S U B M I T T E D B YS A G A R K E L K A R ( 0 2 0 6 M E 1 3 1 1 2 5 )

S A N D E E P C H O U D H A R Y ( 0 2 0 6 M E 1 3 1 1 2 8 )S H I K H A R S K U S H WA H A ( 0 2 0 6 M E 1 3 1 1 4 0 )

S H U B H A M K U M A R ( 0 2 0 6 M E 1 3 1 1 5 0 )S U S H A N T S I D D H E Y ( 0 2 0 6 M E 1 3 1 1 6 7 )

S WA P N I L V I S H WA K A R M A ( 0 2 0 6 M E 1 3 11 6 9 )

Earth Tube Heat Exchanger (ETHE)

Contents

Aim Introduction Earth Tube Heat Exchanger Classification Passive Heat Exchange Principle Factors affecting thermal conductivity Applications of EAT Design guidelines Advantage and limitations Potential issues Conclusion References

Heating and Cooling of given space Using Earth Tube Heat Exchanger System

Challenges

Energy Saving: One of the most important global challenges.

Energy Efficiency: Renewable sources of energy Demand Side: Energy efficient

Aim

Introduction

If building air is blown through the heat exchanger for heat recovery ventilation, they are called Earth Tubes.

These systems are known by several other names, including: air-to-soil heat exchanger, earth channels, earth canals, earth-air tunnel systems, ground tube heat exchanger, hypocausts, subsoil heat exchangers, thermal labyrinths, underground air pipes, and others.

ETHE

• The Earth Air Tunnel (EAT) systems utilizes the heat-storing capacity of earth.

• The fact that the year round temperature approx. four meter below the surface remains almost constant

throughout the year. That makes it potentially useful in providing buildings with air-conditioning.

• It depends on the ambient temperature of the location, the EAT system can be used to provide both

cooling during the summer and heating during winter.

• The tunnels would be especially useful for large buildings with ample surrounding ground.

• The EAT system can not be cost effective for small individual residential buildings.

• The ground temperature remains constant and air if pumped in appropriate amount that allows sufficient

contact time for the heat transfer to the medium attains the same temperature as the ground temperature.

Classification

Classification of EATHE system

According to layout of pipe in ground According to mode of arrangement

There are four different types according to layout of pipe in the ground

Horizontal/ straight Loop Vertical Looped Slinky/ spiral Looped Pond/Helical Looped

Contd….

Passive Heat Exchange

• Passive HE systems are least expensive means of cooling a home which maximizes the efficiency of the building.

•It rely on natural heat-sinks to remove heat from the building. They derive cooling directly from evaporation, convection, and radiation without using any intermediate electrical devices.

•All passive HE strategies rely on daily changes in temperature and relative humidity.

•The applicability of each system depends on the climatic conditions.

•These design strategies helps heat exchange to internal space.

Principle

EARTH-AIR TUBE: PRINCIPLE

Earth acts a source or sink High thermal Inertia of soil results in air temperature fluctuations being dampened deeper in the ground Utilizes Solar Energy accumulated in the soil Cooling/Heating takes place due to a temperature difference between the soil and the air

FACTORS AFFECTING THERMAL CONDUCTIVITY

SOIL: Moisture content

Most notable impact on thermal conductivityThermal conductivity increases with moisture to a certain point

(critical moisture content) Dry density of soil

As dry density increase thermal conductivity increase Mineral Composition

Soils with higher mineral content have higher conductivitySoils with higher organic content have lower conductivity

Soil TextureCoarse textured, angular grained soil has higher thermal conductivity

VegetationVegetation acts as an insulating agent moderating the affect of

temperature

No. Type of ground qE [W/m2]1 Dry sandy 10-15

2 Moist sandy 15-20

3 Dry clay 20-25

4 Moist clay 25-30

Heat exchange rate for different soil types

APPLICATIONS OF EAT’S

EAT’s can be used in a vast variety of buildings:

Commercial Buildings: Offices, showrooms, cinema halls etc.

Residential buildings

University Campuses

Hospitals

Greenhouses

Livestock houses

DESIGN GUIDELINES

IMPORTANT DESIGN PARAMETERS:

The design parameters that impact the performance of the EAT are:• Time-Temperature-Depth • Tube Depth• Tube Length• Tube Diameter• Air velocity• Air Flow rate• Tube Material• Tube arrangement

Open-loop system Closed-loop system

• Pit Area• Slope• Efficiency• Coefficient of Performance (COP)

[3]

Time-Temperature-Depth

Contd…

No Season

Ambient air temperature

Soil temperature

Space temperature

1 Winter 12oC-20oC 25oC-30oC 24oC-26oC

2 Summer

40oC-45oC 22oC-28oC 25oC-28oC

Temperature profile

TUBE DEPTH

Ground temperature defined by: External Climate Soil Composition Thermal Properties of soil Water Content

Ground temperature fluctuates in time, but amplitude of fluctuation diminishes with depth.

Burying pipes/tubes as deep as possible would be ideal. A balance between going deeper and reduction in temperature needs to be drawn. Generally ~4m below the earth’s surface dampens the oscillations significantly.

TUBE LENGTH

Heat Transfer depends on surface area. Surface area of a pipe:

Diameter Length

So increased length would mean increased heat transfer and hence higher efficiency. After a certain length, no significant heat transfer occurs, hence optimize length. Increased length also results in increased pressure drop and hence increases fan energy. So economic and design factors need to be balanced to find best performance at lowest cost.

