+---
+title: Cooling Towers
+category: Mechanical
+toc_depth: 3
+description: >
+ When to use: Open-circuit and closed-circuit (fluid cooler) evaporative heat-rejection equipment for HVAC condenser water systems serving water-cooled chillers, water-source heat pump loops, and process cooling in commercial, institutional, and industrial buildings. Covers field-erected and factory-assembled (packaged) towers; induced-draft and forced-draft configurations; counterflow and crossflow arrangements; galvanized steel, stainless steel, and fiberglass (FRP/HDPE) construction; axial and centrifugal fans with constant-speed, two-speed, and variable-speed drives. Applicable from small rooftop packaged towers through large multi-cell field-erected installations.
+
+ Not intended for: Air-cooled chillers and air-cooled condensers that reject heat directly to ambient air without evaporation (no separate standard required where integral to the chiller — see [[sync/chillers]]); chilled-water generation and the refrigeration machine itself ([[sync/chillers]]); condenser water pumps and the connected piping circuit (pumps in [[sync/hvac-pumps]], piping in [[sync/hydronic-piping]]); chemical water treatment, biocide dosing, and Legionella risk-management program for the circulating water ([[sync/hvac-water-treatment]]); fan motor variable frequency drives ([[sync/hvac-variable-frequency-drives]]); evaporative cooling for direct air conditioning (evaporative/swamp coolers serving the airstream rather than a condenser-water loop); dry coolers and adiabatic fluid coolers where no continuous wetted heat-transfer surface is used; testing, adjusting, and balancing of the connected water system ([[sync/testing-adjusting-and-balancing]]); building automation system controls integration ([[sync/building-automation-system]]).
+---
+
+# Scope
+
+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. 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. Both factory-assembled packaged towers and field-erected towers are addressed, as are induced-draft and forced-draft configurations in counterflow and crossflow arrangements.
+
+A cooling tower rejects heat by evaporating a small fraction of the circulating water; the heat of vaporization carried away by that evaporated water is what cools the bulk stream. This evaporative mechanism is what allows a cooling tower to cool water below the ambient dry-bulb temperature — toward the ambient wet-bulb temperature — which is the entire reason water-cooled systems are more efficient than air-cooled systems in most climates. It is also the source of every characteristic concern of cooling tower equipment: continuous consumption of makeup water, concentration of dissolved solids in the recirculating water, biological growth in warm wetted surfaces, drift (entrained water droplets) carrying that biology into the surrounding air, and freezing of the wetted surfaces in cold weather. This standard establishes both the thermal and mechanical requirements for the equipment and the provisions necessary to manage these concerns over the equipment service life.
+
+The 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. Condenser water pumps and the suction and discharge piping that circulates water between the tower and the chiller condenser are covered in [[sync/hvac-pumps]] and [[sync/hydronic-piping]]. Chemical treatment of the circulating water, the building water-management plan, and Legionella risk management are covered in [[sync/hvac-water-treatment]]. Fan motor variable frequency drives are covered in [[sync/hvac-variable-frequency-drives]]. Controls integration with the building automation system is coordinated under [[sync/building-automation-system]].
+
+Equipment shall be certified for thermal performance under CTI STD-201 and rated for energy efficiency under ASHRAE 90.1. Field acceptance testing, where specified, shall follow CTI ATC-105 for open-circuit towers and CTI ATC-105S for closed-circuit towers. Legionella risk management for the connected system shall follow ASHRAE 188 and CTI GDL-159. Structural support, anchorage, and wind and seismic restraint shall conform to the IBC and ASCE 7. Electrical components shall be listed by a Nationally Recognized Testing Laboratory.
+
+# Referenced Standards
+
+Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited. Where 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) |
+
+# Submittals
+
+## Action Submittals
+
+The Contractor shall submit the following for the Engineer's review and acceptance prior to ordering equipment. Fabrication and procurement shall not proceed until action submittals have been reviewed and returned.
