On Sun, 26 Oct 2003 13:52:23 -0000, "mike.james"
wrote:


"Andy Hall" wrote in message
.. .
I'd let him get on with it,.......



.andy


To a certain extent that's my feeling but I just couldn't resist thinking
about how the pool could be used to make the whole thing work
better and perhaps get to the 20% extra promised by the boiler.
I still sort of think that there should be some way of making use of
a low temperature sink but I'm beginning to see that its
more difficult than I first thought.
mikej


Even if you connect the heat exchanger in parallel to the radiators
(as they should be) there will be a downward effect on the return
temperature to the boiler.

Think about the flows of water and the heat loads. Let's say for
simplicity that you arranged equal flows through the radiators and
through the pool heat exchanger, but that the pool heat exchanger
represents twice the load of the radiators. I am assuming that the
pool heat exchanger is not limited by its dT - which actually with
good sized stainless steel plate jobs will be the case - they can be
capable of transferring 200kW in a very small size. Since everything
else is equal, you will get a twice larger temperature drop on the
return from the heat exchanger than from the radiators. When the
water is mixed to return to the boiler, it will be lower than with
either load connected alone.

I have an arrangement like this for providing heat to my garage
workshop. It runs with a separate circuit and via a heat exchanger,
for a number of reasons. When there is a heat requirement to the
garage (which is generally equivalent to a couple of large radiators),
the boiler return temperature does drop and the burner is wound up a
bit as is the flow.


The one questionmark that I raised with this is that with the pool,
the heat load is going to be vastly greater than that for the
radiators. Therefore to get a reasonable distribution of heat,
some balancing would be needed to effectively throttle back the heat
supply to the pool as IMM suggested.

They do have rather different characteristics as well, which is why
there is generally a switchover arrangement for heating cylinders.
This is why having two separate boilers may have proven to be an
effective solution, simply because the load characteristics are so
different.


..andy

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