How to achieve high seasonal efficiency in balanced thermal networks [34]

Balanced thermal networks (BTN), also known as fifth generation district heating and cooling systems (5GDHC) aim to recover low temperature heat and high temperature cooling within a district via a thermal network. In such systems, the temperature range of the heat source is often wider compared to in conventional liquid source heat pump systems.

The results of this study show that current conventional design parameters should be adjusted to maintain a high efficiency throughout the entire operating range of the BTN. This affects the dimensioning of all components in the refrigerant circuit and the required volume of refrigerant. An operational challenge specific to BTN occurs when there is a low heating demand at a relatively low temperature level (e.g. 35 °C) on the condenser side that coincides with a relatively high temperature (e.g. 25 °C) on the evaporator side, resulting in a high thermal capacity of the heat pumps system during times with limited heating demand from the building.  

The heat pumps connected to BTN systems have the potential to reach a high coefficient of performance (COP), due to the high temperature of the heat source. The challenge is to maintain a high COP throughout entire operation during a season. At the ends of the heat pumps operational temperature range, the efficiency tends to drop considerably. The results from field measurements at a demonstration site of a BTN explains why low efficiencies are sometimes obtained and how these could be increased considerably by altering the design parameters.
These finding can in a longer perspective contribute to the realization of the untapped potential of BTNs, resulting in more efficient use of energy.