+
+- 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
+
+```datasheet
+label: Action Submittals Required
+type: checkbox
+options:
+ - "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)"
+default: "Product data and configuration"
+```
+
+## Closeout Submittals
+
+At 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 ([[sync/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
+
+# Quality Assurance
+
+## Manufacturer Qualifications
+
+Cooling 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. The manufacturer shall maintain an ISO 9001 certified quality management system and 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 Thermal Performance Certification
+
+The cooling tower shall be certified under the Cooling Technology Institute Standard 201 (CTI STD-201) Thermal Performance Certification Program for the applicable equipment class. CTI STD-201 certification means that an independent administrator has verified — through testing of a model selected by the administrator, with annual reverification of a different model — that every model in the manufacturer's published rating line performs thermally in accordance with the published 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 undersized or underperforming tower is not discovered until the connected chiller plant fails to make design capacity on a design day. Where 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.
+
+```datasheet
+label: Thermal Performance Certification
+type: radio
+options:
+ - "CTI STD-201 certified model line (required)"
+ - "Independent thermal test certification of specific selection (non-CTI-certified model)"
+default: "CTI STD-201 certified model line (required)"
+```
+
+## NRTL Listing
+
+The 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. Electrical components not covered by the unit listing shall be individually listed to applicable standards.
+
+## Pre-Installation Conference
+
+A 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. 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.
+
+# Environmental and Service Conditions
+
+The cooling tower shall be selected and rated for the design thermal duty and the environmental conditions at the installation site. The design conditions are [[drawing: as indicated on the mechanical equipment schedules and the condenser water flow diagram]]. The 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.
+
+## Design Entering-Air Wet-Bulb Temperature
+
+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. The 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. 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.
+
+```datasheet
+label: Design Entering-Air Wet-Bulb Temperature
+type: range
+unit: °F WB
+drawing_ref: true
+options:
+ min: 65
+ max: 82
+ setpoints: [65, 68, 70, 72, 74, 76, 78, 80, 82]
+default: 78
+```
+
+## Air Recirculation and Inlet Conditions
+
+The 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. 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. The 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.
+
+## Freeze Protection Conditions
+
+Where 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. Freezing of standing basin water cracks basins and damages piping; freezing of the recirculating water on the fill during cold-weather operation builds ice that adds structural load and blocks airflow. The freeze protection strategy shall be coordinated with the operating sequence and is addressed in the basin and controls sections of this standard.
+
+```datasheet
+label: Freeze Protection Required
+type: radio
+options:
+ - "Yes — climate has sub-freezing ambient temperatures"
+ - "No — installation in a climate that does not freeze"
+default: "Yes — climate has sub-freezing ambient temperatures"
+```
+
+# Tower Type, Draft, and Flow Arrangement
+
+## Tower Type
+
+The fundamental selection is between an open-circuit tower and a closed-circuit tower (fluid cooler). 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. 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; the process fluid never contacts the atmosphere. Closed-circuit towers are 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.
+
+```datasheet
+label: Tower Type
+type: radio
+options:
+ - "Open-circuit — condenser water sprayed directly over fill"
+ - "Closed-circuit (fluid cooler) — process fluid in closed coil, separate spray circuit"
+default: "Open-circuit — condenser water sprayed directly over fill"
+```
+
+Closed-circuit towers cost more, occupy more footprint per ton, and consume additional energy for the integral spray pump, but they protect the chiller condenser or the process loop from the fouling, scaling, and biological burden that an open-circuit system imposes on everything downstream of the basin. Where the cooled loop also serves as a winter free-cooling loop, the closed-circuit arrangement allows the coil to be run dry in cold weather for sensible cooling without the freeze and fouling exposure of an open system.
