Page 48 - Low Temperature Energy Systems with Applications of Renewable Energy

36 Low-Temperature Energy Systems with Applications of Renewable Energy

outside. There it picks up heat from the surrounding air and evaporates (EV). The cold
refrigerant vapor is shunted into the compressor where it is repressurized, its temper-
ature increases, and the cycle repeats.
In cooling mode (B), with the valve pointed at “C”, the discharge side of the
compressor is directed outside where the hot vapor is condensed by the surrounding
air and dissipates heat to the environment. The throttle valve now sees flow in the
opposite direction, but still reduces the pressure thereby lowering the refrigerant tem-
perature and directs it inside the house. There it removes heat and evaporates. The low-
pressure, low-temperature refrigerant vapor is shunted into the compressor where it is
repressurized, its temperature increases, and the cycle repeats.
In large buildings with many rooms, some of which may have higher heat loads
than others, it is possible to use heat pumps to cool some rooms while simultaneously
heating others. This is usually the case for large schools or hospitals where the heat or
cooling needs depend on the building orientation relative to the sun.

1.7.2 Heating mode design guidelines

The following practical guidelines offer design considerations when operating heat
pumps in the heating mode.
• The selection of heating system
When designing the heating system with heat pumps it is very important to select the type
of heating device correctly. Radiant panel heating systems that are placed in the floor or on
walls and do not require high temperature of a heat carrier are the most profitable ones. The

advantage of these systems is that it is possible to lower the room temperature by 2e3 C due
to heat transfer by means of evaporation. One cannot forget that maximal temperature at the

ordinary heat pump outlet is 55e62 C so that is necessary to take into account when the
types and dimensions of heating devices are chosen. Radiator systems require a higher tem-

perature, 90e95 C, and floor radiation and ceiling water panels, require a temperature of

55e60 C. Therefore, the choice of heat application of a heat pump depends on the type
of heating system.
• Heating by means of panels placed in the floor (the “warm floor system”)

This system is profitable due to the fact that the heat carrier temperature of 35 Cis
enough for heating. Its disadvantage is the limitation of maximum power of not more than
2
96 W per m of heating floor area. That is why the combination of the “warm floor” system
with radiator and convector heating devices or fancoils is more widely used. It is advisable to
use the “warm floor” system in combination with fancoils. This is because most fancoils
operate at a 5 C temperature difference with the heat carrier. It is particularly advisable

to use fancoils in the heating system with an ordinary heat pump that operates for room cool-
ing in summer. In such a case a building can be heated in winter and cooled in summer by
means of one system (see the previous section) that reduces greatly capital costs at the build-
ing construction stage.
• Heating by means of panels, placed in the floor, with heating radiators
This variant requires the use of a thermohydraulic regulator (THR) and its own regulating
collector to operate properly. In addition to pipe laying, it is necessary to have a circulating
pipe, which would provide the cycle with water between a THR radiator and heat pipe. A