Sub-Metering Misses the Second Largest Opportunity to Save Energy

Improving the Part-Load Efficiency of Energy Systems is the Second Biggest Opportunity to Save Energy in Complex Systems in Industrial Plants. The Common Approach of Installing Sub-Metering to Measure Only How Much Energy Systems Have Used After the Fact Misses this Huge Opportunity.

Watson: Holmes, your entire career has been spent tuning up existing energy systems in existing buildings. You have been able to consistently produce savings of 10%, 20% and more without Energy Audits, without Benchmarking and without Capital Improvements. Paybacks on the initial investment in the permanent instrumentation required to produce these savings have been weeks or months.

What’s your secret? What problems have you found? What actions have been taken to correct them? How can others do the same in their facilities?

Holmes: As we have discussed in many of our blogs, the best opportunities with the fastest paybacks always come from no-cost, low-cost changes that match the operation of the energy systems to the energy requirements of the facility.

The owner is paying for every KWH or Therm or Gallon that passes through each utility meter. By continuously monitoring each of those meters we can see how much energy is entering the building every minute of every day. The question then becomes where is it going?

Watson: A permanent monitoring system shows you where it is going; what equipment is running and how much energy is going to each major system and large piece of equipment.

The questions then become:

#1 Should that equipment be on? If it isn’t needed, turn it off.
#2 How much energy should that system be using at that point in time to satisfy the needs of the facility?

Holmes: Right on both points. Our reports also show efficiency of energy use and percentage loading of the energy systems along with time of day, day of the week, weather and more. We then assist the owner in determining what equipment should be running to meet the needs of the plant under all conditions.

The difference between what the systems need, what they should be using, and what they are actually using is the waste, the opportunity for savings.

Without continuous monitored data there is no way to insure that all systems operate at the highest efficiency under all conditions on an ongoing basis.

Watson: After matching energy usage to energy needs, what have you found to be the next most common opportunity?

Holmes: Improving the part-load efficiency of energy systems is the second biggest opportunity in all complex facilitiesThat’s why I mentioned that we always monitor the efficiency of energy use for all major systems. The common approach of installing sub-metering to measure only how much energy a piece of equipment has used after the fact misses this huge opportunity.

Watson: Using Chillers as an example, Chiller efficiencies are normally referred to as KW/Ton or the KW of input electrical power divided by the Tons of Cooling produced. The lower the KW/Ton, the less energy required to produce a given tonnage and therefore the more efficient the chiller.

How do you measure the Electrical Power Input, the Tons of Cooling and the efficiency of a Chiller or a Chilled Water System? Doesn’t that require Flow Meters, BTU Meters and Wattmeters on each Chiller? Isn’t that Expensive?

Holmes: No. There’s no need for any type of expensive meters. By including thermodynamics calculations in the software analytics, all that is required is one $125 Current Transformer (CT), the nominal voltage, two $30 temperature sensors in the Chilled Water supply and return lines on each Chiller and a way to input the water flow through the chiller. We use different methods in different facilities. If there is an existing flow meter we connect to it. If the pumps are constant volume, we use the pump curves to determine the flow. If they have VFDs we read the input amps along with the curves. In some projects we have put $100 pressure transducers on the inlet and outlet of evaporators and used the evaporator pressure loss curves to determine the flow. There are a lot of options.

You don’t need high accuracy and expensive instruments to determine the most efficient ways to operate energy systems. We are not producing billing data or measuring power quality. We use the data as a part of a continuous improvement process to expose opportunities for no-cost, low cost changes and verify the results. If the data shows a certain combination of equipment saves 23%, it doesn’t matter if it is 21% or 27%. It’s saving the owner money. What matters is reducing the amount of energy and dollars flowing through the utility meters.

Watson: What’s been your experience in monitoring Chillers Holmes? How much capacity do they use on hot days? How efficiently do they operate across an entire cooling season?

Holmes: In more than 35 years of monitoring chillers, we have never found a facility where the actual load on the Chillers exceeds 60% of the capacity provided (the design load). For most facilities, the design load only occurs a few hours a year. That means that on the average day during a cooling season the Chillers may only be using 15%-30% of capacity and be running at a much lower efficiency than at design conditions. It is not unusual to find the supporting pumps and cooling tower fans (parasitic loads) using more energy than the Chillers themselves !!!

 

Watson: How do you get a handle on the inefficiencies and potential savings?

Holmes: While many people talk about the efficiency of a Chiller in KW/Ton as you mentioned, few look at the total Chilled Water System Efficiency including all of the parasitic loads. But the owner is paying for the energy used by the entire system so that is what we monitor. We track and continuously display energy, tons, % capacity, % efficiency, temperature, flows and more.

Large, complex facilities have multiple chillers, pumps and cooling towers. There are choices to be made on which ones to run each day as the loads and seasons change. The way an owner operates the systems can vary the system efficiency and energy used by as much as 100% !!!

Watson: Why doesn’t everyone take advantage of this opportunity to operate their energy systems at the highest efficiency and lowest cost? It seems so basic and simple.

Holmes: Great question Watson. I think the main reason is that they don’t have the required information; and without monitored data presented in an easy-to-understand format most are unaware of the poor operating efficiencies.

We have yet to find a single facility with the instrumentation required for the owner to determine the most efficient way to operate their energy systems.

Watson: So you are saying that a facility may be able to reduce the cost of running its Chilled Water System by 50% simply by the sequencing of the system components?

Holmes: Absolutely! Not only just the Chilled Water System but other large systems including Compressed Air and sometimes production support systems.

Watson: It seems such a shame that most of the energy profession and facility owners and operators don’t understand the value of permanent instrumentation; the tremendous potential savings from the no-cost, low-cost changes that can allow energy systems to operate at the highest efficiency under all conditions.

They’ve missed the “Elephant in the Room”. Read the Blog