Ground-to-air heat pump

To analyze this type of pump let us consider the example of heat pump with a system of heat take-off from the closed ground (i.e. a cooling medium is circulated in a closed loop, thus taking off the low-grade heat) and with a horizontal ground manifold.

The ground, as known, is the most universal source of dissipated (low-grade) heat, since it stores the solar energy and is being continuously heated by the Earth core. Generally, at a depth of 5-7 m, the temperature is almost constant throughout the year (8-12°С). It is enough to create a highly-efficient heat pump in order to heat buildings in a cold period, and also to ensure the unit operation for rooms cooling in a warm period of the year.

Схема гидравлическая принципиальная работы теплового насоса типа грунт-воздух с отбором тепла от грунта посредством коллектора

Figure 4.1 The ground-to-air heat pump. Schematic diagram.

① – semi-hermetic reciprocating compressor

② – air-cooled condenser being a part of central sectional conditioner

③ - thermal expansion valve

④ – water shell-and-tube evaporator

⑤ – centrifugal pump for intermediate cooling medium (ethylene glycol)

⑥ – ground manifold

Medium reference designation Name State
Inlet of intermediate cooling medium into centrifugal pump
Supply of intermediate cooling medium into evaporator by means of centrifugal pump
Return of chilled cooling medium into ground manifold
Inlet of outside air (or outside air mixed with recirculated air) into central sectional conditioner
Outlet of treated and heated (for winter mode) air from central sectional conditioner
Refrigerant suction by means of compressor Gas
Discharge of compressed hot refrigerant into condenser Gas
Supply of condensed refrigerant to thermal expansion valve Liquid
Refrigerant supply into evaporator Vapour-liquid mixture

The operation principle description. The centrifugal pump (pos. 5) pumps out the cooling medium from the ground manifold (pos. 7) and supplies it (heated and relatively warm, depending on conditions, 8-10 °С) into the water circuit of shell-and-tube evaporator with in-tube refrigerant boiling (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. Having been cooled down in the evaporator, the cooling medium returns to the manifold (pos. 7) and gets warm there again, having taken off the ground heat. Then the evaporated refrigerant comes to the compressor (pos. 1). The compressor compresses the refrigerant vapours, hence, heating them to the temperature in a range of 90-130 °С, and discharges them into the air-cooled condenser (pos. 2) being a part of central sectional air conditioner or supply-and-exhaust unit. In the condenser air duct the air gets warm, cooling and condensing the refrigerant to the liquid state in a freon cavity of the given heat exchanger. The air comes to the conditioner air duct with the help of a radial fan, passing through a filtering section, and getting warm, it comes into the air heating system. 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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