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A New System Approach to Efficient Central Plant and District Heating design
CIBSE AM12:2013 (9.16, p 49) states:
“It is preferable to adopt a variable volume control system for
the DH system and all of the building heating systems
connected. This will ensure that pumping energy is minimised
through reducing the volume of water to be pumped and the
pressure drops to be met, and also reduces heat losses
through ensuring that return temperatures remain low under
part load conditions.”
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“It is recommended that, for new systems, radiator
circuit temperatures of 70ºC (flow) and 40°C(return)
are used with a maximum return temperature of 25°C
from instantaneous domestic hot water heat
exchangers.”
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70/40 is well suited to new radiator systems at
maximum load conditions. In part load conditions,
flow temperatures should be reduced using weather
compensation. The main characteristic of a “70/40”
(60/30 or other) system is a large ΔT and low return
temperature to best suit the lead (low carbon) heatsource .
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Controlling primary return temperatures from domestic hot water production
ObjectiveMaximum return temperatures of 25°C from DHW instantaneous heat exchangers. (CIBSE AM12:2013 & GLA District Heating Manual for London, 2013)
ChallengeAchieving stable DHW flow temperatures and consistently low primary return temperatures under varying load conditions.
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Danfoss TPV Temperature Chart
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The Primed Temperature Set-back lowers the temperature at which the plate heat exchanger is kept warm with app. 8 °C helping to reduce primary return temperatures and system distribution losses.
Danfoss TPV Primed 8ºC Temperature Set-back
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CHP and carbon footprints
Controlling primary return temperatures from heating circuits
Objective
It is recommended that, for new systems, radiator circuit temperatures of 70ºC flow and 40ºC return are used. (CIBSE AM12:2013)
Challenge
Protecting space heating control valves from fluctuating primary system pressures.
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The 70/40 principle - tried and tested
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SAV have put together a CIBSE-accredited CPD Seminar, which explores the main
issues arising from a 70/40 approach to design.
The agenda for this is given under the CPD Seminars tab further along this
website.
The 70/40 method can be expected to have far-reaching implications, and
discussions which are a normal part of each Seminar will sharpen your insight
into developments in this field.
70/40 CPD Seminars
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Read more on on
http://sav-systems.com