45
2 Fundamentals of Energy
Auditing
Geographic location and weather data
•
A list of each piece of equipment that signifi cantly affects the energy
•
consumption
Operating hours of each piece of equipment
•
Electricity and fuel bills for at least 12 months before the audit should be used. Since the bills normally include several cost components in addition to direct expenditures for electricity or fuel, the fi gures appearing on the bills must be interpreted appropri-ately to determine the actual energy consumption. For electricity bills, the most common components of rate schedules include (Capehart et al., 2006)
Administrative/customer charge to cover the utility’s fi xed costs to serve the
•
customer such as providing a meter, reading the meter, and sending a bill Energy charge to cover the actual amount of electricity consumption in
• kWh
Fuel cost adjustment to cover the increased cost of primary fuel for
electric-•
ity generation
Demand charge to allocate the cost of the capital facilities for electricity
• supply
Demand ratchet to charge for creating a large power demand in only a few
•
months of the year
Power factor to charge for a machine with a poor power factor
•
Popular fuels used in food processing facilities include natural gas, fuel oil, and coal. Natural gas rate schedules are similar in structure to electrical rate schedules.
However, natural gas companies normally do not charge for peak demand. They usually place customers into interruptible priority classes with different gas charge rates. Customers with a high priority and high charge rate will not be interrupted while customers with the lowest priority and lowest charge rate will be interrupted whenever a shortage exists. Fuel oils and coal vary in grades and sulfur content. Their billing schedules vary widely among geographical areas. In the United States, natural gas is priced on a per million cubic feet (MCF) basis;
fuel oils are priced on a per gallon basis; and coal is priced on a per ton basis. Coal does not burn as completely as fuel oil and natural gas. If a combustion process is properly controlled, natural gas can be completely burned; fuel oil has only a small amount of unburned residue; and it is diffi cult to burn coal completely. To determine the costs of operating individual pieces of equipment or individual unit operations accurately in a food processing facility, the energy bills must be broken down into their components such as demand charge and energy charges for electrical bills.
Information about the facility layout should also be obtained and reviewed to determine the facility size, fl oor plan, and construction features. For the energy audit of a building, the heating degree days (HDD) and cooling degree days (CDD) are important concepts. The base for computing HDD and CDD is 65°F based on an assumption that the average building has a desired indoor temperature of 70°F and that 5°F of this is supplied by internal heat sources such as lights, appliances, equip-ment, and people. For example, if there were a period of 20 days when the outside
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temperature averaged 50°F each day, the number of HDD for these 3 days would be HDD = (65° − 50°) × 5 days = 75 degree days (Capehart et al., 2006).
Finally, an equipment list and the operating hours of each pieces of equipment should be obtained for a good understanding of major energy-consuming equip-ment at the facility. Knowing the operating hours allows determining whether any loads could be shifted to off-peak times.
2.2.2 NORMALIZING ENERGY CONSUMPTION DATA
Energy consumption is typically related to the production rate and other possible variables such as seasonal weather conditions. The change in energy consumption may not be caused by the change in energy effi ciency itself. It is sometimes neces-sary to normalize the energy consumption data to refl ect changes in production.
Normalizing energy consumption data becomes more complicated when energy use in the process is diversifi ed and more than a single product is produced. Example 2.1 shows how to normalize energy consumption data.
Example 2.1
This example is modifi ed from Witte et al., 1988. A plant making cereal products from grain produces two products, A and B. Product A is a meal produced by grind-ing the grain and then drygrind-ing it to a specifi ed moisture content. Product B is made by further drying the meal and extruding. The schematic process and the energy consumption of each step are shown in Figure 2.1. Please normalize the energy con-sumption to accurately refl ect the trends of energy use in the plant. Table 2.1 gives the production fi gures and total electricity consumption for a 3 month period.
Solution 2.1
The energy consumption per kilogram of products A and B is EA = 6 kWh/kg and EB = 12 kWh/kg, respectively. The total monthly energy consumption, which is related to the volumes of products A and B produced, is
= A+ B
E AE BE
or
( )
= +
A
B A
E E
A E E B
Grinder Dryer
Dryer/extruder Ed= 1 kWh/kg Ed= 5 kWh/kg
B (kg/month) Ed= 6 kWh/kg
A (kg/month)
FIGURE 2.1 Schematic of the process and the energy consumption of each step in a cereal processing facility.
