1. Day 5 INVENTORY ENERGY USE

2. Introduction  Two of the energy auditor's essential tools for fully assessing a facility are the demand profile (i.e. the characterization of the electrical loads in terms of time of use and size) and the load inventory. These two tools are complementary in that they describe in quantitative detail the systems that consume energy in a facility.  The energy auditor needs to know where energy is being consumed, how much is consumed by each system, and how all the systems add up as an aggregate load. It is helpful to know how the total energy load is distributed among various systems.  The load inventory is a systematic way of collecting and organizing this kind of information. It is a useful tool for undertaking "what if" assessments of proposed measures, i.e. estimating the impact of retrofits or other technological or operational change.

3. The Electrical Load Inventory  Making a list or inventory of all loads in a facility answers two important questions:  Where is the electricity used?  How much and how fast is electricity used in each category?  Often, the process of identifying categories of use allows waste to be easily identified, and this frequently leads to low-cost savings opportunities. Identifying high-consumption loads lets you consider the best savings opportunities first. Because the inventory also quantifies the demand (i.e. how fast electricity is used) associated with each load or group of loads, it is invaluable for further interpretation of the demand profile (see Section 6, "Profile Energy Use Patterns").

5.  7.2.1| Compiling a Load inventory  This section outlines a method for compiling a load inventory. Forms and calculations of the load inventory are described in Section C-5, "Electrical Inventory Method." The method is illustrated with sample sheets from the load inventory spreadsheet template included in the "Technical Supplement."  In addition to the load inventory forms (paper or electronic), a clipboard, pencil and calculator are needed. Instrumentation is not a necessity; a simple hand-held power meter is probably the most valuable tool. This and other instruments are discussed in Section C-4, "Instrumentation for Energy Auditing."  To begin the load inventory, choose a period of time corresponding to the utility billing period (usually a month, although it could also be a day, week or year). Select a period that is typical for your operations. Determine the actual demand in kW and the energy consumption in kWh for the period selected. If the period is a month, take information from the utility bill. If the facility demand is measured in kVA, this will require a calculation based on the peak power factor to convert kVA to kW (see Section C-1, "Energy Fundamentals").  Identify each of the major categories of electricity use in the facility. You may have to tour the facility and list categories as you notice them. When identifying various categories of energy use, it is useful to consider both the type of electricity use and the activity in each area. Selecting categories with similar operational patterns is a good approach. Figure 7.2 shows categories of use and the billing information entered.

7.  Figure 7.2 also shows the peak demand and energy consumption of each area of use.  These values are derived from load and time data for individual loads. The two most common load calculations are  motor load method - this estimates motor-connected electrical loads from motor horsepower, loading and efficiency  nameplate or measured connected kW load - this estimates load power consumption based on the nameplate rating of the load or from a power measurement with a power meter  Details of these and a more detailed method involving current and voltage are provided in Section C-5.  Figure 7.3 illustrates sample spreadsheets for use with the motor load method and the nameplate or measured connected kW load method.

8. After all loads in all categories are inventoried, the total demand and energy can be reconciled with the utility billed data for the period selected. Pie charts can be created from the summary information. Figure 7.4 shows a partially completed inventory not fully reconciled with utility bills.

9.  Figure 7.2 also shows the peak demand and energy consumption of each area of use.  These values are derived from load and time data for individual loads. The two most common load calculations are  motor load method - this estimates motor-connected electrical loads from motor horsepower, loading and efficiency  nameplate or measured connected kW load - this estimates load power consumption based on the nameplate rating of the load or from a power measurement with a power meter  Details of these and a more detailed method involving current and voltage are provided in Section C-5.  Figure 7.3 illustrates sample spreadsheets for use with the motor load method and the nameplate or measured connected kW load method.

11. The Thermal Energy Use Inventory - Identification of Energy Flows  Identifying thermal energy flows associated with each energy use in a facility is made simple with an energy flow diagram. A useful diagram will show all energy flows into the facility, all outgoing flows from the facility to the environment, and all significant energy flows within the facility.

13.  The purpose of an energy flow diagram is not to describe a process in detail; it will generally not show specific devices and equipment that are found in its various subsystem "blocks." Illustrating energy flows is the principal objective at this stage.  The sum of the energy outflows should equal purchased energy inflows. When we have the complete picture of the major internal energy flows and those from and to the surroundings, it is often possible to see opportunities for energy reduction and recovery.  7.3.1 | identifying the Type of Energy Flow  Table 7.1 below can be used as a checklist to help identify thermal energy outflows from a subsystem or a facility. Although this list does not contain every possible type of energy flow, it does cover a selection of the more common types - ones that often lead to savings opportunities.

15.  7.3.2 | Calculations for Estimating Energy Outflows  Section C-1 describes how to calculate thermal energy flows. The spreadsheet template "Thermal Inventory.xls" automates many of these methods. See Figure 7.6 for examples of calculations of energy in latent heat in moist airflows and steam flows.

