Turbine Hall Ventilation

Turbine Hall Ventilation

Turbine hall ventilation systems manage massive convective and radiant heat loads from steam turbines, generators, and auxiliary equipment while maintaining acceptable conditions for personnel and equipment operation. A typical 500 MW steam turbine installation releases 3-5 million Btu/hr of sensible heat to the space through surface radiation and convection from turbine casings (400-600°F surface temperatures), generator enclosures (140-180°F), condensers, feedwater heaters, and piping systems. Ventilation design relies on thermal stratification, utilizing natural stack effect through high-bay configurations (60-120 ft ceiling heights) combined with mechanical exhaust to remove heat at elevated levels while supplying conditioned air at working zones.

Heat Load Analysis

Equipment Heat Dissipation

Steam turbine casing losses:

Radiant and convective heat transfer from turbine surfaces:

$$Q_{turb} = A \times (h_r + h_c) \times (T_s - T_a)$$

Where:

• $A$ = Surface area of turbine casing (ft²)
• $h_r$ = Radiation heat transfer coefficient (Btu/hr-ft²-°F)
• $h_c$ = Convection heat transfer coefficient (Btu/hr-ft²-°F)
• $T_s$ = Surface temperature (°F)
• $T_a$ = Ambient air temperature (°F)

Typical turbine heat dissipation values:

Combined heat transfer coefficient calculation:

Radiation component:

$$h_r = \epsilon \sigma \times \frac{(T_s^4 - T_a^4)}{(T_s - T_a)}$$

For typical insulated surfaces: $\epsilon = 0.85-0.90$, $h_r = 1.5-2.5$ Btu/hr-ft²-°F

Natural convection component:

$$h_c = 0.27 \times \left(\frac{\Delta T}{L}\right)^{0.25}$$

For vertical surfaces: $L$ = characteristic height, $h_c = 0.8-1.4$ Btu/hr-ft²-°F

Total heat load estimation:

For a 500 MW combined cycle installation:

$$Q_{total} = Q_{turb} + Q_{gen} + Q_{aux} + Q_{lights} + Q_{solar}$$

Typical breakdown:

• Steam turbines: 1,800,000 Btu/hr
• Generator: 1,200,000 Btu/hr
• Auxiliary equipment (pumps, piping): 800,000 Btu/hr
• Lighting and electrical: 200,000 Btu/hr
• Solar gain through roof: 500,000 Btu/hr
• Total: 4,500,000 Btu/hr

Temperature Stratification

Turbine halls exhibit strong vertical temperature gradients due to buoyancy-driven flows:

Stratification height calculation:

$$\Delta T_{strat} = \frac{Q}{1.08 \times A_{floor} \times V_{vent}}$$

Where:

• $Q$ = Total heat load (Btu/hr)
• $A_{floor}$ = Floor area (ft²)
• $V_{vent}$ = Ventilation air velocity (ft/min)

Typical temperature profile:

Roof Ventilator Design

Natural Ventilation Capacity

Stack effect driving pressure:

Buoyancy pressure differential drives airflow through roof ventilators:

$$\Delta P_{stack} = 7.64 \times H \times \left(\frac{1}{T_o} - \frac{1}{T_i}\right)$$

Where:

• $\Delta P_{stack}$ = Stack pressure (in w.c.)
• $H$ = Height from inlet to outlet (ft)
• $T_o$ = Outside air temperature (°R = °F + 460)
• $T_i$ = Inside air temperature at roof level (°R)

Example calculation:

For a 100 ft tall turbine hall with:

• Outside air: 95°F (555°R)
• Roof level air: 140°F (600°R)

$$\Delta P_{stack} = 7.64 \times 100 \times \left(\frac{1}{555} - \frac{1}{600}\right) = 0.104 \text{ in w.c.}$$

Ventilator airflow capacity:

$$Q = 9290 \times A_{throat} \times C_d \times \sqrt{\Delta P_{stack}}$$

Where:

• $Q$ = Airflow rate (CFM)
• $A_{throat}$ = Free area of ventilator throat (ft²)
• $C_d$ = Discharge coefficient (0.60-0.75 for typical ventilators)

