UNIT- II Energy Audit
2.0 Energy audits are performed by several different groups. Electric and gas utilities throughout the country offer free residential energy audits. A utility’s residential energy auditors analyze the monthly bills, inspect the construction of the dwelling unit, and inspect all of energy-consuming appliances in a house or an apartment.
Ceiling and wall insulation is measured, ducts are inspected, appliances such as heaters, air conditioners, water heaters, refrigerators, and freezers are examined, and the lighting system is checked. Some utilities also perform audits for their industrial and commercial customers. They have professional engineers on their staff to perform the detailed audits needed by companies with complex process equipment and operations. When utilities offer free or low-cost energy audits for commercial customers, they usually only provide walk-through audits rather than detailed audits. Even so, they generally consider lighting, HVAC systems, water heating, insulation and some motors. Large commercial or industrial customers may hire an engineering consulting firm to perform a complete energy audit. Other companies may elect to hire an energy manager or set up an energy management team whose job is to conduct periodic audits and to keep up with the available energy efficiency technology.
2.1 Purpose, Methodology with respect of Process Industries
BASIC COMPONENTS OF AN ENERGY AUDIT
An initial summary of the basic steps involved in conducting a successful energy audit is provided here, and these steps are explained more fully in the sections that follow. This audit description primarily addresses the steps in an industrial or large-scale commercial audit, and not all of the procedures described in this section are required for every type of audit. The audit process starts by collecting information about a facility’s operation and about its past record of utility bills. This data is then analyzed to get a picture of how the facility uses—and possibly wastes—energy, as well as to help the auditor learn what areas to examine to reduce energy costs. Specific changes—called Energy Conservation Opportunities (ECOs)—are identified and evaluated to determine their benefits and their cost-effectiveness. These ECOs are assessed in terms of their costs and benefits, and an economic comparison is made to rank the various ECOs. Finally, an Action Plan is created where certain ECOs are selected for implementation, and the actual process of saving energy and saving money begins.
2.2 The Auditor’s Toolbox
To obtain the best information for a successful energy cost control program, the auditor must make some measurements during the audit visit. The amount of equipment needed depends on the type of energy consuming equipment used at the facility, and on the range of potential ECOs that might be considered. For example, if waste heat recovery is being considered, then the auditor must take substantial temperature measurement data from potential heat sources.
Tape Measures
distances between pieces of equipment for purposes such as determining the length of a pipe for transferring waste heat from one piece of equipment to the other.
Lightmeter
One simple and useful instrument is the lightmeter which is used to measure illumination levels in facilities. A lightmeter that reads in foot candles allows direct analysis of lighting systems and comparison with recommended light levels specified by the Illuminating Engineering Society. A small lightmeter that is portable and can fi t into a pocket is the most useful. Many areas in buildings and plants are still significantly overlighted, and measuring this excess illumination then allows the auditor to recommend a reduction in lighting levels through lamp removal programs or by replacing inefficient lamps with high efficiency lamps that may not supply the same amount of illumination as the old inefficient lamps.
Thermometers
Several thermometers are generally needed to measure temperatures in offices and other worker areas, and to measure the temperature of operating equipment. Knowing process temperatures allows the auditor to determine process equipment efficiencies, and also to identify waste heat sources for potential heat recovery programs. Inexpensive electronic thermometers with interchangeable probes are now available to measure temperatures in both these areas. Some common types include an immersion probe, a surface temperature probe, and a radiation shielded probe for measuring true air temperature. Other types of infra-red thermometers and thermographic equipment are also available. An infra-red “gun” is valuable for measuring temperatures of steam lines that are not readily reached without a ladder.
Infrared Cameras
breakers, transformers, motors and other pieces of electrical equipment. They can also be used to find wet insulation, missing insulation, roof leaks, and cold spots. Thus, infrared cameras are excellent tools for both safety related diagnostics and energy savings diagnostics. A good rule of thumb is that if one safety hazard is found during an infrared scan of a facility, then that has paid for the cost of the scan for the entire facility. Many insurers require infrared scans of buildings for facilities once a year.
Voltmeter
An inexpensive voltmeter is useful for determining operating voltages on electrical equipment and especially useful when the nameplate has worn off of a piece of equipment or is otherwise unreadable or missing. The most versatile instrument is a combined volt-ohm-ammeter with a clamp-on feature for measuring currents in conductors that are easily accessible. This type of multimeter is convenient and relatively inexpensive. Any newly purchased voltmeter, or multimeter, should be a true RMS meter for greatest accuracy where harmonics might be involved.
