The scope of this method statement is to determine the thermal capability of water cooling towers. Its main purpose is to describe instrumentation and procedures for the testing and performance evaluation of water cooling towers.
It is recognized that the data limitations specified throughout this Testing & Commissioning Procedure represent desired conditions which may not exist at the time the test is performed.
In such cases, existing conditions may be used if mutually agreed upon prior to test by client authorized representative, contractor, sub-contractor & third party personnel.
Before commencement of Testing & Commissioning activity, the supervisor/ engineer must ensure that:
All Installations & Pressure Testing of Pipe/ Duct works have been completed & approved by the client.
Determine whether the units occurs damages during the storage, installation & shifting of units into its site location.
Permission to start or Civil Clearances prior to testing & commissioning has been given by the main contractor.
All relevant Approved Shop drawings, manufacturer’s recommendations, specifications etc. for the testing & commissioning of the system shall be available & approved by the client.
Testing & Commissioning activities shall only commence when all associated works by the civil contractor has been completed, Installation activities & all associated works intended & connected to the Cooling Towers has been completed & approved by the client.
Safe access shall be provided by the Main Contractor thru Work Permit in coordination with the Safety in charge at site.
Ensure that at the time of test, the tower shall be in good operating condition.
Water distribution system shall be essentially clear and free of foreign materials which may impede the normal water flow.
Mechanical equipment, if involved, shall be in good working order. Fans shall be rotating in the correct direction, with proper orientation of leading and trailing edges. Fan blades shall be at uniform angle that will yield within +/- 10 % of the specified horsepower loading. In addition, centrifugal fans shall be free of foreign material and properly secured to the shafts.
Drift eliminators shall be essentially clear and free of algae and other deposits which may impede normal air flow.
Fill shall be essentially free of foreign materials such as oil, tar, scale or algae.
Water level in cold water basin shall be at normal operating elevation and shall be maintained substantially constant during the test in order to provide proper airflow to the fill.
Make-up and or blow down streams may be stopped during the test if other test condition requirements are not adversely affected.
Procedures for Testing & Commissioning of Cooling Towers
Operating /Test Conditions
The test shall be conducted within the following limitations:
The wet-bulb and dry-bulb temperatures shall be the inlet values, measured in accordance to this test procedure.
The wind velocity shall not exceed the following:
- Average wind velocity…….10 miles per hour
- One- minute duration……..15 miles per hour
The following variations form design conditions shall not be exceed:
- Wet- bulb Temperature……±10°F
- Dry-Bulb Temperature…… ±20°F
- Range……………………….±20%
- Circulating Water Flow……±10%
The water shall be distributed to all operating cells and/ or parts of the tower.
The total dissolved solid in the circulating water, as determined by evaporation, shall not exceed the greater of the following:
- 5,500 ppm
- 1 times the design concentration.
For a valid test, variations in test conditions shall be within the following limits:
- Circulating water flow shall not vary by more than 5%.
- Heat load shall not vary by more than 5%.
- Range shall not vary by more than percent%.
- Instantaneous air temperature readings may fluctuate, but variations in the averages during the test period shall not exceed the following:
- wet bulb temperature…..2°F
- dry-bulb temperature…..5°F
After reaching steady state conditions, the duration of the test run shall be not less than one hour. If thermal lag time is greater than five minutes, the timed test period shall be at least 1 hour plus thermal lag time.
Readings shall be taken at regular intervals and recorded for future reference.
Measurement Procedures
Water Flow Measurements
- Water flow measurements may be made by means of pitot tube, orifice, venture, volumetric, weir, flow nozzle & turbine meter.
- The accuracy of any of the above shall be presumed to be within ± 1.25%. The selection of location of measurement will be dependent upon the nature of the installation to be tested.
- The water quantities shall be measured in terms of, Circulating water flow to the tower If required, consider make-up water flow & blow-down flow.
- If circulating water flow to the tower is measured by pitot tube traverse, an air-over-water (inverted type) manometer shall be used unless otherwise agreed or instructed. One full traverse (along two axes at 90° to each other) shall be made immediately preceding the test, and a minimum of three center-point readings shall be taken during the test.
Water Temperature Measurements
- Water temperature measurements shall be made by any of the instruments such as resistance thermometers or mercury-in-glass thermometers. Instruments shall be designated to indicate or record in 0.2°F graduations. Temperature sensitive elements shall be carefully located where the water will be thoroughly mixed.
- Hot water circulating water temperature measurement shall be made in tower risers or at the discharge of the inlet riser into the flume or distribution system or, for a multi-cell tower, in the supply header just upstream of the first riser. If the source is a mixture of two or more streams of different temperatures, complete mixing must be assured at the point of measurement or sufficient flow rate and temperature measurements shall be made to ensure an accurate weighted average water temperature.
- Cold Circulating water temperature measurements should preferably be made in a full flowing bleed stream at the circulating pump discharge, and the average corrected for heat added by the pump. If the measurement the measurement is made at a location where temperatures and velocities are not uniform over the stream cross section, sufficient flow rate and temperature measurements shall be made to ensure an accurate weighted average water temperature.
- Make-up water temperature measurement (if applicable), shall be made at the point the make-up water enters the system.
- Blow-down temperature measurement (if applicable), shall be made at the point the blow-down leaves the system.
Inlet Air Temperature Measurements
- The measurement of Inlet Wet-Bulb Temperature is required for the testing of all types of cooling towers. The measurement of inlet dry-bulb temperature is required for natural draft and fan assist cooling towers.
