Techno-environmental analysis of a modular heat pumps system with a latent heat storage for residential applications

Both globally and in Europe, the energy consumption in the building stock represents a considerable share of the final energy consumption. Under this consumption, the production of space heating, space cooling and domestic hot water (DHW) constitute a large proportion, as well as being a source of greenhouse gases when the building energy system is fossil fuels based. Hence, to achieve both energy efficiency and decarbonization goals in the residential sector, the introduction and/or expansion of renewable energy sources and decarbonization-key enabling technologies are essential. Accordingly, implementation of heat pump technology arises as a key technology for the production of heating, cooling and domestic hot water.
Consequently, this work proposes a system of reversible modular heat pumps equipped with a latent heat storage. This system has the capacity to produce domestic hot water, heating in the winter season and cooling during the summer. Due to its modularity, this system further has the particularity of being able to connect the energy carrier fluid (in this case water), in serial or in parallel automatically, depending on the desired supply temperature, the demand flow rate and the acceptable pressure drop in the hydronic circuit. In addition, the use of latent heat storage technologies, allows the elimination of buffer and water storage tanks in order to avoid oversizing the heat pumps, thus increasing the performance of the system and reducing the electrical energy consumption.
This work develops a fully dynamic thermo-hydraulic model in Modelica/Dymola for a building energy system comprising of three major parts that are: a supply side (heat pumps system), building distribution system (hydronic circuit for water distribution equipped with a latent heat storage for DHW) and a demand side represented by a building with occupancy. The integration of these parts into the building distribution system, its optimization, and the investigation of the impact of connecting the heat pumps condenser side in parallel and series on the heat delivery, indoor and DHW temperatures and overall system performance will be the main focus of the present work. This system is going to be investigated based on annual simulations in three different climates (Helsinki, Strasbourg, and Athens), to determine their performance and efficiency under different conditions.
Moreover, the work then studies the technical feasibility of the system and conducts an environmental analysis focusing on the CO2 savings of such an installation compared to a conventional building energy system whereby a gas-fired boiler, hot water tank and electrical air-conditioning system are present.