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, Estoniapressure difference ∆p and the temperature difference∆T between flow and return. Included in this equationis, the pump efficiency η as well as the density ρ andthe thermal capacity of water c p .(1)For the integration of renewable energy into heat gridssome aspects have to be regarded.For solar thermal energy the flow and returntemperature of the network is a major problem. Thisshould be lower than in the existing district heating gridand run with a temperature of about 60 °C / 40 °C. [6]For using deep geothermal heat it depends on the usedtechnology. If it is combined with the electricityproduction, the waste heat after the power plant isnormally below 80 °C.Another major obstacle is the variation of the heatproduction and the demand if using solar thermal heat.During the summer months, the solar radiation is at itspeak, but the heat demand has its peak during thewinter months. To cover a heat grid with a high solarfraction, a long term thermal storage system isnecessary.Description of selected siteFor modeling the integration of solar thermal energyinto a district heating network, a yet to be built housingestate was selected. This housing area is planned witha district heating grid running at a flow temperature ofabout 70 °C. This area is connected with a heatexchanger to the central heating grid of the city, whichis run with flow temperatures between 90 °C and130 °C.Table 2: heat demand selected siteBuilding size[housing units]Number ofbuildingsTotal heatingdemand [MWh/a](room heating +hot tap water)1-2 135 1561More than 3 111 585Sum 246 2146Table 2 gives an overview of the planned houses andtheir heat demand. The whole heating grid will have anlength of about 1,3 km and the total heat demand willbe 2146 MWh/a.Used SoftwareRETscreen is a program to make first feasibility studiesof all kind of green energy projects. In terms for solarthermal heating, it uses an included weather databaseto calculate the expected heat production. Furthermorea product database is included with the necessarytechnical parameters for many different solar thermalcollectors. The needed amount of heat can either becalculated other ways or assumed by the softwaredepending on the amount and size of buildings.Combining those input factors with others, thesimulation tool gives a recommendation of the usednumber of solar collectors and the size of a thermalstorage system. If all input factors are included theprogram calculates the yearly heat production and thesolar fraction. Beyond that, the program can be used toinclude a second heating system for the remainingneeds to get the final payback period and the totalemissions. For the simulation of this paper the version4 (November, 2009) of the named software was used.Financial CalculationThe calculation of the heat costs is based on the netpresent value method. For the internal rate of return thegiven value was used, all other costs included and theheat costs varied to get a net present value of zero.This method gives the current heat price and a furtherincrease during the next years is included. This makesit possible to compare the actual heat price to the givenvalues of other systems. For the economical calculationin the conclusion of this paper, a competitive heat pricefrom now on was realized.The named financial support which is included in thecalculations are subsidies on the capital cost. Theydepend, like mentioned in the introduction, on differentaspects. A research project like the one in Crailsheim,can get a higher support than commercial ones run bylarge companies. [1]Solar thermal heat productionFor the heat supply of the given housing area, differentscenarios based on solar thermal energy weredeveloped. Using the RETscreen software tool thetechnical parameters of the flat plate solar thermalcollectors, weather data from a climate database andthe given heat demand of the area was combined foreach scenario.The scenarios differ in the necessary amount ofcollectors needed to achieve a solar fraction of the totalheating demand of 50 % [scenario 1], a 100 % solarheat production of the used hot tap water (which staysconstant throughout the whole year) [scenario 2] and a134