Water-to-water heat pump. Geothermal heat take-off via apertures

Let us consider an example of the open-type heat pump with low-grade heat take-off system in this article. The ground water, coming into the heat pump evaporator directly from an aperture, is a cooling medium (i.e. a medium, which is cooled down to give off its heat). The water is withdrawn from one aperture for the purpose of heat energy take-off, and the discharged (cooled) water comes into the other one. As these apertures used in the units of given type have different purposes, the special requirements are specified to their position relative to each other – the farther they are located, the less interaction will be between them. But the distance should not be less than 5 m.
The temperature of ground waters is relatively constant throughout the year: from 8 to 12 °С. This parameter is determined by the source depth and depends on climatic and geothermal conditions of an area within the bounds of its formation. The difference in temperatures of the area ground waters is attributed to the sizes of geological structures, containing the ground waters, and to the depth of their penetration, the water velocity, and in some areas to the proximity of warm magma pockets location.

Схема гидравлическая принципиальная работы теплового насоса типа вода-вода с отбором тепла грунтовых вод посредством скважин

Figure 3.1 Water-to-water heat pump. Schematic diagram.

① – semi-hermetic screw compressor

② – water-cooled shell-and-tube condenser (water heater)

③ – thermal expansion valve (TEV)

④ – water plate-type evaporator

⑤ – centrifugal pump for ground water

⑥ – centrifugal pump for heat-transfer fluid (hot water)

⑦ – aperture for ground water take-off

⑧ – aperture for ground water disposal

⑨ – house heating system batteries

Medium reference designation Name State
Suction of ground water by means of centrifugal pump Liquid
Supply of ground water into evaporator by means of centrifugal pump
Return of discharged ground water into aperture
Supply of warmed heat-transfer fluid (water) into house heating system batteries
Outlet of heat-transfer fluid (water) from house heating system batteries and inlet into pump
Supply of heat-transfer fluid into condenser by means of centrifugal pump
 Refrigerant suction by means of screw compressor Gas
Discharge of compressed hot refrigerant into condenser Gas
Supply of condensed refrigerant to thermal expansion valve Liquid
Refrigerant inlet into evaporator Vapour-liquid mixture
Ground waters flow Liquid

The operation principle description. The centrifugal pump (pos. 5) pumps out the water from the producing aperture (pos.7) and delivers the relatively warm (8-12 °С) ground water into the cooling medium circuit of the evaporator (pos. 4). The refrigerant boils in the evaporator, taking off the desired low-grade heat from a natural source – in this case from the ground water. Having been cooled down in the evaporator, the water returns to the utilizing aperture (pos. 8). Then the evaporated refrigerant passes to the compressor (pos. 1). The compressor compresses refrigerant vapours, hence, heating them to the temperature in a range of 90-130 °С and discharges them into the water-cooled condenser (pos. 2). In the condenser water circuit a heat-transfer fluid is heated, cooling and condensing the refrigerant to the liquid state in a freon cavity of the given heat exchanger. The heat-transfer fluid comes to the condenser with the help of the pump (pos. 6), and having been heated it comes into the heating system (pos. 8), being spreading to batteries (pos. 9) or fancoils. The water heater is designed to heat the tap flowing water for needs of such consumers as kitchen (pos. 11), bathroom (pos. 12), shower (pos. 13). Having given off its heat energy the heat-transfer fluid returns to the pump suction. The liquid refrigerant is directed to the thermal expansion valve (pos. 3), in which the expansion pressure sharp drop takes place. After TEV the refrigerant comes to the evaporator and the cycle begins to repeat.

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