Cooling Load Calculation and Chiller Capacity Determination
The cooling load calculation for a five-star hotel is the primary technical basis for chiller selection and must be carried out in strict accordance with Article 7.2.1 of GB 50736, Code for Design of Heating, Ventilation and Air Conditioning of Civil Buildings. The cooling load calculation shall adopt the hourly load calculation method, comprehensively considering multiple dimensions including envelope heat transfer, solar radiation heat gain, internal personnel heat gain, lighting and equipment heat gain, outdoor air load and infiltration air load. The cooling load index for five-star hotels typically ranges from 100-150 W/m², but the specific value varies considerably depending on building scale, climate zone, envelope thermal performance and other factors. Taking a five-star hotel with 400 guest rooms in the Shanghai region as an example, with a total building area of approximately 50,000 m², the summer design cooling load is approximately 5,800 kW, giving a cooling load index of 116 W/m². Of this, the guest room area cooling load is approximately 2,000 kW, accounting for 34.5%; the lobby and public areas approximately 1,500 kW, accounting for 25.9%; the catering and kitchen area approximately 800 kW, accounting for 13.8%; the ballroom and meeting area approximately 1,000 kW, accounting for 17.2%; and other areas approximately 500 kW, accounting for 8.6%. In the load calculation, particular attention must be paid to the kitchen area, where, due to the large exhaust air volume and concentrated equipment heat gain, the cooling load index can reach 300-400 W/m² and must be calculated separately. Article 7.2.2 of GB 50736 stipulates that the total installed capacity of chillers shall be determined by multiplying the calculated cooling load by a simultaneous use factor of 1.1, but should not exceed 1.2 times the calculated cooling load, so as to avoid the chillers operating in a low-efficiency range for extended periods. The Marriott International MIDS standard further requires that chiller selection be based on annual 8,760-hour energy consumption simulation using dynamic energy simulation software such as DesignBuilder or EnergyPlus, ensuring that the selected chillers achieve optimal energy efficiency under year-round operating conditions. Regarding the number of chiller units, the code requires no fewer than 2 units, and when the capacity of a single unit is greater than or equal to 2,000 kW, no more than 4 units should be used. A typical five-star hotel configuration is 3 centrifugal chillers, each with a capacity of approximately 1,900-2,000 kW, giving a total installed capacity of approximately 5,800-6,000 kW. This 3+0 scheme (3 main units, no standby) saves approximately 20% in initial investment compared with a 4-unit 4+1 scheme (4 main units, 1 standby), but requires comprehensive evaluation in light of the hotel's operational characteristics and local climate conditions. Regarding refrigerant selection, in accordance with the requirements of the Kigali Amendment to the Montreal Protocol, new projects should give priority to refrigerants with low GWP values; for example, R134a has a GWP of 1,430, while R513A has a GWP of only 631, reducing the greenhouse effect impact by 55%. Article 7.2.5 of GB 50736 recommends the use of environmentally friendly refrigerants and consideration of refrigerant leak detection and alarm systems.
