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TND416/D
Automatic HVAC Air
Recirculation Made Easy
with Stepper Motors
Abstract
http://onsemi.com

This technical note highlights the system requirements
and operating conditions of automatic air recirculation
valves and reviews compatibility of existing actuator types
with these requirements. When comparing the available
technologies, it becomes clear that air recirculation flap
actuators containing a bipolar stepper motor offer key
advantages over actuators with other motor types. It isshown how specific bipolar stepper motor drive techniques

TECHNICAL NOTE
can contribute to the overall system performance while thetotal system cost is minimized. The technical note elaborates
on availability and key features of motor driver integrated
circuits that allow advanced control of these novel actuators.

INTRODUCTION
addition of an automatic recirculation function. However,small-and medium-sized cars that have advanced engineswith low CO2 emissions will also benefit from a smart
air-recirculation flap because the contribution of the HVAC
fuel consumption is relatively high.
Forecasts indicate that the percentage of cars equippedwith a semi-or fully-automatic HVAC system will increaseyear-on-year. At the same time, the introduction of CO2
refrigerants leads to the potential requirement for additional
sensors to be mounted in the cabin. These trends mean that
the CO2 and IAQ (Interior Air Quality) sensor technologies
already available will increasingly be reused in small cars
and/or in cars with low-specification HVAC systems.
While the sensor aspect of the automatic recirculation
function may have been solved, there is still some workneeded to tackle the issues around flap motorization. This
paper will focus on the recirculation function, system
requirements, the air flap actuator and the driving of that
actuator.

The automotive HVAC market is mature, yet still subject
to high-end innovation. Fuel economy, comfort and safety
are the major drivers for change. In simple HVAC systems,
a continuous inflow of fresh air is conditioned and brought
into the cabin. This air leaves the car through some
ventilation openings. Typically the driver can select, bymeans of a manual control function, whether the fresh air
supply needs to be interrupted (recirculation) or not (fresh
air open).
In recirculation mode, high-end HVAC systems monitor
several cabin air parameters, recirculate the air through the
air conditioning unit back into the cabin and limit the fresh
air inlet to the minimum, while fulfilling the air parameters
set by the driver and/or the system’s specifications.
In theory [1], such automatic recirculation can reduce thefuel consumption of an HVAC system by 35%. Dependingon the climatic conditions and driving cycles, an HVAC
system can consume up to three litres of fuel per 100 km [1].
This indicates that large cars that are equipped witha low-end HVAC system will benefit the most from the

AIR RECIRCULATION SYSTEM
The efficiency of an HVAC system largely depends on theamount of refrigerant supplied to the evaporator. Replacing
the mechanical expansion valve with an electromechanicalvalve controlled by a linear stepper-motor has previously
been proposed [2] to gain better control over the flow of therefrigerant. Alternatively, the average temperature of the
airflow that runs over the evaporator could be decreased (ifthe evaporator is exposed to cooler airflow, then a smaller
refrigerant flow is required, meaning reduced compressor
activity). The lower temperature of air flowing over the

Climate control systems are one of the larger consumersof power in modern cars. In particular, the compressor
consumes thousands of Watts when operational.
One of the ways to reduce the energy consumption ofclimate control systems is to improve compressor
efficiency. However, a more important method for savingenergy is to reduce the “active time” of the compressor. In
order to do this, we need to look downstream at thecompressed refrigerant flow and verify what really happens
during compressor operation.

© Semiconductor Components Industries, LLC, 2014

January, 2014 − Rev. 1

1

Publication Order Number:
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TND416/D
Evaporator

evaporator can be accomplished by re-using, to a large
extent, the cabin air that has already been cooled rather than
the relatively warmer air from outside of the vehicle. This
mixing of the correct amount of fresh air and cabin air canbe performed by an automatic recirculation valve. This
recirculation function is a key element in the overall energy
efficiency of the HVAC system and special care has to betaken to assure correct and optimized operation over the
lifetime of the car. Let us now look at the different systemelements and important parameters and requirements for therecirculation function.

LP

Evaporator

Compressor
HP

LP

The user interface to the ON/OFF recirculation flap today
is typically a push-button. Pushing the same button several
times, the recirculation flap is opened or closed, while an
LED indicates the state of the flap. With the addition of
a second LED, one could enter and indicate a third state
called “automatic recirculation”. This second LED will
require only minimal dashboard space and no otherhardware changes.

