Vfd technology in hvac system

Explanation of savings of electricity through VFD drives in HVAC Systems, benefits of inverter technology in ACs

1. A
Presentation
on
VFD Technology in HVAC
System
and
LEDs
By
GauravGupta
VikasMahala
LalchandMeena

2. Content
VFD Control Technology
◦Induction motor
◦Saving of Energy
◦Speed Control of Induction motor
◦Working Principle of VFD
◦Energy saving calculation
◦Advantages of VFD
◦Limitations of VFD
◦Conclusion
LED and its working
LED Dimmer
References

3. VFD –
Variable Frequency Drive Control
VFD Control means that to vary the speed
of an electric motor by varying the
frequency of source supply.
Variable Frequency drives are devices used
for varying the speed of a driven equipment
(such as pumps, blowers, conveyors,
extruders, etc) to exactly match the process
requirements and achieve energy savings as
well, especially for variable torque loads.

4. Induction motors-
The motor used in Air conditioning system whether in compressor,
blower or pumps is induction motor (Squirrel cage Induction
motor).
Why induction motor –
Induction motors are simple and rugged in construction. They are
robust and can operate in any environmental condition
Induction motors are cheaper in cost due to the absence of
brushes, commutators, and slip rings
They aremaintenancefree motors
3 phase induction motors will have self starting torque unlike
synchronous motors, hence no starting methods are employed
unlike synchronous motor. However, single-phase induction motors
does not have self starting torque, and are made to rotate using
some auxiliaries.
Speed control of Induction motors are easy and smooth,
they are also efficient at low frequency operations.

5. Potential Area’s of energy
saving in AC systems

6. Chiller Systems

7. Saving of Energy -
1. Energy Consumption Cube low -
N= Speed inRPM
Torque Square of Speed (T N
2
)
Power = (N X T) (N X N
2
)
Power Cube of Speed (P N
3
)
10 % Reduction of speed gives 26 % Power Saving
2. Because of Inertia when the induction motor starts it take
very high current and starting torque is about 1.5 to 2 times
of full load torque, which is highly energy consuming.

8. Speed Control of Induction Motor
through Frequency variation -
Speed of Induction motor is given by
N = Ns(1-S)
Ns = 120* Frequency(f)
No. of Poles (P)
N = Rotor Speed (RPM)
Ns = Synchronous Speed (RPM)
S = Slip
N f
The speed of an induction motor is directly
proportional to the supply frequency. By gradually changing the
supply frequency, speed can be increased or decreased
continuously and precisely.

9. Cntd. .
If speed control is to be achieved by changing
frequency, the supply voltage also has to be
changed simultaneously as –
Flux Voltage (v)/ Frequency (f)
◦if frequency (f) is reduced keeping the supplied
voltage (V) constant, flux is increased, which causes
increase in excitation current and larger losses and
thus affects the efficiency of the motor.
◦if the frequency (f) is increased with applied voltage
(V) constant, flux will decrease thereby reducing
torque.
Therefore it is important that constant V/f ratio should
be maintained for VFDs.

10. Speed Torque characteristics of
Induction motor by V/F Control-

11. Working principle of VFD -
To get the variable frequency and variable voltage
AC supply, first we have to convert the main
supply (AC) into DC by Converters and then
again by inverters this DC converted into AC
supply, whether it is single phase or 3 phase
supply.
For this we use semiconductor devices like
SCR(thyristors) or IGBTs
There is a microprocessor is also used to control
the firing angle of SCRs by which desired
frequency and voltage magnitude produces.

12. Simple circuit diagram
Microprocessor to control the firing angle

13. Methods of voltage controls -
1. External Voltage Control -
2. PWM Control -

14. Pulse Width Modulation (PWM) technology is
mostly used in the inverter for voltage and
frequency control, because –
1.By this we get variable voltage within the
inverter without increasing the no. of
stages.,
2.The output of Sinusoidal PWM contains
more high order harmonics than lower
order, as high order harmonics are easy to
remove so it increases the quality of
output voltage waveform

15. Main Circuit diagram of PWM
Inverter –

16. Energy saving Calculation of AC with
VFD Control over conventional AC
Assumptions:-
Room area = 30 sq. meter
COP of Conventional AC =3
Conventional AC works at the 80-20%,
on/off ratio
Cooling load(Sensible + Latent) =3 ton
= 3 x 3.5 = 10.5 kW
Electrical work input = 10.5/3=3.5 kW

17. Contd. .
A 3.5kW AC operating for 14 hours during weekdays and 6 hours during
week ends(Only Saturday). In total 76 hours per week.
a. Energy cost at constant speed
Energy consumption per Year: 3.5kW ×76h ×52 ×.80 = 11065kWh.
Assume electricity rate is Rs 5.00 per kWh
Energy cost per year: 11065 kWh ´×Rs 5.00 = Rs 55,328
b. Energy cost at variable speed
The motor speed varies according to the cooling load variation through the
whole day ( in working hours) with sunshine.
Assumed: Working hours are 8 AM to 10 PM
sectionsTime No. of Hours
(N)
AvgFan Speed
(V) in %
N*V Sum/Total
hours
1 8am–11am 3 50 150
2 11am–1pm 2 80 160
3 1pm–4pm 3 90 270 70%
4 4pm –7pm 3 80 240
5 7pm-10 pm 3 50 150
Total hours - 14 Sum-970

18. Contd. .
By cooling load calculations average speed of electric motor is
about 70%, by including effect of variation of cooling load we
assumed that average speed as 75%
Now corresponding to 75% of avg. speed the power drawn is
42% of rated power consumption (3.5 kW)
Energy consumption per Year:
0.42 ×3.5kW ×76h ×52 = 5809 kWh
Energy cost per year: 416 kWh ×Rs 5.00 = Rs 29,047
c.
Value of energy saved by using “variable speed drive”
Rs 55,328 –Rs 29,047 = Rs 26,281/ year.

