Optimum Performance of Radiator Space Heating Systems Connected

Topics • Consequences of ‘oversizing’ radiators (RADs) & Heat EXchangers (HEXs) • Various RAD

Minimum primary return temperature, tr 1, at altered radiator supply temp. , trf, for

Mode with excessive indoor air heating, simulated instantaneous temperatures space heating system 100 %

Standard temperature program (constant flow) and optimized program (variable flow) no oversizing of radiators

Lowered supply temperature set-point curve & unchanged flowrate (full curves) and optimized program (variable

Low flow balancing (design supply temperature, full curve, and reduced flow, dashed curves) 100%

Difference (in °C) in annual weighted return temperature from space heating heat exchanger versus

Primary return temperature and secondary supply temperature at design heat load, assuming optimal radiator

Conclusions Radiator control should be optimised to minimise primary return temperature By combining control

Slides: 12

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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

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

Minimum primary return temperature, tr 1, at altered radiator supply temp. , trf, for increasing HEX area

Mode with excessive indoor air heating, simulated instantaneous temperatures space heating system 100 % oversized

Standard temperature program (constant flow) and optimized program (variable flow) no oversizing of radiators or heat exchanger

Lowered supply temperature set-point curve & unchanged flowrate (full curves) and optimized program (variable flow, dashed curves). 100% over-sized radiators and heat exchanger

Low flow balancing (design supply temperature, full curve, and reduced flow, dashed curves) 100% over-sized radiators and heat exchanger

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

Primary return temperature and secondary supply temperature at design heat load, assuming optimal radiator circuit flowrate (four different assumptions )

Conclusions Radiator control should be optimised to minimise primary return temperature By combining control optimisation & HEX upsizing gains in primary return of around 10ºC are possible