BMS Implementation in a Dhaka Commercial Office Tower: 28% HVAC Energy Reduction in 18 Months

The building's monthly electricity bill had averaged BDT 18 lakh per month over the 12 months preceding the BMS project — a figure that placed the building in the top quartile of per-square-metre electricity consumption among Banani commercial office buildings of comparable vintage, based on the property manager's benchmarking against peer properties in their portfolio.

The core operational problem was simple: HVAC ran on fixed timer schedules that bore no relationship to actual building occupancy. The chiller plant started at 07:00 and ran until 21:00, seven days a week — including weekends when the building was occupied only by skeleton staff (typically 20-30 persons on a Saturday, zero on Sunday). AHUs on all 14 office floors ran at full capacity from 07:00 to 21:00, regardless of whether any tenant staff were in the office. During public holidays, which occur approximately 20 days per year in Bangladesh, the HVAC ran on the same schedule — cooling an empty building at full capacity.

The chiller sequencing was particularly inefficient. The building's three chillers were controlled manually: the building engineer would start all three chillers at 07:00 and shut them down at 21:00. During early morning hours (07:00-09:00, before most tenants arrived) and late evening hours (18:30-21:00, as tenants departed), two of the three chillers were running at well below 30% load — an operating condition that is thermodynamically inefficient for centrifugal chillers, which perform most efficiently in the 70-90% load range. Running three chillers at 25% load is significantly less efficient than running one chiller at 75% load.

The property manager had attempted to address the weekend HVAC waste by relying on the building engineer to manually switch off AHUs on unoccupied floors each Friday evening and restart them on Monday morning. This procedure was inconsistently followed — the building engineer's evening shift ended at 20:00, and if the engineer was occupied with a maintenance task or had finished a shift early, the Friday shutdown procedure was often skipped. On average, the building engineer estimated that the manual weekend shutdown was successfully completed only 4 out of every 10 weekends.

Tenant sub-metering was a separate but related problem. The building's electricity was supplied through a single main meter, and tenant billing was calculated based on floor area — a rough approximation that created significant inequity between tenants with different operational hours and different energy-intensive equipment. The bank's floors, which operated extended hours and had significant UPS, server, and banking equipment loads, were believed to be systematically under-billed relative to their actual consumption, while the NGO floors — which operated standard office hours with minimal equipment — were likely over-billed. This created ongoing tenant relations friction and, in the case of the bank, a formal billing dispute that the property manager had been unable to resolve without sub-meter data.

SSAL deployed a complete Building Management System based on Honeywell EBI, with 1,200 DDC (Direct Digital Control) control points covering the chiller plant, all floor-level AHUs, tenant sub-metering, and ancillary building services.

Honeywell EBI Platform: The Honeywell EBI BMS server was installed in the building's ground floor plant management office, with the BMS operator workstation providing real-time graphical displays of all building systems, trend logging for all control points, alarm management, and energy reporting. The EBI platform communicates to field controllers via BACnet/IP over the building's existing Cat6 data infrastructure, which SSAL extended to reach the plant rooms and each floor's AHU control panels.

Chiller Plant Sequencing Control: All three chillers were integrated into the BMS via the chillers' BACnet interfaces (all three units had BACnet-capable controllers from their original installation). The BMS now manages chiller sequencing based on cooling load demand rather than manual operation. A chiller sequencing algorithm starts the first chiller at building open time, monitors return water temperature and load percentage, and starts additional chillers only when the running chiller's load exceeds 75% — the efficiency threshold above which a second machine is more efficient than a single overloaded machine. During the low-occupancy weekend periods, the algorithm runs on a reduced-setpoint schedule that typically requires only one 100TR chiller to maintain acceptable comfort temperatures, with the two larger chillers remaining off. Cooling tower fan speed is modulated by VFD (Variable Frequency Drive) control from the BMS, further improving plant efficiency.

AHU Occupancy-Based Control: All 112 AHUs across the 14 office floors (8 AHUs per floor) are controlled by the BMS through DDC controllers at each floor's AHU plant room. The AHU control program implements:

Occupied Schedule: Monday-Friday 08:00-19:00, AHUs run at demand-based variable air volume (VAV), modulated by return air temperature and CO2 sensor feedback.

Unoccupied Schedule: Weekdays before 08:00 and after 19:00, weekends, and public holidays: AHUs shut down or run at minimum ventilation (10% air volume for code compliance). Pre-cooling starts at 07:30 to bring the floor to setpoint before occupants arrive.

Weekend and Holiday Override: Any tenant requiring HVAC access outside the standard schedule can request a temporary override via a web-based tenant portal or by contacting the building management office. Overrides are logged and the energy consumed during override periods is attributed to the requesting tenant in the sub-metering billing.

Tenant Energy Sub-Metering: Honeywell EBI's energy management module was integrated with 14 digital energy meters (one per office floor), installed at each floor's main distribution board. The meters transmit real-time consumption data to the EBI platform via Modbus TCP. Monthly energy consumption reports are automatically generated per floor, with consumption attributed to each tenant based on floor-level meter readings rather than area allocation. The bank's floors are now billed on actual sub-meter consumption — which, as expected, is significantly higher per square metre than the previously allocated amount. The billing dispute has been resolved with actual data.

Energy Dashboard: A dedicated energy management dashboard within EBI displays real-time electricity consumption by floor, hourly and daily consumption trends, chiller plant efficiency (kW/TR), and rolling monthly comparison against the pre-BMS baseline. The dashboard is accessible to the property manager and to each tenant (with access restricted to their own floor's data) via a web browser, enabling tenants to monitor their own energy consumption.