19. Contd..
d. Investment for running a variable speed drive
(approximate figures it is about 200$ for 1HP motor)
◦VFD price (inclusive of semiconductor circuit,
microprocessor and installation)
=Rs 50,000
Total saving –Rs 26,281/ year
e. From the above one, we can see that the payback
period is typically 1.90 years.

20. Advantage of VFD control
Huge energy saving as better control on speed of induction motors
used in AC.
Less mechanical wear tear as soft start of motors, reduces possibility
of water hammer during start and stop so over all increases life of
equipments.
accurate temperature and pressure control can be maintained as the
response time of a VFD is less.
Less payback time, high rate of recovery.
As it limit the starting current (Soft starter) to full load current, this
characteristic reduces the average maximum demand requirement
during starting.
Improves Power factor nearly to unity.

21. Limitation of VFD
VFD control is not a energy saving factor in the
location, where AC is required for all the time at
its full rated power (100%).
In this condition, VFD controlled AC will consume
more power than a Conventional AC as,
all the time Ac have to run on full speed (speed
never slows down), And at the same time the
converter and inverter devices will consume
additional power.
So in this special case AC without VFD control is
more efficient.

22. Other application of VFD control
• Supply Fans
• Exhaust Fans
• Smoke Extract Fans
• Pressure Boosting Fans
• Cooling Tower Fans
• ID Boiler Fans
• Condenser Pumps
• Chilled Water Pumps

23. Conclusion
The majority of HVAC installations which
are operating with constant speed pumps
and blowers can be converted into cost
efficient (with less drawing of reactive
power), energy saving by investing in Variable
Frequency Drives
By this a large reduction of the energy bill,
often 50% or more, very short pay back
period(typically 1.5 to 2 years) and increased
comfort levels are obtained.

24. LED
LED stands for Light Emitting Diode
A diode is an electrical component that only allows current
to flow one way when enough voltage is available.
LED is essentially a p-n junction opto-semiconductor that
emits a monochromatic light when operated in forward bias
direction
A p-n junction is basically a junction between an anode and a
cathode.
The wavelength and color of the LED depends on the band-
gap energy of the materials forming the p-n junction.
LED convert electrical energy in to light energy

25. Excitation
Electron (excited by the biased
forward voltage) is in the conduction
band
Hole is in valance band
Normallytherecombinationtakesplacebetween
transitionofelectronsbetweenthebottomofthe
conductionbandandthetopofthevalanceband
(bandexterma).
The emission of light is therefore;
hc/= E
c-E
v= E
g(only direct band gap allows
radiativetransition)
E
k

26. How does it work?
P-n junction
Electrical
Contacts
A typical LED needs a p-n junction
Junction is biased to produce even more
e-h and to inject electrons from n to p for
recombination to happen
There are a lot of electrons and holes at
the junction due to excitations
Electrons from n need to be injected to p
to promote recombination
Recombination
produces light!!

27. VISIBLE LED
Definition:
LED which could emit visible light, the band gap of the materials that
we use must be in the region of visible wavelength = 390-770nm.
This coincides with the energy value of 3.18eV-1.61eV which
corresponds to colours as stated below:
Violet~ 3.17eV
Blue ~ 2.73eV
Green~ 2.52eV
Yellow~ 2.15eV
Orange ~ 2.08eV
Red ~ 1.62eV
Colourof an
LED should
emits
The band gap, E
g
that the
semiconductor
must posses to
emit each light

28. Why LED?
•Energy Efficient, up to 90% more efficient than traditional
lighting sources
•Long life span, up to 50,000 hours
•Variety of color options
•Low operation costs
•No UV radiation
•No mercury
•Instant on, no start-up time
•Silent operation
•Reduces “Carbon Footprint”
•Roubust
•Cool
•Directional
•Controllable

29. LIGHT OUTPUT

30. Comparison
IMPORTANT
FACTS
LED CFL INCANDESCENT
BULBS
Lifespan(average)50000hours 8000 hours 1200 hours
Containsmercury no yes no
CO2 emissions less moderate high
Sensitivityto low
temperature
no yes some
Sensitivityto humidityno yes some
ON/OFF cycling No effect yes some
Turnson instantlyyes no yes
Durability Very durable Not very durable Not verydurable
Heatemmited less moderate high
Failuremodes Not typical some May be typical

31. LIGHTING CONTROL
Automatic On/Off Switching based on –
Occupancy
Daylight
Automatic Dimming Control
Automatic Stepped Dimming

34. LED Dimmer
To adjust the lumen power of LEDs as
desired, LED dimmer circuits are used.
Light output can be adjusted by varying
the supply voltage through semiconductor
device circuits.
By reducing the voltage, power consumed
by LEDs are also get reduced.

35. Voltage waveforms -
α α
α= Firing Angle
Supply Voltage
Voltage Output from Dimmer
Ckt
Vo = Average Value of Voltage O/P = (2Vm/∏) * cosα
This value of voltage depends on the firing angle (α).
V = Vmsin Φ
Vrms= Vm/(2)^½

36. THANK YOU

37. REFERENCES
Journal Published in ISHRAE by A bhadurititled The
Use of Variable Frequency Drives in Existing
HVAC Installations
http://www.energyland.emsd.gov.hk/en/appAnd
Equip/equipment/air_conditioning/vsd.html
Paper published by F. D. Fisheltitled ENERGY
SAVINGS OF VARIABLE SPEED MOTORS
Book–Variable Frequency drives by CEATI
International