Dehumidifier - DH90 to DR90 (Honeywell) and Fresh Air Damper Questions

[NickTF]

This forum is great. I’ve done quite a bit of reading and decided to go ahead and register. I have a 1700 square foot energy star home built in 2007 in Delaware on the Delmarva Peninsula and it can get quite humid. Back in around 2013 or so the DH90 that came with my home just quit. Me and my budy, who is an HVAC guy, went into the crawl to try to fix the DH90 but it appeared the coil just failed. I was a bit disappointed and frustrated at the time given the $1350 or so cost of these units. Because of the cost and our financial situation at the time and my ignorance to the benefits of the fresh air plumbed in to the DH90 we just got by with portable dehumidifiers I placed by one of the returns. They kept the humidity at bay but we were largely not getting any of the benefit of the fresh air. After having kids in 2016 and them getting sick with enough frequency we bit the bullet and replaced the DH90 with a DR903000A. We’ve had the unit up and running for a bit and I’ve spent a lot of time fulling around with it and reading Teddy Bear’s advice. The unit is plumbed to pull air from one of the home’s two returns and feed the air into our supply plenum for distribution into the home. It is also connected to our fresh air plumbing just like the old DH90 was. I tried running the unit with the furnace fan set to come on when the dehumidification is called for (Vision Pro IAQ commands our two stage gas furnace, indoor unit, outdoor unit, and DR90). The DR90 could never satisfy the 45% humidity setting this way except in the wee hours of the morning. I then changed settings so the furnace fan would only come on during the call for ventilation. Still, the unit didn’t keep up great. I finally set it to I believe what Teddy Bear would recommend which is the DR90 run byitself totally independent of the furnace fan. That was the ticket to being able to achieve the 45% setting. I suppose this makes perfect since as there is no furnace fan blowing water off the dehumidifier coils before the water can drip out of the dehumidifier to the condensate pump. It strikes me odd that the common recommendation is to have the furnace fan run when the dehumidifier does. The dehumidifier seems to be so much more efficient when the unit runs independent of the furnace fan. I’ve since bumped the humidity setting up to 50% as I’d expect the cost of electricity to be much better at this setting. In any event I welcome any comments or suggestions.
Also, I’ve never truly understood the automated fresh air damper. I’ve observed the damper while I have someone turn ventilation from off to auto to the command on setting (have to enter amount of minutes). It didn’t appear that the damper moves at all when observing the shaft for the butterfly. I took a pic of the damper with the filter removed from the dehumidifier to get my hand in there. The damper is ever so slightly cracked open. Is this normal? Should it close completely when ventilation is set to off? Should it be much further opened when there is a command for ventilation?

[teddy bear]

I doubt that the ventilation is working. The damper should open when vent timer activates. Is your replacement dehu like the original or is it the new Honeywell China version?
Start by manually opening the fresh air damp and blocking it open until you get the working. Not opening could be a jammed damper or failed damper. Also the time or relay in the dehu could be the problem.
Sucking on the return and blowing into supply not ideal. Better to suck from the open part of the home and blow into the a/c supply. Also does you a/c control the %RH during long cooling runs without the dehu, if not slow the air flow through you a/c by slowing the fan or by restriction by using bettter filters.
Should maintain 50%RH without the dehu during long runs.
Keep us posted.
Regards Teddy Bear

[NickTF]

I have no idea on where the unit was manufactured it is smaller than the old dh90 externally it seems. If there is something for me to look for let me know.

Teddy, is there a quick continuity test of sorts I can perform on the fresh air damper to determine if it is functioning or not? The installer did wire things incorrectly the first time by connecting the fan control from the controller to the c terminal instead of the fan terminal. It blew a fuse in the dehumidifier when I turned ventilation on which the installer came out and replaced. It is possible something else popped. I have pics but I can’t post them yet as a new member.

[NickTF]

Also, a dedicated return for the dehumidifier is not an option. That said, would you recommend continuing to run the unit as is or using the furnace fan during the call for dehumidification/ventilation?

