Finnish researchers have studied different scenarios for converting a Nordic oil-heated terraced house into a carbon-neutral building. They sized an electric PV-driven heat pump system utilizing hydrogen heat recovery and calculated its life cycle costs. They concluded that the solution is less profitable than grid-connected systems.
The team considered four scenarios to improve the energy efficiency of the 18-apartment heated property in Lahti, southern Finland, with a surface area of approximately 1,100 square meters. Scenario with a 45 kW air source heat pump and a 78 kW electric boiler (EEO); in the second, a 45 kW geothermal heat pump and a 33 kW electric boiler (EE1); the second with a 79 kW geothermal heat pump (EE2); and finally the scenario with a 15 kW ground source heat pump, 16 kW electric boiler, 15 kW heat recovery ventilation and additional roof insulation and renewal of windows and doors (EE3).
For each scenario, they simulated off-grid solar energy with a fuel cell, battery and hydrogen energy storage (HESS) and investigated the effect of waste heat on the dimensioning of system components. The researchers created a calibrated energy simulation model of the current building using IDA ICE 4.8 building performance simulation software. The PV generation was simulated in PVsyst, while the entire system modeling tool was created using Excel and MATLAB.
The fuel cell is supposed to function as a secondary energy source in winter, when the production of solar electricity decreases or is not there at all. The waste heat generated in both the fuel cell and the HESS electrolyzer is intended to be used for space and domestic water heating. “The main heat source for the tool is waste heat, followed by a heat pump and, if necessary, an electric boiler,” the researchers said, noting that waste heat takes priority because its temperature better matches the temperature requirements of hot domestic water. .
The results show that scenario EE0 requires a 325 kW PV system, EE1 and EE2 300 kW, and EE3 265 kW. It is claimed that waste heat can significantly reduce the dimensioning of the components of solar-powered systems. On average, the dimensions of the battery storage system (BESS), fuel cell, electrolyzer, and HESS are reduced by about 20%, 37%, 51%, and 28%, respectively. The reduction in component dimensions between EE0 and EE3 is approximately 33% for BESS, 41% for fuel cell, 27% for electrolyser and 22% for HESS.
“The recovery of waste heat from the fuel cell and the electrolyzer reduces the need for heat production from other heat sources, which affects electricity consumption when heating is based on a heat pump,” the researchers explained. “As a result, the load profile of the electricity changes and both the peak power of the electricity and the energy demand decrease.”
The team calculated that the 30-year life-cycle costs of off-grid systems would be between 2.3 million euros ($2.5 million) and 4.3 million euros, and concluded that “the costs are very high and unprofitable compared to an on-grid system.” They also noted that special safety considerations must be taken into account if the HESS device is used in a residential environment.