Performance evaluation of a hybrid heating system combined a groundwater source heat pump with an existing fuel oil heater for a horticultural greenhouse

ABSTRACT

This paper reports a new hybrid heating system (HHS) installed in a horticultural greenhouse to lower the impact of high and unstable fuel prices on the greenhouse operation cost, to save the energy necessary to heat the greenhouse, and to reduce CO₂ emissions. The HHS consisted of a groundwater source heat pump system for basic heating and an existing fuel oil heater for peak heating. The performance of the HHS, including the fuel oil and energy savings, and CO₂ emissions reduction, was evaluated based on measurements during a heating period from November 2014 through May 2015. The results show that, comparing with only using the existing fuel oil heater to heat the greenhouse, the HHS can save 74.4% fuel oil and 22.8% energy, and reduce 35.5% CO₂ emissions. In order to further increase the performance of the HHS, the operating control of the HHS, indoor hot air delivery system, and local thermal insulation of the greenhouse were improved. Performance evaluation based on measurements from November 2015 through May 2016 shows that the improved HHS can save 88.0% fuel oil and 35.9% energy, and reduce 48.7% CO₂ emissions, which are significantly higher than those of the HHS before improved. Moreover, the comparison indicates that the performance of HHS was almost not changed with three different groundwater pumping rates tested herein. The proposed HHS is particularly suitable for transforming conventional fossil heating systems of horticultural greenhouses into a more energy-saving and thus sustainable heating system with a comparatively low initial cost.

KEYWORDS:

• Greenhouse
• hybrid heating system
• groundwater source heat pump
• energy saving
• co₂ emissions reduction

Acknowledgments

The authors gratefully acknowledge the partially financial support from the model project of GSHP installation of Gunma Prefecture. We gratefully thank Mr. Teruo Niki and all others who have helped in conducting this research. Special acknowledgments are given to the graduate students of Gunma University who helped in analyzing the data. The first author acknowledges the support of the Taizhou Science and Technology Project (1902gy22). We also gratefully thank anonymous reviewers for their valuable and constructive suggestions.

Disclosure statement

No potential conflict of interest was reported by the authors.