Heat Pump vs. Aux Only

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  #1  
Old 12-17-10, 01:19 PM
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Heat Pump vs. Aux Only

When temps are below 30, my heat pump runs constantly. My thermostat has a setting for auxillary heat only (electric coils), which I've been using for the past couple of days. My question is, is it more expensive to use aux only or run the heat pump constantly?
 
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Old 12-17-10, 01:44 PM
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The heat pump should handle temperatures well below 30 without having to resort to AUX or EMG heating. I would first have a service done on the outside unit and the air handler. I found my A coil crudded up with pet hair (filters were inadequate), and thus a very low air flow. Compressor ran almost constantly. After the cleaning...more air... more heating. Of course, as it would be, it died shortly after wards, and I had to put in a new system. But it really helped in the short time to have things cleaned up.
 
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Old 12-17-10, 02:56 PM
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My heat pump is only about 5 years old, but the air handler is original to the house (28 years old) and the coil is really badly corroded/damaged. I realize that it needs to be replaced, but I'm not overly anxious to fork out 4-5k for a new system at this point in time. I may have no choice. Back to my original question--do you think it's more expensive to run aux only or for the heat pump to run constantly?
 
  #4  
Old 12-17-10, 04:40 PM
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When you use your aux. heating (electric strip ) , approx.10-30% of that heat output is lost in the ductwork . This depends on how the house is constructed . If the ductwork is between first floor and a basement ,then your losses are at the low end . But if your house is like houses in FL (no basements) , where ductwork is laid into the attic, then expect about higher end of the heat loss . On the other hand , using the electric strip thru a ductwork will provide convinience and uniform heat distribution. But at the end a simple space heater that dumps 100% of the heat output into the room (without any duct losses ) is the winner of two, in terms of dollars and cents (not in convinience or uniformity departments ) ,if that is the important factor .
 
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Old 12-17-10, 04:46 PM
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Everything depends on the size of the heat pump and how the house is built, insulated, outdoor temp, etc..
My heat pump is oversized for Las vegas cooling, so in the winter, it will heat the house down below 25 and still cycle off and on without auxillary heat. Your unit may be properly sized, therfore it may struggle a little bit with the heating end of the spectrum.
As long as the heat pump is holding the house at the temp you have it set for, it will be far more efficient than running the auxillary heat.
How is your thermostat set up? At constant running, I would want the heat strips to cut in every now and again to get the stat satisfied.
It probably wouldnt hurt to have the unit checked, just incase it is having an issue.
 
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Old 12-17-10, 05:54 PM
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I live in VA, and the current temps are in the low 20's at night. Duct work is in the basement, which is climate controlled. The heat pump alone cannot maintain the set temperature. I typically have it set at 70, but if outside temps are below 25 or so, the thermo doesn't get above 68. Problem is that the aux heat doesn't kick on unless the temp difference is at least 3 degrees, which is hardly the case. Therefore, I'm forced to set the temp higher (71 or 72) to get the aux heat to come on, but then it gets too damn hot in the house. My other option is to set the temp low so the heat pump can reach the setpoint, but then it never gets above 67 degrees, which is too cold. So the best option when temps are this cold is to use auxillary only, which I"m afraid is going to be quite pricey. You would think that the thermostat would have a timer so that if the setpoint isn't reached within a certain amount of time, the aux would kick in. This isn't the case, at least with my t-stat. I may have to bite the bullet and get a new system that can reach at least 72 when outside temps dip into the teens and twenties.
 
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Old 12-18-10, 08:31 AM
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Think about replacing the stat with a good honeywell model that will cycle the auxillary heat in an appropriate manner, instead of that 2 to 3 degree differential.
 
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Old 12-18-10, 09:15 AM
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I live in MD, have a good Honeywell stat and am having the same problem with the aux ht. Even had the repair tech come, he upped the heat 4 degrees, said it was fine and left. Aux heat will not turn on otherwise and the system runs continuously all night to keep temp at 66. Any idea how we can get aux ht to kick on when needed?
 
  #9  
Old 12-18-10, 11:14 AM
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It is expensive no matter when and how you use your Aux heat.Your Aux heat has a C.O.P. of 1.0 it is 100% efficient in making heat.Now your Heat pump depending on age has a C.O.P. of 3 and up that would make it 300% efficient but a heat pump don't make it just takes or borrows it from the out-side air even when it's very cold and transfers it to the inside.Even at 17 degrees your heat pump will have a C.O.P. over 2 so you will get twice has much heat for the money.The first thing to check is the Coils outside and inside I have found TONS of units that won't heat or cool cause they get clogged up.Heat pumps cause they run all year get clogged faster.Heat pumps tend to be sized for cooling if it was sized for heating you would not get the humidity out of the air in the summer that's one advantage of a two-stage unit you can oversize it,well I did and it was 12 degrees the other night and mine had no problems the Aux heat never came on.
 