- The Inlet Wet-Bulb Temperature shall be measured with mechanically aspirated instruments, which meets the following requirements:
- The indicator or recorder shall be graduated in increments of not more than 0.2°F.
- The temperature sensitive element shall be accurate to ± 0.1°F.
- The temperature sensitive element shall be shielded from direct sunlight or from other significant sources of radiant heat. The shielding device shall be within 2°F of the surrounding dry-bulb temperature.
- The temperature sensitive element shall be covered with a wick that is continuously fed from a reservoir of distilled water.
- The temperature of distilled water used to wet the wick shall be approximately the wet-bulb temperature being measured. This may be obtained in practice by allowing adequate ventilated wick between the water supply and the temperature sensitive element.
- The wick shall fit snugly over the temperature sensitive element and extend at least 2cm past the element over the stem. It shall be kept clean while in use.
- The air velocity over the temperature-sensitive element shall be maintained between 950 and 1050 feet per minute.
- For measurement of Inlet Wet- Bulb Temperature, the instrument shall be located within 4 feet of the air intakes. A sufficient number of measurement stations shall be designated to ensure that the test average is an accurate representation of the true average inlet wet-bulb temperature.
- The average of 3 successive readings taken at 10 second intervals at each station shall be considered the wet-bulb temperature at that time at that instrument station. The station averages shall be averaged to obtain the effective wet-bulb temperature for that run. Such runs shall be made every 5 minutes during the test period, and the arithmetic average of these runs shall be considered the inlet wet-bulb temperature and shall be used for the evaluation of results.
- The Inlet Dry Bulb Temperature (if applicable), shall be measured with instruments each meeting with the indicator or recorder which is graduated in increments of not more than 0.2°F; the temperature sensitive element shall be accurate to ± 01.°F; the temperature sensitive element shall be shielded from direct sunlight or from other significant sources of radiant heat. The shielding device shall be within 2°F of the surrounding dry-bulb temperature.
Wind Velocity Measurement
The wind velocity measurement shall be made with an anemometer of the rotating cup type. Measurement shall be made in an open and unobstructed location within 100 feet of and to windward of the tower at a point 5 feet above basin curb elevation.
Fan Driver Power
For mechanical-draft and fan-assist towers, power shall be determined as power input to the motor or driver. In the case of electric motors, power input shall be determined by measurement of voltage, current and power factor, or by direct measurement of the Kilowatt input. If performance guarantee is based on driver output, efficiencies assigned for the driver may be used.
Cooling Tower Start-up Procedure
Cleaning
- Drain the cold water basin with the strainer in place.
- Open the hot water basin covers and remove any dirt or debris from the hot water basins.
- Clean & inspect the fan deck.
- Remove dirt and debris from the fan guards.
- Inspect & clean all spray nozzles.
- Clean & inspect the mechanical components, such as the fan and motor.
- Flush the cold water basin to remove any accumulated dirt & debris.
- Remove, clean, & replace the cold water basin strainer.
Inspection
- Conduct external inspection of the equipment. Check for leaks, corrosion and any structural damage.
- Conduct internal inspection of the equipment. Check for anything unusual such as structural or mechanical component damage.
- Inspect piping connections.
- Thoroughly inspect the fan for any damage.
- Verify proper fan tip clearance.
- At seasonal start-up or after prolonged shutdown, check the motor insulation with an insulation tester prior to motor start-up.
- Check & adjust the belt tension or check gear drive oil levels.
- Check that the float operated make-up valve is operating freely.
Start-Up
- Prior to start-up, lubricate the motor base adjusting screw and the fan shaft bearings. At initial start-up, bearings are factory lubricated prior to shipment. However, if the unit has been idle for more than three months, re-lubricate the bearings.
- Fill the cold water basin with fresh water to the overflow level via the make- up valve.
- Set the make-up valve float so the water shuts off at the operating level.
- Verify the drain plug is installed.
- Check that the float operated make up valve is operating freely. Closely monitor the water level and adjust as necessary during the first 24 hours of operation.
- For the top inlets only, adjust the flow balancing valves to equalize flow to the hot water basins.
- For multi- cell arrangements, balance the flow between the cells to obtain even water distribution.
- Check to ensure the controls for the fan motor are set to allow maximum of six on-off cycles per hour to prevent motor overload.
- Adjust the valve in the tower bleed line to achieve the desired bleed rate by closing or opening the valve.
- Inspect the nozzles heat transfer section.
- Execute one of the following biocide treatment programs while operating the circulating pump and prior to operating the units fans:
- Resume treatment with biocide (or as recommended by water treatment supplier) that was used prior to shut-down. Operate the pump only while maintaining the maximum recommended biocide residual for a sufficient duration as recommended by water treatment supplier. Start fan only after this treatment period is completed.
- Check the pH of the circulating water and, if necessary, adjust it to 7.0-7.6 pH. Then, running the pump only, treat the system with sodium hypochlorite (or as recommended by water treatment supplier) to maintain a level of 4 to 5 mg/l (ppm) free chlorine (as Cl2) over a six hour period. Start the fan only after this treatment period is completed.
- For initial start-up, briefly energize the fan motors and note the direction of rotation. The fan should rotate in the direction indicated by the arrow on the fan cowl.
- Run the fan in manual mode for several minutes to check for any unusual noise or vibrations.
- Check that the starter incorporates a 15 second time delay when switching from high to low speed.
- Check the operation of the vibration cut-out switch.
- Once the cooling tower is operating, check the current and voltage of all three phases of the fan motor with a heat load on the tower under warm ambient conditions. The current must not exceed the motor nameplate rating.