Case 2: Combination of direct heat exchange and a temperature booster If the waste heat temperature exceeds the return temperature from the district heating system, the return flow should be preheated via a heat exchanger and subsequently boosted by a temperature booster. The temperature booster could either be a heat pump or it could be any type of heat source, like a fuel boiler or direct electrical heater. The choice of the boosting application can depend on, for example, the required return temperature to the process or available waste heat capacity.
Case 3: Heat pump boosting Even if the waste heat temperature is lower than the return temperature of the district heating system, it can be hugely beneficial to the district heating system, as the waste heat source can ensure high energy efficiency of the heat pump. Further, as waste heat sources tend to have stable temperature levels over the year, it will ensure that even during winter, the heat pump will have stable and predictable operations, unlike heat pumps that rely on ambient heat sources, air, or water sources.
Heat pump booster application:
Figure 4: An example of a low-temperature waste heat recovery using a heat pump.
Conclusions Waste heat is a valuable resource that should not be wasted; it’s there and can be utilized! District heating systems are key solutions for urban areas to take advantage of available waste heat sources and, by that, make our cities more sustainable, livable, and resilient.
Figure 2: An example of a combination of a direct waste heat recovery using heat exchangers and further temperature boosting using a heat pump.
Boiler booster application:
Further, recycling waste heat reduces pollution, retains money in the local community, and creates local jobs.
And finally, it’s the basis for realizing that the future renewable and sector-coupled energy system will be smart and cost- efficient.
We have no excuse, as all necessary solutions are already commercially available!
For further information please contact: Oddgeir Gudmundsson, og@danfoss.com
Figure 3: An example of a combination of direct waste heat recovery using heat exchangers and further temperature boosting using a fuel or electric boiler.
The boiler could, for example, be an existing boiler on the waste heat source premise, where typically, a smaller share of the capacity is used for boosting the recovered waste heat temperature.
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