VFDs- My Experience

• Introduction- AIRAH DA01 AIRAH DA13

• Why Install VFDs?

• What are VFDs, How do they work?

• Energy saving potential

• Potential issues to be aware of

Lasath Lecamwasam CPEng MAIRAH MCIBSE MASRAE

Why Install VFDs ?

Compliance with BCA Section JFANS: • In Air conditioning/ Ventilation system: Except PAC units, all

supply air fans should have VFDs where supply air quantity can be varied.

• In Exhaust system: Exhaust system with an air flow rate of more than 1000 L/s must have VFD fan

• Carparks: If more than 40 spaces, must have VFD with CO based control- 30 ppm….

PUMPS:• In Air conditioning system: Pump delivering more than 2 L/s

& rated more than 3kW shall have a VFD

Why Install VFDs

• Efficiency- Beyond Section J– Variable Pumping in CHW and HHW Systems.– Demand Controlled Ventilation. Eg. CO₂ and CO– Control of Cooling Tower Fans- wet bulb tracking

• Performance of HVAC Systems– VAV Systems– Avoid shock of DOL starts-– Avoid voltage sags

• Safety– Stairwell Pressurisation Systems

What are VFDs

• VSD or VFD?

• VFDs- for 3ɸ motors. 1ɸ??

• Before VFDs-

– Throttling

– Impellor Replacement or Trimming

– Eddy Current Couplings

– Multi Pole Motors

– Variable Inlet Guide Vanes

Variable Inlet Guide Vanes

Variable Inlet Guide Vanes

Induction Motor

Rotor

Stator

𝑆𝑦𝑛𝑐ℎ𝑟𝑜𝑛𝑜𝑢𝑠 𝑠𝑝𝑒𝑒𝑑 𝑁 =60 𝑥 𝑓

𝑃𝑝

N - 𝑆𝑦𝑛𝑐ℎ𝑟𝑜𝑛𝑜𝑢𝑠 𝑠𝑝𝑒𝑒𝑑𝑓 – Frequency (50Hz)𝑃𝑝 – Number of Pole Pairs

Slip- Typically Rotor speed is 97% of synchronous speed (Slip 2.5-3%)

Voltage

Voltage

Voltage

Time

Time

TimeInput

Low Frequency

High Frequency

How does a VFD work?

𝑄1

𝑄2

=𝑁1

𝑁2

𝐻1

𝐻2

=𝑁1

𝑁2

2

𝑃1𝑃2

=𝑁1

𝑁2

3

With impeller diameter (D) held constant:

Q - Volumetric flow rateD - Impeller diameterN - Shaft rotational speedH - Pressure (head) developed by the pumpP - Shaft power

Pump Affinity Laws

𝑄 ∝ N

𝐻 ∝ N2

𝑃 ∝ N3

𝑃1𝑃2

=𝐷1

𝐷2

5

𝑄1

𝑄2

=𝐷1

𝐷2

3

𝑄 ∝ D3

𝑄 ∝ D5

Impeller trimming:

100%

100% on 50% Duty Cycle

Capacity

Capacity

Time

Time

50%

Capacity

Time

Energy consumption 100%

Energy consumption 50%

Energy consumption 12.5%

Energy saving potential of VFDs

ΔP1

ΔP2

Q2 Q1 Q2 Q1

ΔP1 = ΔP2

𝑃𝑜𝑤𝑒𝑟2𝑃𝑜𝑤𝑒𝑟1

=𝑄2

𝑄1

1.9

Is it 1.9??

𝑃𝑜𝑤𝑒𝑟2𝑃𝑜𝑤𝑒𝑟1

=𝑄2

𝑄1

3

Pump and System curves

RFI

Harmonics

EMC

ActewAGLService Rules

CE Mark

C ✓

AS/NZS61000

AS/NZS61800

Circuit Breaker

Motor

VFD

Isolator!

And Finally!• Very Good technology, Costs have really come down.• Design for Variable Flow, to get best outcome.• Fitting VFDs to old motors- winding failure, bearing currents.• VFD losses? Parasitic losses?• Beware of EMC- Harmonics/RFI.• Installing VFDs to external rotor motors!• IP Rating? Dust Ingress? Heat Rejection?• Bypass VFD? Safe isolation of VFD, motor.• Sizing: 120%? Maximum Ambient Temperature? Altitude?• Resonance- Fan Blades.• Noise- Can add 10dBA to motor noise. Carrier Frequency?• Fire mode operation- AS/NZS 1668 Part 1• Correct Specification. Good Installation- Segregation, screened cables

(80% screening?). Maximum length <30m? Metal isolators, terminal boxes & cable glands. No pig tales

• Protection- Circuit breaker, Overload, Thermistor.

Any Questions?

• Beyond VFDs? Permanent magnet motors?• ECDC Motors• Ask the experts- at the end.

www.esbsconsult.com.auLasath@esbsconsult.com.au