FANs 637.5, 1637.5
Appendix Section
Issue Date
0400
APPLICATION NOTE
Appendix D: Multi-zone Hot and Cold Deck Reset
Resetting Hot and Cold Deck Setpoints .............................................3
Introduction......................................................................................................... 3
Key Concepts...................................................................................................... 4
Hot and Cold Deck Reset ............................................................................................... 4
Zone Temperature vs. Zone Demand ............................................................................. 4
Parameter Names........................................................................................................... 5
Controlling the Zone Mixing Dampers ............................................................................ *6
Pneumatic Zone Temperature Control ............................................................................ 6
Digital Zone Temperature Control................................................................................ *12
Pneumatic Control Reset Based on Temperature ........................................................ *16
Digital Zone Control Reset Based on Temperature....................................................... 18
Procedure Overview ......................................................................................... 20
Detailed Procedures ........................................................................................*21
Defining the Analog Inputs (Pneumatic Zone Temperature Control) ............................ *21
Determining the Milliampere Range for Each Transducer
(Pneumatic Control Reset Based on Temperature)....................................................... 23
Determining the Output High and Low Range for the Analog Inputs
(Pneumatic Control Reset Based on Temperature)....................................................... 25
* Indicates those sections where changes occurred since the last printing.
© 2000 Johnson Controls, Inc.
Code No. LIT-6375195
www.johnsoncontrols.com
2
Appendix
Appendix D: Multi-zone Hot and Cold Deck Reset
Resetting Hot and Cold Deck
Setpoints
Introduction
This application note is relevant when using an AHU (Air Handling
Unit) to control a multi-zone air handler. It explains how to use the
AHU to reset the hot deck and cold deck setpoints.
This bulletin describes how to:
•
define the analog inputs (pneumatic zone temperature control)
•
determine the milliampere range for each transducer (pneumatic
control reset based on temperature)
•
determine the output high and low range for the analog inputs
(pneumatic control reset based on temperature)
3
4
Appendix
Key Concepts
Hot and Cold Deck Reset
An Air Handling Unit (AHU) controller can control a multi-zone air
handler. Typically, the AHU controller also resets the hot deck and
cold deck setpoints, and controls the zone mixing dampers.
This application note is relevant when using an AHU to control a
multi-zone air handler. It explains how to use the AHU to reset the hot
deck and cold deck setpoints. The hot deck is reset based on the zone
with the greatest heating demand. The cold deck is reset based on the
zone with the greatest cooling demand.
Zone with
greatest
Heating
demand
controls the ...
Hot
Deck
Zone 3
Zone 2
N.O.
Zone 1
N.C.
Resets the
Cold Deck
Setpoint
Zone with
greatest
Cooling
demand...
zondemnd
Figure 1: Zones with Greatest Cooling
and Heating Demands
Zone Temperature vs. Zone Demand
Understanding the difference between zone temperature and zone
demand is essential.
Usage of the coldest zone and warmest zone may create some
confusion. In common usage, the coldest zone would be the zone with
the lowest temperature. However, the coldest zone may not be the
zone with the greatest heating demand.
Example
Zone 1 is in the warehouse, and the occupants of Zone 1 have set their
thermostat to 60°F. The temperature in Zone 1 is approximately 58°F.
Zone 1 is technically the coldest zone. However, the zone temperature
is 2°F below the zone setpoint, so Zone 1 has only a 2°F demand for
heating.
5
Appendix D: Multi-zone Hot and Cold Deck Reset
Zone 2 is the accounting office, and the thermostat is set at 74°F. The
current temperature is 68°F, which is well below the setpoint. Zone 2
has a 6°F demand for heating. Although it is not the coldest zone,
Zone 2 has the greatest demand for heating.
In Zone 1,
the thermostat
is set to
60°F
60
and the
temperature is
58°F.
In Zone 2,
Zone 1 is the
COLDEST zone, but ...
the thermostat
is set to
74°F
74
and the
temperature is
68°F.
Zone 2 has the
greatest heating demand.
htgdemnd
Figure 2: Zone Temperature vs. Zone Demand
Parameter Names
The multi-zone applications use parameters that contain the phrases
coldest zone and warmest zone. This application note describes how to
define these parameters, so it refers to the parameters by their given
names.
