1 Scope
NOTE This specification covers open-circuit cooling towers and closed-circuit cooling towers (fluid coolers) that reject heat from HVAC condenser water and process cooling systems by evaporation. (1.1)
NOTE Equipment covered includes the tower structure and casing, cold-water collection basin, hot-water distribution system, fill (heat-transfer surface), drift eliminators, air inlet louvers, fans and fan drives, mechanical equipment support, makeup and overflow provisions, access for maintenance, and the factory-furnished accessories that form part of the tower assembly. (1.2)
NOTE Both factory-assembled packaged towers and field-erected towers are addressed, as are induced-draft and forced-draft configurations in counterflow and crossflow arrangements. (1.3)
NOTE A cooling tower rejects heat by evaporating a small fraction of the circulating water, which allows it to cool water below the ambient dry-bulb temperature toward the ambient wet-bulb temperature; this evaporative mechanism is also the source of every characteristic concern of cooling tower equipment — makeup water consumption, concentration of dissolved solids, biological growth, drift, and freezing of wetted surfaces. (1.4)
1.5This standard establishes both the thermal and mechanical requirements for the equipment and the provisions necessary to manage these concerns over the equipment service life.
1.6The boundary of work under this standard is the cooling tower assembly itself, from the condenser water supply (hot water) connection through the cold-water basin outlet connection, including the integral spray pump on closed-circuit units, the fan and drive, and the factory-mounted accessories.
1.7Condenser water pumps and the suction and discharge piping that circulates water between the tower and the chiller condenser are covered in Hvac Pumps and Hydronic Piping and are not part of this standard. 1.8Chemical treatment of the circulating water, the building water-management plan, and Legionella risk management are covered in Hvac Water Treatment. 1.10Equipment shall be certified for thermal performance under CTI STD-201 and rated for energy efficiency under ASHRAE 90.1.
1.11Field acceptance testing, where specified, shall follow CTI ATC-105 for open-circuit towers and CTI ATC-105S for closed-circuit towers.
1.12Legionella risk management for the connected system shall follow ASHRAE 188 and CTI GDL-159.
1.13Structural support, anchorage, and wind and seismic restraint shall conform to the IBC and ASCE 7.
1.14Electrical components shall be listed by a Nationally Recognized Testing Laboratory.
2 Referenced Standards
2.1Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2Where conflicts exist between referenced standards, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
| Standard |
Title |
| CTI STD-201 |
Standard for the Certification of Water-Cooling Tower Thermal Performance |
| CTI ATC-105 |
Acceptance Test Code for Water-Cooling Towers |
| CTI ATC-105S |
Acceptance Test Code for Closed Circuit Cooling Towers |
| CTI ATC-105DS |
Acceptance Test Code for Dry/Wet Cooling Towers |
| CTI STD-111 |
Gear Speed Reducers |
| CTI GDL-159 |
Legionellosis Guideline: Practices to Reduce the Risk of Legionellosis from Evaporative Heat Rejection Equipment Systems (supersedes WTB-148) |
| CTI STD-136 |
Fiberglass-Reinforced Plastic (FRP) Cooling Tower Structural Components |
| ANSI/ASHRAE 188 |
Legionellosis: Risk Management for Building Water Systems |
| ANSI/ASHRAE/IES 90.1 |
Energy Standard for Buildings Except Low-Rise Residential Buildings |
| ASTM A653 / A653M |
Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated by the Hot-Dip Process |
| ASTM A123 / A123M |
Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products |
| ASTM A1011 |
Steel, Sheet and Strip, Hot-Rolled, Carbon, Structural, High-Strength Low-Alloy |
| ASTM A240 |
Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels |
| ANSI/AMCA 210 / ASHRAE 51 |
Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating |
| NEMA MG 1 |
Motors and Generators (Part 31 — Definite Purpose Inverter-Fed Polyphase Motors) |
| NFPA 70 |
National Electrical Code (NEC) |
| UL 1995 / UL 60335-2-40 |
Heating and Cooling Equipment (electrical safety listing, as accepted by AHJ) |
| IBC |
International Building Code (wind and seismic per applicable edition) |
| ASCE 7 |
Minimum Design Loads and Associated Criteria for Buildings and Other Structures |
| AISC 360 |
Specification for Structural Steel Buildings (steel support framing) |
| ACI 318 |
Building Code Requirements for Structural Concrete (concrete support and basin) |
3 Submittals
3.1 Action Submittals
3.1.1The Contractor shall submit the following for the Engineer's review and acceptance prior to ordering equipment:
- Manufacturer's product data for each tower, including model designation, configuration (type, draft, flow arrangement), nominal capacity, and overall dimensions and operating weight
- Thermal performance selection data stating the design water flow rate, entering (hot) water temperature, leaving (cold) water temperature, and design entering-air wet-bulb temperature, with the resulting range and approach clearly identified
- CTI STD-201 thermal performance certification documentation for the selected model line, or independent thermal performance test certification where the model is not within the CTI-certified line
- Fan and drive data including fan type, fan diameter, number of fans, drive arrangement, motor nameplate data, and sound data
- Sound power and sound pressure data at the locations required by the project acoustic analysis
- Materials of construction for the structure, basin, fill, drift eliminators, hardware, and fan
- Drift eliminator data including drift rate as a percentage of circulating water flow
- Structural support reactions (dead, operating, and dynamic loads) and anchorage requirements for coordination with the supporting structure
- Wind and seismic anchorage calculations and details where required by the applicable building code
- Piping connection schedule and locations (supply, return, makeup, overflow, drain, equalizer)
- Electrical data including fan motor full-load amperes, integral spray pump data (closed-circuit units), basin heater data, and control device schedule
- For field-erected towers, erection drawings and a field assembly sequence
☐ Product data and configuration
☐ Thermal performance selection (flow, range, approach, design wet-bulb)
☐ CTI STD-201 thermal certification documentation
☐ Fan and drive data
☐ Sound power and sound pressure data
☐ Materials of construction
☐ Drift eliminator drift rate data
☐ Structural reactions and anchorage requirements
☐ Wind and seismic anchorage calculations
☐ Piping connection schedule
☐ Electrical data and control device schedule
☐ Field erection drawings (field-erected towers)
3.1.2Fabrication and procurement shall not proceed until action submittals have been reviewed and returned.
