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Heat pump - heat concentrator - Page 2

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Posted by daestrom on June 6, 2008, 12:31 pm

Looking closely at the hole they are installing it in, it looks like it was
cut right into rock.  For this unusual installation, they seem to be using
concrete to 'join' the tubing to the surrounding bedrock.

If this really is bedrock, then concrete would seem a good way to get good
contact between the tubing and the bedrock.  But this is not your common
soil conditions so this would not be the way to go for a lot of others.


Posted by News on June 6, 2008, 1:21 pm

So, if they are down to bedrock, I would have cleaned the surface of the
rock to remove any soil to give good concrete contact.  The contact would
only at the bottom of the hole an the bottom of the concrete block. I would
have had the hole wider and the concrete block thinner and wider - or maybe
the same thickness as it is not expensive to add another 4 or 5 cu metres of
the stuff all at the same time.  Is it work using a SDS drill to bore into
the bedrock at one foot intervals and insert rebar stumps and then pour as
this may give a better contact, and heat transfer, with the bedrock.

The points is. Will this work as a heat collector?  This concrete block
appears only good for heat storage, not collecting.  Is he trying extract
heat from the rock beneath or heat from the surface soil heated by the sun?

The guy is an underfloor heating contractor and is installing it in his own
house.  So I "assume" some calculations have been done.

Scroll down and he explains more in further posts giving a few figures.  But
he appears to have reservations himself that it will work effectively,
saying "Only Time will tell".  So why take the risk?  If it does work then
maybe he could do the work himself and keep costs down without farming out
to an outsider when fitting heat pumps, which are now catching on in off the
gas grid locations, using low temperature UFH. This could be just a trial on
his own property.

Might be worth logging into the forum, or emailing him at his company email,
to see if it is working.  If it is, it is a cost effective way of doing it.
But is it?????

Posted by Jeff on June 6, 2008, 7:19 pm
 News wrote:

   Concrete is a fair thermal conductor, at least compared to dry soil.
The same with the bedrock that the concrete is bonding to. So, the area
that you scavenge heat from is greater than if you were running through
soil. He's not scavenging from the soil above the concrete "block".

  I think if you were doing this in soil, you'd need a much much larger
contact area.

  I've wondered if a concrete slab could be used as a source. I know my
basement stays much cooler in the summer due to the slab's thermal
contact with the ground. But then slabs are often insulated only with
perimeter insulation.  Apparent the shallow depth and the poor
conductivity of soil make that possible.

   Someone correct me if I'm mistaken. There must be some calculations
for this.


Posted by News on June 6, 2008, 9:27 pm

In the UK in some buildings, concrete piles supporting buildings have
plastic pipes run in them for heat pumps to extract heat.

Posted by Larry Caldwell on June 7, 2008, 1:38 am
 jeff@spam_me_not.com (Jeff) says...

There has apparently been a lot of research into thermally conductive
concrete.  A quick google of 'thermal conduct concrete' brings up a lot
of hits.  

Batch design of concrete allows large variations in physical properties.  
In this case, structural strength is not relevant, so you could use ball
bearings or BBs for aggregate.  
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