Please explain CPH settings on thermostat

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  #1  
Old 02-11-07, 05:11 PM
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Please explain CPH settings on thermostat

Just got a new packaged heat pump and trying to understand how it behaves.
There are two "CPH" settings; one for Em. heat mode and one for Compresser mode.
My system was going off and on even though the thermostat said 68/68.
Was this because of the 9 cph it had been set at in Em. mode?
Does this setting bring the unit off and on 9 times per hour, regardless of the temp delta?...if there is one. Also, if the tstat falls below the setting, will the system come on regardless of the CPH setting?
I'm just trying to completely understand this thing.
 
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Old 02-13-07, 02:26 PM
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Question Nobody???

:::: All this info available and nobody can enlighten me on this seemingly simple question? Or is it just to stupid to respond to?
 
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Old 02-13-07, 08:09 PM
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Question

enlighten me on this seemingly simple question?

Boy Im sure sorry But I have no idea what you are talking about. Or what 2 CPH are Em should be EME to turn the elements on from the tstat.

What is the unit what is the tstat whats the brands????
You know info helps us to help you. Have you looked at the paper work for the unit and the paper work on the tstat.
 
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Old 02-14-07, 07:03 AM
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Thanks for responding. I'll try to explain more clearly now that I have a weeks experience with this thing.
It's a Goodman 2.5 ton GPH series, equipped with a 20kw heat strip.
I think most of my question actually involves the new Honeywell Pro 3000 t-stat.

When I run it in regular heat mode (compressor?)and it is around 25 degrees out it seems to run almost constantly even though the t-stat indicates 68/68 and the temp coming out of the floor registers reads 68 as well. This begs the question, why is it running at all? I can also hear the unit occasionally making a loud noise like a valve blowing off.

When I run it in EM. heat mode (heat strip), it behaves predictably and does not seem to cycle excessively.

I have the Auxillary heat cycle rate (Whatever that is) set at 9
I have the Em.heat cycle rate (CPH) set at 3.
I have the Compressor cycle rate set at 3.
These were the recommended settings in the manual.

My question is, are these settings correct, considering it runs and runs in the normal heat mode (set at 68) and if I switch it to Em. heat, it appears to run properly. I have 2 concerns about the way it is running:
1. Is it costing me a lot more to run in Em. heat mode since it seems to run less?
2. In the normal heat mode, is it being damaged by running almost constantly, even though it heats just fine that way as well?
 
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Old 02-14-07, 08:23 AM
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OK now that we know more it helps . So here goes
On that tstat the CPH stands for Cycles Per Hour . like how many times it will come on in the hour. Read all the paper work you got with it. Then play with it till your happy with it.
This begs the question, why is it running at all? I can also hear the unit occasionally making a loud noise like a valve blowing off.
You can set the tstat to a point that with the anticipator in it it will hold within 1o. So if set at 68o and air from it is 68 yes it can run all the time.

loud noise like a valve blowing off.
Could be unit going into defrost. Check defrostboard and see how it is set.
When I run it in EM. heat mode (heat strip), it behaves predictably and does not seem to cycle excessively.
A lot more BTUs comeing out there with that 20 Kw.

#1 Yes and no Dont know what the COP of the unit is.
It can work like this. lots of heatpumps say like At 30o outside temp you get 3 times more heat for a $1 than you would get if you run in just EME heat. So you see as it get colder outside the out put of the heatpump falls off. just when to say go to EME to save $ I CANT SAY.
The one I have in my home when it gets down to 5o or 10o outside I do go over too EME .
Now a lot here is in the size of the unit and the heat loss of the home. As to how long they run at a time. If it is running all the time and cant heat the home some of the elements will kick in to help then shout back off.

#2 No let it run. It will be ok.
 
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Old 02-14-07, 11:39 AM
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Thanx very much Ed.
Just a few more questions:
1. When CPH is set at 3, does this mean it will come on 3 times an hour regardless if heat is not called for; and if heat is called for, will it exceed 3x till the t-stat is happy?
2.Anticipator? What is that?

BTW, the heat holds within one degree in all these settings...that was never a problem. The house seems extremely tight and holds heat a very long time.
The installer did say something about it typically freezing and defrosting itself if the outside temp is much below 30. I was just wondering if all that "on" time was costing more, or possibly hurting the unit. I guess the 400cfm blower alone does not consume much energy(?)
 
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Old 02-14-07, 06:19 PM
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CPH specifies the maximum number of times the system will run per hour. The system will not run more than the CPH no matter what the temp does. It may run less if temp doesn't drop below the set point. Left to little or no limit, a digital thermostat will attempt to maintain a setting with little variance from the set point. A drop of half a degree might trigger it to kick on. Most people don't notice a 2 degree drop let alone a half so this is too much and exactly what the CPH setting is designed to prevent. Em heat seems to act more normally because it is more likely to over shoot the set temp so it has more to drop before kicking in again. Simply put, the less and longer a system cycles, the more efficient it is. Set the CPH as low as you can and still feel comfortable between cycles. I set mine to the lowest available setting last year and no one noticed the change so my heat only kicks on once an hour at the most. at the minimum 4. It's all about what you can be comfortable at.

Doug M.
 
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Old 02-14-07, 06:22 PM
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Almost forgot... changing the temp on my thermostat seems to override the CPH. It may on yours as well. It also seems to reset the CPH clock. The hour starts as of the moment the temp. is changed.

Doug M.
 
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Old 02-15-07, 11:22 AM
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:::: Wow!
Thank you so Much Doug.
You answered and explained very clearly and I am grateful.
Over the last week, I had sort of come to notice the behavior of the system in regards to regular "Heat" setting and "EMHeat" setting, but your explanation made it crystal clear why it is behaving the way it is.

I will likely just use 30 degrees as the point where I slide the switch to Emheat.
This way I can compromise, and keep the compressor from going through the endless cycle of pump,freeze-up,defrost,pump, which it seems to do under 30 degrees.
Thanks again Doug.
 
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Old 02-15-07, 01:53 PM
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I'm glad that made sense to you. When I re-read it it doesn't make much sense to me. That partial sentence "at the minimum 4" shouldn't be there...

I've owned 2 houses with heat pumps and found on both that the electric bill didn't suffer from switching to EM heat at around 30 degrees nearly as much as I did listening to the compressor running constantly trying to keep up.

On a slight tangent: every time a heat pump goes into defrost mode, it sends cold refrigerant into the heat exchanger. The resistant coils run to keep the air from getting cold, but the air from the house still has to pass across the frigid coils. When it does, humidity is pulled out. The more a heat pump runs and goes through defrost cycles, the more moisture the air looses and the colder the house feels.

Simply switching to total resistance heat at the point where the heat pump has trouble keeping up solves a lot of problems.

Doug M.
 
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Old 02-15-07, 02:12 PM
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The COP on a unit is good down to about 20o . Then is when we tell most to turn over to the EME.
 
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