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The Q1 reset stage control has 2 types of control resets and each reset can be used to output in an upwards or downwards type of control. Each reset can use 1 of many types of action variables and the output will be applied to a setpoint of the control area. If no reset action variable is defined or if the action variable is not within the appropriate range (not assigned or not reading properly) the reset will default to the upper limit output value (in the case of the heating setpoint or duct pressure reset) or to the lower value (in the case of the cooling setpoint). By choosing none as the action variable this will show the default output value.

Example: Lower value default value

 

Reset Types:

Timed Bump: The timed bump reset is used to control a setpoint within a dead-band of the user's choosing. The action variable will be monitored and if the value is above or below the decrement and increment value the reset control will start to reduce or increase the setpoint value by the bump amount configured in on the time interval specified, but not above or below upper or lower setpoints. If the action variable is between the decrement and increment value then the setpoint will not be adjusted at all. The interval timer will not be started until the action value is outside of the specified range. If the reset direction is UP then the setpoint will be increased if the value is above the increment value, and the setpoint will be decreased if the action value is below the decrement value. The opposite will happen if the reset direction is DOWN. This type of reset is useful if the action variable is directly affected by the setpoint changing. For instance on duct pressure resets based on damper position the pressure will directly affect the damper position of a VAV holding flow, if the desired max damper position is 75% then the reset will bump down the setpoint until the desired position is achieved and then hold until the setpoint until external forces (need for more or less air) cause the need for a change. If a linear type was used then as the setpoint was modified it would cause the damper to move which would cause a change in the setpoint again, but not necessarily in the correct direction which may induce a cycling effect.

Example: Cooling discharge setpoint on a timed bump every 10 minutes, each change is 0.5°F based on a terminal load(self induced or average cooling need of child zones). No change in setpoint between 25% and 75%.

 

 

Linear: The linear reset will adjust the setpoint based on the location of the action variable on a linear graph. There is no time delay or capped adjustment amount used in linear resets, however the reset control cannot allow the setpoint to increase or decrease the above or below the upper and lower setpoint limits. This type of reset is typically used when the action variable is not directly or minimally affected by the setpoint adjustment. For instance a cooling setpoint based on the outside air temperature. The outside air temperature will not change when the setpoint is reduced, but solar loads may cause the need for additional cooling. A linear reset will adjust based solely on the outside air temperature, but only in proportion to the amount of change in the temperature. A timed bump reset would have reset the setpoint continuously down to the lowest setpoint, even if there was only a marginal change in air temperature as long as it was above the increment setpoint.

Example: The same reset, but based linear and based on the outside air temperature. If the outside air temperature is 60°F or below the cooling setpoint is 65°F. When the outside air temperature is at 95°F the cooling setpoint is 55°F. The setpoint will scale linearly between those 2 numbers.

 

Reset Direction: This is direction of the reset. The further to the right the action variable is on the graph, the harder you would wish to push the setpoint. Typically heating and pressure would reset up and cooling would reset down.

 

Bump Amount(Timed Bump Only): This is the amount of change in the setpoint allowed for each increment or decrement.

 

Time Increment(Timed Bump Only): This is the amount time the reset control waits before applying a bump to the setpoint. This timer does not start until the action variable value is outside of the desired range.

 

Upper Setpoint: This is the maximum allowable setpoint value.

 

Lower Setpoint: This is the minimum allowable setpoint value.

 

Low Limit/Start Decrement: This is the minimum action value on a linear reset or the action value to start decrementing on a timed bump.

 

High Limit/Start Increment: This is the maximum action value on a linear reset or the action value to start incrementing on a timed bump.

 

Action Variable:

None: No reset will take place and the default value will stay unchanged.

Terminal Loading: For heating and cooling setpoints, this is either the on-board terminal load based on the space temperature and setpoints or for an air handler with child zones then it is the average heating or cooling calls from those zones. For the duct pressure reset it is the maximum damper position of the child zones.

Space Temperature: The active space temperature. Typically used to reset the heating and/or cooling setpoints.

Return Air Temperature: The active return air temperature. Typically used to reset the cooling setpoint of a built-up air handler.

Outside Air Temperature: The active outside air temperature. Typically used to reset the heating and/or cooling setpoints.

Return Air Humidity: The active return air humidity. Typically used to reset the cooling setpoint of a built-up air handler.

Space Air Humidity: The active space air humidity. Typically used to reset the cooling setpoint.

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