For $A_{throat} = 50$ ft², $C_d = 0.65$:

$$Q = 9290 \times 50 \times 0.65 \times \sqrt{0.104} = 97,600 \text{ CFM per ventilator}$$

Roof Ventilator Sizing

Number of ventilators required:

$$N_{vent} = \frac{Q_{total,removal}}{Q_{unit}}$$

Where:

• $Q_{total,removal}$ = Total airflow needed for heat removal (CFM)
• $Q_{unit}$ = Capacity per ventilator unit (CFM)

Heat removal airflow requirement:

$$Q_{air} = \frac{Q_{heat}}{1.08 \times \Delta T}$$

For 4,500,000 Btu/hr with allowable 35°F temperature rise:

$$Q_{air} = \frac{4,500,000}{1.08 \times 35} = 119,000 \text{ CFM}$$

Ventilator selection:

Natural ventilators at 97,600 CFM each:

$$N_{vent} = \frac{119,000}{97,600} = 1.22 \rightarrow 2 \text{ units minimum}$$

Practical design approach:

Power plant turbine halls typically employ 4-8 gravity roof ventilators sized at 30-60% of total requirement, supplemented by mechanical exhaust fans for:

• Low ambient temperature conditions (reduced stack effect)
• Peak heat load periods
• Smoke removal during fire events
• Startup and shutdown operations

Typical roof ventilator specifications:

Equipment Cooling Zones

Generator Hydrogen Cooling

Generators require dedicated cooling systems independent of hall ventilation:

Hydrogen-cooled generators:

• Hydrogen pressure: 60-75 psig
• Heat removal: 800-1,500 Btu/hr per kW generator output
• Heat exchangers: Air-cooled or water-cooled
• Exhaust to outdoors: Prevents hydrogen accumulation in hall

Ventilation requirements around generators:

Minimum 4 air changes per hour (ACH) in generator enclosure to prevent hydrogen accumulation in case of seal leakage:

$$Q_{gen,vent} = \frac{V_{enclosure} \times ACH}{60}$$

For 50,000 ft³ generator enclosure:

$$Q_{gen,vent} = \frac{50,000 \times 4}{60} = 3,333 \text{ CFM}$$

Bearing Cooling Air

Turbine and generator bearings require localized cooling airflow:

Oil-cooled journal bearings:

Oil cooler heat rejection:

$$Q_{bearing} = m_{oil} \times c_p \times \Delta T_{oil}$$

Typical bearing oil cooler loads: 50,000-150,000 Btu/hr per turbine unit

Forced ventilation at bearing pedestals:

Supply 500-1,000 CFM per bearing location to maintain <110°F ambient around bearing housings and oil cooling systems.

Auxiliary Equipment Zones

Feedwater pump areas:

High-speed boiler feed pumps generate substantial heat:

• Motor heat dissipation: 2-5% of motor HP as waste heat
• For 5,000 HP motor: 127,500-318,750 Btu/hr
• Ventilation: 8-12 ACH in pump room

Piping and valve galleries:

Steam piping and valve stems emit significant radiant heat:

• Insulated piping heat loss: 20-50 Btu/hr per linear foot
• Valve bodies: 500-2,000 Btu/hr per large valve
• Local exhaust: 1,000-2,000 CFM per major valve station

Worker Comfort Zones

Occupied Zone Design Criteria

Temperature limits per ACGIH guidelines:

Work intensity-based exposure limits:

WBGT = Wet Bulb Globe Temperature accounts for humidity and radiant heat.

