Analysis of Energy Savings and CO₂ Emission Reduction Contribution for Industrial Facilities in USA

Greenhouse gases trap heat and make the planet warmer. Human activities are responsible for almost all of the increase in greenhouse gases in the atmosphere over the last 150 years [1]. The most massive greenhouse gas emissions from social activities in the United States is greenhouse gas emissions from human activities from burning fossil fuels for electricity, heat, and transportation. According to the United States Environmental Protection Agency (EPA), carbon dioxide represents 81.3% of total greenhouse gas emissions in 2018, with a total number of 6677 million metric tons of CO₂ equivalent [2]. The industrial sector is solely or exclusively responsible for 22% of 2018 greenhouse gas emissions. The increase in CO₂ emissions came as a response to the rise in energy demand [3]. The industrial sector is the second-largest end-use sector in the U.S., accounting for 27.7 × 10¹⁵ kJ (26.3 quadrillions BTUs) in 2018, which is 35% of the total energy consumption [4]. Chances exist in most industrial plants where simple changes can save energy at minimal cost or substantial cost savings opportunities. Policies and programs on energy efficiency and greenhouse gases are heading toward setting standards for the industrial sector and processes related to production units, thus standards for environmental and energy management [5,6]. Key elements of those policies include increased auditing and facility management attention to energy efficiency [7]. Moreover, energy auditing is one of the most comprehensive methods of achieving energy savings in the industry to minimize wasteful energy consumption. Consequently, by selecting the appropriate type of audit, the given facility can perform different production operations [8].

Industrial energy efficiency is an integral part of the economic transition toward improved sustainability. For an industrial company, there are four principal means of reducing energy costs, namely, operation changes (more efficient operating and maintenance routines and changed behavior), investments in energy-efficient technologies, time control (load management), and conversion from one energy carrier to another (from natural gas to hydrogen).

Evaluations of implemented energy audits in small- and medium-sized manufacturing companies show that the calculated (mainly technical) energy efficiency potential for improving energy efficiency varies between 16% and 40% of the total end-use energy; electricity represents approximately 60% of energy efficiency potential. Implementing the proposed measures to achieve the improved potential depends on the encountered barriers and driving forces for energy efficiency improvement [9]. As a result, several energy audits concerning selecting cost-effective solutions regarding energy efficiency measures were conducted in many production processes [10,11] or on versatile industrial practices [12]. Therefore, whether making steel, cement, manufacturing glass [13], or food processing [14], it is significant potential to improve industrial energy efficiency, reducing, at low or no cost, the amount of energy used to manufacture most goods by upgrading energy systems or developing energy-efficient technologies [15].

The main problem is that the potential for energy efficiency improvements remains untapped in small- and medium-sized industrial facilities [16]. This problem is that energy consumption was not always seen as a major cost factor within industrial production [17]. Energy cost is receiving relatively little attention from the financial point of view as, in most cases, it is treated as an overhead rather than a cost category [18]. Many academic researchers propose implementing the energy management system as a basic tool to overcome the actors’ barriers, such as decision-makers, financial institutions, and budget limitations [19,20]. The lack of information about the costs and energy savings benefits within industrial processes is seen as a barrier to industrial efficiency measures [21,22].

Many studies [23,24] have focused on the audit’s energy savings benefits as the potential to overcome the barriers mentioned above. Still, they appear to overlook the other potential benefits of energy audits, which can be named as non-energy benefits. Non-energy benefits of making energy efficiency investments [25] can go far beyond energy savings. Examples are such as better working conditions, improved product quality and increased productivity [26], reduced cost of environmental compliance, raw material savings [27], reduced emissions, extended equipment life, and reduced maintenance requirements [28]. Still, no one provided a guideline to all industries or emphasized the CO₂ reduction on a large scale [29–36]; much research has been done on some applications or specific equipment. For instance, in wastewater treatment plants, several efforts have been made to recover heat from the sludge by using different techniques (thermochemical conversion techniques) [37–42] and including the economic study to fill the gap between the research and the industry [43–45].

Our team has been optimizing the energy generation by renewable resources such as wind turbines, hydro turbines, biomass, and solar energy to provide innovative solutions to the different industries [46–50]. The study’s objective is to identify, evaluate, and recommend—through analyses of industrial plant operations—opportunities to conserve energy, minimize waste, and reduce the overall cost of operations. Recommendations are based on observations, and measurements have been made in the plant. Therefore, by considering 152 assessments and more than 167 different recommendations, this paper highlights the energy savings outcome obtained from various industrial sectors and CO₂ emission reduction.

