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Inch or Mile? Indispensable Thumbs Guide Impact Evaluation

By February 3, 2020November 5th, 2021Energy Rant

Hi. How’re you? Jeff Ihnen here. I’m back and almost live. I’ve been away on several temporary assignments that are starting to wind down. We are thrusting forth into the 11th year of the Energy Rant!

Indispensable Thumbs

Unless you have broken one, lost one, or had one immobilized, you probably have no idea of the value of your thumb and its equivalent, the big toe. I’m sitting on an airplane as I bang this out, munching a bag of almonds. Thumb and a finger. Thumb and a finger? That’s how you and I and anyone with a fully functioning hand eat things by hand. Glass of wine? Thumb and any combination of fingers. Pinky in or out? That’s up to you (mine is out), but you should pay attention because you may be sending signals to those around you. Paranoid yet? Ok. Say, is Nikola Tesla by chance?

Rules of thumb in energy efficiency analyses are as important as our real thumbs and big toes. By the way, if you want to know how


important healthy toes are to walking or running, break one, and you’ll find out. I would submit that your big toe benefits your locomotion as your thumb benefits popcorn consumption. You don’t know what a body part does until it’s broken.

Putting Thumbs to Work

Let us examine a recent evaluation of a chiller replacement project[1] I reviewed. The project comprised the replacement of a 500-ton centrifugal chiller for a food processing plant. The load was process cooling. Note that a ton in this context is not a weight (2000 lbs). It is the energy required to melt a ton of ice, which is 12,000 Btu/hr for 24 hours, or 288,000 Btu.

A ton of cooling equals 12,000 Btu per hour. Dazzle your kids with this fact, and tell them the family sports sedan weighs roughly 3,000 lbs. Then ask them how many Btu would be required to melt the sedan. Give them a pencil, paper, and calculator. If they are quiet for a few minutes, God bless ‘em. They may be doomed to a life of engineering.

Let’s say the chiller in question runs balls-out, 24/7. If the chiller is even close to code compliance, it has an efficiency of 0.6 kW per ton of cooling. This would tell us the chiller would use a maximum of 2.6 million kWh. To wit:

What are the reported savings? 1.48 million kWh.

Is 1.48 million kWh savings from a chiller that uses at most 2.6 million kWh per year reasonable? Probably not.

This demonstrates the power of thumbs. I don’t need to know what the specific code requirement is for a full load or integrated part load (average) efficiency to tell if something is out of whack. I only need to know what the whack (or hand grenades and horseshoes) is. In this case, 0.6 kW per ton fits the ticket.

We must determine savings with sound engineering practice, but that begins with an assessment of where on earth are we starting? Is it possible to achieve 1.5 million kWh savings by installing a chiller that uses a maximum of 2.6 million kWh? Yes, but unlikely.

Where on Planet Earth?

Rules of thumb or the evaluator’s thumb sets them up to establish an impactful measurement and verification plan. Tell me about the project. What was the operating lineup and sequence of operation before this new chiller was installed, and likewise, what is it now?

Since it’s basketball season, who were the starting five? The coach may have gone from the large clunky lineup to the small and fast downtown bomber lineup – a complete strategic change. My bet would be that coach replaced the six-foot, ten-inch power-forward clod with a six-foot, eight-inch shooter with a little more finesse than a concrete piling. In other words, customers typically replace chillers of similar capacity or they tack one on if they need more capacity. This is a shame and a lost opportunity, but it is a story for another day.

These are the big questions. Are we dealing with inches or miles? It is essential to sniff things out using rules of thumb before picking up the phone or going on-site to bug the dickens out of a customer with a blizzard of boilerplate and superfluous questions. Or worse, the questions have been answered, the customer’s goodwill is expended, and the gordevilaphant[2] remains. We don’t want to be there! Head it off with a reality check with rules of thumb!

[1] See what that temporary assignment may have entailed?

[2] The abominable triadic beast that is part gorilla, devil, and elephant. The gorilla and elephant remain in the room and the devil is in the details.

Jeff Ihnen

Author Jeff Ihnen

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