Optimal Start Time: Precool and Preheat

Transcription

1 Metasys Network Technical Manual 636 Air Handlers Section Technical Bulletin Issue Date 0191 Optimal Start Time: Precool and Preheat Optimal start logic to determine the precool and preheat times for an air handling unit (primary mechanical equipment) File Name Path Name Main Function Guidelines OST.CMP The following DOS path name indicates the location of the compound: <FMS>\APPS\ENERGY\OST\OST.CMP Optimal start logic to determine the precool and preheat times for an air handling unit (primary mechanical equipment). Both OPTIMAL START PREHEAT and PRECOOL are provided with this compound. However, if only OPTIMAL START PRECOOL is required and not OPTIMAL START PREHEAT (due to a lack of heating source or because it was not specified), then query the OST group compound (OST) and delete only the OPTIMAL START PREHEAT processes (i.e., AHU#\PREHEAT and AHU#\PHADPT). The OPTIMAL START PRECOOL application processes will remain. If only OPTIMAL START PREHEAT is required, delete the OPTIMAL START PRECOOL processes. Modify the appropriate parametric values for both processes for the specific project. It is assumed that either OST PRECOOL or OST PREHEAT will run on any operational day. The following items illustrate how the OST PRECOOL application is applied and started. 1. Disable OST PREHEAT. 2. Make sure BO or BD has scheduled command to start. 3. Enable OST PRECOOL. 4. Trigger precool process in scheduling feature Johnson Controls, Inc. 1 Order No

2 If the user wants the OST PREHEAT application to run instead of the OST PRECOOL, the user should do the following: 1. Disable OST PRECOOL. 2. Make sure BO or BD has scheduled command to start. 3. Enable OST PREHEAT. 4. Trigger preheat process in scheduling feature. Optionally, in place of scheduling the appropriate process (either OST PREHEAT or OST PRECOOL), a process may be added to determine if OST PREHEAT or OST PRECOOL should run for that day. The additional process s logic would be based on the temperature difference between the target and the space temperature. This process will then trigger the appropriate process. Example To see how this compound could be used with other objects and compounds, view the GPL file AHU2. The following DOS path name indicates the location of the file: <FMS>\APPS\AHU\AHU2.(GPL) 2 Air Handlers Optimal Start Time: Precool and Preheat

3 Optimal Start Time: Precool Main Function Accessories How It Works OST PRECOOL Optimal start logic determines the latest possible start time of mechanical equipment such that the space or mass occupancy target (setpoint) is met at occupancy time. The algorithm adapts to the thermal characteristics of a particular building. Space (zone) temperature or mass temperature may be used. The following can be connected to the OST PRECOOL compound as inputs: mass temperature instead of space temperature adjustable space or mass temperature target (setpoint) adjustable PRECOOL MAXIMUM TIME adjustable PRECOOL MINIMUM TIME OST PRECOOL determines the temperature drop required to meet the target occupancy space temperature at occupancy. Next, the PRECOOL BUILDING CONSTANT and PRECOOL DEADTIME are used to estimate the optimal precool time. This time is limited to be between the PRECOOL MINIMUM TIME and PRECOOL MAXIMUM TIME. Then the optimal precool time is compared to the BUILDING OCCUPANCY TIME and METASYS SYSTEM TIME to determine the OST PRECOOL START TIME. When the current METASYS SYSTEM TIME is later than the calculated OST PRECOOL START TIME and earlier than the BUILDING OCCUPANCY TIME, the air handling unit will start and the OST PRECOOL enable input will be true. The OST PRECOOL ADAPTATION process will be initiated so that the PRECOOL BUILDING CONSTANT and PRECOOL DEADTIME may be adapted. When the OST PRECOOL process executes again, it will use the adapted PRECOOL BUILDING CONSTANT and PRECOOL DEADTIME. The PRECOOL ADAPTATION process will have calculated a new PRECOOL BUILDING CONSTANT and PRECOOL DEADTIME either by BUILDING OCCUPANCY TIME, or when the space temperature is within a specified tolerance of the target temperature (PRECOOL DIFFERENTIAL). The process will then cease executing and not execute again until the system is in the OST PRECOOL mode the next operational day. Air Handlers Optimal Start Time: Precool and Preheat 3