Table 1: Parameter Names and Meanings
Parameter Name
In this Application Note, Refers to:
Coldest Zone
Zone with greatest heating demand
Warmest Zone
Zone with greatest cooling demand
This application performs reset based on zone demand, which is the
difference between the zone setpoint and the zone temperature.
Zone Demand = Zone Temperature - Zone Setpoint
Reset should not be based solely on zone temperature or zone setpoint.
6
Appendix
Table 2: Zone Temperature vs. Zone Demand
Zone
Number
Zone
Temperature
Zone
Setpoint
Zone
Demand
Heating or
Cooling
1
58
60
-2
Heating
2
68
74
-6
Heating
3
74
72
2
Cooling
4
77
72
5
Cooling
5
72
72
0
none
Controlling the Zone Mixing Dampers
Each zone has its own set of zone mixing dampers. A zone mixing
damper modulates the supply air to that zone based on the zone
thermostat.
The zone with the greatest demand for cooling has its zone mixing
damper fully open to the cold deck. The zone with the greatest demand
for heating has its zone mixing damper fully open to the hot deck.
All other zones must mix the hot and cold deck air streams to satisfy
the load demands in that particular zone.
Depending on the job, zone control may be accomplished either with
pneumatic or digital controllers. Each method is first discussed in
terms of pneumatics. For the digital application, only the necessary
application information is given. Reading both pneumatic and digital
sections may be required for a full understanding of the digital
application.
Pneumatic Zone Temperature Control
A pneumatic loop with a T-4002 thermostat controlling the zone
mixing damper is one option for zone temperature control. The supply
pressure to all zone thermostats is reliably 19 psig.
All zones in this application have mixing dampers with a nominal
spring range of 8 to 13 psig. Spring range shift is assumed to be
negligible and is ignored in the calculations.
Identifying the Zones with the Largest Demands
A T-4002 thermostat produces a 0-19 psig signal, based on the
difference between the zone temperature and the zone setpoint. The
output is approximately 19 psig on a call for full cooling, and 1 psig
for full heating. The output varies linearly between the two endpoints.
The exact values vary depending upon the calibration.
Appendix D: Multi-zone Hot and Cold Deck Reset
7
19
Cold Deck
Setpoint Reset
Typical
Output (psig)
13
Zone Mixing
Dampers
8
Hot Deck
Setpoint Reset
1
-
0
+
Zone Temperature Minus Setpoint
T4002
Figure 3: Zone Temperature vs. T-4002 Thermostat Output
Pneumatic signals from each zone thermostat are fed into a
C-2220 high/low signal selector. The C-2220 selects the largest and
smallest pneumatic signals. The largest pneumatic signal represents
the zone with the largest cooling demand. The smallest pneumatic
signal is the zone with the largest heating demand.
Two pneumatic-to-electric transducers are required if the
two pneumatic signals produced by the C-2220 are to become analog
inputs on the AHU controller. The FM-IAP101-0 is a suitable
transducer. The pneumatic signals are converted into 4 to
20 mA signals.
The current signals can then be fed into the AHU controller, as shown
in Figure 4. The AHU controller resets the hot deck and cold deck
setpoints, based on these two inputs.
8
Appendix
Mixing Damper Control
Zone
Mixing
Damper
(8-13 psig)
Pneumatic Zone Controller
19
Zone Mixing
Damper Signal
Pneumatic
Output
(psig)
1-19 psig
1
Zone Temperature
minus
Zone Setpoint
Zone Setpoint
and
Zone Temperature
AHU Controller
Hot and Cold Deck Setpoint Reset
High Signal
1-19 psig
H
L
Zone A
Zone
.. B
.
Zone Y
Zone Z
Pneumatic
-toElectric
Transducer
4-20 mA
AI-7
Cold
Deck
Setpoint
Cold Deck
Setpoint
Cooling
Valve
Signal
Hot Deck
Setpoint
Heating
Valve
Signal
Cold DeckReset
Band Signal
Low Signal
1-19 psig
C-2220
High/Low
Signal
Selector
Pneumatic
-toElectric
Transducer
4-20 mA
AI-8
Hot
Deck
Setpoint
Hot DeckReset
Band Signal
AHUMULT
Figure 4: Multi-zone Hot and Cold Deck Reset
HVAC PRO can scale each of these two current inputs to match the
sensitivity range of the zone thermostat, such as a T-4002. The first
step in scaling the inputs is described in the Defining the Parameters
topic in this section.
