Research on energy-saving operating characteristics of water storage groundwater source heat pump heating system in plant factory

SHI Huixian1 REN Yike1 MENG Xiangzhen1 CHEN Huizi1 OUYANG Sanchuan1 ZHOU Qiang

(1.New Rural Development Institute of Tongji University, National Engineering Research Center of Protected Agriculture, Shanghai, China 200092)
【Knowledge Link】air source heat pump

【Abstract】The groundwater source heat pump has high efficiency and environmental protection in greenhouse temperature control. The operating energy consumption could be further reduced if the water storage technology was combined. The energy-saving operating characteristics of a water storage groundwater source heat pump heating system was studied, with the natural light plant factory in Shanghai as an example. The total area was 21 000 m2, of which the heating area was 5 880 m2. The heating system included a groundwater heat exchange system, a heat pump unit, an air conditioning unit, and an energy storage system. Considering the change in electricity price and the change in heat load over time, intermittent operation was adopted for the heating system. At the time of power trough, the heat pump unit was fully open and the energy was stored in the tank while heating. At the peak of power, the heat pump unit was stopped and the system made full use of the heat storage tank for heating. At the time of the level section, reasonable regulation was carried out according to the stored energy of the hot water storage tank and the plant heat load demanded. The typical operating week, February 8–15 in 2017, was selected from the winter heating months. The operation data in the typical week were recorded and analyzed. The outdoor temperature, solar radiation intensity, indoor temperature, indoor relative humidity, and COP (ratio of heat supply to power consumption) of the heat pump were all tested every 5 min in the typical week. The result showed that in winter, the groundwater source heat pump with the energy storage tank heating system could better maintain the indoor temperature at 17 °C–26 °C. The indoor temperature was relatively low at night, but it could meet the growth demand of the crop in winter. The influence of solar radiation was large, and the indoor temperature was basically above 22 °C, even 28 °C. The indoor relative humidity was always 60%–88%, which could avoid indoor high temperature with high humidity. When the system was in stable operation, the heat pump unit COP (coefficient of performance) was about 4.2. February 9, 2017 was selected from the typical week. On the typical day, it was cloudy and the temperature was below 4 °C throughout the day; the solar radiation intensity was 0–160 W/m2 and the average solar radiation intensity was 62 W/m2. The total power consumption of the system was 10 142.71 MJ, and the COP of the system was 3.17. It was further explained for the system characteristics of high efficiency and good stability. Compared with the non-storage ground source heat pump system, the groundwater source heat pump with water energy storage system saved 30.34% of the cost on the typical day. The significant economic benefit of the test system was shown. During the continuous heating period in winter, for the test heating system, the primary energy utilization coefficient was 0.99. Compared with the cold water unit and coal-fired boiler supporting system and chiller and gas boiler supporting system, the energy-saving rate was respectively 81.05% and 74.83%. Different energy heating cost was compared. For the operating cost, the coal, gas, and fuel methods were 1.25, 2.93, and 5.08 times that of the test heating system. For the CO2 emission, it was 2.32, 1.19, and 0.88 times that of the test heating system. Practice showed that the groundwater source heat pump with water energy storage system had good economic and environmental benefits, which could not only reduce the operating costs, but also make full use of geothermal energy and be beneficial to energy conservation.

【Keywords】 thermal energy; pumps; energy saving; natural light plant factory; groundwater source heat pump; water storage; heating system;

【DOI】

【Funds】 National High-tech R&D Program of China (863 Program) (2013AA103006-02)

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(Translated by LIU T)

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This Article

ISSN:1002-6819

CN: 11-2047/S

Vol 34, No. 23, Pages 157-163

December 2018

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Abstract

  • 0 Introduction
  • 1 Water storage groundwater source heat pump heating system in plant factories
  • 2 Basic operating characteristics of water storage groundwater source heat pump heating system in the plant factory
  • 3 Intermittent energy-saving operating characteristics of water storage groundwater source heat pump heating system in the plant factory
  • 4 Energy-saving, economic, and environmental benefits of year-round operation of water storage groundwater source heat pump heating system in the plant factory
  • 5 Conclusions
  • References