6
OM
AGSB-5
Component Description
Unit and Circuit Controller Description
Terminology and Definitions
Accumulator
The accumulator is an electronic “bank” that stores information relative to fan operation and
fan capacity required. It is the heart of the controller’s fuzzy logic feature. Various events
such as cooling load changes and ambient air temperature changes, add or subtract points in
the bank. When a certain number of points are accumulated, a fan will be started.
Active Setpoint
The active setpoint is the setting in effect at any given moment. This occurs on setpoints
that can be altered during normal operation. Resetting the chilled water leaving temperature
setpoint by one of several methods, such as return water temperature, is an example.
Condenser Saturated Temperature Target
The saturated condenser temperature target is calculated by first using the following
equation:
Sat condenser temp target raw = 0.833(evaporator sat temp) + 68.34
The “raw” value is the initial calculated value. This value is then limited to a range defined
by the Condenser Saturated Temperature Target minimum and maximum setpoints. These
setpoints simply cut off the value to a working range, and this range can be limited to a
single value if the two setpoints are set to the same value.
CPU Error
These are problems caused by a malfunction of the central processing unit.
Dead Band
The dead band is a set of values associated with a setpoint such that a change in the variable
occurring within the dead band causes no action from the controller. For example, if a
temperature setpoint is 44
°
F and it has a dead band of
±
2 degrees, nothing will happen until
the measured temperature is less than 42
°
F or more than 46
°
F.
Delta-T
Delta-T is a range of degrees of temperature. For example, a Start Up Delta-T of 5 degrees
means that the water temperature must be 5 degrees above the LWT setpoint before the start
signal is given.
Discharge Superheat
Discharge superheat shall be calculated for each circuit using the following equation:
Discharge Superheat = Discharge Temperature – Condenser Saturated Temperature
Error
In the context of this manual, “Error” is the difference between the actual value of a variable
and the target setting or setpoint.
Evaporator Approach
The evaporator approach is calculated for each circuit. The equation is as follows:
Evaporator Approach = LWT – Evaporator Saturated Temperature
Summary of Contents for AGS 206A
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