Chiller Type Selection and Economic Analysis
The selection of chiller type requires comprehensive consideration of multiple factors including hotel scale, load characteristics, energy prices, site conditions and O&M capability. The commonly used chiller types include centrifugal, screw, magnetic bearing centrifugal and absorption, each with different technical and economic advantages in different application scenarios. Centrifugal chillers are suitable for large systems (single-unit capacity typically above 800 kW); their core advantage lies in high full-load energy efficiency, with COP reaching 6.0-7.0, as well as large single-unit capacity and small footprint. Screw chillers are suitable for medium-sized systems (300-800 kW), with a COP of approximately 5.0-5.5, featuring simple structure, stable operation and relatively good part-load performance. Magnetic bearing centrifugal chillers are energy-saving products that have developed rapidly in recent years; they use magnetic bearing technology to eliminate mechanical friction losses, offer outstanding part-load energy efficiency with an IPLV of 12.0-18.0, and are particularly suitable for scenarios such as hotels that operate under part-load conditions for extended periods. Absorption chillers (direct-fired or steam-type) can be driven by natural gas, waste heat or solar energy and are suitable for hotel projects with access to cheap gas resources or recoverable waste heat, but their COP is typically between 1.2-1.7, and their energy utilization efficiency is lower than that of electrically driven compressor chillers. From a life cycle cost (LCC) perspective, taking a five-star hotel in Shanghai as an example, over a 10-year operating cycle, the magnetic bearing centrifugal scheme (initial investment of approximately RMB 5.8 million + annual operating cost of approximately RMB 850,000, 10-year LCC of approximately RMB 14.3 million) is superior to the conventional centrifugal scheme (initial investment of approximately RMB 4.5 million + annual operating cost of approximately RMB 1.1 million, 10-year LCC of approximately RMB 15.5 million), with a payback period of approximately 3.5 years. However, magnetic bearing chillers have higher requirements for power supply quality; voltage sags may cause unit shutdown, so comprehensive consideration must be given to the hotel's power supply reliability. Article 5.2.1 of GB 50189, Design Standard for Energy Efficiency of Public Buildings, sets mandatory requirements for chiller energy efficiency grades: when the rated cooling capacity is greater than 1,163 kW, the COP of water-cooled centrifugal units shall be no lower than 5.6 (energy-saving evaluation value) and the IPLV no lower than 6.5; when the rated cooling capacity is 528-1,163 kW, the COP of water-cooled screw units shall be no lower than 5.3. The Marriott MIDS standard is even stricter, requiring the comprehensive COP of chillers to be no lower than 6.3 and the IPLV no lower than 10.5, which usually means that Grade 1 energy efficiency products or high-efficiency products such as magnetic bearing units must be selected. Regarding the choice of energy scheme, a technical and economic comparison must be carried out: the gas boiler + electric refrigeration scheme is suitable for areas with lower electricity prices; the direct-fired chiller + electric refrigeration hybrid scheme can take advantage of peak-valley electricity pricing; the heat pump + electric refrigeration scheme is suitable for hotels with heating demand. Article 7.2.8 of GB 50736 emphasizes that chiller selection should be based on a multi-scheme comparison in light of the local energy structure, and recommends the annual cost method for economic analysis.
Cooling Water and Chilled Water System Configuration Scheme
The rational configuration of the cooling water system and chilled water system is the key guarantee for the efficient operation of chillers. According to the requirements of Sections 8.6 and 8.7 of GB 50736 "Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings", system configuration must comprehensively consider multiple factors such as water temperature parameters, pump selection, piping layout, and control strategies. For the chilled water system, the standard design parameters for a five-star hotel are supply/return water temperature of 7/12°C, with a temperature difference of 5°C. However, adopting a large temperature difference design (such as 6/13°C or 5/13°C) can reduce the chilled water pump flow rate and pipe size, lowering transmission energy consumption and initial investment. Article 8.6.3 of GB 50736 stipulates that the chilled water system shall adopt a closed circulation, with pressure maintained by an expansion tank, and shall be equipped with water treatment devices. Variable-frequency drive pumps are recommended for the chilled water pumps, with PID regulation based on the differential pressure of the most unfavorable loop, and the pump frequency range should preferably be between 25-50Hz. The Marriott MIDS standard requires the chilled water pumps to adopt a Primary-Only Variable Flow system, without a traditional primary/secondary pump system, to simplify the control strategy and reduce initial investment. Each chiller corresponds to one chilled water pump in an independent matching arrangement, with a bypass pipe and differential pressure control valve installed between the supply and return water headers to ensure minimum flow protection for the chiller. The cooling water system is designed with a supply/return water temperature of 32/37°C, and the cooling tower approach temperature is generally controlled at 4-5°C. Article 8.7.2 of GB 50736 stipulates that the head of the cooling water pump shall be calculated comprehensively based on the cooling tower nozzle height, cooling water piping resistance, and condenser water resistance, typically 20-28mH₂O. Variable-frequency control is also recommended for the cooling water pumps, but attention must be paid that the lower frequency limit should not be below 30Hz to avoid uneven water distribution in the cooling tower. The cooling water system shall be equipped with an electronic descaling instrument or chemical dosing device to prevent condenser scaling that would degrade heat exchange efficiency. According to ASHRAE research data, for every 0.1mm increase in scale thickness on the condenser side, the chiller COP decreases by approximately 3%-5%. In terms of water quality management, GB 50050 "Code for Design of Industrial Circulating Cooling Water Treatment" requires the pH value of circulating cooling water to be controlled between 7.0-9.0, total hardness ≤200mg/L (as CaCO₃), and turbidity ≤20NTU. For five-star hotels, it is recommended to add a side-stream filtration device, with the side-stream filtration flow set at 1%-3% of the circulating water flow rate, to control suspended solids concentration. Regarding piping materials, galvanized steel pipes are used for chilled water pipes with nominal diameter DN≤80mm, and seamless steel pipes for DN>80mm; for cooling water pipes, due to higher oxygen content, hot-dip galvanized steel pipes or plastic-lined steel pipes are recommended to reduce corrosion risk. GB 50242 "Code for Acceptance of Construction Quality of Building Water Supply and Drainage and Heating Engineering" has clear provisions on pipe connection methods, pressure testing requirements, etc.