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Old 12-20-10, 05:24 AM
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For those who has the digital Honeywell t-stat, sounds like it may not be set up right if your Aux is not coming on with in 1˚ from set point.

The older style non-digital yes, there will be a few degree gap before the Aux comes on.
 
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Old 12-20-10, 04:47 PM
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I originally had a Honeywell digital t-stat, but the problem was that the temperature swing was not adjustable. The t-stat had such a tight tolerance (0 degrees apparently) that it would cycle too often (on for 10, off for 5, on for 10, off for 5, etc.), which was not only irriating but was killing my system's efficiency not to mention decreasing it's lifespan due to the switching on and off so frequently. Is there a digital Honeywell t-stat for a heat pump system with electric aux with adjustable temp swing and adjustable auxillary differential setting???
 
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Old 12-20-10, 07:30 PM
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No, Honeywell does not do the swing.. the CPH would need to be changed. I know they say 9 for electric heat strips, but I always suggest seting it to 3, and you get a much longer run time and down time.
 
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Old 12-21-10, 06:02 PM
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I tried adjusting that setting but there was no difference. Plus, I don't understand how it could run longer if the t-stat is still maintaining a 0-degree swing. Can you explain?
 
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Old 12-21-10, 07:22 PM
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It needs a day or so to relearn. My furnace runs for about 20 minutes, and then shuts down for about 15 min. Hard to tell how it works, see below.


 
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Old 12-29-10, 07:35 PM
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I understand, but I had this particular thermostat connected for several months, and it would always cycle to often. Since I switched to a Ritetemp, I no longer have the problem.
 
  #16  
Old 01-11-11, 02:17 PM
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Heat Pump Keeps Running Too

I'm having a similar problem. I live in Middle Georgia. Have a 1 1/2 year old Goodman heat pump Models in /ASPF313716 and out/SSZ140301.

Last month when we had real cold. for us. Temps lows in the 20's and the unit kept running and would never shut off when reaching the stat setting of 72deg. Once the daytime temp got in the 40's it would work alright. I called the installer and he said the problem was a low refrigerant and added some. It worked fine during the following more moderate weather.

Now for the last week with lows again in the mid 20's and sometimes staying in the high 30's for most of the day it's doing the same thing.

The stat is a Braeburn 1200NC 2 heat/1 cool type. The 1st stage diff is set at .5 and the 2nd stage settings is set at 2.

The thermostat has been set at 72 all day today, is currently reading 71, and the present outside temp is 38.

To get it to shut down I just now lowered the stat setting to 70

Is this normal for low temps in the 20's? From what I read here it is not. What else could it be? The house is 2300 sq. ft.

Thanks
 
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Old 01-11-11, 02:40 PM
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The HP is not sized for heating, it's sized for cooling. So yes, when you get down 20's and lower, it will start running longer or non-stop.

So for your stat, the aux won't come on till the temp drops below 2˚ below set point.
 
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Old 01-12-11, 05:04 AM
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Hi Jay,
Thanks for the info. That's reassuring! The only thying is can it be harmful to the unit running non-stop for 12-18 hours or more?
John
 
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Old 01-12-11, 06:02 AM
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Nothing is harmful. They are made to run. All the starting and stopping is hard on the equipment.
 
  #20  
Old 01-12-11, 12:49 PM
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Thanks again Jay!! I sure do appreciate guys like you being available to help others out with their problems.
J
 
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Old 01-12-11, 04:13 PM
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edit. wrong thread..............................
 
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Old 01-13-11, 06:19 PM
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Can I put in a relay to turn on the heat strips?

I have the same problem everyone else has described. The thermostat is a Honeywell Pro 6000. Are there settings I can optimize?
If not, does EM heat work as simply as the t-stat turns on the fan and the strips? In other words, would it be safe to hook up a relay to make the EM circuit go hot to the heat pump controller whenever the fan turns on? This way the heat pump would get EM help regardless of the temp differential. I would wire in a switch so the relay would only be on when I wanted it to be. Ultimately I would put a thermistor controlled relay out in the unit itself, but I need to know if the system is that simple.
 
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Old 01-13-11, 07:24 PM
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what is the exact problem that you are having? Your stat has setting that you should ensure your aux cph setting is on 3 instead of 9.

It does work as simply as you believe, however doing as you are suggesting is wasting electricity and making your system in efficient. It defeats the point of having a HP instead of just an electric furnace
 
  #24  
Old 01-13-11, 08:21 PM
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Thank you for the straight answer.
The heat coming out of the vents is barely warm. I would only engage the elements when it was below freezing outside to help the heat pump while using my switch/relay idea. The ultimate plan is to set up a thermister based circuit to monitor the temp in the delivery plenum and kick on the heat strips only when it is too cool.
 
