IAQ v. Comfortsense 7000 v. TCONT803 T-stats

[critterdoc]

I'm closing in on three Lennox XC16 or possibly XC19 (one 4-T and two 2-T) split systems as part of a major facelift on our home which has an old and dead 4400 sf Coal Tar Pitch built-up flat roof which will be totally taken down to deck and replaced with seamless sprayed on Bayer Polyurethane roof [SPF] which will require high-end A/C systems to control humidity inside of the house. Trane LX19i or LX21i is a long shot at this time but remains in the running.

I’ve not been able to acquire a specific and clear comparison of the Honeywell IAQ, Lennox Comfortsense 7000, and Trane TCONT803 t-stats or a first hand recommendation based on personal experience with each, and local dealer advice appears to be limited to models which match A-C brands with little relative value being given to the IAQ.

I would greatly appreciate comments that compare and contrast the Honeywell VisionPRO IAQ with the Lennox Comfortsense 7000 and the Trane TCONT803 t-stats in terms of their effectiveness in controlling Two-Stage Variable Speed Gas Furnaces which will match the respective compressors?

Thanks
Doc

p.s. This place rocks for a newbie who knows little about modern HVAC technology! You guys are ramping me up quite nicely for assessing incredibly variable proposals from a number of dealers who seem more interested in signing a contract than in truly determining and servicing my needs.

[RyanHughes]

Hi critterdoc. You already are aware that the VP IAQ can slow down the blower. Trane's TCONT803 (Honeywell VP 8321) can overcool up to a point to dehumidify. Personally, since you have the v/s blower, I'd go with a t-stat that can slow down the blower, which I believe you plan on doing. Not sure if the ComfortSense 7000 can slow down the blower, but since it's Lennox's top t-stat, I've gotta believe it can do something to control humidity. Lennox's v/s blowers can be set up to run special dehumidification ramp profiles; however, you may not need them with dehumidification on demand with the t-stat. Hope this helps. Hope some Dave Lennox dealers can fill you in on the capabilities of Lennox's ComfortSense 7000.

[critterdoc]

Trane's TCONT803 (Honeywell VP 8321) can overcool up to a point to dehumidify.

Pls explain "overcool up to a point to dehumidify." Does that imply increased cooling of air without changing blower speed?

[RyanHughes]

Pls explain "overcool up to a point to dehumidify." Does that imply increased cooling of air without changing blower speed?

If, once the t-stat has reached it's temp setpoint, the humidity setpoint is not reached, then the t-stat will run the cooling to dehumidify I believe up to 3 degrees.

[critterdoc]

If, once the t-stat has reached it's temp setpoint, the humidity setpoint is not reached, then the t-stat will run the cooling to dehumidify I believe up to 3 degrees.

Is that to say that if the t-stat is set to 72 and the humidity is above it's set point, then the stat will take the temp down to 69 until the humidity hits it's target point?

[RyanHughes]

Is that to say that if the t-stat is set to 72 and the humidity is above it's set point, then the stat will take the temp down to 69 until the humidity hits it's target point?

Yes, it will lower the temperature by up to 3 degrees to control the humidity. It's overcooling rather than slowing the blower down to remove the humidity.

[catmanacman]

yes that is what the tcon803 will do but it can be changed to 1 2 or 3 degrees, i would use the honeywell iaq

[beenthere]

What are you doing to the rest of your home that is cutting infiltration down that you thing humidity will be a problem.

[critterdoc]

What are you doing to the rest of your home that is cutting infiltration down that you thing humidity will be a problem.

Not sure what you are asking, BT. Please explain what you mean by "cutting infiltration down."

We live in south Louisiana where humidity is a killer even on a good day. If I understand the new technology, the variable speed blowers matched with high efficiency AC units will reduce mold growth greatly as well as increasing the comfort level at any given air temp. The commercial roofer that has offered to install the SPF roof on my house stressed that controlling humidity inside of the house with a modern A-C system is important for the roof itself, presumably to limit moisture from rising vertically and effecting the foam itself. I had the distinct impression that he would not install the SPF roof unless I upgraded my entire A-C system but A-C rebuild was in the cards even before I met the roofer. I must assume that he knows his stuff because he is the guy who replaced the roof on the Louisiana Super Dome after Katrina kicked it's butt.

[beenthere]

Basically, its the same spray foam that is used to insulate inside walls. But has a 70 to 80% spray over lap.

Unless its sealing your house that less outdoor air can get inside(infiltration), it won't effect your humidity.

Not saying don't get 2 stage, just wondering why you said its required.

[critterdoc]

Basically, its the same spray foam that is used to insulate inside walls. But has a 70 to 80% spray over lap.

Unless its sealing your house that less outdoor air can get inside(infiltration), it won't effect your humidity.

Not saying don't get 2 stage, just wondering why you said its required.

I'm still not clear on what you are saying. Are you suggesting that the roof itself "won't effect [the] humidity"? If that is the case, then I would agree that the effect of the roof on the humidity within the house will be nil, but I would worry that uncontrolled humidity could effect the roof.

I believe that the concern over humidity has more to do with warranty and the long term integrity of the SPF than anything. I did not question the roofer's comment because the expectation was only mentioned as a secondary item when the A-C plan was discussed in the presence of the roofing contractor and it made sense when he said it. Presumably, the requirement has to do with water vapor condensation being a potential problem within the SPF roof itself as absolute humidity rises inside of the house. In a sense, would not the dehumidification potential of the evaporator coil serve as a virtual water vapor retarder by increasing the amount of water vapor that is exiting the building by way of the coil and the condensate drain?