Technical requirements for plant room layout and equipment installation
The rational layout and standardized installation of the chiller plant room are the foundation for ensuring safe equipment operation and convenient daily maintenance. According to Section 8.10 of GB 50736 "Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings" and the relevant requirements of GB 50016 "Code for Fire Protection Design of Buildings", the design of the chiller plant room must meet multiple technical requirements including equipment spacing, ventilation and heat dissipation, drainage and waterproofing, noise control, and fire safety. Regarding plant room location selection, the chiller plant room should preferably be located on the first or second basement level, close to the load center to shorten refrigerant transmission distance and reduce pipeline cooling loss. Article 8.10.1 of GB 50736 stipulates that the refrigeration plant room should be arranged as close as possible to the cooling tower, and the one-way length of cooling water pipes should not exceed 50m to reduce the head and energy consumption of cooling water pumps. Clear height requirements for the plant room: for centrifugal chillers, there should be no less than 1.0m of maintenance space above the unit, and the clear height below the beams in the plant room should preferably not be less than 4.5m; for screw chillers, the clear height of the plant room should preferably not be less than 4.0m. Regarding equipment spacing, the distance between units and walls shall not be less than 1.0m, the aisle width between units shall not be less than 1.5m, and the main aisle width shall not be less than 2.0m. Article 8.10.4 of GB 50736 clearly stipulates that the refrigeration plant room shall be provided with equipment maintenance platforms and lifting holes, and the size of the lifting holes shall meet the transportation requirements of the largest equipment components, typically set at 3.0m×3.5m. Regarding ventilation and heat dissipation in the plant room, the refrigeration plant room shall be provided with an independent mechanical ventilation system, with the ventilation rate determined by the requirement to remove equipment heat dissipation, and the air change rate shall not be less than 6 times/h. When gas or oil-fired equipment is installed in the plant room, an explosion-proof ventilation system shall be provided, along with combustible gas concentration detectors. Section 9.3 of GB 50016 requires that when the gas concentration in the refrigeration plant room reaches 25% of the lower explosive limit, the emergency exhaust fan shall be activated in linkage, with an exhaust rate of not less than 12 times/h. Regarding noise control, the operating noise of chillers is typically 85-95dB(A), and comprehensive noise reduction measures are required: spring vibration isolators or rubber isolation pads shall be installed at the unit base, soundproof enclosures shall be added to compressors, flexible joints shall be used where pipes penetrate walls, and sound-absorbing materials shall be installed on the plant room interior walls. GB 50118 "Code for Sound Insulation Design of Civil Buildings" requires that the nighttime noise in five-star hotel guest rooms be ≤30dB(A), therefore the distance between the plant room and guest room areas shall be determined through acoustic calculation. Regarding foundation construction, equipment foundations shall be poured with concrete of C25 or above, with a foundation height of not less than 200mm, and the foundation surface shall be leveled with a levelness deviation not exceeding 2mm/m. Anchor bolt holes shall be reserved in each unit foundation, with the hole depth and diameter determined according to the equipment installation drawings. GB 50231 "General Code for Construction and Acceptance of Mechanical Equipment Installation Engineering" requires that the levelness deviation after equipment installation shall not exceed 1/1000.