  #25  
Old 01-14-11, 05:21 AM
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Which wire?

According to the diagram in the instructions, there are two possible wires that I could be using. One is described as being for the heater element relay, the other is hot when EM is enabled. I suspect that one tells the heatpump to kick on the strips and the other sends back a signal to the t-stat to let it know the strips came on, or at least that the controller in the heating unit has done what it needs to do to turn them on. The question is, which is which? My first thought is that the one labeled for the relay is the one that the t-stat sets high to cause it to trigger and turn on the elements, while the other is the confirmation signal, but I could be wrong about any number of things in this evaluation, so I don't want to proceed until I am sure.
Which one should I tie into my relay if I go ahead with my idea? I really do not want to fry the control board or t-stat.
I changed that setting you recommended and so far all I noticed is that the system seems to pump out very cold air for a lot longer before it gets warm than it used to. I'll give it a couple of days to see how that goes.
 
  #26  
Old 01-14-11, 01:37 PM
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Midlife, I had a similar complaint with my HP. I found there are thermostats with outside temp sensors that can do what you want and it will be UL approved. Check out this thread. I wouldn't try anything nonstandard around a device like a furnace as it could cause a fire safety issue. The only issue I had is the ouside temp sensor requires a separate wire bundle from the rest of the control wires because of crosstalk problems.

http://forum.doityourself.com/thermo...ml#post1798402
 
  #27  
Old 01-15-11, 03:54 PM
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I haven't found a thermostat that just adds in the EM strips when it gets cold. They seem to all be either/or. You have the HP or the EM running, but never both at the same time. The problem I have is that when my system was replaced just a few years ago the company that did it sold us one that has undersized heat elements: apparently they did not want to deal with redoing the electrical wiring. I'm considering talking to a lawyer about this situation and seeing if I can force them to straighten out their mistake on their dime. Money has been tight and at this point I don't have the cash flow or credit to get it done myself.
Because the EM is undersized, I have to have the pump running. I just want the EM to help it out when it gets very cold.
I'm also not happy with the Honeywell 1 degree comfort temperature setting. The system is constantly on - off - on - off, which is neither energy efficient or good for the moving parts.
I found a thermostat where the swing is adjustable for 1 to 4 degrees and will at least install that.
If anyone knows of a thermostat that is compatible with an Armstrong HP unit and does what I need, please feel free to let me know about it.
 
  #28  
Old 01-15-11, 04:15 PM
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you can add an outdoor stat that will send a signal to turn on strip heat with the HP when the outdoor temp is below the set point
 
  #29  
Old 01-16-11, 07:46 AM
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Thank you. I've done a little research and of course the only sample instructions don't match my current thermostat by connection label. The ones I have found appear to be mechanically operated contacts. A temperature sensitive spring causes a cam to turn, which closes the contact. This means that they are literally two wire installations. Can you describe the best points to connect to (by function, not color code) on the heat pump control board? The wiring diagrams I have seen so far appear to tap into the heat strip signal from the indoor t-stat, which is not going to help me. I need the thing to go hot below the outdoor setpoint whenever the heat comes on, even if the indoor t-stat is only calling for the HP. The diagrams I have found look like they will disable the strips above the set point, which means they will only come on when the indoor t-stat calls for them and the outdoor temp is below set point. These outdoor t-stats should work for me, I just need to know where to make the connections.
 
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Old 01-16-11, 08:16 AM
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this will allow the strip heat to run below set point and also run the heat pump when running the heat. attach one wire from outdoor stat to Y and the other to W2 both of these connection can be done right at the HP wiring

 

Last edited by hvactechfw; 01-16-11 at 08:57 AM.
  #31  
Old 01-18-11, 09:43 AM
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Thank you for the diagram. My system spends what seems like an awful lot of time blowing cold air. What would happen if I made the connection to the fan circuit instead of the compressor?
 
  #32  
Old 01-18-11, 02:56 PM
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wow !

gotta love diy's ! brave, smart, and sometimes just knowledgeable enough to be dangerous (that is unfortunately true of some technicians). but that's ok. keep digging and keep inquiring. nothing wrong with getting onboard with the program.

no doubt, thermostat designers are aware of the threshold problems you guys are experiencing. you have to wonder why there has not been a quick fix to override normal functions under various circumstances. i think the answer to that is that most of the variables involved in these issues have more to do with the bigger picture. by that, i mean ductwork design, building insulation, system sizing errors, maintenance issues, freon level, seer rating, etc. in other words, the machines can only do what they can do. modifying the sequence of operation is not necessarily the solution to your problems. it may seem cut and dried, but sometimes performance problems exist due to equipment working against conditions they are not designed to work under. it's kind of like a refrigerator running too much because of a leaky door gasket. what seems like a regulation problem can sometimes be attributable to other factors. having said all that, i do understand what you are trying to accomplish. the notion of kicking it up a notch when the temp drops outside indicates a need to acknowledge the system is inadequate. of course, that is what aux heat is for. the use of aux heat is automatic within that temp differential as discussed. if comfort cannot be attained, especially during abnormally cold temperatures, consider emergency heat temporarily or drop the set point and add a sweater. i don't need to tell you, but there are more inadequately designed systems out there than those designed with a lot of forethought. this is because contractors cut corners and use sub-contractors who cut corners. just remember that if you ever have to upgrade and do your homework then. good luck all.
 
