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Copyright Carrier Corporation 2001
Slide 0
Technical Technical Program
Effects of
Altitude
The Carrier Technical
Training World of HVAC
Copyright Carrier Corporation 2001
Slide 1
OUTLINE• INTRODUCTION
• REVIEW OF ENGINEERING GUIDE
• CENTRIFUGAL FANS
• DERATION METHOD
• DIRECT DRIVE FANS
• ALTITUDE VS. ARID CLIMITE
• CONCLUSION
Copyright Carrier Corporation 2001
Slide 2
REVIEW OF ENGINEERING GUIDE
• Carrier’s Engineering Guide for
Altitude Effects
• Published 1967
• The first thing I read in 1991
• Effects of altitude.pdf
Copyright Carrier Corporation 2001
Slide 3
Three Effected Areas
• Psychrometric Properties
• Temperature Levels of Steam Coils
• Air Density
• All effected by increases in altitude
Copyright Carrier Corporation 2001
Slide 4
Psychrometric Air Properties
• Enthalpy Values
• Increases at higher altitudes
• Dew Point
• Decreases at higher altitudes
• Specific Humidity
• Increases at higher altitudes
• Different Psychrometric Charts are
available for various altitudes
Copyright Carrier Corporation 2001
Slide 5
2,500 Ft Altitude
Copyright Carrier Corporation 2001
Slide 6
5,000 Ft Altitude
Copyright Carrier Corporation 2001
Slide 7
7,500 Ft Altitude
Copyright Carrier Corporation 2001
Slide 8
Steam Heating Coils
• Higher altitudes reduces heating capacity
• Actual operating pressure is lower at higher
altitudes for the identical gage pressure
• Saturated temperature is therefore lower at
higher altitudes for identical gage pressures.
• Heating coil’s heating performance is therefore
lower for identical gage pressures
Copyright Carrier Corporation 2001
Slide 9
Air Density
• Air density is lower at higher altitudes
• Most common property effected on HVAC
equipment
• Effect directly correlates to air density
• Table is published on page 12
Copyright Carrier Corporation 2001
Slide 10
Air Density Ratio Table
Copyright Carrier Corporation 2001
Slide 11
Air Density
• HVAC systems depends on heating and
cooling the air molecules through the coil or
heat exchanger,
• Higher altitudes have less mass (air
molecules) per CFM
• To provide the same capacity as sea level,
the CFM be increased at a rate inversely
proportional to the ADR
• Many times that is not possible
Copyright Carrier Corporation 2001
Slide 12
A Practical Guide
• Carrier’s Engineering Guide For Altitude
Effects is a practical guide to determine the
effects (typically negative effects) of
altitude on HVAC systems you are
designing.
Copyright Carrier Corporation 2001
Slide 13
Centrifugal Fans
• Air density – Yes• RPM Constant (Direct Drive)
» Airflow volume is reduced
» BHP of motor is reduced
• RPM Increased (Belt drive)
» Airflow can be adjusted to equal volume flow as SL
» BHP of motor is reduced
» Divide SL TSP by ADR to calculate equivalent TSP
» Look up in fan curve RPM & BHP. This is the actual RPM
» Multiply BHP by ADR for actual BHP required
• Psychrometrics – No
• Steam Heating - No
Copyright Carrier Corporation 2001
Slide 14
Direct Drive
Furnace/Fan Coil Fan
Belt Drive
Fan
Direct Drive
Plenum Fan w/ VFD
Copyright Carrier Corporation 2001
Slide 15
Centrifugal Fans• Fan performance/selection at
altitude overview
• Determine the air density ratio
• Divide required TSP by ADR
• Look up fan performance at this
pseudo point
• This determines the required RPM
• Multiply BHP at pseudo point by
ADR to get actual BHP
• ..\2011\AHU-5000 CFM.pdf
Copyright Carrier Corporation 2001
Slide 16
Centrifugal Fan Selection
Copyright Carrier Corporation 2001
Slide 17
Centrifugal Fans• Volume (CFM) Vs. Mass flow
(Lbs/min)
• Previous example was 5000 CFM
• At 6,000 ft altitude, RPM was 1,309
• At sea level, RPM needed was 1,180
• At 6,000 ft, 1,180 RPM can not achieve
3.0” (5,000 CFM @ 2.4”)
• At 1,309 RPM
• Volume flow is 5,000 CFM
• Mass flow is equal to 4,000 CFM @ SL
Copyright Carrier Corporation 2001
Slide 18
Effects of lower mass flow
• Pros
• Lower BHP to deliver the same volume
• Less energy required to meet required
ventilation rates Getting away with
murder)
• Cons
• Lower delivered cooling capacity of
AHU
» Especially chilled water coils
• Lowers suction temperatures
» Freezing coils
» Wasted energy on latent capavcity