The Industrial Assessment Center (IAC) is a program funded by the United States Department of Energy through the Advanced Manufacturing Office (AMO). This program aims to further sustainable manufacturing through implementing Energy Efficiency Opportunities, reducing energy and waste production, and improving manufacturing productivity. The IAC is widely dispersed across the nation, and the University of Wisconsin-Milwaukee (UWM) is one of the centers that provide such service for the participating companies. Within the past 6 years, the companies’ energy audits have been proposed into three main steps: the first step is auditing procedure, second step energy flow analysis, and third step benefits of energy audits.

The energy audit starts with a pre-audit questionnaire including the most basic information about the facility in terms of manufacturing profile, production scale, process, and most energy consumers in a format that is easy for non-energy-oriented engineering staff to understand. The questionnaire also includes the annual usage and costs of electricity, natural gas (or any other fuel), water, and any recycling process. This questionnaire gives the IAC hints to possible energy conversion processes and allows the team to identify potential improvements to identify potential improvement areas. For the initial analysis, a pre-assessment meeting is held at the IAC office by the energy team, comprising qualified engineers from different majors and qualified engineers from different majors and sufficient experience in conducting energy audits.

Based on the company’s utility bills, the IAC team analyzes the energy usage, addresses the energy spikes, and points out to the reason behind these spikes to avoid or improve. The next step is the assessment visit to the client’s facility, where another meeting with the company’s energy team is held to discuss the primary findings of the IAC team before going to the initial walk-through for data collection and measurements. After the initial walk-through, a brainstorming session is held with the facility staff to review the initial outcomes and consider potential recommendations. A final walk-through is always needed to collect any data needed for the savings calculations.

Based on the information collected during the visit, all the assumptions and analyses that lead to the presented benefits are documented in the form of a technical report submitted to the DOE to be reviewed and approved, then to be sent to the facility staff only after 60 days from the assessment date. After 6 to 9 months from the assessment date, an implementation survey is conducted with the facility personnel to follow-up and ensure that the provided recommendations were effective (Fig. 1).

In this study, 167 different recommendations varied by manufacturing profile, difficulty, and approach complexity. In some cases, most of these recommendations can be repeated in various factories because of standard practices such as lighting, compressed air system, and motors. As a result, the total number of recommendations for the 152 assessments is 1330, with an average of eight recommendations per facility, serving 20 different industries.

• Energy savings; the most significant and touchable effect of the energy audits always returns to energy savings. In basic recommendations, the use of one source of energy will be reduced within one process, for example, installing light-emitting diode (LED) lights. Similarly, some recovered forms of energy can be utilized by other manufacturing processes such as heat recovery systems to preheat the input streams. The energy savings are typically described as shown in Eq. (1)

  $Es=Ec−Ep$

  (1)
• Cost savings; based on the energy savings, the cost savings are determined by the product of energy savings and its unit price, as shown in Eq. (2). However, this price can be split into many components, such as demand, transmission, waste, etc., elements related to energy consumed during a time (power). Based on this cost and the implementation cost (IMC), equation’s time to recover the investment costs (3)

  $Cs=Es×R$

  (2)

  $PB=IMCCS$

  (3)

• Emission reduction; Based on the data measured and gathered on-site, the calculation of CO₂ emissions can be performed using the equivalencies calculator shown in Fig. 2 developed by the U.S. EPA. This straightforward calculator provides conversions from one unit of energy to the equivalent amount of CO₂ emission expected from using this amount.

Two major software packages were used for some specific calculations. The first software is measur [52], which is developed to help manufacturers improve energy systems and equipment efficiency. The second software is the Solar Advisor Model (SAM) [53], a technoeconomic model designed to facilitate decision making for people involved in the renewable energy industry. Besides these software packages, several pieces of equipment were used during the assessments for measurement purposes, depending on the equipment or the recommendation, for example, DEWALT laser distance measurer [54], EXTECH INSTRUMENTS environmental meter [55], FLUKE Infrared (IR) thermometer, and FLIR IR thermal camera [56]. Also, data loggers were installed on some equipment to determine/calculate specific running and load elements.

