Heating Industrial and commercial 1
basics
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Higher energy efficiency in heating systems and improved
building insulation can have major implications for flow rates
and heat emissions. Ian Vallely reports
T
wo major changes in the industrial/commercial course, size the terminal units accordingly, but even in
heating sector have influenced the way heating a refurbishment, the radiators tend to be oversized so
systems are designed and specified. The first the issue of whether they will be able to handle lower
is a move to heat sources such as condensing flow rates does not arise.’
boilers and heat pumps that work most efficiently at Ron Barker, group product manager of Ideal Boilers,
reduced temperatures and lower flow rates. The second agrees. Referring to refurbishment projects, he says:
is construction or refurbishment of buildings with ‘Even in a large building which might contain several
lower heat demand because of their higher insulation wings that are zoned off, possibly needing different flow
standards. rates, provided you have pumps that are correctly sized,
The requirement to use condensing boilers at and – if the system demands it – there are reasonable
peak efficiency has led to typical flow and return quality adjustable flow valves, then it isn’t going to be
temperatures of 55/35 deg C, as this arrangement too problematic to set things up.’
will maximise energy savings. Similarly, many more Flow rates are normally only a problem in heating
projects are making use of ground-source or air-source systems after the low loss header, so they have little
heat pumps as a heat source, necessitating flow and impact on the running of a boiler, according to John
return temperatures of around 50/45 deg C to improve Bailey, commercial heating and systems director at
My advice
the coefficient of performance. Vaillant. He adds: ‘The flow rate from the boiler(s) is
The lower flow rates used with heat generators such actually governed by the controls sensor in the low loss
to consultants as condensing boilers and heat pumps have potential header; this would then modulate the boilers and pump
is to get back
implications for the heat emitters (typically radiators) to suit the required flow rate.
to basics and
which, in older buildings, may have been designed to ‘It’s true that the traditional UK design delta T of
operate with higher flow rates. 82/71 deg C is becoming irrelevant when designs of
really establish However, for historical reasons, this does not 60/40 or even 50/30 are used. These designs ensure
at the front of
generally present a problem, according to Pete Mills, that condensing boilers operate in condensing mode
the project what
technical service support manager at Buderus. longer; this can sometimes make them difficult to
He says: ‘Lower flow rates mean that terminal units control due to the low temperature range, but they
the heat and hot – radiators etc – will have to be sized to the higher certainly aren’t problematic as far as I’m aware.
water demand
delta T (the differential between the flow and return ‘The problem actually lies in ensuring that the chosen
will be
temperatures). However, what we find in older systems heat emitters, either radiators or underfloor heating, are
is that radiators were typically oversized anyway. If sized correctly. Underfloor systems are easier to control
– Pete Mills you are designing the system from new you will, of because they never require temperatures above 50C, >
50 CIBSE Journal February 2010 www.cibsejournal.com
CIBSEfeb10 pp50-55 feature_Heating.indd 50 29/1/10 14:31:07
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