16.  7.3.3 | Calculations for Estimating Energy inflows  Using an energy flow diagram, you can begin to quantify the inflows of energy in terms of rate (kW) and amount (GJ per day, month or year).  In many cases, the information necessary to perform these energy calculations is readily available for several pieces of equipment and processes.  Nameplate Ratings  Equipment specifications provide thermal energy requirement data. Fuel- fired equipment is rated in terms of fuel input rates. Oil-fired boilers are often rated according to energy input rates such as Btu/hr. or MBtu/hr. Given equipment operating times, energy use can be estimated by means of the energy calculation methods presented in Section C-1, "Energy Fundamentals." Figure 7.7 shows a sample inventory of energy inputs from the fuel systems spreadsheet template. 

18.  Steam Flow  There may be steam flow metering available in your plant. Steam-consuming equipment will have a specified requirement for steam flow rate. Section C-1 details methods of estimating energy use from steam flow rates. Figure 7.8 shows a sample steam calculation spreadsheet for estimating the cost of energy from steam. 

19.  Application to a Sample Energy System  Section 7.3 introduced the concept of the energy flow diagram as a way to develop a thermal energy-use inventory for a facility. Figure 7.9 illustrates a simple industrial food-processing system. 

21.  Figure 7.10 represents the simplified energy flow diagram that was used to build the energy use inventory shown in Table 7.2. All calculations are based on the methods outlined in this chapter.  All energy figures for this example are for one day's operation of a lobster processing plant - a 10-hour operating period. The heat of fusion (freezing and melting) for water is assumed to be 360 kJ/kg. The amount of lobster processed during this 10-hour period is assumed to be equivalent to 1000 kg of water in heat capacity. The reference water temperature is assumed to be 10°C. 

23. Energy Inventories and the Energy Balance  One of the implications of the energy balance principle underlying the audit is that we can quantify all energy inputs and balance them against all energy outputs. The energy flow diagram for the industrial food-processing plant is balanced - the energy inflow equals the energy outflows. A convenient graphical representation of this is the Sankey diagram, which is illustrated with reference to a boiler in Figure 7.11.

24.  The Sankey diagram summarizes the energy balance for a given system, indicating (1) the magnitude of all energy inputs and outputs by the size of the arrows and (2) the approximate sequence in which outputs occur along the energy flow path. Other Sankey diagrams are shown in Section C-2, "Details of Energy-Consuming Systems."

25.  7.4.1 | Building Envelope Energy Heat Loss  Another example of a thermal energy balance is the analysis of heat loss from the envelope of a building. This involves calculating heat loss through windows, doors, walls, roofs and ventilation and exhaust systems. The spreadsheet in Figure 7.12 illustrates a very simple heat loss calculation for a building, showing all energy outflows, with the contribution to space heat from internal heat gains such as electricity and human heat taken into account. The result is a breakdown of energy use into the major categories. A Sankey diagram for building envelope heat loss is shown in Section C-2.

27. Finding EMOs in the Energy Inventory  The electrical load inventory and thermal energy use inventory are good starting points in the search for EMOs.  The process of evaluating the breakdown or distribution of energy use can often unearth potential savings opportunities. While considering each piece of equipment, group of loads or heat-consuming systems, take into account operating time, the justification for each load and the need for the equipment to be operating at any given time.  7.5.1 | Special Consideration for the Thermal Energy-Use Inventory  The results of the thermal energy-use inventory can help to identify savings opportunities.  Opportunities for Energy Flow Reduction

28.  The magnitude of each outflow depends on several factors, such as temperatures, flow rates, humidity, time and the characteristics of materials. Finding savings opportunities involves considering which of these factors, if any, may be changed to reduce the amount of energy consumed.  Can flows be reduced? Can temperatures be changed? In most cases, there are valid reasons for present values being what they are. But taking a look at the type and magnitude of existing energy outflows often reveals some worthwhile savings opportunities.  So far we have not concerned ourselves with the technical details of the systems and equipment involved with the energy flows under consideration. Now, however, it is time to turn our attention to the hardware itself and consider the possibility of changing one or more aspects of how the system functions in order to reduce energy flow.  Is it possible, for example, to reduce the amount of energy consumed by a ventilation system that provides general ventilation for an office area of a building? Ventilation systems of this kind are responsible for increased consumption of winter heating energy because they introduce cool, fresh outside air that must be heated to replace warm, stale building air that is exhausted. The factors that influence the amount of energy consumed in this system are the rate at which outside air is brought in, the temperature difference between outside and inside air, and the duration of the ventilation. 

