For the past three weeks, I’ve been writing about variable speed drives (VFDs) and the benefits they offer beyond constant pressure. While delivering constant water pressure is still the most recognized benefit of these systems, their potential far exceeds that one application. This week’s examples are more regional in nature, but hopefully they will help you start thinking about other ways VFDs can solve problems.
In many parts of the western US, wells are frequently pumped faster than they can recharge, making some type of dry run protection necessary. As a result, these installations have Pumptec or a similar type of dry run (underload) protection. However, VFDs already have this protection built into them. In addition, not only do they have protection by design against underload, most also have overload (bound pump) protection built in, as well as undervoltage and overvoltage protection. In cases where you know that an installation may face challenging conditions, for a small incremental cost—remember, besides a Pumptec, you also need control box in a conventional system—you can use a VFD such as SubDrive for even better protection of the pump and motor.
Another niche application for variable speed systems is operating installations where fire codes are in effect. Particularly in dry areas of the country, local fire codes dictate the minimum size pump required for fire protection. In the majority of cases, the GPM the pump is required to deliver in case of fire far exceeds the output required for regular daily residential usage. Here’s a real world example that I’ve seen myself: 35 GPM required for fire protection vs. 10 GPM required for daily use. Sizing a conventional system like this can be frustrating, because you end up with way more pump than the home will ever need. To maintain the one-minute run time (required by the Franklin AIM Manual) in the 35 GPM worst-case scenario, the pressure tank will also need to be far larger than daily use requires. A VFD makes a lot of sense in this case. By using a SubDrive with that 35 GPM pump, the system will operate at a speed to meet actual demand, not pump away at 35 GPM every time someone takes a shower. A VFD lets you control the pump instead of letting it control you.
Once again, in both of these examples, the homeowner also gets all the benefits of a constant pressure system that will deliver superior water pressure and performance. Everyone wins.
Side note: This week I came across an excellent explanation of what I tried to describe in the first post of this series: how constant pressure systems really compete against conventional systems more than each other. If you have a minute, read this post from marketing guru Seth Godin, who does a great job of explaining this aspect of competition.