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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