Copyright Carrier Corporation 2001
Slide 19
Direct Drive Fans
• Direct drive fans at altitude really hurt
• High speed is high speed
• Lowers Volumetric flow (CFM)
• Double Wammy when taking into account Air
Density Ratio (1400 CFM sl on 5 ton)
• Oversize blowers when possible
• Rooftops can’t be done
• Split systems up to 4 tons can (2 ton ACU / 2.5
ton furnace)
Copyright Carrier Corporation 2001
Slide 20
Effects on Compression
• Air Density – No
• Psychrometrics – No
• Steam Heating – No
• No Effects
Copyright Carrier Corporation 2001
Slide 21
Water Cooled Condensers
• Air Density – No
• Psychrometrics – No
• Steam Heating – No
• No Effects
Copyright Carrier Corporation 2001
Slide 22
Air Cooled Condensers
• Air Density – Yes
• Typically prop fans
• Airflow is held constant
• Air mass is decreased @ higher altitudes
• Performance is reduced
• Psychrometrics – No
• Steam Heating – No
Copyright Carrier Corporation 2001
Slide 23
Copyright Carrier Corporation 2001
Slide 24
Evaporative Condensers
• Air Density – No
• Psychrometrics – Yes
• Typically Prop Fans
• Airflow is held constant
• Enthalpy increases at altitude
• An increase in performance is caused
• Steam Heating – No
Copyright Carrier Corporation 2001
Slide 25
Evaporative Condensers
Copyright Carrier Corporation 2001
Slide 26
Chiller Barrells
• Air Density – No
• Psychrometrics – No
• Steam Heating – No
• No Effects
Copyright Carrier Corporation 2001
Slide 27
Absorption Chillers
• Air Density – No
• Psychrometrics – No
• Steam Heating – Yes
• Gage pressure at altitude has a lower operating
pressure compared to identical gage pressure at
seal level
• Lower actual pressure gives lower performance
• Typically corrected by setting at higher gage
pressure.
Copyright Carrier Corporation 2001
Slide 28
Absorption Chillers
Copyright Carrier Corporation 2001
Slide 29
Air Cooled Condensing Units
• Air Density – Yes
• Typically prop fans
• Airflow is held constant
• Air mass is decreased @ higher altitudes
• Performance is reduced
• Compressor / Condenser cross plot reduces the
effects compared to a straight condenser
• Psychrometrics – No
• Steam Heating – No
Copyright Carrier Corporation 2001
Slide 30
Air Cooled Condensing Units
Copyright Carrier Corporation 2001
Slide 31
Air Cooled Chillers
• Air Density – Yes
• Typically prop fans
• Airflow is held constant
• Air mass is decreased @ higher altitudes
• Performance is reduced
• Compressor / Condenser cross plot reduces the
effects compared to a straight condenser
• Psychrometrics – No
• Steam Heating – No
Copyright Carrier Corporation 2001
Slide 32
Air Cooled Chillers
Copyright Carrier Corporation 2001
Slide 33
Chilled Water Coils
• Air Density – Yes
• Centrifugal fans can be adjusted to deliver
identical airflows
• Face areas of coils typically limit increasing
CFM (Increasing to published max helps)
• Coil ratings typically are done by comparing
identical air mass rates for altitude
• Multiply the altitude CFM by the ADR to
obtain seal level CFM rates
• Obtain coil performance from sea level
tables/charts
Copyright Carrier Corporation 2001
Slide 34
Chilled Water Coils
• Psychrometrics – Yes
• If coil performance includes significant
dehumidification, higher altitudes will release
more moisture and increase the capacity of the
cooling coil performance.
• Less CW flow is required to obtains the same
SL performance.
• If coil is 95% sensible (like our climate), CW
flows are identical
• Steam Heating – No
Copyright Carrier Corporation 2001
Slide 35
Chilled Water Coils
Copyright Carrier Corporation 2001
Slide 36
DX Coils
• Air Density – Yes
• Centrifugal fans can be adjusted to deliver
identical airflows
• Face areas of coils typically limit increasing
CFM (Increasing to published max helps)
• Coil ratings typically are done by comparing
identical air mass rates for altitude
• Multiply the altitude CFM by the ADR to
obtain seal level CFM rates
• Obtain coil performance from sea level
tables/charts
Copyright Carrier Corporation 2001
Slide 37
DX Coils
• Psychrometrics – Yes
• If coil performance includes significant
dehumidification, higher altitudes will release
more moisture and increase the capacity of the
cooling coil performance.
