Description Of The Refrigeration Cycle With Heat Recovery; Controlling The Heat Recovery Circuit And Installation Recommendations - Daikin EWYD-BZ Series Installation, Maintenance & Operation Manual

Description of the refrigeration cycle with heat recovery

The low-temperature refrigerant gas from the evaporator is drawn by the compressor through the electric motor, which
gets cooled by the refrigerant. It is subsequently compressed and during this process the refrigerant mixes with the oil
from the oil separator.
The high-pressure oil-refrigerant mixture is introduced into the centrifuge-type high-efficiency oil separator, where the oil
is separated from the refrigerant. The oil accumulated on the bottom of the separator is forced by the pressure difference
back into the compressor while the oil-free refrigerant is sent to the partial recovery heat exchanger where it cools down
by reducing its superheat temperature while warming the water which travels through the heat exchanger. From the
outlet of the heat exchanger, the refrigerant fluid first passes through the 4-way valve, then it enters the air heat
exchanger (in chiller mode) or the water heat exchanger (in heat pump mode), where it is condensed and subcooled
while heating the outside air (forced ventilation) or the water respectively.
The subcooled fluid flows through the high-efficiency filter dryer and then it reaches the expansion element through
which a pressure drop takes place resulting in the vaporisation of part of the refrigerant liquid.
The result at this point is a low-pressure and low-temperature liquid-gas mixture that is introduced into the water heat
exchanger (chiller mode) or air heat exchanger (heat pump mode), where it takes the heat required for vaporisation.
After the liquid-vapour refrigerant has been evenly distributed into the tubes of the heat exchanger, it exchanges heat
with the water to be cooled (in chiller mode), thus reducing the water temperature, or with the outside air (in heat pump
mode) while it gradually gets completely vaporised and then superheated.
Once it has reached the superheated-vapour state, the refrigerant leaves the heat exchanger and is once again taken
into the compressor to repeat the cycle.

Controlling the heat recovery circuit and installation recommendations

The partial heat recovery system is available in both chiller and heat pump mode and is not managed and/or controlled
by the machine. The installer should follow the suggestions below for best system performance and reliability:
1. Install a mechanical filter on the heat exchanger inlet pipe.
2. Install shut-off valves to isolate the heat exchanger from the water system during periods of inactivity or system
maintenance.
3. Install a drain valve that allow the heat exchanger to be emptied in the event that air temperature is expected to
fall below 0°C during periods of inactivity of the machine.
4. Install flexible anti-vibration joints on the heat recovery water inlet and outlet piping, so that transmission of
vibrations, and therefore of noise, to the water system is kept as low as possible.
5. Do not load exchanger joints with the weight of the heat recovery piping. The water joints of the exchangers are
not designed to support the weight of the piping.
6. Should heat recovery water temperature be lower than ambient temperature, it is advised to switch off the heat
recovery water pump 3 minutes after having switched off the last compressor.
Heat recovery has been designed as an additional source of external heat; in fact, the availability of recovered heat is
guaranteed only with a cooling circuit which functions when cooled water is requested.
In particular, it cannot function correctly if the water entering the exchanger is cooler than 35°C for periods exceeding
the normal time needed for the system to reach normal running conditions (about 15 minutes): functioning for
prolonged periods under such conditions can cause malfunctions in the cooling circuit and will trigger off the
protective devices. The installer must also ensure that the temperature of the water in the recovery circuit reaches
the minimum value allowed as soon as possible.
For the same reasons, there must be no water flowing through the exchanger when the cooling circuit is switched off.
ATTENTION
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