+
+## Draft Type
+
+```datasheet
+label: Draft Type
+type: radio
+options:
+ - "Induced draft — fan on air discharge, draws air through tower"
+ - "Forced draft — fan on air inlet, blows air through tower"
+default: "Induced draft — fan on air discharge, draws air through tower"
+```
+
+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 of saturated air back into the inlet. 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. 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 allowing operation in environments where an exposed top-mounted fan and gearbox are undesirable. Forced-draft centrifugal towers are also selected where the tower must be ducted or installed indoors with the discharge ducted to atmosphere, because centrifugal fans can develop the external static pressure that axial fans cannot.
+
+## Flow Arrangement
+
+```datasheet
+label: Flow Arrangement
+type: radio
+options:
+ - "Counterflow — air moves vertically upward against downward water flow"
+ - "Crossflow — air moves horizontally across downward water flow"
+default: "Counterflow — air moves vertically upward against downward water flow"
+```
+
+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; the distribution system is a pressurized closed spray system that resists fouling and freezing and is fully enclosed against sunlight, which limits algae growth. In a crossflow tower, air moves horizontally across the downward-falling water, fed from open gravity-flow hot-water distribution basins on top of the fill; crossflow towers offer easier access to the distribution basins and fill for inspection and cleaning, lower pump head (the water is distributed by gravity rather than spray pressure), and quieter operation, at the cost of a larger footprint and open distribution basins that require sunlight management to control algae. Both arrangements are fully acceptable; the selection follows the project priorities of footprint, pump energy, maintenance access, and water treatment strategy.
+
+## Assembly Method and Cell Arrangement
+
+```datasheet
+label: Assembly Method
+type: radio
+options:
+ - "Factory-assembled (packaged) — shipped substantially complete"
+ - "Field-erected — assembled on site from components"
+default: "Factory-assembled (packaged) — shipped substantially complete"
+```
+
+Factory-assembled packaged towers are shipped substantially complete and set in place as a unit or in a small number of modules; they are the standard choice for commercial and institutional projects up to the largest size that can be shipped and rigged. 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 — two or more cells operating in parallel on a common basin or on adjacent basins with an equalizer — provide capacity staging and redundancy; the number and arrangement of cells shall be [[drawing: as indicated on the mechanical equipment schedules]].
+
+# Thermal Performance
+
+## Design Water Flow Rate
+
+The design recirculating water flow rate establishes the hydraulic size of the tower and shall match the condenser water flow of the connected chillers or process load. Flow shall be [[drawing: as indicated on the mechanical equipment schedules]]. The tower shall be selected to perform at the design flow; 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.
+
+```datasheet
+label: Design Water Flow Rate
+type: range
+unit: gpm
+drawing_ref: true
+options:
+ min: 50
+ max: 20000
+ setpoints: [50, 100, 200, 300, 500, 750, 1000, 1500, 2000, 3000, 5000, 7500, 10000, 15000, 20000]
+default: 900
+```
+
+## Nominal Capacity
+
+```datasheet
+label: Nominal Capacity
+type: range
+unit: nominal tons
+drawing_ref: true
+options:
+ min: 10
+ max: 5000
+ setpoints: [10, 25, 50, 75, 100, 150, 200, 300, 400, 500, 750, 1000, 1500, 2000, 3000, 5000]
+default: 300
+```
+
+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) and is useful only for rough comparison. The governing requirement is always the specified flow, range, approach, and design wet-bulb — not the nominal tonnage. The nominal capacity is included for schedule coordination and shall be reconciled against the actual specified thermal duty.
+
+## Cooling Range
+
+```datasheet
+label: Cooling Range
+type: range
+unit: °F
+drawing_ref: true
+options:
+ min: 5
+ max: 25
+ setpoints: [5, 8, 10, 12, 15, 18, 20, 25]
+default: 10
+```
+
+Range is the difference between the entering (hot) water temperature and the leaving (cold) water temperature — the number of degrees the tower cools the water. Range is set by the heat load and the water flow rate (range equals load divided by flow), not by the tower itself; a given heat load circulated at higher flow produces a lower range, and vice versa. 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.