4 When the current METASYS SYSTEM TIME is earlier than the calculated OST PRECOOL START TIME, the air handling unit or mechanical equipment will not operate in the OST PRECOOL mode or be changed as a result of the OST PRECOOL enable input being false. In addition, the OST PRECOOL ADAPTATION process will not be initiated. Thus, the PRECOOL BUILDING CONSTANT and PRECOOL DEADTIME remain the same values as the last time OST PRECOOL process executed. Guidelines You can find important instructions and guidelines for using compounds in How to Use the Metasys GPL HVAC Library, located at the beginning of the App. Notes: GPL HVAC Library section. For information on the definition and the initial configuration of the objects and the function blocks, use GPL to examine this compound. The PRECOOL BUILDING CONSTANT initializes as 5.0 minutes/ ( F) 2 [16.2 minutes/( C) 2 ]. The process period of the OST PRECOOL process is 00:02:00. The process period of the OST PRECOOL ADAPTATION process is 00:01:00. PRECOOL DEADTIME is the time it takes for the space or mass temperature to start responding after equipment startup. The BUILDING OCCUPANCY TIME is derived from the BO object s early start time attribute. Thus, the BO object must have the appropriate start schedule before OST PRECOOL can be enabled to run. If a start time does not exist, the OST PRECOOL process will run but will be unreliable, since the early start time attribute is 00:00:00 and unreliable. In turn, the start command will not be issued and the adaptation process will not run. The start command to the BO object is at priority 7. This is the same priority at which the Scheduling feature issues commands. A Binary Data object may be used instead of the Binary Output object. The command and (command type) connection blocks in the OST PRECOOL process must be deleted and new blocks must be added in their place. The command block must be configured as a SET BD command with a value of 1. The binary signal being routed to the PCOOL-EN connection block must also be routed to the ENABLE INPUT of the SET BD command block. PRECOOL MAXIMUM TIME provides an upper limit on the calculated PRECOOL time. PRECOOL MINIMUM TIME provides a lower limit on the calculated PRECOOL time. 4 Air Handlers Optimal Start Time: Precool and Preheat

5 The PRECOOL ADAPTATION process uses PRECOOL DIFFERENTIAL in estimating the PRECOOL DEADTIME and PRECOOL BUILDING CONSTANT. When an adjustable value is desired for the PRECOOL MAXIMUM TIME, substitute an Analog Data object for the constant block called PC-MAX. When an adjustable value is desired for the PRECOOL MINIMUM TIME, substitute an Analog Data object for the constant block called PC-MIN. When using this application, specify the appropriate values for the following inputs: - PRECOOL MAXIMUM TIME (must be > 0) - PRECOOL MINIMUM TIME (must be > 0) When MASS TEMPERATURE is used in place of the SPACE (ZONE) TEMPERATURE, connect the appropriate AI object to the connection block called SP-T. You may wish to modify the block name so that the connection block s name reflects the fact that MASS TEMPERATURE is used instead of SPACE TEMPERATURE. You may provide unique space temperature targets (setpoints) for PREHEAT and PRECOOL. If the OST PRECOOL is to be used on multiple air handling units on the same NC, then make the following shared variables unique for each OST PRECOOL application (i.e., for each air handling unit): - ST_PC_TM - ST_PC_TE - PCB_CNST - PC_DTIME - PC_SUMTE - ADPT_PCP The above shared variable names must be exactly the same for the specific air handling unit s OST PRECOOL process and OST PRECOOL ADAPTATION process due to the sharing of data between the two processes. The OST PRECOOL process must be scheduled to be triggered at 00:01:00 (or before BUILDING OCCUPANCY TIME minus PC-MAX time) on each operational day when the OST PRECOOL application is to be executed. The OST PRECOOL ADAPTATION process will be triggered by the OST PRECOOL process. Thus, do not schedule the OST PRECOOL ADAPTATION process. Air Handlers Optimal Start Time: Precool and Preheat 5

