McQuay MicroTech 200 Series, Operating Manual

Page: 25 / 46

OM 200MICRO 25
Menu 12, Leaving Evap Set Points
Item
Screen Line Display Field Range Extended Name
Local Lvg Set Point Source
Spt Source=Local 1
Network 1
Active Spt=xx.x°F 2 Current Active Set Point
Local Spt=44.0°F 1 40-80 User Adjustable Chw Set Point
2
Startup DT=3.0°F 2 1-10 Startup Delta Temp
Network Spt=xx.x°F 1 Chw Spt Supplied by Network
1
3
Shutdn DT=3.0°F 2 1-3 Shutdown Delta Temp
No Reset
Return
4-20mA
OAT
Chw Reset=No Reset 1
Ice
Chw Reset Method
1
Max Lvg Spt=54.0°F 2 10-80 Upper Chw Set Point Limit
Return Spt=54.0°F 1 20-80 Set point for Return Water Reset
2
No Reset at 70°F 2 10-90 Lower OAT Reset Limit
Reset Signal=xx.xmA 1 0-20mA External Reset Signal Amplitude
2
3
Max Reset At=50°F 2 10-90 Upper OAT Reset Limit
3 1 Pulldn Rate=0.5/m 1 0.1-5.0 Maximum Chw Pulldown Rate
Spt Source= The value selected determines the source for the set point.
Auto:Local —Will allow the chiller to use it's internal set point selected in this menu screen 1, line
2 (local spt). Local is also the selection if a master/slave arrangement exists between two 200
series controllers for the purpose of lead/lag control and load balance control.
Auto:Network —Will control the chiller from a remote panel such as a Chiller System Controller
(CSC) . A network implies two or more 200 series controllers connected to a level 1 device.
Active Spt= This is a status value and cannot be changed. Active spt indicates the current set point
(factoring in any reset signals) that is controlling the chiller and can be used to determine if the chiller
is maintaining leaving chilled water temperature set point.
Local Spt= This is the actual chilled water leaving temperature for the chiller to maintain if there is not
a network. Local spt is active depending upon which set point source was selected. A value must be
entered into local spt . This is the default value used to control the chiller if a network communication
failure occurs.
Startup Dt= This value is added to the active spt set point. When the chiller is waiting for load and
the water circulating through the evaporator exceeds the active spt plus the startup dt , the chiller will
start operation. Example: active spt = 44, startup dt = 10, the chiller will start when the water
temperature exceeds 54.
The startup dt along with the shutdn dt can be used to reduce cycling of the chiller.
Network Spt= This value cannot be adjusted. It is the value supplied by the network if a network
exists. The active spt can be compared to the local spt and network spt to determine which set point
is controlling the chiller.
Shutdn Dt= This value is subtracted from the active spt . When the leaving chilled water temperature
reaches this calculated value, the chiller will shutdown. Example: active spt = 44, shutdn dt = 4, the
chiller will shutdown when the water temperature leaving the evaporator is less than 40.
The shutdn dt along with the startup dt can be used to reduce cycling of the chiller.
Chw Reset= There are several methods that can be selected to reset the leaving evaporator chilled
water temperature.
No Reset —This does not provide any reset and is the default value.
Return —This measures the evaporator return water temperature and as the return comes back
cooler (indicating cooling load is reduced) the leaving water temperature is increased. This
reduces motor amps and provides an operational cost savings.