+
+## Approach
+
+```datasheet
+label: Approach
+type: range
+unit: °F
+drawing_ref: true
+options:
+ min: 4
+ max: 15
+ setpoints: [4, 5, 6, 7, 8, 9, 10, 12, 15]
+default: 7
+```
+
+Approach is the difference between the leaving (cold) water temperature and the design entering-air wet-bulb temperature. Approach is the truest measure of tower size and thermal effort: it is the one performance parameter the tower designer controls, and it is the most expensive degree to buy. 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, more airflow, and a larger tower — an approach below approximately 4°F to 5°F is generally uneconomical, because the tower size grows asymptotically as the cold-water temperature is pushed toward the theoretical limit of the wet-bulb. A tighter approach lowers condenser water temperature and improves chiller efficiency, so the optimum is a plant-level energy tradeoff between tower first cost and chiller energy.
+
+## Energy Efficiency
+
+The 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. For 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. For closed-circuit towers the rated efficiency includes the integral spray pump motor power in addition to the fan motor power, reflecting the additional energy the spray circuit requires. Compliance 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.
+
+```datasheet
+label: ASHRAE 90.1 Energy Efficiency Compliance
+type: radio
+options:
+ - "Documented at ASHRAE 90.1 standard rating condition (gpm/hp)"
+ - "Exempt — equipment class not addressed by ASHRAE 90.1"
+default: "Documented at ASHRAE 90.1 standard rating condition (gpm/hp)"
+```
+
+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 by the energy standard where their other attributes (low discharge velocity, base-mounted fan, ductability) are required, but they should not be selected on efficiency grounds.
+
+# Construction and Materials
+
+## Structural and Casing Material
+
+The corrosive, continuously wetted environment of a cooling tower makes material selection the dominant determinant of service life. The structure, casing, and basin material shall be selected for the water chemistry, the atmospheric environment, and the required service life.
+
+```datasheet
+label: Structure and Casing Material
+type: select
+options:
+ - "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"
+default: "Hot-dip galvanized steel, G-235 (Z700) per ASTM A653 — standard commercial"
+```
+
+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. Field-erected steel components too large for mill galvanizing shall be hot-dip galvanized after fabrication per ASTM A123. Stainless steel construction (Type 304 or, for high-chloride and coastal service, Type 316) provides substantially longer service life and is specified 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 entirely and is selected for marine, chemical, and other severely corrosive environments. The basin material warrants particular attention because the basin holds standing water continuously and is the most common location of corrosion failure.
+
+## Stainless Steel Cold-Water Basin
+
+```datasheet
+label: Cold-Water Basin Material
+type: select
+options:
+ - "Galvanized steel matching tower construction"
+ - "Type 304 stainless steel basin (recommended upgrade)"
+ - "Type 316 stainless steel basin (coastal/high-chloride)"
+ - "FRP basin"
+default: "Type 304 stainless steel basin (recommended upgrade)"
+```
+
+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 and cost-effective strategy, because the basin fails from corrosion first while the upper structure, which drains and dries between operating cycles, lasts considerably longer. A stainless basin also eliminates the white-rust passivation concern that affects new galvanized basins during the first weeks of operation.
+
+## Hardware and Fasteners
+
+All fasteners, hardware, and connection components in the wetted and splash zones shall be Type 304 or Type 316 stainless steel. 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. Stainless hardware is inexpensive insurance against losing structural connections to corrosion long before the structure itself fails.