3.2 Closeout Submittals
3.2.1At or before substantial completion, the Contractor shall provide the following:
- Operation and maintenance manuals for each tower, including manufacturer's installation, startup, operation, and maintenance instructions
- As-built configuration drawings reflecting any field modifications
- Startup and commissioning records, including water distribution verification and fan rotation and balance verification
- Field thermal performance test report where acceptance testing per CTI ATC-105 or ATC-105S is specified
- Water treatment startup coordination record referencing the building water-management plan (Hvac Water Treatment)
- Warranty documentation from the manufacturer and from any sub-suppliers (fill, drift eliminators, gear reducer)
- Spare parts list with manufacturer part numbers
☐ Operation and maintenance manuals
☐ As-built configuration drawings
☐ Startup and commissioning records
☐ Field thermal performance test report (where specified)
☐ Water treatment startup coordination record
☐ Warranty documentation (manufacturer and sub-suppliers)
☐ Spare parts list with part numbers
4 Quality Assurance
4.1 Manufacturer Qualifications
4.1.1Cooling towers shall be the product of a manufacturer with a minimum of ten years of continuous experience designing and producing evaporative heat-rejection equipment for commercial and institutional service.
4.1.2The manufacturer shall maintain an ISO 9001 certified quality management system.
4.1.3The manufacturer shall be able to supply replacement parts and service support for the model line for a minimum of fifteen years from the date of manufacture.
○ CTI STD-201 certified model line (required)
○ Independent thermal test certification of specific selection (non-CTI-certified model)
4.2.1The cooling tower shall be certified under the Cooling Technology Institute Standard 201 (CTI STD-201) Thermal Performance Certification Program for the applicable equipment class.
4.2.2Where the selected model is outside the manufacturer's CTI-certified line, the manufacturer shall furnish an independent thermal performance test certification of the specific selection.
NOTE CTI STD-201 certification means an independent administrator has verified, through testing of an administrator-selected model with annual reverification of a different model, that every model in the published rating line performs in accordance with its ratings; this third-party certification is the single most important quality requirement for a cooling tower because thermal performance cannot be visually inspected and an underperforming tower is not discovered until the chiller plant fails to make design capacity on a design day. (4.2.3)
4.3 NRTL Listing
4.3.1The complete cooling tower assembly, including the fan motor, integral spray pump (closed-circuit units), basin heater, and all factory-mounted electrical components, shall be listed and labeled by a Nationally Recognized Testing Laboratory (NRTL) to UL 1995 or UL 60335-2-40 as accepted by the Authority Having Jurisdiction.
4.3.2Electrical components not covered by the unit listing shall be individually listed to applicable standards.
4.4 Pre-Installation Conference
4.4.1A pre-installation conference shall be held before tower installation begins, attended by the Contractor, the mechanical sub-contractor, the structural contractor responsible for the supporting steel or concrete, the controls sub-contractor, the water treatment contractor, and the Owner's representative.
4.4.2The conference agenda shall include rigging and setting sequence, structural support and anchorage verification, airflow clearance verification, piping and electrical connections, water treatment startup, freeze protection commissioning, and the startup and acceptance test schedule.
5 Environmental and Service Conditions
5.1The cooling tower shall be selected and rated for the design thermal duty and the environmental conditions at the installation site.
5.3The tower shall be capable of operating across the full ambient range of the project location without damage, loss of function, or freeze damage to wetted surfaces.
5.4 Design Entering-Air Wet-Bulb Temperature
6582
656870727476788082
Default: 78 °F WB
5.4.1The tower shall be selected at the design wet-bulb established for the project location, typically the ASHRAE 0.4% or 1% evaporation design wet-bulb for the climate zone.
