Daikin RDT, Руководство по установке и обслуживанию, Страница: 49 / 152

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www.DaikinApplied.com 49 IM 893-10 • ROOFPAK SINGLEZONE UNITS
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The following sequences of operation are for a typical “D”
vintage applied rooftop unit equipped with MicroTech III, an
economizer, mechanical cooling, 3 to 1 turn down burner,
variable frequency drives (VFD), a return air fan and an
external time clock. These sequences describe the ladder
wiring diagram logic in detail; refer to Wiring Diagrams on page
51 as you read them. Note that your unit’s sequences of
operation may vary from those described here. Refer to the
wiring diagrams supplied with the unit for exact information.
For detailed description of operation information relating to
the MicroTech III controller’s software, refer to the appropriate
operation manual (see Table 1 on page 3 ). These manuals
describe the various setpoints, parameters, operating states,
and control algorithms that affect rooftop unit operation.
Power-up
When primary power is connected to the unit, 115 V (ac)
power is fed through control circuit transformer T1 and control
circuit fuse F1C (line 166, Figure 61 ) to compressor crankcase
heaters HTR-1, HTR-2, HTR-3 and HTR-4 (lines 836 - 848,
Figure 67 ).
When system switch S1 (line 203, Figure 65 ) is closed, low
voltage transformers T2 (line 203, Figure 65 ), T3 (line 251,
Figure 65 ) and T9 (line 802, not shown) energize, and 115 V
(ac) power is supplied to the following:
• The supply fan VFD (line 135-137, Figure 61 )
• M40A to energize the return fan VFD (line 147-149,
Figure 61 )
• Heating control panel (line 603, Figure 66 )
• Economizer actuator (lines 256-257)
Transformer T2 supplies 24 V (ac) power to terminals
24V and COM on the main control board MCB (lines 207
and 208). Transformer T2 supplies 24 V (ac) power to the
following (see Figure 60 and Figure 61 ):
• Switch S7 On-Auto-Off (line 217)
• Enthalpy sensor OAE (line 247)
• External time clock contacts (line 215)
• Airflow interlock switch PC7 (line 228)
• Dirty filter switches PC5 and PC6 (lines 242 and 247, not
shown)
• Gas furnace alarm relay R24 (line 225, not shown)
• Freezestat switch FS1 (line 244, hot water or steam heat
only, not shown)
• Smoke detectors SD1 and SD2 (line 237)
The time clock, S7 switch, and emergency shutdown
terminals (lines 217-222) control fan operation.
NOTE: Unit ships with factory installed jumpers between TB2
101 and 105 and between 101 and 106.
Fan Operation
When the main control board (MCB) commands the supply and
return fans to start, the unit enters the Startup operating state.
As a result, a 3-minute timer is set, output MCB-BO3 (line 307)
energizes, and relay R26 energizes (line 306, not shown).
After the 3-minute timer expires, the unit enters the Recirc
operating state. As a result, output MCB-BO1 energizes relay
R67 (line 401). This gives a start signal to supply fan drive
AFD10 (line 445). Four seconds after MCB-BO1 is energized,
output MCB-BO2 energizes relay R68 (line 404). This gives a
start signal to return fan drive AFD20 (line 445).
Within 120 seconds after the fans start, the controller expects
airflow switch PC7 (line 228) to close and thus energize binary
input MCB-BI6. (If MCB-BI6 does not energize, the controller
assumes the fans did not start. It then shuts down the unit and
generates an alarm.)
During the Recirc operating state, the outside air damper is
held closed. The controller does this by energizing output
MCB-BO5 (line 318). On VAV units, output MCB-BO12, the
VAV box output, is also de-energized (line 309) during the
Recirc state.
The supply fan adjustable frequency drive (AFD10) is
modulated to maintain the duct static pressure setpoint. When
energized, output MCB-BO14 (line 407) drives AFD10 toward
increased capacity; MCB-BO13 (line 405) drives it toward
decreased capacity. On VAV units or CAV units equipped with
return fan capacity control, the adjustable frequency drive
(AFD20) is modulated to maintain an acceptable building static
pressure (using either VaneTrol logic or direct measurement
of building pressure; see the appropriate OM for more
information). When energized, output MCB-BO16 (line 409)
drives AFD20 toward increased capacity; MCB-BO15 (line 411)
drives them toward decreased capacity.
NOTE: If the inverter bypass switch S4 (lines426 and 430)
is in the bypass position, MMP30 and MMP40 (line
132 and 144) protect the fans from excessive current
draw. If either the supply or return fan is drawing
excessive current, one of the MMPs triggers an
auxiliary contacts (line 426) and open the circuit,
causing both fans to stop.