Transcript Terminal Unit Overview

T.U. Overview
Terminal Unit Overview
Evan Himelstein, P.Eng.
Application Engineering
Price Industries
October 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
Discussed Today
• Control / Exhaust Valves
Discussed Today
– Siemens LGE
• Venturi Air Valves
• Dual Duct Terminals
• Fan Powered Terminals
Discussed Today
– Constant Volume / Series Flow
– Variable Volume / Parallel Flow
• Induction Terminal Units
• Retrofit Terminal Units
• Flow Measurement Devices
– Siemens LGF
Discussed Today
For more information on
terminal unit types not
covered see the Price
website,
www.price-hvac.com
Flow Measuring Devices
Siemens 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”)
T.U. Overview
Single Duct - Exhaust Terminals
Siemens LGE
• Basic unit includes
– Damper
– Flow Sensor
• SP200
• Orifice
– Duct Type
• Galvanized
• Stainless Steel
• Teflon Coated
• Model LGH discontinued
T.U. Overview
Single Duct Terminals
Siemens 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
T.U. Overview
LGS Casing Leakage
Unit
in CFM
Size 1.00” 3.00” 6.00”
4
1
2
3
6
1
2
3
8
1
2
3
10
1
2
3
12
1
2
4
14
2
3
5
16
2
4
7
18
3
6
12
in % of Max Flow
1.00” 3.00” 6.00”
0.40% 0.90% 1.30%
0.30% 0.60% 0.90%
0.20% 0.40% 0.70%
0.20% 0.30% 0.50%
0.10% 0.30% 0.40%
0.10% 0.20% 0.30%
0.10% 0.20% 0.20%
0.10% 0.10% 0.20%
T.U. Overview
LGS Damper Leakage
Unit
Size
4
in CFM
% of Maximum Flow
1.50” 3.00” 6.00” 1.50” 3.00” 6.00”
4
5
6
1.78% 2.22% 2.67%
6
4
6
11
8
10
12
14
16
18
5
6
8
6
13
98
7
7
12
10
21
154
10
10
19
16
38
305
0.89%
0.63%
0.44%
0.38%
0.20%
0.33%
1.23%
1.33%
0.88%
0.52%
0.57%
0.33%
0.53%
1.93%
2.44%
1.25%
0.74%
0.90%
0.53%
0.95%
3.81%
Single Duct
Damper Construction
• Toggle-Lock Sandwich
Construction
• 2 pieces of 22 gauge
galvanized sheetmetal riveted together
• No welding required
– Zinc anti-rust protection
is not ruined
– No heat distortion of
blade (leakage)
T.U. Overview
Single Duct
Damper Seal
• 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 Duct
Damper Shaft
• 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
T.U. Overview
Single Duct
Damper Shaft Bearings
T.U. Overview
• 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
Single Duct
Inlet Tube Construction
• Rolled Bead
– Stronger
– More Round
– Stop for hard duct
• Seam
– Riveted connection
– Sealed with caulk
T.U. Overview
• 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
SP200
Air 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
Sensible Sampling
Port Locations
Static-Pressure
Ports
Price’s SP-200 has
strategically-located
Total Pressure ports,
based on extensive
lab-tested fine-tuning.
Better than the “ducttraverse” method.
Total-Pressure Ports
T.U. Overview
Unbiased Representation
• Center-Averaging Collection Chamber
Pressure-averaging at the
center of the SP-200 gives
assurance that all four of
the quadrants’ velocities
have equal representation.
T.U. Overview
Amplification and Error
• Reliable Accuracy at Low Airflows
– Most controls require at least 0.02”-0.03”w.g. sensoroutput 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
T.U. Overview
Flow Sensing Problems
• Inlet Condition
Problems
90 deg.
Elbow
High
Velocity
No Velocity
(turbulent)
T.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)
Price only supplies
accessories for
Venturi Air Valves
T.U. Overview
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 Valve
Pressure & 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
T.U. Overview
Downstream Static Pressure
• Pressure from Downstream of Terminal Unit to
Atmosphere
T.U. Overview
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
Mid Frequency
Hz
2
3
4
5
6
7
125
250
500
1000
2000
4000
• Octave band 2
through 7 usually
associated with
terminal units
• Refers to centerline
frequencies of 125 to
4000 Hz
T.U. Overview
Noise Sources
Diffuser Noise
Damper Noise
Reciprocating and
Centrifugal Chillers
Transformers and
Fluorescent Ballasts
Terminal Boxes
Fan and Pump Noise
Structure-Borne Vibration
16
31.5
63
125
250
500
1000
Octave Band Center Frequency, Hz
2000
4000
8000
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
T.U. Overview
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 Coil
General Construction
• ½” Copper Tubes
• Aluminum Fins for Heat Transfer
• Access door for cleaning and inspection
• Right or left handed connections
T.U. Overview
Water Coil
Construction 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 Coil
Application 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 Coils
Other 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 Factors
Water 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 Calculation
Givens
• 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 Coil
How 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 Coils
Prioritization 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 Coils
Hardware 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??