NOTE The design entering-air wet-bulb temperature is the single most important environmental input to cooling tower selection because evaporative cooling drives the cold-water temperature toward the wet-bulb, not the dry-bulb; selecting at a wet-bulb lower than the true site design wet-bulb produces a tower that cannot make design cold-water temperature on a humid design day, starving the chiller of adequate condensing. (5.4.2)
5.5 Air Recirculation and Inlet Conditions
5.5.1The tower location shall provide unobstructed air inlet and discharge with adequate separation from walls, adjacent equipment, and other towers to prevent recirculation of saturated discharge air back into the air inlet.
5.5.2The manufacturer's published minimum clearances shall be maintained, and the layout shall be reviewed for prevailing-wind recirculation potential where towers are installed in pits, between parapets, or in close-spaced multi-cell arrangements.
NOTE Recirculation artificially raises the entering-air wet-bulb at the tower inlet above the ambient wet-bulb and degrades thermal performance in a way that no amount of fan power corrects. (5.5.3)
5.6 Freeze Protection Conditions
○ Yes — climate has sub-freezing ambient temperatures
○ No — installation in a climate that does not freeze
5.6.1Where the installation is in a climate with sub-freezing ambient temperatures, freeze protection shall be provided for the cold-water basin, exposed piping, and the wetted heat-transfer surfaces during operation and during shutdown.
5.6.2The freeze protection strategy shall be coordinated with the operating sequence and is addressed in the basin and controls sections of this standard.
NOTE Freezing of standing basin water cracks basins and damages piping, and freezing of the recirculating water on the fill during cold-weather operation builds ice that adds structural load and blocks airflow. (5.6.3)
6 Tower Type, Draft, and Flow Arrangement
6.1 Tower Type
○ Open-circuit — condenser water sprayed directly over fill
○ Closed-circuit (fluid cooler) — process fluid in closed coil, separate spray circuit
6.1.1Closed-circuit towers shall be selected where the cooled fluid must be kept clean (water-source heat pump loops, free-cooling loops, glycol loops, and process cooling), where the fluid must not be exposed to airborne fouling, or where winter dry operation is required.
NOTE In an open-circuit tower the condenser water being cooled is sprayed directly over the fill and is in direct contact with the atmosphere; it is the most efficient and lowest-first-cost arrangement and is the standard choice for water-cooled chiller condenser duty. (6.1.2)
NOTE In a closed-circuit tower the process fluid circulates inside a closed coil bundle while a separate spray-water circuit is evaporatively cooled over the coil; closed-circuit towers cost more, occupy more footprint per ton, and consume additional spray-pump energy, but they protect the chiller condenser or process loop from the fouling, scaling, and biological burden an open-circuit system imposes, and where the loop also serves as a winter free-cooling loop the coil can be run dry in cold weather for sensible cooling without the freeze and fouling exposure of an open system. (6.1.3)
6.2 Draft Type
○ Induced draft — fan on air discharge, draws air through tower
○ Forced draft — fan on air inlet, blows air through tower
NOTE Induced-draft towers locate the fan at the air discharge, pulling air through the fill and discharging it upward at high velocity, which minimizes recirculation; induced-draft axial-fan towers are the predominant arrangement for field-erected and large packaged towers because of their recirculation resistance and good energy efficiency. (6.2.1)
NOTE Forced-draft towers locate the fan (typically a centrifugal blower) at the air inlet, blowing air through the tower; they discharge at low velocity and are more prone to recirculation, but the fan and motor are at the base outside the saturated airstream, simplifying maintenance, and centrifugal forced-draft towers are also selected where the tower must be ducted or installed indoors because centrifugal fans can develop the external static pressure that axial fans cannot. (6.2.2)
6.3 Flow Arrangement
○ Counterflow — air moves vertically upward against downward water flow
○ Crossflow — air moves horizontally across downward water flow
6.3.1Both counterflow and crossflow arrangements are fully acceptable; the selection follows the project priorities of footprint, pump energy, maintenance access, and water treatment strategy.
NOTE In a counterflow tower air moves vertically upward through the fill in direct opposition to the downward-falling water, producing the most thermally efficient temperature gradient and the smallest footprint for a given duty, with a pressurized closed spray distribution system that resists fouling and freezing and is enclosed against sunlight to limit algae growth. (6.3.2)
NOTE In a crossflow tower air moves horizontally across the downward-falling water from open gravity-flow hot-water distribution basins on top of the fill, offering easier access to the distribution basins and fill, lower pump head, and quieter operation, at the cost of a larger footprint and open distribution basins that require sunlight management to control algae. (6.3.3)
6.4 Assembly Method and Cell Arrangement
○ Factory-assembled (packaged) — shipped substantially complete
○ Field-erected — assembled on site from components
NOTE Factory-assembled packaged towers are shipped substantially complete and set in place as a unit or in a small number of modules and are the standard choice for commercial and institutional projects up to the largest size that can be shipped and rigged. (6.4.2)
NOTE Field-erected towers are assembled on site from structural components and are used for the largest installations, for capacities beyond shipping limits, and where site access prevents delivery of a packaged unit; multi-cell towers operating in parallel on a common basin or adjacent basins with an equalizer provide capacity staging and redundancy. (6.4.3)
7.1 Design Water Flow Rate
5020000
50100200300500750100015002000300050007500100001500020000
Default: 900 gpm
7.1.2The tower shall be selected to perform at the design flow.
