Terminal Unit Overview

Evan Himelstein, P.Eng.Application EngineeringPrice IndustriesOctober 11, 2004

T.U. Overview

Agenda• Terminal Unit types and characteristics

– Single Duct Terminals• LGF – Flow Measurement• LGE - Exhaust Terminal• LGS - Supply Terminal• Construction & tube construction• Flow Sensors (SP200 & Orifice Ring)

– Venturi Air Valve• Pressure Definitions• Terminal Unit Sound / Acoustics• Hot Water Coils• General Pitfalls• Questions

T.U. Overview

Terminal Unit Types• Single duct terminal units

– Controller type – Siemens LGS – Mechanical type

• Control / Exhaust Valves– Siemens LGE

• Venturi Air Valves• Dual Duct Terminals• Fan Powered Terminals

– Constant Volume / Series Flow– Variable Volume / Parallel Flow

• Induction Terminal Units• Retrofit Terminal Units• Flow Measurement Devices

– Siemens LGF

Discussed Today

Discussed Today

Discussed Today

For more information on terminal unit types not covered see the

Price website,

www.price-hvac.com

T.U. Overview

Discussed Today

Flow Measuring DevicesSiemens LGF

• Laboratory Air Flow Station• Not really a terminal unit, but...• Galvanized Steel with optional

316L Stainless Steel Continuously Welded Construction

• Orifice Ring Sensor Available in sizes 4, 6, 8, 10, 12, 14, 16, 18, 20, 22

• SP200 Sensor Available in sizes 6, 8, 10, 12, 14, 16

• New shorter version (8”)

Single Duct - Exhaust TerminalsSiemens LGE

• Basic unit includes– Damper– Flow Sensor

• SP200• Orifice

– Duct Type• Galvanized• Stainless Steel• Teflon Coated

• Model LGH discontinued

T.U. Overview

Single Duct TerminalsSiemens LGS

• Basic unit includes– Damper– Flow Sensor (SP200)– Heating Coil (optional)– Attenuator (optional)

• Operation– Varies air volume to

space– Monitors air flow

sensor– Pressure independent

T.U. Overview

Pressure Dependent vs Independent• Pressure Dependent

– Flow rate varies with system inlet pressure fluctuations.

– Flow rate dependent on inlet pressure and damper position

• Pressure Independent– Flow rate is constant regardless of inlet pressure

fluctuations– Achieved by adding a flow sensor and flow controller– Controller maintains a preset flow through the inlet by

modulating the damper in response to the flow signal.

T.U. Overview

Single Duct Terminals

• Options– Hot Water Coils

• 1, 2, 3 or 4 rows• Standard access door for inspection & cleaning

– Sound Attenuators • 3 or 5 foot

• Price can support Specials!

T.U. Overview

Single Duct Terminals Liner

• This system integrates an engineered polymer foam which provides excellent insulating characteristics.

• The foam edges are self sealing due to the material’s composition.

• Material has a water vapor permeability of 0.0%, and will not initiate mold growth.

T.U. Overview

Siemen’s Specific Features

• Standard FF (Fiber Free) Liner

• Access door in LGS casing not in water coil

• Sensor tubes in brass fittings not rubber grommets

• Standard Extra low leakage construction

• Individually packaged – 2x Weight Cardboard Cartons

• Special Siemens Labeling

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LGS Casing Leakage

T.U. Overview

Unit in CFM in % of Max Flow

Size 1.00” 3.00” 6.00” 1.00” 3.00” 6.00”

4 1 2 3 0.40% 0.90% 1.30%

6 1 2 3 0.30% 0.60% 0.90%

8 1 2 3 0.20% 0.40% 0.70%

10 1 2 3 0.20% 0.30% 0.50%

12 1 2 4 0.10% 0.30% 0.40%

14 2 3 5 0.10% 0.20% 0.30%

16 2 4 7 0.10% 0.20% 0.20%

18 3 6 12 0.10% 0.10% 0.20%

LGS Damper Leakage

T.U. Overview

UnitSize

in CFM % of Maximum Flow

1.50” 3.00” 6.00” 1.50” 3.00” 6.00”

