Page 62 - Low Temperature Energy Systems with Applications of Renewable Energy

Characteristics of low-temperature energy sources for heat pumps 51

2.2.2 Underground constructions

Significant potential heat variations, operational irregularities, and the distance from
potential heat consumers can prevent the effective use of ventilation air. However,
there are no such disadvantages for ventilation exhausts from certain underground ob-
jects, for example, subways, metropolitan railways, and coal mines. Due to the high
thermal inertia of these objects, the temperature of ventilation exhausts is not lower

than 12e16 C even in the coldest season, which guarantees a high heat pump COP
and economic competitiveness. Metropolitan railways and mines use external heat en-
ergy for their own needs and thus are the consumers of the used ventilation waste heat.
The effectiveness of using heat pumps in metropolitan railways, for example, has
been demonstrated experimentally by designing and constructing a test heat pump sys-
tem in a railway station in Kiev, Ukraine [7]. Test runs showed that under metropolitan
conditions the COP of the off-the-shelf ambient-air heat pump was significantly higher
than the certified value of 3.1 and reached 4.9 in the air-heating mode. The main tech-
nical characteristics of the base case of the heat supply and heat pump system for the
Kiev system are given in Table 2.1.
Furthermore, it should be noted that, since heat pumps can be operated in both heat-
ing and cooling modes, the use of heat pumps in heat ventilation metropolitan systems
allows combining functions of separate heating, ventilation, and air conditioning sys-
tems in one heat pump system. Thus they can cool ventilation air in a warm period
which improves both working conditions for staff as well as general technical and
economical heat pump performance.

Table 2.1 Technical characteristics of base case and heat pump systems of heat supply.
Values
Heat pump system
Base
Item Units case Calculated Actual

Calculated heating temperature C 21 21 21
Average heat capacity of room heating kW 26.2 26.2 26.2
Annual heating period h 4500 4500 4500
Annual heat consumption GJ 424.4 424.4 424.4
Heat pump chilling capacity kW e 21.6 21.6
Electric power for powerhouse hall cooling kW 30.4 5.6 5.35
system and serviced heating rooms
Annual powerhouse hall cooling period h 6935 6935 6935
Annual electricity consumption MWh 210.82 38.84 37.10
COP e e 5.4/4.7 a 5.6/4.9 a
a
Lower values include electricity used to drive an additional axial ventilator.