NOTE Operating substantially below the design flow can cause incomplete fill wetting and channeling, while operating above it can flood the distribution system and increase drift. (7.1.3)
7.2 Nominal Capacity
105000
1025507510015020030040050075010001500200030005000
Default: 300 nominal tons
7.2.1The governing requirement is always the specified flow, range, approach, and design wet-bulb, not the nominal tonnage, and the nominal capacity shall be reconciled against the actual specified thermal duty.
NOTE A "nominal ton" of cooling tower capacity is a rating convention (historically 3 gpm of water cooled from 95°F to 85°F at a 78°F wet-bulb, rejecting 15,000 Btu/h) useful only for rough comparison and schedule coordination. (7.2.2)
7.3 Cooling Range
525
58101215182025
Default: 10 °F
NOTE Range is the difference between the entering (hot) water temperature and the leaving (cold) water temperature and is set by the heat load divided by the water flow rate, not by the tower itself; a 10°F range (95°F entering, 85°F leaving) is the traditional design condition for chiller condenser water, though larger ranges are increasingly used to reduce condenser water flow and pump energy. (7.3.1)
7.4 Approach
415
456789101215
Default: 7 °F
NOTE Approach is the difference between the leaving (cold) water temperature and the design entering-air wet-bulb temperature and is the truest measure of tower size and thermal effort, being the one performance parameter the tower designer controls and the most expensive degree to buy. (7.4.1)
NOTE A 7°F approach (85°F cold water at a 78°F wet-bulb) is a common, economical design point; tightening the approach toward the wet-bulb requires disproportionately more fill, airflow, and tower size, and an approach below approximately 4°F to 5°F is generally uneconomical, while a tighter approach lowers condenser water temperature and improves chiller efficiency, making the optimum a plant-level energy tradeoff between tower first cost and chiller energy. (7.4.2)
7.5 Energy Efficiency
○ Documented at ASHRAE 90.1 standard rating condition (gpm/hp)
○ Exempt — equipment class not addressed by ASHRAE 90.1
7.5.1The tower fan system shall meet the minimum energy efficiency required by ASHRAE 90.1 for the applicable equipment class, expressed as gallons per minute of water flow per fan motor nameplate horsepower (gpm/hp) at the standard rating condition.
7.5.2For open-circuit axial-fan induced-draft towers, the rating condition is 95°F entering water, 85°F leaving water, and 75°F entering-air wet-bulb.
7.5.3For closed-circuit towers the rated efficiency shall include the integral spray pump motor power in addition to the fan motor power.
7.5.4Compliance with the applicable minimum gpm/hp shall be documented in the submittal at the ASHRAE 90.1 standard rating condition, separately from the project design condition.
NOTE Axial-fan induced-draft towers carry a substantially higher minimum gpm/hp than centrifugal-fan forced-draft towers because the axial fan moves air far more efficiently at the low static pressure of a cooling tower; centrifugal forced-draft towers are permitted where their other attributes are required but should not be selected on efficiency grounds. (7.5.5)
8 Construction and Materials
8.1 Structural and Casing Material
Hot-dip galvanized steel, G-235 (Z700) per ASTM A653 — standard commercial
Hot-dip galvanized after fabrication per ASTM A123 — field-erected steel
Type 304 stainless steel — extended life, aggressive water or coastal
Type 316 stainless steel — severe/coastal/high-chloride service
Fiberglass-reinforced plastic (FRP) — corrosion-immune, marine and chemical
8.1.1The structure, casing, and basin material shall be selected for the water chemistry, the atmospheric environment, and the required service life.
8.1.2Field-erected steel components too large for mill galvanizing shall be hot-dip galvanized after fabrication per ASTM A123.
NOTE Hot-dip mill galvanized steel with a G-235 (Z700) coating weight per ASTM A653, the heaviest standard mill coating, carrying 2.35 oz of zinc per square foot of sheet (both sides combined), is the standard commercial cooling tower material and provides good service life in well-treated water. (8.1.3)
NOTE Type 304 or, for high-chloride and coastal service, Type 316 stainless steel provides substantially longer service life where the water chemistry is aggressive, where a long maintenance-free life is required, or where the basin must resist the chloride concentration that develops as solids cycle up; fiberglass-reinforced plastic is immune to galvanic corrosion and is selected for marine, chemical, and other severely corrosive environments, and the basin material warrants particular attention because it holds standing water continuously and is the most common location of corrosion failure. (8.1.4)
8.2 Stainless Steel Cold-Water Basin
Galvanized steel matching tower construction
Type 304 stainless steel basin (recommended upgrade)
Type 316 stainless steel basin (coastal/high-chloride)
FRP basin
NOTE The cold-water basin holds standing water at all times the tower is in service and concentrates dissolved solids as water evaporates; upgrading the basin to stainless steel while keeping galvanized construction elsewhere is a common, cost-effective strategy because the basin fails from corrosion first while the upper structure, which drains and dries between cycles, lasts considerably longer, and a stainless basin also eliminates the white-rust passivation concern that affects new galvanized basins during the first weeks of operation. (8.2.1)
8.3 Hardware and Fasteners
8.3.1All fasteners, hardware, and connection components in the wetted and splash zones shall be Type 304 or Type 316 stainless steel.