OutsideCooling Air
Condensor(Liquid −> Gas)

(Gas −> Liquid)

Air tocool

OutsideHeated Air

LP, liquid

User Interface

HP

Electronic Control Unit

The Electronic Control Unit (ECU) operates therecirculation function based on the readings from the sensor
and a pre-set value. The ECU closes the control loop of the
fresh air regulation and operates the recirculation flap
actuator (Figure 2) in order to maintain the required CO2
levels. The frequency of operation of the circulation flap is
a function of the maximum allowed number of occupants,
the minimum volume of air in the car interior and the
maximum allowed deviation from the desired CO2 level. It
is easily calculated that five people in a 3 m3 interior will
increase the CO2 concentration by 100 ppm within 30 s.

HP, liquid

EXV
Figure 1. HVAC System
Sensors

The adaptive air recirculation system will need tocontinuously monitor the quality of the cabin air. A lack ofsufficient fresh air can lead to discomfort, headache anddrowsiness and, because this is not immediately noticed by
the driver, can result in potentially dangerous situations. Oneof the dominant indicators of fresh air consumption byhumans is the decrease of O2 and the increase of CO2 andH2O. Nowadays, CO2 sensor technology is available fromseveral Tier-1 and Tier-2 manufacturers, while O2 or H2O
sensors could also be used for sensing changes in the cabin
air composition. These interior air quality sensors differ
from the exterior air quality sensors, which focus ondetecting polluted air and preventing it from entering thecabin. The minimum requirement for a good adaptive air
recirculation system is a closed loop control based oninterior air quality. As well as the controlled – yet still
acceptable − decrease of fresh air, a slight increase of
humidity might be observed. This, however, depends largely
on interior and exterior conditions, HVAC systemparameters, cabin volume and the number of passengers. In
any case, because the interior air will be recirculated over theevaporator, it will be continuously dried. From thisobservation, it is not expected that the windscreen will show
increased fogging (hence the installation of an additional
fogging sensor might not be required).

set

ECU

fb

DriverCooledAir toCabin

The condensed water from the evaporator will needa high-quality drain and good separation from theheater-core. This is to prevent the water from re-evaporating(which would increase humidity in the cabin). Furthermore,
to avoid recirculation of germs and bad odours from theevaporator, an active sterilization system (e.g. UV-light) at
the evaporator should be considered. Note that this also
applies to HVAC systems that have no automatic
recirculation.

Recirculation Flap
Actuator
Actuator
Feedback

Fresh Air
Inlet

Cabin :
Passengers
ConsumeFresh AirInterior Fresh
Air Sensor

Figure 2. Automatic Recirculation System

The air recirculation control loop requires mainly
low-speed interventions to compensate for pressure andairspeed changes in the “Fresh Air Inlet” (Figure 2). This
happens frequently when the driving speed varies, forexample in − or in the vicinity of − cities. The airflow
through the fresh air inlet also changes when the pressure at
the suction side of the blower changes with blower speed.
For optimal control, a (low-noise) blower induces a variable
airstream across the evaporator to compensate forfluctuations in sunlight (e.g. due to a winding road orintermittent shade caused by buildings, trees or clouds). As
a result, the variable amount of fresh air through the air inlet
needs to be matched with the constant production of CO2 by
the occupants. The continuous but slow adjustment of therecirculation flap setting can easily be accommodated
within the execution time of existing software cycles.

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air that will flow into the cabin. The metering of this amountis relatively simple and is handled by means of a damper ora butterfly valve. For stable control algorithms, the flap
position should be known at all times, so some sort ofposition feedback is a must. Because the control system isfrequently re-adjusting the actuator position, contactless
operation of the motor and sensorless position feedback isdesired. The following discusses in more detail therequirements of the flap actuator.

However, the software algorithm itself will require special
attention because it is a matter of safety to ensure that thedriver is supplied with the correct amount of fresh air under
all circumstances.
Flap Actuator

The air recirculation flap actuator is a small motorized
valve that is operated by means of a driver inside the ECU.
The function of the flap is to control the amount of outside

