McQuay MicroTech II User Manual

Page 62 OM 780-2
1. The stage-up timer has expired. (See “Interstage Timers” above.)
2. The Control Temperature is greater than the Tower Stage
x
Setpoint, where
x
is the next higher tower stage (1 through
12).
3. The current tower stage is less than the Max Tower Stage setting of the highest active sequence.
Stage-Down Control: The CSM stages down when the Control Temperature is too low. This occurs whenever the
following two conditions are satisfied:
1. The stage-down timer has expired. (See “Interstage Timers” above.)
2. The Control Temperature is less than or equal to the Tower Stage
x
Setpoint minus the Tower Stage Differential,
where
x
is the current tower stage (1 through 12).
Figure 25. Tower Staging Only
70.0
71.0
74.0
75.0
Control Temperature
72.0
73.0
76.0
77.0
78.0
21.0
23.0
22.0
24.0
25.0
Stage 1
Spt
1
Spt
2
Stage 2 Stage 3 Stage 4(°F)(°C)
Spt
1
– Df
Spt
2
– Df
Spt
3
Spt
3
– Df
Spt
4
Spt
4
– Df
Spt
5
Spt
5
– Df
Spt
6
Spt
6
– Df
Stage 5 Stage 6
24.5
23.5
22.5
21.5
off
on
on
off
off
on
on
off off off
on on
Legend
Spt1 Tower Stage 1 Setpoint
Df Tower Stage Differential
79.025.5
a0160
Tower Staging with Low-Limit Controlled Bypass Valve
If the Tower Valve Control Option variable is “Valve Setpoint,” the tower stages are controlled as described below.
Stage-Up Control: The CSM stages up when the Control Temperature is too high. This occurs whenever the following
four conditions are satisfied:
1. The stage-up timer has expired. (See “Interstage Timers” above.)
2. The Control Temperature is greater than the Tower Stage
x
Setpoint, where
x
is the next higher tower stage (1 through
12).
3. The current tower stage is less than the Max Tower Stage setting of the chillers in the highest active sequence.
4. The bypass valve position is greater than the Maximum Tower Valve Position Setpoint. (This ensures that the valve is
sufficiently open to the tower.)
Stage-Down Control: The CSM stages down when the Control Temperature is too low. This occurs whenever the
following two conditions are satisfied:
1. The stage-down timer has expired. (See “Interstage Timers” above.)
2. The Control Temperature is less than or equal to the Tower Stage
x
Setpoint minus the Tower Stage Differential,
where
x
is the current tower stage (1 through 12).

McQuay MicroTech II Specifications

General

Brand	McQuay
Model	MicroTech II
Category	Controller
Language	English