Clamp On Ammeter
These are very useful instruments for measuring current in a wire without having to make any live electrical connections. The clamp is opened up and put around one insulated conductor, and the meter reads the current in that conductor. New clamp on ammeters can be purchased rather inexpensively that read true RMS values. This is important because of the level of harmonics in many of our facilities. An idea of the level of harmonics in a load can be estimated from using an old non-RMS ammeter, and then a true RMS ammeter to measure the current. If there is more than a five to ten percent difference between the two readings, there is a significant harmonic content to that load.
Wattmeter/Power Factor Meter
Consumption and power factor of individual motors and other inductive devices. This meter typically has a clamp-on feature which allows an easy connection to the current-carrying conductor, and has probes for voltage connections. Any newly purchased wattmeter or power factor meter, should be a true RMS meter for greatest accuracy where harmonics might be involved
Combustion Analyzer
Combustion analyzers are portable devices capable of estimating the combustion efficiency of furnaces, boilers, or other fossil fuel burning machines. Two types are available: digital analyzers and manual combustion analysis kits. Digital combustion analysis equipment performs the measurements and reads out in percent combustion efficiency. These instruments are fairly complex and expensive. The manual combustion analysis kits typically require multiple measurements including exhaust stack temperature, oxygen content, and carbon dioxide content. The efficiency of the combustion process can be calculated after determining these parameters. The manual process is lengthy and is frequently subject to human error.
Airflow Measurement Devices
Measuring air flow from heating, air conditioning or ventilating ducts, or from other sources of air flow is one of the energy auditor’s tasks. Airflow measurement devices can be used to identify problems with air flows, such as whether the combustion air flow into a gas heater is correct. Typical airflow measuring devices include a voltmeter, an anemometer, or an airflow hood.
Blower Door Attachment
generator can also be used in residences, offices and other buildings to find air infiltration and leakage around doors, windows, ducts and other structural features. Care must be taken in using this device, since the chemical “smoke” produced may be hazardous, and breathing protection masks may be needed.
Safety Equipment
The use of safety equipment is a vital precaution for any energy auditor. A good pair of safety glasses is an absolute necessity for almost any audit visit. Hearing protectors may also be required on audit visits to noisy plants or areas with high horsepower motors driving fans and pumps. Electrical insulated gloves should be used if electrical measurements will be taken, and asbestos gloves should be used for working around boilers and heaters. Breathing masks may also be needed when hazardous fumes are present from processes or materials used. Steel-toe and steel-shank safety shoes may be needed on audits of plants where heavy materials, hot or sharp materials or hazardous materials are being used.
Miniature Data Loggers
Vibration Analysis Gear
Relatively new in the energy manager’s tool box is vibration analysis equipment. The correlation between machine condition (bearings, pulley alignment, etc.) and energy consumption is related and this equipment monitors such machine health. This equipment comes in various levels of sophistication and price. At the lower end of the spectrum are vibration pens (or probes) that simply give real-time amplitude readings of vibrating equipment in in/sec or mm/sec. This type of equipment can cost under $1,000. The engineer compares the measured vibration amplitude to a list of vibration levels (ISO2372) and is able to determine if the vibration is excessive for that particular piece of equipment. The more typical type of vibration equipment will measure and log the vibration into a database (on-board and downloadable). In addition to simply measuring vibration amplitude, the machine vibration can be displayed in time or frequency domains. The graphs of vibration in the frequency domain will normally exhibit spikes at certain frequencies. These spikes can be interpreted by a trained individual to determine the relative health of the machine monitored. The more sophisticated machines are capable of trend analysis so that facility equipment can be monitored on a schedule and changes in vibration (amplitudes and frequencies) can be noted. Such trending can be used to schedule maintenance based on observations of change. This type of equipment starts at about $3,000 and goes up depending on features desired.
