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Krishna, My apologies for the delay in getting back to you about this question. I needed to check with the master of PID controllers in TRNSYS (Michael Kummert) before replying coherently. There are two ways that you can use Type23 in a cooling mode application. If you have a cooling case in which (for example) you are using a PID as a flow controller to keep a temperature below some desired set point then you can set Type23's proportional gain constant to a negative value in which case the PID will increase flow as the monitored temperature gets higher and higher. In this case minimum control signal (parameter 4) should be zero and the maximum control signal should be a positive value. In another case, you might want your PID to provide both heating and cooling. In this situation, the control signal's magnitide should increase as you get farther and farther from the setpoint but the sign of the control signal should change depending on whether you are above or below the setpoint. In this case, you set the proportional gain to a positive value but you allow the Type23 calculated control signal to vary between a negative and a positive number. I will send you an example that Michael was kind enough to generate. I do not want to clog up everyone's InBox so I will send it in a seperate email. Kind regards, David Krishna wrote:
-- ** David BRADLEY Solar Energy Laboratory University of Wisconsin - Madison 1500 Engineering Drive Madison, WI 53706 United States Ph: +1 608 263 1589 Fax: +1 608 262 8464 Email: dbradley@engr.wisc.edu |