Table 1 shows all the covered manufacturing sectors with their North American Industry Classification System (NAICS) code. The more assessments are considered, the more energy savings will be. However, to compare the manufacturing sectors to each other, all calculations are based on each sector’s average per assessment. The assessment recommendations were categorized into eight sections, listed as follows:

• HVAC systems

• Heat recovery systems

• Electrical demand management and utility bills (EDMUB)

• Motors

• Compressors

• Waste management and productivity enhancement (WMPE)

• Lighting

• Building envelope

Starting with the HVAC system, Fig. 3 shows the energy savings for all the manufacturing sectors. Four main spikes can be seen at 331, 332, 334, and 541. For 331 and 332, since the significant energy consumers at these facilities are furnaces, almost all the recommendations focused on installing or increasing the gas/electrical furnaces’ insulation, which reduces the heating load removed by the HVAC systems. The electricity savings for 334 is dominant as the gas in such facilities is only used for heating purposes and not part of the process. The main products in these facilities are electronic components where specific environmental factors shall be maintained, mainly temperature and humidity. However, these unusual conditions are only required during the manufacturing process.

Consequently, all HVAC recommendations focused on mitigating thermal comfort conditions at human-occupied spaces during non-working hours. Finally, for the testing laboratories and scientific, technical services (NAICS code 541), it can be observed that most of the savings were in electricity and is mainly because most of the installed space conditioning units are for thermal comfort in offices. Two significant recommendations contributed to this spike. The first recommendation was related to the HVAC unit’s maintenance by replacing the air filters on the rooftop units to clean air with better airflow. The accumulative dirt on the air filter can cause several problems, including, not limited to, blocking the cooling coil, which reducing system effectiveness or blocking the blower fan itself, which leads to a more costly repair. The second recommendation was related to adjusting the set-point temperature according to the thermal comfort range recommended by American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) during the cooling or heating season. Most of the office’s areas are over-conditioned in both ways, either cooling or heating. One more noticeable energy waste is that the HVAC system runs simultaneously at the same set-point temperature even if the facility is unoccupied. Consequently, adjusting the set-point temperature based on the season is recommended during the unoccupied time. These two recommendations are applied for wastewater treatment plants (221) as well.

For the other industries, besides the recommendations mentioned above, another ad hoc recommendation was applied. For the mining industry, installing a radiant heater for spot heating was recommended. The main reason is that it is impractical to use conventional heaters for the big space and open-door buildings because once the air is heated, it will blow away with the air movement. Another plausible reason is that since space has many sand particles in such industry, the radiant spot heaters are decreasing the air circulation inside the room and the corresponding spreading of airborne particles. The same recommendation is applied in big closed spaces such as shipping rooms where spot heating is required to achieve thermal comfort to the people occupying a specific area in the room. All the recommendations mentioned above represent significant energy savings for the remaining industries but with a different amount as the equipment capacities, types, geometry varies from one to another.

Figure 4 shows the heat recovery energy savings for all industries. Mining and chemical manufacturing was the highest two industries in terms of gas and electricity savings, respectively. For the mining industry (212), the sand is mined, washed, screened, and stored in piles to supply various grades. The sand needs to be dried to the required moisture content before it is sold or further processed. In this industry, the rotary dryers [57] are standard and used widely for the previously mentioned purpose. The heat from the exhaust gases, Fig. 5, is recovered to preheat the combustion air through the air to the air heat exchanger, consequently improving the combustion process and reducing natural gas consumption. The average resultant gas savings from this recommendation was 27,000 MMBTU.

On the other side, the electricity savings were the highest for the chemical manufacturing sector (325), which is an excellent example that the heat recovery is not limited only to fuel savings but also depends on the source of heat in the shape of electricity. In this case, high-temperature thermal extruders were used to heat the product and propel it through a die to produce sheets and strips of plastics. In these facilities, a lot of water is used to cool down the equipment during the manufacturing process. The used cooling water flowrate was 200 gallons per minute, and for such large capacities, a cooling tower is needed. The energy-saving here came by intercepting the water at its warmest point before it arrives at the cooling tower and passing it through pipes to heat the raw materials before the extrusion process, leading to 197,000 kWh electricity savings. For the other manufacturing sectors, the heat recovered varies based on equipment. Besides using waste heat from hot flue gases to preheat combustion air, recovering the compressor exhaust’s heat came as the second-highest recommendation. As the air compressor uses, that was expected to include spraying crops and ventilating soils in agricultural facilities, running pneumatic machinery in manufacturing plants, operating laundry presses in dry cleaners, and various food and beverage processes manufacturing oil and gas operations and more [58].

