Mitsubishi Electric PUHY-P250YJM-A Data Book page 46

(5) Practical System Examples and Circulation Water Control
Since the water heat source CITY MULTI is of water heat source system, versatile systems can be constituted by combining
it with various heat sources.
The practical system examples are given below.
Either cooling or heating operation can be performed if the circulation water temperature of the water heat source CITY
MULTI stays within a range of 10~45°C [50~113°F]. However, the circulation water temperature near 32°C[90°F] for cooling
and 20°C[68°F] for heating is recommended by taking the life, power consumption and capacity of the air conditioning
units into consideration. The detail of the control is also shown below.
Example-1 Combination of closed type cooling tower and hot water heat storage tank (using underground hollow slab)
Cooling water pump
By detecting the circulation water temperature of the water heat source CITY MULTI system with T1 (around
32°C[90°F]) and T2 (around 20°C[68°F]), the temperature will be controlled by opening/closing V1 in the summer and
V2 in the winter.
In the summer, as the circulation water temperature rises exceeding the set temperature of T1, the bypass port of V1
will open to lower the circulation water temperature. While in the winter, as the circulation water temperature drops,
V2 will open following the command of T2 to rise the circulation water temperature.
The water inside the heat storage tank will be heated by the auxiliary heat source by V3 being opened with timer
operation in the night-time. The electric heater of the auxiliary heat source will be controlled by T3 and the timer. The
start/stop control of the fan and pump of the closed type cooling tower is applied with the step control of the fan and
pump following the command of the auxiliary switch XS of V1, that operates only the fan at the light load while the fan
and pump at the maximum load thus controlling water temperature and saving motor power.
Closed type
cooling tower
T1~T4 : Thermostat
V1~V2 : Proportional type
motor-driven 3-way valve
V3 : Motor-driven 3-way valve
XS : Auxiliary switch
MG : Magnetic switch
EH : Electric heater
Expansion tank
Circulation
water pump
V1
XS
T1
Heat
source
unit
Heat exchanger
Heat storage
tank pump
Heat storage tank
- 37 -
T2
V2
EH
MG
T4
V3
Auxiliary
heat source
T3