Math Blocks — Add, Subtract, Multiply, Divide

Addition (+) — Monthly EB Bill

Three sections of an office floor:

Section A = 35 people
Section B = 28 people
Section C = 32 people
Total     = 35 + 28 + 32 = 95 people

BMS example — total building energy:

Floor 1 meter = 450 kWh
Floor 2 meter = 380 kWh
Floor 3 meter = 520 kWh
Total         = 1,350 kWh → shown on energy dashboard

Subtraction (-) — Home Water Tank Consumption

Morning tank level = 85%
Evening tank level = 42%
Consumed today    = 85 - 42 = 43%

BMS example — filter differential pressure:

Pressure before filter = 250 Pa
Pressure after filter  = 180 Pa
Differential           = 70 Pa → if above 150 Pa → alarm: change filter

Multiplication (×) — Air Flow Calculation

Air velocity in duct = 4.5 m/s (from velocity sensor)
Duct cross-section area = 0.8 m² (fixed value)
Volume flow rate  = 4.5 × 0.8 = 3.6 m³/s

BMS uses this to verify AHU is delivering correct airflow against design.

Division (÷) — Average Zone Temperature

Zone 1 = 23°C, Zone 2 = 25°C, Zone 3 = 24°C, Zone 4 = 26°C
Sum    = 98°C
Average = 98 ÷ 4 = 24.5°C → Used for chiller plant optimisation

One faulty sensor does not drive the whole system wrong. Average of four sensors gives true floor temperature.

Related Topics

• What is BMS integration? — how a BMS connects with VFDs, energy meters, BACnet/Modbus devices and other building systems
• How to design a BMS system step by step — the complete BMS design methodology covering site survey, IO list, controller selection, sequence of operations
• What is a Building Management System (BMS)? — fundamentals of BMS controls and architecture for HVAC, lighting, energy and access
• What is BMS commissioning? — the disciplined commissioning process that turns a BMS install into a working building brain
• Browse all Control Loops & FBD topics — more from this section of the EnSmart BMS Library