GEOTHERMAL HEAT PUMP – THE CHOICE IS YOURS

The technology of the day has made it possible that your home, office building, factory or farm land – the place of your choice – can become source of your geothermal energy for Heating and Cooling (H&C). This was not true about geothermal energy few decades earlier. Geothermal energy comes from the hot inner core of Earth which exists because of the original formation of the planet and because of radioactive decay of minerals. Since long there have been Hot Springs used for bathing and the oldest known spa is a stone pool on China’s Lisan mountain built in the 3rd century BC. The world's oldest geothermal district heating system in Claudes-Aigues, France, has been operating since the 14th century.
Geothermal power has historically been limited to areas near tectonic plate boundaries. But recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as space heating or cooling. The more demanding applications receive the greatest benefit from a high natural heat flux, ideally from using a hot spring. The next best option is to drill a well into a hot aquifer. If no adequate aquifer is available, an artificial one may be built by injecting water to hydraulically crack or fracture the bedrock. This last approach is called Hot Dry Rock Geothermal Energy or Enhanced Geothermal Systems (EGS). Much greater potential may be available from this approach than from conventional tapping of natural aquifers.
Today, geothermal energy is a clean, renewable resource that provides energy around the world in a variety of applications and resources. Geothermal energy is being used for electricity production, for commercial, industrial, and residential direct heating purposes, and for efficient home heating and cooling through geothermal heat pumps.
• Geothermal Electricity is developed from geothermal resources by drilling of wells into a geothermal reservoir. The wells bring the geothermal water to the surface, where its heat energy is converted into electricity at a geothermal power plant.
• Geothermal Heating is a direct use of earth’s heat, without involving a power plant or a heat pump, for a variety of applications such as space heating and cooling, food preparation, hot spring bathing, agriculture, aquaculture, greenhouses, and industrial processes.
• Geothermal Heat Pumps (GHPs): Geothermal heat pumps take advantage of the Earth’s relatively constant temperature at depths of about 10 ft to 300 ft. GHPs can be used almost everywhere in the world, as they do not share the requirements of fractured rock and water as are needed for a conventional geothermal reservoir. GHPs circulate water or other liquids through pipes buried in a continuous loop, either horizontally or vertically, under a landscaped area, parking lot, or any number of areas around the building. The Environmental Protection Agencies consider them to be one of the most efficient heating and cooling systems available. GHPs reduce electricity use by 30–60% compared with traditional heating and cooling systems, because the electricity which powers them is used only to collect, concentrate, and deliver heat, not to produce it.
Geothermal heating and cooling is currently applied in three different ways:
1. The first one (low temperature up to 30°C) is based on the relatively stable groundwater and ground temperatures at shallow depths (up to 500 m) – and therefore also near structural elements of buildings. Typically, heat pumps are used to extract energy from the ground and raise (and amplify) the energy to the temperature (and thermal efficiency/capacity) level required by the heating systems for the thermal conditioning of spaces and processes. The ground or groundwater can also be used for cooling, whereby at the right conditions the temperature can be applied directly. Furthermore the heat pump installation can also be used to provide cooling to the building or process, again providing the required temperature and amplifying the thermal capacity of the source. In certain conditions and configurations, the geothermal system can be used to (to control and optimise) ground temperatures artificially, in order to be used as heat or cold storage – UTES (Underground Thermal Energy Storage).
2. The second one extracts the heat from ground and groundwater at higher depths and temperature around 150°C. Direct applications are found in agriculture (horticulture, drying, fish-breeding), industrial processes, and balneology. It may also be applied to supply energy to a district heating or a combined heat and power installation or to drive local absorption heat pumps to provide cooling to the grid. District heating (and cooling) may also be supplied from residual heat left over after the production of electricity from a high enthalpy geothermal heat source.
3. Low to medium temperature applications can also make use of available surplus heat/cold from building heating/cooling application or from integration with solar thermal.

