HVAC construction design of an international trade city
Introduction XX International Trade City Phase II Project is located in Block E of the International Trade City Park, with a total construction area of about 540000 square meters. It is composed of two market trading areas, F and G (including 1 # connector). The main building has six floors, including one underground floor and five floors above the ground. The floor height is 4.5-5.1 meters. The structure type is full frame and full cast-in-place. The civil works were commenced on September 20, 2003 and completed on September 20, 2004. The HVAC installation project within the scope of this bidding consists of two bid sections, namely, Zone F and Zone G (including 1 # connector), with a building area of about 260000 square meters in Zone F and 290000 square meters in Zone G (including 1 # connector). The HVAC installation works in each bid section are divided into three systems: air conditioning system, ventilation system, fire smoke control and smoke exhaust system (constructed by the fire construction unit). The basement is a garage, equipment room, etc. In wartime, it was used as a shelter for Class VI civil air defense personnel. The mechanical forced ventilation system is set. The exhaust air volume is calculated as per 6 air changes, and the supply air volume is calculated as per 5 air changes. The exhaust system is also used as the mechanical smoke exhaust system in case of fire, and the air supply system is also used as the air supplement system in case of fire. Smoke exhaust fan and forced draft fan are located in the interlayer at the top of the basement, with a clear height of 2.3m from the bottom of the interlayer to the ground. The floor slab in the interlayer is designed without beams, and the bottom is opened with manholes to facilitate transportation, equipment installation and maintenance. A ductless induction ventilation system is set on the top of the garage, which is combined with the mechanical ventilation system to improve the air quality of the garage. The exhibition and trading areas on the first to third floors are central air conditioning systems. A centralized refrigerator room is set on the basement. The units are water-cooled centrifugal chillers. The large space air conditioning of the exhibition and trading area is realized by the assembled variable air volume air handling unit, which adopts the primary return air mode. The assembled variable air volume air handling unit consists of fresh air and return air mixed filtering and silencing section (bag filter), surface cooling section (including water baffle), forced draft fan section (equipped with multi speed motor), and air supply and silencing section, which are respectively located in the air handling room on the basement and the fifth floor. The air duct passes through the floor through the independent fire shaft, and insulation air duct is respectively laid in the ceiling, and the top diffuser is used for air supply, Each business location is equipped with a diffuser with air volume control valve, and the lower part of the public walkway is centralized to return air to the air conditioning room. The business negotiation area on the fourth to fifth floors is a small household central air conditioning system, which uses air-cooled heat pump pipe type air conditioning units. The indoor unit shall be connected to the air supply plenum by hose and supplied with air by diffuser. Units above 14KW still use air duct for air supply to avoid air volume imbalance. The outdoor units are required to be in the form of upward blowing to adapt to the heat dissipation condition of the roof. In this project, the outdoor unit is higher than the indoor unit. The allowable height difference between the outdoor unit and the indoor unit is not less than 15m, and the allowable equivalent length of the connecting pipe of the indoor and outdoor unit is not less than 50m. The air conditioning circulating water system adopts the traditional primary pump constant speed variable flow system, and the supply and return water temperatures in summer are 7 ℃ and 12 ℃. Due to the huge scale of the project, the refrigerating machine room and air handling machine room are set in a centralized manner, and the water consumption of a single air handling unit is huge. Once the unit is shut down for maintenance, it will cause a large hydraulic imbalance. The design requires that ZL-4M (ZL47F) series self operated flow balance valves be used at the water side of the air handling unit to solve the hydraulic balance of the system pipeline. Circulating water pipe materials shall be selected. When the pipe diameter is less than 100mm, galvanized steel pipe shall be used, and standard accessories shall be connected with screw threads. When the pipe diameter is greater than 100 mm, the seamless steel pipe shall be used for trial installation and hot galvanized secondary installation, and welded, flanged or standard grooved pipe joints shall be used for connection. When the pipe diameter is greater than 600mm, the thickness of spiral seam electric welded steel pipe is 13mm. As the working pressure of the air conditioning circulating water pipe in this project is 1.0MPa, the pressure resistance grade of fittings and valves is 1.6MPa. The insulation of the pipeline system shall be made of Class B1 incombustible rubber and plastic materials. When the pipe diameter is less than DN50 and the thickness is 19mm; When the pipe diameter is DN70-DN80, the thickness is 25mm; When the pipe diameter is DN100-DN200, the thickness is 32mm plate; When the pipe diameter is DN250-DN400, the thickness is 40mm plate; When the pipe diameter is DN600, the thickness is 50mm plate. In addition to the insulation layer, the exposed part shall also be provided with 1.2mm thick aluminum alloy protective shell, and the joints shall be overlapped and fixed with M3 tapping screws. All ventilation ducts, exhaust ducts and air conditioning ducts in the exhibition and trading areas on the first to third floors of the project shall be made of galvanized steel plate, and the thickness shall be determined according to the national general air duct standards. Flanged or seamed connections shall be made. Wide and flat air ducts shall be strengthened. The air duct shall be insulated with Class B1 incombustible rubber and plastic materials with a thickness of 20mm. The air conditioning ducts in the business negotiation area on the fourth to fifth floors adopt the composite glass fiber silencing and thermal insulation duct (SUPER DUCT).
