Experimental study on intermittent operation of ground-source heat pump in winter condition (1)

Abstract: This paper describes the experimental results of the intermittent operation of ground source heat pump in winter. During the operation of ground-source heat pump, the ground temperature can be recovered through controllable intermittent process to make up for the lack of heat transfer in the soil. The rules and trends of temperature change have been changed to realize the good heat transfer and heat pump operating conditions.
Keywords: geothermal energy recovery soil source heat pump intermittent operation
The intermittent movement test of ground source pump in winter

Dalian Unversity of Technology FAN Ping-ping DUAN Mu-lin SHU hai-wen

Shenyang Gas & Heat Research and Design Institute of Construction Ministry WANG Xue-long

Abstract : This text introduced the intermittent movement test result of ground source pump in winter. Certificated that in ground source heat pump (GSHP) of geothermal energy utilization system, a concept of intermittent process (GSHP on or off) was proposed to restore underground temperature and compensate insufficient rock heat transfer. And changed the temperature variety regulation and trend. Intensify the heat transfer and good work condition of heat pump.

Keywords : geothermal energy; ground temperature restoration; ground source heat pump; intermittent movement

1 Introduction

Ground energy is a clean renewable natural energy, it is perennial temperature stability characteristics, is the heat pump ideal form of heat. However, due to its weak heat transfer capacity, geothermal energy systems with soil source as the main body require large heat exchange area and floor space, and large initial investment of equipment has restricted the development of this technology. Therefore, researchers put forward the idea of ​​controllable intermittent operation [1] . The concept of intermittency is an effective measure to efficiently utilize geothermal energy based on the intermittent nature of the operation of the heating and cooling system in the building environment and the recoverable characteristics of the geothermal. Through the artificial control of the intermittent operation of heat pump units, can enhance the heat transfer process. If we can take full advantage of the intermittent make up for the slow heat of underground shortcomings, we can achieve full heat transfer, to minimize the number of buried heat exchanger borehole, reducing its initial investment.

Intermittent heat recovery in underground heat exchangers can change the trend of temperature change, increase or decrease the equilibrium temperature, and make the heat pump work under the ideal working conditions. For the temperature drop of the heat sinks or the temperature rise of the exothermic well, the operating conditions of the heat pump unit are mainly affected by the minimum temperature range of the temperature drop and the maximum temperature range of the temperature rise. Control of heat pump import and export of the ideal temperature is an important guarantee for its efficient operation. To this end, the test based on the theory of controlled intermittent operation to develop a reasonable operation of the program, ground source heat pump winter operating conditions for experimental study [1,2] .

2 test system

The experimental temperature measurement using all PT100 copper - Kang copper thermal resistance, the allowable error of ± 0.3 ℃, all parameters measuring point all the introduction of the control system, the implementation of uninterrupted automatic acquisition and control, and automatically store data.

The temperature test is mainly underground pipe wall temperature test, water temperature test.

(1) buried pipe wall temperature test

Underground buried pipe experimental system a total of 9 underground buried pipe, buried in 75 meters depth and 50 meters buried underground pipe wall measuring points

The layout is a measuring point of 10m each, while the 25m depth is one measuring point every 5m. There are two groups of thermocouples buried in the buried pipe in the depth of 75m. Figure 1

Figure 1 temperature measuring point layout

Fig2-1Schematic of the sensors distribution of temperature

(2) water temperature test

The water temperature measured in this experiment is mainly underground pipe import and export water temperature and heat pump import and export water temperature.

3 experimental results analysis

Due to the soil source heat pump by the soil and climate conditions are greatly affected, here to Dalian's soil and climate conditions for experimental study, the soil characteristics of the parameters shown in Table 1

Table 1 soil characteristics of the parameter table

3.1 data processing methods

The calculation of instantaneous average heat exchange within each test day:

(3-1)

Where:

Instantaneous average heat transfer of Q-tube heat exchanger within each test day, kW;

- circulating fluid density, kg / m 3 ;

c p - specific heat of circulating fluid, kJ / (kg · ° C);

-U-type heat exchanger water flow, m 3 / s;

t o - U-shaped tube outlet average temperature in each test day, ° C;

t i - average temperature of the U-tube inlet in each test day, ° C.

Underground heat exchanger unit depth of heat exchange calculation formula:

(3-2)

Where: q l - heat exchange unit depth, W / m;

- Shaft depth, m.

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