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Old 01-18-11, 03:04 PM
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if you cut the fan then if you were to run your fan 24/7 then it would turn on strip heat if below the outdoor stat setpoint. also, why would you want to do this and have to run additional wiring back inside when all these connections can be made outside?
 
  #34  
Old 01-18-11, 03:17 PM
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final thought

hvactechfw is suggesting a control that is actually used extensively in the hvac field on the commercial side and more so now in the residential side on more modern systems that utilize thermidistats, variable speed blowers, two stage compressors and communicating user interface. of course, these systems address issues much differently and fine tuning is possible.

an outdoor thermostat can be used as input to a computer board, but it could also be used to parallel to the indoor thermostat as it is being suggested. it seems the most direct way to accomplish your objective. the net result is that either the outdoor thermostat or the second stage of the indoor thermostat (aux heat setpoint) will turn on electric heat, whichever closes first. sounds reasonable and shouldn't adversly affect the system in a way that would compromise safety. the only additional thought is that the adjustable setpoint should maybe only do this if the outdorr thermostat dips below a low limit outdoor setpoint as opposed to setting it just below the indoor temperature. what do you think, hvactechfw ? my honest impression, mr crisis, is that none of these bandaids is going to make you happy. i think there are variables we cannot discern from here. good luck anyway.
 

Last edited by nomadpeo; 01-18-11 at 03:29 PM. Reason: verbage
  #35  
Old 01-18-11, 03:22 PM
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you got it nomad......... this is what he was asking to do and is the simplest way to do just that
 
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Old 01-18-11, 03:33 PM
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since we're both online right now, make sure you read my final editing. i'm enjoying the exchange. is it just me, or is this hobby a bit addicting ? i teach hvac principles at a community college and i find some of the stuff i see out here to be fascinating as well as informative. keeps us on our toes, right ?
 
  #37  
Old 01-18-11, 04:08 PM
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agreed nomad! .....................................
 
  #38  
Old 01-18-11, 04:40 PM
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Why would I need to run another wire? Can't I mount it in the control area of the HP and use the 24v connection points that the wire coming from the thermostat runs to?
I thought I was clear earlier that there is indeed something going on. The company that installed the unit sold me one with grossly inadequate EM strips. So I can't switch over to EM when it gets cold because the EM isn't strong enough to keep up by itself. My short term solution (until I have the money to get the wiring upgraded and heavier heating strips installed) is to run both of them at the same time when it is cold enough to need it.
Even when it is not all that cold, the system spends too much time pumping out cold air, so it seems reasonable to make the EM strips come on whenever it is cold out and the fan is blowing, so the air won't be so cold.
I gather from the tone of one of the posts (just enough to be dangerous) that there is a serious flaw in my logic. What is it? I appreciate constructive feedback and if I'm being an idiot, I want to know about it, I just want to know why too.
 
  #39  
Old 01-18-11, 05:04 PM
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its not a flaw in your logic.........
What would happen if I made the connection to the fan circuit instead of the compressor?
if you use the fan ciruit... 1. the fan wire (GREEN) it is not sent outdoors as the hp has no control over the indoor fan. Therefore if off splice off the fan wiring as you suggested then you would have to supply an additional signal to the outdoor stat requiring you to have another wire run to the HP 2. if you were to turn your fan to on instead of auto at the thermostat, then the aux heat has the potential to turn on with out there being an actual call for heat if the outdoor temp was below the setpoint of the outdoor stat. Do as I provided in the diagram of splicing off Y signal and then below the setpoint of the outdoor stat the aux heat will kick on along with the heat pump and only with a call for heat.
 
  #40  
Old 01-18-11, 05:14 PM
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what component will you use as the outdoor stat? the t1 and t2 box could be a simple toggle switch you can flip when things get chilly.

another idea is to put a 1500 watt space heater on a heavy duty timer down in the basement or first floor near the air return. set it to come on in the evening when the temps drop and run for 5-6 or more hours. the heat will rise thru the house and be circulated by and assist the heat pump.

I did this for years during January and February until I recently added a tstat with external sensor and hp lockout. It added $20-30 per month to the electric bill but kept the heat pump from running constantly.
 
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