Hot and Cold Deck Reset
Figure 5 shows the output range for a pneumatic zone controller, such
as a T-4002. The range is divided into thirds. The upper third is used to
reset the cold deck setpoint. The lower third is used to reset the hot
deck setpoint. The middle third is used to modulate the zone mixing
damper.
Appendix D: Multi-zone Hot and Cold Deck Reset
9
19
Cold Deck Reset
13
Zone Mixing Damper
8
Hot Deck Reset
1
Output of
the
Zone Controller
(psig)
SEQUENCE
Figure 5: Output from Pneumatic Zone Controller
On zones other than warmest and coldest, the pneumatic signal will be
in the middle third, between 8 and 13 psig. This signal tells the zone
mixing damper what mixture of hot deck and cold deck air to supply to
the zone.
If the zone temperature rises far enough above the zone setpoint, the
pneumatic zone controller calls for full cooling. The zone mixing
damper is fully open to the cold deck. At this point, the signal from the
pneumatic zone controller is used to reset the cold deck setpoint. If the
current cold deck setpoint cannot meet the cooling needs, the cold
deck setpoint should be lowered. This procedure corresponds to the
upper one third of the pneumatic sequence.
If the zone temperature falls far enough below the zone setpoint, the
pneumatic zone controller calls for full heating. The zone mixing
damper is fully open to the hot deck. At this point, the signal from the
pneumatic zone controller is used to reset the hot deck setpoint. If the
current hot deck setpoint cannot meet the heating needs, the hot deck
setpoint should be raised. This procedure corresponds to the lower
one third of the pneumatic sequence.
Choosing a Method for Scaling the Analog Inputs
There are two methods for defining the zone limits and reset bands in
the AHU controller.
1.
Scaling the Analog Inputs into Psig (Demand)
This method allows each zone to have its own setpoint, plus the
multi-zone unit still maintains true zone load sequencing of the
zone mixing damper, as well as the cold and hot deck setpoints.
2.
Scaling the Analog Inputs into Temperature (% Demand)
This method is only valid when the setpoints of all zones are
identical (fixed). Refer to Zone Temperature vs. Zone Demand at
the beginning of this document.
10
Appendix
Defining the Parameters
The first step is defining the parameters for hot and cold deck reset in
HVAC PRO. The following two tables list the parameters and their
appropriate values.
Note:
The AHU Applications Application Note (LIT-6375080) in
the HVAC PRO User’s Manual (FAN 637.5) has a
description of each parameter.
Table 3: Defining the Hot Deck Reset Schedule Parameters
Parameter
Long Name
Value
Is Obtained
from...
Determines...
Hot Deck RBand
20.00°F
normal range for
hot deck
output range of hot
deck reset schedule
lower one third of
sequence bar in
Figure 5
input range of hot deck
reset schedule
Hot Deck Low Lim
75.00°F
Cld Zone RBand
- 7.00 psig*
Cld Zone Hi Lim
8.00 psig
* The minimum signal produced by a C-2220 signal selector is 1 psig by design.
Table 4: Defining the Cold Deck Reset Schedule Parameters
Parameter Long
Name
Value
Is Obtained
from...
Determines...
Cold Deck RBand
20.00°F
normal range for
cold deck
output range of cold
deck reset schedule
upper one third of
sequence bar in
Figure 5
input range of cold
deck reset schedule
Cold Deck Low Lim
55.00°F
Hot Zone RBand
- 6.00 psig
Hot Zone Hi Lim
19.00 psig*
*The maximum signal produced by a C-2220 signal selector is 19 psig.
The deck reset bands and limits are in degrees. The zone reset bands
and limits are in psig. The analog inputs are scaled in units of psig.
The range of each analog input is determined by the zone low/high
limit and the zone reset band. The range for the cold zone is from
1.0 to 8.0 psig. The range for hot zone is from 13.0 to 19.0 psig.
The range of the cold zone becomes the input range for the hot deck
reset schedule. The range of the hot zone is used as the range of inputs
for the cold deck reset schedule.
The output range of the reset schedules is determined by the deck’s
low or high limit and the deck reset band. The range for the hot deck
setpoint is 75.0 to 95.0. The range for the cold deck setpoint is
55.0 to 75.0.
