lowering blower speeds

[lyork]

O.K.--I have searched the forums and read quite a bit of good information here, but have a question or two that I thought you all might be able to answer. I live in Kansas City in a 2800 s.f. front to back split, southwest exposure. Last year I had a new heat pump system installed, a Lennox hp26 4 ton, a G51mp 48c 110 furnance, matching 4 ton lennox cased coil with TXV valve. This replaced the 15 year old 3-1/2 ton Carrier system. No load calc was done (obviously). The reasoning for the upsize was that my older system wouldn't cool the house down on the hottest days and upsizing would gain me some on the heating end of the deal as well as help with the cooling. Well I went on to install siding with a little insulation and new energy efficient double pane windows. Guess what problem I'm having now? Short cycling of the A.C. (at least I think so) Well here's what I'm getting---18 to 20 degree drop, return to supply, inside humidty 39 to 44 percent @ 73 to 74 degrees, cycle times of 8 to 12 minutes on, 8 to 12 minutes off (outside temp in the mid 80's). I know this isn't too bad, but what if I dropped the blower speed a notch? Would this increase the head pressure? If I were to drop the blower speed would the freon charge need to be changed? Will I be able to get longer run times with a lower blower speed ? I have a Lennox T8611G(honeywell) digital setback stat that calls for heat or cool at a 1 degree difference,is there a Heatpump stat that has a 2 degree setting? Or should I just leave well enough alone and quit bothering you all with petty questions? Any advice will be greatly appreciated.

[Edited by lyork on 06-19-2005 at 11:45 PM]

[BaldLoonie]

Humidity is already rather low so I don't see a problem there. Without knowing static pressure on the system and consulting a blower chart, I wouldn't suggest lowering the blower speed. That's a 4 ton drive on a 4 ton air but most duct systems are more restrictive than typical so you already could be moving less than 1600 CFM.

[t527ed]

find out if differential can be increased on thermostat.

[teddy bear]

Originally posted by lyork
O.K Guess what problem I'm having now? Short cycling of the A.C. (at least I think so) Well here's what I'm getting---18 to 20 degree drop, return to supply, inside humidty 39 to 44 percent @ 73 to 74 degrees, cycle times of 8 to 12 minutes on, 8 to 12 minutes off (outside temp in the mid 80's). I know this isn't too bad, but what if I dropped the blower speed a notch? Would this increase the head pressure? If I were to drop the blower speed would the freon charge need to be changed? Will I be able to get longer run times with a lower blower speed ? I have a Lennox T8611G(honeywell) digital setback stat that calls for heat or cool at a 1 degree difference,is there a Heatpump stat that has a 2 degree setting? Or should I just leave well enough alone and quit bothering you all with petty questions? Any advice will be greatly appreciated.

[Edited by lyork on 06-19-2005 at 11:45 PM]

Lowering the air flow makes the ducts colder- more prone to sweating and poorer air circulation. Also the SEER decreases with lower air flow which increases cooling cost. Humidity is already very low. Wait for the cool wet weather without any sensible cooling load to check your ability to control humidity. A week of rainy weather is the challange. Also fresh air ventilation is part of the indoor air quality package. Suggest calibrating your %RH meter with wet salt in a sealed plastic. Wet salt @ 75^F = 75%RH.

[casturbo]

Originally posted by teddy bear
Suggest calibrating your %RH meter with wet salt in a sealed plastic. Wet salt @ 75^F = 75%RH.

Could you elaborate more on this RH calibration?....is it regular table salt and exactly how do you do it. THanks!

[teddy bear]

A cup with a couple tbl. spoon of table salt, wet salt until water is visible. Place cup in sealed plastic bag with the meter. Regular room temp ok, should register 75%RH after 30 minutes. Mark deviation on the face. Digital meters are inaccurate at the extreme high/low, 30-80%RH-ok. thermastor.com has digital meters with max/min memory for 10-20 dollars.