"IMM" wrote in message ...
"Pete C" wrote in message
...
On 1 May 2004 06:05:25 -0700, (N. Thornton) wrote:

extra complication, extra cost, thats the problem.

Not really, apart from a small ground source of some type it just
requires a small pump and some tubing. Rather than use the ground
source to supply all the heat, just use it as a buffer to even out
temperature swings.

This should allow a heat pump to operate more efficiently as the
average monthly winter temperature in the UK rarely drops below 0°C :

http://www.metoffice.com/climate/uk/seriesstatistics/ewtemp.txt

Even the average monthly temperature last summer was 17°C, so it could
be used for air conditioning or even normal air cooling too.

With some simple temperature control on the pump the ground source
could only be used when necessary and it's temperature change reversed
when the air temperature allows.


If you having ground loop then it is best to ditch the air sourced heat pump
and go for a full ground source loop, rather than a half cocked affair.
Then to warm the ground loop, using purchased energy can only be
inefficient. You then would be heating the earth around the loop. Much of
this heat, depending on earth temp, may just convect away, and may never be
re-extracted when needed.

You could have a "large" water/glycol filled pipe loop, using a pump to
circulate. This, when buried deep enough will extract useful heat that may
be used to re-heat, or heat, a cylinder, or thermal store. Only using a
pump. The size of the loop would have to be calculated, depending the
temperature at certain depths and the local ground conditions.


In principle one could use air temp to warm the loop at times, or add
a solar panel to the loop. Adding solar like this, after the water
comes out the ground and before the heat pump, would presumably help
the heat pump efficiency by raising the source temp some of the time.
Also I would imagine that the extra heat input might enable a slightly
smaller ground loop to be used.

Bear in mind solar panels can be made very cheaply with a metal frame,
twinwall plastic front (or just glass if you have a divertor valve &
thermostat) and microbore pipe, and a bit of rockwool round the edges.

Or for the more daring one can use nothing more than a painted house
radiator wrapped in polythene - not very efficient but a very cheap
and simple way to capture a bit of free heat. Bare rads have been used
before as preheat panels with low cost and low temp rise.

Finally the ground loop can provide a bit of cooling in summer too.


Regards, NT

On 3 May 2004 04:32:06 -0700, (N. Thornton) wrote:

"IMM" wrote in message ...
If you having ground loop then it is best to ditch the air sourced heat pump
and go for a full ground source loop, rather than a half cocked affair.
Then to warm the ground loop, using purchased energy can only be
inefficient. You then would be heating the earth around the loop. Much of
this heat, depending on earth temp, may just convect away, and may never be
re-extracted when needed.

Hi IMM,

I never meant that the ground should be heated using purchased energy,
only that is should be heated from the air when the air temperature
allows.

In principle one could use air temp to warm the loop at times, or add
a solar panel to the loop. Adding solar like this, after the water
comes out the ground and before the heat pump, would presumably help
the heat pump efficiency by raising the source temp some of the time.
Also I would imagine that the extra heat input might enable a slightly
smaller ground loop to be used.

Bear in mind solar panels can be made very cheaply with a metal frame,
twinwall plastic front (or just glass if you have a divertor valve &
thermostat) and microbore pipe, and a bit of rockwool round the edges.

Or for the more daring one can use nothing more than a painted house
radiator wrapped in polythene - not very efficient but a very cheap
and simple way to capture a bit of free heat. Bare rads have been used
before as preheat panels with low cost and low temp rise.

Finally the ground loop can provide a bit of cooling in summer too.

I think adding a solar water heater would increase and complicate
things quite a bit!

This is how it could work:

1) Above 0°C use heat from the air.

2) Below 0°C use heat from the ground loop.

3) When the air temperature is above the ground loop, heat the ground
loop from the air.

Since a standard outdoor unit already has a finned coil for air heat
exchange, this could also be used for ground loop heat exchange by
stopping the fan and pumping water from the ground loop over it. Also
the outdoor unit could be used for step 3) when it is running
normally.

I would expect that a standard outdoor unit and a small ground is far
cheaper than having a specialised system with a full ground loop.

cheers,
Pete.

"Pete C" wrote in message
...
On 3 May 2004 04:32:06 -0700, (N. Thornton) wrote:

"IMM" wrote in message
...
If you having ground loop then it is best to ditch the air sourced heat
pump
and go for a full ground source loop, rather than a half cocked affair.
Then to warm the ground loop, using purchased energy can only be
inefficient. You then would be heating the earth around the loop. Much
of
this heat, depending on earth temp, may just convect away, and may
never be
re-extracted when needed.

Hi IMM,

I never meant that the ground should be heated using purchased energy,
only that is should be heated from the air when the air temperature
allows.

In principle one could use air temp to warm the loop at times, or add
a solar panel to the loop. Adding solar like this, after the water
comes out the ground and before the heat pump, would presumably help
the heat pump efficiency by raising the source temp some of the time.
Also I would imagine that the extra heat input might enable a slightly
smaller ground loop to be used.

Bear in mind solar panels can be made very cheaply with a metal frame,
twinwall plastic front (or just glass if you have a divertor valve &
thermostat) and microbore pipe, and a bit of rockwool round the edges.

Or for the more daring one can use nothing more than a painted house
radiator wrapped in polythene - not very efficient but a very cheap
and simple way to capture a bit of free heat. Bare rads have been used
before as preheat panels with low cost and low temp rise.

Finally the ground loop can provide a bit of cooling in summer too.

I think adding a solar water heater would increase and complicate
things quite a bit!

This is how it could work:

1) Above 0°C use heat from the air.

2) Below 0°C use heat from the ground loop.

Air to air are inefficient near to 0C, they cannot provide enough heat for
DHW, only acrting as a pre-heat.