4 4 5 6 1.78% 2.22% 2.67%

6 4 6 11 0.89% 1.33% 2.44%

8 5 7 10 0.63% 0.88% 1.25%

10 6 7 10 0.44% 0.52% 0.74%

12 8 12 19 0.38% 0.57% 0.90%

14 6 10 16 0.20% 0.33% 0.53%

16 13 21 38 0.33% 0.53% 0.95%

18 98 154 305 1.23% 1.93% 3.81%

Single DuctDamper Construction

• Toggle-Lock Sandwich Construction

• 2 pieces of 22 gauge galvanized sheet-metal riveted together

• No welding required– Zinc anti-rust

protection is not ruined

– No heat distortion of blade (leakage)

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• Polyurethane Gasket• Flexible material provides excellent seal• Does not dry out and crack with age• 1.5 million cycle operational test resulted in no

measurable change in leakage rate– Equates to 100 full damper cycles per day, ( complete

open and closures) for 42 years

Gasket

Single DuctDamper Seal

• Solid Steel Shaft• Anti-rust Nickel Plating• Damper position indicator on end of shaft• Self-lubricating, tight-fit, low-leak bearings• Much stronger than plastic or aluminum shafts• Retaining-Clips for accurate centering

Single DuctDamper Shaft

T.U. Overview

Single DuctDamper Shaft Bearings

• Set of three bearings• Made from high density Polyethylene• Will operate to inlet static pressures up

to 6 inches W.G. with minimal leakage• Only manufacture to use 3 bearings• Tested to 1.25 million cycles

– Equates to 100 full damper cycles per day, ( complete open and closures) for 35 years

T.U. Overview

Single DuctInlet Tube Construction

• Rolled Bead– Stronger– More Round– Stop for hard duct

• Seam– Riveted connection– Sealed with caulk

• Long– Eliminates need for

straight duct before the inlet

T.U. Overview

Valve Sizing• Size Valve based on maximum and

minimum airflow– With Maximum Flow review

• Sound• Pressure Drop• Flexibility• Cost

– With Minimum Flow• Control Accuracy• Type of Controls• Select above 400 FPM duct velocity

T.U. Overview

SP200Air Volume Sensor

• The “Heart” of VAV Control

• Velocity Sensor performance is a function of:

– Cross Sectional Area

– Number and Pattern of Sensing Ports

– Amplification Factor

– Center averaging capabilities

T.U. Overview

Air Volume Sensing

• Pt = Total Pressure – Combination of Static and Velocity

• Ps = Static Pressure – The Pressure in the duct pressing in all directions

• Pv = Velocity Pressure – The pressure in the duct due to the velocity

of the air (NOT DIRECTLY MEASURABLE)

Pt = Ps + Pv OR Pt - Ps = Pv

T.U. Overview

Total-Pressure Ports

Price’s SP-200 has strategically-locatedTotal Pressure ports,based on extensivelab-tested fine-tuning.Better than the “duct-traverse” method.

Sensible Sampling

Port Locations

Static-PressurePorts

T.U. Overview

Pressure-averaging at the

center of the SP-200 gives

assurance that all four of

the quadrants’ velocities

have equal representation.

• Center-Averaging Collection Chamber

Unbiased RepresentationT.U. Overview

• Reliable Accuracy at Low Airflows– Most controls require at least 0.02”-0.03”w.g. sensor-

output signal for reliable operation

– The SP-200 flow sensor provides 0.025”w.g. at 400

FPM, – Sensors w/ low gain & poorly-averaged (worst case)

have a safe low-end of 700 to 800 FPM

Amplification and ErrorT.U. Overview

• Inlet Condition Problems

High Velocity

No Velocity(turbulent)

90 deg.Elbow

Flow Sensing ProblemsT.U. Overview

Orifice Plate Air Volume Sensing

• Orifice Ring Sensing– 4 Sensing points– Non Clogging design

• Very Robust

• Measures static pressure differential

– Airflow = k * (ΔP)½

• Watch for inlet conditions

T.U. Overview

Venturi Air Valves

• Mechanically pressure independent

• Requires a minimum static pressure ( 0.3” L.P., 0.6” M.P.)

• Consists of– Cone

• Springs• Aerodynamic shape

– Orifice Ring (Flow sensing)

T.U. Overview

Price only supplies accessories for Venturi Air Valves

Venturi Air Valve• Flow ~ Area*Sqrt(dP)

• Spring inside cone expands or compresses to compensate for changes in pressure across valve.

