Saving on copper

Last week I provided just one example of how variable speed, constant pressure systems aren’t always about constant pressure. Specifically, I showed how a variable speed controller can extend system life. My example was an older system that was getting heavy usage (and cycling) with an irrigation system.

Here’s a slightly different example. I’ve never given a seminar or presentation on constant pressure systems without someone asking, “How much do they cost?” Although I can usually provide a ballpark list price and refer them back to the distributor for their pricing, my answer is “it depends.” The reason is that although there is additional cost associated with a variable speed drive, there can also be some significant savings that offset this cost.

The example cited most often is being able to use a small tank. However, an overlooked, sometimes far more significant savings can be obtained because of the smaller cable required. Here’s why … Regardless if the input is single- or three- phase, most VFDs generate a three-phase output voltage (Franklin Electric’s MonoDrive and SubDrive2W are notable exceptions). So, we use a three-phase motor, and for the same horsepower, the current (amp) carrying requirements are smaller for a three-phase motor than for a single-phase. Therefore, in many installations, we can go with a smaller gauge of drop cable if it’s three-phase.

Here’s an example: Let’s say you’ve got a 3 horsepower system with a total cable run of 500 feet. From the single-phase cable charts on page 11 of the AIM Manual, #8 is only good for 470 feet. So, to ensure adequate voltage to a single-phase 3 horsepower motor, you’re going to need #6, which is good for 750 feet.

However, it we use a SubDrive 150 and a 3-phase motor, we use the three-phase charts on page 16 of the AIM Manual. In this case, #10 is good for 620’. So, by adding a VFD into the system, we’ve gone from 500 feet of #6 cable to 500 feet of #10 cable.

Now, with the price of copper, and therefore drop cable, these days, your savings on 500 feet of #10 versus #6 cable will be very significant, probably in the hundreds of dollars. In some cases, you may even save money with a VFD.

This is just one example. But, the point is that whenever you bidding a job, it’s a good idea to run the scenario above. You may be surprised at how little the difference is between the system cost of a conventional system and a variable speed system. And, once again, you’ll have all the benefits of constant pressure.

It’s not always about the pressure

Last week, I argued that the real competition for variable speed, constant pressure water systems isn’t similar products from competitors, but conventional systems. I also mentioned that some contractors are having remarkable success selling constant pressure systems against conventional systems.

In many cases, the key to this success has been finding niches for variable speed products. Interestingly, some of these niches have nothing to do with constant pressure.

A great example is using a variable speed controller to extend system life. Here’s the scenario: the homeowner has an older system, say ten to fifteen years old. There are a lot of those out there. The home has an irrigation system, and the water system gets heavy usage, cycling many times each day. Today, everything is still working fine, but given the age of what’s downhole, you’re going to have to pull and replace the pump sometime in the next few years. It could be tomorrow or in another ten years. Either way, in the scheme of things, this is one of the more expensive scenarios for the homeowner.

Here’s where variable speed comes in. Like most mechanical and electrical things, pumps and motors want to start and just run. They don’t like starting and stopping, and we properly size systems to minimize this. However, anytime we can reduce the cycling of a system, we can extend the life of that system. Franklin Electric, along with a few other manufacturers, now offers controllers that can be retrofitted into existing systems. So, without pulling the pump and in just a few minutes, this system can be retrofitted with a variable speed controller that will always match output to water demand. As a result, during the irrigation cycle, the pump will do exactly that … just come on and operate continuously at the right speed, thereby eliminating the cycling. Bottom line is that we’ve probably extended the life of that pump.

Now, it’s important to explain to the homeowner that given the age of the pump, it’s impossible to say how much its life will be extended. A fifteen-year-old pump could still fail tomorrow. However, we’ve likely achieved something very positive in terms of cost-versus-benefit. In the meantime, the homeowner has all the benefits of constant pressure as a bonus. And, when that pump does need to be replaced down the road, that variable speed controller you put in today will still be there–along with the homeowner’s new preference for the constant pressure it provides. Everyone wins.

12 AWG, 12 gauge, and #12

To many contractors, the AWG nomenclature used to specify wire gauge must be one of the more confusing things out there. It starts with the somewhat peculiar abbreviation, AWG, which stands for American Wire Gauge. This numbering scheme was established way back in 1857, and today, remains the standard in North America that specifies the cross-sectional area of a conductor, and therefore its current carrying capability.

The confusion continues with all the ways AWG can be abbreviated. For example, you or I might say or jot down that a conductor is “12 gauge”. But, that can also be expressed as 12 AWG, #12, No. 12, No. 12 AWG, or 12 ga. They all mean the same thing and are used interchangeably.

But, the confusion really sets in when we realize that the heavier the wire, the smaller the AWG designation. So, 10 AWG is far heavier than 12 AWG. That leads to the question of, “what happens when we hit zero?”  Well, we just start adding zeros. For example, 0 AWG, 00 AWG, 000 AWG … Not to be outdone, 000 AWG can also be expressed as 3/0 and #000. These are commonly pronounced (but not written) as “aught”. So, “00” is “2 aught” and “0000” is “4 aught”.

