Anti-Freezing Control For Winter - Hitachi SAMURAI Series Service Manual

2. Control Functions
Control functions on the module

2.1.7 Anti-Freezing Control for Winter

When operation is stopped during winter, the temperature of cold water decreases and may induce freezing of the water-
side heat exchanger or the piping system. The outdoor temperature and cold water temperature are detected, to operate
the cold water circulation pump automatically, and protect the chiller unit from freezing.
There are 2 modes to define the run/stop conditions of the cold water circulation pump. Select the most appropriate mode
depending on the system structure and usage purpose.
1 Mode I (Factory default)
Mode I is used mainly for systems composed of 1 chiller unit, or those with fixed flow. Since the entire water circuit is
protected, the cold water pump is operated from a comparatively high water temperature.
Example of system where Mode I is recommended
a. When outdoor temperature is under 2ºC
When outdoor temperature falls under 2ºC, the operation order of cold water circulation pump is output, and the
continuous operation of the cold water pump starts automatically. Here, when cold water temperature becomes
higher than 15ºC, operation becomes intermittent, with the pump running for 5 minutes, then stopped during 55
minutes. When cold water temperature rises even further, above 25ºC, the cold water circulation pump operation
order output is set to OFF.
b. Automatic release of anti-freezing operation
This operation is released when outdoor temperature becomes higher than 4ºC.
25
△
15
△
10
2
(a) When outdoor temperature is decreasing
Explanation diagram of automatic operation control of the pump to prevent freezing in winter (Mode I)
17
SMGB0097 rev.0 - 07/2015
Load
Chiller
unit
25
More than
Less than
15
More than
Less than
More than 10
Less than
4
(b) When outdoor temperature is increasing
3-Way Valve
△
Cold water
circulation pump
More than
Less than
△
More than
Less than
△
More than
Less than
2 4
planation of codes
Ex
Continuous pump operation

Intermitent pump operation
5 minutes run
55 minutes stop
× Pump stop
→ C hange trend of cold water
temperature
2