• At low pressure drop, spring pushes cone out, increasing flow area.

• At high pressure drop, cone compresses spring, decreasing flow area.

T.U. Overview

Venturi Air ValvePressure & Flow Variation

T.U. Overview

Venturi Air Valves• Accessories

– Sound Attenuators• 3 or 5 foot

– Hot Water Coils• 1 Row• 2 Row• 3 & 4 Row optional

– Materials• Standard: aluminum body & cone, teflon-coated stainless steel cone

rod, brackets, linkage and control arm• Heresite-coated body and cone available for corrosive exhaust

applications

T.U. Overview

Pressure

• What do all these catalog terms mean?– Minimum operating pressure– Inlet Static pressure– Downstream Static Pressure

– Differential Static Pressure (ΔPs)

T.U. Overview

Minimum Operating Pressure

• Static Pressure Drop or Loss• Wide Open Damper Position• Minimum Operating Pressure• Pressure Loss of Terminal and Accessories

T.U. Overview

Inlet Static Pressure

• Pressure From Inlet to Atmosphere

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Downstream Static Pressure

• Pressure from Downstream of Terminal Unit to Atmosphere

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Differential Static Pressure

• Pressure Drop Across Terminal Only• Not Inlet Static Pressure

• ΔPS = Inlet SP-Downstream SP

T.U. Overview

Sound Standards

• ARI 880-98 Air Terminal Test Standard

• ASHRAE 130-1996 Air Terminal Test

Method

• ARI 885-98 Application Standard

• ADC 1062 – Obsolete and replaced with

ARI Standards

T.U. Overview

Testing Standards

• ASHRAE Standard 130-1996– Specifies the methods and procedures for

performance testing of constant and variable volume air terminal units.

• ARI Standard 880-98– Determines the requirements for testing and

rating air terminals• References ASHRAE Standard 130-1996• Establishes the procedures, rating points and

tolerances for conformance to the ARI 880 Certification Program.

T.U. Overview

Catalog Sound Data

• Due to the vast scale of sound pressures over the normal range of human hearing, the Log of the actual value is used. (Makes scale smaller)

• Reference power is 10-12 Watts• The reference pressure is 0.0002 MicroBars.• dB are measured with respect to frequency• The frequencies are grouped into ‘octave

bands’

T.U. Overview

Octave Band

• Octave band 2 through 7 usually associated with terminal units

• Refers to centerline frequencies of 125 to 4000 Hz

T.U. Overview

Octave Band

Mid Frequency

Hz

2 125

3 250

4 500

5 1000

6 2000

7 4000

Noise Sources

Octave Band Center Frequency, Hz

16 31.5 63 125 250 500 1000 2000 4000 8000

Damper Noise

Fan and Pump Noise

Structure-Borne Vibration

Diffuser Noise

Reciprocating andCentrifugal Chillers

Transformers andFluorescent Ballasts

Terminal Boxes

T.U. Overview

Catalogue Sound Data

• Certified in accordance with ARI 880 Certification Program

T.U. Overview

ARI Certification

• Price units are ARI Certified, Siemens working on there Application for Certification.

• Test data submitted to ARI• Data listed in ARI Directory (and website)• Yearly Random Tests• Tested at an Independent Lab• Test Failures are Published and Penalized• Price has had a 100% Test Success Rates

since 1994

T.U. Overview

Noise Criteria (NC)

• The NC value is the most commonly specified sound criteria for diffusers and terminal equipment.

• Standard curves used to describe a spectrum of measure sound pressure levels with a single number.

• Sound pressure is not cataloged.– Must be calculated from Sound Power (in catalog)

and taking deductions (from ARI Standard 885)

T.U. Overview

NC Curves

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Sound Warning

• Compare NC values between manufacturers carefully!– Attenuation allowances between

manufacturers are not always the same.– Engineers do not specify this correctly

• Need to educate engineer on ARI Standard 885

– Prudent for labs to examine attenuation allowances since they are usually harder, i.e. noisier than the typical office space.

T.U. Overview

Application Standards

• ARI Standard 885-98– “Procedure for Estimating Occupied Space

Sound Levels in the Application of Air Terminals and Air Outlets.”

