GEOTHERMAL (GROUND SOURCE) HEATING
Geothermal heating (sometimes called ground source heating) is an exciting advance in heating technology and is the way of the future for home and commercial heating. Central Heating New Zealand now offers geothermal heating systems in conjunction with GeoEnergy Systems. There is a developing market for geothermal energy and Central Heating New Zealand is committed to research and development in this area.
What is Geothermal?
Geothermal means to heat from the earth. Geothermal, or Ground Source Heating as it is also known, is not necessarily referring to the natural hot springs that are found around New Zealand. In these areas, the hot spring water is piped directly into houses to heat them. The geothermal heating that we are referring to is the transfer of heat from earth that is not naturally hot.
How does it work?
These systems draw heat from under the ground using pipes in a vertical borehole or a series of pipes laid horizontally a few metres below the surface. For horizontal installations, the pipes are laid in a 'slinky' formation. The image to the right shows the 'slinky' coil of geothermal pipe loops rolled up ready for transportation to site, and the
top right image shows the 'slinky' coils laid in a trench.
Solar energy from the sun is absorbed by the ground during the year. Protected from extremes of heat or cold air temperatures, the ground here will remain at about 15°C all year round. The heat you get from the pipes in the ground will not in itself be warm enough to heat the home. It must be ‘boosted’ to the level needed for heating a home using an electrical appliance known as a ‘geothermal or ground source heat pump’. Put another way, the earth produces a huge amount of low temperature heat that the heat pump converts into a small amount of higher temperature heat suitable for heating the house.
In a well designed system, every unit of electrical energy put in will yield up to five units of heat energy even when the outside air temperature is below freezing.
Different types of sites require different installation methods. The photos below were taken by the CHNZ team on site at two different geothermal projects during December 2008. Geothermal Pipe Installation A uses slinky loops in a horizontal trench because the property is in a suburban area where space is at a premium. Installation B uses horizontal straight pipe loops because there is sufficient land area available to use a geothermal pit instead of a trench to collect energy from earth. The slinky coils are also very labour intensive to put together so it works out slightly cheaper for the installation of the straight pipe loops.
As well as using the earth to extract energy from, it is possible to have coils of pipe submerged in a pond or lake, river or sea and transfer this heat through the geothermal heatpump and into the house. Using well water pumped directly through the geothermal heatpump is another method that is also encompassed by these systems. This latter method has the best energy transfer of them all.
Electricity is not particularly cheap, and is mostly generated by fossil fuel or hydro stations. A geothermal heat pump is the most environmentally friendly user of electricity because of its ability to squeeze the most out of a kilowatt of electricity. It quite simply is the best renewable energy possible as it can be used 24 hours of the day 365 days of the year.
Geothermal / Ground Source Heating Systems
A Ground Source Heat Pump system consists of three elements;
1. A ground heat exchanger, which collects heat from the ground.
2. A water-to-water or water-to-air heat pump, which raises the heat collected to a useful temperature and transfers it to the house.
3. A heat distribution system which provides the heat to the house for example underfloor heating.
What is a heat pump?
You will almost certainly have a heat pump in your home already, as they are used to keep fridges cool - basically by ‘pumping’ heat out. Most air conditioning units are also heat pumps. Both of these are generally air-source systems that extract heat from the air. The geothermal heat pump extracts heat from the ground and produces more heat than the air source units without variation in output performance.
Background
Geothermal / ground source heat pumps have been in use since the 1960’s in America and Europe. In the last 10 years their popularity has exploded due to the advances in heat pump technology and the rapid rise in energy costs. The largest benefit from geothermal heat pumps has come from the commercial sector, where heating and cooling costs are large and the savings that can be made are significant. The saving on the national electricity grid is also benefitted and in most American States, the local power utilities offer incentives for people to change to geothermal because of the reduction in load on the grid. This is not available yet in New Zealand, however home owners can now significantly reduce their heating and cooling energy bills using this technology.
Applications
Geothermal heat pumps/ ground source heat pumps are particularly suitable for new build as the technology is most efficient when used to supply low temperature distribution systems, such as underfloor heating. They can also be used for retrofit, especially in conjunction with measures to reduce heat demand. Geothermal heat pumps can be particularly cost effective in areas where mains gas is not available, or in developments where there is an advantage to simplifying the infrastructure provided.
Advantages of Geothermal Heating / Ground Source Heating
As well as reducing purchased energy consumption and CO2 emissions, geothermal heat pumps have a number of other environmental and operational advantages:
■ High reliability (few moving parts, no exposure to weather).
■ High security (no visible external components to be damaged or vandalised).
■ Long life expectancy (typically 20 – 25 years for the heat pump and over 50 years for the ground coil).
■ Low noise.
■ Low maintenance costs (no regular servicing requirements).
■ No boiler or fuel tank.
■ No combustion or explosive gases within the building.
■ No flue or ventilation requirements.
■ No local pollution.
Is Geothermal Heating environmentally friendly?
In order to be environmentally beneficial, the whole heating system must be properly specified and the house must be very well insulated (certainly more than is specified by current NZ Building Code). You can vastly improve the efficiency of your existing property by taking simple energy conservation measures - see Energy Efficiency for ideas.
The efficiency of a heat pump is given by its coefficient of performance, or COP. A system operating at COP3 will be giving 3 units of heat energy for every unit of electricity used. Most heat pumps supplied by Central Heating New Zealand have a COP of 4 or more so this makes the systems very energy efficient and therefore environmentally friendly.
Learn about the Delonghi Geothermal Heat Pumps that CHNZ sells.
Learn about other Heat Sources available for central heating.