Appendix D: Multi-zone Hot and Cold Deck Reset
75
Cold Deck
Setpoint
( F)
55
13
19
Analog Input Range (psig)
(N.C. to Cooling)
cdreset
Figure 6: Cold Deck Reset Schedule
95
Hot Deck
Setpoint
( F)
75
1
8
Analog Input Range (psig)
(N.O. to Heating)
hdreset
Figure 7: Hot Deck Reset Schedule
11
12
Appendix
Input Range
The range for the analog inputs must be determined so that is does not
become unreliable.
To review, each zone’s controller is producing a pneumatic signal.
This signal could be any value in the output range of the zone
controller. From all of these zone signals, the C-2220 selects the
lowest and highest signals. Again, the output range of the C-2220
could be any value in the output range of the zone controller.
The two outputs from the C-2220 are transduced into a current signal.
The output range of the transducer determines the range for the analog
input.
An analog input will become unreliable if the signal is less than the
input range low value or greater than the input range high. These
two values must be set to the low and high ends of the transducer’s
output.
Digital Zone Temperature Control
A digital controller, such as a UNT (Unitary) using a 0 to 10 VDC
signal, could be used to control the zone mixing damper. Since a
generic input/output point multiplexer UNT controller is capable of
sideloops, we could control two zones with a two analog output
controller.
In this application, we define two side loops. They are AI
(Analog Input) to AO (Analog Output), PI (Proportional plus Integral)
control with reset schedule. Each controls a zone damper. The reset
input is the setpoint potentiometer and is used to provide a remote
setpoint for each loop. Most likely the TE-6400 room sensor would be
used for the room element and setpoint potentiometer. The temporary
occupied/boost modes would not be usable in this application.
Table 5 and Table 6 show the parameters necessary in HVAC PRO
configuration of remote zone setpoints.
Table 5: Remote Setpoint AI Ranges
Value
Input Range
Output Range
Low
0.0 ohms
18°C (65.0°F)
High
1660.0 ohms
29°C (85.0°F)
Table 6: Reset Schedule Values
Input/Output
Value
Input 1
18°C (65.0°F)
Input 2
29°C (85.0°F)
Output 1
18°C (65.0°F)
Output 2
29°C (85.0°F)
Appendix D: Multi-zone Hot and Cold Deck Reset
13
Identifying the Zones with the Largest Demands
Each side loop provides a zone demand for heating or cooling as
indicated by an analog output value of 0 to 100. A zero indicates that
full heating is required and a value of 100 indicates that full cooling is
required. Further, since these loops are proportional plus integral,
setpoint error could be eliminated over time by integration biasing of
the output signal to the limits of 0 and 100. The tuning values of each
loop should be similar so that one zone would not dominate the
heating or cooling demand.
100.0
Cold Deck
Reset
66.6
Zone Mixing
Dampers
33.3
Hot Deck
Reset
0.0
-
0
+
Zone Temperature Minus Setpoint
ZONETEMP
Figure 8: Zone Temperature vs. Controller Output
Signal Selection
As in the pneumatic applications, define the AHU controller as a dual
duct with hot/cold deck reset. HVAC PRO defines two analog inputs
as the coldest and warmest zone temperatures. The default for these
inputs are resistive nickel, they must be changed to voltage type
inputs.
Networked applications would use GPL, JC-BASIC, or signal
selection to choose the greatest heating and cooling demands.
Alternately, standalone applications can use a UNT to signal select the
greatest heating and cooling demand for up to six zones.
Each zone controller output (6-10 VDC) is wired in parallel to the
zone mixing damper actuator and an AI of the UNT acting as a signal
selector.
14
Appendix
AI-1
Zones
Temperature
AI-2
Zone 1
Setpoint
SL-1
AI/AO
with
Reset
UNT 1
AO-1
Zone 3
AO-1
Zone 1
AO-2
Zone 2
AO-2
Zone 4
AO-1
Zone 5
UNT 2
AO-2
Zone 6
UNT 3
TE-6400 Room Sensor
Zone 1
(Typical of 6)
AI-6
AI-5
AI-4
AI-3
AI-2
AI-1
Zone 1
Damper Actuator
(Typical of 6)
AHU
SL-1
MIN
SL-2
MAX
Coldest Zone AI-7
AO-1 Coldest
Warmest Zone AI-8
AO-2 Warmest
UNT 4
ditgwire
Figure 9: Application Using UNTs for Zone and Signal Selection for AHU
In the UNT designated for signal selection, define six analog inputs as
voltage according to Table 7.