6 You must define system and object names for all objects. You must define the hardware location for each object. I/O Requirements Table 1: Precool I/O Requirements Input Requirements Name Of Block Type Of Data Engineer Units Req? Range Default Value Description SP-T Analog F ( C) Yes - - Space temperature TARGET Analog F ( C) Yes - - Space temperature target (precool) PCB-CNST Analog Minutes/ ( F) 2 Yes >0 5.0 Minutes/( F) 2 [6.2 Minutes /( C) 2 ] Precool building constant PC-DTIME Analog Minutes Yes >0 10 Minutes Precool deadtime PC-MAX Analog Minutes Yes >0 480 Minutes Precool maximum time PC-MIN Analog Minutes Yes >0 20 Minutes Precool minimum time OCC_TIME Time HH:MM:OO Yes - - Building occupancy time Output Requirements Name Of Type Of Connection Data Engineer Units Req? Range Default Value Description PCOOL-TM Time HH:MM:OO No - - Precool clock time calculated PCOOL-EN Binary T/F No - - Precool enable PC-FANSS Command Start Yes - - Fan start command (at pri = 7) Process? Example Yes, two process compounds exists. The OST PRECOOL APPLICATION consists of two processes: OST PRECOOL process and OST PRECOOL ADAPTATION process. To view the compound s process information, click once on the compound block. To see how this compound could be used with other objects and compounds, view GPL file AHU2. The following DOS path name indicates the location of the file: <FMS>\APPS\AHU\AHU2.(GPL) 6 Air Handlers Optimal Start Time: Precool and Preheat

7 OST Preheat Main Function Accessories How It Works OST PREHEAT Optimal start logic determines the latest possible start time of mechanical equipment such that the space or mass occupancy target (setpoint) is met at occupancy time. The algorithm adapts to the thermal characteristics of a particular building. Space (zone) temperature or mass temperature may be used. The following can be connected to the OST PREHEAT compound as inputs: mass temperature instead of space temperature adjustable space or mass temperature target (setpoint) adjustable PREHEAT MAXIMUM TIME adjustable PREHEAT MINIMUM TIME adjustable PREHEAT MINIMUM TIME based on outdoor air temperature OST PREHEAT determines the temperature change (rise) required to meet the target occupancy space temperature at occupancy. Next, the PREHEAT BUILDING CONSTANT and PREHEAT DEADTIME are used to estimate the optimal preheat time. This time is limited to be between the PREHEAT MINIMUM TIME and PREHEAT MAXIMUM TIME. Then the optimal preheat time is compared to the BUILDING OCCUPANCY TIME and the METASYS SYSTEM TIME to determine the OST PREHEAT START TIME. Air Handlers Optimal Start Time: Precool and Preheat 7

8 When the current METASYS SYSTEM TIME is later than the calculated OST PREHEAT START TIME and earlier than the BUILDING OCCUPANCY TIME, the air handling unit will start and the OST PREHEAT enable input will be true. The OST PREHEAT ADAPTATION process will be initiated so that the PREHEAT BUILDING CONSTANT and PREHEAT DEADTIME may be adapted. When the OST PREHEAT process executes again, it will use the adapted PREHEAT BUILDING CONSTANT and PREHEAT DEADTIME. The PREHEAT ADAPTATION process will have calculated a new PREHEAT BUILDING CONSTANT AND PREHEAT DEADTIME either by BUILDING OCCUPANCY TIME, or when the space temperature is within a specified tolerance of the target temperature (PREHEAT DIFFERENTIAL). The process will then cease executing and not execute again until the system is in the OST PREHEAT mode the next operational day. When the current Metasys system time is earlier than the calculated OPTIMAL PREHEAT START TIME, the air handling unit or mechanical equipment will not operate in the OST PREHEAT mode or be changed as a result of the OST PREHEAT enable input being false. In addition, the OST PREHEAT ADAPTATION process will not be initiated. Thus, the PREHEAT BUILDING CONSTANT and PREHEAT DEADTIME remain the same values as the last time OST PREHEAT process executed. Guidelines You can find important instructions and guidelines for using compounds in How to Use the Metasys GPL HVAC Library, located at the beginning of the App. Notes: GPL HVAC Library section. For information on the definition and the initial configuration of the objects and the function blocks, use GPL to examine this compound. The PREHEAT BUILDING CONSTANT initializes as 10.0 minutes/ ( F) 2 [32.4 minutes/( C) 2 ]. The process period of the OST PREHEAT process is 00:02:00. The process period of the OST PREHEAT ADAPTATION process is 00:01:00. PREHEAT DEADTIME is the time it takes for the space or mass temperature to start responding after equipment startup. The BUILDING OCCUPANCY TIME is derived from the BO object s early start time attribute. Thus, the BO object must have the appropriate start schedule before OST PREHEAT can be enabled to run. If a start time does not exist, the OST PREHEAT process will run but will be unreliable, since the early start time attribute is 00:00:00 and unreliable. In turn, the start command will not be issued and the adaptation process will not run. 8 Air Handlers Optimal Start Time: Precool and Preheat