2.3 Energy Audit of Thermal Power Plant
Energy Audit Energy audit is the first step forward systematic efforts for conservation of energy like financial audit. It involves and collection of energy related data on regular basis. It tells how and where the energy is being consumed and it also tells how efficiently and effectively the energy is being used. It is not only study to identify various weak areas but also tells the tool to take corrective actions and monitor the performance. Energy audit provides with the tool to bench mark your consumption against your best figure
Walk Through Audit:
procedures. Repairing or replacing small items which are in poor working condition. Use the Walk-Through Checklist to identify the easy, low- to no-cost improvements you can make in your facilities. Once the audit has been completed, you will be able to identify energy-saving improvements. Unit 1(209.3 MW) was chosen for conducting energy audit test. After discussions with the power station engineer, the following studies/tests were decided to carry out:
1. Boiler efficiency test 2. Air heater leakage test 3. Furnace radiation losses 4. Turbine heat rate
5. Condenser performance
6. Regenerative system performance 7. Auxiliary power consumption
Boiler and Its Auxiliaries Pulverized coal is put in boiler furnace. Boiler is an enclosed vessel in which water is heated and circulated until the water is turned in to steam at the required pressure.
Boiler Efficiency Test
Due to poor combustion, poor operation, heat transfer fouling and maintenance, the performance of boiler is reduced with time. There are two other causes which also lead to poor performance of boiler i.e. Deterioration of fuel quality and water quality. Efficiency testing helps
to observe, how far the boiler floats away from the best efficiency.
Indirect method:
The indirect method is also called the heat loss method. The efficiency can be calculated by subtracting the heat loss fractions from 100 as follows:
Efficiency of boiler (n) = 100 - (i + ii + iii + iv + v + vi + vii)
Whereby the principle losses that occur in a boiler are loss of heat due to:
1. Dry flue gas
3. Evaporation of moisture in fuel 4. Moisture present in combustion air 5. Un-burnt fuel in fly ash
6. Un-burnt fuel in bottom ash
7. Radiation and other unaccounted losses
Coal
Analysis of coal is very important part during boiler efficiency test. This analysis helps find out the quality of coal. Quality of coal is calculated by the percentages of different constituents which help in categorizing it as a high grade or lower grade coal. There are two types of tests involved in the analysis of coal:
i. Proximate analysis of coal
It includes the determination of carbon moisture, ash and volatile matter and fixed carbon. This gives quick and valuable information.
ii. Ultimate analysis of coal
It includes the estimation of ash, carbon, hydrogen, oxygen and nitrogen. It is essential
for calculation heat balance in any process. Proximate analysis of coal is done in thermal power plant but ultimate analysis of coal is not performed, it is also done on annual basis.
Signification of Proximate Analysis
The main purpose of coal sample analysis is to determine the rank of the coal along with its intrinsic characteristics.
Moisture
Moisture is a main property of coal. All types of coal are mined wet. Groundwater and
other extraneous moisture are known as adventitious moisture. Moisture may take place in four possible forms within coal:
a) Surface moisture
b) Hydroscopic moisture
Water held by capillary action within the micro fractures of the coal.
c) Decomposition moisture
Water held within the coal’s decomposed organic compounds.
d) Mineral moisture
Water comprises part of the crystal structure of hydrous silicates such as clays.
ii) Ash
After coal is burnt, ash content of coal is the non-combustible remains left. During combustion, it represents the bulk mineral matter after carbon, oxygen, sulfur and water (including from clays) have been driven off.
iii) Fixed carbon
The fixed carbon content of the coal is the carbon found in the material. These are left after volatile materials are driven off. The total sum of percentages of moisture and ash subtracted from 100 gives the percentage of fixed carbon.
e) Radiation Loss
Radian losses are heat losses from boiler enclosure through insulation. Least conductive insulation can minimize the losses.
RL =
% RL = (RL/GCV) x 100
2.4 Energy Audit in Boilers:
abnormal deviations could therefore be investigated to pinpoint the problem area for necessary corrective action. Hence it is necessary to find out the current level of efficiency for performance evaluation, which is a pre requisite for energy conservation action in industry.
Purpose of the Performance Test
ĂŻ To find out the efficiency of the boiler ĂŻ To find out the Evaporation ratio The purpose of the performance test is to determine actual performance and efficiency of the boiler and compare it with design values or norms. It is an indicator for tracking day-to-day and season-to-season variations in boiler efficiency and energy efficiency improvements.
