tim.... wrote:
"The Natural Philosopher" wrote in message
...
tim.... wrote:
"Tim Watts" wrote in message
...
Piers Finlayson
wibbled on Monday 05 July 2010 09:02


Of course, heat pumps depend on large amounts of (grid provided)
electricity. I seem to recall something like 1/4 to 1/3 of the total
overall heat energy produced by a heat pump needs to be provided with
electricity to power it.

Given the state of our generating infrastructure in this country I
would not want to be dependent on relatively cheap (and available!)
electricity for my heating in the medium and long term.
I was talking to an air-con engineer last Saturday. He was saying that,
according to the contact he's had with manufacturers and various
seminars,
that the big push is to get air source pumps into a viable state as it
is
well recognised that ground source is too expensive and/or difficult for
the
majority to adopt.

Apparently, they have air source producing useful output at air
temperatures
slightly below freezing and producing useful temperatures on the output
side, so as always the effort is to make it viable commercially.

It sounded potentially quite promising. Not sure if it's going to be a
matter of years or a decade, but watch this space...
Surely this only works for cooling. The outside air is normally going to
be colder than the inside air so this is a cheaper way to cool the
inside.

It is never going to work for heating up a house (except in some very
extreme outside conditions that I think we can ignore)

I dont think you understand what a heat pump is.

I think I do (BICBW)

Thats like saying a fridge only works if the room is at -5C..

No, because you can run the fridge down to -5 by putting more power in.

The idea of an "efficient" heat pump is that you use less power to "extract"
the heat from somewhere else that you would use to heat up the place
instead.


Fraid you still dont get the point.

A heat pump will pump in a single stage about 40 degrees C at about 4:1
uplift in power in to power out of the hot end. It will do about 50C at
about 3:1. You can do more with multiple stages.

So it doesn't matter what the outside temperature is, as long as the
working fluid doesn't freeze, it works.

What matters is that below about -10C, its barely able to get the output
up to 30C. You need a two stage pump, or simply add top up resistive
heating.



tim