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Old 09-03-2011, 02:54 AM   #1
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Thermostat Question


http://www.prothermostats.com/produc...product=172406

Hey guys,
First of all thanks for the forum and for any answers you may be able to give.

Can some one tell me with reasonable certainty if the thermostat that I linked to above will control two stages of AUX resistance heat independently?

In other word will it behave as follows?

Call for stage one (heat pump) if needed call for stage two (first stage if resistance heat) also if needed call for stage three (second stage if resistance heat).

If it will or will not are there any others that will? (preferably a cheaper model.)

Again thanks for any help.

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Old 09-03-2011, 04:42 AM   #2
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Thermostat Question


Yes, it can control the heat as you want.

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Old 09-03-2011, 08:39 AM   #3
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Usually the second stage of electric strips (your 3rd stage) is controlled in the unit by a time delay sequencer. Or they are wired to bring on all the strips at once.
What kind of air handler do you have? And what is the kw total of the strips?
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Old 09-03-2011, 12:55 PM   #4
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Originally Posted by Master of Cold View Post
Usually the second stage of electric strips (your 3rd stage) is controlled in the unit by a time delay sequencer. Or they are wired to bring on all the strips at once.
What kind of air handler do you have? And what is the kw total of the strips?

It is a goodman aruf unit. It has a 10kw and a 5kw. Right now they are wired to come on all at once. I want to wire the second stage to the 5 kw and the third to the 10kw hoping it will keep the 10 from coming on unless absolutely necessary.
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Old 09-03-2011, 02:01 PM   #5
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Im assuming your new stat has w-1,2 and 3.
The issue is in the defrost cycle. The condenser is going to send a signal back to the air handler during the defrost period, to turn on the heat strips. The unit is in the cooling mode during this time. Usually (but not always) its the white wire that goes to the air handler from the condenser that gets energized. This will enable the strips to come on. How many strips you need to come on is going to be determined by the outdoor temp, the size of the unit, and the indoor temp. I keep the house at 75 in the winter. My average defrost time is about 45 seconds, at 32 outdoor temp.
If your system takes longer to defrost, and you don't have enough strip heat going, you will be cooling your house. Each strip is roughly 18k btu.
So if you need 10kw to come on during defrost, you will only be able to use the w1 and 2 terminals on the thermostat.
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Old 09-03-2011, 04:32 PM   #6
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Quote:
Originally Posted by Master of Cold View Post
Im assuming your new stat has w-1,2 and 3.
The issue is in the defrost cycle. The condenser is going to send a signal back to the air handler during the defrost period, to turn on the heat strips. The unit is in the cooling mode during this time. Usually (but not always) its the white wire that goes to the air handler from the condenser that gets energized. This will enable the strips to come on. How many strips you need to come on is going to be determined by the outdoor temp, the size of the unit, and the indoor temp. I keep the house at 75 in the winter. My average defrost time is about 45 seconds, at 32 outdoor temp.
If your system takes longer to defrost, and you don't have enough strip heat going, you will be cooling your house. Each strip is roughly 18k btu.
So if you need 10kw to come on during defrost, you will only be able to use the w1 and 2 terminals on the thermostat.
I have considered this. I was thinking I would use a relay to energize both strips on a defrost.

Before I got too deep into figuring out how to do this I wanted to make sure I could get a stat that would do what I wanted.

Does my defrost approach sound reasonable?
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Old 09-03-2011, 05:02 PM   #7
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Post the full model number of the outdoor unit. You may only need 10KW of strip on during defrost.
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Old 09-03-2011, 05:08 PM   #8
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yes, you could use a relay to control both stages on a defrost call and also control them independently from the stat.
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Old 09-03-2011, 05:28 PM   #9
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My outdoor unit is a goodman ssz140421ad.
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Old 09-03-2011, 05:33 PM   #10
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By only bringing on 10KW of strip, at worse during defrost, the air temp out of the registers will be 6 degrees cooler then room air temp. But some people are uncomfortable if that cooler air blows on them. So you need to decide if your comfort is more important for those few minutes. or the operating cost.
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Old 09-03-2011, 05:45 PM   #11
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Quote:
Originally Posted by beenthere View Post
By only bringing on 10KW of strip, at worse during defrost, the air temp out of the registers will be 6 degrees cooler then room air temp. But some people are uncomfortable if that cooler air blows on them. So you need to decide if your comfort is more important for those few minutes. or the operating cost.
Thanks for the info I had been considering just using the 10kw for defrost.

While we are on the topic of defrost what do you think would be a proper defrost timer setting for central Alabama? I am pretty sure it is set for 30 min which is way to short in my opinion but I want to make sure that it does not need to be that short for this region. Thanks again.
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Old 09-03-2011, 06:55 PM   #12
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I would go 60-90.
Maybe beenthere can tell us if this unit has demand defrost control, or just a run timer
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Old 09-03-2011, 06:57 PM   #13
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Dead center halfway between Birmingham and Huntsville.
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Old 09-03-2011, 06:58 PM   #14
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I am pretty sure it is just timer.
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Old 09-03-2011, 07:56 PM   #15
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Set it to 90. Goodman heat pumps are timer. They don't have any models that use on demand defrost.

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