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Therefore, the energy consumption for each unit of B produced is equivalent to EA/EB units of A. Specifi cally, in terms of energy consumption, each kilogram of B is equivalent to 2 kg of A. The monthly energy can thus be normalized in terms of energy per equivalent A produced by dividing E by the quantity of A + 2B. The energies normalized to simple total production A + 2B and to equivalent A production are given in Table 2.1. Table 2.1 shows that
Energy consumption shows a sharp increase from January to February
•
If this energy consumption is normalized simply on the basis of total kilogram
•
of production A and B, the energy consumption trend is the same
If the difference in energy requirements of the two products is taken into
•
account, the actual per unit energy consumption remained approximately con-stant during the period
2.2.3 FACILITY INSPECTION
It is necessary to conduct tours at different times to the entire facility to examine the operational patterns and equipment usage. Capehart et al. (2005) list nine major systems within a facility that should be examined for understanding and managing energy utilization within the facility. These nine major systems include
Building envelope
•
Heating, ventilating, and air conditioning (HVAC) system
•
Electrical supply system
•
Lighting system
•
Motors
•
Boiler and steam distribution system
•
Hot water distribution system
•
Compressed air distribution system
•
Manufacturing system
•
When utilities offer free or low-cost energy audits to commercial customers, they usually provide only walk-through audits rather than detailed audits. They generally consider the lighting, HVAC system, water heating, insulation, and some motors (Capehart et al., 2006).
Table 2.1
Production Figures and Total Electricity Consumption for a 3 Month Period
Month A (kg) B (kg)
Total Energy (kWh)
Normalized by A + B (kWh/kg)
Normalized by A + 2B (kWh/kg)
January 20,000 0 122,000 6.10 6.10
February 10,000 10,000 178,000 8.93 5.93
March 6,000 12,000 182,000 10.11 6.07
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The facility inspection may have six main steps, which include (Capehart et al., 2005)
Introductory meeting with the facility manager and the maintenance
super-•
visor to explain the purpose of the energy audit and the information needed
Audit interviews with the general manager, chief operating offi cer, facility/
•
plant manager, fi nancial offi cer, fl oor supervisors, equipment operators, and maintenance supervisor for correct information on facility equipment and operation
Initial walk-through tour with facility/plant manager to obtain a general
•
understanding of the facility’s operation
Gathering detailed data by examining the nine major energy-using systems
•
in the facility
Preliminary identifi cation of energy saving opportunities based on the audit
•
and on the knowledge of available energy effi ciency technologies
Preparation for an energy audit report to provide fi nal results of the energy
•
analyses and energy cost saving recommendations
Among the above six steps, process measurements will be required to gather detailed data on the nine major energy-using systems in the facility. The defi nition of data is thus a matter of critical importance. These data may include the following:
Accurate fl ow sheets are necessary for the process as a guide to the fl ows of
•
mass and energy.
Past records of fuel and electricity usage and related production data for
•
normalization and establishment of a baseline for plant energy consumption are needed.
Nameplate specifi cations of major energy-using equipment are needed to
•
determine the operating effi ciency.
Material properties including thermodynamic, physical, and chemical
prop-•
erties are needed for energy balance calculations and analyses of technical and economical feasibility.
Dimensional data such as the length and diameter of pipes and thickness of
•
insulation and available space for retrofi tting equipment are important in estimating energy losses and evaluating the feasibility of implementing energy conservation measures.
Equipment operating profi les are required to determine the accurate load
•
profi les of equipment.
Current and projected fuel and electricity costs are important to estimate
•
the potential savings to be realized from the implementation of energy con-servation technologies.
Safety is a critical part of an energy audit. The audit person or team should be thoroughly briefed on safety equipment and procedures. Adequate safety equipment should be worn at all appropriate times. Capehart et al. (2006) gives a safety checklist:
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1. Electrical
Avoid working on live circuits, if possible.
