Post on 21-Aug-2021
transcript
Introduction to BAS Technology
Dave Kahn, P.E.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 PositionPosition 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 reset1’ of element below setpointSetpoint changes with altitude (set higher 1º/1000 ft)
SmokeUL ListedTemp Limits 32°-120°Location
PressureManual reset
UL864-UUKL
Network Protocols BACnet LonWorks Others
ProprietaryOpenModbus
ANSI/ASHRAE 135
BTL
ANSI/EIA 709.1B
LonMark Certified
--------Standard Protocols---------
Physical Media Gateways & Routers
Transport protocol - Ethernet (ISO 8802-3)
***Don’t specify BIBBs & Profiles***
Ins & outs thru the networkVFD'sChillersBoilersAir HandlersHeat Pumps“Other” systems
Two Position Control
PID ControlProportional ControlResponds to the error from setpointe = r-c error = setpoint – measured temperatureM=(B +Kp * e)
M = Output
B = Bias Term
Kp = Proportional Gain
e = Error
PID ControlIntegral Control
Responds to the time from setpointe = r-c error = setpoint – measured temperature
M = i ∗ e Ƭ dƬ
M = Output
Ki = Integral Gain
e = Error
Ƭ=Variable of integration; takes on values from time 0 to the present .
PID ControlDerivative ControlResponds 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
GraphicPictorial good for operator training
Web BasedRemote 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 understandOff-line debugging Flexibility for novel or complex applicationsWho’s really going to program the system
ASHRAE Guideline 13-2014Specifying Direct Digital
Control Systems Purpose of Guideline:Provide the new or experienced designer or developer of BAS systems including:
BAS background informationRecommendations of good
practicesProject scopeDetailed discussions of optionsPerformance monitoring
ASHRAE Guideline 13-2007Specifying Direct Digital
Control Systems Example specification languageExplanation of why to include
featuresExplanation of components and
systemsAnnex 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 ListTag Object Name Type Alarm Graphic Trend Notes
A-1 AHU-1 Space Temperature
AI 60/801 AHU1 5 min Report 1
A-2 AHU-1 CO2 Level AI 18001 AHU1 5 min Report 1
A-3 AHU-1 Supply Air Temperature
AI 40/1001
AHU1 5 min Report 1
A-4 AHU-1 SA Humidity Level
AI 801 AHU1 5 min Report 1
A-5 AHU-1 Humidifier Modulate
AO
A-6 AHU-1 Supply Fan Status
BI Fail AHU1 COV Report 1
A-7 AHU-1 Supply Fan Start/Stop
BO AHU1
A-8 AHU-1 CW Coil Valve Modulate
AO AHU1
SequenceSECTION II – SEQUENCE OF OPERATIONThe 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 MODE1. The supply fan shall be energized.2. There shall be separate heating and cooling space temperature setpoints
with a 5F deadband between the heating and cooling3. 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 CO2
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,
otherwise closed
CW valve Modulate in sequence with
HW valve
Open if OAT < 35, otherwise
closed
Closed Closed Modulate Open if OAT <35,
otherwise 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