Table 7: Signal Selection AI Definition
Value
Input Range
Output Range
Low
0.0 VAC (Volts Alternating Current)
0.0%
High
10.0 VAC
100.0%
In this same UNT, define the AOs as coolest and warmest. They
default to voltage. 0-100% command gives 0-10 volts. See Table 8.
Table 8: Analog Output Definition for Deck Setpoint Reset
Command Range
Voltage
0.0 % Command
0.0 VAC
100.0 % Command
10.0 VAC
Appendix D: Multi-zone Hot and Cold Deck Reset
15
Define two multiple AIs to AO side loops, choosing all of the used AIs
as the inputs. The first is defined as input conditioning: Select
minimum value, with the output going to AO-1, previously defined as
the coldest zone. You must chose a control logic, so select reset
schedule and set the input1/output1 to 0.0 and input2/output2 to 100.0.
The second is defined as input conditioning: Select maximum value,
with the output going to AO-2, previously defined as the warmest
zone. Set up the control logic parameters the same as the first side
loop.
The two analog outputs of the side loops defined in this UNT represent
the greatest heating and cooling demand of zones, and serve as inputs
to the AHU controller on the multi-zone unit. The bottom one third of
the signal, 0 to 3.3 volts, will reset the hot deck temperature, middle
one-third, 3.3 to 6.6 volts, will throttle the zone mixing damper, and
top one-third, 6.6 to 10.0 volts will reset the cold deck temperature.
In HVAC PRO, definition of hot and cold deck reset schedules (for the
AHU) is a bit unusual. The cold zone low limit is not temperature.
Rather, it is the voltage that is applied to the actuator when it is fully
open to the hot deck, i.e., 3.3 volts. The cold zone range is 3.3 volts as
well. The hot zone high limit is 6.6 volts and has a range of 3.4 volts.
Note that the (filename) .PRN print out shows these as temperatures.
By following this procedure, this multi-zone now has load based deck
temperature reset.
The first step is defining the parameters for hot and cold deck reset in
HVAC PRO. Table 9 and Table 10 list the parameters and their
appropriate value.
The deck reset bands and limits shown in Table 9 and Table 10 are in
degrees Fahrenheit. The zone reset bands and limits are in % of the
command sent to the zone actuator. The analog inputs are scaled in
units of %.
Note:
AHU Applications Application Note (LIT-6375080) in the
HVAC PRO User’s Manual (FAN 637.5) has a description of
each parameter.
Table 9: Defining Hot Deck Reset Schedule Parameters
Parameter
Long Name
Value
Is Obtained
from...
Determines...
Hot Deck RBand
20.0°F
Hot Deck Low Lim
75.0°F
normal range for
hot deck
output range of hot deck
reset schedule
Cld Zone RBand
33.3%
Cld Zone Hi Lim
33.3%
lower one third of
sequence bar in
Figure 11
input range of hot deck
reset schedule
16
Appendix
Table 10: Defining Cold Deck Reset Schedule Parameters
Parameter Long
Name
Value
Is Obtained
from...
Determines...
Cold Deck RBand
20.0°F
Cold Deck Low Lim
55.0°F
normal range for
cold deck
output range of cold deck
reset schedule
upper one third of
sequence bar in
Figure 5
input range of cold deck
reset schedule
Hot Zone RBand
33.3%
Hot Zone Hi Lim
100.0%
Pneumatic Control Reset Based on Temperature
The analog inputs are defined as units of temperature, vs. scaling in
psig as in the Pneumatic Zone Temperature Control and Digital Zone
Temperature Control topics in this section. The analog input, in
degrees, is used to reset the hot deck and cold deck setpoints.
Optional Procedure
This section describes the complete procedure for scaling the inputs
into units of temperature. This provides a good tool for learning how
the analog inputs are scaled.
You can also use a BASIC program to perform this task. This program
runs under BASIC on an IBM®-compatible PC (Personal Computer),
and automatically does all of the scaling of the analog inputs into units
of temperature. The program can be retrieved from The Advisor online
network. The filename is PNEUAHMZ.EXE.
Required Information
The following information must be known to scale the analog input
into units of temperature:
!
cold zone high limit
!
cold zone reset band
!
hot zone high limit
!
hot zone reset band
!
milliamperes that define zone limits and reset bands
Parameters in the Print File
The first four items in the previous list can be viewed in the
HVAC PRO print file (filename.prn). It is created and updated when a
configuration file is saved in HVAC PRO and the Options/Generate
PRN on Save is selected. Default values for these four items are shown
in Table 11.