9 The start command to the BO object is at priority 7. This is the same priority at which the Scheduling feature issues commands. PREHEAT MAXIMUM TIME provides an upper limit on the calculated PREHEAT time. PREHEAT MINIMUM TIME provides a lower limit on the calculated PREHEAT time. The PREHEAT MINIMUM TIME is derived from the outdoor air temperature as follows: as the outdoor air temperature varies between F and 50.0 F the PREHEAT MINIMUM TIME varies between minutes and 20.0 minutes. The outdoor air temperature is not required. Thus, the OA-T connection block and the span block may be removed and a constant block may be used in their place connected to the PH-MIN connection block. The PREHEAT ADAPTATION process uses PREHEAT DIFFERENTIAL in estimating the PREHEAT DEADTIME and PREHEAT BUILDING CONSTANT. When an adjustable value is desired for the PREHEAT MAXIMUM TIME, substitute an Analog Data object for the constant block called PH-MAX. When an adjustable value is desired for the PREHEAT MINIMUM TIME, substitute an Analog Data object for the constant block called PH-MIN. When using this application, specify the appropriate values for the following inputs: - PREHEAT MAXIMUM TIME (must be > 0) - PREHEAT MINIMUM TIME (must be > 0) When MASS TEMPERATURE is used in place of the SPACE (ZONE) TEMPERATURE, connect the appropriate AI object to the connection block called SP-T. You may wish to modify the block name so that the connection block s name reflects the fact that MASS TEMPERATURE is used instead of SPACE TEMPERATURE. A Binary Data object may be used instead of the Binary Output object. The command and (command type) connection blocks in the OST PREHEAT process must be deleted and new blocks must be added in their place. The command block must be configured as a SET BD command with a value of 1. The binary signal being routed to the PHEAT-EN connection block must also be routed to the ENABLE INPUT of the SET BD command block. You may provide unique temperature targets (setpoints) for PREHEAT and PRECOOL. Air Handlers Optimal Start Time: Precool and Preheat 9

10 If the OST PREHEAT is to be used on multiple air handling units on the same NC, then make the following shared variables unique for each OST PREHEAT application (i.e., for each air handling unit): - ST_PH_TM - ST_PH_TE - PHB_CNST - PH_DTIME - PH_SUMTE - ADPT_PHP The above shared variable names must be exactly the same for the specific air handling unit s OST PREHEAT process and OST PREHEAT ADAPTATION process due to the sharing of data between the two processes. The OST PREHEAT process must be scheduled to be triggered at 00:01:00 (or before BUILDING OCCUPANCY TIME minus PH-MAX time) on each operational day when the OST PREHEAT application is to be executed. The OST PREHEAT ADAPTATION process will be triggered by the OST PREHEAT process. Thus, do not schedule the OST PREHEAT ADAPTATION process. You must define system and object names for all objects. You must define the hardware location for each object. 10 Air Handlers Optimal Start Time: Precool and Preheat

11 I/O Requirements Table 2: Preheat I/O Requirements Input Requirements Name Of Block Type Of Data Engineer Units Req? Range Default Value Description SP-T Analog Yes - - Space temperature TARGET Analog Yes - - Space temperature target (preheat) PHB-CNST Analog Yes > Minutes/( F) 2 [2.4 Minutes /( C) 2] Preheat building constant PH-DTIME Analog Yes >0 10 Minutes Preheat deadtime PH-MAX Analog Yes >0 480 Minutes Preheat maximum time PH-MIN Analog Yes >0 20 Minutes Preheat minimum time OCC-TIME Time Yes - - Building occupancy time Output Requirements Name Of Type Of Connection Data Engineer Units Req? Range Default Value Description PHEAT-TM Time HH:MM:OO No - - Preheat clock time calculated PHEAT-EN Binary T/F No - - Preheat enable PH-FANSS Command Start Yes - - Fan start command (at pri = 7) Process? Example Yes, two process compounds exist. The OST PREHEAT APPLICATION consists of two processes: OST PREHEAT process and OST PREHEAT ADAPTATION process. To view the compound s process information, click once on the compound block. To see how this compound could be used with other objects and compounds, view the GPL file AHU2. The following DOS path name indicates the location of the file: <FMS>\APPS\AHU\AHU2.(GPL) Air Handlers Optimal Start Time: Precool and Preheat 11

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24 Notes Controls Group FAN E. Michigan Street Metasys Network Technical Manual P.O. Box 423 Revision Date 0191 Milwaukee, WI Printed in U.S.A. 24 Air Handlers Optimal Start Time: Precool and Preheat