Return to the Heating & Air Conditioning Forum | Post a Follow-Up

 o
Force Emergency Heat?

Posted by rjexit5 (My Page) on
Wed, Dec 26, 12 at 10:40

I have a Bryant Evolution Controlled heat pump; electric only. Does it ever make economical sense to force the system to run on emergency heat if the outside unit is functional? During cold periods(<30F) the outside unit seems to run and run and then defrost (thawing out, getting the coil to 70F) and the cycles back through running the heat pump until the coils is about 15-20F just to defrost again. The auxiliary heat runs while the defrost cycle is taking place so we are partially using the strip heating then.

At some point it would seem cheaper/more efficient to just let the emergency heat run getting the house warm and then shutting off rather than cycling so much and wasting the electric outside heating the coils to 70F just to suck that defrost generated heat back via the heat pump operation.

I am newer to the heat pump world and our electric use is not out of control but it seems wasteful to be defrosting frequently just to essentially take the defrost energy back into the house as heat pump product. The heat pump seems to run with few defrost cycles when the outside temp is 35+F but below 30F there is an increase is the defrost cycles.

Thoughts?


Follow-Up Postings:

 o
RE: Force Emergency Heat?

Yes there is a temperature where it makes sense to not use the heat pump and only use the auxiliary heat.

It sounds like your Evolution controller has not been set up properly for temperature lock out temperatures. I believe the controller has two lock out temperature settings. You can set one temperature to lock out the heat pump, and a second to lock out the auxiliary heat. In between the two temperatures the controller will use both as needed.

Based on what you have said, I suggest the heat pump should locked out at 35 degrees, and the auxiliary heat should be locked out at 40 degrees. In between these two temperatures the heat pump should come on first and then switch to auxiliary if the controller decides it is taking too long to satisfy the temperature.

I think you will need to go into the service menu to set these temperatures.


 o
RE: Force Emergency Heat?

Thanks for the direction Mike. I checked and I only have 1 lockout setting. Under Setup-Heat Pump-Elec Lock Out, when outside temp above this temp the electric heat will not operate. (currently set for 35F).

I only have a 1 fuel system(electric) so I am not sure where the other lockout setting would be (if it exists)

Any suggestions?


 o
RE: Force Emergency Heat?

Below is a link for the installation instruction. It explains the settings in the set up menu.

It looks like what I described is only available if you have a hybrid heat pump and furnace set up. Sorry for the misinformation. I have this thermostat but use it with furnaces and not heat pumps.

It looks like you can only lock out the auxiliary electric heat and not the heat pump in heating mode.

Here is a link that might be useful: Bryant Evolution Installation Instructions


 o
RE: Force Emergency Heat?

Here is another document which describes the algorithm the Infinity/Evolution Controller will use. On page 11 it states heat strip only heating is available but it doesn't explain how it works.

I suppose as long as the heat pump COP is greater than one, then it is more efficient than the electric heat strips. The COP is supposed to account for defrost cycles.

Perhaps one of the heat pump experts can provide more information.

Here is a link that might be useful: Sequence of Operation


 o
RE: Force Emergency Heat?

RJ

Could you provide your location and typical winter climate?

I would not lock out heat pump condenser unless outside temp is 10 degrees and below. Then you could run auxiliary/emergency heat only.

Unfortunately for Bryant/Carrier, they do not offer real electronic demand defrost. With time defrost like you have, you get many unnecessary, nuisance, and expensive defrost calls. Here the auxiliary/emergency heat is needed to temper the AC air that is entering your home.

I would lock out auxiliary heat at 38-40 degrees and above. If much lower, then you will get chilled from the AC air entering your home.

Shame on Carrier/Bryant not making the upgrade to EDD.

IMO


 o
RE: Force Emergency Heat?

We live in southern end of the north east. (Eastern panhandle wv). We tend to be in the low 30s during the day and upper teens in the evening.

Thanks for your comments.


 o
RE: Force Emergency Heat?

I would say below 10 to 15 degrees cut the pump. Without demand defrost you might be better off sticking to 15. I have demand defrost and cut mine at 10 but I also have a pellet stove in the basement for power outage heat and I run it when it gets down in the teens or colder so the strips stay off as much as possible.


 o
RE: Force Emergency Heat?

Do you have to force the system into emergency heat manually? Are there thermostats which you can program a temperature?


 o
RE: Force Emergency Heat?

Yes Mike many newer stats with the use of an outdoor temp sensor can be programmed to lock out both the aux heat and heat pump depending on temperature outside.

Any temp above 35 and no matter what my heat strips will not activate. The only reason for this temp is if the heat pump did fail I wouldn't want anything to freeze which even at 30 is highly doubtful but I am not taking the chance the way my luck runs.

The heat pump shuts off below 10 degrees and the strips carry it from there. So I am pump only above 35, pump with strips to 10 and below 10 strip only.

If we are going to be gone for days and I set the stat at 65 and come home and its 40 degrees out and crank it to 73 a reg stat would kick on both strips and pump to roll that temp up wasting $$.


 o
RE: Force Emergency Heat?

Countryboy...our thermostat does allow for lockout but only a lockup of the heat strips. I have a Bryant Evolution controller but since it is a single fuel system(electric) it does not allow the heat pump to be locked out. If I want to lockout the heat pump I think I will have to manually force emergency heat, not ideal.

mike... Do you know if the newer Bryant Evolution controllers allow for single fuel systems to lockout the heat pump.


 o
RE: Force Emergency Heat?

It looks like the new Evolution Connex Control will allow you to lock out the heat pump. It is described on page 35 as heat source and heat pump lockout.

I don't understand why your current controller can't perform the same function. If it has the ability to lock out the heat pump in a dual fuel set up, then why not in a heat pump and heat strip configuration?

Did you try asking the Bryant dealer who installed your equipment? You can also try calling Bryant customer service. Maybe the set up can be configured to look like a dual fuel configuration.

Here is a link that might be useful: Evolution Connex Control installation manual


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Heating & Air Conditioning Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here