This next confusion factor is less obvious. The AWG numbers are not linear. That is, the difference in size between 12 gauge and 10 gauge isn’t the same as the difference between 14 gauge and 12 gauge. But, here’s a rule of thumb: For every 3 changes in AWG size, the cross-sectional of the wire doubles. So, #9 is twice as heavy in terms of cross-sectional area as #12. The cross-sectional area of 0 AWG is half of 0000 AWG. Continue reading

Geothermal and current loops… it all comes around

These days, quite a few of you are installing closed loop geothermal systems. These systems use long loops of flexible pipe installed underground or underwater to heat or cool a building or residence. Of course, a pump keeps the fluid moving around the loop.

Now jump to variable speed, constant pressure water systems. If you are involved with these systems, especially larger ones, you’ve probably seen or heard the term “4 to 20 milliamp pressure transducer” or “4 to 20 milliamp current loop”. These are loops as well, but loops of electrical current instead of water. And once again, it’s terminology that gets thrown out there without much explanation. So, let’s explain.

Many variable frequency drives (VFDs), especially larger units such as Franklin Electric’s HPX, utilize these 4-20 milliamp loops in conjunction with a pressure transducer. “Transducer” is just a general term for a device that converts a mechanical measurement into an electrical signal. In our case, that parameter is going to be pressure, And, keep in mind that you’ll hear the terms transducer and sensor used interchangeably in our industry.

A small power supply in the drive sends out a low DC voltage to the transducer. In the case of the HPX, its 24 volts DC. These are the “4-20 mA” terminals on the HPX. In our geothermal system, this would be the pump. Two wires connect the power supply to the transducer. This makes “the loop” or the flexible pipe. The transducer then limits the amount of current passing through it based on the amount of water pressure it is experiencing. For example, the 4-20 mA transducer used with the HPX will allow 4 milliamps to flow if the pressure is 0 psi. The upper limit of pressure can be programmed into the HPX, and at this pressure, say 80 psi, the pressure transducer will allow 20 milliamps to flow. Hence the name 4 to 20 milliamp current loop. The VFD controller then knows exactly how much pressure is out there by the amount of current “in the loop”. Continue reading

Ductile Iron and Franklin Submersible Turbines… not just jargon

Advertising and product literature are full of jargon and buzz words. They are thrown at us with such authority, with such confidence, that we are made to think something must be better because it sounds better. My cell phone has an “advanced Lithium Ion battery”. Must be better… I guess… not sure why.

I thought of this recently while reviewing a literature piece for Franklin Electric’s ST Series of turbine pumps. The discharge brackets, suction brackets, and the bowls are all made from ductile iron. I like the way that sounds, but my bet is that most people in our industry can’t tell you what ductile iron is, or why it’s better. Here’s why it actually is…

As it turns out, ductility refers to the ability of a material to flex without breaking under tensile stress. That is, from stretching, pulling or bending. Ductile is the opposite of malleable, which is a material’s ability to bend and deform without breaking under compressive stress, such as being beat with a hammer.

Ductile iron isn’t just iron, but an alloy. Alloys really took off a few thousand years ago when someone discovered that mixing melted tin with melted copper created a new metal that became known as bronze. This metal had completely different properties than either copper or tin. In this case, it was greater hardness and a superior ability to hold an edge. This turned out to be especially handy in the manufacture of the weaponry of the time. Continue reading

PID: 3 letters made simpler

Hang around any one of our industry trade shows for long, and you’re going to hear the term VFD. Of course, a lot of you are installing VFDs to deliver constant pressure and already know that a VFD is a Variable Frequency Drive.

Hang around or read about VFDs a little longer, especially on the commercial side, and you’re going to see or hear, “our VFD uses a PID controller.” But, as a rule, no tells you what a PID controller actually is, or even what it stands for. That’s probably because PID stands for Proportional, Integral, and Derivative. That right there probably explains why no one goes any further.

But, like many things, it’s not as intimidating as it sounds. A PID controller isn’t a physical device, but a piece of software inside the VFD. PID controllers are used in tons of applications beyond VFDs, and your brain has a pretty good one built right in. You use it for just about everything that requires physical action.

For example, you’re coming up on a stoplight that just went from green to yellow. Without you consciously thinking about it, your brain determines 3 things: How far am I from the light? How long has it been yellow? And, how fast am I approaching it? These get integrated into a decision that results in the correct (hopefully) physical action.

Thinking in terms of a pump now, the job of the PID controller is simple: “How fast should I tell the VFD hardware to run the pump at any given moment?” And, like your brain, it takes the answers to 3 questions (P, I, and D) to come up with the right answer under all the different circumstances and installations.

The proportional part of PID answers the question of, “How far are we off?” That is, “what’s the difference between the target pressure and the actual pressure coming from the sensor?” On one hand, it seems like that’s all we need to know. However, as it turns out, if we only tell the pump how fast to turn based on this question, there’s a tendency to chase and constantly overshoot our target. We no longer have constant pressure. Continue reading