Electrical demand management and utility bills are shown in Fig. 6, where the savings are related only to electricity. In this section, when it comes to electricity savings, solar energy is one of the most viable recommendations. Sometimes, this recommendation is not useful for three main reasons: the company’s low investment budget, the company, does not consume a lot of energy, making the payback (PB) period too long, and the solar system is already installed or in process. These three reasons contributed to have zero electricity savings in three sectors: 212, 316, and 337. For the mining industry (212), installing a solar system is challenging as mining, maintenance, or processing activities result in the release of dust particles into the air. This harsh environment covers the solar panels with layers of dust, which weakens the panels’ harsh environment’s performance covering the solar panels with layers of dust, which undermine the panels’ performance, or even reduce their lifespan.

Starting with the utilities-water treatment (221), the treatment process mainly occurs in an open space and only a small building for the offices and administrative work. This large area makes Fig. 7, installing solar panels seductive, especially with the incentives of electricity providers. The average electricity generated by the solar system per facility is 200,000 kWh. The solar panels system contribution still has the most prominent portions of electricity savings for the remaining industries but with different percentages based on the location and the available space (roof or ground) for installing solar panels.

In 311, the second-largest electricity-saving recommendation, after installing solar panels, was related to utilizing controls to operate motors for auger conveyor only when needed. With the same concept but different equipment such as fans, blowers, air conditioners, and other special machines, turning off the equipment when not in use is the highest electricity-saving practice with no or minimal implementation cost, which makes an immediate payback period. Finally, the last promising method is installing thermal energy storage (TES) systems to shift cooling energy use to off-peak time. Such an approach is appropriate when the maximum cooling load is significantly higher than the average load. High demand charges, and a significant differential between on-peak and off-peak rates, also help make TES systems economical. They may also be appropriate where more chiller capacity is needed for an existing system or where back-up or redundant cooling capacity is desirable. Besides shifting load, TES systems may also reduce energy consumption. The energy savings result from chillers operating at full load nearly all the time, potentially at higher efficiency. And the operation is generally at night when lower ambient temperatures make for cooler condenser temperatures, reducing energy use [59]. This recommendation was applied mainly in five main industry sectors, 321, 331, 332, 335, and 336, which explains why their electricity savings are higher.

Motors, regardless of their type, are vital electric machines for all industrial needs. Examples of applications include industrial fans, blowers, pumps, machine tools, power tools, turbines, compressors, alternators, ships, rolling mills, paper mills, movers, and other special applications [60]. Figure 8 shows the electricity savings obtained from the motors. The highest electricity savings can be seen in two primary industries: mining (212) and wastewater treatment plants (221) where the electricity-saving is 450,000 kWh each. That was expected as both are relying on the motors in their industry. The mining industry has the most oversized motors in terms of size and number, especially for transportation conveyors. The wastewater treatment plants are using a lot of compressors and pumps in the process. The motors in the different industries are limited to transportation conveyors mainly, but in the motors are smaller in size and more substantial in numbers compared with the motors are smaller in size and more significant in numbers than those used in the previously mentioned industries. Three main energy recommendations were focused on using synthetic lubricant [61–63], use variable frequency drive [64,65], and use energy-efficient V-cogged belts [66,67].

One of the most indispensable machines is the air compressor. It is impossible to see a stagnant list of air compressors used as they are considered the industrial infrastructure's backbone. That is seen in Fig. 9, where different industries are relying on the compressor during the manufacturing process such as sandblasting in (325), air guns for cleaning surfaces in (331, 332, 336), pneumatic nail guns in (321), operating air tools on production lines and finishing and packaging with pneumatic devices used for liquid padding, carton stapling, appliance sanding, dry powder transporting, and fluidizing (all sectors except 221).

