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CH design for condensing boiler
QUESTION:I'm in the process of reviewing my CH system, and have re-calculated all my
heat losses and compared them with the radiators currently fitted. Many of
the rads are over generous - partly because they were fitted a long time ago
when the house was far less well insulated.
I currently have a conventional boiler, and run the system at a mean water
temperature of about 76 degC (82 flow and 70 return), giving a typical
Delta-T of 55 degC. At some point in the future I may replace the boiler
with a condensing model (probably won't have a choice!) and would like to
re-asses the adequacy of my rads for running at a lower Delta-T.
What value should I be using?
ANSWER: 60 flow 40 return. Top quality (expensive) boilers can modulate down to 3
to 5kW, which is still high when the house is up to temp. 90% plus of run
time boiler is on part-load so does not need 82C - 70C.
Assess your DHW, a heat bank may be the better option with TRVs on all rads
and a Smart pump on the CH and also mains pressure DHW. Then a cheaper
simpler boiler can be used to heat the heat bank.
Or a packaged solution: ACV Heat Master (integrated outside weather
compensator), Gledhill Gulfstream or Atmos Multi. These makers will provide
a Smart pump with the units if requested.
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