+
+# Fill and Drift Eliminators
+
+## Fill Type
+
+```datasheet
+label: Fill Type
+type: radio
+options:
+ - "Film fill — closely spaced PVC sheets, high efficiency, clean water only"
+ - "Splash fill — staggered bars/grids, fouling-tolerant, larger tower"
+default: "Film fill — closely spaced PVC sheets, high efficiency, clean water only"
+```
+
+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; it is highly efficient and allows a compact tower, and it is the standard choice for clean, well-treated water. Film fill's close passages are intolerant of dirty or scaling water — suspended solids, biological growth, and scale bridge the narrow gaps, collapse airflow, and destroy performance, sometimes catastrophically when fouled fill collapses under its own waterlogged weight. Splash fill consists of staggered bars or grids that repeatedly break the falling water into droplets; it 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. Splash 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.
+
+```datasheet
+label: Fill Low-Fouling Provision
+type: select
+options:
+ - "Standard film fill (clean treated water)"
+ - "Low-fouling (wide-flute) film fill — moderate water quality"
+ - "Splash fill — poor water quality or high fouling potential"
+default: "Standard film fill (clean treated water)"
+```
+
+## Fill Fire Resistance
+
+PVC fill shall have a flame-spread index of 25 or less when tested per ASTM E84. 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. Where 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.
+
+## Drift Eliminators
+
+Drift eliminators shall be installed downstream of the fill (and downstream of the spray distribution) to strip entrained water droplets from the leaving airstream. Drift is liquid water carried out of the tower in the discharge air; unlike evaporation, drift carries the full chemistry and biology of the recirculating water — including any Legionella — into the surrounding air, where it can be inhaled or deposited on adjacent surfaces and air intakes. Minimizing drift is therefore both an energy-and-water conservation measure and a primary public-health control. Drift eliminators shall achieve a drift rate not exceeding the specified percentage of the recirculating water flow rate.
+
+```datasheet
+label: Maximum Drift Rate
+type: select
+options:
+ - "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)"
+default: "0.001% of recirculating flow (standard for new installations)"
+```
+
+A drift rate of 0.001% of recirculating water flow is the current standard for new installations and is readily achievable with modern multi-pass cellular eliminators. A 0.0005% 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. The drift eliminator media shall be the same corrosion class as the fill and shall be removable in sections for inspection and cleaning.
+
+# Fans and Drives
+
+## Fan Type
+
+```datasheet
+label: Fan Type
+type: radio
+options:
+ - "Axial (propeller) — induced or forced draft, low static, high efficiency"
+ - "Centrifugal — forced draft, develops external static, low noise"
+default: "Axial (propeller) — induced or forced draft, low static, high efficiency"
+```
+
+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 the lower discharge noise of a centrifugal blower is needed; their air-moving efficiency is considerably lower than an axial fan, which is reflected in the energy standard's lower allowable efficiency for centrifugal towers. Fans shall be statically and dynamically balanced and rated per ANSI/AMCA 210.
+
+## Fan Material
+
+```datasheet
+label: Fan and Hub Material
+type: select
+options:
+ - "Aluminum blades with galvanized or aluminum hub (standard)"
+ - "FRP (fiberglass) blades — corrosive environments"
+ - "Stainless steel hub with aluminum or FRP blades"
+default: "Aluminum blades with galvanized or aluminum hub (standard)"
+```
+
+## Fan Drive Arrangement
+
+```datasheet
+label: Fan Drive Arrangement
+type: select
+options:
+ - "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"
+default: "Gear drive (right-angle gear reducer) — large axial-fan towers"
+```
+
+Belt drives are economical for small and mid-size towers but require periodic belt tensioning and replacement, and belts in the wet airstream wear faster than in dry service. Gear drives (right-angle gear reducers conforming to CTI STD-111) are the standard for large axial-fan induced-draft towers; the gear reducer is mounted on a rigid mechanical support with a drive shaft from 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 the fan speed and motor speed allow. The gear reducer, where used, shall be rated for continuous cooling tower service with a service factor appropriate to the fan inertia and start frequency, and shall be provided with an external oil level indicator and a means to change oil without entering the airstream.
