How to optimize cascade couplings for best use of low temperature sources

Kraftringen and COWI A/S have worked together on a paper that describes the analysis of energy efficiency in heat pump systems that recover waste heat from low temperature heat sources for District Heating. Martin Gierow, chemical engineer and project manager at Kraftringen, introduces the report that you can download below.

What is the main purpose of the report?

The main purpose was to study parameter variations of cascade couplings of heat pumps used to produce district heating based on low temperature heat sources of 7-23°C. The studies will form a basis for the upcoming demonstration projects at the demo sites in Cool DH.

What are the main findings in your studies?

The main finding is that you achieve the highest performance when similar heat pumps work under similar conditions. This means that each heat pump in the system should work with the same temperature differences on both the hot and cold side. We could also conclude that lower district heating supply temperatures results in higher performance values. This has a significant influence on the heat pump performances making it more feasible for low temperature district heating. Furthermore, a theoretical study of the refrigerants used as working fluid in the heat pumps showed that R717 (ammonia) resulted in the highest performance of the refrigerants investigated.

Diagram showing results from the parametric study of the intermediate temperature between HP1 and HP2, TInt,HP1-HP2. TInt,HP2-HP3 is fixed to 60°C in this case.

Results from the parametric study of the intermediate temperature between HP1 and HP2, TInt,HP1-HP2. TInt,HP2-HP3 is fixed to 60°C in this case.

What happens now?

We will present the results in a workshop, to be held in November within the scope of the Cool DH project. Some of the results will be implemented when designing the heat recovery systems in Lund and Høje-Taastrup.

Read the report

You will find the report under the Report and document section.

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