Appendix D: Multi-zone Hot and Cold Deck Reset
17
Table 11: Parameters Obtained from the Print File
Long Name
Type
Address
Default
Cld Zone Hi Lim
ADF
138
72.00°F
Cld Zone RBand
ADF
139
-4.00°F
Hot Zone Hi Lim
ADF
142
78.00°F
Hot Zone RBand
ADF
143
-6.00°F
Selecting a Range to Prevent an Unreliable Input
The pneumatic signal could be any value in the output range of the
zone controller. It is not confined to the range of pressure above and
below the zone mixing damper’s spring range.
The maximum and minimum pneumatic signals that the zone
controller could produce are determined. Then, the maximum and
minimum outputs that the transducer could produce are determined.
Since the transducer output is the analog input on the AHU controller,
the output low range and output high range values are designed so the
input value never goes out of range. This prevents the input from
becoming unreliable. The input may become unreliable if the range is
any smaller.
After calculating and entering the new values for low and high range,
an unreliable condition could only be the result of a component failure,
such as a transducer malfunction.
18
Appendix
Digital Zone Control Reset Based on Temperature
Required Information
The following information must be known to scale the analog input
into units of temperature:
!
cold zone high limit
!
cold zone reset band
!
hot zone high limit
!
hot zone reset band
!
voltages that define zone limits and reset bands
Parameters in the Print File
The first four items in the previous list can be viewed in the
HVAC PRO print file (filename.prn). It is created and updated when a
configuration file is saved in HVAC PRO and the Options/Generate
PRN on Save is selected. Default values for these four items are shown
in the following table:
Table 12: Parameters Obtained from the Print File
Long Name
Type
Address
Default
Cld Zone Hi Lim
ADF
138
72.00°F
Cld Zone RBand
ADF
139
-4.00°F
Hot Zone Hi Lim
ADF
142
78.00°F
Hot Zone RBand
ADF
143
-6.00°F
Item 5 is determined by the following:
This application, as in the previous method that relies on demand, uses
UNT controllers for both the zone control and the coldest and warmest
zone selection. The advantage of this application over the demand
method is that the zone dampers could be modulated using incremental
dampers.
Note:
Do not use the remote setpoint so that all zone setpoints can
be set to identical values. This is because the selection UNT
selects the coldest and warmest zones based on actual zone
temperature as opposed to the control signal.
Appendix D: Multi-zone Hot and Cold Deck Reset
19
All of the zone temperature AIs are paralleled with the six AIs on the
selection UNT. Sensor sharing is accomplished in the selection UNT
by defining the AIs as Resistive Nickel (R-NI) and then setting the
AI switches for 2 volts.
Define two multiple AIs to AO side loops, choosing all of the used AIs
as the inputs. The first is defined as input conditioning: Select
minimum value, with the output going to AO-1, previously defined as
the coldest zone. You must choose a control logic, so select reset
schedule and set the input1/output1 to 65 and the input2/output2 to 85.
The second is defined as input conditioning: Select maximum value,
with the output going to AO-2, previously defined as the warmest
zone. Set up the control logic parameters the same as the first side
loop.
20
Appendix
Procedure Overview
Table 13: Resetting Hot and Cold Deck Setpoints
To Do This
Follow These Steps:
Define the Analog Inputs
(Pneumatic Zone Temperature
Control)
Double-click on AI-7 and verify that its long
name is coldest zone. Change the sensor type
to Current (C). Double-click on AI-8 and verify
that it is the warmest zone, and make it a
current input. For an FM-IAP101, set the input
range low to 4 mA and input range high to
30 mA. Enter the remainder of the analog input
definitions as shown in Table 14.
Determine the Milliampere
Range for Each Transducer
(Pneumatic Control Reset
Based on Temperature)
Determine the pressure ranges below and
above the zone damper for the application.
Determine the sensitivity of the transducer.
Calculate the output range (in milliamperes) for
the coldest and warmest zones.
Determine the Output High and
Low Range for the Analog
Inputs (Pneumatic Control
Reset Based on Temperature)
Use the algebraic equation for a straight line to
determine the high and low range for the
analog inputs. Determine sensitivity for the
coldest zone in mA/degree by using the
milliampere range. Use a linear equation to
scale the input into engineering units. Solve
the equation for the analog input by
substitution. Determine the sensitivity for the
warmest zone in mA/degree by using the
milliampere range.
