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Old 01-29-2011, 10:24 AM   #1
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Can we use a lower RPm fan? Other ideas?


Hi all I'm a jack of many trades and master of none. I am a maintenance guy. We have a problem at our church in the main church room. Here is our system:

Forced hot air not sure of air handler about 5 years old.
Newer small efficient Natural Gas wall mounted burners supplying hot water via circulators to single speed air handler.
Supply and return registers in church are on the floors and space has your typical very high church ceilings. They don't have the money for ceiling fans quitely running at slow speed to pull/push hotter air trapped at high ceilings back down to pews.

All/most supply and return duct work is insulated. Goes from basement to 2nd story where heating Sanctuary/space is located.

Problem: it is not a variable speed air handler or multiple speed it is a single speed. The single speed is so loud that parishioners complain constantly about it. We keep the heat on 45 degrees unoccupied since there are no water pipes to freeze anywhere near this space. The unit seems to cycle too much off and on because the room is thermally cold the unit kicks on and runs for 20 minutes hits 67 degrees and shuts off only to come on 2 minutes later because the air is warm temporarily with high circulation but the wall area where stat is is still cold. We programmed stat to pre-heat the room a couple hours bringing it up to 60 and then calling for 67 about an hour before service. That helped little but the thing still cycles on-off every 3-5 minutes even after pre-heat after service starts and well after that too. Here is my question:

Can we change the blower motor to a lower speed/rpm motor which would run for a longer time to satisfy but would be quieter? We just want it quieter. I know this would reduce the CFM output but wouldn't the actual temp. at registers be as warm or warmer since less cool cfm is going through the air handler or is it canceled out by the duct-work run? A hvac person told us he would " I would like to come down to the church and see if I can adjust the shives to reduce the noise" What's that all about and is it worth it? Also is there a way to easily change/modify a single speed blower/air handler into a multi or variable speed or is it cost prohibitive?

One other thing I noticed is that since both the supply and return registers are on the floor while the unit is running everyone hates the noise but likes the heat. Within two minutes after stat is satified and blower stops, people start to get cold again. I figured that maybe since both the supply and return registers are on the floors that the heat is circulating at a lower height area keeping them warm while blower is running then they're cold. Would running it longer at a lower and quieter RPM/cfm during the entire service be the answer?

Many thanks, the cfm noise disturbed church goers......


Last edited by hoarybat; 01-29-2011 at 10:29 AM.
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Old 01-29-2011, 10:43 AM   #2
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Can we use a lower RPm fan? Other ideas?


Churches with their huge volume of air to be heated and air currents/drafts are always difficult to deal with. Seriously, the ceiling fans help a lot. Doubt if anyone over the internet can come up with a solution as an experienced tech would have to see the actual setup and go from there. Every church is built differently and insulated differently so I would try find a parishioner or friend of one in the HVAC business and see if they will donate their time to help you. Ask your parishioners to talk amongst themselves and see if they know such a person. If you reduce speeds you can overheat the system and w/o seeing it I would not recommend you do so. Everything is expensive so there is no cheap fix. Once again the ceiling fans are inexpensive but need wiring run to them. Perhaps you have a willing electrician in your flock?

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Old 01-29-2011, 07:18 PM   #3
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Can we use a lower RPm fan? Other ideas?


Could be the duct work is too small. Could be the air handler is too large. Could be the wrong registers were used. A smaller horse power motor may help, or it may burn out quickly.

This is something that really needs to be looked at by someone that knows duct work, blowers, and air circulation.
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Old 01-29-2011, 09:49 PM   #4
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Can we use a lower RPm fan? Other ideas?


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Old 01-30-2011, 06:29 PM   #5
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Can we use a lower RPm fan? Other ideas?


I really don't understand your description of the system, the gas fired part, the architecture, the window design, the insulation adequacy, nothing. Sounds like heat is supplied at baseboard in addition to the air distribution?? Baseboard, in adequate capacity, plus ceiling fans for destratification should provide good comfort. Floor ducts, not so much.

If thermostat calls this quickly, could it be that it is too close to the warm air being delivered, and being influenced by it? Is it on an outside wall, a wall not well insulated? Or in a draft from an outside door?
I agree, slowing down the air delivery isn't the answer. The volume and supply register selection should provide a 'throw' of air that is sufficient to circulate. True, duct sized too small and poor diffuser selection will cause noise. Sounds like it needs to be re-engineered, and I know you don't want to hear that. How old is the building or the heating system? Probably old enough that there is no recourse against the builder. Likely an accumulation of donated time, equipment, and talent, that wasn't totally professional, now requiring reapplication of same, of a better grade, to correct problems.

If you get a different thermostat, or correctly wire this one, you can make the fan run full time but cycle the heat, to eliminate that back and forth. Insulation and thermostat placement still may need attention.
Take action and pray for God's wisdom on your advisors.

Last edited by donaldo88; 01-30-2011 at 06:33 PM.
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Old 01-30-2011, 07:33 PM   #6
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Can we use a lower RPm fan? Other ideas?


Quote:
Originally Posted by hoarybat View Post
Thanks
Your blower motor is probably a standard PSC 1075 RPM motor. Anything slower for a blower would be a special motor.

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