Walker Car Wash
This car wash had requested rebates from Consumers Energy (the local electric utility) for installation of Variable Frequency Drives (VFD) on its car wash dryers. It uses 12 dryers, each 15 hp. Historically this car wash has had a lot of trouble with motors, has tried soft starts and abandoned them, and has had a programmable logic controller (PLC) installed to sequentially start the dryer motors after a single input signal from its Datatrax controller. The dryer motors are left running as long as there is a car in the tunnel.
Consumers requested some sort of verification that the VFD’s would in fact reduce energy consumption. Consumers was concerned that perhaps the VFD’s would reduce current inrush on startup, but would not actually reduce energy used. Since their rebate program is predicated upon Kilowatt Hour (KWH) reduction, we set up a test to verify the savings.
Test:
We chose dryers #2 and #3, as they are mounted on the same arch, and the work required of them is identical. We left dryer #2 alone, so that the PLC would start it when it started the other dryers, and it would stay running if there were a car in the tunnel. We connected an accumulating KWH meter to determine how much power this dryer required over a period of time.
Dryer #3 we used a dedicated Datatrax relay to start and stop independently of the other dryers. We started this dryer with a gentle ramp up when a car was approaching, and shut it off between cars. We also attached an identical accumulating KWH meter.
After running these nozzles for a test period, dryer #2 had used 165 KWH and dryer #3 had used 69.2 KWH. The wash had processed 789 cars. Here in West Michigan, our net electrical cost after sales tax is 12.4 cents per KWH, so we did the math, and realized that dryer #2 using its PLC program and magnetic starter cost 2.6 cents per car to operate (.2091 KWH), and dryer #3 using a VFD and dedicated relay did the same drying for 1.1 cents per car (.0877 KWH).
The installation of all 12 VFD’s indicated a savings of 1.5 cents per car per dryer, or 18 cents per car total. That’s $180 per thousand cars, and $9,000 on 50,000 cars. Total savings on electrical consumption alone is almost 57%.
In addition to the dollar savings, the use of VFD’s will also reduce mechanical wear on impellers and motors, and will reduce noise, vibration, and current overload.
