I have a Trane XV80 furnace (80k 3/4 hp size), a 3.5 ton XR13 AC, 4 ton coil w/TXV, 16x25x4 filter, and a VisionPro IAQ thermostat. Question about the CFM/ton settings:
Trane provides for a Low setting of 350 CFM/ton (for "comfort and humid climate") and Standard of 400. Additionally the Comfort-R setting reduces the flow by 20% for the first ~8 minutes. A Comfort-R pocket guide someone posted here suggested that the system should be set to 400 CFM/ton if Comfort-R was enabled.
On top of that, a correctly set up thermostat and wiring will further reduce the flow by 20% if the humidity is higher than the set point.
So depending on how it's set up you could be running anywhere from 400 down to ~225 CFM (350 CFM nominal, Comfort-R enabled, dehumidification reduction active = 350x0.8x0.8(?) ). Is it "safe" for the system to be running that low? The Comfort-R guide recommendation seems to suggest that 320 CFM might be a minimum (400x0.8). Likewise if you had it set up for 400 CFM w/dehumidification, it could run at 320 CFM virtually all the time. If both were enabled it may run at ~255 for 8 minutes before increasing to 320.
My interest here is in maximizing dehumidification and run time and minimizing noise. The home (2400 sqft, 3 story townhouse, 1st floor is partly below grade) is in a humid climate (MD) and I suspect based on run times that the AC is somewhat oversized @ 3.5 tons with undersized/questionable ductwork. Coming off the coil, the duct splits with one branch serving the 1st and 2nd floors and the other going to the 3rd floor. In order to maintain relatively even temperatures I have to close the damper on the 1st/2nd floor branch about halfway. I believe with the filter in place the static pressure is 0.7-0.8.
So ultimately I'm trying to understand at what minimum CFM I can safely operate the system. Thanks!
jeff
Trane provides for a Low setting of 350 CFM/ton (for "comfort and humid climate") and Standard of 400. Additionally the Comfort-R setting reduces the flow by 20% for the first ~8 minutes. A Comfort-R pocket guide someone posted here suggested that the system should be set to 400 CFM/ton if Comfort-R was enabled.
On top of that, a correctly set up thermostat and wiring will further reduce the flow by 20% if the humidity is higher than the set point.
So depending on how it's set up you could be running anywhere from 400 down to ~225 CFM (350 CFM nominal, Comfort-R enabled, dehumidification reduction active = 350x0.8x0.8(?) ). Is it "safe" for the system to be running that low? The Comfort-R guide recommendation seems to suggest that 320 CFM might be a minimum (400x0.8). Likewise if you had it set up for 400 CFM w/dehumidification, it could run at 320 CFM virtually all the time. If both were enabled it may run at ~255 for 8 minutes before increasing to 320.
My interest here is in maximizing dehumidification and run time and minimizing noise. The home (2400 sqft, 3 story townhouse, 1st floor is partly below grade) is in a humid climate (MD) and I suspect based on run times that the AC is somewhat oversized @ 3.5 tons with undersized/questionable ductwork. Coming off the coil, the duct splits with one branch serving the 1st and 2nd floors and the other going to the 3rd floor. In order to maintain relatively even temperatures I have to close the damper on the 1st/2nd floor branch about halfway. I believe with the filter in place the static pressure is 0.7-0.8.
So ultimately I'm trying to understand at what minimum CFM I can safely operate the system. Thanks!
jeff
