Use of heating pump to reduce carbon footprint of greenhouse heating

Heat pumps are highly efficient tools in reducing the CO2 output in heating as compared to directly burning fossil fuels. However, their technical and economic characteristics are not well understood for greenhouse heating in Latvia climatic conditions. In this research, a commercially available regular air to water heat pump 5 kW (10 kW heat power) supported by solar panels (PV) 7.5 kW peak power and a solar hot water system 15 kW peak power were used to heat an experimental tomato greenhouse (50 square m) located at a commercial production facility in South-East of Latvia. To reduce the capital expenses the DC output from PV panels was fed directly into the hot water boiler. The results obtained during late summer and during September 2021 are analysed. While the climatic conditions were rather typical, the energy market for both natural gas and electricity (Nordpool prices) showed extraordinary variations with electricity prices striking record 1000 EUR•MWhE−1 at some points. The results were compared with those of the industrial production facility that was heated by natural gas boilers. In periods of very low subzero temperatures and/or very high electricity prices, the heating with natural gas boiler was cheaper, while at temperatures close to zero and above the freezing point the heat pump outperformed the natural gas heating economically. At the climatic and market conditions of the second half of 2021 a heating system using natural gas or biomass boilers at periods of low air temperatures or high electricity prices and an air-to-water heat pump supported by PV panels and solar water heaters at periods of higher outdoor air temperatures and during low electricity prices has the best economic performance. We have estimated that using such hybrid system in greenhouse heating we can achieve 3-fold reduction of CO2 emissions without increasing the heating