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George hoetricks, evapco
 

George hoetricks, evapco

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  • Step one to avoid recirculation is to make sure that the top of the cooling tower should be at least level with the enclosure. Today , we as engineers are still fighting daily with architects on this issue ! or the right measurements to avoid recirculation are it is completely overlooked
  • Often VFD’s are promted to save energy in applications using electrical motors. Are we saving energy when applying VFDs on cooling towers ? We know that by lowering the condensing temperature with 1°F , the chiller efficiency improves with 3% . At the same time are the fan kw of the cooling towers more or less 5 % of the motor kw of the chiller. In other words , we will not save energy when considering all elements when reducing the cooling tower fan speed by using VFD’s.
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  • Fans are selected for a given air flow and static pressure caused in the cooling tower. Fan design parameters or characteristiques include the diameter, speed , the number and the shape of the blades and blade width. The paramters have all their influence on cost , power consumption and noise.
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George hoetricks, evapco George hoetricks, evapco Presentation Transcript

  • Cooling Towers for District Cooling Georges Hoeterickx Evapco Europe
  • Cooling Towers for District Cooling Design considerations
    • Approach :
    • Difference between cooling tower water outlet temp. and design entering wb temp.
  • Design considerations Cooling tower size versus approach Approach ° F
  • Design considerations Minimum approach
    • CTI Certification under STD-201
    • Certification is limited to thermal operating conditions….. and a cooling approach of 2.8°C (5°F) or greater….
  • Cooling Towers for District Cooling Cooling tower range
    • Range :
    • Difference between cooling tower water
    • inlet and cooling tower outlet temperature.
  • Design considerations Cooling tower size versus range Range C.T. Size
  • Cooling Towers for District Cooling Design considerations
    • Avoid recirculation :
    • Bypass of warm discharge air into the cooling tower air inlet will cause capacity losses.
  • Design considerations Avoid recirculation
    • Top of cooling tower should be at least level
    • with enclosure.
  • Design considerations Avoid recirculation
    • Fan discharge velocity : min. 1200 fpm (6 m/sec).
    • Downward velocity : max. 600 fpm
    • (3 m/sec).
  • Design considerations – two side air inlet Avoid recirculation
    • Limit downward velocity - two side air inlet units
  • Design considerations – single air inlet Avoid recirculation
    • Limit downward velocity - single air inlet units
  • Cooling Towers for District Cooling Fan motors
    • High efficiency
    • 50° C Rise
    • Space heaters
    • (avoid condensation)
    • VFD compatible
    • (insulated end shields)
  • Cooling Towers for District Cooling Fan Motors
    • Use of VFD’s for fan motors :
    • Allow to control air flow through the cooling tower
    • Safe Fan KW
  • Design considerations VFD’s for fan motors
    • Energy saving ?
    • Condenser water temp 1°F
    • Chiller efficiency 3%
    • Cooling tower kW = ~ 5 %
    • Chiller kW.
  • Design considerations VFD’s for fan motors
    • Water consumption :
    • Air flow Water consumption
    • Plume formation :
    • Air flow Plume formation tendency
    • Noise control @ night
    • Fan @ half speed : – 9 dBA fan noise
    • (60% capacity)
  • Design considerations VFD’s for fan motors
    • Min. RPM for gear
    • (motor speed ≥ 450 RPM)
    • Gear with mechanical oil pump for proper lubrication
  • Cooling Towers for District Cooling
    • Cooling Tower Basin :
    • Hold circulating water of the tower.
  • Design considerations Cooling Tower Basin
    • Common basin
    • + Easier basin and cooling tower construction.
    • + No need for equalizing connection
    • - Maintenance – sump cleaning
  • Design considerations Cooling Tower Basin
    • Individual Basin per Cell
    • + Easier for maintance (water)
    • - Need equalizing between basins.
    • - More costly construction
  • Design considerations Water Outlets
  • Design considerations Cooling Tower Bassin
    • Sound mats to reduce water noise
    • Noise reduction function
    • number of layers
    • distance mats – water in basin !
    • Sound mats will obstruct basin access : maintenance !
  • Cost distribution main items
  • Cooling Tower Structure
    • Typical requirements :
  • Cooling Towers for District Cooling FRP Structure
    • Reputable manufacturers have their components third party tested per
    • ASTM E 84 for strength values and flamability
    • Ask if these evidences are part of contract submittals !
  • FRP Structure Boron Free Advantex glass assures a longer life of the structure
  • FRP Structure Obtain the specified quality
  • FRP Structure UV protection
    • UV degradation and moisture penetration will have influence life time of an FRP cooling tower
    • The UV rays will cause the decomposition of the polymers holding the fibre glass together
  • FRP structure UV protection
    • Surface veil material of non woven polyester fabric to prevent fiber blow out
    • Surface veil creates a resin rich surface area to provide enhanced UV protection
    • One mil thickness of surface veil =
    • 2 – 3 years life time