[teddy bear]

Running the fan is a must when dehumidifying to prevent recirculating the dry air from the dehu back through the a/c cooling coil to the dehu if the a/c fan is not running.
Not a big deal on the units origin.
Fresh air when occupied during the mild seasons is important.
Regards Teddy Bear

[NickTF]

Looks like I can just check to verify 24v is present when calling for ventilation to rule out whether the issue is the actuator (my suspicion) or on the control side.

I see regarding the fan and that does make sense. For what it's worth as far as I know the humidistat is located in the Vision Pro IAQ so despite the possible re-circulation of dry air back through the coil when the AC isn't running the dehumidifier appears to be achieving the desired humidity in the house living space.

[teddy bear]

Could be ok. Monitor the temperature of the ducts after the dehu operates for some time. If by feeling the ducts for warmth, you can tell where the warm dry air going. If most of the warm dry is going into the home instead warming up the air handler, it working ok.
Let us know how it works out.
Regards Teddy Bear

[NickTF]

I checked the connection from dehumidifier to damper and sure enough 26v when command for ventilation and zero v when no command for ventilation. Also noticed the actuator on my eard6 damper and it was warm like something isn’t quite right. Looks like it is definitely the issue there.

I zip tied the damper wide open and ran the dehumidifier that way for a bit. Turned the house into the amazon. It was a very humid day but wow. Will have to pick my days for fresh air I suppose. A bit disappointed figured the dehumidifier would keep up much better than that.

[teddy bear]

Check the amount of moisture being removed per hour with and without fresh air on. You may be getting to much fresh air. Expect 3 lbs. of moisture removal per hour. That is enough to handle 70-90 cfm of fresh air with a 70^F dew point reduced to 55^F dew point. Also when the a/c operates, it will remove 2-3 lbs. per hour per ton.
Fresh air when occupied and calm winds.
Keep us posted.
Regards Teddy Bear

[NickTF]

Teddy, if I was to decide to put a dedicated return in for the dehumdifier, what would be the minimum area required for the return for the DR903000A? I suppose the easy answer would be absolutely no smaller than the intake of the dehumidifier itself which is 10" in diameter I believe. Long ago I installed an infinite baffle subwoofer system with two manifolds sunk into the floor each carrying 2 18" infinite baffle subwoofers with 2.5" of travel. I don't know if the wife will be too keen on adding any more holes in the floor hence my original resistance to the idea.

[teddy bear]

10" diameter would be ideal. Could be smaller because some air also comes from the outside and if the return from the open part of the home is not very long. Also consider some air from the basement (if there is) to the dehumidifier and some dry air to the basement as part of the ducting.
Regards Teddy Bear

[NickTF]

10" diameter would be ideal. Could be smaller because some air also comes from the outside and if the return from the open part of the home is not very long. Also consider some air from the basement (if there is) to the dehumidifier and some dry air to the basement as part of the ducting.
Regards Teddy Bear

The house is a single story rancher of 1700 square feet with a fully conditioned crawl space. If I decided to run the dedicated return i'd just run the current 10" return over to a 12" x 12" square x 10" round ceiling register I cut into the floor with a slightly larger grill fastened over top somewhere in the living room floor area under one of pieces of furniture which is wide open. I saw some ducting which was a 10" round to a 6 x 4 square vent opening but that seems way too restrictive at less than half the area of the 10" diameter supply side of the dehumidifier.

[teddy bear]

May also be noisy because of the 200 cfm flow through the .166 sq.ftl opening. You could try it. It will not too restrictive because of the restriction is very short, the thickness of the floor.
Better enlarging the opening. Hope you are having a contractor do the work.
Regards Teddy Bear

[NickTF]

May also be noisy because of the 200 cfm flow through the .166 sq.ftl opening. You could try it. It will not too restrictive because of the restriction is very short, the thickness of the floor.
Better enlarging the opening. Hope you are having a contractor do the work.
Regards Teddy Bear

You mean the contractor who wired the dehumidifier wrong and blew a fuse? The contractor who said the damper worked fine but never bothered to check and turns out it is obviously a bad actuator? With all due respect putting a squar box through the floor and covering it with a fancy grill while taping up some insulated flex ducting is super simple compared to building a pair of infinitely baffle subwoofers in the crawl so I will do what I should’ve done in the first place and take care of it all on my own. I wish I had contractors like you around but I’m done throwing money in the fire and instructing people I pay how to fix their mistakes.

