DIYbanter - View Single Post - Cheaper to set back heat pump at night or leave at same temp?

wrote:
Heat pump in question has no emergency heat installed. Location is
Phoenix, AZ.

Is it better to turn it down at night or not. User is on a time of
use plan from Salt River Project. Peak time in winter starts at 5am
but user gets up at 4am and can turn it on then.

Saw this in another group, is it true?

If one has an electric heat pump and is on a time of usage plan with
the power company there are two more considerations.

The power rate goes up at 5am so you are likely to be re-heating with
more expensive power. Also, a heat pump is less efficient as the
outside temperature drops. As it is usually coldest just at dawn,
kickiing the systm on then to re-heat is making it try to work when it
is at it's least efficient state

It is really difficult to say. Set backs for heat pumps are marginal.
Your time of day ratings complicate the thing even more. In general most
authorities suggest a minimal set back if any. Local conditions,
insulation, efficiency etc all come into play so what works for one may not
work for another.

My suggestion is that when the outside temperature is so low as to force
it into resistance heating mode, then use the set back. What you want to
avoid is the opposite where you are set back during the time when the
outside temps allow normal operation only to delay the recovery to the part
of the day (generally early morning) when it would be coldest and would be
more likely to go into resistance mode.

--
Joseph Meehan

26 + 6 = 1 It's Irish Math