+
+## Fan Motor
+
+```datasheet
+label: Fan Motor Enclosure
+type: select
+options:
+ - "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"
+default: "Totally Enclosed Air Over (TEAO) — in airstream, induced draft"
+```
+
+Fan 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. A standard TEFC motor placed in the discharge airstream of an induced-draft tower will fail prematurely from moisture intrusion. Motors connected to variable frequency drives shall be inverter-duty rated per NEMA MG 1 Part 31; VFDs shall conform to [[sync/hvac-variable-frequency-drives]].
+
+```datasheet
+label: Fan Motor Voltage
+type: select
+options:
+ - "208V / 3-phase"
+ - "460V / 3-phase"
+ - "575V / 3-phase"
+default: "460V / 3-phase"
+```
+
+## Fan Speed Control
+
+```datasheet
+label: Fan Speed Control
+type: select
+options:
+ - "Variable frequency drive (VFD) — modulating capacity control"
+ - "Two-speed motor — staged capacity control"
+ - "Single-speed (constant) — cycling control only"
+default: "Variable frequency drive (VFD) — modulating capacity control"
+```
+
+Cooling tower capacity is controlled primarily by fan airflow, and fan power varies with the cube of fan speed — so reducing fan speed yields dramatic energy savings at part load, which is where the tower operates the overwhelming majority of the time. ASHRAE 90.1 requires fan speed control (VFD or two-speed) on cooling tower fan motors above a defined threshold. A variable frequency drive provides the smoothest capacity control, the lowest part-load energy, reduced mechanical and thermal shock on the gear drive, and the ability to hold a stable leaving-water temperature setpoint. Two-speed motors are a lower-first-cost alternative that captures much of the fan-law energy benefit in two discrete steps. Single-speed fan cycling shall be used only on the smallest towers where speed control is not cost-justified, recognizing that frequent cycling stresses the drive and produces a sawtooth water temperature. The VFD minimum speed shall respect the manufacturer's minimum fan speed required for gear lubrication and to maintain water distribution over the fill.
+
+# Basin, Makeup, and Blowdown
+
+## Cold-Water Basin and Outlet
+
+The 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. Air drawn into the pump suction from a vortexing basin causes pump cavitation and loss of flow; see [[sync/hvac-pumps]] for the connected pump suction requirements. The basin shall be sloped to a drain connection so that it can be fully emptied for cleaning, which is a fundamental requirement of the water-management plan because a basin that cannot be fully drained always retains a stagnant biological reservoir.
+
+## Makeup Water
+
+```datasheet
+label: Makeup Water Control
+type: select
+options:
+ - "Mechanical float valve (basic)"
+ - "Electronic level control with solenoid makeup valve (recommended)"
+ - "Conductivity-controlled makeup with metering (integrated treatment)"
+default: "Electronic level control with solenoid makeup valve (recommended)"
+```
+
+Makeup water replaces water lost to evaporation, drift, and blowdown. A simple mechanical float valve is the most basic provision; 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. The makeup water connection shall include backflow prevention as required by the plumbing code, coordinated with [[sync/backflow-prevention]].
+
+## Blowdown (Bleed)
+
+As water evaporates, the dissolved solids it leaves behind concentrate in the recirculating water; blowdown (also called bleed) continuously or intermittently discharges a portion of the concentrated water and is replaced by fresh makeup, holding the cycles of concentration within the limit the water treatment program allows. Without adequate blowdown the recirculating water scales, fouls, and corrodes; with excessive blowdown, water and treatment chemicals are wasted. Blowdown 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 [[sync/hvac-water-treatment]]. The tower shall be provided with a blowdown connection separate from the basin drain.
