Dave Kahn, P.E.Dave Kahn, P.E.

Sometimes you get what you ask for resulting in:

The perfect job

ORUnhappy owners & occupantsUnexpected network limitations Product and application problemsAccuracy not correct for applicationInstallation problems RFI’s, Change orders

Thermister (Negative Temperature Coefficient)

Advantages Large resistance change with temperatureLong term stability (<0.05F/year)Fast responseAccuracy ± 0.36FLow cost

DisadvantagesNon LinearSingle point sensing (Series parallel for averaging)Many different resistances available 10K most common

RTD Temperature Sensors(Restive Temperature Devices)

Advantages LinearLong term stability (0.005F/Year)Easier to configure for averaging applications1000 Ohm platinum most commonAlso copper & nickel-iron

DisadvantagesLow resistance Vs. temp changeCostAccuracy depends on quality specified

± 0.25% or 0.15% of range

Sensor-Transmitter

Advantages LinearAccurateNoise ImmuneAdjustable span2-20 mA Most Common

DisadvantagesCostDriftAccuracy depends on Quality Specified

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

AirSpace Static

Low range, medium accuracy (1% FS), high proof pressure (5psi), stability (1% / year)

Duct StaticMedium range, medium accuracy (1% FS), high proof pressure (5 psig) stability (1% / year)

WaterDifferential PressureSpan to match system, medium accuracy, high (3000 psig) proof pressure

Never tap the top or bottom of the pipe.

Slope 1” per Foot Minimum

5 valve manifold a must

Fan Status (think Analog)Damper/valve position (think Analog)Alarms

Filter (think Analog)Low Temp LimitFire Alarm Contact Closure

KW pulseKWH

Types:GlobeBall or Characterized BallRotary segmented Plug ValveButterflyPressure independent2-way, three-way, no wayPlug characterization – linear, equal percentage

SelectionPressure drop rulesH= (GPM/Cv)2

Location within the systemRangeabilityASHRAE Research Project 1454

DampersTypes:

Parallel BladeOpposed BladeMixedFire - Fire/Smoke - Smoke

SelectionPressure drop curvesLocation within the systemVelocity 1000+ fpm

Selecting Outdoor, Return, and Relief Dampers for Air Side Economizer Systems

Mixing boxes don’t mixReturn dampers generally parallelOA dampers generally parallelRelief damper generally opposed blade

SelectionUses the Alpha valuesOA damper size “not Critical”

Position of device without powerNO Normally OpenNC Normally Closed

How?Spring returnBattery or capacitor

Where?Outside airSome large heating valves

Other Option ?Fail in place

Low Temp LimitManual reset1’ of element below

setpointSetpoint changes with

altitude (set higher 1º/1000 ft)

SmokeUL ListedTemp Limits

32-120Location

PressureManual reset

UL864-UUKL

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 BIBs & Profiles***

VFD'sChillersBoilersAir Handlers“Other” systems

Proportional 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

Integral ControlResponds to the time from setpointe = r-c error = setpoint – measured temperatureM =

M = Output

Ki = Integral Gain

E = Error

Derivative 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

totalI+ bias

D PP

I + Bias

D

Text Based Simple, Quick

GraphicPictorial good for operator training

Web BasedRemote access Any web browser with correct password

Building controllers Larger I/O count, more powerful processor, Fully programmable

Custom application controllersMid size I/O count, medium processor, programmable or configurable, limited capacity & memory

Application specific controllers (ASCs)VAV boxes, small air handlers Configurable not programmableSmall low capacity processors

Most manufacturers support these three types of controllers with comparable functionality.

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

Purpose of Guideline:Provide the new or experienced designer or developer of DDC systems including:

DDC background informationRecommendations of good practicesProject scopeDetailed discussions of options

Example specification languageExplanation of why to include featuresExplanation of components and systems

28 Air side system typesThings to considerSystem schematicObject listSequenceMode table

Tag 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

SECTION 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 5 F 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).

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

SimpleFan status & fan command mismatchLow mixed air temperature

MediumHeat valve open discharge temp low, Boiler on, pumps on

ComplexMonitor chiller data detect impending failure

InitialGet the system you paid forBase line for future operations

Retro commissioningGet back to working statusASHRAE 1137 RP commission as often as the energy savings pays back typically 3-5 years

Continuous Keep things fully functionalFine tune

ASHRAE Guideline 13ASHRAE Sequences CDBooks

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.Automated Buildings (http://www.automatedbuildings.com/). This site is an e-zine on building automation and controls. There are a wealth of articles on a wide variety of control issues.ALI Control ClassesBe involved with ASHRAE