Carel FLSTDMAHUE, User Manual

Page: 43 / 94

ENG
“FLSTDMAHUE” +030220961 - rel. 1.1 - 28.08.2019 43
Based on the efficiency of the heat recovery unit, a deviation (delta) must
be set between the return and outside temperature. The more efficient the
heat recovery unit, the lower the delta. The differential (diff_recov) is used
to switch off the devices in advance, so as to reduce energy consumption,
above all relating to operation of the heat wheel or pump for the run-around
coil heat recovery unit. For heat recovery units consisting of a plate heat
exchanger, on the other hand, flow through the heat exchanger increases
pressure drop and consequently fan power consumption.
Control
Control by temperature depends on the set point and the temperature
differentials, based on the percentage of request reserved for the heat
recovery unit. See the paragraph “Cascade control”. As regards control by
enthalpy, the control differential needs to be set, based on which the heat
wheel rotation speed will vary. For run-around coil heat recovery units, the
pump will be on or off according to the activation graphs shown in the
previous paragraph.
Set_enth
E
100%
diff_enth
0%
Wheel_speed
Key
Wheel_speed Heat wheel speed
diff_enth Enthalpy control differential
Set_enth Enthalpy set point
E Enthalpy
Screen index Display description Def Min Max UOM
Gfc31 Enthalpy control
Enthalpy differential
5 0 99.9 kJ/kg
Heat recovery unit frost protection function
The heat recovery unit frost protection function prevents problems due to
frost forming on the heat recovery unit. The actions undertaken depend on
the type of heat recovery unit: in any case, the bypass damper is fully open.
Given that the exhaust air has a defrosting effect:
•
the run-around coil heat recovery unit pump continues operating;
•
the heat wheel continues operating.
Activation and control
To enable the function, define the probe that measures the temperature,
enable (optional) a defrost heater and define the activation set point and
differential. For modulating heat wheels, the speed during frost protection
can also be selected.
Screen index Display description Selection
Ha14 Heat recovery type
…
Defrost probe
None ¦ External-Return (*)
¦ Exhaust ¦ External
Recovery heater No ¦ Yes
Hb41 Heater heat recovery unit Position ≠ 0
(*) Arithmetic average between the 2 probes.
Screen index Display description Def Min Max UOM
Gfc32 Heat recovery defrost
Setpoint
-1 -99.9 10 °C
Differential 4 0 99.9 °C
Heater offset 3 0 99.9 °C
Minimum speed (enthalpy wheel) 100 0 100 %
Hc18 Heat recovery
Defrost delay
Start
120 0 999 s
End 60 0 999 s
Clogged alarm delay 60 0 300 s
Once the heat recovery unit frost protection alarm is activated, for example
when the frost protection thermostat contact closes, a delay from the start of
the signal and a delay from the end of the signal can be set.
VISUALIZATION
A
ALARM
ON
OFF
ON
OFF
B
Key
A Start B End
Below is a graph showing activation of the damper and frost protection
heater, based on the defrost probe reading.
o ff set
O N
O FF
O FF
A
B 1
O N
B
di ff
di ff
S et
Key
A Heat recovery unit frost protection heater Set Setpoint
B Bypass damper offset Offset
B1 Defrost probe diff Differential
9.10 Cascade control
The cooling request and heating request can be shared between freecooling/
freeheating and the coil, and between the heat recovery unit and the coil.
Screen index Display description Def Min Max UOM
Gfc20 Cooling cascade
Freecooling
50 0 100 %
Coil 50 0 100 %
Recovery 40 0 100 %
Coil 40 0 100 %
Gfc21 Heating cascade
Freeheating
50 0 100 %
Coil 50 0 100 %
Recovery 40 0 100 %
Coil 40 0 100 %
As regards heating, the heating request can be further shared between the
preheating and reheating coils.
Note : overlapping operation of the preheating and reheating coils is
also possible.
Screen index Display description Def Min Max UOM
Gfc22 Heating cascade
Reheating
80 % 0 100
Example 1: partition of request between devices.
100%
0%
Req
Heating Cooling
Free_heat/ Reheat
Preheat
Cool Free_cool/
recovery
Device_opening
100% 50%
recovery
33% 66%
100%