Bulgarian Geothermal Association
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Lindal diagram suggests the possible uses of geothermal fluids at different temperatures.
cascade and combines useof the application of geothermal
sources.
1. What is the temperature of the thermal water in Bulgaria?
Bulgarian territory is rich in thermal water of temperature in the range of 20oC-100oC. About 43% are waters with temperature between 40oC- 60oC.
2. How can be used the thermal water in Bulgaria?
Thermal water is used for balneology (prevention, treatment and rehabilitation, bathing and swimming pools), space heating and air-conditioning, greenhouses, geothermal ground source heat pumps (GSHP), direct thermal water supply, bottling of potable water
3. What is a Ground source heat pump?
A geothermal or
“ground-source” heat pump is an electrically-powered device that uses
the natural heat storage ability of the earth and/or the earth’s
groundwater to heat and cool your homeor business.
4. How efficient is a Ground source heat pump?
The GSHP is one of the most efficient residential heating and cooling systems
available today, with heating efficiencies 50 to 70% higher than other
heating systems and cooling efficiencies 20 to 40% higher than available
air conditioners.
5.How safe are Ground source heat pumps?
The systems are safe and protected. With no exposed equipment outdoors,
children or pets cannot injure themselves or damage exterior units.
GSHPs have no open flame, flammable fuel or potentially dangerous fuel
storage tanks.
6. How much does a Geothermal Heat Pump cost?
The initial investment for a GSHP system is greater than that of
a conventional system. However, when you consider the operating
costs of a geothermal heating, cooling, and water heating system,
energy savings quickly offset the initial difference in purchase
price.
7. How do Ground source heat pumps protect the environment?
GSHP systems conserve natural resources by providing climate control
very efficiently-thus also lowering emissions. GSHPs also minimize
ozone layer destruction by using factory-sealed refrigeration systems,
which will seldom or never have to be recharged.
About geothermal enegry
Geothermal energy is the energy contained asheat in the Earth‘s interior. The origin of this heat is linked with the
internal structure of our planet and the physical processes occurring there.
Despite the fact that this heat is present in huge, practically inexhaustible
quantities in the Earth’s crust, not to mention the deeper parts of our planet,
it is unevenly distributed, seldom concentrated, and often at depths too great
to be exploited industrially.
The heat moves from the Earth’s
interior towards the surface where it dissipates, although this fact is
generally not noticed. We are aware of
its existence because the temperature of rocks increases in depth, providing
that a geothermal gradient exists: this gradient averages 30oC/km of
depth.
There are, however areas of the
Earth’s crust which are accessible by drilling and where the gradient is well
above average. This occurs when, not far from the surface (a few kilometers)
there are magma bodies undergoing cooling, still in a fluid state or in a process
of solidification, and releasing heat. In other areas, where magmatic activity
does not exist, the heat accumulation is due to particular geological
conditions of the crust such that the geothermal gradient reaches anomalously
high values.
The extraction and utilization of
this large quantity of heat requires a carrier to transfer the heat toward
accessible depth beneath Earth’s surface. Generally, the heat is transferred
from depth to subsurface regions firstly by conduction and than by convection,
with geothermal fluids acting as the carrier in this case. The fluids are
essentially rainwater that has penetrated into the Earth’s crust from the
recharge areas, has been heated on contact with the hot rocks, and has
accumulated in aquifers, occasionally at high pressure and temperatures (up to
above 300oC). These aquifers (reservoirs) are the essential parts of
most geothermal fields.
In most cases the reservoir is
covered with impermeable rocks that prevent the hot fluids from easily reaching
the surface and keep them under pressure. We can obtain industrial production
of superheated steam or steam mixed with water, or hot water only, depending on
the hydrogeological situation and the temperature of rocks present.
Wells are drilled into the reservoir
to extract the hot fluids, and their use depends on the temperature and
pressure of the fluids: generation of electricity (the most important of the
so-called high-temperature uses) or for space heating and industrial uses
(low-temperature uses).
Geothermal fluids, as opposed to
hydrocarbon fields, are generally systems with a continuous circulation of heat
and fluid, where fluid enters the reservoirs from the recharge zones and leaves
reservoir by reinjecting through wells the waste fluids from the utilization
plants. The reinjection process may compensate for at least part of the fluid
extracted by production, and will to a certain limit prolong the commercial
lifetime of the field. Geothermal energy is therefore to some extent a
renewable energy sources, hot fluid production rates tend to be much larger
than recharges rates. “
“Geothermal utilization is divided in two
categories – electrical energy production and direct use. Conventional
electrical power production is limited to fluid temperature above 150oC,
but considerably lower temperatures can be used in binary systems, also called
organic Rankine cycles (in this case the outlet temperatures of the geothermal
fluid are commonly above 85oC). The ideal temperature of thermal
waters for space heating is about 80oC, but larger radiators in the
houses or use of heat pumps or auxiliary boilers means that thermal water with
temperatures only a few degrees ambient temperature can be used beneficially.”
From:
Enrico Barbier (1998)-
Geothermal Resources, In:Proceedings, ISS, Heating greenhouses with geothermal
energy, ed. K.Popovski and A.Rodriges, Ponta Delgada (Azores), Portugal, Sept.,1998.
Enrico Barbier (1998)
- The status of world geothermal development. In:Proceedings, ISS, Economy of
integrated geothermal projects, ed. K.Popovski and A.Rodriges, Ponta Delgada
(Azores), Portugal, Sept.,1998.