•
Securely lock off circuits and switches before working on a piece of
•
equipment.
Always keep one hand in your pocket while making measurements on
•
live circuits to help prevent cardiac arrest.
2. Respiratory
When necessary, wear a full-face respirator mask with adequate fi
ltra-•
tion particle size.
Use activated carbon cartridges in the mask when working around low
•
concentrations of noxious gases.
Use a self-contained breathing apparatus for work in a toxic environment.
• 3. Hearing
Use foam insert plugs while working around loud machinery to reduce
•
sound levels up to 20 decibels.
2.2.4 ENERGY ANALYSISAND ENERGY ACTION PLAN
After the audit visit to the facility, the data collected should be examined, organized, and reviewed for completeness. In some cases, not all of the data required for com-prehensive evaluations of the energy conservation opportunities can be obtained.
The audit team will have to rely on their judgment to fi ll in missing information. In many cases, it is necessary to make indirect estimations of some quantities. These estimations are based on fi gures and tables presented in engineering handbooks, manufacturer’s literature, and technical periodicals.
The preliminary energy saving opportunities identifi ed during the audit visit should be reviewed. Each energy conservation opportunity must be reviewed to determine whether it is technically applicable to the process. If so, it should further determine what the associated energy savings would be in the particular operation being evalu-ated. The evaluation procedure consists of calculating energy and mass balances for each item if the energy conservation modifi cation is made. The actual analysis of the equipment or operational changes should be conducted. The cost of the modifi cation must be considered and lifetime economic evaluation must be carried out to deter-mine the profi tability of the measure. Economics of the potential energy saving opportunities should be determined. Economical and fi nancial analyses such as simple payback period and discounted benefi t–cost ratio are discussed in Chapter 3.
Witte et al. (1987) provide the following guidelines for evaluation:
Energy savings should be cited separately from the economic saving
•
because it may be desirable to consider energy savings alone.
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It is necessary to consider fuel costs over the lifetime of the project not
•
simply at present levels.
Various measures of economic and fi nancial performance may be used.
•
Example 2.2
A food processing plant needs a 10 kW motor for a new process, which will run at a full load for two shifts a day or 4800 h per year. The company has two choices: a standard motor at an effi ciency of 85% and a high-effi ciency motor at an effi ciency of 90%. The higheffi ciency motor costs about $150 more than the standard effi -ciency motor. The electricity price is $0.05/kWh. Determine the simple payback period for the high-effi ciency motor.
Solution 2.2
The simple payback period is the initial cost divided by the annual saving. The initial cost for this energy opportunity is the price difference of two motors: $150.
The annual saving is 10 kW × 4800 h/year × (1/0.85 – 1/0.9) × $0.05/kWh = $157/
year. The simple payback period is thus $150/$157/year = 0.96 years. This is a very attractive energy saving opportunity. More sophisticated economic fi nancial analyses are discussed in Chapter 3.
2.2.5 ENERGY AUDIT REPORT
After the energy consumption data have been collected and analyzed, and the energy action plan for energy savings has been recommended for the facility, an energy manage-ment program should be set up to implemanage-ment the audit recommendations. The report should begin with an executive summary that provides the manager of the facility with a brief of the total savings available and the highlights of each energy saving opportunity.
The report should describe the facility that has been audited and provide information on the operation of the facility that is related to energy costs. The energy costs should be analyzed. The recommended energy saving opportunities are then recommended along with the analyses of costs and benefi ts and the cost effectiveness criterion.
Witte et al. (1988) and Capehart et al. (2006) give an outline for a typical energy audit report:
Executive summary (the audit procedures, primary results, and a table of
•
energy conservation recommendations)
Introduction (the concept of the audit, the energy systems of the facility, and
•
the major points of energy use within the facility)
Energy audit procedures (the general procedures carried out in the audit)
•
Plant energy distribution
•
Evaluation of energy conservation opportunities
•
Recommendation of an energy action plan for project implementation
•
Appendixes may also be provided to include data compilation, example calculations, and equipment cost estimates and quotations.
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2.3 MEASUREMENTS, INSTRUMENTATION,