Hydronic configurations of hybrid heat production systems in buildings: General design methodology and case studies

Abstract

Hybrid heat production systems, in which sustainable technologies such as Combined Heat and Power (CHP) or heat pumps are combined with auxiliary heaters, have the potential to increase energy efficiency in buildings. In order to exploit this potential, a proper hydronic configuration of the production system is of uttermost importance. Unfortunately, both scientific literature and design guides have focussed little on this aspect.Therefore, this paper proposes a general simulation-based design methodology for selecting the hydronic configuration of a hybrid production system. To illustrate the methodology, it is applied on different case studies in which either a CHP or an Electrical ground-coupled Heat Pump (EHP) is assisted by an auxiliary boiler. The considered apartment building is equipped with a collective heating system for both space heating and domestic hot water (DHW) production, and four different combinations of the temperature levels are considered.Results show that if a CHP is considered, the auxiliary boiler should be implemented in parallel and be assisted by a modulating valve: this increases the Relative Primary Energy Savings (RPES) with up to 6.2 percentage points. EHPs require a separate circuit in the production system for space heating and DHW, preferably with preheating of the domestic cold water (an increase in RPES of up to 16.1 percentage points was reported).The use of a new type of Load Duration Curve to analyse the simulation results proved to be a comprehensible measure for decision making at the level of every stakeholder in the design process. In conclusion, the proposed methodology can assist these stakeholders in their pursuit of high performance hybrid heat production systems.