Earth Air Tunnel

Installation Process of Earth Air Tunnel

The size of earth air tunnels varies depending on the site’s needs. In general, a 100–120 m earth air tunnel requires a depth of 6–8 m. The pipe material can be HDPE or concrete, and the diameter of the pipe should be 450 to 500 mm.

The pipework should be airtight so that it doesn’t have air leakage and other issues. One end of the pipe is exposed to the wind catchers, and the other end is fixed to the AHU, which humidifies and dehumidifies the air as needed. From here, the air is disturbed in the room. A solar chimney is also installed inside the building, which evacuates the hot air from the building. (This is the best process for Indian conditions.)

Working of the earth’s air tunnel

• A wind tower/windcatcher is installed outside the main building in the direction of the flow of air around the area.
• It is then connected to an underground duct or tunnel to force it to move in the direction of the main building.
• The depth of the tunnel should be more than 2 m or between 3 m and 4 m. [6]
• The optimal ground temperature required for conditioning the air is 3 m (10 feet) deep. At any other depth, the temperature is not of the optimum value. [8]
• Through the duct, it reaches an area where it is treated for temperature, humidity, and to remove dust particles. [7]
• From here, it reaches inside the building, and the air is circulated throughout the building.

Earth air tunnel design parameters (Design Guidelines)

Duct/Pipe depth

• Ducting can be decided according to different factors like the thermal properties of the soil, the type of soil, the external climate, and the water content below the surface.
• In general, we use a depth of 4 meters. [5]

Duct/Pipe Length

• An increased length of the pipe helps reduce the air pressure and also increases the fan’s energy.
• The greater the duct depth, the better the heat transfer and efficiency. But it should be economical, so various types of arrangements are available for ducting. [5][6]

Diameter of the pipe

• Because of the friction in the pipe, a smaller diameter pipe requires more energy to move the air.
• provide improved thermal performance.
• The diameter of the pipe varies from 75 mm (3 inches) to 750 mm (30 inches). [5] [6]

Air Flow

• An increase in air velocity reduces the temperature while exiting the pipe.

Material of the pipe

• Economic factors like corrosion, strength, and durability all influence material selection.
• PVC ducts are usually preferred over galvanized iron as there is not much difference in the thermal conductivity of the two materials. [8]

Duct Layout

• The metallic duct placed underground faces a certain amount of weight from the soil on top. In order to prevent the duct from collapsing due to the soil weight, its thickness is designed using a flexural formula.
• The weight of the soil is considered while designing the layout of the duct. It is necessary so that the duct doesn’t collapse during backfill and thereafter. [8]

Arrangement of the Pipe Network

• Closed loop System:– Inside air circulates through the earth air tunnel, and fresh air can be added as needed.
• Open loop System:- Outside air is passed through the ductwork and transferred to the buildings.

Classification of an Earth Air Tunnel Heat Exchanger

Based on the layout of the pipe below ground

• Horizontal/Straight Loop
• Vertical Loop
• Slinky/Spiral Loop
• Pond/Helical Loop [5]

Applications of Earth Air Tunnel  

• In Commercial buildings like: Offices, Showrooms, cinema halls etc.
• Residential Buildings
• Institutional Buildings
• Hospitals [5]

Advantages of Earth air tunnel

• It reduces the heat gain inside the building.
• Reduces electricity consumption by 8 to 10%.
• Reduces the demand for air conditioning by 5 to 10%.
• Has a long life, initial investment is a little more than the air conditioners, but their maintenance is much less.
• Low operating costs.
• Completely eco-friendly.[5][6]
• This system can replace coolers in summer and heater in winter.
• It is noise-free and doesn’t require water topping as compared to a cooler.
• This system can last for 40-50 years.
• Totally a sustainable way to convert air as per climatic conditions.

Disadvantages of Earth air tunnel

• It cannot be used for changing humidity directly.
• This system requires a larger digging ground area to set up all of the ducting systems, which can be a problem at some places. [8]
• Give a limited amount of cooling or heating effect.
• The installation cost is higher.
• When the outside air becomes too hot or too cool, this system is not as effective.

Considerations while installing it on any site

• Various factors and parameters are considered before installing the earthen air tunnel on any site. [5]
• You can’t use it in all regions because of different earth properties.
• There should not be any bedrock near the site.
• Should have an ample amount of space on the site. [6]
• The water table should be kept below 6 to 7 meters from the ground surface.
• Opting for mechanical fans rather than going with natural airflow. [1]