Calculate Required Air ventilation and Heat generation of D.G Set


Heat Generated by Generator:

  • For generator set installations, the heat radiated by the generator can be estimated by
  • H (kW) =P X ((1/Eff)-1)
  • H (Btu/min) =P X ((1/EFF)-1) x56.9
  • Where:
  • H = Heat Radiated by the Generator (kW), (Btu/min)
  • P = Generator Output at Maximum Engine Rating (kW)
  • Eff = Generator Efficiency % / 100%
  • Example: 975 kW standby generator set has a generator efficiency of 92%. The generator radiant heat for this genset can be calculated as follows.
  • P = 975 kW
  • Efficiency = 92% = 0.92
  • H = 975 x ((1/92%) – 1)
  • H= 84.78 kW
  • H = 975 x ((1/92%) – 1) x 56.9
  • H = 4824 Btu/min

 Types of Ventilation System:

  • Type:1 (Preferred Design) (Routing Factor of 1)
  • Outside air is brought into the engine room through a system of ducts. These ducts should be routed between engines, at floor level, and discharge air near the bottom of the engine and generator. .
  • Ventilation air exhaust fans should be mounted or ducted at the highest point in the engine room. They should be directly over heat sources. This system provides the best ventilation with the least amount of air required.
  • Type 2 (Skid Design) (Routing Factor of 1)
  • Outside air into the engine room through a system of ducts and routes it between engines.
  • Type 2, however, directs airflow under the engine and generator so the air is discharged upward at the engines
  • The most economical method to achieve this design is to use a service platform. The platform is built up around the engines and serves as the top of the duct
  • Ventilation air exhaust fans should be mounted or ducted at the highest point in the engine room. They should be directly over heat sources.
  • This system provides the best ventilation with the least amount of air required.
  • Type 3 (Alternate Design) (Routing Factor of 1.5)
  • If Ventilation Type 1or Type 2 is not feasible, an alternative is Type 3; however, this routing configuration will require approximately 50% more airflow than Type 1.
  • Outside air is brought into the engine room utilizing fans or large intake ducts. The inlet is placed as far away as practical from heat sources and discharged into the engine room as low as possible. The air them flows across the engine room
  • Ventilation air exhaust fans should be mounted or ducted at the highest point in the engine room. Preferably, they should be directly over heat sources
  • Type 4 (Less Effective Design) (Routing Factor of 2.5)
  • If Ventilation Type 1, Type 2 and Type 3 are not feasible, then Type-4 method can be used; however, it provides the least efficient ventilation and requires approximately two and a half times the airflow of Ventilation Type 1
  • Outside air is brought into the engine room using supply fans, and discharged toward the turbocharger air inlets on the engines.
  • Ventilation exhaust fans should be mounted or duct from the corners of the engine room
  • This system mixes the hottest air in the engine room with the incoming cool air, raising the temperature of all air in the engine room.
  • It also interferes with the natural convection flow of hot air rising to exhaust fans.
  • Engine rooms can be ventilated this way, but it requires extra large capacity ventilating fans.

Ventilation for Generator:

  •  When Generator set installations in Room proper ventilation is required for Generator set.
  • A properly designed engine room ventilation system will maintain engine room air temperatures within 8.5 to 12.5°C (15 to 22.5°F) above the ambient air temperature.
  • For example, If the engine room temperature is 24°C (75°F) without the engine running, the ventilation system should maintain the room temperature between 32.5°C (90°F) and 36.5°C (97.5°F) while the engine is in operation.
  • Ensures engine room temperature does not exceed 49°C (120°F).
  • Required Ventilating Air is calculated as
  • V=((H / D x Cp x T)+ Combustion Air) X F
  • Where:
  • V = Ventilating Air (m3/min), (cfm)
  • H = Heat Radiation i.e. engine, generator, aux (kW),(Btu/min)
  • D = Density of Air at air temperature 38°C (100°F). The density is 1.099 kg/m3 (0.071 lb/ft3)
  • CP = Specific Heat of Air (0.017 kW x min/kg x °C),(0.24 Btu/LBS/°F)
  • T = Permissible temperature rise in engine room (°C), (°F)
  • F = Routing factor based on the ventilation type
  • Example: The engine room for generator set has a Type 1 ventilation routing configuration and a dedicated duct for combustion air. It has a heat rejection value of 659 kW (37,478 Btu/min) and a permissible rise in engine room temperature of 11°C (20°F).
  • V=((659 / 1.0099X0.017X11)+ 0)X1
  • V = 3206.61 m3/min
  • V=((659 / 0.071 X 0.024 X 20)+ 0)X1
  • V = 109970.7 cfm
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