McQuay AGS 225D, Operating Manual

Page: 32 / 82

32 OM AGSD-1
Reset Type – 4-20 mA
The Active Leaving Water variable is adjusted by the 4 to 20 mA reset analog input.
Parameters used:
1. Cool LWT setpoint
2. Max Reset setpoint
3. LWT Reset signal
Reset is 0 if the reset signal is less than or equal to 4 mA. Reset is equal to the Max Reset
Delta T setpoint if the reset signal equals or exceeds 20 mA. The amount of reset will vary
linearly between these extremes if the reset signal is between 4 mA and 20 mA. An
example of the operation of 4-20 reset in Cool mode is shown below.
20
(54)
Cool LWT Set
Point (44)
4
4-20 mA Reset - Cool Mode
0
Max Reset
(10)
Active
LWT
(
o
F)
Reset Signal (mA)
Reset Type – OAT
The Active Leaving Water variable is reset based on the outdoor ambient temperature.
Parameters used:
1. Cool LWT setpoint
2. Max Reset setpoint
3. OAT
Reset is 0 if the outdoor ambient temperature is greater than 75 F. From 75 down to 60 F
the reset varies linearly from no reset to the max reset at 60 F. At ambient temperatures less
than 60 F, reset is equal to the Max Reset setpoint.
75
Cool LWT+Max Reset
(54)
Cool LWT Set-Point
(44)
OAT Reset
60
Max Reset
(10)
OAT (
o
F)
Active
LWT
(
o
F)