Macro Audit

Macro Audit –

                    As the suggests in this type of audit rough estimates of energy purchase, production, utilization, wastage etc. are made. The estimates are mostly made on plant/unit/division wise to get a feel about the problem and to decide the areas priority-wise for further investigations. The priority is based on the maximum utilization of energy or in some cases based on the potential for energy conservation. The collection of information for this audit is mostly based on records and it does not involve actual measurements for calculations.

Micro Audit –

                   Micro audit follows macro audit, in which the measurements and calculation about various aspects of energy utilization and losses are done through actual measurement. The studies are carried out unit/division wise, for which the priority has already been decided through macro audit.

Billing Audit –

                     Billing audit is the part of energy audit carried out by collecting information based on the bills for purchase of raw material etc. for production of energy or for purchase of energy itself. The bills are studied over the years so that an estimate could be made based on the payments made for energy production and utilization.

Field Audit –

                 In field audits, the data is collected by surveyors who visit the actual sites, measure and collect data for calculation of various aspects of energy production, utilization and losses.

                 Fig. 1 gives the clear picture about the role of these audits in an energy conservation program. It can be seen that, all the above Macro audit, Micro audit, Field audit, Field audit and Billing audit give a comprehensive data base for further investigation in the energy conservation program. The audits are followed by comparison of actual and theoretical energy balances so that the energy conservation opportunities could be further studied and planning in that direction could be carried out. 

   

Energy conservation opportunities can be classified as :

• Good house keeping
• Installing additional equipment
• Equipment replacement
• Operating strategy
• Process integration/networking
• Process changes

These are briefly explained below:-

1. Good house keeping does not mean merely switching off equipment when not in use. It could mean improved monitoring and control, reduction of leakages, steam trap maintenance, etc. This typically involves low cost and can be quickly implemented.
2. Installing an additional equipment may help reduce the losses with the waste streams(e.g. adding a recuperate to recover some of the waste heat from the flue gases exiting a chimney).(At times the existing equipment is inefficient and it is viable to replace it by more efficient equipment e.g.    replacement of Aluminium blades in cooling tower fans by fiber Reinforced Plastics FRP blades result in energy savings of 10-15%. In the domestic sector conventional copper chokes in tube lights which consume 11-18W can be replaced by electronic ballasts which consume only 1-3W.) using economizers, super heaters efc. In boiler assemblies.
3. Normally equipment efficiency deteriorates drastically at off-design and part load conditions. For instance a standard 10 Hp motor may have a full load efficiency of about 90% which drops down to 85% at about 50% load and 78% at 25% load. In many cases it may be desirable to replace an oversized motor by a motor of lower rating. Energy efficient motors are available which have designs optimized for improving efficiency and which have less deterioration in performance at part loads.
4. Changes in operating strategies can also result in significant savings. In boilers and furnaces operating with high excess, air reducing the excess air results in less energy lost with the flue gasses and improves the operating efficiency. Changes in operating strategy may also involve investment in additional equipments. For example in a motor pump system, operating at part loads, the control is usually achieved by throttling.
5. In large industrial systems, the optimal operating strategy is not intuitively obvious. It is worthwhile to model the system and determine the optimal operating strategy. It is dependent on the fuel, electricity prices, equipment characteristic and plant steam or power requirements.
6. In many industries savings are possible by process integration or networking. The principle is to use the hot streams and cold streams available within the process to the maximum extend and to reduce the requirement of external utilities. A systematic procedure for designing optimum networks has been evolved based on the laws of thermodynamics and is known as Pinch Analysis.    

The simplest energy audit definition is as follows :-

               An energy audit serves the purpose of identifying where a plant facility uses energy and identifies ECOs . There is direct relationship to cost or the audit(amount of data collected and analyzed) and the number of energy opportunities to be found.

              

The Preliminary Energy Audit

                     The preliminary energy audit(PEA) is an initial data gathering exercise and is known by many names such as ’Short Audit’ or ‘Initial Survey’. Typically, the PEA can be completed without sophisticated instrumentation and uses only data already available. Data from plan records are collected and supplemented a ”Walk Through” of the plant, in which the audit team observes the general conditions of equipments, the standard of equipments and the level of operations control exercised by management. The PEA can be completed in short time, the energy auditors rely on their experience to gather written, oral and visual information for a rapid diagnosis of the energy situation at the plant. For a small to medium size plant, a PEA will typically take one to two weeks for a large industrial facility, such a refinery of steel plant PEA may take 2-3 weeks to complete. The typical output of a PEA may include a series of low cost ‘Housekeeping’ measures as well as list of obvious sources of energy waste , such as a poor combustion control , missing insulation, steam leaks and broken instruments. In addition and most importantly , the PEA identifies the need for, and scope of a Detailed Plant Audit.

The Detailed Energy Audit :-

                      The DEA is an instrumented survey of energy consuming equipment and processes in a plant, followed by a detailed analysis of the different systems. It is normally conducted after a PEA , although it could of course be performed independently. In that case, The initial time for collecting general data, normally invested during the PEA, must be added to the time taken for the DEA. A variety of portable instruments should be available to the energy auditors in order to obtain adequate data for quantifying energy consumption and establishing the operating efficiency of key equipments and processes. From this information, the potential savings are estimated, such instruments are indispensable in plants where fixed instrumentation is lacking( which is often the case). In other plants, the portable equipment can be used to check on the fixed instruments.