1) Condenser, 2) Expansion valve, 3) Evaporator, 4) Compressor.
The stylized diagram shows how a heat pump works. The compressor (4) compresses the refrigerant fluid, which heats as it compresses. The fluid passes through the condenser, where much of the heat is transferred through heat exchange to air or another medium such as water (for hot water for domestic or heating use). The cooled refrigerant then flows to an expansion valve, where it is forced to expand into a larger pipe. In order to expand, it must change from a liquid into a gas, picking up heat from its surroundings to do so. This change of state takes place in the evaporator and heat is picked up from wherever this is located open air, water, underground, etc. This extracted heat is then carried in the gas to the compressor, where it is added to the heat created by the compressors operation.
The operating cost of the system consists of the electrical power consumed by the compressor but much of this is converted by the compressor into heat for the refrigerant. The heat extracted by the evaporator is essentially free. In a system extracting heat from the outside air, the amount of heat output from the condenser can be 2-3 times the amount of energybeing consumed but this output reduces as the outside air temperature drops because the temperature difference between the outside air and the refrigerant has reduced. Air-to-air systems therefore usually require a separate heating system to provide top up heat at the coldest times of the year.
Geothermal or ground-source systems do not experience these problems and the heat output can be up to 5 times the amount of energy being consumed, or even more.
What is a geothermal heat pump?
A geothermal heat pump uses the ground as its source of heat rather than the air and is often therefore referred to as a ground-source heat pump. Once you get several feet below the surface of the ground, the ambient temperature tends to be much the same all year round. The temperature in the depths of a cave is generally between 50 and 60F (10-16C), depending on the latitude. This is why our remote ancestors lived in caves during the Ice Age. Subterranean groundwater also tends to be liquid even when surface water is frozen solid. It is this kind of temperature difference that is tapped by geothermal heat pumps.
Ground heat can be utilized in several ways. The ground heat collector may be a closed loop vertical, horizontal or radial system. Open loop systems may be employed when there is an appropriate volume of ground water available at surface or subterranean level.
The various types of heat collector
Vertical closed loop
In a vertical closed loop system, holes are drilled into the ground, spaced16-20 feet (5-6m) apart. The drill depth would be typically 75-500 feet(23-150m) depending on a variety of climatic and geological factors. A pair of
linked pipes is laid in each hole, which is then filled with a special grout to
assist heat transfer between the ground and the pipe. A typical detached house requiring 10 kW (3 tons) heating capacity would require 3 boreholes. This is the most expensive geothermal system to install but is also the most efficient,offering a rapid payback, and requires little land area for installation.
Horizontal closed loop
In a horizontal closed loop system, interlinked pipes are laid in a trench,below the frost line, at a depth of 4-7 feet (approx. 1-2m). A typical detachedhouse as above would require 3 loops, each 400-600 feet (120-180 m) long. When the loops are placed at a shallow depth, they pick up stored warmth from the Sun but this becomes depleted in the coldest part of the year. During long cold winters, the ground temperature can drop considerably because of the amount of cold being dumped by the system with no replenishment from passive solar heating, causing the heat pump to use much more electricity than designed. This problem can be mitigated by installing the loops deeper in the ground and/or by installing a reversible system that would also provide air conditioning during Summer, storing heat in the ground for use in colder months. Both these options increase the initial cost of the system but result in lower electricity bills, creating a faster return on investment.
Radial closed loop
In a radial closed loop system, the loops are laid in small-diameter boreholes drilled horizontally. This technique, called horizontal directional drilling or HDD, enables piping to be laid under driveways, gardens and existing structures, thereby maximizing the space available. It is an ideal system for retrofitting in lots with existing buildings and/or other structures. The radial spokes all return to a central hub, reducing the amount of space required. The system is slightly more expensive than a standard horizontal closed loop system but requires much less space, making it much more accessible to consumers in general.
Tips and criteria forchoosing your geothermal heat pump system
Although contractors may wish to minimize the size of the collection system and possibly undersize it as a means of making the cost as attractive as possible, it is better to oversize the collection system to some extent. This will ensure lower electricity consumption from the compressor,creating greater energy savings and providing faster payback even though the
initial cost is a little higher for a system that covers for nasty surprises
from the weather.
For maximum energy efficiency, oversized vertical loops are usually more
cost-efficient than oversized and/or extra-deep horizontal loops and require
much less space. Radial systems offer a useful compromise between cost and space, especially in already built-up areas or areas scheduled to be heavily built up.
A geothermal or ground-source heat pump is one of the most energy-efficient technologies available for providing space and water heating. The systems can be built to be reversible to provide air conditioning in summer. The installation costs are higher than for an air-air system but the efficiency is much higher: the difference in cost is usually paid back in energy savings in from 3 to 10 years.
System life is estimated at 25 years for the inside components and more than 50 years for the ground loop. More than a million geothermal or ground-source heat pump systems have been installed world-wide (figure from a survey in 2004) and the figure is growing by around 10% a year.
Recent determination of the amount of additional heat (ca. 20%)provided by the low-level radioactivity in granite would tend to make avertical loop system installed in granite bedrock even more cost-efficient(see Granite may extend the range of geothermal energy use).
When installing any new or upgraded heating or cooling system,it is always advisable to ensure that the relevant space is correctlyinsulated.
https://suite101.com/a/using-a-geothermal-heat-pump-to-heat-your-home
