AKTIVA design and integration of building outer surfaces for multi-functional space heating and cooling applications

Abstract

In modern highly-insulated buildings the summer operation is getting more important and comfort cooling of buildings becomes increasingly an issue, in particular for office buildings. Free cooling during night-time by convection and radiation of an activated outer surface such as an absorber or collector has rarely been considered in practical operation for Swiss climate conditions, yet, but has shown interesting potentials in recent studies. An even more beneficial operation, though, would be to use the same outer surface also for space heating in winter operation, for instance as a heat source for a heat pump, as well as in summer operation for DHW heating. Thus, the objective of the project is the optimisation of properties of outer building surfaces for both heating and cooling operation, e.g. regarding the selectivity of the outer surface. Furthermore, adapted options for the system integration into a hydronic system are investigated by simulations. The results of the simulations are compared to lab measurements. As first step the properties of an unglazed collector with different degrees of selective coating and different inclination angles have been lab-tested. In parallel, a collector model based on the data sheet parameters has been implemented in Matlab-Simulink and compared to the lab test data with good agreement. Subsequently, the unglazed collector has been integrated into a system simulation model consisting of a heat pump or chiller, respectively, a source storage connected to the collector for the winter heat pump operation as well as a direct connection of the collector to the differently oriented building zones for summer cooling. The building zones are equipped with thermally-activated building systems (TABS), which are often applied in office buildings and offer favourable conditions for low temperature heating and high temperature free-cooling operation. Simulation results show a high degree of coverage for the Zurich average year weather data according to SIA 2028 for both operation modes. For single office use based on SIA 2024 loads, degree of coverage of winter source energy is about 75% corresponding to an SPF of the heat pump around 4. In summer cooling mode, about 90% of the cooling energy can be covered by free cooling. Results vary depending on the selectivity and inclination, so based on the requirements parameters can be optimised for heating or cooling. An integration of the source storage in cooling mode increases the degree of coverage up to 10%, in particular in adverse conditions like high selectivity of the collector or warm summer climate like Lugano warm year. As result of the project recommendation on the design, integration and control of outer surfaces for multi-functional operation in different applications will be concluded and verified by lab measurements of enhanced prototypes.