Variable Speed Drive Systems

Over the last few years Bridge have seen a huge surge in the popularity of Variable Speed Drive Systems, or V-Drives (also known as Frequency Controllers). Growers simply can no longer ignore the huge energy savings that can be made by installing these drives.

The most common application is to install a v-drive on a heating transport pump. The V-Drives can either be controlled by the environmental computer, which calculate the energy required, and adjusts the speed of the pump accordingly. Alternatively, the V-Drive can work as stand-alone unit, which is most common when we retro fit the drives in an existing system. When installed in this way V-Drives control themselves and adjust the pump speed based on the difference between the flow and return temperatures.

Electrical motors consume about 60% of all electrical energy that is produced today! Almost half of that is used to drive variable torque loads such as pumps & fans.

One problem with these applications is that the motors are not “smart devices” and unless controlled will run at full speed regardless of the demanded load. This is an inefficient use of electricity and will reduce the life expectancy of your motor.

By utilizing less energy to drive loads, we are able to maximize our motor efficiency, save energy and reduce cost. Two good examples of this are: Transport or ring main circulation pumps & irrigation system pumps. Both pumps generally tend to be quite large and during the course of a year run for a substantial amount of time.

3v Drive Units

Lets take the example of running a 7.5kW transport pump at full speed for 335 days a year, 24 hours per day (8040 hours), with an electrical cost of 0.8 pence per kWh. If we take that same pump and vary its speed using a Bridge V-Drive, you will notice a substantial saving.

Example: Cost to run a 7.5kW transport pump at 100% speed: (7.5kW x 8040hrs x £0.08/kWh) = £4,824-00

Cost to run the transport pump with a Bridge V-Drive based on the following duty cycle:

100% speed for 10% of the time: 7.5kW x 100% x 804hrs x £0.08 = £482-40

50% speed for 60% of the time: 7.5kW x 50% x 4824hrs x £0.08 = £1,447-20

10% speed for 30% of the time: 7.5kW x 10% x 2412hrs x £0.08 = £144-72

100% duty = £4,824-00 — Variable duty = £2,074-32 = £2,749-68 or 57% saving