29.  Because building occupants have a legitimate need for fresh air, we ordinarily cannot reduce the amount of air brought in and exhausted. When considering ventilation and temperature, there are regulatory requirements that must be adhered to. For example, the Ontario Ministry of Labour's Occupational Health and Safety Act (available at www.e-laws.gov.on.ca/index.html) provides for standards governing workplace conditions. In addition, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) is an international organization that publishes standards for workplace ventilation and temperature. Visit ASHRAE's Web site (www.ashrae.org) to obtain these standards.www.e-laws.gov.on.ca/index.html)www.ashrae.org  Given the need to maintain the amount of air brought in by a ventilation system, how can the parameters of the system be manipulated to yield energy savings?  Time: It may be possible to control operation of the ventilation system more effectively, reduce operating time, and match it to building occupancy more closely.  Flow: Although the airflow rates during occupied periods cannot be adjusted, the rate of unneeded ventilation at night could be reduced by using dampers that seal properly when closed, or perhaps the system could be shut down completely at night.  Temperatures: If the system must run for extended periods to clear stale air properly, it may be possible to reduce the temperature of the air during unoccupied periods, using some sort of temperature setback method.  These are simple examples, but they illustrate the value of addressing each of the factors that influence energy consumption. Actual reduction in energy flows is achieved through specific changes to equipment, devices and operational practices. 

30.  Reducible or Recoverable Energy  An energy flow can be either reducible or recoverable, and energy savings will be realized accordingly:  Reducible: A flow directly associated with a purchased energy form. In this case, reducing the flow will directly result in a reduction of purchased energy. Examples are (1) reducing heat flow through the walls of a building by adding insulation and (2) reducing warm air lost by trimming hours of ventilation.  Recoverable: A flow of waste heat, the reduction of which will not directly reduce purchased energy. A good example of this is cooling water from water- cooled air compressors. This energy flow cannot be reduced - nor should it be, since it serves a useful purpose. However, there is real value in the heated water, and it could be used to replace the purchased energy being used in another system. This is called energy recovery or heat recovery.  It is important to determine precisely the type of flow in the facility. In some cases, it may be a mixture. The method of calculation of savings is different for reducible and recoverable energy flows.

31.  7.5.2 | special Consideration for the Electrical Load inventory  Examine each load in the inventory by means of a quadrant analysis (see Section 8.2.5). Look first at the required energy being provided - light, air or water power, process energy or heat. Also consider the following factors.  The Diversity Factor  A high value indicates a load that is contributing heavily to the peak demand. Is this necessary? Could it be avoided?  Operating Hours  Loads that have valid extended operating hours are good candidates for efficiency improvement. Could lamps be upgraded? Are pumps and fans the most efficient? Could a higher-efficiency motor be used?  Load Grouping  Are there large groups of loads that have similar operating hours simply because they operate or are switched only as a group? A good example of this is lighting. Can lights be zoned or switched automatically by occupancy detectors, time clocks or photocells?

32.  The Night Load  If you have a demand profile available, can you justify the night load? Do all loads that operate during night or unoccupied hours need to operate?  Loads That Require Monitoring  Are there loads or groups of loads that consume a significant portion of the overall energy and demand? Could these loads be monitored for excessive running time or power consumption? A good example of this would be a large refrigeration system in a supermarket or food-processing operation.  7.5.3 | Load Flexibility Assessment  Load flexibility can be defined as the degree to which the pattern of electrical use in a facility can be changed. One goal of assessing load flexibility is to shift energy consumption from one daily time period to another (less expensive) time of day.  A secondary goal might be to free up capacity of a fully loaded system by spreading the load out. The idea of flexible loads should be of interest to energy users who are considering alternative electric rates, such as time-of- use and real-time pricing.

33.  After performing a detailed load inventory and analysis of your existing operation, you will have a better understanding of  load groups by function (lighting, process, cooling, heating, etc.)  dependencies of the loads or load groups on external factors (weather, production, occupancy, etc.)  interdependencies between loads or load groups (e.g. which loads must be operated together or in a predetermined schedule)  Using this knowledge, you can examine your loads for any flexibility in their operation. Flexible loads usually fall into one of the following scenarios.  Energy storage: For practical purposes, this would be hot water or cold (ice) water storage. Insulated storage tanks can be used to stockpile electrically heated hot water during off-peak periods, so the heaters can be shut down in peak periods. Example of cooling storage: Some dairies operate refrigeration to produce and store "sweet water"  (ice water) during production down time; the sweet water is then used during processing instead of a large refrigeration plant supply cooling on demand.  Product storage: In a plant that produces several different products or in which the production is in distinct stages that can be run independently, different products can be manufactured in a specific shift and stockpiled for the following shift. One example of this approach is a rock quarry that staggers different processes to smooth out loads on the electrical system.  Task rescheduling: In a plant where industrial processes are independent of each other, it may be possible to schedule some tasks or processes to a different shift, away from the more expensive electrical time of day.