HVAC Design for Aquatic Stadiums — Natatorium Design Guide India

HVAC Design

HVAC Design for Aquatic Stadiums — Natatorium Design Guide

Aquatic facility HVAC design is one of the most technically demanding specialisations in the MEP field. The combination of high latent load from pool evaporation, corrosive chloramine atmosphere, very high ceiling volumes, and the need to maintain strict thermal comfort for both swimmers and spectators makes natatorium design a unique engineering challenge.

1. Understanding the Natatorium Environment

Parameter	Indoor Pool (Competition)	Leisure Pool	Spectator Area
Air temperature	27–29°C (1–2°C above water temp)	29–31°C	20–22°C (cooler — sedentary)
Relative humidity	50–60%	55–65%	40–55%
Water temperature	26–28°C (competition)	28–32°C (leisure)	N/A
Air velocity at pool deck	<0.25 m/s — avoid draft on swimmers	<0.3 m/s	<0.5 m/s
Fresh air	Minimum ASHRAE 62.1 or NBC requirement	Same	Per occupancy load

2. Evaporation Load Calculation

The pool water surface is the primary source of latent load. The Shah equation (simplified) estimates pool evaporation:

E = A × (0.1 + 0.3V) × (Pw – Pa) / 100

Where: E = evaporation rate (kg/hr), A = pool surface area (m²), V = air velocity over water (m/s), Pw = saturation pressure at water temp (Pa), Pa = partial pressure of water vapour in room air (Pa)

Pool Type	Typical Evaporation Rate	Latent Load Impact	Design Basis
Competition pool (50m × 25m)	80–120 kg/hr	High — dominates system load	Full dehumidification system required
Training pool (25m × 15m)	30–50 kg/hr	Moderate	Dedicated pool dehumidifier + OA
Leisure pool (wave, children)	40–70 kg/hr (per 1000 m²)	High — active splashing	High evaporation rate factor
Hot tub / spa (40°C water)	15–25 kg/hr per unit	Very high — high water temp	Enclosed with separate exhaust

3. Dehumidification System Options

System	How It Works	Best For	Energy Implication
Refrigerant-based dehumidifier (DX)	Condensation on cooling coil	Small to medium pools	Moderate energy — heat recovery from condensation possible
Heat pump dehumidifier	DX + heat recovery to pool water or air	All sizes — recommended	Best energy efficiency — heat recovered
100% OA system	Dilute humidity with dry outdoor air	Climates with dry ambient (Delhi winter)	High energy in humid climates — not viable in Mumbai
Desiccant wheel	Chemical adsorption of moisture	Extreme humidity control, spas	High energy — regeneration heat required

4. Air Distribution in Natatoriums

Air distribution is critical — improper design causes condensation on windows and structural elements, discomfort to swimmers, and poor corrosive atmosphere control.

Supply air from below spectator level or from side walls — avoid top-down supply over pool
Floor-level supply diffusers around pool deck perimeter — low velocity discharge (< 0.5 m/s)
Extract at high level — removes moist warm air from the ceiling zone where condensation risk is greatest
Positive pressure relative to changing rooms and corridors — prevents chloramine migration
Dedicated supply to spectator tier — separate zone, cooler temperature

5. Corrosion Protection — Chloramine Environment

Chloramines (formed when chlorine reacts with nitrogen in urine, sweat, and other organic matter) are highly corrosive and damaging to HVAC equipment. All equipment in the pool hall must be specified for corrosive environment:

AHU casings: fibreglass or stainless steel — never galvanised sheet metal
Coil fins: copper tubes with stainless steel or phenolic-coated aluminium fins — not standard aluminium
Fan wheels: fibreglass or stainless steel — no carbon steel or aluminium
Ductwork: fibreglass duct or hot-dip galvanised with epoxy coating
Controls and sensors: IP65 minimum — sealed against chloramine penetration

6. Energy Recovery

Natatoriums have large volumes of warm, humid exhaust air. Energy recovery is critical for efficient operation:

Runaround coil system: indirect heat recovery — no cross-contamination (chloramines in exhaust)
Heat pump dehumidifier: recovers latent heat — heats pool water or supply air
DO NOT use rotary heat wheels in natatoriums — chloramines transfer from exhaust to supply

HVAC Design for Aquatic Stadiums — Natatorium Design Guide India