Carel FLSTDMAHUE, User Manual

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ENG
“FLSTDMAHUE” +030220961 - rel. 1.1 - 28.08.2019
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Set_enth
E
MAX
diff_enth
MIN
Req_enth
Key
Req_enth Control request
diff_enth Enthalpy control differential
Set_enth Enthalpy set point
9.9 Heat recovery
Definition
If the AHU is fitted with a heat recovery unit, the heat contained in the
exhaust air is recovered and transferred to the primary air so as to preheat
or precool it, if the conditions are favourable: consequently freecooling/
freeheating and heat recovery are mutually exclusive. When the AHU is in
heat recovery mode, the bypass damper on the heat recovery unit is closed.
In cascade control the request is shared between the various devices available.
Heat recovery is thus considered a free source of energy free, activated with
priority in cascade control in cooling and heating modes.
Enabling
The heat recovery function can only be enabled if a heat recovery unit is
installed and enabled. The bypass damper (Ha01) may not be necessary.
Below is a list of possible combinations.
Ha14 Type of heat recovery
Bypass
damper Cross flow Double ON/OFF
coil
Modulating
run-around coil Modulating
wheel On/Off
wheel
No YES YES
YES
YES YES
On/Off YES YES YES YES YES
Modulating YES YES YES NO YES
Tab. 9.e
ON/OFF Devices
Screen index Display description Enable
Hb39 Heat recovery unit pump (double coil) Position ≠ 0
Heat wheel (ON/OFF) Position ≠ 0
Bypass damper (ON/OFF) Position ≠ 0
Hb69 Heat recovery pump (analogue output) Position ≠ 0
Tab. 9.f
Modulating devices
Hb63 Heat wheel Position ≠ 0
Hb56 Bypass damper (ON/OFF) Position ≠ 0
Tab. 9.g
Types of heat recovery unit
Cross - flow heat recovery unit: no dedicated output.
The efficiency of the heat recovery unit can be displayed once the probes
have been configured: outside (T1), return (T3), temperature after heat
recovery unit (T4), according to the formula shown in the figure:
T1
T 2
T3
T4
7
20
9 18
E x tern a l a ir
Intern a l a ir
η = T4 - T1
T3 - T1
HE A T EX C H AN GE R
Screen index Temperature probe
Hb03 Outside
Hb02 Return
Hb23b After heat recovery unit (supply)
Hb15 Exhaust
D88 Heat recovery unit efficiency
Run - around coil heat recovery unit: only one digital output is activated,
which starts the pump. If the bypass damper has On/Off operation, activation
of the pump will be the reverse to the damper. With modulating dampers, the
pump will remain on while heat can be recovered and the bypass damper
will modulate the quantity of heat recovered, depending on the request.
Modulating heat wheel: an analogue output is managed for modulation
of wheel rotation speed and an On/Off output for the bypass damper. The
heat recovery request acts directly on the wheel speed, which may have a
minimum limit set. The bypass damper will be activated when no heat can
be recovered.
On/Off heat wheel: an on/off output is managed to control the heat recovery
unit. The bypass damper will be activated when no heat can be recovered.
Screen index Display description Selection
Ha14 Heat recovery type 1: None ¦
2: Plate exchanger ¦
3: Run-around coil ¦ 4: Modulating rotary ¦
5: On/Off rotary
Note: with on/off or modulating heat wheels, heat can also be recovered by
controlling the enthalpy conditions.
The function has two stages:
1.
check whether the return temperature or enthalpy conditions are
favourable compared to the outside air conditions;
2. the request of summer/winter acts on the speed of the heat wheel or on
the modulating bypass damper.
Activation
Note: the following graphs consider the outside temperature to be
constant. Heat recovery is activated when the return temperature is
closer to the temperature set point than the outside temperature.
RECOVER Y IN COOLING (cooling request active)
Set
ABILITAZIONE/
ENABLE
RetT ExtT
T
delta
ON
diff
OFF
ON: ExtT-RetT> delta_recov; OFF: ExtT-RetT< delta_recov – diff_recov
RECOVER Y IN HEATING (heating request active)
Set
ABILITAZIONE/
ENABLE
RetT ExtT
T
delta_recov
ON
diff_recov
OFF
ON: RetT-ExtT-> delta_recov; OFF: RetT-ExtT < delta_recov – diff_recov
Key
diff_recov Recovery differential Set Set point
RetT Return temperature delta_recov Recovery delta
ExtT Outside temperature
Screen
index Display description Def Min Max UOM
Gfc31 Heat recovery temperature activation
Delta recovery
5 0 99.9 °C
Differential 3 0 99.9 °C
Note: for heat recovery by enthalpy, only applicable to the wheel, the
same rules apply for activation. The enthalpy delta is fixed at 4 kJ/kg and
the differential is fixed at 2 kJ/kg.