The application of traditional hydrogeological survey in the water source heat pump market - taking the water source heat pump project of Beijing People's Police College as an example

(Beijing Geological Engineering Survey Institute)

Abstract: Hydrogeological survey technology is the core of groundwater ground source heat pump technology and is also the key to the success of groundwater ground source heat pump projects. key to practice. This article discusses this by introducing an example of the water source heat pump project of the Beijing People's Police College.

Introduction

Water source heat pump technology consists of mature HVAC technology, heat pump unit technology and geological survey technology. In our country, HVAC technology and heat pump unit technology have been widely used for a long time and are very mature. Therefore, the key to the successful application of water source heat pump technology is whether geological survey technology can solve the problems of energy extraction and water resource protection. In the process of promoting water source heat pump technology, due to the complexity and variability of geological and hydrogeological conditions in various regions, the thermal conductivity and hydrogeological parameters of rock (soil) layers vary greatly. An underground heat exchange system that can be successfully applied in a region , often not applicable in another region. At present, because some water source heat pump project contractors (mainly heat pump unit manufacturers, system integrators and HVAC installation companies) do not understand the geology, hydrogeological conditions and recharge processes of various regions, they blindly contract water source heat pump system projects, resulting in the emergence of Many problems that should not occur, such as the pumped groundwater failing to recharge or the amount of recharge being insufficient, not only waste precious groundwater resources but also cause adverse ecological, environmental and economic consequences. This article takes the Beijing People's Police College water source heat pump project as an example to introduce in detail the application of traditional hydrogeological survey technology in the water source heat pump market.

1 Project Introduction

The Beijing People’s Police College is located in the north of Xinzhuang Village, Nankou Town, Changping District, and to the west of Taipingzhuang. The total construction area of ??the project is approximately 180,000 m2.

There are more than 20 multi-story buildings on campus***. The administrative teaching and research building has 5 floors and 1 underground floor; the auditorium has 3 floors and 1 underground floor; the rest are 2 to 4-story buildings. The exterior wall material is 300mm thick aerated concrete blocks, with a heat transfer coefficient of 0.82W/(m2·K). The roof insulation material is 60mm thick polystyrene board or metal insulation board, with a heat transfer coefficient of 0.6~0.78W/(m2·K). The exterior window is an aluminum alloy double-glazed window with a heat transfer coefficient of 3.5W/(m2·K).

2 Heat pump technology solution selection

After comprehensively comparing various traditional heating and cooling solutions, the engineering designer decided to adopt the economical, environmentally friendly, and energy-saving heat pump central air-conditioning technology to achieve winter Heating, summer cooling and year-round domestic hot water. According to calculations by the designer, the heating load is 15153kW and the air conditioning cooling load is 16081kW.

The Beijing Geological Engineering Survey Institute was entrusted by the Preparatory Office of the Beijing People’s Police College to undertake the survey, design and construction of the underground heat exchange system of the heat pump technical solution. Based on local hydrogeological conditions, it is planned to use groundwater ground source heat pump technology.

After accepting the task, our institute immediately organized geological and hydrogeological experts to conduct a preliminary survey of the site, combined with analysis and collation of the results of previous work, and initially identified:

(1) The site is located at the top of the Huyu flood fan. The Quaternary strata are mainly composed of sand and gravel layers interspersed with silt and clay layers. The burial depth is between 40 and 90m. The underlying Wumishan Formation of Jixian County Limestone, the lithology of the site strata is shown in Table 1.

Table 1 Site stratigraphic lithology table

(2) The Quaternary aquifer in the site is dominated by sand, pebbles and gravel layers, with uneven water richness. The water output of a single well is generally less than 150m3/d. Since the site is located at the top of the alluvial fan, the groundwater is deeply buried. The original agricultural wells in the site have a groundwater level of 77.20m, and most of the sand, gravel and gravel layers are in a dry state.

(3) The main sources of quaternary groundwater recharge in the site include: surface runoff infiltration caused by rainy season floods, atmospheric precipitation infiltration and lateral runoff of bedrock groundwater in mountainous areas. Groundwater consumption in the site is mainly lateral runoff and artificial mining.

(4) The groundwater dynamics in the site area obviously have the characteristics of phreatic dynamics at the top of the alluvial fan. The groundwater is at the lowest level before the rainy season, and the water level rises rapidly during the rainy season, with a range of 10 to 20m.

The above analysis of hydrogeological conditions shows that there are two main problems in using underground pipe ground source heat pump technology in the site area: ① Preliminary calculations show that in order to meet the maximum load operation of the system, each hole must be drilled to a depth of 100m. Calculated for a single U, PE pipe, about 4,000 holes need to be drilled. Since the ground in the site is mainly a sandy gravel layer, it is extremely difficult to construct small-diameter holes (<150mm) and is almost impossible to complete. If the hole diameter is increased, the cost will be significantly higher. Rise; ② If 4,000 holes are arranged in a square shape, it will require an area of ??more than 100,000 m2, and the site cannot meet this condition. It can be concluded that the underground pipe ground source heat pump technology has two unsolvable technical obstacles in the site area and cannot be adopted.

3 Investigation of water source heat pump groundwater heat exchange system

Through preliminary hydrogeological investigation and demonstration, the only heat pump technology solution that can be adopted in the site is the groundwater ground source heat pump solution. According to calculations by the design department, when the system is operated at maximum load, the total water demand is 1170m3/h.

The water richness of the Quaternary aquifer in the site area is uneven and greatly affected by seasonality. During the dry season, the aquifer has been partially drained and does not have stable water supply significance.