After earlier discussions I lowered my blower speed from "high" setting to "medium/low" setting and getting longer run times 15-20 mins versus 8-10 mins. I was able to find specs on furnace blower speeds via Carrier website. According to their site the "high" blower setting is 2400 CFM, "med/low" 2200 CFM, and "low" 1700 CFM (5 ton/12 seer unit). My question is if 400 CFM per ton is the ideal fan setting then why in the world would they default set the cooling fan speed on "high" which is 2400 CFM (6x what you need)!
Does this sound like accurate information or is there much more to it?
I was initially having humidity problem which I could only attribute to short cycles. I've had unit checked twice in 6 weeks and everything is to spec. I was hoping that setting back to "medium" speed would increase humidity removal by extending run times. Do you guys think I'm harming the system by lowering to "medium" speed ? According to Carrier's chart thats only 200 CFM less than max speed. If I do need to switch back to "high" setting do you guys have any suggestions to remedy short cycles/humidity problems?
I definitely do not want to harm the compressor but the high setting is just not allowing the evaporator to pull the moisture out of the air. I think the unit is oversized anyways (5 tons for 2400 sq ft, 2 story). The "high" speed is blasting air out of the registers and satifying the thermostat quickly. I have even partially closed off all of the downstairs registers to avoid that problem. If lowering the blower to medium setting is going to harm the compressor then I guess I will have to live with the humidity for now. The humidity consistently runs in the low 60's regardless of how low I set the thermostat.
That seems to be a better option than installing damper/baffle system throughout. Got a bid last year that was $2300.00. I will try to "low" setting tomorrow. Do I just listen for louder humming coming from compressor?
temp difference is 15 degrees....I'm pretty much a novice at this so I'm assuming that a sweating compressor is bad. Last summer the compressor was sweating so badly that a stream of water was coming out from underneath the condensing unit. It was under warranty at the time so I had install company come out to check. They told me that it was normal for compressor to sweat on very hot/humid day. Was I sold a bill of goods?
Originally posted by mrb8828
"high" blower setting is 2400 CFM
"med/low" 2200 CFM
"low" 1700 CFM (5 ton/12 seer unit).
My question is if 400 CFM per ton is the ideal fan setting then why in the world would they default set the cooling fan speed on "high" which is 2400 CFM (6x what you need)!
2,400 High / 2,000 CFM Nominal = 1.2
..OR.. only 20% over Nominal
WHO stated that 400 CFM / ton is Ideal setting?
400 CFM is a Nominal flow rate for measuring Air Handler performance in 'test' conditions or Average so to speak.
15' F delta T, you should have ~20'F for improved humidity control ( 50% R.H.).
So Medium setting will likely increase dT to ~17' or 18'F. RESULT ~ 55% R.H.
AND You never mentioned your Location ...
_ Maine or Texas _
5-ton is just about right size ..
but depends on Location, House / Window Orientation,
Insulation, Tightness, amount of duct in the Attic and WINDOWS .. Glass Tinting / # / Area.
Designer Dan
It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
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