Occupied zone definition:

In turbine halls, occupied zones are typically:

• 0-10 ft above operating floor
• Control room areas: 72-78°F year-round
• Maintenance work areas: 75-85°F maximum during operation
• Crane cab: Air-conditioned, 75°F maximum

Supply Air Distribution

Floor-level supply strategy:

Low-velocity displacement ventilation at floor level:

$$Q_{supply} = \frac{Q_{occupiedzone}}{1.08 \times (T_{room} - T_{supply})}$$

For occupied zone cooling of 1,200,000 Btu/hr with 60°F supply air and 80°F room temperature:

$$Q_{supply} = \frac{1,200,000}{1.08 \times (80-60)} = 55,560 \text{ CFM}$$

Supply air configuration:

• Floor grilles or low sidewall diffusers
• Supply velocity: 200-400 FPM at grille face
• Temperature differential: 15-25°F below space temperature
• Distribution spacing: 20-30 ft on center
• Throw distance: 30-50 ft to cover floor area

Stratification maintenance:

Supply air must remain below turbine deck level to avoid disrupting thermal stratification that drives roof ventilator performance. Supply grilles placed at 0-6 ft elevation ensure cool air remains in occupied zone.

Spot Cooling Systems

For maintenance activities near hot equipment:

Portable cooling units:

• Capacity: 3-10 tons (36,000-120,000 Btu/hr)
• Discharge: High-velocity directed air (1,000-2,000 FPM)
• Coverage: 150-300 ft² per unit
• Application: Turbine inspections, valve maintenance

Fixed cooling stations:

Permanent air-conditioned enclosures at frequently accessed locations:

• Electrical cabinets: 75°F maximum
• Instrument racks: 70-80°F
• Tool storage: 85°F maximum

Mechanical Ventilation System

Exhaust Fan Sizing

Supplemental mechanical exhaust:

Sized to provide full design airflow when natural ventilation is inadequate:

$$Q_{exhaust} = 1.25 \times Q_{design}$$

Safety factor accounts for filter loading, duct losses, and degraded performance.

For 119,000 CFM design requirement:

$$Q_{exhaust} = 1.25 \times 119,000 = 148,750 \text{ CFM}$$

Fan selection criteria:

Supply Air Handling Units

Makeup air requirements:

Supply air equals exhaust air to maintain slight negative pressure (0.02-0.05 in w.c.) preventing hot air migration to adjacent spaces.

Air handler specifications:

• Cooling capacity: 80-120 tons for 500 MW plant
• Supply temperature: 55-65°F
• Filtration: MERV 8 minimum (industrial environment)
• Outside air: 100% (economizer mode when available)
• Humidification: None (dry cooling preferred)

Economizer operation:

When outside air temperature is below 60°F and humidity is low:

• 100% outside air cooling
• No mechanical cooling
• Substantial energy savings (60-80% of cooling hours)

Design Standards and Codes

Applicable standards:

• NFPA 850: Recommended Practice for Fire Protection for Electric Generating Plants
  • Smoke removal requirements
  • Fire-rated separation from control rooms
  • Emergency ventilation capacity
• IEEE 112: Standard Test Procedure for Polyphase Induction Motors and Generators
  • Generator cooling requirements
  • Ambient temperature limits
• ASHRAE Applications Handbook, Chapter 28: Power Plants
  • Heat load calculation methods
  • Ventilation rates
  • Comfort criteria for industrial environments
• OSHA 1910.94: Ventilation
  • Minimum ventilation for occupied industrial spaces
  • Heat stress prevention
• ACGIH TLV for Heat Stress: Work/rest regimens and engineering controls
• AMCA 500-D: Laboratory Methods of Testing Dampers for Rating
  • Gravity ventilator performance testing

Typical design parameters summary:

• Roof exhaust ventilation rate: 15-25 air changes per hour (ACH) at roof level
• Occupied zone supply: 4-8 ACH at floor level
• Makeup air: 90-100% of exhaust (slight negative pressure)
• Occupied zone maximum: 85-90°F dry bulb during operation
• Emergency smoke exhaust: 6-10 ACH whole building volume within 10 minutes
• Control room isolation: Positive pressure 0.05-0.10 in w.c., HEPA filtration for emergency conditions

Turbine hall ventilation design requires integration of natural stack-driven airflow, mechanical exhaust and supply systems, localized equipment cooling, and occupied zone conditioning to manage extreme heat loads while maintaining safe working conditions for operations and maintenance personnel throughout the facility lifecycle.

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