Introduction to BAS Technology Dave Kahn, P.E.
Why Back to basics? Sometimes you get what you ask for resulting in: The perfect job OR Unhappy owners & occupants Unexpected network limitations Product and application problems Accuracy not correct for application Installation problems RFI s, Change orders
Temperature Sensors Thermister (Negative Temperature Coefficient) Advantages Large resistance change with temperature Long term stability (<0.05F/year) Fast response Accuracy ± 0.36F Low cost Disadvantages Non Linear Single point sensing (Series parallel for averaging) Many different resistances available 10K most common
Temperature Sensors RTD Temperature Sensors (Restive Temperature Devices) Advantages Linear Long term stability (0.005F/Year) Easier to configure for averaging applications 1000 Ohm platinum most common Also copper & nickel-iron Disadvantages Low resistance Vs. temp change Cost Accuracy depends on quality specified ± 0.25% or 0.15% of range
Temperature Transmitters Sensor-Transmitter Advantages Linear Accurate Noise Immune Adjustable span 2-20 ma Most Common Disadvantages Cost Drift Accuracy depends on Quality Specified
Installation Tips Averaging Elements: Temp Sensor perpendicular to coil piping Low temp safety Parallel to coil pipes Space Sensors Interior walls Seal behind the sensor Insulated base for exterior walls
Pressure Transmitters Air Space Static Low range, medium accuracy (1% FS), high proof pressure (5psi), stability (1% / year) Duct Static Medium range, medium accuracy (1% FS), high proof pressure (5 psig) stability (1% / year) Water Differential Pressure Span to match system, medium accuracy, high (3000 psig) proof pressure
Installation Tips DPTs Never tap the top or bottom of the pipe. Slope 1 per Foot Minimum 5 valve manifold a must
Digital Inputs Fan Status (think Analog) Damper/valve position (think Analog) Alarms Filter (think Analog) Low Temp Limit Fire Alarm Contact Closure KW pulse KWH
Control Valves Types: Globe Ball or Characterized Ball Rotary segmented Plug Valve Butterfly Pressure independent 2-way, three-way, no way Plug characterization linear, equal percentage Selection Pressure drop rules H= (GPM/Cv) 2 Location within the system Rangeability
Dampers Dampers Types: Parallel Blade Opposed Blade Mixed Fire - Fire/Smoke - Smoke Selection Pressure drop curves Location within the system Velocity 1000+ fpm
Dampers Fundamentals Handbook
Normal Position Position of device without power NO Normally Open NC Normally Closed How? Spring return Battery or capacitor Where? Outside air Some large heating valves Other Option? Fail in place
Hard Wired Safety Devices Low Temp Limit Manual reset 1 of element below setpoint Setpoint changes with altitude (set higher 1º /1000 ft) Smoke UL Listed Temp Limits 32-120 Location Pressure Manual reset UL864-UUKL
Network Protocols --------Standard Protocols--------- BACnet LonWorks Others ANSI/ASHRAE 135 BTL ANSI/EIA 709.1B LonMark Certified Proprietary Open Modbus Physical Media Gateways & Routers Transport protocol - Ethernet (ISO 8802-3) ***Don t specify BIBBs & Profiles***
Ins & outs thru the network VFD's Chillers Boilers Air Handlers Heat Pumps Other systems
Two Position Control
PID Control Proportional Control Responds to the error from setpoint e = r-c error = setpoint measured temperature M=(B +Kp * e) M = Output B = Bias Term Kp = Proportional Gain e = Error
PID Control Integral Control Responds to the time from setpoint e = r-c error = setpoint measured temperature M = i e Ƭ dƭ M = Output K i = Integral Gain e = Error Ƭ=Variable of integration; takes on values from time 0 to the present.
