Geothermal Heat Pump

Overview

A few metres down, the ground holds a near-constant temperature all year, cool relative to a summer afternoon, warm relative to a winter night. A geothermal heat pump exploits that stability. It is a refrigeration machine that pumps heat between a building and a buried pipe loop: in winter it pulls warmth out of the ground and delivers it indoors, and in summer it runs in reverse, dumping the building's heat back into the earth. Because the ground source barely changes temperature, the machine works against a small thermal lift, which is why it can move three to four units of heat for every unit of electricity it draws.

How it works

The heart of the machine is the Scroll Compressor, a hermetic scroll unit whose orbiting and fixed scrolls squeeze refrigerant vapour to a high pressure and temperature. That vapour enters the Refrigerant Circuit, where it gives up heat in one coil and absorbs heat in the other. A Reversing Valve swaps which coil is the condenser and which is the evaporator, so the same hardware heats in winter and cools in summer, while a Expansion Valve drops the refrigerant pressure between the high and low sides.

The "ground" side of the exchange is the Ground Loop Heat Exchanger, buried HDPE pipe filled with a glycol mix that the Circulation Pump pushes around the circuit. On the cold low-pressure coil the refrigerant absorbs heat from that loop fluid; on the hot side it rejects heat into the building's water or air. An optional Desuperheater siphons off some of the hottest discharge gas to preheat domestic hot water almost for free.

Indoors, the Air Handler blows return air across the refrigerant coil and into the ducts. Sequencing all of this, staging the compressor, switching the reversing valve, modulating the pumps from its temperature sensors, is the job of the Controller & HMI board, which presents a touchscreen for the occupant. The compressor and coils sit inside an insulated Cabinet that keeps the machine quiet and free of condensation.