RECIRCULATION FLAP ACTUATOR MAIN OPERATING CONDITIONS AND REQUIREMENTS
be able to maintain position (holding torque) under the
influence of external forces − ideally with minimum current
consumption. The actuator also needs to be robust enoughto run once in a while against an obstruction such as an
end-stop. The recirculation flap is operated typically at ornear its “closed” position. Suppose that an HVAC system isdesigned for a car that is able to carry five persons. The air
inlet is then designed to supply enough fresh air for
comfortable driving of all people at average speeds.
However, average car-occupancy is only slightly greaterthan one. Taking into account increased air pressure atelevated speeds, it becomes clear that, for most of the time,
the range of flap operation will be within the first 20% of its
full range.
This puts a quality requirement on the mechanical andelectrical stability of the actuator: it needs to be stableenough to move continuously during its life in a relatively
limited position range with no degradation on motor, sensor
or gears. Other factors that need to be considered are that theoperation of the actuator should have low EMC emissions
and the cost of the actuator, the cost of the required driver inthe ECU and the cost of the wiring between ECU andactuator should be as low as possible.
Let us now have a look at some available HVAC flap
actuator technologies and discuss their fitness for use in an
automated recirculation flap.

The flap actuator is positioned in the HVAC system,
which is already relatively bulky due to the air-ducts. As in
most automotive systems, the weight and size of the actuator
are important parameters. Typically, the actuator consists ofa plastic housing, an electric motor with connector anda gear-reduction system and, sometimes, a position sensor.
Because of the different materials involved, there are manyfactors influencing weight and size of actuators. Over theyears, companies have found ways to balance required
motor torques against gear-ratios and to optimize actuatorweight and size for a given functionality. Despite this there
is still some room for improvement, not least in the removalof position sensors and the introduction of new motor
technologies.
Low acoustic noise is another important consideration as
the actuator is operating in an airstream that flows directly
into the passenger compartment. Furthermore, the flap iscontinuously operated (new target positions are frequently
given) and acoustic noise should not increase significantly
over life.
The position update rate depends on the application
software loop-time and is, for example, every few seconds.
Between these position updates, the actuator is required tohold its last position despite the application of any external
torque to the flap (e.g. from a bump in the road or increased
wind speed air pressure). This means that the actuator should

AVAILABLE RECIRCULATION FLAP TECHNOLOGIES
Several solutions exist to move HVAC air flaps, including
the recirculation air flap. They differ in type of motor usedin the flap actuator and the specifics and features of the
motor control.

rotor windings; therefore, a dynamic magnetic field isgenerated inside the motor when a voltage is applied acrossthe brushes. BDC motors are made in a mature and relatively
inexpensive technology. Only two wires lead from the driverto the motor terminals. It is simple to control a BDC motor;
e.g. bidirectional drive can be achieved by means of two
transistor half-bridges. In case position feedback is required– as with the air recirculation flap − a position sensor needs
to be added. A variety of sensors exist, the most common
being Hall Effect sensors and potentiometers. This sensor(e.g. a potentiometer as depicted in Figure 3) together withthe associated ECU wiring and the impact of the size of theelectrical connector makes up a significant part of the system
cost.

Brushed DC Motors

A brushed DC (BDC) motor is an internally commutatedelectric motor, which rotates when voltage is applied to its
two terminals. It does not require a controller to switch
current in the motor windings; the commutation of thewindings of a BDC motor is done mechanically.
A segmented copper sleeve, called a commutator, resides on
the axle of a BDC motor. As the motor turns, carbon brushes
slide over the commutator, coming in contact with thedifferent segments. The segments are attached to different

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ECU

Flap Actuatorapproach is that only half the number of windings areenergized at any time (basically the unipolar stepper motor
carries double the amount of copper than that required tomove the motor).

Gear
driverBrushed DC
motor

mC

To
Flap

Vreg

Flap Actuator

ECU

Poti

supplyFigure 3. Brushed DC Flap Actuator with Sensor
mC

Other − often patent-protected − techniques exist(e.g. pulse-count), which operate without sensors but withadditional complexity to the motor driver and control
algorithm. It is also important to note that the brushes andcommutator are the parts of a BDC motor that are most prone
to wear. Because of the need for frequent operation of the air
recirculation flap, brush degradation puts a stress conditionon the long-term mechanical reliability of a recirculation
flap equipped with a BDC motor. The brushed commutation
principle in BDC motors also means continuous and quick
switching of high currents into a highly inductive load,
which can cause sparking at the commutator. Electrical arcs
such as these emit electromagnetic radiation in the form of
an electric field across a wide band of the spectrum; hence
special care needs to taken to meet the state-of-theart
Electro-Magnetic Compatibility (EMC) requirements.