NOTE Mixed-metal fastening (carbon steel bolts in galvanized or stainless structure) creates galvanic cells that corrode rapidly in the conductive recirculating water and is a frequent cause of premature connection failure. (8.3.2)
9 Fill and Drift Eliminators
9.1 Fill Type
○ Film fill — closely spaced PVC sheets, high efficiency, clean water only
○ Splash fill — staggered bars/grids, fouling-tolerant, larger tower
Standard film fill (clean treated water)
Low-fouling (wide-flute) film fill — moderate water quality
Splash fill — poor water quality or high fouling potential
9.1.1Splash fill, or a low-clog film fill, shall be specified where the water quality is poor, where the makeup water is high in solids, or where the tower serves a process load with fouling potential.
NOTE Fill is the heat-transfer surface where water and air exchange heat and the evaporation occurs; film fill consists of closely spaced thermoformed PVC sheets over which the water spreads in a thin film, exposing a very large surface area to the airflow, and is highly efficient and compact but intolerant of dirty or scaling water because suspended solids, biological growth, and scale bridge the narrow gaps, collapse airflow, and destroy performance. (9.1.2)
NOTE Splash fill consists of staggered bars or grids that repeatedly break the falling water into droplets and is far more tolerant of poor water quality and fouling because its open structure does not clog, at the cost of a larger tower for the same duty. (9.1.3)
9.2 Fill Fire Resistance
9.2.1PVC fill shall have a flame-spread index of 25 or less when tested per ASTM E84.
9.2.2Where the tower is field-erected and exposure to hot work during the tower's service life is anticipated, fire-retardant fill should be specified and a dry-fill fire watch protocol established for any hot work near the tower.
NOTE Cooling tower fill has burned during construction and during dry maintenance periods when ignition sources (welding, grinding) were present and the fill was dry; low-flame-spread fill limits this risk. (9.2.3)
9.3 Drift Eliminators
0.005% of recirculating flow (basic)
0.001% of recirculating flow (standard for new installations)
0.0005% of recirculating flow (low-drift, near sensitive intakes/occupancies)
9.3.1Drift eliminators shall be installed downstream of the fill and downstream of the spray distribution to strip entrained water droplets from the leaving airstream.
9.3.2Drift eliminators shall achieve a drift rate not exceeding the specified percentage of the recirculating water flow rate.
9.3.3A 0.0005% drift rate shall be specified where the tower is near building air intakes, operable windows, pedestrian areas, or other locations where drift exposure is a heightened concern.
9.3.4The drift eliminator media shall be the same corrosion class as the fill and shall be removable in sections for inspection and cleaning.
NOTE Drift is liquid water carried out of the tower in the discharge air; unlike evaporation it carries the full chemistry and biology of the recirculating water — including any Legionella — into the surrounding air, so minimizing drift is both an energy-and-water conservation measure and a primary public-health control, and a 0.001% drift rate is the current standard for new installations, readily achievable with modern multi-pass cellular eliminators. (9.3.5)
10 Fans and Drives
10.1 Fan Type
○ Axial (propeller) — induced or forced draft, low static, high efficiency
○ Centrifugal — forced draft, develops external static, low noise
10.1.1Fans shall be statically and dynamically balanced and rated per ANSI/AMCA 210.
NOTE Axial (propeller) fans move large air volumes against the low static pressure of a cooling tower at high efficiency and are the standard choice for induced-draft and most forced-draft towers; centrifugal fans develop higher static pressure and are required where the tower discharge must be ducted or where lower discharge noise is needed, but their air-moving efficiency is considerably lower, which is reflected in the energy standard's lower allowable efficiency for centrifugal towers. (10.1.2)
10.2 Fan Material
Aluminum blades with galvanized or aluminum hub (standard)
FRP (fiberglass) blades — corrosive environments
Stainless steel hub with aluminum or FRP blades
10.3 Fan Drive Arrangement
Belt drive (V-belt) — small to mid-size towers
Gear drive (right-angle gear reducer) — large axial-fan towers
Direct drive (close-coupled motor) — where applicable
10.3.1Gear reducers, where used, shall conform to CTI STD-111 and shall be rated for continuous cooling tower service with a service factor appropriate to the fan inertia and start frequency.
10.3.2The gear reducer, where used, shall be provided with an external oil level indicator and a means to change oil without entering the airstream.
