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