PID Control Derivative Control Responds to the speed and direction of the deviation from setpoint M = D -- Like in don t use M = Output Kd = Derivative Gain E = Error
PID Control
OPERATOR INTERFACE Text Based Simple, Quick Graphic Pictorial good for operator training Web Based Remote access Any web browser with correct password Dashboards
Operator Interface
Operator Interface
Programming Languages 10 IF AINP1:AV > AINP2:AV THEN 20 ELSE 30 (compare input 1 and 2) 20 HIGH:AV = AINP1:AV (If input 1 is high the set HIGH to equal input 1) 30 HIGH:AV = AINP2:AV (If input 2 is high the set HIGH to equal input 2) 40 IF AINP3:AV > HIGH:AV THEN 50 ELSE 60 (compare input 3 to HIGH) 50 HIGH:AV = AINP3:AV (If input 3 is high the set HIGH to equal input3) 60 IF AINP4:AV > HIGH:AV THEN 70 ELSE 80 (compare input 4 to HIGH) 70 HIGH:AV = AINP4:AV (If input 4 is high the set HIGH to equal input3) 80 RETURN (Start over) Easier to learn and understand Off-line debugging Flexibility for novel or complex applications Who s really going to program the system
ASHRAE Guideline 13-2014 Specifying Direct Digital Control Systems Purpose of Guideline: Provide the new or experienced designer or developer of BAS systems including: BAS background information Recommendations of good practices Project scope Detailed discussions of options Performance monitoring
ASHRAE Guideline 13-2007 Specifying Direct Digital Control Systems Example specification language Explanation of why to include features Explanation of components and systems Annex currently out for public review on Performance Monitoring
ASHRAE Sequences of Operation for Common HVAC Systems 28 Air side system types Things to consider System schematic Object list Sequence Mode table
Control Drawing
Object List Tag Object Name Type Alarm Graphic Trend Notes A-1 AHU-1 Space Temperature AI 60/80 1 AHU1 5 min Report 1 A-2 AHU-1 CO2 Level AI 1800 1 AHU1 5 min Report 1 A-3 AHU-1 Supply Air Temperature AI 40/100 1 AHU1 5 min Report 1 A-4 AHU-1 SA Humidity Level A-5 AHU-1 Humidifier Modulate AI 80 1 AHU1 5 min Report 1 AO A-6 AHU-1 Supply Fan Status BI Fail AHU1 COV Report 1 A-7 AHU-1 Supply Fan Start/Stop A-8 AHU-1 CW Coil Valve Modulate BO AO AHU1 AHU1
Sequence SECTION II SEQUENCE OF OPERATION The occupancy mode (Occupied or Unoccupied) shall be determined through a user-adjustable, graphical, seven-day schedule with a holiday schedule. Whenever the supply fan is de-energized, as sensed by the status switch, the outside and exhaust air dampers shall be closed and the return air damper shall be open, the heating and cooling valves shall be closed or positioned as described below and the humidifier shall be locked out. A. OCCUPIED MODE 1. The supply fan shall be energized. 2. There shall be separate heating and cooling space temperature setpoints with a 5 F deadband between the heating and cooling 3. The heating coil valve and cooling coil valve shall modulate in sequence to maintain supply air temperature setpoint. There shall be a deadband between heating and cooling. 4. Minimum Outside Air: The minimum OA flow rate is established by the required outdoor air flow with no occupants (Vat) and the required outdoor air flow at design occupancy (Vot). The damper positions corresponding to these two airflow rates shall be set in conjunction with the balance contractor. The OA damper shall modulate between the no occupants position and the design occupancy position as the space CO2 concentration varies from 400 ppm (ambient) to 1,500 ppm (adjustable).
Mode Summary Device Occupied Unoccupied Safeties Off Setback Warm-up Pre-cooling S Fan On Off Cycles On On Off OA Damper Modulate to maintain CO 2 setpoint subject to min position Closed Closed Closed Closed Closed HW Valve Modulate in sequence with CW valve Cycle if OAT < 35, otherwise closed Modulate Modulate Closed Cycle if OAT <35, otherwis e closed CW valve Modulate in sequence with HW valve Open if OAT < 35, otherwise closed Closed Closed Modulate Open if OAT <35, otherwis e closed
Commissioning Initial Get the system you paid for Base line for future operations Retro commissioning Get back to working status ASHRAE 1137 RP commission as often as the energy savings pays back typically 3-5 years Continuous Keep things fully functional Fine tune
Learning More ASHRAE Guideline 13 ASHRAE Sequences CD Books Fundamentals of HVAC Direct Digital Control Frank Shadpour DDC Online (http://www.ddc-online.org). This website details the network architecture of a core group of controls manufacturers. ALI Control Classes Be involved with ASHRAE
Questions