Modelling of Thermal and Energy Systems Research Group

Development of a new DMS-CO2 heat pump system with latent heat thermal storage for DHW and room-heating to boost the implementation of zero-emission buildings (HPCO2Pro) (2024-2026)

This is a project funded by the Ministry of Science and Innovation, Spain and the support of the European Regional Development Fund (PID2022-139566OA-I00).

The objective of this proposal develop and assess the performance of a competitive air-water CO2 heat pump with direct mechanical subcooling (HP–DMS) prototype able to provide domestic hot water (DHW) and space-heating (30-60°C), and to work with photovoltaic energy. The prototype will be coupled to a latent heat thermal storage (LHTES) system (i.e. a tank filled with phase change materials (PCM) packs within a water bath) to cover the thermal demand of a building and to provide the capacity for electricity-load shifting. Besides, this projects seeks to develop and validate with the experimental data obtained a numerical model that coupled with the building demand could evaluate the performance of the prototype under different operative and climatic conditions. Other objectives are:

• Analyse theoretically/numerically different types of HP configurations using CO2 and select a refrigerant with low GWP in the DMS cycle (such R1234ze(E) or others) and select the most efficient solution.

• Build a prototype of the air-to-water HP solution proposed early in the project and analyse different control strategies of operation with one or two cycles and optimise control loops of the HP and the rest of the systems to maximise its COP and minimise the gas-cooler optimal pressure. Study virtual connections of the new HP prototype to an existing photovoltaic facility of the research group located in another building to feed the HP prototype. In this case, the photovoltaic facility will not be directly connected to the HP but its actual power generation profile will feed the HP compressors.

• Development of TRNSYS/numerical model and validate it with the data obtained in WP4 to have a tool to evaluate the performance of the prototype alone and coupled with LHTES and a photovoltaic facility under different operative conditions. Validation with data from experimental tests with the idea of being applicable to different EU climate conditions and building demands.

• Experimentally characterise of the prototype, evaluate the electricity-load shifting strategies and optimise of the design and coupling of the LHTES tank based on: the temperature of phase change, the volume ratio of PCM/water, the tank initial temperature and the water flow rate in the HP-tank coupling strategy to increase ~50% the energy storage compared to standard sensible (water) thermal storage and maximise the system COP.

• Execution of the experimental tests to characterise the performance of the system.

• Evaluate the sustainability of the solution through the assessment of GHGE and energy savings, energy self-sufficiency and profitability analysis. The objective is to identify the best electricity-load shifting strategy to reach ZEB comparing this one with others based on batteries.