NOTE Belt drives are economical for small and mid-size towers but require periodic belt tensioning and replacement and wear faster in the wet airstream; gear drives are the standard for large axial-fan induced-draft towers, with the reducer mounted on a rigid mechanical support and driven by a motor located outside the airstream on forced-draft units or on the mechanical support on induced-draft units; direct-drive arrangements eliminate the belt and gearbox where fan and motor speed allow. (10.3.3)
10.4 Fan Motor
Totally Enclosed Air Over (TEAO) — in airstream, induced draft
Totally Enclosed Fan Cooled (TEFC) — outside airstream, forced draft
Weather Protected Type I (WP-I) — large outdoor motors
208V / 3-phase
460V / 3-phase
575V / 3-phase
10.4.1Fan motors located in the saturated airstream of an induced-draft tower shall be totally enclosed air-over (TEAO) type, specifically rated for cooling tower duty in a 100% saturated, intermittently wetted environment.
NOTE A standard TEFC motor placed in the discharge airstream of an induced-draft tower will fail prematurely from moisture intrusion. (10.4.3)
10.5 Fan Speed Control
Variable frequency drive (VFD) — modulating capacity control
Two-speed motor — staged capacity control
Single-speed (constant) — cycling control only
10.5.1Cooling tower fan motors above the threshold defined by ASHRAE 90.1 shall be provided with fan speed control (VFD or two-speed).
10.5.2Single-speed fan cycling shall be used only on the smallest towers where speed control is not cost-justified.
10.5.3The VFD minimum speed shall respect the manufacturer's minimum fan speed required for gear lubrication and to maintain water distribution over the fill.
NOTE Fan power varies with the cube of fan speed, so reducing fan speed yields dramatic energy savings at part load, where the tower operates the overwhelming majority of the time; a VFD provides the smoothest capacity control, the lowest part-load energy, reduced mechanical and thermal shock on the gear drive, and a stable leaving-water temperature, while two-speed motors capture much of the fan-law benefit in two discrete steps and single-speed cycling stresses the drive and produces a sawtooth water temperature. (10.5.4)
11 Basin, Makeup, and Blowdown
11.1 Cold-Water Basin and Outlet
11.1.1The cold-water basin shall be provided with a suction outlet connection, an anti-vortex provision or suction screen at the outlet to prevent air entrainment into the condenser water pump suction, and a removable debris strainer over the basin outlet.
11.1.2The basin shall be sloped to a drain connection so that it can be fully emptied for cleaning.
NOTE Air drawn into the pump suction from a vortexing basin causes pump cavitation and loss of flow (see
Hvac Pumps for the connected pump suction requirements), and a basin that cannot be fully drained always retains a stagnant biological reservoir, which is why full drainability is a fundamental requirement of the water-management plan.
(11.1.3) 11.2 Makeup Water
Mechanical float valve (basic)
Electronic level control with solenoid makeup valve (recommended)
Conductivity-controlled makeup with metering (integrated treatment)
11.2.1The makeup water connection shall include backflow prevention as required by the plumbing code, coordinated with Backflow Prevention. NOTE Makeup water replaces water lost to evaporation, drift, and blowdown; a simple mechanical float valve is the most basic provision, while an electronic level control with a solenoid valve provides more reliable and precisely controlled basin level and integrates with the building automation system and the water treatment controller. (11.2.2)
11.3 Blowdown (Bleed)
○ Conductivity-controlled blowdown (recommended)
○ Timed/metered blowdown
○ Continuous fixed-rate bleed (basic)
11.3.1Blowdown shall be controlled by conductivity (the direct measure of dissolved solids) rather than by a fixed bleed rate, and the blowdown control and setpoint shall be coordinated with Hvac Water Treatment. 11.3.2The tower shall be provided with a blowdown connection separate from the basin drain.
NOTE As water evaporates, the dissolved solids it leaves behind concentrate in the recirculating water; blowdown continuously or intermittently discharges a portion of the concentrated water, replaced by fresh makeup, holding the cycles of concentration within the limit the water treatment program allows, because without adequate blowdown the recirculating water scales, fouls, and corrodes, while excessive blowdown wastes water and treatment chemicals. (11.3.3)
11.4 Basin Heater
Electric immersion basin heater(s) with thermostat and low-water cutout
Steam or hot-water basin coil
Remote (indoor) sump tank — basin drains down on shutdown
None (non-freezing climate)
11.4.1Where freeze protection is required, the cold-water basin shall be provided with an immersion heater (electric or, where available, a steam or hot-water coil) sized to maintain the basin water above freezing at the design winter ambient temperature during shutdown.
11.4.2Basin heater capacity shall be selected for the design minimum ambient temperature and wind condition.
11.4.3The heater shall be controlled by a basin thermostat with a low-water cutout to prevent energizing a dry heater.