+
+```datasheet
+label: Blowdown Control
+type: radio
+options:
+ - "Conductivity-controlled blowdown (recommended)"
+ - "Timed/metered blowdown"
+ - "Continuous fixed-rate bleed (basic)"
+default: "Conductivity-controlled blowdown (recommended)"
+```
+
+## Basin Heater
+
+Where 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. The basin heater protects the standing basin water when the tower is off; it 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). Basin heater capacity shall be selected for the design minimum ambient temperature and wind condition, and the heater shall be controlled by a basin thermostat with a low-water cutout to prevent energizing a dry heater.
+
+```datasheet
+label: Basin Freeze Protection
+type: select
+options:
+ - "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)"
+default: "Electric immersion basin heater(s) with thermostat and low-water cutout"
+```
+
+```datasheet
+label: Basin Heater Design Minimum Ambient
+type: range
+unit: °F
+drawing_ref: true
+options:
+ min: -40
+ max: 32
+ setpoints: [-40, -30, -20, -10, 0, 10, 20, 32]
+default: 0
+```
+
+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.
+
+# Legionella and Water Treatment Provisions
+
+## Water-Management Plan Coordination
+
+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 [[sync/hvac-water-treatment]] and are not duplicated here. This standard establishes the physical equipment provisions that the water-management program depends on. The tower and the treatment system shall be coordinated so that the chemical feed, monitoring, and control devices specified in [[sync/hvac-water-treatment]] have the connection points, access, and basin configuration they require.
+
+## Provisions Required of the Tower
+
+The 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
+
+```datasheet
+label: Water Treatment Equipment Provisions (by tower)
+type: checkbox
+options:
+ - "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"
+default: "Fully drainable cold-water basin"
+```
+
+## Sunlight and Algae Control
+
+Open distribution basins on crossflow towers shall be provided with covers, screens, or distribution-deck covers to exclude sunlight, because sunlight on standing nutrient-bearing water drives algae growth that fouls the fill and consumes biocide. Counterflow towers with enclosed pressurized distribution systems inherently exclude light from the distribution water and do not require this provision for the distribution system; the basin shall nonetheless be screened against debris and light where practical.
+
+# Sound
+
+## Sound Performance
+
+Cooling tower sound is dominated by the fan and, on some configurations, by the cascade of falling water into the basin. The 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. Sound data shall be provided in octave bands so that the design team can evaluate transmission to specific receptors.
+
+```datasheet
+label: Sound Attenuation
+type: select
+options:
+ - "Standard fan and tower (no added attenuation)"
+ - "Low-sound fan (oversized, low-speed) selection"
+ - "Intake attenuators"
+ - "Discharge attenuators"
+ - "Intake and discharge attenuators"
+default: "Standard fan and tower (no added attenuation)"
+```
+
+Where the standard tower does not meet the receptor noise limit, 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 and energy penalty of attenuators. Intake and discharge sound attenuators reduce noise further but add airflow resistance that the fan must overcome, increasing fan energy; they shall be specified only where the fan selection alone cannot meet the requirement. Variable-speed fan operation also reduces the time-averaged sound level, because the fan runs at reduced speed during the part-load hours that dominate operation.
+
+# Factory and Field Testing / Commissioning
+
+## Factory Inspection
+
+The manufacturer shall inspect each factory-assembled tower before shipment for completeness, correct fan rotation and balance, water distribution integrity, and freedom from shipping damage. For field-erected towers, the manufacturer shall provide field technical assistance during erection and a startup inspection upon completion.
+
+## Field Thermal Performance Test
+
+Where 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. 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 after acceptance) and is generally not warranted for small packaged towers on routine commercial projects.
+
+```datasheet
+label: Field Thermal Performance Test
+type: radio
+options:
+ - "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"
+default: "Not required — rely on CTI STD-201 certified rating"
+```
+
+## Startup and Commissioning
+
+The Contractor shall perform startup and commissioning in accordance with the manufacturer's instructions, including: verification of structural anchorage and level setting; verification of fan rotation, blade pitch, and vibration within the manufacturer's limits; verification of uniform water distribution over the entire fill with no dry or flooded areas; verification of basin level control and makeup operation; functional testing of the fan speed control through its full range and 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. Commissioning shall be coordinated with the initial water treatment passivation and disinfection required by [[sync/hvac-water-treatment]].
