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18 - PARTIAL HEAT RECLAIM USING DESUPER-HEATERS (OPTION 49)
18.3 - Installation
The water connections on the desuperheater water inlets and
outlets must not cause any mechanical local constraint at the heat
exchangers. If necessary, install flexible connection sleeves.
Install water flow control and balancing valves at the heat
exchanger outlet.
The volume of the desuperheater circuit water loop must be as
low as possible so that the temperature can increase rapidly when
the unit is started up.
The minimum entering water temperature at the desuper-heater
is 25°C. This requires the use of a three-way valve (item 31 in the
diagram), with a controller and the sensor controlling the minimum
required entering water temperature.
The desuperheater water loop must include a relief valve and an
expansion tank. When selecting these, consider the water loop
volume and the maximum temperature (90°C) when pump
operation is stopped (item 20 in the diagram).
18.4 - Control configuration with the
desuperheater option
The unit can operate in two modes.
18.4.1 - Efficiency priority mode (standard)
In this mode unit control optimises unit efficiency. Heat reclaim is
based on the saturated condensing temperature. The percentage
of the reclaimed heating capacity compared with the total capacity
rejected by the condenser increases in proportion to the saturated
condensing temperature. This temperature is directly linked to the
condenser entering air temperature (entering air temperature in
cooling mode and water temperature in heating mode).
18.4.2 - Reclaim priority mode
In cooling mode only this configuration allows the user to enter a
setpoint that is relative to the minimum condensing temperature
(default = 40°C) to increase the heating capacity reclaimed at the
desuperheaters, if required. This configuration is only effective if the
desuperheater contact is activated on the control board (user
connection block). This function is not available for 30RQSY units.
For setpoint control of the minimum saturated condensing
temperature and to find the position of the connection block on
the board refer to the 30RB/RQ Touch Pilot Junior control manual.
Other parameters directly affecting the effective capacity reclaimed
at the desuperheater are principally:
• The unit load rates, that decide whether the unit operates
at full load (100%) or part load.
• The water entering temperature in the desuperheater as
well as the condenser entering air temperature.
18.5 - Operating limits
Desuperheater
Entering water temperature at start-up
Leaving water temperature during operation °C
Air condenser
Outside operating temperature
(1) The entering water temperature at start-up must not be lower than 25°C. For
installations with a lower temperature a three-way valve is necessary.
Minimum Maximum
°C
25
60
(1)
30
65
Minimum Maximum
°C
-10
46
51
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