Carrier AquaSnap 30RB 672 - Operating Range (Desuperheater Option); Control Configuration with Desuperheater Option

48
11.3.4 - Installation
The water supply of each desuperheater is arranged in
parallel. 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. Water flow control and balancing can be
done by reading the pressure drop in the heat exchangers.
This must be identical on all of them with the total water flow
rate given by the "Electronic catalogue" selection program.
Refer to the pressure drop curves below to control the
balancing valves before starting up the installation. The water
flow control of each desuperheater can de refined when the
unit operates at full load by trying to obtain leaving water
temperatures that are absolutely identical for each circuit.


Heat exchanger water ow rate, l/s
1 Circuit with one compressor
2 Circuit with two compressors
Heat exchanger pressure drop, kPa
Operation of the pump (see typical diagram - item 20 of
chapter 11.3.3) of the desuperheater water circuit can be
linked to the start-up of the first unit compressor. This requires
the installation of an additional electronic board in the
control box: option 156, Energy Management Module.
Output No. 25 of the additional board of this option allows
control of the pump operation - the pump will start up when
the unit starts. A flow switch (item 29) can be installed to
generate an alarm if there is a problem with the pump.
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 desuperheater is 25°C. This may
require the use of a three-way valve (item 31), with a control-
ler and the sensor controlling the minimum required entering
water temperature.
The desuperheater water loop must include a safety valve
and an expansion tank. When selecting these, consider the
water loop volume and the maximum temperature (120°C)
when pump operation is stopped (item 20).
11.3.5 - Operating range
  
Entering water temperature at start-up °C 25* 75
Leaving water temperature during operation °C 30 80
  
Outside operating temperature °C 0** 46
* 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.
** The minimum outside temperature is 0°C; -20°C with the winter operation option.
11.3.6 - Control configuration with the desuperheater option
This configuration allows the user to enter a setpoint that is
relative to the minimum condensing temperature (default
= 30°C) to increase the heating capacity reclaimed at the
desuperheaters, if required. The percentage of the reclaimed
heating capacity compared with the total capacity rejected
by the condenser increases in proportion to the saturated
condensing temperature.
For the setpoint control of the minimum saturated condensing
temperature refer to the Pro-Dialog 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 (depending
on the number of compressors per unit circuit).
• The water entering temperature in the desuperheater
as well as the condenser entering air temperature. See
the curve below.




0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
40 45 50
55
60
A
B
C
Desuperheater entering water temperature,°C
Coecient of the reclaimed heating capacoty
A Entering air temperature = 45 °C
B Entering air temperature = 35 °C
C Entering air temperature = 20 °C
3 Circuit with three compressors
4 Circuit with four compressors