ASHRAE Journal - January 2020 - 54

TECHNICAL FEATURE

capacity, a model to be used in cold regions. The area
for air-conditioning/heating in winter was 5000 m2
(53,820 ft2), and the area for cooling in summer was
10 000 m2 (107,639 ft2). Using system switching management, the pump aided in replenishing the soil, at different supply areas and period to eliminate cold accumulation. A set of the different well spacing of 4 m, 5 m, 6 m
(13 ft, 16 ft, 20 ft) was observed to evaluate the soil recovery efficiency. It was observed that balanced winter and
summer running duration was not equal to the impact
of the lower ground heat pump COP generated by the
total heat storage of the soil. After the operation period,
COP value can reach an average of 5.25 during summer,
and 2.98 in winter, which is considered a good performance. Under this mode of operation, the soil temperature was running for a period and was balanced. This
provides a significant data foundation for future related
projects.
With the change of the heat/cooling condition of the
soil-source heat pump, the soil temperature field exhibited a periodic sinusoidal variation, which conformed to
the sinusoidal structure of Equation 7. The extent of the
change depended mainly on local climatic conditions,
soil thermal properties parameters and heating/cooling
load. We strongly recommend that the local climate and
environmental temperature, geological conditions and
building load characteristics should be fully considered
in the design and operation regulation of soil-source
heat pump.
The small change of soil temperature field during the
transition season indicated that the soil thermal diffusion capacity was very weak and hence, the response to
thermal diffusion was delayed. In this paper, the soil
thermal balance was restored by measuring the distance
between the water pipe and upon compare between
three different pipe spacing, the soil recovery rate was
better at 6 m (20 ft) distance. Therefore, it is not possible
to achieve the balance of soil temperature field in cold
regions by relying on only the self-recovery ability of soil
temperature field in a transition season,
For the soil source heat pump GSHP, the operating
conditions of the heat pump were not only related to
the thermal properties of the soil, but also related to
the layout form, length and operation time of the geothermal heat exchanger, that is, the outlet temperature
of the circulating heat medium of the geothermal heat
exchanger was relatively large. The operating conditions
54

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JAN UARY 2020

FIGURE 16 Monthly heat production for ground source heat pumps at 11 months,

and outdoor average temperature.
Temp.

of the ground source heat pump were mainly determined by the temperature of the ground, in that, when
the ground temperature was high, the performance of
the groundwater source heat pump unit was close to
the performance parameters of the nominal working
condition. Moreover, in the low groundwater temperatures, the operating conditions of the ground source
heat pump unit in winter were quite different from the
nominal conditions.
In the design of the corresponding ground source heat
pump system in severe cold regions, not only the influence of pipe spacing on the thermal equilibrium of the
system but more significantly, the influence of ground
temperature on COP should be considered. Because the
composition of the ground temperature is different, and
the effect of ground temperature on COP is greater than
the actual effect of tube spacing.

Acknowledgements
This project was funded by the Safety Production
Science and Technology Project of the State
Administration of Work Safety, "Study on Optimization
and Operation and Maintenance of Tunnel Smoke
Exhaust System in Severe Cold Region" (Project No.: Jilin
-0004-2017AQ). This study was financially supported by
the National Key Research and Development Program of
China (2016YFC0700100).

References

1. Zhu, J.L. et al. 2015. "A review of geothermal energy resources,
development, and applications in China." Current Status And
Prospects, Energy 93, 466e483.

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