Indian Standard for Boiler Efficiency Testing Most standards for computation of boiler efficiency, including IS 8753 and BS845 are designed for spot measurement of boiler efficiency. Invariably, all these standards do not include blow down as a loss in the efficiency determination process. Basically Boiler efficiency can be tested by the following methods:
1) The Direct Method: Where the energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel.
2) The Indirect Method: Where the efficiency is the difference between the losses and the energy input.
The Direct Method Testing Description
Measurements Required for Direct Method Testing Heat input
Both heat input and heat output must be measured. The measurement of heat input requires knowledge of the calorific value of the fuel and its flow rate in terms of mass or volume, according to the nature of the fuel.
For liquid fuel: Heavy fuel oil is very viscous, and this property varies sharply with temperature. The meter, which is usually installed on the combustion appliance, should be regarded as a rough indicator only and, for test purposes, a meter calibrated for the particular oil is to be used and over a realistic range of temperature should be installed. Even better is the use of an accurately calibrated day tank.
For solid fuel: The accurate measurement of the flow of coal or other solid fuel is very difficult. The measurement must be based on mass, which means that bulky apparatus
must be set up on the boiler-house floor. Samples must be taken and bagged throughout the test, the bags sealed and sent to a laboratory for analysis and calorific value determination. In some more recent boiler houses, the problem has been alleviated by mounting the hoppers over the boilers on calibrated load cells, but these are yet uncommon.
Heat output
There are several methods, which can be used for measuring heat output. With steam boilers an installed steam meter can be used to measure flow rate, but this must be corrected for
temperature and pressure. In earlier years, this approach was not favoured due to the change in accuracy of orifice or venturi meters with flow rate. It is now more viable with modern flow meters of the variable-orifice or vortex-shedding types. The alternative with small boilers is to measure feed water, and this can be done by previously calibrating the feed tank and noting down the levels of water during the beginning and end of the trial. Care should be taken not to pump water during this period. Heat addition for conversion of feed water at inlet temperature to steam, is considered for heat output.
2.5 Energy conservation for Boilers: Load Reduction
Insulation
—steam lines and distribution system —condensate lines and return system —heat exchangers
—boiler or furnace Repair steam leaks Repair failed steam straps Return condensate to boiler Reduce boiler blowdown Improve feed water treatment Improve make-up water treatment Repair condensate leaks
Shut off steam tracers during the summer Shut off boilers during long periods of no use Eliminate hot standby
Reduce flash steam loss
Install stack dampers or heat traps in natural draft boilers Replace continuous pilots with electronic ignition pilots
Waste Heat Recovery (a form of load reduction) Utilize flash steam
Preheat feed water with an economizer Preheat make-up water with an economizer Preheat combustion air with a recuperator
Recover flue gas heat to supplement other heating system, such as domestic or service hot water, or unit space heater
Install condensation heat recovery system —indirect contact heat exchanger
—direct contact heat exchanger
Efficiency Improvement Reduce excess air
Provide sufficient air for complete combustion Install combustion efficiency control system —Constant excess air control
—Minimum excess air control
—Optimum excess air and CO control Optimize loading of multiple boilers Shut off unnecessary boilers
Install smaller system for part-load operation —Install small boiler for summer loads —Install satellite boiler for remote loads Install low excess air burners
Repair or replace faulty burners
Replace natural draft burners with forced draft burners Install turbulators in fi retube boilers
Install more effi cient boiler or furnace system
—high-effi ciency, pulse combustion, or condensing boiler or furnace system Clean heat transfer surfaces to reduce fouling and scale
Improve feedwater treatment to reduce scaling Improve make-up water treatment to reduce scaling
Fuel Cost Reduction
Switch to alternate utility rate schedule —interruptible rate schedule
—switch between alternate fuel sources —install multiple fuel burning capability
—replace electric boiler with a fuel-fired boiler. Switch to a heat pump
—use heat pump for supplemental heat requirements —use heat pump for baseline heat requirements Other Opportunities
Install variable speed drives on feed water pumps Install variable speed drives on combustion air fan Replace boiler with alternative heating system Replace furnace with alternative heating system Install more efficient combustion air fan
Install more efficient combustion air fan motor Install more efficient feedwater pump
Install more efficient feedwater pump motor Install more efficient condensate pump Install more efficient condensate pump motor
2.6 Energy Conservation opportunities in Steam Systems
General Operations
1. Review operation of long steam lines to remote single-service applications. Consider relocation or conversion of remote equipment, such as steam-heated storage tanks.
