I did away with Auxillary heat, So far so good.

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Old 12-07-13, 08:08 AM
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I did away with Auxillary heat, So far so good.

I have a 3 ton Bryant heat pump installed in early 10. It defrosts every 2 or 2.5 hours if it needs it or not. So it runs the 20kw heat strips when It defrosts and I figured every time it defrosted it used 3.3 kwh in just strip heat, so I disconnected all of the relays for all of the heat strips and now there is no way for the auxiliary heat to kick on.

I don't care if the registers blow ice cold when defrosting, And I don't care if the temp drops below the 4.5 degree set point of my thermostat which is where the thermostat will kick on the auxiliary heat.

The temp only drops .5 to 1 degree when the unit defrosts and the thermostat was set at 71 last night and it was 68 in house this morning, this was on a 10 degree night. Now the heat pump ran all night but I figured out that its still 1.5 times cheaper to run the heat pump vs the strip heat at 0-10 degrees. The COP of my unit is high.

I have ran this way since last winter and it works for me.
 
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Old 12-07-13, 11:00 AM
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I'll pay the dollar for comfort
 
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Old 12-07-13, 11:12 AM
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You probably could have just disconnected the one wire to the relay/sequencer so that it could be reconnected easily if needed. On some units there is a separate electrical disconnect just for the heating coils.
 
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Old 12-07-13, 11:46 AM
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I would look into adding insulation and sealing the house before eliminating the heat strips.
 
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Old 12-07-13, 03:21 PM
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I just pulled the input wires off of the relays, I can connect them back in a matter of minutes. It saves a matter of about 33 cents every defrost cycle, Its never a comfort issue for me, There are two breakers on the furnace, one controls 10 kw of strips, the other controls the other 10 kw of strips and all of the electronics so its not just a matter of shutting off the breakers.

The house is well insulated, its just a matter of saving 30-50 a month. The heat pump always ran continuously when it was 0-10 degrees out even with the strip heat.


The heat pump can run for an hour and use the same amount of electricity that the strips use in 10 minutes. Its worth it to me.
 
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Old 12-08-13, 04:01 AM
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Do all heat pumps run the heater strips when doing a defrost? I see my upstairs unit do a defrost pretty often (see the outside condenser covered with frost) but it seems to only take 5 mins to compleate.
 
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Old 12-08-13, 11:18 AM
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Yes. Electric heat kicks in during defrost. Savings would be minimal if you didn't use it. Maybe a $1 a day savings ( maybe ). Two fan motors and a compreser running none stop would eat up most of that savings
 
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Old 12-13-13, 05:39 PM
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Ok, I ran with and without auxiliary heat. For a day where the heatpump ran 20 hours, the unit would have defrosted 10 times at 10 minutes each defrost cycle. 20 kw heatstrips would have used 33.3 kwh in this time spent defrosting. Thats 3.60 cents spent on this particular day.

My heat pump only uses 3-4 kwh an hour when running, the heat pump can run 8 hours on what the strips use on just defrosting.

I ran the heat pump only with no way for auxiliary to come on and it got down to zero degrees one night with a high of 20. A setpoint of 72 degrees the house got down to 66 at night with the heat pump never shutting off, it ran all day and when I got home it was 71 in house.
The heat pump uses a maximum of 96 kwh a day when running non stop, its usually less but thats the max, the 20kw heat strips can run for 4.8 hours and use the same 96kwh.

When I ran with straight heat strips and the furnace ran about half the time on a 0 degree night. Thats over 200 kwh a day.

I will keep the heatpump running 24 hours a day when its zero, vs using heat strips.
 
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Old 12-13-13, 05:48 PM
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When the heat pump does a defrost.... the system goes back to normal air conditioning and it extracts the heat from inside to use outside to defrost the coil. During that period.... since the system is extracting the heat from the house you would get cool/cold air coming out of the registers. The re-heat coils keep that air warm.


Civicminded...... Interesting results there
 
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Old 12-13-13, 05:58 PM
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Civicminded...... Interesting results there
I was thinking the same thing, but I am also wondering if running the heat pump without the strips will shorten the compressor life. I assume it's a scroll compressor and probably has a 10 year warranty.
 
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Old 12-13-13, 06:04 PM
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Yes it's very interesting. My unit just had the heat strips go bad and I noticed and measured the air blowing from the ducts at 56 deg. durring defrost. I'm not sure but I think my unit senses the need for defrost, so it only does defrost on those rainy cold days.
 
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Old 12-13-13, 06:43 PM
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Most heat pumps have a defrost thermostat that senses the coil temperature. Usually when the coil hits 32f it goes to defrost. Some units are strictly timer controlled and other measure when the temperature reaches around 57f and then go back to heat mode.

The amount of moisture in the air is what causes the coil to ice up and the outside temperature determines how fast it will freeze.
 
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Old 12-13-13, 06:49 PM
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Mine has DIP switches on it and you can select how often it defrosts. The max time is every 2 hours, whether it needs it or not.... It locks out defrost at 50 degrees, I am not sure if it stops defrost at a certain temp.

I wish it had demand defrost...
 
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Old 12-14-13, 03:06 AM
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Are you sure you have 20 Kwatt of electric heat? Wouldn't that require 80 amps?
 
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Old 12-15-13, 10:08 AM
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Even if you had 20kw it's going to be staged so I doubt that the 20k would ever come into play specialy not in 10 minutes.
 
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