Unipolar SM

Gear

4x
Low
Side
DriverTo
Flap

Figure 4. Unipolar Stepper Flap Actuator

Bipolar Stepper Motor
A bipolar stepper motor has one winding per phase.
Compared to a unipolar motor, this gives a size and weightadvantage because the amount of copper in the winding isroughly half of that for a bipolar motor with similar motor
characteristics. This is an important benefit of the bipolar
stepper motor architecture, as it allows engineers to achieve
optimal energy economics with minimum volume andweight. The two windings are electrically connected with
the ECU as depicted in Figure 5, so typically only four wires
are needed for motor operation (compared to five fora unipolar stepper motor or a BDC motor with sensor).
A bipolar stepper motor is typically driven by a dual
full-bridge transistor combination, one for each winding.
Automotive-qualified bipolar stepper motors formechatronics flap actuators have existed for many years andare found in high-end HVAC systems. These motors can
now be re-used for a dedicated low-cost air-recirculation
valve with a drive configuration as depicted in Figure 5.
Here the stepper motor driver is located inside the ECU andis is connected by means of only four wires to the sensorless
actuator.

Stepper Motors

A stepper motor is a synchronous electric motor that
divides a full rotation into an integer number of steps. It is
brushless and hence not prone to mechanical wear-out
linked to brush commutations. A stepper motor has a fixedamount of “phases” equal to the amount of “toothed”
electromagnets arranged around a central gear-shaped pieceof iron. The electromagnet is energized by an external circuit
controlling the voltage or current in the electrical windingaround the electromagnet. Using a proper electromagnet
energizing scheme, the motor can be turned by a precise
angle.
Unipolar Stepper Motor
A unipolar stepper motor has two windings per phase.
These windings are electrically connected with the ECU as
depicted in Figure 4 and, as with the BDC motor solution(with sensor position feedback), typically requires fivewires. The choice of using unipolar stepper motors inmotorized valves has mainly been dictated by theavailability of low-cost driver ICs or driver circuits;e.g. a 4 low-side driver circuit. Like BDC motors, they areoften present in the (semi-)automatic HVAC systems foundin low- to medium-end cars. One drawback of the unipolar

Flap Actuator

ECU

Bipolar SM

mC

2x
Full
BridgeDriverGear

Figure 5. Unipolar Stepper Flap Actuator

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TND416/D
STEPPER MOTOR DRIVER TECHNOLOGY
and the thermal expansion of the air-ducts and mechanicaltolerances around the flap, the full stroke of an actuator canchange over tens of full steps. Now it is important to realizethat the amount of air that flows through a nearly closed flap
is a non-linear function of the flap position. As a result, fora flap that controls small amounts of airflow, a relatively
large error on the airflow is seen. So to control accurately
and fully proportionally the amount of air flowing throughan HVAC duct, an adaptive and closed loop algorithm must
be employed. The closed-loop aspect (or merely pseudo
closed-loop) consists of running deliberately into stalled
condition once in a while. The stall detection then allows
accurate marking of the new positions starting from the fully
closed flap position. By doing this, even the smallest
flap-openings can be maintained accurately and reachedrepeatedly, yielding true proportional control. It is clear that
this mode of working offers advantages over traditional
methods that utilize open-loop absolute positioning basedon counting steps. Because these methods cannot regeneratea reference position, any permanent root cause for position
offset (like step-loss from an overload condition) needs to be
avoided, resulting in an over-dimensioned, hence
sub-optimal system. Other methods (without stall detection)
are relatively blind to where the exact end-stop position is.
Hence to be sure that the end-stop is reached in a referencing
run, these methods require driving the stepper motor
multiple steps beyond the estimated end-stop position. This
results in a blocked motor with associated acoustic noise andmechanical as well as magnetic wear-out. To guarantee thelong-term reliability, a special type of actuator is required,
which survives the mechanical vibrations present in thismode of operation. Now a device that detects the end-stopwithin one full-step will avoid the noise and vibration during
the stall condition. Stall detection within a single full-stepalso allows the rotor and stator-magnetic fields to remain
synchronized. This avoids any risk of magnetic wear-out
caused by demagnetization of the rotor due to AC magnetic
fields from the stator, and will help to maintain a stable
actuator torque over life-time.

