Johnson Controls A350R Data Sheet

FANs 930, 930.5, 125, 121 Product/Technical Bulletin A350R Issue Date April 8, 2014

System 350



A350R Electronic Temperature Reset Control (with Relay)

The A350R Electronic Temperature Reset Control is designed to raise or lower the setpoint of supply water temperature based upon a proportionate drop or rise in temperature at the master (outdoor) sensor. The control output is a Single-Pole, Single-Throw (SPST) relay with Light-Emitting Diode (LED) relay status indication.

The A350R’s differential may be adjusted for a given application. An adjustable reset ratio adapts to a variety of weather zones and to the specific heat loss characteristics of most buildings.

As are all System 350 housed in a NEMA 1, high-impact plastic enclosure. The modular design provides easy, plug-together connections for quick installation and future expandability.

products, the A350R is

Figure 1: A350R Electronic Temperature

Reset Control

Features and Benefits

Modular Design Enables stage, display, and transformer

modules to be purchased and installed as necessary

 Adjustable Master Reset

Setpoint (M.R.S.)



 Adjustable Minimum and

Maximum Supply Temperature



 Selectable Warm Weather

Shutdown Temperature



 Adjustable Setback

Temperature



Enables the user to select a master (outdoor) sensor temperature starting point for the supply reset ramp

Permits compliance with equipment manufacturer’s specifications

Saves energy by disabling equipment when master sensor temperature rises to a point where heating is no longer required

Saves energy by lowering the supply temperature setpoint at night or during unoccupied periods

pplication

The A350R Electronic Temperature Reset Control can be used as a standalone device or in conjunction with plug-together accessory modules. The addition of an S350A or S350C for on/off output, or an S350P for a proportional or proportional plus integral control, allows this system to control a variety of single or multiple stage Heating, Ventilation, and Air Conditioning (HVAC) applications. Typical applications include reset of single or multistage boilers.

peration

IMPORTANT: Use this A350R Electronic

Temperature Reset Control (with Relay) only as an operating control. Where failure or malfunction of the reset module could lead to personal injury or property damage to the controlled equipment or other property, additional precautions must be designed into the control system. Incorporate and maintain other devices, such as supervisory or alarm systems or safety or limit controls, intended to warn of or protect against failure or malfunction of the reset module.

IMPORTANT: Utiliser ce A350R Electronic

Temperature Reset Control (with Relay) uniquement en tant que dispositif de contrôle de fonctionnement. Lorsqu'une défaillance ou un dysfonctionnement du reset module risque de provoquer des blessures ou d'endommager l'équipement contrôlé ou un autre équipement, la conception du système de contrôle doit intégrer des dispositifs de protection supplémentaires. Veiller dans ce cas à intégrer de façon permanente d'autres dispositifs, tels que des systèmes de supervision ou d'alarme, ou des dispositifs de sécurité ou de limitation, ayant une fonction d'avertissement ou de protection en cas de défaillance ou de dysfonctionnement du reset module.

The A350R operates on 24 VAC/VDC and provides a Single-Pole, Single-Throw relay output. A front panel

LED lights to indicate the relay is energized. Features include:

 adjustable reset ratio  adjustable master reset setpoint  adjustable minimum and maximum supply

temperature

 adjustable differential  selectable relay for Minimum ON Time  selectable warm weather shutdown temperature  adjustable setback temperature

Celsius Scale Conversion

As shipped from the factory, each A350R is installed with the Fahrenheit temperature scale decal. A Celsius temperature scale decal is provided under the cover of the A350R. If the Celsius scale is desired, see the Installation and Wiring section.

Reset Ratio Adjustment

Reset ratio is defined as the ratio of the change in master sensor temperature to the change in supply temperature setpoint. Example: For an application with a reset ratio of 1:2, a one degree drop in master sensor (for example, outdoor air) temperature causes a two degree rise in the supply temperature setpoint. Refer to Figure 2 for an example.

Reset ratio adjustment is made using the potentiometer marked RESET RATIO. Refer to Figure 4 for location.

Minimum Supply Temperature and Master Reset Setpoint Adjustments

The minimum supply temperature and the master reset setpoint adjustments determine the starting point for the reset ramp. As the master (outdoor) sensor temperature falls below the master reset setpoint, the supply setpoint rises according to the reset ratio. As the master sensor temperature rises above the master reset setpoint, the supply setpoint will be maintained at the minimum supply temperature. Refer to Figure 2 for an example.

Minimum supply temperature adjustment is made using the potentiometer marked MIN SUPPLY, and master reset setpoint adjustment is made using the potentiometer marked M.R.S. Refer to Figure 4 for locations.

2 System 350 A350R Electronic Temperature Reset Control (with Relay) Product/Technical Bulletin

Maximum Supply Temperature Adjustment

The maximum supply adjustment determines an end point for the reset ramp. Refer to Figure 2 for an example.

As the master sensor temperature drops below the master reset setpoint, the supply setpoint temperature rises according to the reset ratio. Upon further reduction in master sensor temperature, the supply setpoint temperature continues to rise until it reaches the maximum supply temperature setpoint. The supply temperature is maintained at the maximum supply temperature setpoint even on a further decrease in master sensor temperature. Use the formula found in Adjustments section to determine the reset ratio.

Maximum supply temperature adjustment is made using the potentiometer marked MAX SUPPLY. Refer to Figure 4 for location.

