Pay Now or Pay Forever Commissioning the Design of Control System Software

Transcription

1 Pay Now or Pay Forever Commissioning the Design of Control System Software Bill Gnerre Interval Data Systems May 2, 2007

2 The Classic Struggle Construction First cost Design it right Pay now Operations Lifetime cost Fix it later Pay forever

3 Case Study Background University business school building 110K sqft 3 AHUs 218 VAVs All with reheat Some fan powered Central plant provides chilled water & steam JCI Metasys with 8,150 points

4 Good Intent, Bad Design Control design intent issues 40% 43% Controls implementation issues 17% Control operator errors

5 Hardware Hardware Software Software Software Hardware Hardware Hardware Hardware Hardware & & Software Software

6 Example: Warm-Up Control Morning warmup sequence will be performed based on the lowest room temperature served by this air handler. The AHU will be commanded into morning warmup up to an hour (adjustable) before the scheduled occupied time is to occur. The amount of time the unit will be in morning warmup will be based on how far the lowest zone temperature is away from 68 degf. That amount of time will be based on the following table. 64 zone temperature (adjustable in GPL) 60 minutes (adjustable in GPL) 68 zone temperature (adjustable in GPL) 0 minutes (adjustable in GPL) The following will occur when unit is commanded into morning Warmup The Differential CFM between the supply & return fan will be adjusted to 0 CFM. The mixed air dampers will go to 0% ODA. The supply air setpoint will be adjusted to 95 degf (adjustable). Morning warmup will end if the unit is commanded into the occupied mode or if the zone temperature reaches its target setpoint (adjustable).

7 Example: Warm-Up Control AHU increases supply air temp to mid-90 s, but does not tell VAVs that warm-up is in progress Room temps rise to 80 + as VAVs try to cool with hot air Warm-up command triggered off one of few rooms below setpoint Warm-up command setpoint

8 A Pandemic Issues like these exist everywhere

9 An Operational Design Specification Design is not just what it looks like and feels like. Design is how it works. Steve Jobs

10 An Operational Design Specification Goals for specification: Minimize the mystery Minimize technical jargon Define integration details Describe facilities business obligations Provide integrated organizational approach Address cultural barriers

11 An Operational Design Specification Goals for building/operations: 1. Achieve comfort and IAQ in every space 2. Meet #1 at the lowest possible cost 3. Operate automatically, without operator assistance, 24x365

12 Anatomy of an Operational Spec Six main sections: Philosophy Comfort / IAQ Hardware Points Control strategies Acceptance

13 Philosophy Overview of approach Non-technical and technical audience Framework for rest of specification

14 Comfort / IAQ Define comfort & IAQ requirements in non-ambiguous terms ASHRAE standards Methodology for measurement

15 Hardware Sensors Selection Location Calibration Explain the need/value of each sensor

16 Points Name standardization List points to be exposed and why Expose points for operators Expose points for data collection/historical record Collection interval Points used for calculations

17 Control Strategies Detailed spec for software programs Predictable Repeatable Identify all points of integration Logic diagrams with English descriptions Tied to specific hardware selection

18 Acceptance Assure system meets customer obligations Verify operations, not a hardware functional test Space conditions Component operations System-level (integration) operations

19 Operations Manual Train operators How system works (not just how individual components work) How to address issues/ complaints Reduce/eliminate the 17% self-inflicted errors Increase persistence 17% Control operator errors

20 Conclusions Software is a critical component of control systems Separate from hardware Requires its own specification Must improve over typical sequence of operations to ensure predictable, repeatable result Opportunity exists for design stage Cx Challenge exists to deal with sophisticated software design and development We must get the software right before DDC will finally deliver on its potential

21 Thank You For additional information: Bill Gnerre Interval Data Systems, Inc