Unit IVBuilding Services for Special Buildings

HVAC & Ventilation

Cooling a sealed tower — and breathing life into its basements.

≈ 40 min + studio task

A modern glass tower is a sealed box that would cook in the sun without mechanical cooling, and suffocate in its basement without mechanical ventilation. Learn the central air-conditioning plant and the refrigeration cycle behind it — including the ton of refrigeration that is a rate of cooling, not a weight — then the air changes per hour that keep a car park, a kitchen and a toilet fit to breathe.

Learning objectives

By the end of this lesson, you will be able to — mapped to the course outcomes for Building Services for Special Buildings:

CO4 · Understand

Describe the central air-conditioning plant and the refrigeration cycle.

CO4 · Understand

Define the ton of refrigeration and compare chiller types.

CO4 · Apply

Apply VRV/VRF and packaged systems to building zones.

CO4 · Apply

Apply mechanical ventilation and air changes per hour.

Chillers, AHUs, the TR

The central plant

Chillers make chilled water by the refrigeration cycle; cooling is sized in the ton of refrigeration — a RATE (1 TR = 3.517 kW), not a weight.^[6]

DiagramThe refrigeration cycle — evaporator, compressor, condenser and expansion valve

DiagramThe ton of refrigeration is a rate of cooling — 1 TR = 12,000 BTU/hr = 3.517 kW

Chillers, AHUs, ducts

A large building is cooled by a CENTRAL PLANT. CHILLERS make chilled water by the refrigeration cycle (evaporator → compressor → condenser → expansion valve); AIR-HANDLING UNITS (AHUs) pass building air over chilled-water coils and push it through DUCTS to diffusers. AIR-COOLED chillers reject heat to the air (simple, no water); WATER-COOLED chillers with COOLING TOWERS are 30–40% more efficient for large loads. VRV/VRF systems serve mid-size zones with refrigerant directly; packaged and split units serve small ones.^[6]

Air changes & shafts

Ventilation & integration

Windowless spaces need mechanical ventilation (air changes per hour — basement ~6 normal, ~12 fire); and HVAC shapes the building, so design with it.^{[6, 4]}

DiagramBasement car-park ventilation — about 6 air changes per hour normally, 12 in fire mode

Air changes per hour

Where there is no window — a basement car park, an internal kitchen, a toilet — air must be moved MECHANICALLY, measured in AIR CHANGES PER HOUR (ACH), the number of times the room's whole air volume is replaced each hour. NBC 2016 requires a basement car park to have about 6 ACH in normal use, rising to 12 ACH in smoke/fire mode to clear smoke. Kitchens and toilets need high exhaust. Fresh-air supply (per ASHRAE 62.1) keeps the occupied air healthy.^{[6, 4]}

The HVAC facts

At a glance

Aspect	One	The other
Chiller type	Air-cooled: simple, no water	Water-cooled + tower: 30–40% efficient
The cooling unit	Myth: TR = a weight of metal	Reality: a RATE — 1 TR = 3.517 kW
System scale	Central chillers + AHUs: whole building	VRV/VRF, split: zones / small spaces
Ventilation measure	ACH: air volume replaced per hour	Basement: ~6 normal, ~12 fire (NBC)
Relation to design	Plant room, shafts, floor height	HVAC shapes the building, not vice versa

Vocabulary

Key terms

Chiller

The plant that makes chilled water by the refrigeration cycle — air- or water-cooled.

Air-handling unit (AHU)

Passes building air over chilled-water coils and pushes it through ducts.

Cooling tower

Rejects a water-cooled chiller's heat to the air — 30–40% more efficient for large loads.

Ton of refrigeration (TR)

A RATE of cooling — 1 TR = 12,000 BTU/hr = 3.517 kW (heat to melt 1 ton of ice in 24 h).

VRV / VRF

Variable refrigerant flow — refrigerant-based system serving multiple mid-size indoor zones.

Air changes per hour (ACH)

How many times a room's whole air volume is replaced each hour.

Basement ventilation

~6 ACH normal, ~12 ACH in fire/smoke mode for a car park (NBC 2016).

Fresh-air supply

Outdoor air (per ASHRAE 62.1) brought in to keep the occupied air healthy.

Apply it

Studio task

For an office floor, estimate the cooling load in tons of refrigeration (rule of thumb ~1 TR per ~10 m²) and sketch where the AHU room, the chilled-water risers and the duct routes would go — then show how the basement is ventilated.

Check your understanding

Self-assessment

1. One ton of refrigeration (1 TR) is —

2. Compared with an air-cooled chiller, a water-cooled chiller with a cooling tower is —

3. NBC 2016 requires a basement car park to be ventilated at about — in normal use.

In a nutshell

Recap

A central plant cools a large building — chillers make chilled water, AHUs and ducts distribute it; water-cooled chillers are 30–40% more efficient than air-cooled.

Cooling is sized in the ton of refrigeration — a RATE (1 TR = 3.517 kW), not a weight; VRV/VRF and split units serve smaller zones.

Windowless spaces need mechanical ventilation, measured in air changes per hour — a basement car park ~6 ACH normal, ~12 in fire mode (NBC).

HVAC shapes the building — plant rooms, shafts and floor heights — so the architect must design with the services, not around them.

The evidence

References & further reading

[4]National Building Code of India 2016, Part 8 Section 3 — Air Conditioning, Heating and Mechanical Ventilation. BIS.
[6]ASHRAE Handbook — HVAC Systems and Equipment; and the ton-of-refrigeration definition. https://en.wikipedia.org/wiki/Ton_of_refrigeration