Building Services Engineering: Cooling Loads, Lighting, Water, Drainage and Fire
Building Services Engineering in IESL Part III tests the design and coordination of the environmental, electrical and plumbing systems inside a building: air conditioning and ventilation, lighting, water supply and drainage, fire protection, lifts and the building's electrical distribution.
Core rules and concepts
- Cooling load is built up from conduction through fabric, solar gain through glazing (use shading coefficients), internal gains from people, lights and equipment, and ventilation outdoor air with both sensible and latent components. The sensible heat ratio SHR = sensible/(sensible + latent) determines the supply air condition and apparatus dew point.
- Psychrometric states are fixed by any two of dry-bulb, wet-bulb, dew point, humidity ratio and enthalpy; the coil process line must reach the room load line.
- Lighting design by the lumen method: N = (E × A)/(Φ × CU × LLF) for maintained illuminance E, area A, luminaire flux Φ, coefficient of utilisation CU and light loss factor LLF.
- Water supply: convert fixture units to probable simultaneous demand; check residual pressure at the most remote outlet, plus static head and friction losses.
- Drainage: falls of about 1:60 to 1:100 for branch wastes, vent pipes to protect trap seals, and no trap should be double-swilled.
- Fire: sprinkler design density over the assumed operating area, hydrant/hose reel coverage, and smoke ventilation rates.
Worked example
A 10 m × 8 m office (80 m²) needs 500 lux maintained. Luminaires deliver 4000 lm each, CU = 0.60 and LLF = 0.80. Required flux = 500 × 80 = 40 000 lm. Flux per luminaire in service = 4000 × 0.60 × 0.80 = 1920 lm. N = 40 000/1920 = 20.8, so specify 21 luminaires, arranged in a layout that gives acceptable uniformity rather than merely the count.
Traps that cost marks
Adding ventilation latent gain into the room sensible load; using the volume-based air-change method for a design cooling load; confusing lux with lumens; omitting the light loss factor; quoting pump head in kPa without converting to metres; and ignoring diversity in water demand.