In short
A variable frequency drive (VFD) saves the most energy on pumps and fans because their power falls with the cube of speed — running at 80% speed needs roughly half the power. Size the drive by the motor's full-load current and duty, and allow for heat in Pakistani summers.
Key facts
- On centrifugal pumps and fans, power is roughly proportional to speed cubed: 80% speed ≈ 51% power.
- Savings are largest where the flow is currently throttled with a valve or damper.
- Size a VFD by the motor's full-load current and the load type, not by kW alone.
- Drives derate at high ambient temperatures — panel ventilation matters in Pakistan's summer.
- Danfoss solenoid and expansion valves must be matched to the refrigerant, capacity and pressure difference.
Many plants control pump and fan flow by throttling — partly closing a valve or damper while the motor runs at full speed. It works, but it wastes a lot of energy. A variable frequency drive (VFD) slows the motor instead, and on pumps and fans the savings can be dramatic.
Why VFDs save so much on pumps and fans
Centrifugal pumps and fans follow the affinity laws:
- flow is proportional to speed;
- pressure (head) is proportional to speed squared;
- power is proportional to speed cubed.
| Speed | Flow | Approximate power |
|---|---|---|
| 100% | 100% | 100% |
| 90% | 90% | 73% |
| 80% | 80% | 51% |
| 70% | 70% | 34% |
So if a fan only needs 80% of its design airflow most of the time, running it at 80% speed needs roughly half the power — far less than throttling, which leaves the motor near full load. In systems with a large static head, such as a pump lifting water to a high tank, savings are smaller, because the pump must still produce that head at any speed.
Other benefits include soft starting (less mechanical shock and lower starting current), less water hammer, and the ability to hold a pressure or temperature set-point automatically with the drive's built-in PID control.
How to size a VFD
- Motor full-load current (FLA) — the drive's output current rating must be at least the motor's nameplate current. Size by current, not just kW.
- Supply — industrial drives in Pakistan typically run on 3-phase 380–440 V, 50 Hz.
- Load type — pumps and fans are variable-torque loads and can use a normal-duty rating. Conveyors, crushers and mixers are constant-torque loads and need a heavy-duty rating.
- Ambient temperature — drives lose capacity above their rated ambient. Panels in hot plant rooms need ventilation or cooling, or a larger drive.
- Cable length and motor — long motor cables may need output filters, and old motors should be checked for insulation suitable for drive operation.
Our variable frequency drives cover 0.75 kW to 160 kW, with V/f, sensorless vector and PID control.
New or reconditioned drive?
A new drive has the full warranty and the current feature set. A reconditioned, bench-tested drive can be the practical answer when a failed drive must be replaced quickly or on a tight budget. Where a model has been superseded, we offer the current equivalent and confirm that its frame size, rating and control wiring still suit your panel.
Danfoss refrigeration valves
The same range covers Danfoss components for refrigeration and process cooling.
Solenoid valves
A Danfoss solenoid valve opens and closes a refrigerant or liquid line electrically.
- Direct-acting valves can open with zero pressure difference.
- Servo-operated (pilot-operated) valves use line pressure to open and need a minimum pressure difference to work properly — fitting one where there is little or no pressure drop is a common reason for "valve won't open" complaints.
- Check the coil voltage (for example 220 V AC or 24 V DC) and the connection type (solder, flare or flanged).
Expansion valves
An expansion valve meters refrigerant into the evaporator to hold a steady superheat.
- Thermostatic expansion valves (TXV) sense suction-line temperature with a bulb.
- Electronic expansion valves (EXV) are driven by a controller and give tighter control across changing loads.
- The valve and its orifice must match the refrigerant (R22, R134a, R404A, R407C or ammonia) and the system capacity. A wrongly sized orifice causes hunting, flooding or a starved evaporator.
Get the right drive or valve
Send the motor nameplate (kW, voltage, current) and the application for a drive, or the refrigerant, capacity and existing model number for a valve. See Danfoss valves and VFDs or send an enquiry.
Frequently asked questions
How much energy does a VFD save on a pump or fan?
Because the power of a centrifugal pump or fan is roughly proportional to the cube of its speed, running at 80% speed needs about 51% of full power. Savings are largest where flow is currently controlled by throttling a valve or damper, and smaller where the system has a high static head.
How do I size a VFD for my motor?
Choose a drive whose output current rating is at least the motor's full-load current, rated for your supply voltage (typically 380–440 V three-phase), and with a heavy-duty rating for constant-torque loads. Allow extra capacity if the panel runs in a hot environment.
Why won't my servo-operated solenoid valve open?
Servo-operated (pilot-operated) solenoid valves need a minimum pressure difference across the valve to open. If the pressure difference is too low, use a direct-acting valve. Also check that the coil voltage matches the supply.
Is a reconditioned VFD reliable?
A properly reconditioned drive that has been bench-tested before dispatch can be a reliable, faster and lower-cost replacement, especially to restore production quickly. A new drive gives a full manufacturer's warranty.