GEOTHERMAL HEATPUMPS

Unlike the other renewable energy sectors, geothermal heat pump industry is currently the most dynamic one. Low enthalpy ground source (the shallow systems) have been experiencing a rapid growth without the requirement of structural subsidies (governmental support).
There are different types of GHP heating and cooling applications:
1. Closed loop applications (vertical boreholes)
2. Closed loop applications (horizontal, shallow excavated systems)
3. Closed loop applications (foundation integrated systems)
4. Direct expansion
5. Groundwater applications (well based systems)
The current industry standard geothermal heat pump installations use vertical closed loop borehole collectors. A small number, mostly small residential applications use horizontal collectors.

DIRECT USES OF GEOTHERMAL HEATPUMP

There is no principle geographical restriction for the production of geothermal energy, geothermal heating and cooling supply can match the H&C demand anywhere because the resource is available everywhere. At present, geothermal energy is being used for district heating, as well as for heating (and cooling) of individual buildings, including both small (5-50 kW installed heat pump capacity), medium (50-500 kW) and large schemes (capacities > 1 MW) (offices, shops, health care, residential houses, schools, university buildings, commercial buildings, greenhouses, bathing etc. ).
Existing housing infrastructure represents an overwhelming share of the low temperature energy demand that can be logically supplied by geothermal district heating systems. Current benchmark studies indicate that direct use geothermal energy and district heating grids are probably the most effective option for this market, both in terms of carbon footprint and economics. However these developments are intrinsically fairly complex; necessitating the replacement of existing fossil energy based infrastructures which therefore require longer development times.

KEY CHALLENGES
The key challenge for the widespread direct use of geothermal heat will be the ability to reliably design, engineer and control geothermal heat pump installations, in order to be able to use the all-round potential of geothermal heat pump systems for sustainable energy efficiency. Intelligent planning with follow-up actions and cost reductions will allow the evolution of the current ‘hunter-gatherer’ economy of geothermal energy to a systematic and organized exploitation of geothermal resources.
The share of Shallow Geothermal Energy in our daily life can be increased by taking following steps:
Integration of geothermal energy in standard housing energy systems. Such a step necessitates the increased penetration of geothermal heat pumps into the market for new residential and commercial buildings. This advancement is dependent on Renewable Energy Systems (RES) becoming standard in new energy efficient buildings in all countries.
Develop Heating & Cooling networks integrating geothermal heat pumps and geothermal storage (UTES).Such a development would mean widespread Heating & Cooling networks based on geothermal energy in a time frame, followed by a constant part of the market of tertiary building and small Heating & Cooling networks. This would be based upon the rapid diffusion of Heating & Cooling networks, which have to become standard in urban planning.
Develop geothermal solutions for retrofitting of existing infrastructure. This advancement is based upon a number of critical factors. Firstly, products and methodologies for cost effective building energy refurbishment must be developed. Secondly, there must be a higher performance of high temperature heat pumps, or adoption of the buildings to low temperature space heating. Finally, the importance of improved energy efficiency standards, as part of renovation activities, is to be stressed in buildings regulation.

COSTS INVOLVED
To provide the readers with a feel of costs involved, a summary is tabulated below which is sourced from European Geothermal Energy Council.
Heating and Cooling (Average rates in European Markets)
Deep Geothermal - District Heating 7 $-cent/kWh
Geothermal Heat Pumps – large systems and UTES 8 $-cent/kWh
Geothermal Heat Pumps – small systems 13 $-cent/kWh
European Continent is very active in development of residential geothermal heat pumps. Geothermal Heat pumps with a capacity of 10 kW are routinely installed at a cost of around USD 3000 – 4000 per kW for closed loop systems. When the capacity is over 100 kW (large residential and tertiary buildings, schools, museums), open loop systems cost range is USD 700 - 1000 per kW. UTES systems for commercial and institutional buildings as well as for district heating and cooling have a capital cost of USD 130,000-190,000 per MWth (10% of the investment cost) referring to Swedish and Dutch experiences with a running cost of USD 30-40 per MWh.