hajdu HB300C Manuel De Mise En Service, D'opération Et D'entretien page 64

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Operation explanation
4.2.
According to the facts mentioned above, the "energetic
capacity" of heat pump is based on heat transfer through heat
extraction from free source (in this case, it is the environmental air)
with lower temperature than the material to be heated (in this case, it
is the water in the tank of the water heater). Electric power is required
for the operation of the compressor (that leads to change of state of
matter of the cooling fluid within the cooling circuit), thus for the transfer
of heat energy. Cooling fluid passes along a closed hydraulic circuit
where the fluid changes into liquid or gaseous state of matter in
connection with its temperature and pressure. The main elements of
the hydraulic circuit (Figure 2.2-1) are the following:
1 compressor, which ensures cycle running through increasing
–
the pressure and the temperature of the cooling fluid (which has a
gaseous state of matter in this cycle).
2 – first heat exchanger located in the water tank of the water
heater: heat exchange between the cooling fluid and the sanitary
water to be heated up is produced on its surface. As in this phase, the
state of matter of the warm cooling fluid changes and it condenses
into liquid while transferring its heat to the water, this heat exchanger
is defined as condenser.
3 – expansion valve: it is an equipment through which the
cooling fluid passes just when its pressure and temperature are
reducing, following the expansion of the liquid perceivably as a result
of pipe cross-sectional area increase above the valve.
4 – second heat exchanger located in the upper part of the water heater, which
surface has been increased by fins. The second heat exchanger performs heat
exchange between the cooling fluid and the environmental air drifted artificially by
either the free source or by a special fan in a proper way. As in this phase, the cooling
fluid evaporates and extracts heat from the environmental air, this heat exchanger is
defined as evaporator.
As heat energy is able to flow from a higher temperature level to a lower
temperature level exclusively, the temperature of the cooling agent located in the
evaporator (4) has to be lower than the environmental air acting as free source, in the
same time, in order to transfer heat, the cooling agent located in the condenser (2) has
to possess a temperature higher than the temperature of the water to be heated in the
tank.
The temperature difference within the heat pump circuit is produced by the
compressor (1) located between the evaporator (4) and the condenser (2) and by the
expansion valve (3), due to physical features of the cooling fluid.
The efficiency of the heat pump circuit can be measured by the coefficient of
performance
(COP). COP is the ration of incoming energy into the appliance (in this case, it is the
heat transferred to the water to be heated) to the electric power used (by the
compressor and the supporting equipment of the appliance). COP may change
depending from the type of the heat pump and the related operational circumstances.
A value of 3 for COP means, for example that the heat pump transfers 3 kWh to the
material to be heated after 1 kWh electric power used, from which 2 kWh is extracted
from the free source. The rated COP values of HB300(C(1)) heat pump water heater
Figure 2.2.-1.