In 1995 Southland Auto Wash increased drying horsepower at one of its busy sites from 100 to 195. At that time, we felt that there had to be a good way to reduce electrical consumption, or reduce the starting load that blower fans create. We did extensive testing with an electrical engineer and graphed savings of 45% total KWH used for a blower motor running on a VFD compared to an identical motor with identical program running on an across the line magnetic starter.

We have studied both the use of a soft start and the use of a Variable Frequency Drive (VFD) instead of a magnetic motor starter. Either of these devices will reduce the incoming current rush and consequent spike which is not only expensive electrically, but is also damaging over time to motor windings, fan bearings, and the fan itself. So both a soft start and a VFD will reduce wear and increase life for all of these components, and will reduce the overall electrical consumption.

Many carwash industry suppliers advocate a soft start with blast gates as the ideal way to operate a blower fan. While this setup does control start current, and can reduce the current between cars effectively, it requires mechanical as well as electrical components. A properly sized and wired VFD is generally less expensive than a combined soft start and blast gates, and in fact is not much more expensive than a simple soft start alone. The VFD provides the ability to control start current and avoid the inrush as well as the over-torque of components, and in addition, it allows the operator to determine at what speed to run the motors. This eliminates the need for mechanical blast gates to reduce amp draw between cars, but more importantly, the VFD instead of blast gates and a soft start also gives the operator the ability to program any preset speed(s) based on either wash type input or other input (ambient temperature, for example).

Why is it beneficial to be able to control the speed of the fans? Because they are variable torque loads. Variable torque loads are most often found in variable flow applications, such as fans and pumps. Examples of applications include fans, centrifugal blowers, centrifugal pumps, propeller pumps and turbine pumps. VFD’s offer the greatest opportunity for energy savings when driving these loads because horsepower varies as the cube of speed and torque varies as square of speed for these loads. For example, if the motor speed is reduced 20%, motor horsepower is reduced by a cubic relationship (.8 X .8 X .8), or 51%. Because of these potential savings, utilities often offer subsidies (rebates) to customers investing in VFD technology for their applications. Many VFD manufactures have free software programs available for customers to calculate and document potential energy savings by using VFD’s. Using a VFD to reduce blow-out in open bed trucks, as well as to seasonally reduce overall electrical, is a matter of simple programming.

Choosing to run a slower fan speed for a less expensive wash has become popular where operators are realizing that a $3 customer is not a profitable business opportunity. So to cut costs and reduce the expenses required to wash that $3 car, we’ve seen washes reduce their blower speed quite a bit, even to the point where there is significant impact on the quality of drying. While these type of decisions need to be individually tailored to the operation and its competitive situation, it is very easy with a VFD to select one or more preset speeds to provide “higher” or “lower” speed drying options, tailored to the wash type purchased.

In addition to using VFD technology to reduce the wear, increase the life, and reduce the electrical cost of blower fan operation, we have devised methods for controlling water and hydraulic pumps in a way that dramatically reduces heat build-up, energy waste, and pump wear and tear. Again, we find that many carwash industry suppliers categorically state that we should not run water pumps with VFD’s. This is incorrect. In fact, one of the tests used by utility companies to determine whether or not a VFD qualifies for a rebate is whether or not a bypass valve was removed from a water pump. The use of pressure transducers to “read” the actual pressure at which a pump operates can be scaled to the VFD so that one or multiple pressures are available. This can equate to speed control (hydraulics) or pressure control (water pumps). The investment is not significant, and the savings are dramatic.

The real question that many in the carwash industry have not answered correctly is this: Do the motors in your facility require a variable output? Engineers, designers and equipment builders may not recognize that the bypass and relief valves, blast gates and pressure variables used in our industry are, in fact, variable output, which can be easily and cost effectively controlled with a VFD rather than a variety of mechanical components. The mechanical wear reduction alone on fans, bearings, pumps and motors justify the extra cost of a VFD over the cost of a magnetic starter. And the ability to easily program variable output (speed) to any motor justifies any extra cost of a VFD over a soft start.