Special cases exist in wastewater treatment facilities where the air compressors are used for the aeration process. Two main recommendations share 65% of the total energy savings, eliminating leaks in compressed air lines and installing compressor air intakes in the coldest locations. Starting with air leaks, usually, these leaks result from low maintenance and occasionally improper installation. Sometimes the air leaks are responsible for wasting 20–30% of the air compressor’s output by dropping the system set pressure and consequently forcing the compressor to cycle more (increasing running time). Thus, the air leaks are responsible for unnecessary compressor’s operation, which includes higher energy costs and waste. Another recommendation can be extracted from air leaks, which is reducing set pressure to a minimum. Most of the visited facilities were using set pressure of 125 psi, although only 85–90 psi is needed. This exaggerated precaution’s main reason is to overcome the losses made through air ducts caused by air leaks. The first recommendation can be made by using ultrasonic leak detection equipment.

For changing the air intake location, as per ideal gas law, when the ambient temperature increases, the air density decreases, which means for the same mass rate, its volume increases. Cold air is denser and already more compressed than hot air and needs less energy to be compressed. Using hot air from the services area to feed a compressor will inevitably decrease the compressor efficiency. Cool, clean, and dry intake air leads to more efficient compressor operation. Compressor intake air should always be drawn from the coolest possible source. Use cooler outside air wherever possible. Another 20% of the electricity savings go for eliminating or reducing compressed air for cleaning purposes. Wherever high flow and low pressure is adequate, the system must always be running, noise is not a big issue, and there is plenty of space, a blower operated system is the best option to be used instead of an air compressor.

Moving forward to the waste management and productivity enhancement, in this section, it is almost impossible to predict specific practice or recommendation. Still, all recommendations were customized and only occurred once and cannot be generalized as previous sections; HVAC, Heat Recovery, EDMUB, Motor, and Compressors. Starting with the data in Fig. 10, the maximum electricity savings were obtained from the industrial sector, 323. Only one recommendation contributed to this spike, which is redesign flow to maximize mass transfer. Most of the manufacturing machines were in building 5,4,2, as shown in Fig. 11, and they are independent. The paper scrap in building five is sent to building 6 by several big blowers at the rooftop. The machines in building 1 were small and movable, which make switching them with the trim collector in building six more beneficial. The energy savings here came from reducing the transferring distance and reducing the blowers’ power consumption either by reducing the capacity or reducing the number of blowers used. This recommendation was proposed only once among all the assessments and was responsible for saving 3,793,482 KWh, but only 345,718 kWh can be seen in the figure because of the averaging.

Another unique recommendation is to save 6276 MMBTU (average 497 MMBTU in 333), which uses softened water for the boiler to reduce the energy used to heat the water. The impact of hard water hits heavily on energy use and associated maintenance costs. Hard water contains dissolved solids that accumulate on the heating elements and boilers’ internal surfaces, causing scale buildup and impairing efficiency. Scale buildup reduces the equipment’s ability to heat surrounding water, causing it to consume more energy (thus, raising utility costs). Problems associated with hard water can easily be minimized by using a water softener, which reduces scale forming and hardness ions (calcium and magnesium). This action helps to prevent scale buildup and to overheat of hot water using equipment [68].

For the 311 and 332, it was recommended to repair or replace the steam traps on the steams lines to save the natural gas usage because if a steam trap fails and is not restored or replaced, a significant amount of steam can escape through the orifice. For the wastewater treatment plants (221), all the waste management is related to the sludge and utilizing the excess digester gas to generate electricity by considering the combined heat and power system. This recommendation can be generalized for all the wastewater treatment plants depending on the amount of gas generated from the digester. The highest electricity generated was 1,071,671 kWh (on average, 77,439 kWh per facility).

Moving to the wood manufacturing, 321, it was recommended to replace the mercury vapor ultraviolet (UV) light curing system with an LED UV light curing system to save energy consumption. Also, the electricity savings, in this case, are not only limited to the savings from lights change but also electricity savings from eliminating the exhaust fan. The main reason is that mercury lamps emit lots of heat to the surrounding, making the exhaust fan necessary. Finally, replacing pneumatic equipment with electrical equipment was recommended in chemical manufacturing, 325; one example is replacing existing diaphragm pumps with electric ones to reduce electricity use on the belt.

Water and tangible savings can be seen in Fig. 10. Regardless of the industry’s type, it is recommended to recycle or minimize water usage, used for cooling or washing purposes, or the process itself. It is recommended for solid waste to recycle or resale any kind of solid waste, which could be in the form of sawdust and wood scrap in 321 and 337 or aluminum/metal scrap in 327/337 or any electronic components as in 325.

