In a sustainable energy supply, district heating networks provide answers to questions of flexibility, energy efficiency, and air quality. Even within apartment buildings or collective housing facilities, mini-district heating networks, specifically the combi-loop, offer solutions to phase in decarbonization and even sustainably add new needs and functionalities such as cooling (or prosumers).
The key role within district heating networks and combi-loop systems, ranging from classic high-temperature to very innovative combined cooling/heating configurations, is reserved for the delivery set or Heat Interface Unit (HIU). The HIU, in its simplest form, provides the uptake of heat from the network (and possibly also injection into the network) and converts it into space heating, hot water, etc., depending on the needs of the residential unit. The possible configurations of an HIU are almost endless, ranging from direct-indirect, individual storage with electric backup heating, to booster heat pumps for cooling and integrated hybrid solar panels. There is, therefore, a significant difference in performance, both in terms of delivered comfort and contribution to energy-efficient district heating networks. For instance, in a district heating network, allowing HIUs of inferior quality will always result in a high return temperature, leading to unnecessary heat loss in the distribution lines, lower production efficiency, and an increased risk of issues related to discomfort (overheating) and hygiene (Legionella). This typical example clearly demonstrates the need for a quality framework for thermal networks and delivery sets, or HIUs in particular. There is a need for a quality protocol and accompanying test infrastructure to test and characterize such units or to evaluate them with a view to targeted improvements. Internationally, some protocols have already been developed, but these are often limited to specific types of delivery sets and are not at all designed to test new functionalities. To partially address this, a test stand for HIUs has been developed. The test stand will bridge the gap between theory (simulations) and practice (measurements, manufacturer datasheets, stress testing, etc.). The service provided is the impartial reporting of characteristics according to a predefined protocol. This allows for optimizations to be made to the device.
The developed quality framework, measurement protocol, and evaluation methodology should enable manufacturers to improve the functionality of their products in all aspects (comfort, cooling, efficiency, etc.) in response to this changing energy market and to communicate this clearly with their installers. The latter is also important for engineering firms, building managers, etc., who have a desired product functionality in mind and can now request it more clearly.