Constant air flow, Aprilair 1720 dehumidifier
#1
03-26-07, 08:24 PM
Constant air flow, Aprilair 1720 dehumidifier
I want to achieve constant air flow to create positive air pressure inside the house relative to the outside. I used to have an Ultra-Air whole house dehumidifier that connected to the HVAC ductwork. It had separate controls for the fan and dehumidifier so I could set the fan to run constantly, thus creating the positive air pressure. It died and I replaced it with an Aprilair 1720 dehumidifier. Was led to believe I could do the same but it does not have the separate fan controls that the Ultra-Air had. It does have installer settings for the cycle period and cycle time.
My question is, would it be possible to set the cycle period and cycle time such that the fan would run constantly or near constantly? And would this damage the system?
Thanks.
My question is, would it be possible to set the cycle period and cycle time such that the fan would run constantly or near constantly? And would this damage the system?
Thanks.
#3
03-29-07, 01:10 PM
Why ducted dehumidifer
I'm no expert but here is my understanding.
An HVAC is optimized to heat or cool air efficiently. As a by-product of cooling, it also dehumidifies the air, but it does that very inefficiently and expensively. Having a separate dehumidifier connected into the HVAC ductwork will add humidity removal even when the AC is not running. Also, you do not need to physically move as much air to dehumidify as you do to cool. Less humid air is more comfortable at a higher temp, so I can set the AC on 80 and still be comfortable when the dehumidifier is running. Without the dehumidifier, I have to set the AC on 76 to feel comfortable.
Net is, the AC runs less, the dehumidifier runs more. Tradeoff on energy usage is positive since the dehumidifier is smaller and uses less energy. Overall comfort is improved. Another positive, is that since I live in a 97 year old, historic home, lower humidity is a benefit to the structure.
Now, back to my original question. In addition to the humidity removal, I also want to have constant air flow while bringing in outside air (through the dehumidifier first.) This is needed to create a positive air pressure differential to the outside air. (Reasons for this have to do with lead remediation and are somewhat complex. If anyone is interested I'll post the explanation later.)
Aprilair says I can do this two ways. (1) The Model 1720 can be connected to control the HVAC blower and configured with a cycle time and cycle period that will accomplish this. Problem with this solution is it means the larger (and more costly, I think) HVAC blower runs almost constantly. (2) The Aprilair can be rewired so that the dehumidifier blower runs constantly. I just found that out from a request to Aprilair tech support. I think that is the solution I will use.
An HVAC is optimized to heat or cool air efficiently. As a by-product of cooling, it also dehumidifies the air, but it does that very inefficiently and expensively. Having a separate dehumidifier connected into the HVAC ductwork will add humidity removal even when the AC is not running. Also, you do not need to physically move as much air to dehumidify as you do to cool. Less humid air is more comfortable at a higher temp, so I can set the AC on 80 and still be comfortable when the dehumidifier is running. Without the dehumidifier, I have to set the AC on 76 to feel comfortable.
Net is, the AC runs less, the dehumidifier runs more. Tradeoff on energy usage is positive since the dehumidifier is smaller and uses less energy. Overall comfort is improved. Another positive, is that since I live in a 97 year old, historic home, lower humidity is a benefit to the structure.
Now, back to my original question. In addition to the humidity removal, I also want to have constant air flow while bringing in outside air (through the dehumidifier first.) This is needed to create a positive air pressure differential to the outside air. (Reasons for this have to do with lead remediation and are somewhat complex. If anyone is interested I'll post the explanation later.)
Aprilair says I can do this two ways. (1) The Model 1720 can be connected to control the HVAC blower and configured with a cycle time and cycle period that will accomplish this. Problem with this solution is it means the larger (and more costly, I think) HVAC blower runs almost constantly. (2) The Aprilair can be rewired so that the dehumidifier blower runs constantly. I just found that out from a request to Aprilair tech support. I think that is the solution I will use.
#4
03-29-07, 07:34 PM
Well first to pull the warm moist air in from out sideinto the home. Will cost you a arm and a leg. If you put in a V/S blower you can set a humidistat so it will slow down the blower and pull more humidity out that way. Then go back up to speed
