824 Programmable Comfort Control
18-HD72D1-1
page 29
6. Basic Operation
6.1 PI Control
The 824 Control uses Trane’s proprietary control schemes
to provide both comfort and energy efficiency. The Control
samples the indoor temperature every five seconds and
determines the capacity needed based on the following
parameters:
•
Mode of operation
•
Proportional Error - distance from set point
•
Integral Error - Time away from set point
6.2 Load Value
The 824 uses Proportional Error plus Integral Error to
determine the amount of capacity required. The calculated
capacity is displayed as Load Value. Load Value is a
numerical representation of the needed capacity to maintain
the desired set point. The Load Value range is dependent
on the applied system.
72º
B
C
D
Set Point
Temperature
2 Seconds
Integral Error
Room
Temperature
A
B
+
C
+
D...
= Integral Error
A
= Proportional Error
6.3 Duty Cycles
Indoor temperature control is achieved by duty cycling the
equipment when the load value is less than 100% of the
current stage of operation. The duty cycle rate is dependent
on the calculated load value.
The duty cycle chart below indicates the number of cycles
at 50% load (i.e. LV = 50).
1 Hour
6 CPH
2 CPH
As with all PI-based controls the indoor temperature will
fluctuate above and below the user selected set point to
maintain comfort in the space. Adjusting the factory set
CPH (Cycles per Hour) can affect how tight the control
operates around the set point. The CPH can be adjusted
in the Installer Settings>Advanced>Equipment (2 – 6 CPH)
•
Factory default for compressor operation is 3 CPH
•
Factory default for indoor heat is 5 CPH
Effects of changing the cycle rates
Lower CPH results in longer run cycles with less cycling
but the indoor temperature may deviate above and below
set point.
Higher CPH results in highter indoor temperature control
but shorter, more frequent cycles.
6.4 Overshoot Clamp
The 824 Control will enforce an “off cycle” anytime the
control overshoots more than 2.5°F. Once the indoor
temperature is within .75°F of set point an “on cycle” is
allowed dependent on load value and minimum off times.
Show illustration…
6.5 Stage Thresholds
The threshold to allow operation is a Load Value greater
than 5 and operation is always terminated with a Load
Value less than 1.
Load Value also determines when additional stages of
operation are requested. To prevent rapid cycling between
stages, a stage threshold is enforced. The stage threshold
is dependent on the applied system.
LV=100
LV=200
ST
A
GE 3
ST
A
GE 1
STAGE 2
COMPRESSOR STAGING THRESHOLDS
100-115
100-115
100-125
100-125
100-110
100-110
Y1 to Y2 - 100-110
Y1 to Y2 - 100-110
HP to W1 - 100-115
HP to W1 - 100-115
HP to Dual Fuel - 100-125
HP to Dual Fuel - 100-125
LV=100
LV=200
LV=300
LV=400
ST
A
GE 5
ST
A
GE 1
STAGE 2
STAGE 3
STAGE 4
AUX HEAT STAGING THRESHOLDS
100-215
100-215
100-315
100-315
100-
115
100-
115
Compressor to W1 - 100-115
Compressor to W1 - 100-115
W1 to W2 - 100-215
W1 to W2 - 100-215
W2 to W3
100-315
W2 to W3
100-315
LV=100
LV=200
LV=300
ST
A
GE 4
ST
A
GE 1
STAGE 2
STAGE 3
FOSSIL HEAT STAGING THRESHOLDS
W1 to W2 100-190
W1 to W2 100-190
W2 to W3 100-290
W2 to W3 100-290
100-
125
100-
125
Inhibit - Compressor to W1 - 100-125
Inhibit - Compressor to W1 - 100-125
