TOMORROW'S DISTRICTHEATING IN DENMARKIn cooperation with Ramboll, three Danishmunicipalities in S. Jutland are converting to newflexible district heating solutions.

Denmark's goal to becomeindependent of fossil fuels, togetherwith an unstable market forelectricity has encouraged threeDanish district heating plants,Logumkloster, Vojens and Gram, tothink big and far-reaching to ensurea cost-competitive andenvironmentally friendly heatsupply to local consumers in thefuture.

First step in Logumkloster was astrategic plan

In Logumkloster, a CHP plant forapprox. 1500 consumers, thecooperation with Ramboll startedwith the formulation of a strategicplan for Logumkloster's future heatproduction. In the process, a seriesof heat production technologieswere studied, including differenttypes of electric heat pumps,absorption heat pumps, solarheating and thermal storage ofvarious sizes, biomass boilers,electric boilers as well asoptimisation of existing gas

engines. The many technologicalalternatives were combined intoreal-life scenarios where Rambollsimulated operations and analysedthe output of each scenario. The result was a strategic masterplan with the most interesting andfeasible combination for the futureprovision of heat in Logumkloster.The plan also includes building anentirely new heat central andadministration alongside theexisting plant. This will make itpossible for Logumkloster districtheating to gather all activities onthe outskirts of the town and beable to close down the old plant inthe centre of the city. The new heatcentral will accommodate a woodpellet boiler, an absorption heatpump, an electric hybrid heat pumpas well as a heat exchange stationfor one of the world's largest solarheating facilities at 50,000 m2 witha 150,000 m3 heat storage pond.

RAMBOLL ENERGY

CONTACTChristian Teil FyhnTeam Coordinator, Solar EnergyEnergy & District Heating WestTel. + 45 5161 5786chtf@ramboll.dk

Solar heating

The analyses indicated that it wouldbe a wise economic move forLogumkloster to make a substantialinvestment in solar heating. Inaddition to being a renewableenergy source and cost competitivein relation to the currentproduction, solar energy wouldprovide heat at stable prices for theentire plant lifecycle of an expected30 years. Operations andmaintenance costs are low and thusthe main cost would bedepreciation, at a known level inupcoming years, as opposed to therisk of ever-changing fuel pricesaffecting other energy production.

SOLAR HEATING IN VOJENS AND GRAM

Excavation for a solar heating plant of 71,000 m2 and anadjacent heat storage pond of approx. 200,000 m3 is wellunderway in Vojens. Vojens already has a solar heatingplant, and initial years of operation have shown suchconvincing results from this technology that work hasbegun to establish the world's largest plant with a solarheat storage pond in an abandoned gravel pit, close to thesolar heating plant.

Gram is starting work from a flat field instead, to establisha 110,000 m3 solar heat pond. Gram is tripling the size ofits solar heating facility, with assistance from Ramboll, tocover a total area of 44,000 m2. At the same time, thetown is establishing a central heat exchange for the solarheating plant and is expanding its district heating centralwith a 10 MW electric boiler, which will participate in thepower regulation market, and with a 900 kW electric heatpump to optimise the output from the solar heating plant.

Optimising output

Heat pumps will enhance outputfrom the solar heating plant and theexisting gas engines where an extraflue gas cooler has been installedon one of them. With this heatpump, the flue gas from the enginecan be cooled to approx. 20degrees Celcius and the heat yieldincreased, raising the overall rate ofefficiency to exceed 100%. This willmake the gas engine more costcompetitive and able to run formore hours in an electricity marketcharacterised by periods with lowelectricity prices. The heat pumpscan also lower the temperatures inthe solar heating plant and thusreduce heat loss and increase theannual output by up to 15%.

Absorption heat pump

An absorption heat pump is run byheat, which from utilisation of aconcentrated saline solution canabsorb humidity and thus maintainan evaporation process in avacuum.

The resultant heat then returns at alower temperature, so that theabsorption heat pump does notconsume any energy other than themodest amount of electricity usedin the circulation pumps. Combinedwith a heating unit which candeliver heat at an excessively hightemperature, the absorption heatpump can thus practically extractenergy for free from the lowtemperature source. This principlewill be applied at Logumkloster, asthe wood pellet boiler can producesuper-heated water at 150 degreesCelcius to run the absorption heatpump, which can then deliver 75degrees Celcius to the districtheating network, and at the sametime cool down the flue gas in thegas engine and the entry waterleading to the solar heating plant.

Hybrid heat pump

The electric hybrid heat pumpworks using a coolant which is amixture of ammonia and water. Thehybrid heat pump also uses an

absorption process to achieve asubstantial temperature shift and anexpected high coefficient ofperformance (COP) value of 4.5,which makes it advantageous for adistrict heating network such as inLogumkloster.

Solar pond for heat storage

Construction of the heat central isin full swing and moving steadilyforward on schedule. The plannedsolar heating plant is expected tomeet 50% of the demand for heat.This requires storing the heatproduced during the summer forthe fall and winter, in a seasonalthermal storage. That is why thereare plans in Logumkloster to createa solar heat storage pond for150,000 m3 water, involving anenormous excavation where thedug-up soil is used to make anembankment around the hole,forming the sides of the storagechamber. The pond will then befilled with water and covered with afluid insulation cover.

The best managed andoptimised solarheating facility canutilise more than 45%of the annual solarradiation and convertthis to district heating.When the upcomingDanish facilities areestablished in 2015,the total solar heatingto district heating willamount to more than600,000 m2. We inRamboll are proud tohave contributed to anextensive number ofthese plants.