Figure 25. Tower Staging Only - McQuay MicroTech II Operation Manual

1. The stage-up timer has expired. (See "Interstage Timers" above.)
The Control Temperature is greater than the Tower Stage x Setpoint, where x is the next higher tower stage (1 through
2.
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.)
The Control Temperature is less than or equal to the Tower Stage x Setpoint minus the Tower Stage Differential,
2.
where x is the current tower stage (1 through 12).

Figure 25. Tower Staging Only

25.5 79.0
25.0 78.0
24.5 77.0
24.0 76.0
23.5 75.0
23.0 74.0
22.5 73.0
22.0 72.0
21.5 71.0
21.0 70.0
(°C) (°F)
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.)
The Control Temperature is greater than the Tower Stage x Setpoint, where x is the next higher tower stage (1 through
2.
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.)
The Control Temperature is less than or equal to the Tower Stage x Setpoint minus the Tower Stage Differential,
2.
where x is the current tower stage (1 through 12).
Page 62
Legend
Spt1 Tower Stage 1 Setpoint
Df Tower Stage Differential
on
Spt
2
on
Spt
1
Spt
Spt – Df
2
off
Spt – Df
1
off
Stage 1 Stage 2
on
Spt Spt
4
on
Spt
3
Spt – Df Spt – Df
4 5
off
– Df
3
off
Stage 3 Stage 4
on on
Spt
5 6
Spt – Df
6
off off
Stage 5 Stage 6
a0160
OM 780-2