Wet-Bulb Temperature Verification and Selection Calculation of Cooling Tower Capacity
Accurate verification of cooling tower capacity is a prerequisite for ensuring the efficient operation of chillers, and its core lies in capacity correction based on the local summer outdoor design wet-bulb temperature for air conditioning. According to Article 8.7.1 of GB 50736 "Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings," the selection of cooling towers shall be based on the summer outdoor design wet-bulb temperature of each region such as Shanghai, Beijing, and Guangzhou, which can be found in the meteorological parameter tables of major cities nationwide. For example, the summer outdoor design wet-bulb temperature is 27.9°C in Shanghai, 26.6°C in Beijing, and 28.1°C in Guangzhou. The selection capacity of cooling towers shall comprehensively consider parameters such as design cooling water temperature, wet-bulb temperature, approach, water flow, and atmospheric pressure. The standard design condition of cooling towers is generally: inlet water temperature 37°C, outlet water temperature 32°C, wet-bulb temperature 28°C, approach 4°C. When the actual wet-bulb temperature differs from the standard condition, capacity correction is required. The heat exchange capability of cooling towers can be corrected using the capacity coefficient K: K = cooling capacity under actual condition / cooling capacity under standard condition. In actual selection, it is recommended that the cooling tower capacity be determined by multiplying the calculated heat load by a safety margin factor of 1.1-1.2 to cope with extreme high-temperature weather and cooling tower performance degradation. Specific calculation steps: Step 1, determine the heat exchange rate of the cooling tower Q (kW) = heat dissipation of the chiller condenser + shaft power of the cooling water pump. The condenser heat dissipation is approximately equal to cooling capacity × (1+1/COP); when COP=6.0, the condenser heat dissipation ≈ cooling capacity × 1.167. Step 2, calculate the cooling water flow G (m³/h) based on the heat exchange rate = Q×3600/(Cp×ΔT×ρ), where Cp is the specific heat capacity of water 4.187kJ/(kg·°C), ΔT is the cooling water temperature difference 5°C, and ρ is the density of water 1,000kg/m³. Step 3, select the cooling tower model based on the cooling water flow and design wet-bulb temperature, and verify whether the approach of the cooling tower is within the range of 4-5°C. Selection of cooling tower structure type: Cross-flow cooling towers and counter-flow cooling towers are commonly used in five-star hotels. Cross-flow cooling towers have a large air inlet area, low airflow resistance, and are easy to maintain, but occupy a relatively large floor area; counter-flow cooling towers have high heat exchange efficiency and a small floor area, but are relatively tall. According to GB/T 7190.1 "Glass Fiber Reinforced Plastic Cooling Towers Part 1: Small and Medium Glass Fiber Reinforced Plastic Cooling Towers," the drift loss of cooling towers shall not exceed 0.015% (i.e., 0.0015%) of the circulating water flow, and shall be controlled within 0.005% in water-scarce areas. For packing selection, PVC honeycomb packing or modified polypropylene packing is recommended for five-star hotels, with a packing height generally of 1.2-1.5m and a packing spacing of 12-19mm. The packing shall have flame retardant performance with an oxygen index of not less than 30%.
