Heat sources
Heat sources
Capacity MW
Capacity MW
200 %
Peak and reserve load
100 %
Around 5 - 15 % of production
Reserve load
0 - 2 % of production
98 - 100 % of production
Around 85 - 95 % of production
100 %
50 %
Base load capacity
Base load capacity
Heat demand
50 %
Heat demand
Annual days
Annual days
0
365
0
365
Figure 1: Duration curve heat demand – ranked from coldest day
Figure 2 Increased delivery and decreased heat loss
the lost heat in figure 1 can be delivered to consumers without additional investment in production capacity. Figure 2 shows an example of a design where the supply loss is reduced by expanding heat networks. The base load capacity, in this case, delivers between 50% and 80% of capacity (MW) but up to 95% of the total heat demand (MWh). The share can vary greatly from plant to plant and de- pends on local conditions and available heat sources. Com- pared to the previous example shown in figure 1, the potential heat loss shown in the blue shaded area is reduced by 40% to 70%, depending on the heat demand profile. This design is very common today. The heat loss is often re- duced further if the heat source is a fossil fuel-based CHP plant, not necessarily needing to produce when the electricity price is low and heat demand also is low in the summertime. It often can be beneficial to add a heat storage system making it possi- ble to produce the heat according to electricity prices making electricity production independent of heat demand simulta- neously. The storage also decreases the need for reserve and peak load heat capacity. It reduces the fuels used for reserve and peak load, which can be important due to low carbon re- quirements, and to avoid using expensive fuels like oil and gas for peak load purposes. The blue shaded loss in figure 2 will be more difficult to re- move if the waste heat source is constantly producing – from waste incineration plants or from industries. Design future heat source supply system The constant running baseload heat capacity needs to be re- duced or constructed to around 45% to 55% of the total peak- load heat capacity demand to reduce the blue-shaded loss shown in figure 2 to a very low level. Suppose tap water heat- ing uses 25% of production year-round and heat loss in the network, for example, is 20%. In that case, the lowest capacity
the security of supply. The area below the red line and blue shaded area shows the actual delivery of heat covering 98 – 100% of heat demand in the district heating network. The blue shaded area shows how much more heat the waste heat source could deliver by the installed capacity if delivering is constant at full capacity. The shaded area can easily be up to half the possible heat delivery. If a heat supplier needs to pro- duce power, incinerate waste, or produce industrial goods, the waste heat in the blue-shaded area will be lost, which is not an issue if the price for power, waste, or goods covers costs. The only problem may be the lost energy, which could have been used to reduce carbon emissions and save resources elsewhere in the energy system. Suppose the power plant, the waste incineration plant, or the industrial plant, due to competition, are getting dependent on the income from heat. In that case, the symbiosis between dis- trict heat networks and waste heat suppliers may not work the same way anymore. The heat supplier may need to stop pro- duction when heat demand is not present, for example, in the summertime. This can be an issue for CHP plants and waste incineration plants, losing the ability to compete on electricity or municipal waste prices if heat cannot be sold. The district heating network company then may not have a reliable and constant baseload supply anymore. This issue can be solved, and the solutions are discussed in the next sections. Adjusted original heat source design In most urban areas, district heating networks are not covering all buildings, and some areas may be industrial, using natural gas, which could be replaced by district heating. There may be block-centrals or nearby district heating networks based on boilers or other more expensive heat sources. Heat sales will increase if the district heating network can expand the cov- ered area by connecting more consumers and/or establishing a transmission line to neighbouring networks. Then a part of
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HOTCOOL SPECIAL COLLECTION no.2 / 2022
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