You can swap traditional incandescent bulbs with others in most lighting fixtures that will save on energy and offer more illumination. Figure 12 shows the electricity savings from lighting. Depending on the industry and the facility configuration, some industries are using lights more than other sectors. Most of the lights are indoor for mining, and because of the high-rise buildings, they are using many bulbs of high wattage; they could reach 1000 W. While for the chemical, plastics, and metal industries, the vast majority of the lights are used to provide enough lumens for product quality inspection. The significant three recommendations are as follows: using energy-efficient LED light bulbs instead of fluorescent lights, installing occupancy sensors, and reducing illumination by delamping to minimum necessary levels. It is recommended for the offices’ area to utilize natural light by installing daylight sensors; consequently, the light bulbs will work only when the daylight is not enough to provide sufficient lumens.

When it comes to the building envelope, as shown in Fig. 13, then air infiltration is one of the most critical problems. Infiltration is the unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through the use of doors for passage. Infiltration is sometimes called air leakage. The leakage of room air out of a building, intentionally or not, is called exfiltration. That means that the building can gain or lose heat in the winter or summer season, respectively, which is undesired. Both deficiencies affect the HVAC system, which could be in the shape of extra electricity or gas consumption. Several recommendations can be applied regarding this problem, depending on the source of leakage. For example, installing a vinyl strip/high-speed/air curtain door represents 70% of the total energy savings. Another candidate is to seal the gaps around windows and truck loading dock doors.

Based on the previous survey and implemented recommendation, Fig. 14 shows the contribution of each category to the carbon dioxide reduction, which is calculated by using the online calculator developed by EPA. According to the electricity savings and gas savings, the total carbon dioxide reduction is 98,663 metric tons. Almost all the categories share the same percentage in carbon dioxide reduction except two categories: the lowest; 6% and 2% for the waste management and building envelope, respectively.

To make it easier for tracking the recommendations per industry, Table 2 was developed to show grayscale for the energy savings where the black color represents the highest saving level compared with the other categories in the same industry sector. For example, the heat recovery energy savings in the mining industry (212) are the highest, followed by motors and lights. The same procedure can be followed for the other industries. This table works as a guide for the plant managers, energy engineers, and other personnel involved in the energy assessment process to anticipate the potential energy savings per category.

Twenty manufacturing sectors have been audited. The savings obtained from these audits were energy savings (electricity and natural gas), water savings, and solid waste savings. Eight different categories were used to evaluate each manufacturing sector. In conclusion, the findings are:

1. In HVAC systems, the most considerable energy savings go for the industrial sectors, using gas/electrical furnaces or the industries where specific environmental conditions must be maintained, such as electronic component manufacturers. As a result, the heat recovery opportunities in such facilities are high.

2. The solar panels contribute to the highest electricity production in the facilities where a large area is available such as water treatment facilities.

3. The compressors, eliminating leaks in compressed air lines and introducing cold air to the compressor inlet, give 65% of the total energy savings.

4. The waste management and production enhancement recommendations were customized according to the industry type and the processes procedure, leading to all types of savings in electricity, gas, water, and solid waste savings.

5. Although LED lights are well known for a long time, some industries are still using fluorescent bulbs because they lack awareness of the assumption that the cost savings would not be significant enough or the energy consumption is not a lot. Specific industries are consuming more light energy than other sectors, either because of building configuration or excessive lumens.

6. Air infiltration/exfiltration is one of the easy problems that can be solved by proper sealing to doors and windows, which represents almost 70% of the total building envelope energy savings.

7. Almost 100 thousand metric tons of carbon dioxide emissions are being reduced where the waste management and building envelope represents 6% and 2%, respectively. More than 80% of the carbon dioxide emission reduction is obtained from motors, heat recovery, compressor, HVAC, and lights with an almost equal share.

8. An innovative energy-saving map has been developed to predict energy-saving potentials per category for each industrial sector.

The study is funded by the US Department of Energy under DE-EE0007716.

There are no conflicts of interest.

The datasets generated and supporting the findings of this article are obtainable from the corresponding author upon reasonable request. The authors attest that all data for this study are included in the paper. Data provided by a third party listed in Acknowledgment. No data, models, or code were generated or used for this paper.

C =

cost

E =

energy

R =

Rate

Ib =

pound

c =

current

p =

proposed

s =

savings