vfds- my experience - airah€¦ · why install vfds •efficiency- beyond section j –variable...
TRANSCRIPT
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.