Common HVAC System Design Issues
Issue 1: Deviation in heating and cooling load calculation — the common cause is using index estimation instead of the hourly load calculation required by GB 50736. Solution: Strictly implement the hourly calculation method using EnergyPlus/HAP, with particular attention to kitchen loads (350-450W/m2), banquet hall full loads (300-350W/m2), and lobby solar radiation heat gain. Issue 2: Hydraulic imbalance in water pipe systems — commonly caused by the absence of detailed hydraulic calculations and the failure to install balancing valves. Solution: Clause 8.5.9 of GB 50736 requires hydraulic balancing devices in water systems, with a dynamic balancing electric control valve on each branch and a reverse-return layout for water piping design. Issue 3: Resistance imbalance in duct systems — commonly caused by the absence of guide vanes at branch tees. Solution: Detailed pipe resistance calculation (specific frictional resistance 1-3Pa/m), installation of guide vanes at branch tees, and a volume control damper at each air outlet. Issue 4: Design errors in smoke control and exhaust systems — commonly caused by insufficient spacing between smoke exhaust outlets and supply air outlets (should be no less than 20m) and smoke exhaust ducts not being installed independently. Solution: Strictly implement the requirements of GB 50016. Issue 5: Unreasonable design of condensate drainage pipes — commonly caused by insufficient slope and undersized pipe diameter. Clause 8.5.22 of GB 50736 requires a drainage pipe slope of no less than 8‰ and a main collection pipe of no less than 5‰.
Common Issues in Electrical and Extra-Low-Voltage Systems
Issue 1: Insufficient power supply capacity or unreasonable load distribution — commonly caused by later-added equipment exceeding the design margin. Solution: Reserve 15%-20% of distribution capacity in design, reserve 20%-25% of circuit positions in distribution cabinets, conduct regular load analysis, and optimize three-phase balance. Issue 2: Excessive neutral-to-ground voltage causing instability of IT equipment — GB 50174 requires neutral-to-ground voltage below 2V (for important IT equipment). Solution: Adopt the TN-S five-wire system with strict separation of the N line and PE line. Issue 3: Low integration of intelligent systems leading to information silos — commonly caused by BAS, RCU, and fire alarm systems being independent of each other. Solution: Design the IBMS platform according to the Grade A standard of GB 50314, achieving interconnection through BACnet/IP. Issue 4: Lamp flicker and inconsistent color temperature — commonly caused by poor-quality LED drivers (flicker depth >30%). Solution: Select high-quality drivers compliant with GB/T 24823 (flicker depth <5%), with color temperature consistency within MacAdam 3-step SDCM. Issue 5: RCU execution deviation — commonly caused by misjudgment of card insertion signals and abnormal communication between thermostats and the RCU. Solution: The RCU system adopts CAN bus or RS485 communication, with control logic parameters settable from the back end.
Common Issues in Plumbing and Fire Protection Systems
Issue 1: Excessive waiting time for hot water — commonly caused by unreasonable circulation system design or insufficient circulation pump flow. GB 50015 requires no more than 10 seconds; Marriott MIDS requires no more than 5 seconds. Solution: Optimize the circulation network with the most unfavorable loop not exceeding 50m, variable-frequency control of circulation pumps, return water temperature of 60°C, and thermostatic valves on branch pipes. Issue 2: Drainage pipe blockage and odors — commonly caused by insufficient main pipe slope and destruction of the water seal in traps. GB 50015 requires a minimum drainage pipe slope of no less than 0.012 for DN100. Solution: Strictly control the slope, install a dedicated vent stack in buildings over 10 stories, and ensure the water seal depth of traps is no less than 50mm. Issue 3: Conflict between fire sprinklers and ceiling elevation — commonly caused by sprinklers not being adjusted in sync after fine-decoration ceiling adjustments. Solution: Conduct coordinated detailed design of sprinklers and ceilings before fine decoration; use pendant sprinklers where ceiling height is less than 3.5m and upright sprinklers where greater than 3.5m. Issue 4: Improper setting of fire pump start pressure — commonly caused by pressure switches not being adjusted according to actual hydraulic conditions. Solution: Set the jockey pump at static pressure + (5-10mH2O) and the main pump at static pressure - (5-10mH2O).
Common Issues in Pipeline Coordination and Construction Coordination
Issue 1: Insufficient clear height control leading to compressed ceiling height — commonly caused by insufficient depth of BIM pipeline coordination. Solution: Set clear height control lines in the LOD350-precision BIM model at the design stage (guest room corridors no less than 2.4m, lobby no less than 3.5m, banquet hall no less than 4.5m). Prioritize the elevation of large-cross-section ducts; water pipes and cable trays should yield, passing through beams or along walls. Issue 2: Conflict between MEP points and fine-decoration finishes — commonly caused by conflicts among air outlets, sprinklers, and luminaires with fine-decoration modeling. Solution: Recheck MEP terminals after fine-decoration detailing, use BIM clash detection, maintain spacing between air outlets and luminaires of no less than 300mm and between sprinklers and luminaires of no less than 300mm. Issue 3: Omissions in reserved openings and embedded parts leading to later drilling — commonly caused by failure to check reserved openings during the structural construction stage. Solution: Prepare dedicated drawings for reserved openings and embedded parts, including the positioning of all wall sleeves and equipment foundation reservations. Issue 4: Chaotic construction sequence leading to damage to finished products — commonly caused by drilling for MEP after fine-decoration finishes are completed. Solution: Strictly implement process management: structural construction → main pipeline installation → branch pipe installation → wiring → terminal positioning → fine-decoration ceiling → closing.