Optimization of Cooling Tower Installation Location and Anti-Heat Reflux Design
The rationality of the cooling tower installation location directly affects its heat dissipation efficiency. Heat reflux (i.e., the hot and humid air discharged from the cooling tower being re-drawn into the air inlet) can cause the inlet air temperature to rise by 1-3°C, causing the cooling tower outlet water temperature to rise by 0.5-1.5°C, which in turn causes the chiller COP to drop by 3%-8%. Therefore, preventing heat reflux is the primary goal of optimizing the cooling tower installation location. According to Article 8.7.3 of GB 50736 "Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings," cooling towers shall be set in well-ventilated locations to prevent hot air reflux and short-circuiting, and shall not be set in enclosed spaces such as inside buildings or basements. Appendix B of the GB/T 7190.1 standard provides recommended values for cooling tower installation spacing. The key technical requirements for optimizing the cooling tower installation location are as follows: (1) Cooling towers shall be set on the building roof or in open ground areas, with sufficient air inlet space around them; the minimum distance from the air inlet to the building exterior wall shall not be less than 1.5 times the cooling tower height and not less than 2m. (2) When multiple cooling towers are arranged in parallel, the spacing between adjacent cooling towers shall not be less than 1.5 times the width of the cooling tower air inlet and not less than 2m. When the spacing is insufficient, wind deflectors shall be set between adjacent cooling towers, with the height of the wind deflector not less than 1.2 times the cooling tower height. (3) The cooling tower exhaust outlet shall be at least 1.5m above the roof, and the exhaust direction shall be away from the air inlet area. (4) Cooling towers should not be set in locations prone to hot air accumulation such as building recesses, patios, and inner courtyards. When installation in a recess is unavoidable, CFD airflow simulation analysis shall be conducted to ensure the heat reflux rate is controlled below 5%. For the architectural aesthetic requirements of five-star hotels, cooling towers usually require decorative enclosures. Decorative enclosures shall not obstruct the cooling tower air inlet; the horizontal distance from the enclosure to the cooling tower air inlet shall not be less than 1.5m, and the top of the enclosure shall be at least 0.5m lower than the top of the cooling tower air inlet. The enclosure should adopt a permeable design (such as louvers or grilles) to ensure smooth air intake. In coastal areas, anti-salt spray corrosion measures shall also be considered for cooling towers: the protection level of fan motors shall not be lower than IP55, the tower body material shall be 316L stainless steel or FRP glass fiber reinforced plastic, and fasteners shall be stainless steel. The Marriott MIDS standard requires that the horizontal distance from the cooling tower installation location to the hotel guest room windows shall not be less than 15m, and the exhaust outlet shall not face the main landscape areas and guest areas. Vibration damping springs shall be set at the cooling tower base, sound insulation pads shall be set between the base and the roof, and rubber flexible joints shall be set on the inlet and outlet pipes to minimize vibration transmission. GB 50016 "Code for Fire Protection Design of Buildings" requires that the fire separation distance between cooling towers and combustible building components shall not be less than 2m; when cooling towers are set on the roof of high-rise buildings, the roof load-bearing requirements shall be met.
Noise Control and Environmental Compliance Requirements
The operating noise of cooling towers is an important environmental compliance indicator for five-star hotels and a key factor affecting guest experience. The noise sources of cooling towers mainly include: fan noise (the primary noise source, accounting for about 70%), water splashing noise (about 20%), and motor noise (about 10%). According to GB 22337 "Emission Standard for Community Noise," the boundary noise limits for hotels located in commercial districts are: daytime ≤60dB(A), nighttime ≤50dB(A). However, five-star hotels typically apply stricter internal control standards, requiring nighttime noise in guest room areas of ≤30dB(A) with windows closed and ≤40dB(A) with windows open. Low-noise selection and installation technical measures for cooling towers include: (1) Select low-noise cooling towers by adopting large-diameter low-speed fans (speed controlled at 150-250rpm), equipped with variable-frequency motors, and optimized fan blade shapes (using airfoil or swept-curved blades), which can reduce noise by 8-12dB(A). (2) Install sound attenuation facilities: install intake silencers at the cooling tower air inlet, exhaust silencer elbows or silencer hoods at the exhaust outlet, and sound-absorbing pads (honeycomb sound insulation material) below the water splashing area. (3) Set up sound barriers: install sound barriers on the side of the cooling tower facing guest room areas, with barrier height determined by acoustic calculation (generally not less than 1.5 times the cooling tower height), using sound-absorbing and sound-insulating composite panels (such as color steel plate + rock wool sandwich, surface density ≥20kg/m²). (4) Optimize operating hours: reduce fan speed or the number of operating units at night, coordinated with the chilled water storage operation strategy of chillers. According to the noise standards of GB/T 7190.1 "Glass Fiber Reinforced Plastic Cooling Towers": standard cooling tower noise ≤65dB(A) (at 1m from the tower), low-noise type ≤55dB(A), and ultra-low-noise type ≤50dB(A). Five-star hotels are recommended to select ultra-low-noise cooling towers, combined with sound barriers and sound attenuation facilities, to ensure that cooling tower boundary noise meets environmental requirements. The minimum distance between the installation location and guest rooms should be calculated through noise propagation attenuation: for every doubling of distance, noise attenuates by approximately 6dB(A). Environmental compliance during cooling tower operation also includes water quality management: circulating cooling water blowdown must not be discharged directly into the rainwater pipe network, but should be discharged into the sewage pipe network or discharged after treatment meets standards. Cooling water requires regular water quality testing and dosing of corrosion and scale inhibitors, bactericides and algicides, and discharge should comply with the requirements of GB 8978 "Integrated Wastewater Discharge Standard." Legionella control is an important hygiene issue in cooling tower operation. Article 8.7.5 of GB 50736 requires that cooling tower circulating water should be regularly tested for Legionella, with colony counts not exceeding 100CFU/mL.