Appendix D: Multi-zone Hot and Cold Deck Reset
21
Detailed Procedures
Defining the Analog Inputs (Pneumatic Zone Temperature Control)
Note:
These procedures are performed with the dual path hot/cold
deck reset configuration file open in HVAC PRO.
To define the analog inputs:
1.
Double-click on AI-7 and verify that its long name is coldest
zone. Change the sensor type to Current (C), as shown in
Figure 10.
2.
Double-click on AI-8 and verify that it is the warmest zone, and
make it a current input.
Sensor type is
Current (C).
Input Range Low
and
Input Range High
Must be changed
to 4.00.
aimod10
Figure 10: Input Range
Note:
Because these are current inputs, the input ranges low and
high are defaulted to 0.00 and 20.00 milliamperes,
respectively. This default range is suitable for a pressure-toelectric transducer, which produces a 0-20 mA current. To
use a transducer that produces 4-20 mA output, such as an
FM-IAP101, change the input range low to 4.00.
3.
For an FM-IAP101, set the input range low to 4 mA and input
range high to 30 mA. The conversion remains correct for the
transducer even though the supply pressure only reaches 19 psig.
4.
Enter the remainder of the analog input definitions as shown in
Table 14.
22
Appendix
Table 14: Defining the Analog Inputs
Parameter
AI7
Value
AI8
Long Name
Coldest Zone
Hottest Zone
Sensor Type
Current (C)
Current (C)
Decimal Precision
1
1
Units
psig
psig
Filter Value
1
1
Input Range Low (mA)
4.0
4.0
Input Range High (mA)
20.0
20.0
Output Range Low (psig)
0.0
0.0
Output Range High (psig)
25.0
25.0
Enable Alarm
N
N
Since we do not know the calibration of each T-4002, it is more
practical to display the values in psig. In this example, all of the
T-4002s are direct acting, so the highest pressure is the warmest zone
and the lowest pressure is the coolest zone.
Appendix D: Multi-zone Hot and Cold Deck Reset
23
Determining the Milliampere Range for Each Transducer
(Pneumatic Control Reset Based on Temperature)
Note:
Refer to the example application described earlier in this
document for details of the pneumatic sequencing and
transducer type.
To determine the milliampere range for each transducer:
1.
Determine the pressure ranges below and above the zone damper
for the application. The ranges for this example are shown in
Table 15.
19
Cold Deck Reset
13
Zone Mixing Damper
8
Hot Deck Reset
1
Output of
the
Zone Controller
(psig)
SEQUENCE
Figure 11: Pressure Ranges for Reset Signals
Table 15: Pressure Ranges for Reset Signals
Signal
Range (psig)
Coldest Zone Reset Signal
1 to 8
Warmest Zone Reset Signal
13 to 19
2.
Determine the sensitivity of the transducer. The equation for the
sensitivity of a transducer is:
Sensitivity (mA/psig) = Transducer’s Output Range (mA)
Transducer’s Input Range (psig)
Applying this equation for sensitivity to the FM-IAP101
(a 4-20 mA transducer) yields the following calculations:
Transducer Output Range = (20-4) mA = 16 mA
Transducer Input Range = (25-0) psig = 25 psig
Sensitivity = 16 mA/25 psig
Sensitivity = 0.64 mA/psig
24
Appendix
3.
Calculate the output range (in milliamperes) for the coldest and
warmest zones. The following equation uses the pneumatic signal
and the transducer sensitivity to determine the transducer output,
in milliamperes:
(Signal Sensitivity) + 4 mA = Output (mA)
where signal is the pneumatic signal in psig
The pneumatic signals from Table 15 and the previously
calculated sensitivity are substituted into the above equation.