NOTE The basin heater protects the standing basin water when the tower is off but does not protect the wetted fill during operation, which is managed by the operating sequence (fan and flow control to keep ice off the fill); a remote indoor sump alternative, in which the basin drains by gravity to a heated indoor tank whenever the tower stops, eliminates the outdoor freeze exposure entirely and is the most robust freeze protection where the building layout allows an indoor tank below the tower elevation. (11.4.4)
12 Legionella and Water Treatment Provisions
12.1 Water-Management Plan Coordination
12.1.1The tower and the treatment system shall be coordinated so that the chemical feed, monitoring, and control devices specified in Hvac Water Treatment have the connection points, access, and basin configuration they require. NOTE The cooling tower is the single highest-risk building water system for Legionella because it produces and disperses aerosol at scale from a warm, nutrient-rich, sunlit, continuously wetted reservoir; treatment of the recirculating water, biocide dosing, monitoring, and the written water-management program required by ASHRAE 188 are specified in
Hvac Water Treatment and are not duplicated here, while this standard establishes the physical equipment provisions that the water-management program depends on.
(12.1.2) 12.2 Provisions Required of the Tower
12.2.1The tower shall be furnished with the following provisions to support the water-management program in accordance with ASHRAE 188 and CTI GDL-159:
- A cold-water basin that drains completely for cleaning and disinfection
- A basin sweeper or eductor system connection, or a basin slope and sump configuration that supports solids removal, where specified
- Connection points for biocide and treatment chemical injection at locations that provide mixing before the water reaches the pump suction
- Connection points and accessible sample ports for conductivity, biocide residual, and microbiological sampling
- Access to the distribution system, fill, and drift eliminators for inspection, cleaning, and disinfection without dismantling the tower structure
- Drift eliminators meeting the specified low drift rate, which directly limit aerosol release of any waterborne organisms
☐ Fully drainable cold-water basin
☐ Basin sweeper/eductor connection or solids-removal sump
☐ Chemical injection connection points (pre-pump mixing)
☐ Conductivity and biocide sample/sensor ports
☐ Removable fill and drift eliminators for cleaning
☐ Side-stream filtration connection
12.3 Sunlight and Algae Control
12.3.1Open distribution basins on crossflow towers shall be provided with covers, screens, or distribution-deck covers to exclude sunlight.
12.3.2Counterflow towers with enclosed pressurized distribution systems inherently exclude light from the distribution water and do not require this provision for the distribution system, but the basin shall nonetheless be screened against debris and light where practical.
NOTE Sunlight on standing nutrient-bearing water drives algae growth that fouls the fill and consumes biocide. (12.3.3)
13 Sound
Standard fan and tower (no added attenuation)
Low-sound fan (oversized, low-speed) selection
Intake attenuators
Discharge attenuators
Intake and discharge attenuators
13.1.1The tower sound power levels and resulting sound pressure levels at the property line, at adjacent occupied windows, and at any noise-sensitive receptor shall be documented and shall comply with the project acoustic requirements and the applicable noise ordinance.
13.1.2Sound data shall be provided in octave bands so that the design team can evaluate transmission to specific receptors.
13.1.3Where the standard tower does not meet the receptor noise limit, intake and discharge sound attenuators shall be specified only where a low-sound fan selection alone cannot meet the requirement.
NOTE Cooling tower sound is dominated by the fan and, on some configurations, by the cascade of falling water into the basin; a low-sound fan selection (a larger, slower fan moving the same air at lower tip speed) is the most energy-efficient first step because it reduces noise without the airflow penalty of attenuators, which add resistance and increase fan energy, while variable-speed operation also reduces the time-averaged sound level. (13.1.4)
14 Factory and Field Testing / Commissioning
14.1 Factory Inspection
14.1.1The manufacturer shall inspect each factory-assembled tower before shipment for completeness, correct fan rotation and balance, water distribution integrity, and freedom from shipping damage.
14.1.2For field-erected towers, the manufacturer shall provide field technical assistance during erection and a startup inspection upon completion.
○ Required — CTI ATC-105 (open-circuit) by licensed agency
○ Required — CTI ATC-105S (closed-circuit) by licensed agency
○ Not required — rely on CTI STD-201 certified rating
14.2.1Where field thermal performance acceptance testing is specified, the test shall be conducted in accordance with CTI ATC-105 for open-circuit towers or CTI ATC-105S for closed-circuit towers, by a CTI-licensed independent testing agency.
NOTE The test verifies that the installed tower achieves the specified cold-water temperature at the design flow and the test-day wet-bulb, corrected to design conditions; field acceptance testing is recommended for large and critical installations (district energy plants, data centers, hospitals, and any installation where a performance shortfall would be costly to remedy) and is generally not warranted for small packaged towers on routine commercial projects. (14.2.2)
14.3 Startup and Commissioning
14.3.1The Contractor shall perform startup and commissioning in accordance with the manufacturer's instructions, including verification of structural anchorage and level setting; fan rotation, blade pitch, and vibration within the manufacturer's limits; uniform water distribution over the entire fill with no dry or flooded areas; basin level control and makeup operation; functional testing of the fan speed control through its full range with identification of any resonant speeds to be locked out; functional testing of the basin heater and freeze protection sequence; verification of the blowdown and water treatment control; and verification of all building automation system points.
