12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaHEAT LOAD REDUCTIONS AND THEIR EFFECT ON ENERGY CONSUMPTIONChristian Johansson 1 and Fredrik Wernstedt 21Blekinge Institute of Technology, PO Box 520, SE-372 25, Ronneby, Sweden, chj@bth.se2 NODA Intelligent Systems AB, Drottninggatan 5, SE-374 35, Karlshamn, Sweden, fw@noda.seABSTRACTIn this paper we investigate the consequences of usingtemporary heat load reductions on consumersubstations, from the perspective of the individualconsumer as well as the district heating company. Thereason for using such reductions are normally to saveenergy at the consumer side, but the ability to controlthe heat load also lie at the core of more complexcontrol processes such as Demand Side Management(DMS) and Load Control (LC) within district heatingsystems. The purpose of this paper is to study the waydifferent types of heat load reductions impact on theenergy usage as well as on the indoor climate in theindividual buildings. We have performed a series ofexperiments in which we have equipped multiapartmentbuildings with wireless indoor temperaturesensors and a novel type of load control equipment,which gives us the ability to perform remotelysupervised and coordinated heat load reductionsamong these buildings. The results show that asubstantial lowering of the heat load and energy usageduring periods of reductions is possible withoutjeopardizing the indoor climate, although we show thatthere are differences in the implications whenconsidering different types of heat load reductions.INTRODUCTIONThe main purpose of this paper is to investigate theconsequences of using temporary heat load reductionson consumer substations within a district heatingnetwork. The most common way to perform temporaryheat load reductions is to use night time set-back, i.e.to lower the wanted indoor temperature during nighttime while social activity is expected to be low.Emerging technologies like Demand Side Management(DMS) and Load Control (LC) also use temporary heatload reductions in order to accomplish system widecontrol strategies, although the characteristic of thesehead load reductions differ significantly from night timeset-back.In the context of this study we regard a heat loadreduction to be the whole process from the initialchange of heat load, through the return to normal heatload, and until no evidence of the heat load reductioncan be noticed in the dynamics of the building energy244balance. This definition is based on the fact that theheat load reduction will continue to exert an influenceon the buildings thermal buffer for some time even afterthe heat load reduction in itself is ended. The length ofthis interval is specific to each building and is related tothe thermal inertia of the building in question.In this paper we study the consequences of usingdifferent types of heat load reductions, and try toanalyse the way the thermal buffer of the building isaffected along with the actual heat load and energyusage from both a local and a global perspective. Westudy the performance of both long low-intensity heatload reductions (e.g. night time set-back) as well asshort high-intensity reductions (e.g. those frequentlyused in DMS schemes). The use of night time set-backhas received some attention in previous works, e.g [1],and the possibilities to use the building as a heat bufferhas been evaluated [11], but heat load reductions suchas those used in DSM and LC have to the knowledgeof the authors not been thoroughly investigated.Night Time Set-backNight time set-back means to lower the wanted indoortemperature during night time, with the purpose ofsaving energy through reduced heat losses due todecreased difference between indoor and outdoortemperature. This is the most common way to performtemporary heat load reductions, and many commercialcontrol systems support this feature. This is normallydone by a parallel displacement of the heat controlcurve during night hours. During night time set-back thewanted indoor temperature will be set to one, or a few,degrees lower than during normal operations. There is,however, an ongoing debate on whether night time setbackactually gives an energy saving or not [4], andmost practical implementations of night time set-backsuffer from morning peak loads when the controlsystem returns to the original operational level. Still,almost all control equipment companies sell equipmentthat facilitates the use of night time set-back, and theuse of this technique is widespread.Demand Side Management and Load ControlWhile night time set-backs are a solely local energysaving technique, DMS and LC are usually performedwith a system wide perspective in mind. A building