2. Review operation of steam systems used only for occasional services, such as winter-only steam tracing lines. Consider use of automatic controls, such as temperature-controlled valves, to assure that the systems are used only when needed.
3. Implement a regular steam leak survey and repair program.
4. Publicize to operators and plant maintenance personnel the annual cost of steam leaks and unnecessary equipment operations.
5. Establish a regular steam-use monitoring program, normalized to production rate, to track progress in reduction of steam consumption. Publicize on a monthly basis the results of this monitoring effort.
6. Consider revision of the plant-wide steam balance in multipressure systems to eliminate venting of low-pressure steam. For example, provide electrical backup for currently steam-driven pumps or compressors to permit shutoff of turbines when excess low-pressure steam exists. 7. Check actual steam usage in various operations against theoretical or design requirement. Where significant disparities exist, determine the cause and correct it.
8. Review pressure-level requirements of steam-driven mechanical equipment to evaluate feasibility of using lower pressure levels.
9. Review temperature requirements of heated storage vessels and reduce to minimum acceptable temperatures.
10. Evaluate production scheduling of batch operations and revise if possible to minimize startups and shutdowns.
Steam Trapping
1. Check sizing of all steam traps to assure they are adequately rated to provide proper
condensate drainage. Also review types of traps in various services to assure that the most effi cient trap is being used for each application.
Condensate Recovery
1. Survey condensate sources presently being discharged to waste drains for feasibility of condensate recovery.
2. Consider opportunities for flash steam utilization in low-temperature processes presently using first-generation steam.
3. Consider pressurizing atmospheric condensate return systems to minimize flash losses. Mechanical Drive Turbines
1. Review mechanical drive standby turbines presently left in the idling mode and consider the feasibility of shutting down standby turbines.
2. Implement a steam turbine performance testing program and clean turbines on a regular basis to maximize effi - ciency.
3. Evaluate the potential for cogeneration in multipressure steam systems presently using large pressure-reducing valves.
Insulation
1. Survey surface temperatures using infrared thermometry or thermography on insulated
equipment and piping to locate areas of insulation deterioration. Maintain insulation on a regular basis.
2. Evaluate insulation of all uninsulated lines and fittings previously thought to be uneconomic. Recent rises in energy costs have made insulation of valves, flanges, and small lines desirable in many cases where this was previously unattractive.
3. Survey the economics of retrofitting additional insulation on presently insulated lines, and upgrade insulation if economically feasible.
2.7 Energy conservation in Air conditioning and refrigeration system
professional engineering design, and careful implementation. Properly designed, installed and maintained HVAC systems are efficient, provide comfort to the occupants, and inhibit the growth of moulds and fungi.
Energy efficiency measures for HVAC systems required of a green office building are listed below.
Equipment
Buildings usually operate under less than full-load heating and cooling conditions. Therefore, the greatest overall annual efficiency improvements will result from giving special consideration to part-load conditions and selecting equipment accordingly. Chiller manufacturers now provide a standard ratings for part-load efficiency, reflecting the fact that chillers operate at less than full load 99% of the time. Staging multiple chillers or boilers to meet varying demand also greatly improves efficiencies at low and moderate building loads. Pairing different-sized chillers or boilers in parallel offers greater flexibility to central plant equipment. Units should be staged with microprocessor controls to optimize system performance.
Ice and Snow Melting
Sidewalks and driveways should be designed so they can be manually cleared of ice and snow and should not rely on ice- and snow-melting heaters. Where ice- and snow-melting heaters are required, they must have automatic or accessible manual on/off controls. The controls are to be clearly labelled and provided with an indicator light.
Cooling with Outdoor Air (Air Economizer)
ď‚· "Air economizer" systems that reduce mechanical cooling energy by direct use of outdoor air must be able to provide outdoor air volumes from 100% of design supply air (S/A) down to the minimum outdoor air flow required for acceptable indoor air quality. These systems must mix outdoor air and return air to a temperature as near as possible to the S/A temperature required to condition the space, except when on-coil temperatures for D/X systems must be higher to prevent coil freeze-up.