+
+# Installation
+
+## Structural Support
+
+The cooling tower shall be supported on structural steel or concrete designed for the tower's dead, operating (water-filled), and dynamic (fan) loads as [[drawing: detailed on the structural drawings]]. Support steel shall be designed per AISC 360 and concrete support and basins per ACI 318. The 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; an unsupported span or a support that does not align with the tower's load-bearing members can overstress the basin and structure. Operating weight (the weight with the basin and fill fully wetted, which substantially exceeds the dry shipping weight) shall govern the support design.
+
+## Anchorage, Wind, and Seismic Restraint
+
+The 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. 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. Anchorage details and the calculations supporting them shall be [[drawing: shown on the structural drawings]] and coordinated with the manufacturer's published anchorage requirements and base reactions.
+
+```datasheet
+label: Wind and Seismic Anchorage
+type: select
+options:
+ - "Wind anchorage per ASCE 7 (all installations)"
+ - "Wind and seismic anchorage per ASCE 7 / IBC"
+ - "Wind and seismic with vibration isolation rails (occupied buildings)"
+default: "Wind and seismic anchorage per ASCE 7 / IBC"
+```
+
+Where 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; the isolation rails shall be integrated with the seismic restraint so that both functions are satisfied.
+
+## Clearances for Airflow and Maintenance
+
+The 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. 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. Clearances shall be verified against the as-built surrounding construction (walls, parapets, adjacent towers, screening) before the tower is set.
+
+```datasheet
+label: Air Inlet and Discharge Clearance
+type: radio
+options:
+ - "Manufacturer's published minimum clearances verified for the as-built site"
+ - "Clearances exceed manufacturer minimums (preferred where space allows)"
+default: "Manufacturer's published minimum clearances verified for the as-built site"
+```
+
+## Piping and Electrical Connections
+
+Condenser water supply (return-to-tower hot water) and the basin outlet (supply-to-pump cold water) connections shall be made per [[drawing: the mechanical piping details]] with flexible connectors where the tower is vibration-isolated. Makeup, overflow, blowdown, and drain connections shall be piped to the locations shown on the drawings; overflow and drain shall discharge to an approved location per the plumbing code. Electrical 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.
+
+# Delivery, Storage, and Handling
+
+Towers and components shall be delivered, stored, and handled per the manufacturer's instructions to prevent corrosion, distortion, and contamination. Galvanized components shall be stored to prevent wet-stack white-rust staining, which occurs when freshly galvanized surfaces are stacked or stored wet without ventilation. Fill and drift eliminators shall be stored out of direct sunlight and protected from heat distortion and physical damage. Rigging shall use the manufacturer's designated lifting points; cooling tower structures are not designed to be lifted from arbitrary points and can be permanently distorted by improper rigging. Components shall be protected from construction debris entering the basin and distribution system before startup.
+
+# Warranty
+
+The manufacturer shall warrant the cooling tower against defects in materials and workmanship for a minimum of one year from substantial completion. An 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. Where stainless steel basin or structure is provided, the manufacturer may offer an extended basin or structural corrosion warranty, which should be obtained in writing.
+
+```datasheet
+label: Warranty Period
+type: select
+options:
+ - "1 year — standard"
+ - "5 years — fan motor and mechanical drive"
+ - "5 years — basin and structure (stainless construction)"
+ - "Extended per manufacturer's program"
+default: "1 year — standard"
+```
+
+# Spare Parts
+
+The manufacturer shall furnish the Owner with a spare parts list with part numbers and recommended stocking quantities. For 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.
+
+```datasheet
+label: Spare Parts to Furnish
+type: checkbox
+options:
+ - "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"
+default: "Basin strainer screen"
+```