Table 16: Milliampere Output for the Coldest Zone
Reset Signal
Signal
(psig)
Sensitivity
Signal
Sensitivity
+ 4.0 mA
Output
1
0.64
0.64
4.0
4.64
8
0.64
5.12
4.0
9.12
The range is determined by the difference between the high and
low outputs, in milliamperes. The milliampere range for the
coldest zone reset signal is:
Coldest Zone Range = High Output - Low Output
Coldest Zone Range = (9.12-4.64) mA
Coldest Zone Range = 4.43 mA
Table 17: Milliampere Output for the Warmest Zone
Reset Signal
Signal
(psig)
Sensitivity
Signal
Sensitivity
+ 4.0 mA
Output
13
0.64
8.32
4.0
12.32
19
0.64
12.16
4.0
16.16
The milliampere range for the warmest zone reset signal is:
Warmest Zone Range = High Output - Low Output
Warmest Zone Range = (16.16-12.32) mA
Warmest Zone Range = 3.84 mA
Appendix D: Multi-zone Hot and Cold Deck Reset
25
Determining the Output High and Low Range for the Analog Inputs
(Pneumatic Control Reset Based on Temperature)
To determine the high and low range for the analog inputs:
1.
Use the algebraic equation for a straight line to determine the high
and low range for the analog inputs. The analog input processing
follows the standard linear equation:
y = mx + b
Y represents the value of the analog input, which has units of
degrees temperature.
A correlation must be made between the zone thermostat’s
pneumatic output signal, in psig, and the transducer’s current
output signal, in milliamperes. This correlation determines the
zone limit temperature.
The first two columns in Table 18 and Table 19 use results from
Table 16 and Table 17. The Limit column is determined by the
cold zone low limit, found in the .PRN file. The coldest zone limit
and the warmest zone limit can be the same temperature value but
must not overlap.
Table 18: Coldest Zone
Signal (psig)
8
Output
Limit
9.12
72
Output
Limit
12.32
72
Table 19: Warmest Zone
Signal (psig)
13
26
Appendix
2.
Determine sensitivity in mA/degree by using the milliampere
range. The sensitivity of the transducer in this example is
0.64 mA/psig.
Sensitivity (mA/degree) =
milliampere range
absolute value of coldest zone reset band
Sensitivity = (9.12 - 4.64)/4°F
Sensitivity = 4.43 mA/4°F
Sensitivity = 1.1075 mA/degree
3.
Use a linear equation to scale the input into engineering units. The
slope m of that equation is the reciprocal of sensitivity, or:
m = 1/sensitivity
m = 1/1.1075 mA/degree
m = 0.9029 degree/mA
4.
Solve the equation for the analog input by substitution. By doing
this, you will determine the effective output low range and output
high range of the analog input. B is the y-intercept of the value y
when x equals zero.
y = mx + b
72.0°F = (0.9029 degree/mA * 9.12 mA) + b
Solving for b:
b = 63.7656°F
80
72
Y ( F)
70
63.8
60
0
5
10
9.12
X (mA)
CLDZN2
Figure 12: Coldest Zone
Appendix D: Multi-zone Hot and Cold Deck Reset
27
The output low range for the coldest zone is:
y = (0.9029 degree/mA * 4 mA) + 63.7656°F
y = 67.4°F
The output high range for the coldest zone is:
y = (0.9029 degree/mA * 20 mA) + 63.7656°F
y = 81.8°F
Table 20: Coldest Zone
Output Range
Signal (psig)
Output (mA)
Value
Low
0
4
67.4
High
25
20
81.8
5.
Determine the sensitivity in mA/degree by using the milliampere
range. The sensitivity of the transducer in this example is
0.64 mA/psig.
Sensitivity (mA/degree ) =
milliampere range
absolute value of warmest zone reset band
Sensitivity = (16.16 - 12.32) mA/6°F
Sensitivity = 3.84 mA/6°F
Sensitivity = 0.64 mA/degree
m = 1/sensitivity
m = 1/0.64 mA/degree
m = 1.5625 degree/mA
Solve for b:
y = mx + b
72.0°F = (1.5625 degree/mA* 12.32 mA) + b
Solving for b:
b = 52.75°F
28
Appendix
70
72
Y ( F)
60
52.75
50
0
5
10
15
12.32
X (mA)
wrmzn2
Figure 13: Warmest Zone
The output low range for the warmest zone is:
y = (1.5625 degree/mA * 4 mA) + 52.75°F
y = 59.0°F
The output high range for the warmest zone is:
y = (1.5625 degree/mA * 20 mA) + 52.75°F
y = 84.0°F
Table 21: Warmest Zone
Output Range
Controls Group
507 E. Michigan Street
P.O. Box 423
Milwaukee, WI 53201
Signal (psig)
Output (mA)
Low
0
4
Value
59.0
High
25
20
84.0
www.johnsoncontrols.com
Release 8.0
Printed in U.S.A.