HVAC Applications
COMMON TERMINOLOGY
VFD (VARIABLE FREQUENCY DRIVES)
AFC (ADJUSTABLE FREQ. CONTOLLER)
ASD (ADJUSTABLE SPEED DRIVES)
VSD (VARIABLE SPEED DRIVES)
FREQ. DRIVE
INVERTER
DRIVE
“Inverter Duty” Motors = ?? = New motors
meet
NEMA MG 1, Part 31
=
peak voltage of
1600 volts and a minimal rise time of 0.1
Typical Large HVAC System
Return Fan Supply Fan Secondary Hot/Chilled Water Pumps Primary Hot/Chilled Water PumpsCooling Tower Fans
Condenser Water Pump
Good Retrofit Candidates
Large energy cost saving possibility
Large motors
Poor present efficiency
Flows manually throttled back
Malfunctioning mechanical flow modulation
Inefficient control methods
High energy costs
Why Flow Control?
HVAC systems are designed for “worst
case” situations. Most of the time they
have excess capacity.
Controlling flow
Saves energy
Methods of Flow Control
Air flow
Inlet guide vanes
Outlet dampers
Variable pitch in motion fan
Adjustable speed
Fluid flow
Throttling valve (two-way)
Bypass valve (three-way)
Why Adjustable Speed?
Energy savings
Energy Requirements
0 100 200 300 400 500 600 Flow 0 5 10 15 20 25 30 35 40 45 50 P re s s u re 0 100 200 300 400 500 600 Flow 0 5 10 15 20 25 30 35 40 45 50 P re s s u reEnergy Requirements
Two-Way Valve (Throttling)
0 100 200 300 400 500 600 Flow 0 5 10 15 20 25 30 35 40 45 50 P re s s u re
Energy Requirements
Three-Way Valve (Bypass)
Why Adjustable Speed?
Energy savings
System control
Reduced maintenance
Why Adjustable Frequency
Drives?
High efficiency
Easy retrofit
Replace the existing motor starter
Flexible mounting
Simple control
Typical Large HVAC System
Heat Rejection Section
Chiller Cooling Tower Fans
Cooling Tower & Fluid Cooler Fan
Cooling Tower Fan
Cooling Tower Fan
Notes
Traditional Control Methods
None
Poor efficiency
Staging cells in multi-cell towers
Poor efficiency
High mechanical stress
Dual-speed motors
Moderate efficiency
Cooling Tower Fan
Notes, continued
Traditional Control Methods, continued
Variable pitch in motion fans
Good efficiency, when functioning
High maintenance, often don’t function
Other Concerns
Wasting highly treated water
Condenser Water Pump
Cooling Tower Fan
Condenser Water Pump
Cooling Tower
Condenser Water Pump
Notes
Traditional Control Methods
No active control
It is important to maintain design flow for
Proper cooling tower operation
Proper chiller operation
However the pump is often over-sized to
compensate for pipe scaling later on
Condenser Water Pump
Cooling Tower Fan
Condenser Water Pump
Heat Rejection Section
Chiller
Chiller Notes
While the chiller has a large motor,
Inaccurate control can cause major
problems
Some chillers require constant torque
Less energy savings
Be sure you know its design and
Rooftop Units
Notes
Rooftop units generally don’t have
cooling towers and condenser water
pumps
They are often direct exchange (DX) heat
with the outside air
It can be economical to retrofit drives in
CHW, HW (Water Source Heat Pump
Circulating & Booster)
Primary
Pumps
Primary Hot/Chilled Water Pump
Primary Pumps
Primary Pump
Notes
Traditional Control Methods
No active control
The pump is often oversized
Flow is reduced by
Trimming the pump’s impeller
Closing a pressure reducing valve
Primary Pump
Notes
Although some modern chillers can
accept some amount of flow variation, be
careful about attempting to actively
Secondary Pumps
Primary Hot/Chilled Water Pump Secondary Hot/Chilled Water Pump Boilers or Chillers Automatic valves at each coil control the flow of water to the coil.Variable flow in the secondary loop. Constant or
Secondary Pump
Secondary Pump Motor
Secondary Pump
Secondary Pumps
Motors
Secondary Pump
Notes
Traditional Control Methods
Valves control flow through each coil
Two-way — throttling valve
Three-way — bypass valve
For proper operation, drive systems require
two-way valves
Secondary Pump
Notes
Tertiary pump systems are much like
secondary pump systems
Because the size of the motors is generally
quite small, energy savings may also be
Single Pump Loop
Hot/Chilled Water Pumps Boilers or Chillers
3-Way Valve
Variable flow through the coils.
Constant or Variable flow through the
boiler/chiller.