• Less CW flow is required to obtains the same
SL performance.
• If coil is 95% sensible (like our climate), CW
flows are identical
• Steam Heating – No
Copyright Carrier Corporation 2001
Slide 38
DX Coils
Copyright Carrier Corporation 2001
Slide 39
Cooling Coil Face Velocities
• Air Density – Yes
• Less air molecules to cause condensate water
carry-over
• Increases the published maximum air velocities
• Psychrometrics – No
• Steam Heating – No
Copyright Carrier Corporation 2001
Slide 40
Cooling Coil Face Velocities
Copyright Carrier Corporation 2001
Slide 41
Steam Coils
• Air Density – Yes• Centrifugal fans can be adjusted to deliver identical
airflows
• Air mass is reduced
• Capacity is reduced
• Psychrometrics – No
• Steam Heating – Yes• Gage pressure at altitude has a lower operating pressure
compared to identical gage pressure at seal level
• Lower actual pressure gives lower performance
• Typically corrected by setting at higher gage pressure.
Copyright Carrier Corporation 2001
Slide 42
Steam Heating Coils
Copyright Carrier Corporation 2001
Slide 43
Steam Heating Coils
Copyright Carrier Corporation 2001
Slide 44
Hot Water heating Coils
• Air Density – Yes
• Centrifugal fans typically can be adjusted to
give identical airflow
• Face area of coils typically limit increasing
CFM.
• Less mass flow reduces capacity
• Coil ratings obtained by using correction factor
on performance at seal level
• Psychrometrics – No
• Steam Heating - No
Copyright Carrier Corporation 2001
Slide 45
Hot Water heating Coils
Copyright Carrier Corporation 2001
Slide 46
Electric Heaters
• Air Density – Yes
• Capacity is not reduced since the capacity is
based on power consumption of the heating
element (Higher LAT’s)
• Minimum published airflows must be increased
to avoid tripping thermal overloads
• Psychrometrics – No
• Steam Heating – No
Copyright Carrier Corporation 2001
Slide 47
Electric Heaters
Min Airflow = published min / ADR
Copyright Carrier Corporation 2001
Slide 48
Gas Heat Exchangers
• Air Density – Yes
• Heat exchanger and flue systems are designed
for constant air volume
• Lower air density causes reduction in
combustible air at higher altitudes
• Reduces capacity 4% / 1,000 FT of elevation
• Psychrometrics – No
• Steam Heating - No
Copyright Carrier Corporation 2001
Slide 49
Direct Combustion Gas Heat& Power Burners
• Direct Combustion MUA’s and Power Burner
Boiler system state that they do not have any
reduction in output capacity at higher elevations.
• This is true if the natural gas is not de-rated by the
utility company – also called ‘Hot Gas.”
• Most utility companies derate their gas, so
installing contractors do not need to change the
gas orifices.
• Since they do derate the gas, the same 4%/1000 ft
should be used for direct fired and power burned
applications.
Copyright Carrier Corporation 2001
Slide 50
Room Fan Coils
• Air Density – Yes
• Typically direct drive centrifugal fans – Air
volume is decreased!
• Air mass is decreased (lower CFM & ADR)
• Performance is reduced
• Psychrometrics – No
• Steam Heating - No
Copyright Carrier Corporation 2001
Slide 51
DXRoom Fan Coils
Copyright Carrier Corporation 2001
Slide 52
CW Room Fan Coils
Copyright Carrier Corporation 2001
Slide 53
Package Rooftops
• Air Density – Yes• Centrifugal fans typically can be adjusted to give
identical airflow
• Face area of coils typically limit increasing CFM.
• Cooling ratings are typically done by comparing
identical air flow rates for SL at Altitude
• Obtain coil performance from sea level tables/charts
and multiply by correction factors for total and sensible
capacity
Copyright Carrier Corporation 2001
Slide 54
Package Rooftops
Copyright Carrier Corporation 2001
Slide 55
Air Friction Loss
• Air Density – Yes
• Reduces friction loss at same velocities
• Multiply ACFM by ADR to determine SCFM
• Look up SL friction loss in SL table
• The SL friction loss at the SCFM is the actual
loss for the ACFM at altitude
• Psychrometrics – No
• Steam Heating - No