Schreiber Chillers 15medWC - Manual (Page 24)

Chilled Water Reservoir
The insulated chilled water reservoir inside the chiller is designed to eliminate wide swings in
temperature during changing loads. It also provides a convenient location from adding water and
glycol to the system.
A float in the reservoir tells the controller that the water level is too low. The low lever alarm
still allows the chiller to run, but water must be added immediately. Since the reservoir is open to
the atmosphere, a small amount of water may be lost due to evaporation. The local weather
conditions will dictate how often the reservoir should be topped off. If water needs to be added
more than once a month, there is a possibility of a leak in the system.
Flow Switch
There is a flow switch on each piping loop to protect the chilled water system. When the switch
is open (no flow) the pump on that loop will not run. If the flow switch is open on the GCHE
loop, it will also lock out the compressors to keep from freezing the evaporators. On pump
startup, there is a short time delay 15-25 seconds, to allow flow to be established before
generating an error. When running, there is another time delay of 5-10 seconds to allow for flow
disruptions caused by a changed in valve position or bubbles in the system.
Backflow Kit
Since the chilled water reservoir is vented to the atmosphere, water in pipes above the water
level of the reservoir will flow back and overflow the reservoir when the pumps are shut off. To
prevent this, a backflow kit consisting of a solenoid valve on the return line on each loop , and a
check valve on the GCHE loop is provided. The solenoid valve is a normally closed valve that is
energizes whenever the pump contactor is energized.
The backflow kit also keeps the entire piping loop full of water during shut down. In some cases
(including startup) the pump will start when the pipe is not full. Since the flow switch is on the
return line, the pump may alarm on a flow error on pumped startup, because the time required to
fill the pipes and trigger the flow switch was longer than the time delay at pump startup. The
alarm can be reset, or the flow time delay temporarily increased to allow for pipe filling.