Advanced stepper motor drive technologies have beendeveloped to optimize actuator operation in terms of factors
such as acoustical and electrical noise production andlong-term reliability. Compared to traditional architectures,new bipolar stepper motor actuator technologies offer
a balanced solution: more system benefits (i.e. an optimized
mix of features and quality) without overall system cost
penalties.
Micro-Stepping

Basic movement of a stepper motor is accomplished byswitching the windings, which energize the electromagnets,
in an alternating on/off fashion. This is called a “full-step”
movement because it aligns the rotor to the stator
tooth-by-tooth or step-by step. This is a rough mode ofoperation and can cause the system to vibrate, contributing
to increased acoustic noise during operation. Anotherpossible effect is loss of steps, (i.e. steps are skipped).
Without proper design this means that the system is nolonger aware of the exact actuator position. These effects
can be avoided or at least alleviated by operating the stepper
motor in micro-stepping mode, meaning that the windings
are energized together in such a way that the motor moves
from step to step position via several sub-positions or
micro-steps. Moving the motor in this more continuous way
has a positive impact on the stability of the motor system andresults in better performance in terms of acoustic noise andstep-loss avoidance.
Sensorless, Closed-Loop Operation

Most stepper motor driver operating schemes use an
open-loop principle and, due to the lack of feedback in thesystem, the stepper motor has to be over-dimensioned to
avoid unnoticed step-losses in all system-relevant cases(which are a function of, for example, motor load).
Over-dimensioning can be reduced by means ofa closed-loop approach using sensorless step-loss detection.
Stepper motors inherently contain a “virtual” sensor; themotor’s operation modes (running at speed, stall condition,etc) can be deducted from monitoring the backelectromechanical force or the bemf signal.

Adaptive Speed Control
Speed-critical positioning is important in situations inwhich a flap needs to be closed as fast as possible:
e.g. closing of the recirculation flap when an exterior sensor
detects the presence of polluted outside air. The back-emf
signal makes speed critical operation possible for stepper
motors by means of dedicated adaptive-speed motor drive
algorithms. This allows stepper motors to challenge one of
the main advantages of brush DC motor actuators, notably
the ability to rotate as quickly as the supply voltage and load
allows. The stepper motor is operated at the fastest speed
possible, adapting speed automatically to the actuator andflap characteristics (e.g. load). During this adaptive-speed
operation, sensor-less stall detection is operational,

Reliable End-Stop Detection and Accurate Proportional
Control
Air-conditioning flap control actuators can also benefit
from this bemf sensor capability. A stepper motor driver,with an embedded stall detection algorithm based on thebemf signal, allows the system to detect very accurately theend-stop of a flap in an HVAC air distribution channel.
Typically this end-stop is reached on purpose during
a movement – for example when the flap is operated ina near-closed position. Hitting the end-stop can also happen
due to erroneous operation or because of small mechanicaltolerances. Typically more than a thousand full steps are
required to bring a flap from a fully opened to fully closed
position. Because of the gear construction inside the actuator

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attached easily to the system. A second difficulty is thata mounted sensor should not change mass or friction of the
motor-axis, as this alters the resonance behaviour being
measured. Now this is solved easily if the resonancebehaviour and related rotor-movement is observed throughthe “embedded virtual sensor”. Please refer to [3] for more
information.

guaranteeing error-free positioning. These algorithms allow
speeds up to 1000 full steps per second.
Resonance Avoidance
The bemf signal proves to be very useful, not only for stall
detection and adaptive speed control, but also fortrouble-shooting resonance issues. A first difficulty withsolving resonance issues is that a suitable sensor cannot be

FLAP ACTUATOR TECHNOLOGIES SUMMARY
Table 1 summarizes the “fit for use” of the flap actuator
technologies discussed. Both brush DC and unipolar stepper
motors offer their advantages but also show weak points.

The bipolar stepper motor technology seems to offer the bestof both worlds and is compatible with all reviewed
requirements.

Table 1. SUMMARY OF ACTUATOR TECHNOLOGIESBrush DC

UnipolarStepper

Bipolar
Stepper

Wear-Out & Durability

−

++

++

No Brushes in Stepper

Audible Noise

−

+

++

Microstepping in Bipolar Stepper

EMC

−

+

+

Commutation Sparks in Brushed Motor

Holding Torque

−

++

++

Hold-current in Stepper

Sensorless Operation

+

++

++

BDC Requires Pulse-count if Sensorless

Cost of Control Circuit

+

++

−

Unipolar Requires only 4 Low-side Switches

Cost of Motor

++

−

++

Unipolar Stepper has 2× Cu vs. Bipolar

Number of Wires

2 to 5

5

4

Stall Detection

++

−

++

Recently Developed for Bipolar Stepper

High-speed Flap Closing

++

−

++

Recently Developed for Bipolar Stepper

Actuator Characteristic

It is up to the Tier-1 HVAC system manufacturers toassign the correct weighting to all these functions.
Observation: the system level cost is comparable for theComment

three actuator types, however if only the purchasing cost of
the motor driver itself is taken into account, then the car
manufacturer might end-up with a sub-optimized solution.

