Project Background
A commercial complex in GuangZhou,comprising a 38-storey office tower and a connected retail podium with a total gross floor area exceeding 120,000 m²,was experiencing persistently high electricity costs from its HVAC system.The building’s mechanical and electrical installation included eight chilled water pumps(ranging from 55kW to 110kW),twelve AHU supply and return air fans,and six cooling tower fans—all operating at fixed speed under the original design.
The building’s BMS(Building Management System)data showed that the HVAC system was running at or near full capacity for less than 15%of annual operating hours.For the remaining 85%of the time—including nights,weekends,and shoulder seasons—motors were running at full speed against a partial load,a classic symptom of oversized fixed-speed HVAC design.Chilled water differential pressure was difficult to maintain consistently,tenant comfort complaints were frequent,and the building’s energy performance rating was well below the benchmark expected for a Grade A commercial property in the region.
Solution
Goalliance was contracted to engineer and deliver a full HVAC variable speed drive upgrade covering all major motor-driven subsystems.The project was executed in phases to avoid disruption to building occupants and ongoing retail operations.
Chilled Water Pump System
All eight chilled water pumps were retrofitted with Schneider Electric Altivar Process VFDs,selected for their built-in pump and fan control algorithms,advanced energy-saving modes,and native BACnet/Modbus communication capability.The primary and secondary chilled water circuits were configured under differential pressure reset control—a strategy that continuously adjusts pump speed to maintain the minimum differential pressure required to satisfy the most-loaded zone in the building,rather than maintaining a fixed setpoint regardless of actual demand.This approach eliminates the chronic over-pumping that is typical in fixed-pressure primary-secondary chilled water systems,and delivered the largest single energy saving of the entire project.
AHU Fan Systems
The twelve AHU supply and return air fans were equipped with Siemens SINAMICS G120 series drives,integrated with the building’s existing CO₂and temperature sensors to implement demand-controlled ventilation(DCV).Under DCV logic,fan speed is modulated in real time based on occupancy-driven CO₂concentration and zone temperature feedback,delivering precisely the volume of conditioned air each zone requires at any given time—no more,no less.This is particularly effective in office environments where occupancy varies significantly throughout the day and across different floors and zones.
Cooling Tower Fan System
The six cooling tower fans were fitted with INOVANCE MD500 series VFDs under wet-bulb temperature reset control—automatically adjusting fan speed to maintain optimal condenser water supply temperature based on ambient conditions rather than running at fixed speed year-round.In Vietnam’s tropical climate,where ambient temperatures and humidity vary significantly between day and night and across seasons,this strategy produces consistent energy savings while protecting the refrigeration cycle from the efficiency losses caused by over-cooling condenser water.
BMS Integration
All VFD systems were fully integrated into the building’s Johnson Controls Metasys BMS platform via BACnet/IP protocol,enabling centralised monitoring of drive status,energy consumption,fault diagnostics,and setpoint adjustment from the building management console.A custom energy dashboard was configured to display real-time kW consumption,cumulative kWh savings against the pre-retrofit baseline,and system efficiency metrics—giving the building management team full visibility of HVAC energy performance at all times.
Results
- Overall HVAC system energy saving rate:41%across all subsystems
- Chilled water pump subsystem energy reduction:47%
- AHU fan subsystem energy reduction:38%
- Cooling tower fan subsystem energy reduction:35%
- Chilled water differential pressure stability significantly improved—tenant comfort complaints reduced by over 80%
- Building energy performance rating upgraded,supporting Green Building certification requirements
- Full investment payback period:26 months
- Estimated annual CO₂reduction:approximately 590 tonnes
