Page 66 - Low Temperature Energy Systems with Applications of Renewable Energy

Characteristics of low-temperature energy sources for heat pumps 55

It is shown from Table 2.3 that the distance between the wells must be increased with
an increase of water consumption. The table is valid for soils having about 20% porosity.
When porosity is 10%, the distance should be increased by 5%, and when it is 30%, it
should be decreased by 5%. If natural water movement in the water-bearing bed is
detected during the hydrological test, the disposal well must be placed at a distance
no less than 5 m from the water well and in the direction of the water movement [5].
The system of using soil-water heat can be simplified [5] if the object with the heat
pump is located near a pond and the water-bearing bed is naturally fed with the water
out of that pond (Fig. 2.3).
This system differs from the previous one by the fact that the cooled water is drained
into the pond rather than the water-bearing bed, the former being hydraulically connected
with the latter. In order that water from the pond does not lower the soil-water temper-
ature that is used in the heat pump, the well 4 must be drilled at a distance from the pond
shoreline according to Table 2.3 considering the pond to be similar to the receiving well.
If the soil water quality does not meet the requirements of the heat pump manufacturer
and it is considered to be chemically aggressive, then in such a case the scheme shown in
Fig. 2.4 can be used. The soil water with aggressive properties is cooled in the heat
exchanger 9, transferring heat to glycol that circulates in the intermediate circuit between
the heat exchanger 9 and heat pump evaporator. Soil water cooled in the heat exchanger
is drained through the well 5 into the water-bearing bed or pond close to where the object
with the heat pump is located. When soil water with aggressive properties is used, the
heat pump efficiency decreases and it is desirable to examine the possibility of using
other heat sources, in particular soil heat by means of a soil heat exchanger.

2.3.2 Water of open ponds
When constructing buildings near open ponds, the possibility arises of using the ther-
mal energy of these ponds as sources of low-potential heat in the heat pump. The

Fig. 2.3 Schematic of using filtrated water from a pond: see Fig. 2.2 for terms; 8, pond.