Apparently, the nauseating term “low-hanging fruit” is not even a relevant idiom. According to Priceonomics.com, low-hanging fruit is all there is these days. Priceonomics says growers have for centuries been developing the modern Frankenfood-producing apple trees of today, but this miserable term lives on anyway. Priceonomics produced the following chart showing the use of four idioms for “easy” in recent decades. First, I must ask, why is pie easy? Making a good crust is as easy as dunking two basketballs at once. And why are fish in a barrel? My choice for replacing the miserable “low-hanging fruit” is “can of corn” (canacorn as we used to say), referring to an easy catch in baseball. Try that next time – the canacorn is gone!
Okey dokey. This canacorn came to mind as I was contemplating the DOE’s recently released Energy Conservation Standards for Pumps. Why? Because I know a few things about pumps, pumping systems, efficiency, and energy use. As with other components and systems, pump efficiency hardly matters. System design and equipment selection is where energy is either grotesquely wasted or merely vanilla wasted. This is not a canacorn.
The Pump Standard
Using the high end for the canacorn savings estimated by the DOE effort, the standard would save consumers $1.4 billion over a 30 year analysis period from 2020 to 2049. The incremental cost would be $0.3 billion over the same period. I only include the energy savings because emissions savings they note are not yet, and may never be, monetized.
What does the pump standard do? Simply, it knocks what are currently the worst pumps off the shelf. Pumps with efficiencies in the lowest 25th percentile would be packing for pump heaven. On a percentage basis, the standard is estimated to reduce pumping energy by a measly 1%. Woohoo!
Energy Codes and Pumps
Pump efficiency is not part of the energy code. There are, however, some pumping system design requirements in the code. One of the requirements includes maximum flow rates (speed limits) for various pipe sizes. This is shown in the table to the left. Designers may pay attention to these but I’d bet my right arm any code compliance assessment will not include this.
Similar to heating and cooling water pumping systems, our hearts, veins, and arteries are a pumping system. Arteries supply blood to tissues and veins return blood. Like systems in a building, the pipes are largest leaving and entering the pump and get smaller downstream as loops branch off to different parts of the body.
The human circulatory system is beautifully balanced. Heating and cooling water systems in buildings? Not so much.
Building System Design
First, building systems consist of discrete pipe sizes rather than infinitely varying sizes of veins, arteries, capillaries, etc. Second, building systems have sharp elbows, tee connections, (fittings) strainers, many valves, and heat exchangers. Third, buildings have all kinds of physical constraints and are not designed with a plant that is centralized as the human circulatory system is. Finally, off-the-shelf pumps, each with fixed specific characteristics, must be selected to serve these designed systems.
Pump Selection Problems
The designer/engineer lays out the network of building arteries, fittings, and so forth, and then adds it all together for the requirements at the pulmonary vein and artery location where the heart/pump sits. The purpose of the pump, of course, is to move enough heating or cooling water to all locations of the building to keep it warm/cool.
Flow and pressure are directly related for both the pump and system. With system pumping requirements in hand, we move to a chart like the one to the right, courtesy of Bell and Gossett. Flow is on the horizontal axis and pressure is on the vertical. For example, my design might need 1,000 gallons per minute (gpm) at 70 feet of head. From the chart, it appears 5BD may do the trick. More likely, 6BD may be chosen just in case, for extra capacity.
Now we can move on to the chart, specifically for that pump, shown on the right. The shaky red line is my series of arteries and veins, or piping system. As flow increases, pressure required increases.
The dot at the intersection of 1,000 gpm and 70 feet is where we will operate. The percentages along the top of the green curve are efficiencies. The “eye” is peak efficiency at 89%. Guess what: we will already lose two percentage points (87% rather than 89%) of efficiency because the pump does not perfectly match the system. Canacorn: gone. And this is a very good fit to boot.
From here, the system requires artificial balancing to ensure enough flow makes it to the most constrained destination at all times. Think of 80% blocked arteries to arms and legs to ensure the brain gets enough blood. What that means: the heart/pump works harder. In buildings, these blockages are called balancing valves or circuit setters. They waste energy; a lot of energy.
The energy code also requires that circuit setters be “proportionally balanced” to minimize losses, and that pump impellers be trimmed or speed adjusted to meet design conditions.
Pumps can be massively over-sized while circuit setters or other throttling valves are severely pinched. More canacorn, gone. The code doesn’t prevent this, and no one knows it’s there until an observant retro-commissioning agent comes along and frees up the system. I won’t go into how that’s done.
ANSI/ASHRAE/IES Standard 90.1-2010. Energy Standard for Buildings Except Low-Rise Residential Buildings. (I-P ed.). Atlanta, GA