Single Pump Loop
Notes
Pumping systems that do not have
separate primary and secondary loops
present unique problems
It will take significant work to convert it to a
primary/secondary system
Vary the flow through a chiller based
manufacturers specifications
Typical Large HVAC System
Air Supply Section
Supply Fan
Air Supply Section
Supply Fan
Supply Fan
Notes
Traditional Control Methods
Constant air volume systems have no direct
method of reducing air flow
The flow of water through the coils determines
the temperature of the conditioned space
Variable air volume systems use VAV boxes
Supply Fan
Notes
Methods of reducing fan capacity
Outlet dampers
Low efficiency
Require maintenance
Inlet guide vanes
Moderate efficiency
–One per fan
Require maintenance
Variable pitch in motion fans
Better efficiency
–
Often multiple
Supply Fan
Notes
Old methods of reducing fan capacity
Variable speed belt drives
Low efficiency
High maintenance
Eddy current drives
Supply and Return Fans
Supply Fan
Return Fan Notes
Notes
Traditional Control Methods
Not controlled
Controlled like the supply fan
The method of providing the control
signal depends on the control system
A fixed amount less than supply flow
Return Fan Notes
Notes
The main purpose of the return fan is to
keep from over-pressurizing the building
Examples of Some
Air Supply Systems
A wide variety of systems are used to
control air flow
Some are easy to retrofit with drives
Others require more work to retrofit with
drives
VAV System with
Fan Capacity Control
Open Loop VAV System
VAV System with
Perimeter Terminal Reheat
The sensors and control signals for drives are already present.
Dual Duct VAV System
VAV System with
Bypass Boxes
Close bypass part of VAV boxes.
Dual Duct System
Terminal units designed for constant air flow
Multi-Zone System
Terminal Reheat System
Induction Reheat System
Application Interfacing
Operator’s controls
Plain language for
Operation
Fault display
Programming
Manual speed control
Remote mounting
Application MACROs
Hand/Off/Auto control
OFF HAND
Single Motor Bypass
Circuit Breaker, Bypass &
Output contactors and fuses to
service the drive while running
Points to consider
Can the system run at full speed?
Drive fusing
Safety interlocks
Automatic bypass
Application Interfacing
Operator’s controls
Bypass
PI and PID Controller
(Closed Loop / Set Point)
Compares the desired
process variable with the
“set point” value
Proportional to the error
Integral function adds
errors over time
Derivative function
considers the rate of
change of error (only for
fast response systems)
Controlled
System
Other Considerations
Environment
Enclosure type
NEMA 1
NEMA 12
Circulating dust
Dripping non-corrosive liquid
NEMA 3R
Other Considerations
Environment
1 - 50 HP: NEMA 1 & 12, & 3R
Outdoors = -15 to 50ºC (5 to
122ºF) No De-rate
60 HP - 550 HP: NEMA 1 & 12
-15 to 40
C (5 to 104F)
Non-linear loads
draw non-sinusoidal current from a
sinusoidal line (
current doesn’t look like voltage
):
Non-incandescent lighting
Computer Equipment
UPS (Uninterruptible Power Supplies)
Telecommunications equipment
Copy machines
Variable Frequency Drives
Electronic/Controls for Facility Elec. Equip. /
Systems, Security, HVAC / Mech. equipment
Any load with a solid state AC to DC power
converter
Harmonic
Voltage
Distortion —
Increased heating in motors and other
electromagnetic equipment
Noisy operation of electromagnetic
equipment
Malfunctioning of sensitive electronics
Nuisance tripping of electronic circuit
breakers
Overheating of PF correction capacitors
Tripping of PF protection equipment
Equipment downtime
Premature component failures
Failed motors and capacitors
Harmonic
Current
Distortion —
Added heating in transformers and cables,
reduces available capacity
May stimulate a resonance condition
Excessive voltage
Shutdown / damage to electronic
equipment
May cause telephone or electronic
interference
Failed transformers, equipment
Not in Compliance with CODES,
STANDARDS, REGULATIONS, IEEE,
“GOOD DESIGN PRACTICE”
Include: Reactors (Chokes)
Least expensive when
specified to be included with
base drive package
5% impedance AC line reactors
-or- DC link reactors
Both types provide similar
harmonic benefits
Also Suppress voltage transients
that can cause equipment
damage
Harmonic Distortion
RFI / EMI
RFI = RADIO FREQ.
INTERFERENCE
conducted through the
air
EMI =
ELECTROMAGNETIC
INTERFERENCE conduct
through AC power line
RFI / EMI Hardware
RFI / EMI FILTERS: WILL BE
INCLUDED IN ALL VFD SIZES
ACH 550:
Meets EMC PRODUCT
STANDARD EN61800-3 FOR
THE FIRST Environment
restricted level
BENEFIT:
