The Initial Setpoints section in the microblock dialog box determines the starting setpoint for the equipment and the minimum and maximum allowable setpoints. The microblock determines the setpoint with a "trim and respond" calculation using the settings in the following statement: Every _____ mins, Trim by ____ and Respond by ____ but no more than ____. For cooling, you should use a positive Trim by value and a negative value for the Respond by and but no more than properties. For heating, you should use a negative value for Trim by and a positive value for the Respond by and but no more than properties. Setpoints are calculated using the following formula:
New Setpoint = Previous Setpoint + trim by + (respond by x number of requests)
Example 1
The initial setpoint for a VAV air handler (which is the source of cold air for a number of VAV boxes) is 60 degrees, with a minimum of 55 degrees and a maximum of 65 degrees. The trim and respond properties are set as follows: Every 2.0 mins, Trim by 0.25 and Respond by -0.50 but no more than -3.0. If the current setpoint is 57 degrees and 4 requests are received, the new setpoint would be 55.25 degrees (57 degrees + .25 trim + (-.50 x 4) respond).
Example 2
The same VAV air handler later receives seven cooling requests. The trim and respond properties are set as follows: Every 2.0 mins, Trim by 0.25 and Respond by -0.50 but no more than -3.0. If the current setpoint is 55.25 degrees, the new setpoint would be 52.5 degrees (57 degrees +.25 trim + (-3.0) respond). Because the number of requests (7) multiplied by the Respond by value (-.50) is greater than the no more than value, the no more than value is used in the calculation instead.
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