Supply T emperature

Setpoint (°F)

200

T =20

Maximum Supply

Tempe r at ur e = 200

OFF

160

155

150

(Relay de-energized)

(Rela y en er gized)

Supply Set point = 160° F

Dif ferential = 7 Degree s

Figure 3: Example of Differential

Minimum Relay ON Time Selection

In addition to the differential, the relay operation is also affected by the selectable Minimum ON Time delay. Once the relay is energized, it remains energized until both the Minimum ON time has expired, and the supply temperature is equal to or greater than the calculated setpoint. The time delay applies only to the relay internal to the A350R. A jumper block, located on the cover mounted circuit board (refer to Figure 4), is used to select one of four minimum ON time delay settings: OFF, 1 min., 2 min., or 3 min.

180

Reset Ratio

160

140

120

100

Minimum Supply

Temper ature = 100

20 40 60

Master S ensor Tempe r ature (°F)

(T = Design Temperature of the Building)

= (70-20):(200-100) = 50:100 = 1:2

Master Reset Setpoint = 70

Figure 2: Example of Reset Schedule for a

Hot Water Boiler Application

Differential Adjustment

Differential is the change in supply temperature required to energize and to de-energize the relay. Figure 3 is an example.

Warm Weather Shutdown Temperature Selection

The A350R has a feature that automatically shuts down the heating equipment when the master sensor temperature rises to a value where heating is no longer desired. When the master sensor drops 3°F (1.7°C) below the warm weather setpoint temperature, the A350R returns to standard operation.

A jumper block located on the base-mounted circuit board is used to select one of five shutdown settings. (Refer to Figure 4.) Available settings are OFF, 60°, 64°, 68°, and 72°F (OFF, 16°, 18°, 20°, and 22°C). Placing the jumper block horizontally across the center set of pins (OFF position) disables warm weather shutdown. As shipped from the factory, the warm weather shutdown feature is set to the OFF position.

IMPORTANT: Do not place the jumper across the

top or bottom two pins. This disables the warm weather shutdown, and causes a small shift in the maximum supply setpoint and the master reset setpoint.

The differential can be adjusted between 1 and 30F° (0.5 to 17C°). Adjustment is made using the potentiometer marked DIFF, as shown in Figure 4.

System 350 A350R Electronic Temperature Reset Control (with Relay) Product/Technical Bulletin 3

Setback Adjustment

The A350R has an integral setback feature which, when enabled, lowers the calculated supply setpoint by the setback value. This calculated supply setpoint will not go below the Minimum Supply Temperature setting.

Setback is enabled by an external time clock switch that shorts terminals IN and COM together. The CLK350 Time Control, which is compatible with the A350R, requires a 24 VAC source. Other external time controls may be used with the A350R, but they must have a minimum switch rating of 5 mA at 5 VDC.

When enabled, the Setback LED on the face of the A350R illuminates to indicate the control is operating in the setback mode. Setback is adjustable from 0 to 30F° (0 to 17C°) via the setback potentiometer located at the top of the cover-mounted circuit board. See Figure 4 for its location.

dd-on Modules

The S350 Stage Modules, D350 Digital Temperature Display Module, and Y350R Power Module connect together and plug into the A350R via female connectors located on the left side and male connectors located on the right side of each module. The maximum number of add-on modules is listed in Table 1.

Table 1: Maximum Number of S350 Stage Modules per A350R

Power Source

Y350R

External Class 2 Transformer

Number

of S350A

or S350C

Modules

Allowed

9 6 4 9 8 7

Number of S350A or S350C

Modules

(with

1 S350P)

Allowed

Number of S350A or S350C

Modules

(with

2 S350Ps)

Allowed

S350A On-Off Stage Modules

S350A On-Off Stage Modules receive power, setpoint, and sensor input from the A350R Reset Control. The S350A Stage Modules perform switching functions based on the A350R’s calculated supply setpoint and supply sensor temperature, but the offset and differential are selected within the S350A.

Note: Plug the S350A only into the right side of the

A350R. The S350A will not function properly if plugged into the left side of the A350R.

For more information on these modules, refer to

System 350 S352 Pressure On/Off Stage Modules Product/Technical Bulletin (LIT-930080).

S350 Temperature, S351 Humidity, and

S350C Slave Stage Modules

S350C Slave Stage Modules receive power, and sensor input from the A350R Reset Control. S350C Slave Stage Modules perform switching functions based on the setpoint and differential selected at the S350C.

Note: Unlike the S350A, the S350C can plug into

either side of the A350R. When the S350C is plugged into the left side of the A350R, it controls to the S350C setpoint based on the master sensor temperature input. When the S350C is plugged into the right side of the A350R, it controls to the S350C setpoint based on the supply sensor temperature.

For more information on these modules, refer to

System 350 Module Product/Technical Bulletin (LIT-930084).

S350C Temperature Slave Stage

S350P Proportional Stage Modules

S350P Proportional Stage Modules receive power, setpoint, and sensor input from the A350R Reset Control. The S350P Proportional Stage Module responds with an analog 0 to 10 VDC and 0 to 20 mA output signal based on the A350R’s calculated supply setpoint and sensor temperature, as well as the offset and throttling range selected at the S350P.

Note: For each S350P added, the number of S350A

or S350C Stage Modules that can be used with a Y350R decreases by two. If an external transformer is used, the number of S350A and S350C Stage Modules used decreases by one for each additional S350P.

4 System 350 A350R Electronic Temperature Reset Control (with Relay) Product/Technical Bulletin

Note: Plug the S350P only into the right side of the

A350R. The S350P will not function properly if plugged into the left side of the control.

For more information on these modules, refer to

System 350 Temperature Stage Module Product/Technical Bulletin (LIT-930086).

S350P Proportional Plus Integral

+ 9 hidden pages