3) When the air temperature is above the ground loop, heat the ground
loop from the air.

You will be heating the earth around the loop, and much will escape. This
cots energy in heat pump and.or water pump.

Since a standard outdoor unit already has a finned coil for air heat
exchange, this could also be used for ground loop heat exchange by
stopping the fan and pumping water from the ground loop over it. Also
the outdoor unit could be used for step 3) when it is running
normally.

I would expect that a standard outdoor unit and a small ground is far
cheaper than having a specialised system with a full ground loop.

For the cost involved, you may as well convert a complete near south facing
roof to a solar panel. Then store the water in a large thermal store and
use low temp under floor heating (temps will be low in winter, but enough
for UFH).

On Tue, 4 May 2004 01:19:29 +0100, "IMM" wrote:

This is how it could work:

1) Above 0°C use heat from the air.

2) Below 0°C use heat from the ground loop.

Air to air are inefficient near to 0C, they cannot provide enough heat for
DHW, only acrting as a pre-heat.

Hi,

The high efficiency ones would be about 15% less efficient at 0°C.
With a COP of 6 to 6.5 that's still pretty good

They are not really intended for DHW, for that electricity could still
be used. Though heat pumps with UFH capability are coming available.

3) When the air temperature is above the ground loop, heat the ground
loop from the air.

You will be heating the earth around the loop, and much will escape. This
cots energy in heat pump and.or water pump.

There is no need to use a heat pump for this, and a water pump would
only be about 20-50W. The main purpose would be to top up the ground
source after it had been used during a cold spell.

For the cost involved, you may as well convert a complete near south facing
roof to a solar panel. Then store the water in a large thermal store and
use low temp under floor heating (temps will be low in winter, but enough
for UFH).

How much would this cost and how would it cope when the sky is
overcast?

cheers,
Pete.

"Pete C" wrote in message
...
On Tue, 4 May 2004 01:19:29 +0100, "IMM" wrote:

This is how it could work:

1) Above 0°C use heat from the air.

2) Below 0°C use heat from the ground loop.

Air to air are inefficient near to 0C, they cannot provide enough heat
for
DHW, only acrting as a pre-heat.

Hi,

The high efficiency ones would be about 15% less efficient at 0°C.
With a COP of 6 to 6.5 that's still pretty good

They are not really intended for DHW, for that electricity could still
be used. Though heat pumps with UFH capability are coming available.

In future homes DHW will consume more energy than CH. Having DHW run off
peak electricty which is 3 to 4 times more expensive than gas is not the
way.

3) When the air temperature is above the ground loop, heat the ground
loop from the air.

You will be heating the earth around the loop, and much will escape.
This
cots energy in heat pump and.or water pump.

There is no need to use a heat pump for this, and a water pump would
only be about 20-50W. The main purpose would be to top up the ground
source after it had been used during a cold spell.

If you had a cold spell and heat was extracted from the ground cooling the
ground around the loop, then when the air warms, you are saying use a pump
to run water though a radiator, extract heat from the air and into the
ground. If the air is less than the ambient ground temp this is useless.
It is best to leave the ground and allow the ground to warm up by convection
from the warmer surrounding earth.

In the USA it is common to have foam insulation under the ground, in an
umbrella formation around the house. The highest point would be the house.
The upper part of the ground is the part which is affected most by the
ambient air temp above. Then the convected heat is gained from the warmer
earth beneath.

It is best to have two ground loops. One operational and one recovering,
and switch between the two.

For the cost involved, you may as well convert a complete near south
facing
roof to a solar panel. Then store the water in a large thermal store and
use low temp under floor heating (temps will be low in winter, but enough
for UFH).

How much would this cost

Probably not as much as an expesove to run heat pump that is high in capital
cost.

and how would it cope when the sky is
overcast?

That is what the large thermal store is for. Store enough heat to last 3 or
4 days. Or have a battery of them. A very large collector can produce heat
from even a cloudy day. Low temp heat, but probably enough to run a UFH
system in very well insulated house. Very cheap to run.

On Tue, 4 May 2004 23:40:31 +0100, "IMM" wrote:

If you had a cold spell and heat was extracted from the ground cooling the
ground around the loop, then when the air warms, you are saying use a pump
to run water though a radiator, extract heat from the air and into the
ground. If the air is less than the ambient ground temp this is useless.

Hi,

I did say:

3) When the air temperature is above the ground loop, heat the ground loop from the air.

cheers,
Pete.

"Pete C" wrote in message
...
Air to air are inefficient near to 0C, they cannot provide enough heat
for
DHW, only acrting as a pre-heat.

The high efficiency ones would be about 15% less efficient at 0°C.
With a COP of 6 to 6.5 that's still pretty good

Still struggling to see how these reach that COP figure as the laws of
thermodynamics tend to get in the way. Talked to a friend who's more into
physics and he's asking Hitachi for more information.

Though his first reply was along the lines of audio amplifiers in that it
was "COP music power"

On Wed, 5 May 2004 19:48:58 +0100, "G&M" wrote:


"Pete C" wrote in message
.. .
Air to air are inefficient near to 0C, they cannot provide enough heat
for
DHW, only acrting as a pre-heat.

The high efficiency ones would be about 15% less efficient at 0°C.
With a COP of 6 to 6.5 that's still pretty good

Still struggling to see how these reach that COP figure as the laws of
thermodynamics tend to get in the way. Talked to a friend who's more into
physics and he's asking Hitachi for more information.

Though his first reply was along the lines of audio amplifiers in that it
was "COP music power"
Hi,

AFAIK the theoretical limit is still some way off, give it 5 years or
so and a COP of 8 might be possible.

Still it's a better than only getting quoted only BTUs, or possibly
even watts as well if your lucky.

cheers,
Pete.