[teddy bear]

You mean the contractor who wired the dehumidifier wrong and blew a fuse? The contractor who said the damper worked fine but never bothered to check and turns out it is obviously a bad actuator? With all due respect putting a squar box through the floor and covering it with a fancy grill while taping up some insulated flex ducting is super simple compared to building a pair of infinitely baffle subwoofers in the crawl so I will do what I should’ve done in the first place and take care of it all on my own. I wish I had contractors like you around but I’m done throwing money in the fire and instructing people I pay how to fix their mistakes.

I also wish we had better contractors around for these new concepts. Many are excellent at what they do everyday. A few are into learning new concepts and getting to the bottom of the problems.
Hang in there and keep us posted. This is all part of the learning process for all including me.
Regards Teddy Bear

[HVAC_Marc]

Nick, you should have enough posts now to put up pictures.

[NickTF]

Here is a picture of how the DR90 was wired when it blew a fuse. The green wire from the controller is on the wrong terminal. Moving it over to the fan terminal (one terminal to the left) fixed the problem after the installer had to open the dehumidifer and replace an internal fuse which blew upon the call for ventilation.



Here is the diagram in the DR90 manual which illustrates how the unit should've been wired.



Here is the damper position when the call for ventilation was present. No, the small crack is not a result of the damper being set to a stop. The actuator motor is moderately warm while the call for ventilation is in place and 26v is present from the dehumidifer during the call for ventilation (0 volts when no call for ventilation).



Here is the damper zip tied wide open. As indicated previously in this thread, when running like this the house turned into an absolute rain forest in about 1.5 hours. My ventilation is controlled by my vision pro iaq which has an input of 1700 square feet and indicates it meets the ashrae (I think I got that right) standard. The humidity reported only 52-53 with 45% being commanded and I believe if I continued to run like this humidity would have continued to climb. Despite the rh only being reported as 52-53% I was sweating while sitting feeding my children.

[NickTF]

Here is how the actuator is wired. You'll note the wires are opposite of what is spelled out in the diagram for the EARD6 actuator. I don't know if this matters or not and if this has anything to do with why my actuator isn't working and is warm to the touch upon the call for ventilation???????



Here is the diagram of how the actuator for the damper is supposed to be wired. You can use the above photo and the photo of the dehumidifier to decipher that the actuator is wired inverse of how this diagram says. Again, will wiring this as indicated in the diagram matter or does it not matter which direction the current/switching moves through the actuator?

[NickTF]

Check the amount of moisture being removed per hour with and without fresh air on. You may be getting to much fresh air. Expect 3 lbs. of moisture removal per hour. That is enough to handle 70-90 cfm of fresh air with a 70^F dew point reduced to 55^F dew point. Also when the a/c operates, it will remove 2-3 lbs. per hour per ton.
Fresh air when occupied and calm winds.
Keep us posted.
Regards Teddy Bear

I reviewed the settings on my vision pro setup document again last night. Teddy, if I reduce the CFM setting (presently set at 90) on the vision pro how does that actually translate to reducing the flow on my equipment? I don't believe it slows the fan in my DR90. Does it call for ventilation less? I don't believe it can open the damper partially so how would it reduce flow exactly?

[teddy bear]

This type of adjustment changes the minutes on/off to decrease or increase the amount of fresh that blown into the home. It does not change the speed of the fan. Small ducts, 6", allow lesser amounts of fresh air into the home. Like 70-80 cfm which is 3 lbs. of moisture load with a 70^F outdoor dew point. I search Vison Pro info and did not find a clear description of what it did.
Your dehu and a/c should be able to handle that much fresh air 24/7 and maintain <60%RH.
Hope this helps. May be we have others on the site that know exactly what changes.
Regards Teddy Bear