1. Originally posted by marca
In my opinion, it is a waste of both electricity and heat pump wear and tear to operate a system in this fashion at low temperatures. That is the reason I switch OFF the heat pump and switch ON the resistance heat during periods of low outside temperature. My logic is; if the heat pump is unable to satisfy within a reasonable period of time, then it should not be running. Makes sense?
It's your opinion. Just doesn't make it right nor does your logic make sense.

A heat pump provides useable heat well below 20°F, and it costs more to run strip heat only.

Sit down and do some math. You'll need the following information: BTUH capacity of your strip heat; running amps of your strip heat; running amps of your heat pump; BTUH output of your HP; KW-H cost; heat loss of your structure at 20°F.

Now see what's cheaper to run. I bet you'll find that the HP running continuously with b/u heaters bumping intermittently is significantly cheaper than only running the b/u heaters.

I've done the math. I want you to see for yourself.

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Originally posted by jrbenny
Originally posted by marca
In my opinion, it is a waste of both electricity and heat pump wear and tear to operate a system in this fashion at low temperatures. That is the reason I switch OFF the heat pump and switch ON the resistance heat during periods of low outside temperature. My logic is; if the heat pump is unable to satisfy within a reasonable period of time, then it should not be running. Makes sense?
It's your opinion. Just doesn't make it right nor does your logic make sense.

A heat pump provides useable heat well below 20°F, and it costs more to run strip heat only.

Sit down and do some math. You'll need the following information: BTUH capacity of your strip heat; running amps of your strip heat; running amps of your heat pump; BTUH output of your HP; KW-H cost; heat loss of your structure at 20°F.

Now see what's cheaper to run. I bet you'll find that the HP running continuously with b/u heaters bumping intermittently is significantly cheaper than only running the b/u heaters.

I've done the math. I want you to see for yourself.

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I agree with jrbenny,leave t-stat set and let the system do it's job.Don't over try to second guess science.

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Originally posted by marca
Filterchanger -- Yes, if both heat sources are operating simultaneously, plenum temp. will be much higher. However, if second stage kicks in, meaning that there was a 2-3F drop that called first stage on, then another 2-3F drop that called for second stage to kick on, then you are fighting a losing battle. Once the resistance heat satisfies that additional 2-3F drop, it will shut off. However, the heat pump will continue to run, and run, and, run; but it will NEVER satisfy the original 2-3F drop. Now, the cycle will continue..... another 2-3F drop, calling for second stage heat, second stage satisfies while first stage keeps running, first stage can not keep up, another 2-3F drop, second stage kicks in again, etc, etc., etc. In my opinion, it is a waste of both electricity and heat pump wear and tear to operate a system in this fashion at low temperatures. That is the reason I switch OFF the heat pump and switch ON the resistance heat during periods of low outside temperature. My logic is; if the heat pump is unable to satisfy within a reasonable period of time, then it should not be running. Makes sense?
Unless there's something wrong with your heat pump, running nonstop is not a sign that it's inefficient. It's simply the result of your homes heat loss exceeding the heat output of your heat pump. And running nonstop isn't really bad for your heat pump. Someone around here even has a signature saying - "The worst thing you can do to a compressor is to start it." So given a choice between running nonstop and frequent starts and stops, nonstop is preferrable.

From a strictly efficiency point of view, you'll probably find that the heat pump is more efficient than resistance heating even at 0°F. Here's my computation for how much more efficient the heat pump is compared to resistance heating. The numbers below are based on my setup which is a Goodman CPLT48 heat pump with a Goodman AEPT60 air handler which has a 10kw heating coil.

Looking at the manufacturer specs on my heat pump/air handler combination, I can see that at 0°F, it can generate about 25K BTU/H at a COP of about 2.2. So even at 0°F, it's generating 2.2x as much heat as it is consuming in electricity. But we need to take into account the loss due to the heat pump's defrost cycle.

My heat pump is setup to defrost every 90 minutes. At 0°F, it will probably defrost for a full 10 minutes each time it enters the defrost cycle. So a complete heat/defrost cycles is 100 minutes long. Now let's calculate how much total heat is generated and how much electricity is consumed.

For the 90 minutes that the heat pump is heating at 25K BTU/H, it generates a total of 37.5K BTU's (since 90 minutes is 1.5 hours). The electricity it consumes during the 90 minutes is 37.5K BTU / 3.412K BTU/KWH / 2.2 = 5.0 KWH.

During the 10 minutes that the heat pump is defrosting, the heat pump is removing heat from the house at a rate of about 48K BTU/H offset by the 34K BTU/H generated by the 10KW heat strip in the air handler. The net loss of heat from the house during the 10 minutes is 14K BTU/H * 1/6 hour = 2.3K BTU's. The electricity consumed during the 10 minute defrost is about 0.6KWH for the heat pump and 1.7KWH for the 10KW heat strip (10KW * 1/6hour).

So during the 100 minute heat/defrost cycle at 0°F, the net heat output is 35.2K BTU (37.5K-2.3K). The electic usage is 7.3KWH (5.0+0.6+1.7).

Had you used resistance heating, 7.3KWH would have generated 24.9 KWH (7.3*3.412). So the heat pump is still 41% more efficient than resistance heating even at 0°F (for my setup). Do you own math and make your decision.

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Thank you all for your replies! Regarding my Trane 3 ton heatpump model TWY036B100A1, could you please let me know if this unit was manufactured with an anti-short cycling timer installed in the unit? If not, I thought it a good idea to install the delay on break timer with brownout protection. Any thoughts or recommendations regarding timer model? Also, if I perform the install myself (it is simple and straightforward), will this effect my 10 year Trane warranty? Thanks bunches.

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