  • FRP structure UV protection STRUCTURAL RESIN 55-25% GLASS 45-75% WOVEN ROVEN AND CONTINUOUS GLASS 250 MILS OR MORE CORROSION BARRIER RESIN 60-70 % GLASS 30-40% MAT OR CLOTH 40-60 MILS EXTERNAL LINER RESIN RICH 80-90% GLASS 10-20% 15-20 MILS SURFACING VEIL TYPE C 10-20 MIL THICKNESS
  • FRP structure UV protection
    • Useful life of UV projected components
  • FRP structure UV protection
    • How to verify UV protection quality ?
    • Have samples of different weight veil material for comparison.
    • Variation in the visibility of the Continious
    • Filament Mat.
  • FRP Structure Fire retardancy
    • Fire resistance and damage control of the
    • FRP structure.
  • FRP structure Fire retardancy
    • Design with high quality, heat resistant / fire retardant resin systems, Class 1 type
    • Specify self extinguishing
    • High glass content = minimum burn rate
  • Obtain the required quality FRP structure
    • Major part of the cooling tower cost
    • Most critical item for the cooling tower life time !
    • How to obtain the required quality ?
  • Obtain the required quality FRP structure
    • 1. Demand cooling tower supplier names the FRP source and ask delivery certificates from the FRP manufacturer.
    • 2. Reserve the right to inspect before delivery to verify Quality Process Map is complied with.
  • Obtain the required quality FRP structure
    • 1. Demand cooling tower supplier names the FRP source and ask delivery certificates from the FRP manufacturer.
    • 2. Reserve the right to inspect before delivery to verify Quality Process Map is complied with.
  • Obtain the required quality FRP structure
    • 1. Demand cooling tower supplier names the FRP source and ask delivery certificates from the FRP manufacturer.
    • 2. Reserve the right to inspect before delivery to verify Quality Process Map is complied with.
  • Cooling tower fans
  • Obtain the best quality Fans
    • Fans are selected for a given airflow and static pressure
    • Fan design parameters :
    • diameter – speed – nbr and shape of blades – blade width
    • Fan design parameters influence :
    • cost – power consumption – noise
  • Cooling tower fans Noise definition
    • Specify sound pressure
    • in dB(A) measured 1,5 meter
    • above fan discharge
    • (per CTI std ATC – 128)
  • Cooling tower fans Noise
  • Cooling tower fans Comparison - 2000 ton tower - 196 m³/ sec @ 160 Pa pressure drop Fan dia Nbr Blades Rpm Tip speed Sound Power Fan shaft Power Fan ft     m/sec dB(A) kW US $ 14 6 270.8 60.5 100.3 59.3 2100 16 7 193.9 49.5 95.6 53.2 3600 18 5 186.8 54.2 99 46 13500 18 * 4 137 40 86.3 54.9 45000
  • Cooling tower fans Fan power vs cost – 2000 ton tower – 196 m³/sec @ 160 Pa pressure drop Fan dia Tower price Fan Power ft % kW 14   - -  16 + 1, 25 % - 11 % 18 +8 % - 22 %
  • Cooling tower fans Comparison - 5000 ton tower - 375 m³/ sec @ 160 Pa pressure drop Fan dia Nbr Blades Rpm Tip speed Sound Power Fan shaft Power Fan ft     m/sec dB(A) kW US $ 22 6 226 44.2 106.3 106.3 9500 26 9 104.8 43.5 97.9 87.1 26000 26 6 89.7 37.2 90.6 104.2 60000 28 6 82.6 36.9 90 102.3 65000
  • Cooling tower fans Fan power – noise vs cost - 5000 ton tower – 375 m³/ sec @ 160 Pa pressure drop Fan dia Tower price Power Sound Power ft % kW dB (A) 22     106.3 26 + 7 % - 18 % 97.9 26 20% -2% 90.6 28 + 22% -4% 90
  • Obtain the required quality Fan stacks
  • Fan stacks Material
    • Height : 7– 10 ft - …
    • Material : Class 1 – flame spread rating 25
    • (Class II and Class III = Cheaper !)
    • UV resistance (gelcoat 20 mil).
    • Access door or removable panel
    • Assembly hardware SST
  • Fan stacks
    • Make sure fan deck floor opening matches fan cylinder
    • Smooth air inlet
    • Fan tip clearance : 0,5% fan dia
  • Obtain the required quality Air inlet louvers Water stays in … Sunlight stays out!
  • Air inlet louvers Single pass FRP Blade louvers
    • Waterdroplets tend to splash out when fans are shut off.
    • Sunlight still enters the cooling tower basin !
  • Air inlet louvers Two pass PVC air inlet louvers
    • Minimise splash-out
    • Direct sunlight is blocked from the water inside the tower and reducing the potential for algae formation !
    • Minimum pressure drop
  • Two Pass Air inlet louvers
    • Typical two pass air inlet louvers
  • Obtain the required quality Drift eliminators
  • Obtain the required quality Drift eliminators
    • Drift rates : 0,01 to 0,0005 % of tower flow rate
    • Drift rate function of type DE, air velocity, water loading and spray nozzle types, …
  • Drift eliminators Quality
    • Drift rate dependends on:
    • Waterloading
    • Air velocity
    • Spray nozzle arrangement
  • Drift eliminators Efficiency comparison
  • Drift eliminators Efficiency confirmation
    • Ask your cooling tower supplier names manufacturer of DE
    • Demand independent test certifications according to accepted standards
    • Air passes through area with minimum resistance
    • Air bypass reduces cooling effect
    • Water loss because of higher air velocity
    Drift eliminators Execution on site
  • Drift losses Design considerations : air seals
  • Cooling Towers Fill Obtain the right quality
    • Performance
  • Cooling Tower Fill Film Fill Design Considerations
  • Cooling Tower Fill Vertically Offset Flute PVC Film Fill
  • Cooling Tower Fill Vertically Fluted PVC Film Fill
  • Cooling Tower Fill
    • PVC
    • Fill spacing: min 19 mm
    • Fill thickness: 10 – 20 nils before formation
    • Flamability (ASTM E84 – max 5)
    • Designed to accomodate operational and specified Live load
    Cooling Tower Fill
  • Cooling Towers for District Cooling
  • Cooling Towers for District Cooling
    • Obtain the specified and correct
    • quality level !
    • Thank you
    • Georges Hoeterickx