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4.4 Secondary boiler back up systems (either/or systems)
For plant where a secondary back up is required this can be achieved by the use of a plate heat exchanger
placed within the flow line.
The ideal situation is that either the heat pumps will be providing the full load or the back up boiler i.e. An
either or system. This is because if the return temperature from the heating distribution system is higher
than the control set point in the heat pump the heat pump will not operate and the back up boiler will
take the whole load. Care must be taken when setting up the BMS, as it may take some time for the sys-
tem to come up to temperature.
By using a plate heat exchanger the two systems are hydraulically separated.
Abbreviations
2PCV - 2 port control valve
AAV - Automatic air vent
HTG F - Heating flow
HTG R - Heating return
IV
- Isolation valve
LTHW - Low temperature hot water
It is recommended that the BMS/Instrumentation Engineer contact Kensa if unsure on any aspects of
the control of the system, i.e. Regarding:-
•
Time delays
•
Expected temperatures
•
Compressor run-times
•
Compressor starts per hour.
•
etc
Plant Room Heat Pump Manual Version 11.1
Page 12 of 34
NRV - Non return valve
P
- Pressure gauge
PV
- Purge valve
STR
- Strainer
T
- Temperature gauge
TP
- Temperature/ pressure sensor
Fig 4 Secondary boiler back up
From Heat Pumps
To Heat Pumps
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