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From: ajs@hpfcla.UUCP
Newsgroups: net.consumers
Subject: Re: Heat pump/water heater energy conservation
Message-ID: <42000016@hpfcla.UUCP>
Date: Fri, 13-Dec-85 10:27:00 EST
Article-I.D.: hpfcla.42000016
Posted: Fri Dec 13 10:27:00 1985
Date-Received: Fri, 20-Dec-85 05:43:21 EST
References: <237@neurad.UUCP>
Organization: 13 Dec 85 08:27:00 MST
Lines: 28

> ...the manual for my heat pump recommends setting one temperature and
> making no further adjustments.
> ...the major problem seems to be that the heat pump
> contains two thermostatic switches; one for the heat pump compressor,
> and one for the aux. heating coils.

You nailed it.  The problem is, you never want to run the aux heat if
you can help it, but any sudden change greater than the preset delta
(about two degrees) will do it.  There's nothing wrong with a smooth (or
small-step) transition; I often fake this manually.  Just so the heat
pump does all the work, not the aux heat, and you never restart the
compressor within a couple of minutes of it turning off (it takes time
to equalize some pressures which stress it if quickly restarted).

I suspect the reason you can't (easily) buy a heat-pump set-back
thermostat is that it's tough to make a cheap (mechanical) one which is
also sufficiently flexible (programmable).  An electronic solution would
be better, but probably hard to make cheap and portable (will it work
with YOUR heat pump?  what's the time to ROI?).

Related note:  When the weather is continuously cold enough that the
heat pump is inefficient or turns itself off, expect the house to
average "delta" degrees cooler, as the aux heat does all the real work
but has a set-point "delta" degrees lower.

Sigh, it's an AI problem...

Alan Silverstein