressors. For example, we can dehumidify with chilled water coil. And exhaust fans are most definitely dehumidifiers! Commercial systems are available that use a desiccant media. And yes, windows are great dehumidifiers. The problem is what happens to all that water!

@Debbie, there are a couple of ways you can reduce your DH costs. (a) Raise set-point to the high 50's, still within comfort range. No point in paying extra to get to "50% or lower", when you can be very comfortable at a higher setting.
(b) Move the unit to a location where you won't notice the extra heat, or a cooler part of the house. As long as can communicate with the rest of the house (e.g., no closed doors), moisture levels will equalize fairly quickly wherever you put it.

By: Roy

Roy — Tue, 23 Sep 2014 01:39:13 +0000
Debbie,

Debbie,

I feel your pain. Space constraints are always a problem. However, there are other additional issues with going to a split system dehumidifier. I am sure that the product cost is higher, installation costs are higher, and then you have to worry about proper refrigerant charging after field installation. Also, for your particular application, do you think that having cool air blowing on you in the kitchen with a split dehumidifier would be less uncomfortable than warm air?