"Ian Stirling" wrote in message
...
Rob Morley wrote:
snip
Could they not have used a wind pump instead of electric?

A heat pump is more than simply a pump.
It's basically a refrigerator cooling the field where the coil is buried
and heating the church.
While in theory you could run this from wind power, it'd be a really
large and complex installation to do so. (in combination with battery
bank to level the load, and ...).

There was ample land around that church to have installed a freestanding
solar array. This could generate low grade hot water stored in a large
thermal store. This would then heat the UFH of the church. That would not
have been more expensive than the heat pump.

"Pete C" wrote in message
...
On 09 Oct 2004 14:40:32 GMT, Ian Stirling
wrote:


Let's be optimistic, and say that the heat pump takes 1Kwh to pump
7Kwh of heat. (about the theoretical maximum efficiency for pumping
from 0-40C.)
But, electricity is some 3-4 times dearer than gas.
So, unless you are comparing it with electric heating it's not looking
so rosy.

Hi,

With a typical GSHP it would be 3:1 or 5:1 for a very good one.

It's (eventually, assuming it lasts for ever) 7 times cheaper than
electricity.
But, it's only about 2 times cheaper than gas.

What makes it worthwhile for a building with a lot of thermal mass is
that you can heat overnight on economy 7 and the building will keep
warm in the day.

That makes sense only if you have heavy insulation on the cold side of the
mass.

Also the thick walls will average out the outside temp to around 5°C
for NI winters, averaging out the heat load which helps heat pump
capacity and efficiency.

It was in the republic.

AFAICS the economy 7 rate in NI is 3.44p and the gas rate is 2.1p, so
with a 4:1 heat pump running overnight it comes out at 3.44/5 = 0.688,
3x cheaper than gas.

That's if you can store all that heat in the mass and hope it last all day
and evening. Superinsulation is essential.

Payback can happen faster if energy prices rise (gas and electricity
will tend to rise together unless we go nuclear), but it will never
outperform adding insulation unless electricity is free.

Electricity will lag behind a bit, so the saving will increase
slightly as gas prices rise.

I'll take a guess that the walls of the church are 75cm stone on average.
That's a R value of around .6, or a U value of 1.6W/m^2/K.
To halve the thermal loss you only need about 10-20mm extra insulation.

True, if they dry line the walls that would make a big difference as
heat is released through the floor so can only escape through the
walls, windows and roof.

Forget the silly church. Using a heat pump overnight to heat thermal mass.
The house would need to be superinsulated. The heat pump would need to heat
large sections of thermal mass. In short, the ceilings and walls over night,
not heating the air. The floor during the day if the temperature drops.
Depending on the size of the house, the superinsulation would eman that only
a small heating system, if at all, need be installed.

IMM wrote:

"Ian Stirling" wrote in message
...
Rob Morley wrote:
snip
Could they not have used a wind pump instead of electric?

A heat pump is more than simply a pump.
It's basically a refrigerator cooling the field where the coil is buried
and heating the church.
While in theory you could run this from wind power, it'd be a really
large and complex installation to do so. (in combination with battery
bank to level the load, and ...).

There was ample land around that church to have installed a freestanding
solar array. This could generate low grade hot water stored in a large
thermal store. This would then heat the UFH of the church. That would not
have been more expensive than the heat pump.

Agree totally, if planning permission could be obtained for it.
Personally, I'd not go for a large thermal store, but an effin huge one,
if possible.

At the very least a weeks worth of heating, with the collectors double
or triple the nominal heat requirement.

And as a bonus, you've got a 'free' olympic sized pool.
(well, maybe not quite that much)

"Ian Stirling" wrote in message
...
IMM wrote:

"Ian Stirling" wrote in message
...
Rob Morley wrote:
snip
Could they not have used a wind pump instead of electric?

A heat pump is more than simply a pump.
It's basically a refrigerator cooling the field where the coil is
buried
and heating the church.
While in theory you could run this from wind power, it'd be a really
large and complex installation to do so. (in combination with battery
bank to level the load, and ...).

There was ample land around that church to have installed a freestanding
solar array. This could generate low grade hot water stored in a large
thermal store. This would then heat the UFH of the church. That would
not
have been more expensive than the heat pump.

Agree totally, if planning permission could be obtained for it.
Personally, I'd not go for a large thermal store, but an effin huge one,
if possible.

You size it accordingly. You may be on about an inter-seasonal store.

At the very least a weeks worth of heating,
with the collectors double
or triple the nominal heat requirement.

A very large array of cheap collectors can deliver a lot of low grade heat,
which is what UFH operates on. The odd high efficient collector for DHW may
be handy.

And as a bonus, you've got a 'free' olympic sized pool.
(well, maybe not quite that much)