Milking equipment uses a large amount of energy on dairy farms,
but now there's a way to cut those energy costs in half. A variable
frequency drive (VFD) controller is a computerized device that alters
the motor speed of the vacuum pump in order to maintain a vacuum set
point. A pressure sensor is installed in the vacuum line close to the
receiver jar and is connected to the VFD controller which constantly
monitors the vacuum level and alters the motor speed accordingly.
Studies have found that energy use during milking can be typically
reduced by 60 percent — making a variable speed vacuum pump one of the
better investments you can make for your dairy.
The advantages of using a variable-speed vacuum pump are:
- Milk pump uses at least 50% less electricity - The VFD
determines the motor speed necessary to maintain the set point vacuum
level in the vacuum system, responding by slowing down or speeding up
the motor. The pump may operate at a fraction of its capacity during
normal operation — which is the majority of the time. This can drastically
reduce energy use. Studies have found the energy savings to be from 30 percent
up to 80 percent with the typical saving about 60 percent. Different variable-speed
drive systems may vary in appearance.
- The motor runs only as fast as necessary - Before
variable-speed vacuum pumps were developed, dairy operators had no choice
but to run the pumps at a constantly high speed — often 7 to 10 cubic feet
per minute (cfm) per milking unit. In fact, it was a common misconception
that a high motor speed is necessary to control pump levels, improve vacuum
stability and clean the system. But recent scientific research has found
that the amount of airflow needed for "steady state" milking — when all milking
units are attached without any squawking teat cups or air leaks — is as little
as 1.5 to 2.5 cfm per unit.
- Stable vacuum maintained - A vacuum pump hooked up to a VFD
responds quickly and produces a vacuum level with little variability. In other
words, the vacuum level remains constant as the motor speed changes. If a
milking unit falls off or if the system has a leak, the VFD immediately speeds
up the vacuum pump motor to remove excess air. Variable-speed vacuum pumps
maintain the level as well as and sometimes better than conventional systems.
- Your vacuum pump will last longer - A vacuum pump running at
full speed will have a shorter life span than one that regularly runs at a
lower speed. Operating a vacuum pump at reduced RPMs is easier on bearings
and other internal components, which may extend the pump's operating life.
- A lot less noise will be produced by the motor - A vacuum pump
equipped with a VFD controller will frequently operate at only half the RPMs
than it would have without a VFD, and lower RPMs are easier on the ears.
- It can pay for itself in two years or less - The money saved by
installing a VFD depends on many factors. These include size and type of vacuum
pump, size and type of milking system and the amount of time required for milking
and washing each day. Typically, a dairy milking 3 times per day or greater than
6 to 8 hours per day can justify a variable speed vacuum pump based on energy
savings.
Save money by using less electricity at your dairy. Your WPS
agricultural consultant can help you calculate your potential savings and answer
questions about variable speed vacuum pumps. Not only could the VFD pay for itself in
a few years, but you'll enjoy lower electric bills along the way.
