Actually, backup heat (resistqance heaters) are not a bad thing.  They
allow you to size the heatpump for *most* of ones heating, and letting
resistance do the heavy lift on the coldest nights.

Even in Maryland, the average daytime high even in Jan and Feb is above
40F, though it plunges to the single digits and teens many nights.  But on
average over the 6 omnths season, the "average" temp is well over 40F, so
don't oversize and pay more for a big system when an "average system" will
do augnemnted by some more expensive backup heat.

Bob

-----Original Message-----
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Peri Hartman via
EV
Sent: Wednesday, November 29, 2017 10:07 AM
To: Electric Vehicle Discussion List
Cc: Peri Hartman
Subject: Re: [EVDL] Heat pump vs resistive Heater (OT, but somewhat EV
related)

The issue with a heat pump is sizing, at least when I did my whole house
research. Down to, say, 40F a heat pump will do exceptionally well. As it
gets colder, it takes more work to compress the heat from outside.
>From strictly a performance point of view, that will still always beat a
resistance heater. However, now you need a larger unit. There comes a
point when you need to make a size v efficiency trade off. So, if you
choose a heat pump, make sure it will generate the BTUs you need at your
coldest temperature or supplement it with some resistance heating.

Peri

------ Original Message ------
From: "Cor van de Water via EV" <ev@lists.evdl.org>
To: "Electric Vehicle Discussion List" <ev@lists.evdl.org>
Cc: "Cor van de Water" <cwa...@proxim.com>
Sent: 29-Nov-17 1:31:40 AM
Subject: Re: [EVDL] Heat pump vs resistive Heater (OT, but somewhat EV
related)

>Heat pump heating is always more efficient than resistive heating
>because the losses in the pump are added to the heat output, so when
>temp delta increases and efficiency drops, you approach the case of the
>resistive heating. Most heat pumps are applied to protect from
>excessive pump operation and wear by adding resistance heating below
>certain amb temps.
>
>
>Sent from my T-Mobile 4G LTE Device
>-------- Original message --------From: Alan Arrison via EV
><ev@lists.evdl.org> Date: 11/29/17  6:11 AM  (GMT+02:00) To:
>ev@lists.evdl.org Cc: Alan Arrison <bigg...@comcast.net> Subject: Re:
>[EVDL] Heat pump vs resistive Heater (OT, but somewhat EV related) Heat
>can't magically be obtained from cold air.
>
>As the temperature drops, the pump must do a lot more work for an ever
>smaller amount of heat.
>
>Al
>
>
>On 11/28/2017 11:03 PM, Bill Dube via EV wrote:
>>Thanks for the Wikipedia reference. Here is the link:
>>https://en.wikipedia.org/wiki/Heat_pump
>>
>>Folks are often puzzled by the "up to 4x efficiency" of heat pumps.
>>"How is that even possible?" is the most common question. (And the
>>common sense question as well...) Well, heat pumps do indeed deliver,
>>typically 3x to 4x the heat as a resistive heater given the identical
>>wattage input, occasionally even a bit more. They indeed work, whether
>>you believe in the theory or not.
>>
>
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