Lee Hart via EV wrote:
4. Tankless demand heaters (that only heat the water when it is actually
needed) are more efficient that anything you can do with a tank-type
waterheater, regular or hybrid.
Jay Summet <[email protected]>
Yes, when comparing gas tankless to gas tanked heaters.
NO for Electrically operated tankless heaters vs hybrid (heat pump) water
heaters with a tank.
Good catch. :-) I was assuming gas; not electric. I've never seen a big
tankless electric water heater, for exactly the reason mentioned (too
high a peak load). Tankless electric water heaters are usually little
under-the-sink units, to provide hot water for a cup of tea or to wash
your hands.
So I wasn't thinking of electric heat pump based water heaters. Though
it's still a complicated question, with no easy one-size-fits-all answers.
There are circumstances where a heat pump is more efficient; and others
where it is less efficient. As I said, I live in Minnesota, where
heating is frequent and A/C is rare. Where does a heat pump get its heat
in the winter? When it can't get it from outside air, it falls back to
electrically powered resistors.
There are ground-based heat pumps that get their heat via a network of
buried pipes. This works in the winter, if they are buried deep enough.
But this can get very expensive. The decision is economic: How many
thousands of dollars will you spend to save a dollar a month? A complex
system can break down or wear out before you achieve paypack.
Robert Bruninga via EV wrote:
>> Heatpump water heater heating at one third the electric energy
>> cost still beats a tankless hands down.
That's true in the right circumstances. But you can't assume they are
always right. How long is it between when the water is heated, and when
it is used? The longer it sits, the higher your standby losses. The
demand heater doesn't lose any energy to these standby losses.
The savings are hard to estimate because they depend so much on where
you live, and your lifestyle. Is the heater in a hot garage, or a cold
basement? How much hot water do you use a day? Just one person, or a big
family?
In my case (water heater in MN basement, a 2-person household that uses
less than 10 gal/day) a heat pump water heater is uneconomical.
--
Problems that go away by themselves will be back with friends.
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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