Water Economizer (Alternate to Air Economizer)
"Water economizer" systems that reduce mechanical cooling energy use by using outdoor air to chill cooling distribution fluid must be capable of cooling supply air to provide 100% of the cooling load when:
 outdoor air wet bulb temperature is 7° C or below, if distribution fluid is cooled by direct or indirect evaporation, or both;
 outdoor air dry bulb temperature is 10° C or below, if distribution fluid is cooled by sensible heat transfer only.
Fan Power of Constant Volume Systems
Constant-volume fan systems with 10kW or more of combined nameplate supply return and relief fan power must not exceed 1.6 W per L/s of supply air delivered to the conditioned spaces Control of HVAC Systems
A supply air handler shall be able to achieve supply air temperature without:
ď‚· heating previously cooled air (unless for process humidity control for areas such as computer rooms, or when the reheat energy is not from electricity or fossil fuels)
ď‚· cooling previously heated air
ď‚· heating outdoor air, alone or in mixed air, which is in excess of the minimum required for ventilation
Except for systems with a minimum S/A of 2 L/s per m² of floor area, systems that control temperature of a space by heating or cooling previously cooled or heated air, respectively, must be equipped with S/A reset controls that will automatically adjust the temperature of:
ď‚· the cool air supply to the highest temperature that will satisfy the temperature control zone requiring the coolest air, and/or
ď‚· the warm air supply to the lowest temperature that will satisfy the temperature control zone requiring the warmest air.
2.8 Energy conservation in Pumps:
aspect of energy efficiency in a pumping system is matching of pumps to loads. Hence even if an efficient pump is selected, but if it is a mismatch to the system then the pump will operate at very poor efficiencies. In addition efficiency drop can also be expected over time due to deposits in the impellers. Performance assessment of pumps would reveal the existing operating efficiencies in order to take corrective action. 7.2 Purpose of the Performance Test
• Determination of the pump efficiency during the operating condition
• Determination of system resistance and the operating duty point of the pump and compare the same with design.
7.3 Performance Terms and Definitions Pump Capacity,
Q = Volume of liquid delivered by pump per unit time, m3 /hr or m3 /sec Q is proportional to N, where N- rotational speed of the pump
Total developed head, H = the difference of discharge and suction pressure.
The pump head represents the net work done on unit weights of a liquid in passing from inlet of the pump to the discharge of the pump.
There are three heads in common use in pumps namely (i) Static head
(ii) Velocity head
(iii) Friction head. The frictional head in a system of pipes, valves and fittings varies as a function (roughly as the square) of the capacity flow through the system.
Field Testing for Determination of Pump Efficiency
To determine the pump efficiency, three key parameters are required: Flow, Head and Power. Of these, flow measurement is the most crucial parameter as normally online flow meters are hardly available, in a majority of pumping system. The following methods outlined below can be adopted to measure the flow depending on the availability and site conditions
.
The following are the methods for flow measurements: • Tracer method BS5857
• Ultrasonic flow measurement • Tank filling method
• Installation of an on-line flowmeter
Tracer Method
The Tracer method is particularly suitable for cooling water flow measurement because of their sensitivity and accuracy.
This method is based on injecting a tracer into the cooling water for a few minutes at an accurately measured constant rate. A series of samples is extracted from the system at a point where the tracer has become completely mixed with the cooling water.
Ultrasonic Flow meter
Operating under Doppler effect principle these meters are non-invasive, meaning measurements can be taken without disturbing the system. Scales and rust in the pipes are likely to impact the accuracy.
• Ensure measurements are taken in a sufficiently long length of pipe free from flow disturbance due to bends, tees and other fittings.
• The pipe section where measurement is to be taken should be hammered gently to enable scales and rusts to fall out.
Tank filing method
In open flow systems such as water getting pumped to an overhead tank or a sump, the flow can be measured by noting the difference in tank levels for a specified period during which the outlet flow from the tank is stopped. The internal tank dimensions should be preferable taken from the design drawings, in the absence of which direct measurements may be resorted.
Installation of an on-line flowmeter
If the application to be measured is going to be critical and periodic then the best option would be to install an on-line flowmeter which can get rid of the major problems encountered with other types.
Determination of total head, H Suction head (hs)
This is taken from the pump inlet pressure gauge readings and the value to be converted in to meters (1kg/cm2 = 10. m). If not the level difference between sump water level to the centerline of the pump is to be measured. This gives the suction head in meters.
