IOM 1242-2 • PATHFINDER
®
MODEL AWV CHILLERS
90 www.DaikinApplied.com
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Definitions
Active Set Point
The active set point is the setting in effect at any given
moment. This variation occurs on set points that can be altered
during normal operation. Resetting the chilled water leaving
temperature set point by one of several methods, such as
return water temperature, is an example.
Active Capacity Limit
The active set point is the setting in effect at any given
moment. Any one of several external inputs can limit a
compressor’s capacity below its maximum value.
Deadband
The deadband is a range of values surrounding a set point
such that a change in the variable occurring within the
deadband range causes no action from the controller. For
example, if a temperature set point is 44
°
F and it has a
deadband of ± 2°F, nothing will happen until the measured
temperature is less than 42
°
F or more than 46
°
F.
DIN
Digital input, usually followed by a number designating the
number of the input.
Error
In the context of this manual, “Error” is the difference between
the actual value of a variable and the target setting or set point.
Evaporator Approach
The evaporator approach is calculated for each circuit.
Evaporator Approach = LWT – Evap Saturated Temp
Evap Recirc Timer
A timing function, with a 30-second default, that holds off any
reading of chilled water for the duration of the timing setting.
This delay allows the chilled water sensors (especially water
temperatures) to take a more accurate reading of the chilled
water system conditions.
EXV
Electronic expansion valve, used to control the flow of
refrigerant to the evaporator.
Load Limit
An external signal from the keypad, the BAS or a 4-20 mA
signal that limits the compressor loading to a designated
percent of full load. Frequently used to limit unit power input.
Load Balance
Load balance is a technique that equally distributes the total
unit load among the running compressors on a unit or group of
units.
LWT
Leaving water temperature. The “water” is any fluid used in the
chiller circuit.
ms
Millisecond
OAT
Outside ambient air temperature
Offset
Offset is the difference between the actual value of a variable
(such as temperature or pressure) and the reading shown on
the controller as a result of the sensor signal.
Refrigerant Saturated Temperature
Refrigerant saturated temperature is calculated from the
pressure sensor readings for each circuit. The pressure is fitted
to an R-134a temperature/pressure curve to determine the
saturated temperature.
Soft Loading
Soft Loading is a configurable function used to ramp up the
unit capacity over a given time period, usually used to influence
building electrical demand by gradually loading the unit.
SP
Set point
Suction Superheat (SSH)
Suction superheat is calculated for each circuit using the
following equation:
Suction Superheat = Suction Temp – Evap Saturated Temp
Stage Up/Down Accumulator - Fans
The accumulator can be thought of as a bank storing
occurrences that indicate the need for an additional fan.
Stage up/Stage down Delta-T
Staging is the act of starting or stopping a compressor or fan
when another is still operating. The Delta-T is the “deadband”
on either side of the set point in which no action is taken.
Stage Up Delay
The time delay from the start of the first compressor to the start
of the second.
Startup Delta-T
Number of degrees above the LWT set point required to start
the first compressor.
Stop Delta-T
Number of degrees below the LWT set point required for the
last compressor to stop.
Vdc
Volts, direct current
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