– Provides methods to use ARI Standard 880 sound ratings to estimate the sound levels which will occur in the conditioned, occupied space.

– Appendix E created with “Typical Attenuation Values” for offices

T.U. Overview

Hot Water CoilGeneral Construction

• ½” Copper Tubes

• Aluminum Fins for Heat Transfer

• Access door for cleaning and inspection

• Right or left handed connections

T.U. Overview

Water CoilConstruction Features

Construction features that have the most effect on performance …

• Fin Height / Fin Length (Coil Area)

• Number of Rows

• Fin Spacing (FPI)– 10 FPI is standard, 8 and 12 are optional

T.U. Overview

Water CoilApplication Variables

• Variable that have the most effect on performance …

– Target Variable – Coil Capacity - BTU’s / Hr (MBH)

• Airflow – CFM (cubic feet per minute)• Water Flow – GPM (gallons per minute)• Entering Air Temperature – EAT (°F)

• Entering H2O Temperature – EWT (°F)

T.U. Overview

Water CoilsOther Important Factors

• Water Pressure Drop (ft.wg.)– Can affect pump / pipe / valve sizing– Depends largely on Number of Circuits

• Air Pressure Drop (in.wg.)– Effects central fan sizing– Effects units fan capacity

• Leaving Water Temperature– Can cause problems in Hydronic System

T.U. Overview

Water Coils FactorsWater Velocity

• Laminar flow in coils produces very large MBH variations from small changes in Flow (GPM).

• Fully turbulent flow variations produce small MBH changes, high head loss, and tube pitting.

• Transitional flow is desirable, which is between the laminar and turbulent regions.

• Transitional flow range occurs between 0.5 and 8 FPS depending on many factors.

T.U. Overview

Water Coil CalculationGivens

• CFM or Airflow rates– More air = more heat

• But not PROPORTIONAL

• Entering Water & Air Temperatures– EWT has significant impact on capacity– EAT can be a mix of return, supply and fan air

• Standard coil configuration– FPI, # of circuits and rows, find type, metal thickness.

T.U. Overview

Water CoilHow variables inter-relate

• As the GPM Increases– Heat transfer & leaving air temp increases– Leaving water temperature increases– Water pressure drop increases (fast!)

• As the number of rows increase– Air pressure drop and leaving air temp increases– Water Pressure drop might increase– Leaving water temperature decreases

T.U. Overview

Water CoilsPrioritization of Parameters

• Coil must meet or exceed true MBH load– If a little low on capacity, call engineer or check– Double check MBH using Air delta T calcs– ATR (°F) = 927 x MBH / CFM

• Do not exceed the sum of specified GPMS’s– OK for a given coil to vary– Total cannot be higher, or pump & pipe change

• Keep the head below the max scheduled– Could increase the equipment requirements

T.U. Overview

Water CoilsHardware Related Choices

• Number of Coil Rows– Extra expense and air pressure drop– Sometimes specified by the Engineer– Check Spec.

• Overall Terminal or Coil Size– Larger boxes have more coil area = more

potential capacity– Can create control problems

T.U. Overview

Terminal Selection Pitfalls

• Smaller terminals for lower discharge noise

• Don’t oversize• Size 12 and over

locate over non critical area

T.U. Overview

Terminal Unit Suggestions

• Do not over pressurize ductwork– Increases Sound & Noise

• Use lined duct (in non-critical areas)– Reduces high frequency noise

• Do not have any diffuser closer than 4’ from the outlet of the terminal unit

• Limit velocity in ductwork to 1000 fpm – Best sound performance.

T.U. Overview

TU Noise - Troubleshooting

• Noise from a terminal can be due to a variety of conditions, and sometimes can be difficult to eliminate.

• First steps is to isolate the type, source and direction of the noise

• If noise is heard at the air outlet – discharge noise

• If noise is heard through the ceiling – radiated noise

T.U. Overview

Discharge Noise

• Usually caused by– High Static– Little or no internal duct lining downstream

of the terminal.– Sometimes air outlet dynamics (damper?)

• Can be reduced by– Reducing flow– Increasing air outlet size– Reducing inlet static pressure– Adding attenuation materials

T.U. Overview

Questions & Comments??T.U. Overview