DRIVER INTEGRATED CIRCUITS
applying the “next” pulses defines the speed of the motor
movement while the state of the “direction” pin (see DIR pin
in Figure 6) defines the direction in which the motor rotates.
A simple but highly effective stall detection algorithm isimplemented and can be activated by means of the SPI bus.
For more advanced control, the sensorless function provides
motor bemf samples, which can be read out via SPI
communication. The collected samples can then be used, forexample, in an adaptive speed control algorithm for closing
the recirculation flap at maximum speed.
The HVAC system’s electronics need to be protectedagainst stress and error conditions, which are potentiallypresent in automotive applications. Therefore, proper
diagnostic functions are implemented to detect all relevant
error conditions and to prevent system and IC damage. The
IC has an interrupt output pin to warn the microcontroller
when an error occurs (see ERRB in Figure 6).

Integrated circuits that drive bipolar stepper motors
according to the technologies described in “Stepper Motor
Driver Technology” section are now available. A typical
block diagram of such an IC is shown in Figure 6. This IC
is placed inside the ECU and two full H-bridges drive thetwo phases of the bipolar stepper motor. The ECU’s
microcontroller communicates with the IC via an SPI
interface and a set of dedicated signals. A current translator
table, embedded in the driver applies the correct current to
the windings. The microcontroller needs to set only once the
SPI registers that define the winding current peak value,
micro-step mode and default direction of movement. After
this, the micro can step through the translator table byapplying only “next” signals to the IC (see NXT pin in
Figure 6). The motor driver then takes full responsibility andgenerates the requested current waveforms for full-step,
half-step or sinusoidal micro-step motions. The speed of

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VBB

Timebase

CLK
CSB

STALL

PWM

TSD

SPI

Open/
Short

DO

DIR

I−sense

MOTXN

EMC

MOTYP
PWM

Logic
&
Registers

NXT

MOTXP

EMC

Translator

DIInternal Voltage
Regulator 3.3 V

OTP

MOTYN

I−sense
POR

RHB
ERRB

Bandgap

NCV70501

TST

GND

Figure 6. Bipolar Stepper Motor Driver IC (NCV70501) − Block Diagram

CONCLUSION
actuators show incompatibilities with some of the technicalrequirements. A bipolar stepper motor valve in combination
with a novel driver offers the best possible technical solution
to meet the high-quality operation requirements of the air
recirculation valves of the future.

Automatic air recirculation valves can contribute to fueleconomy of small-and medium-sized cars. Existing flap
actuator technologies have been discussed in view ofoperating requirements of such a recirculation valve. Bothbrushed DC motor actuators and unipolar stepper motor

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REFERENCES[3] Christiam Gasparini and Johannes Vorenholt:“Stepper Motor Resonance Measurement Setup with
the AMIS-3052x/NCV7052x Evaluation Kit”,
www.onsemi.com, AND8371/D, Feb-2009.

[1] Thomas E. J. Heckenberger, Peter Kroner, Marcus
Weinbrenner, Ralf Manski, Andreas Kemle and John
Tepas: “Contribution of the Air Conditioning System
to Reduced Power Consumption in Cars”,
Convergence 2008, Detroit, Michigan, October
2022, 2008.
[2] Bart De Cock: “LIN Mechatronics Applied to HVAC
Expansion Valves”, European Mechatronics Meeting,Paris, France, June 24 & 25 2009.

GLOSSARYHVAC: Heating, Ventilation and Air-Conditioning

EMC:

Electro-Magnetic Compatibility

IAQ:Interior Air Quality

AC:

Alternating Current

IC:

Integrated Circuit

Bemf:

Back-Electro-Mechanical Force

ECU:

Electronic Control Unit

SPI:

Serial Peripheral Interface

UV:

Ultraviolet (light)

EXV:

Expansion Valve

LED:

Light Emitting DiodeLP:

Low Pressure

BDC:

Brush(ed) Direct Current (motor)

HP:

High Pressure

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TND416/D