Cooling Tower Water Treatment and System O&M Management
Cooling tower water treatment is an important O&M procedure for ensuring chiller heat exchange efficiency and the service life of the cooling tower itself. During operation, cooling tower circulating water continuously concentrates, leading to increased mineral concentration, increased dissolved oxygen, and microbial growth, thereby producing three core problems: scaling, corrosion, and Legionella. According to the requirements of GB 50050 "Code for Design of Industrial Recirculating Cooling Water Treatment," the water quality control indicators for cooling circulating water are: pH 7.0-9.0, total hardness ≤200mg/L (as CaCO₃), total alkalinity ≤500mg/L, chloride ≤250mg/L (≤100mg/L for stainless steel heat exchangers), turbidity ≤20NTU, conductivity ≤2,500μS/cm. Cooling water treatment solutions mainly include two major categories: chemical and physical methods. Chemical method: regular dosing of corrosion and scale inhibitors, dispersants, bactericides, and algicides through automatic dosing equipment is the most widely applied method. The dosage of corrosion and scale inhibitors is generally 5-10mg/L of circulating water volume; bactericides use alternating oxidizing (such as sodium hypochlorite, with residual chlorine maintained at 0.5-1.0mg/L) and non-oxidizing agents, dosed once per week. Physical method: includes electronic descaling instruments, magnetized water treaters, side-stream filtration, etc. Electronic descaling instruments change the crystal morphology of ions in water through high-frequency electric fields, causing them to form loose aragonite structures rather than dense calcite structures, thereby preventing scaling. Side-stream filtration systems are set at 1%-3% of circulating water volume as side-stream filtration flow, using sand filtration or microfiltration to remove suspended solids in water. Five-star hotels are recommended to adopt chemical + physical composite water treatment solutions. Cooling tower blowdown management is key to controlling water quality: blowdown valves are automatically controlled through conductivity, and when conductivity exceeds the set value (typically 2,500μS/cm), automatic blowdown occurs, with blowdown volume controlled at 0.5%-1.0% of circulating water volume. In terms of system O&M, a regular inspection and maintenance system for cooling towers needs to be established: (1) Daily inspection: fan operating current, inlet and outlet water temperatures, and whether the makeup water float valve operates normally. (2) Weekly inspection: water quality testing (pH, conductivity, turbidity), dosing of corrosion and scale inhibitors and bactericides. (3) Monthly inspection: fan belt tension, bearing lubrication, water distributor rotation, fill scaling conditions. (4) Quarterly: clean the collection basin and filters, check fan blade angle consistency. (5) Annually: comprehensive cleaning or replacement of fill (recommended replacement every 3-5 years), fan bearing replacement, motor insulation testing. Article 11.1.4 of GB 50243 "Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works" requires that cooling towers undergo single-machine trial operation for no less than 2h, checking fan current, vibration values, and noise to ensure all parameters meet equipment technical requirements.