TUBE DIAMETER

Heat Transfer depends on surface area. Surface area of a pipe:

Diameter Length

Smaller diameter gives better thermal performance. Smaller diameter results in larger pressure drop increasing fan energy requirement. Increased diameter results in reduction in air speed and heat transfer. So economic and design factors need to be balanced to find best performance at lowest cost. Optimum determined by actual cost of tube and excavation cost.

[4]

AIR VELOCITY

As the velocity of air increases the exit temp decreases.

[6]

AIR FLOW RATE

For a given tube diameter, increase in airflow rate results in:

Increase in total heat transfer Increase in outlet temperature

High flow rates desirable for closed systems

For open systems airflow rate must be selected by considering:

Outlet temperature Total cooling or heating capacity

TUBE MATERIAL The main considerations in selecting tube material are:

Cost Strength Corrosion Resistance Durability

Tube material has little influence on performance.

Selection would be determined by other factors like ease of installation, corrosion resistance etc.

Spacing between tubes should enough so that tubes are thermally independent to maximize benefits.

TUBE ARRANGEMENT EAT can be used in either:

Closed loop system Open loop system

Open Loop system: Outdoor air is drawn into tubes and delivered to AHUs or directly to the inside of the building Provides ventilation while hopefully cooling or heating the building interior. Improves IAQ

Closed Loop system: Interior air circulates through EATs Increases efficiency Reduces problem with humidity condensing inside tubes.

Hybrid System: EATHE system is coupled to another heating/cooling system, which may be an air conditioner , evaporative cooling system or solar air heater

TUBE ARRANGEMENT

EAT can be used in either: One-tube system Parallel tubes system

One tube system may not be appropriate to meet air conditioning requirements of a building, resulting in the tube being too large

Parallel tubes system More pragmatic design option Reduce pressure drop Raise thermal performance

EAT EFFICIENCY

Calculating benefits from EAT is difficult due to: Soil Temperatures Conductivity

Performance of EAT can be calculated as:

where;

To = Inlet Air Temperature To (L) = Outlet Air Temperature Ts = Undisturbed ground temperature

CO-EFFICIENT OF PERFORMANCE(COP)

COP based on:

Amount of heating or cooling done by EAT (Heat Flux) Amount of power required to move the air through the EAT

Q= Heat Flux W= Power

COP decreases as system is operated COP can be integrated into system control strategies When COP down to a certain point, EAT should be shut down and

conventional system should take over

Advantage

ETHE based systems cause no toxic emission and therefore, are not

detrimental to environment.

Ground Source Heat Pumps (GSHPs) do use some refrigerant but much less

than the conventional systems.

ETHE based systems for cooling do not need water - a feature valuable in arid

areas like Kutch. It is this feature that motivated our work on ETHE

development.

ETHEs have long life and require only low maintenance

Low operating cost.

LIMITATIONS

Require large space to make setup.

Give a limited cooling effect.

Initial cost high.

POTENTIAL ISSUES

Moisture Accumulation And IAQ Problems

ISSUE• Condensation inside the tubes

has been observed• Condensation occurs if temp. in

the tube is lower that dew point temp.

• Condensation occurs in systems with low airflow and high ambient dew point temperature

• Removal of moisture from the cooled air is always an issue and system may be used with a regular air conditioner or a desiccant

• Water in tubes also results in growth of mould or mildew leading to IAQ issues

SOLUTIONS• Good construction and

drainage• Tubes are tilted to prevent

water from standing in the tubes

• In the service pit at the lowest point water can be captured and pumped

• Water tight tubes can be used to prevent ground water from entering into the system

CONCLUSIONS

EATs are based on the following principles

Using earth as a source or sink Uses Soil Thermal inertia Depends on the Thermal Conductivity of Soil

Various Factors affect the performance of EAT which need to be optimized to maximize performance.

Integrate the EAT into the building systems to maximize performance and maximize energy savings.

REFRENCES

1. A passive solar system for thermal comfort conditioning of buildings in composite climates†,1 p. RAMAN, SANJAY MANDE and V. V. N. KISHORE received 19 august 1998; revised version accepted 13 october 2000

2. Earth air heat exchanger in parallel connection manojkumardubey1, dr. J.L.Bhagoria2, Dr. Atullanjewar M.Tech student1 MANIT Bhopal professor mech deptt. , MANIT bhopal asst. Professor mech deptt, MANIT bhopal(figures)

3. Jalaluddin, Miyara A, Thermal performance investigation of several types of vertical ground heat exchangers with different operation mode, Applied Thermal Engineering 33-34 (2012) 167–74.

4. Performance analysis of earth–pipe–air heat exchanger for winter heating Vikas Bansal *, Rohit Misra, Ghanshyam Das Agrawal, Jyotirmay Mathur

5. Performance analysis of earth–pipe–air heat exchanger for summer cooling Vikas Bansal *, Rohit Misra, Ghanshyam Das Agrawal, Jyotirmay Mathur

6. Performance evaluation and economic analysis of integrated earth–air–tunnel heat exchanger–evaporative cooling system Vikas Bansal , Rohit Misra, Ghanshyam Das Agrawal, Jyotirmay Mathur∗

7. Thermal performance investigation of hybrid earth air tunnel heat exchanger Rohit Misraa, Vikas Bansala, Ghanshyam Das Agarwala, Jyotirmay Mathura, , Tarun Aserib∗

8. ANALYTICAL MODEL FOR HEAT TRANSFER IN ANUNDERGROUND AIR TUNNEL MONCEF KRARTI and JAN F. KREIDER (received 27 october 1994; received for publication 11 july 1995)

THANK YOU