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Old 11-19-2007, 12:33 PM   #1
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Energy usage puzzle


I have a certain GE blower motor (HVAC) that is used in my condo. It's a very unique heating/cooling setup which I won't go into here (I've asked a different question in the HVAC forum where I detail the setup).

My main question is this...how can I determine the wattage draw this motor uses every....lets say hour.

I hope I'm phrasing the question the right way. I basically want to find out how much more efficient my (and the condo association) setup would be if we had programmable thermostats instead of the non-programmable ones we now have. Imagine an owner leaves to work for the day and is gone for 9 hours. How much could he save a day by having his heating or cooling get automatically turned down during his absence?

Thanks for your help!

Here are the specs of a blower motor similar to mine:
Type:Shaded Pole
Base:Resilient rings w/ extended clamp screws (no base)
'C' Dimension (inches):20.0
Full Load Amps @ N.P. Volts:3.7
Model Number:5KSP39DG4936T
Special Features:Double Shaft
Item:AC Mtr 1/10 HP 1050 RPM 115 V FR Shaded Pole Open

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Old 11-19-2007, 01:57 PM   #2
Join Date: Nov 2007
Posts: 301

Energy usage puzzle

Watts = Volts * Amps They list Full Load amps as 3.7, Full load indicates the speed the motor will run when putting out full-rated output torque or horsepower.

Running at full load would be 120v * 3.7 = 444 watts or if you want to use their 115v would be 115v * 3.7 = 426 watts.

Difficult to answer how the programmable thermostat would do. You'd need to do a heat load analyses on the condo, then collect the heating degree days of the area it's located, then you have a chance of figuring that out but, the short answer is programmable thermostats are estimated to save you 1% of your energy per degree setback. That's to say, if you set your thermostat back 10F for 8 hours/day you should reduce your energy use 10%. Expect more savings in severe climates, and less for mild. Set it back 5F for an 8 hour period and you should save 5%.

Programmable thermostats work on 3 principles, everyone knows the one where the less temperature difference inside vs. out the less energy lost and one of the principles. But, that's not the only thing. The other is that the longer and harder your boiler/furnace has to run the more efficient, having it work hard to get back up to temp is your boiler working at its top efficiency. Cycling and maintaining temps are not as efficient. The last, the less cycling of your boiler/furnace the less maintenance and since programmable thermostats reduce cycling they should extend the life of the unit hence/lower maintenance costs.

If you have a heat pump system, you need one that's heat pump compatible as heat pumps have electric boost backup. Telling it you need to warm it up a few F will usually just have the heat pump kick on. Telling it you need to warm it up 10F causes heat pumps to panic and kick on electric heat backup boost to get you there and may end up costing more electricity than not having it. With Heat Pump compatible programmable thermostats they have algorithms that tricks heat pumps into not turning on the electric boost backup unless necessary. I have a programmable thermostat the only thing I regret is not getting a lighted one, they're not particularly easy to see without being backlit and, I'm always looking at the temp cause I heat with wood now and if my programmable thermostat says 66F time to put in a fire.

Last edited by Piedmont; 11-19-2007 at 03:04 PM.
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Old 11-19-2007, 03:11 PM   #3
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Posts: 7

Energy usage puzzle

Wow, thanks Piedmont. You have really helped me out. As I had mentioned, I had posted another thread in the HVAC area but have not gotten much traction on it. I think I have closed it down properly. I'm pasting the description of our HVAC from there to here:

I live in a condo complex that was built in the 70's and works by using what seems to be a very unique method. Water is circulated through a series of pipes into all the condos, these pipes feed into a galvanized metal box which houses a large blower motor (GE 5ksp39mg 6162AT). The pipes run through a radiator. Hot or cold water runs through this setup depending on the season. When the thermostat senses a certain temperature in the living space, it turns the blower motor on, which draws living space air through the radiator, heats it up or cools it down, the air then passes into the hvac ducts which feed into the rooms. The thermostat keeps the motor running until the desired temperature is reached and then it shuts off power.

The thermostats are line-level.

I've spoken to Honeywell, White-Rodgers and all the different thermostat companies that make some of the thermostats we use in our condos.

Here is the PDF for my thermostat. I think ours is called a "Fan-Coil system".


They all say that they don't make a line-level programmable thermostat for Fan-Coil systems.

If this is the case, I'm wondering what it would take to add in millivolt thermostats, and would even they work since this setup is just opening and closing the power feed back to the fan blower unit.
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Old 11-19-2007, 03:16 PM   #4
Electrician philosopher
Join Date: Aug 2007
Location: Lilburn, GA
Posts: 838

Energy usage puzzle

We are much smarter than the HVAC guys as a rule. Let me ponder a minute.....

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Old 11-20-2007, 08:31 AM   #5
Join Date: Nov 2007
Posts: 301

Energy usage puzzle

How bout this one? Line voltage fan-coil compatible programmable thermostat.


Last edited by Piedmont; 11-20-2007 at 09:54 AM.
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Old 11-20-2007, 11:18 AM   #6
Join Date: Nov 2007
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Energy usage puzzle

OMG, Piedmont, I have been googling, calling, reading, studying, pulling hair out for on and off a year, and finally, I think I'm coming to a resolution.

I just got off the phone with a head technician from the company in that link you sent, and it looks like he has a solution. He really knew his stuff and told me he has the only line-voltage, fan-coil, programmable thermostat in the US. No one else makes it.

Thank you so much!

Love this forum.

Happy Holidays all!

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