Optimum Performance of

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• Optimum Performance of
• Radiator Space Heating Systems
• Connected to District Heating Networks
• via Heat Exchangers
• Patrick Ljunggren, Janusz Wollerstrand
• Svend Frederiksen
• Lund Institute of Technology
• Department of Energy Sciences
• Sweden

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Topics

• Consequences of oversizing radiators (RADs)
  Heat EXchangers (HEXs)
• Various RAD circuit control methods
• Constant or variable RAD circuit flow
• Various methods of upsizing HEXs
• ?? ºC lower DH return temperature

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• Minimum primary return temperature, tr1, at
  altered radiator supply temp., trf, for
  increasing HEX area

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Mode with excessive indoor air heating, simulated
instantaneous temperatures
space heating system 100 oversized
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Standard temperature program (constant flow) and
optimized program (variable flow)
no oversizing of radiators or heat exchanger
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Lowered supply temperature set-point curve
unchanged flowrate (full curves) and optimized
program (variable flow, dashed curves).
100 over-sized radiators and heat exchanger
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Low flow balancing (design supply temperature,
full curve, and reduced flow, dashed curves)
100 over-sized radiators and heat exchanger
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Difference (in C) in annual weighted return
temperature from space heating heat exchanger
versus reference case with a return temperature
of 44.9 C
0 oversized HEX 100 oversized HEX
0 oversized radiators, constant flowrate 0 -0.5
0 oversized radiators, optimized flowrate -1.8 -3.3
100 oversized radiators, low flow balancing, constant flowrate -12.3 -13.5
100 oversized radiators, lowered set point curve, constant flowrate -12.1 -12,3
100 oversized radiators, Optimized flowrate -14.9 -16,2
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Primary return temperature and secondary supply
temperature at design heat load, assuming optimal
radiator circuit flowrate (four different
assumptions )
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Conclusions

• Radiator control should be optimised to minimise
  primary return temperature
• By combining control optimisation HEX up-sizing
  gains in primary return of around 10ºC are
  possible