14.3.2Commissioning shall be coordinated with the initial water treatment passivation and disinfection required by Hvac Water Treatment. 15 Installation
15.1 Structural Support
15.1.1The cooling tower shall be supported on structural steel or concrete designed for the tower's dead, operating (water-filled), and dynamic (fan) loads as detailed on the structural drawings. 15.1.2Support steel shall be designed per AISC 360 and concrete support and basins per ACI 318.
15.1.3The full-length support under continuous bottom-supported towers, or the point loads under towers supported on isolated beams, shall match the manufacturer's required support arrangement.
15.1.4Operating weight, the weight with the basin and fill fully wetted, which substantially exceeds the dry shipping weight, shall govern the support design.
NOTE An unsupported span or a support that does not align with the tower's load-bearing members can overstress the basin and structure. (15.1.5)
15.2 Anchorage, Wind, and Seismic Restraint
Wind anchorage per ASCE 7 (all installations)
Wind and seismic anchorage per ASCE 7 / IBC
Wind and seismic with vibration isolation rails (occupied buildings)
15.2.1The tower shall be anchored to the supporting structure to resist wind uplift and overturning per ASCE 7 for the project wind speed and exposure, and seismic forces per ASCE 7 and the IBC where the seismic design category requires.
15.2.2Anchorage details and the calculations supporting them shall be shown on the structural drawings and coordinated with the manufacturer's published anchorage requirements and base reactions. 15.2.3Where the tower is mounted on a building roof over occupied space, spring vibration isolation rails between the tower and the structural support shall be provided to prevent transmission of fan vibration into the building, integrated with the seismic restraint so that both functions are satisfied.
NOTE Cooling towers are large, exposed, relatively light (when dry) structures with high wind profiles and are a frequent casualty in high-wind events when inadequately anchored. (15.2.4)
15.3 Clearances for Airflow and Maintenance
○ Manufacturer's published minimum clearances verified for the as-built site
○ Clearances exceed manufacturer minimums (preferred where space allows)
15.3.1The tower shall be installed with the manufacturer's published minimum clearances on all air-inlet faces and above the air discharge, and with maintenance access to the fan, drive, distribution system, fill, and basin.
15.3.2Clearances shall be verified against the as-built surrounding construction (walls, parapets, adjacent towers, screening) before the tower is set.
NOTE Inadequate air-inlet clearance starves the tower of air and causes recirculation, both of which degrade thermal performance permanently and cannot be recovered by any adjustment after installation. (15.3.3)
15.4 Piping and Electrical Connections
15.4.1Condenser water supply (return-to-tower hot water) and the basin outlet (supply-to-pump cold water) connections shall be made per the mechanical piping details with flexible connectors where the tower is vibration-isolated. 15.4.2Makeup, overflow, blowdown, and drain connections shall be piped to the locations shown on the drawings, and overflow and drain shall discharge to an approved location per the plumbing code.
15.4.3Electrical power and control wiring shall be installed per NFPA 70, with disconnect provisions at the tower for the fan motor, integral spray pump (closed-circuit units), and basin heater.
16 Delivery, Storage, and Handling
16.1Towers and components shall be delivered, stored, and handled per the manufacturer's instructions to prevent corrosion, distortion, and contamination.
16.2Galvanized components shall be stored to prevent wet-stack white-rust staining, which occurs when freshly galvanized surfaces are stacked or stored wet without ventilation.
16.3Fill and drift eliminators shall be stored out of direct sunlight and protected from heat distortion and physical damage.
16.4Rigging shall use the manufacturer's designated lifting points.
16.5Components shall be protected from construction debris entering the basin and distribution system before startup.
NOTE Cooling tower structures are not designed to be lifted from arbitrary points and can be permanently distorted by improper rigging. (16.6)
17 Warranty
1 year — standard
5 years — fan motor and mechanical drive
5 years — basin and structure (stainless construction)
Extended per manufacturer's program
17.1The manufacturer shall warrant the cooling tower against defects in materials and workmanship for a minimum of one year from substantial completion.
17.2An extended warranty on the fan motor and drive (gear reducer) and on the fill and drift eliminators may be specified where the application or the Owner's maintenance program warrants.
17.3Where stainless steel basin or structure is provided, the manufacturer may offer an extended basin or structural corrosion warranty, which should be obtained in writing.
18 Spare Parts
☐ Spare fan belt set (belt-drive towers)
☐ Gear reducer oil and filter (gear-drive towers)
☐ Spare fan motor
☐ Spray nozzles (counterflow distribution)
☐ Basin strainer screen
☐ Drift eliminator section
☐ Basin heater element and thermostat
18.1The manufacturer shall furnish the Owner with a spare parts list with part numbers and recommended stocking quantities.
18.2For installations where downtime is costly, the Owner should stock the wear and consumable items that are most likely to be needed and most disruptive to obtain on short notice.