Carrier 38APD115, Manual

Page: 74 / 242

74
Sequence of Operation — The MBB monitors the space tem-
perature input together with the unit configurations to make a
determination of Control Point Run Status
o
VIEW
o
CTPT .
The control will call for a low cool set point, Setpoints
o
COOL
o
CSP.1 (Cooling Setpoint 1) or high cool set point
Setpoints
o
COOL
o
CSP.2 (Cooling Setpoint 2) depending on
the difference between the Space Temperature ( Run Status
o
VIEW
o
SPT ) and the space temperature set point ( Set-
points
o
COOL
o
SPS.P ). CSP.1 should be greater than CSP.2 .
CSP.1 or CSP.2 will be used as the basis for the Active Set
Point ( Run Status
o
VIEW
o
SETP ) based on the configura-
tion settings, Low Cool On Set Point ( Setpoints
o
COOL
o
L.C.ON ), High Cool On Set Point ( Set-
points
o
COOL
o
H.C.ON ), and Low Cool Off Set Point ( Set-
points
o
COOL
o
L.C.OF ) to determine the control point.
If the Space Temperature rises above the SPS.P + L.C.ON ,
the system will start with CSP.1 as the Control Point. Space
Temperature Control Mode ( Run Status
o
VIEW
o
SPT.M )
will indicate 1 (Lo Cool). As long as the Space Temperature
does not rise above SPS.P + L.C.ON + H.C.ON , the unit will
continue to supply conditioned air with CSP.1 as the Control
Point until the Space Temperature falls below SPS.P + L.C.ON
– L.C.OF . If the Space Temperature falls below SPS.P +
L.C.ON – L.C.OF , mechanical cooling will cease. Space Tem-
perature Control Mode, SPT.M will indicate 0 (Cool Off). If
the Space Temperature rises above SPS.P + L.C.ON +
H.C.ON , the unit will change the Control Point to CSP.2 .
Space Temperature Control Mode, SPT.M will indicate 2 (Hi
Cool). CSP.2 will remain the Control Point until the Space
Temperature falls below SPS.P + L.C.ON – ( L.C.OF /2) at
which time the Control Point will change to CSP.1 . CSP.1 will
remain the Control Point until the Space Temperature falls be-
low SPS.P + L.C.ON – L.C.OF . Space Temperature Control
Mode, SPT.M will indicate 0 (Cool Off).
The following example illustrates this control scheme.
Given:
SPS.P = 72 F,
L.C.ON = 1,
H.C.ON = 3,
L.C.OF = 2 F,
CSP.1 = 60 F,
CSP.2 = 55 F
If Space Temperature equals 73 F ( SPS.P + L.C.ON [Low
Cool On]) cooling will begin and the Control Point equals 60 F
( CSP.1) . As long as Space Temperature does not exceed the
High Cool On setting ( SPS.P + L.C.ON + H.C.ON ), CSP.1
will remain the Control Point until the Space Temperature falls
below 71 F ( SPS.P + L.C.ON – L.C.OF [Low Cool Off])
when mechanical cooling will cease.
If space temperature rises above 76 F ( SPS.P + L.C.ON +
H.C.ON [High Cool On]), control point set point changes to
55 F ( CSP.2 ). CSP.2 will remain the Control Point until the
Space Temperature falls below 72 F ( SPS.P + L.C.ON –
L.C.OF /2 [High Cool Off]), control point transitions back to
60 F ( CSP.1 ). If space continues to fall below 71 F ( SPS.P +
L.C.ON – L.C.OF [Low Cool Off]), the unit is shut off.
Figure 84 summarizes this example.
68.0 69.0 70.0 71.0 72.0 73.0 74.0 75.0 76.0 77.0
CSP.1
CSP.2
H.C.ON
L.C.ON
L.C.OF/2
L.C.OF
SPS.P
L.C.ON
Low Cool On
High Cool On
High Cool Off
Low Cool Off
°F
Fig. 84 — C-TYP=5, Space Temperature Control Example