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Re: Solar water heating system value - Page 9

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Posted by meow2222 on March 10, 2006, 5:19 pm
 
AJH wrote:

I realised this isnt so. Once the panel circuit fills with water, the
pump is only pumping against the running friction, and not the head.
The panel output piping is filled with water after a second or 2, so
gravity has the same effect on both sides, so no extra pumping
resistance.

NT


Posted by Doctor Drivel on March 10, 2006, 7:33 pm
 


It is pumping against the head (pressure) always.  Gravity asserts pressure.
A 3 floor British house with attic.  Inc' space between floor it could be 10
foot per floor.  A radiator in the attic space and the pump at the bottom of
the ground floor. The pump has to overcome 1 bar (~30 foot), one atmosphere,
to get to the top, even in a sealed system.  OK is assisted a little when
the water is dropping from 30 foot on the return, but it still has to
overcome one atmosphere plus system friction.  Gravity doesn't care if it is
open vented or sealed.


Posted by nicksanspam on March 10, 2006, 10:01 pm
 


Wrong. Eric Hawkins at Powertech Ltd (UK) has been done this for years in lots
of systems with no loss of prime (the vacuum in the Apricus evac tube header
loop above the unpressurized tank) after initial priming. Then again, they
don't shut off the pump at some max water temp. So a "slow draindown system"
with a small hole in the return pipe above the tank water line should work
fine, with a lower flow and higher head to start with and higher flow and
lower head after the pump has pushed all the bubbles out of the underwater
return pipe.

Nick


Posted by Doctor Drivel on March 10, 2006, 11:57 pm
 

I was on about a sealed system, any system whether hearting or whatever.
Hawkins vacuum is not new.

<http://powertech-solar.com/article.php?newsID >


Eric Hawkins is pushing product that is clear.  In his house:



- He stripped out the copper pipe in his house and installed plastic.  Most
new homes are fitted out in plastic these days, with copper where pipes are
seen.  What he thought he would gain with plastic is beyond me,



- He fitted solar panels fitted to a thermal store in his loft/attic.  I
have a thermal store in my loft too. Nothing special there.



- He insulated pipes in the loft.  All new homes require that exposed pipes
are insulated. Nothing new there.



- He fitted solar panels to heat his thermal store. Nothing new there.



- Now!  He stripped out his NG boiler and fitted an air to water heat pump
in the loft.  In the UK gas is approx 4 times cheaper than electricity. And
the condensing boilers are very small in physical size and highly efficient.
So a heat pump that "averages" COP 4 would equal a NG boiler in running
cost. NG condensing boilers are cheap (some 26kW version were available from
B&Q for 300 [same as your Home Depot]), heat pumps are not cheap at all.
NO GAIN THERE at all, except a very cold loft, as that is where he is moving
the heat from.  No wonder he needs to insulate the hell out his pipes up
there.



- He fitted low temperature underfloor heating in his house. One hell of an
upheaval in an existing house.  But nothing new there.  Low temperature UFH
is ideal for solar panels.



What he has done is have a thermal store heated by solar panels that heats
wet underfloor heating.  For backup he has an air to water heat pump.



He would have been wiser to keep, or update to, a NG condensing boiler.
Much cheaper and guaranteed to give heat when needed, which the heat pump is
not, and then insulate the hell out of his house.  Cavity wall insulation is
cheap enough.  We have cavities in the UK and this is now very popular with
recent energy price hypes, with government grants too. It is pumped into the
cavity.  So a wrap round blanket of insulation.  He then could have had
400mm of Warmcell celluloid insulation sprayed on the floor of the loft
(this seals up the ceiling/loft too).  Then did some air tight measures
around the house. That would have dropped his heating bills further than his
180 per ann, with the heat pump and wind turbine.  Service for NG boilers
is comprehensive, not so for heat pumps.



The rainwater harvesting is off the shelf stuff. Mandatory in the BenNeLux
countries in new builds. It is worth it I believe with a 7 year payback.
Nothing special there.



PV panels are not new and so far not worth it.  Micro turbines in a built up
area are difficult to get permission to erect.  They also have long payback
periods, but fine in off-the-grid locations.



His point is: Has the Traditional Boiler Had Its Day?  A long time to go
yet.  Heat pumps are fine for off the gas grid systems.  Even then you have
to do your arithmetic well to justify one.  The capital cost of them is
horrendous in the UK.  Solar panels a thermal store and low temperature UFH
could be worth it. Unless the air to water heat pump is the same price as a
NG boiler, I would think very hard.






Posted by nicksanspam on March 11, 2006, 12:09 am
 


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