USE OF EARTH AIR TUNNEL AND CAVITY WALL AS PASSIVE COOLING IN A GARMENT FACTORY OF BANGLADESH FOR ENERGY CONSERVATION

INTRODUCTION

ü       Any building or factory with a large number of occupants in the hot and humid regions can reach high level of thermal stress.

ü       One of the major design criteria of a building in a warm and humid climate is its cooling system.

ü       The cooling load is a predominant factor in terms of energy consumption.

ü       Adoption of passive cooling as an alternative to artificial cooling can bring important benefits to the energy, environmental and financial sectors.

ü       Only passive cooling alone cannot provide the appropriate thermal comfort standard without addition of active cooling.

ü       Addition of active cooling system using air-conditioning and refrigeration generate multiple impacts on stratospheric ozone layer.

ü       Release of refrigerants and emission of green house gases (GHG) make combined contribution to global warming.

ü       Buildings that operates on a mixed cooling system in a warm-humid climates are able to balance the need for comfort, eco friendliness  and energy efficiency through the year.

ü       Little work has been reported in the thermal performance of building that utilizes active and passive cooling in Bangladesh.

MOTIVATION

●        Per capita energy consumption in Bangladesh is only 157 kgoe (2003).

●        Per capita electricity generation is 167 kWh and per capita consumption is 136 kWh (2005-2006)

●        Average electricity demand is 4500 MW and generation capacity is only  3300 MW

●        It is an energy crisis situation

●        With increased demand for energy, the cost of energy is also increasing

●        Steps should be taken for adoption of various mechanism towards an effective and significant saving of conventional energy

OBJECTIVES

●        Cost effective active and passive cooling system design for a garment factory

●        Cool comfortable and dust free environment inside production floors

●        Low installation cost, energy conservation and easy maintenance for sustainability

SPECIFIC REQUIREMENTS OF THE USER

The desired temperature and humidity level to be achieved for indoor comfort was set as 28-29°C and humidity level 60-65%.

DESIGN CONCEPTS

●        To achieve the set conditions a dual cooling system was designed and installed in a four-storied garment factory named Section Seven Ltd. at Chittagong, Bangladesh

●        In our design of cooling system we have utilized the following steps:

Cooling load reduction by architecture

►     Ground coupled EAT as passive cooling

►     Programmed active cooling and dehumidification

SITE LOCATION

SITE LOCATION

CHITTAGONG – The port city of Bangladesh

SITE INFORMATION

Location of the Site:

               Chittagong – The main port city of Bangladesh.

●  Geographical position:

               Latitude:         22°-16’ north

               Longitude:      91°-82’ east

●  Climate Condition:

               Mostly hot and humid apart from few months of winter.

●  The mean temperature:

               In January:     20°C

               In July:           27.5°C

●  Section Seven Ltd. Is a garment factory located in

        Chittagong Export Processing Zone (CEPZ).

PRODUCTION ROOM DIMENSIONS (COOLING LOAD)

●        52 meter wide facing west as front and east as rear per floor.

●        30 meter long sides facing as north and south per floor.

●        4.3 meter room height

●        Total number of floors: 3

COOLING LOAD REDUCTION BY ARCHITECHTURE

●        Reduction of heat gain by cavity wall facing east and west sides

●        Increase of Room Height for Air Circulation

●        Reduction of window size facing east and west sides

●        Recessed window filled with tinted glass

HEAT GAIN DUE TO SUNSHINE HOUR IN USUAL BUILDING CONCEPT (Design considerations)

Exposed solid wall along Sun-path results 5°-7° Celsius room heat gain. Temperature rises from 31°-38° Celsius within building envelope due to long Sun-exposed solid wall and large windows in east and west sides.

INTERNAL HEAT GAIN (Design considerations)

●        Heat gain due to occupants

●        Heat gain due to Machine Operation

●        Convection

●        Temperature rises from 31°-38° Celsius

CONSTRUCTION OF CAVITY WALL (PASSIVE COOLING)

●        Reduced heat transmission

●        Removes heated air through natural air movement

●        Internal wall works as condenser or heat absorber

GROUND COUPLED EAT AS PASSIVE COOLING

Earth Air Tunnel (EAT) is a large underground tunnel composed of number of smaller tunnel.

The use of Earth Air Tunnel (EAT) technology as a ground coupled building as passive cooling system have been employed in many parts of the world.

The ground has infinite heat absorbing capacity. Therefore, room air if made to circulate through an appropriate inlet and outlet duct and passed into the EAT, that ground coupled under the ground floor of a building would attain the same temperature of the ground temperature.

The continuous forced circulation of room air through EAT would maintain the air temperature closed to that of Earth temperature.

GROUND COUPLED EAT SYSTEM DESIGN

GROUND COUPLED EAT SYSTEM OPERATION

●        Circulating the hot air from room (32°-33°) through earth air tunnel (25°-26°)

●        Keeping room temperature within 29°-30° through continuous conduction

●        Addition of fresh air

FORCED AIR CIRCULATION OF ROOM AIR THROUGH EAT

●        Blower used : 16 (big) – 4000 CFM - 2 hp, 3 phase motors, 1200 RPM

●        Booster blower used : 16 (small) – 300 CFM, 200 watt single phase, 400 RPM

●        Operation time : 10 hr per day

ADDITION OF WINDOW TYPE AIR-CONDITIONER AS ACTIVE COOLING AND DEHUMIDIFICATION

●        18 ACs of 27,000 Btu/hr cooling capacity were installed in each floor

●        2 ACs were installed face to face in the rear and front wall as one modular set

●        The cooling outlet of 2 ACs were connected by a duct for uniform air discharge by mixing with air of EAT

●        Operating hour : 8 hr per day

●        Total active cooling installed in 3 floors (18x3)                 = 54 ACs equivalent to 122 tons

ADDITION OF WINDOW TYPE AIR-CONDITIONER AS ACTIVE COOLING AND DEHUMIDIFICATION

OPERATION OF WINDOW TYPE AIR-CONDITIONER AS ACTIVE COOLING AND DEHUMIDIFICATION

●        Applying active cooling using 18 nos Air-conditioner (27000 B.T.U. per AC) 

●        Placing Two AC Face-to-Face (9 set) reducing the requirement of additional blower for air distribution

●        Removal of moisture and dehumidification

PROGRAMMED ACTIVE COOLING AND DEHUMIDIFICATION

Window type room air-conditioner (AC) were added to each floor to provide a programmed (35 minutes ON and 7 minutes OFF) active cooling and dehumidification inside the room.

The room air discharge system were designed to deliver the air by combining the air from AC and EAT.

OPERATION OF THE DESIGNED SYSTEM

1. Continuous uniform suction of room air at the ceiling level to EAT

2. Ground conduction and dust removal through EAT by blowers

3. A fraction of fresh air intake

4. Mixing of incoming air from EAT with cold and dehumidified air from AC

5. Discharge of processed air uniformly from little above the human height level through AC to AC duct slits

ESTIMATION OF COOLING LOAD

Room area load

            52 meter width x 30 meter length x 4.3 meter height

            Total 6,700 cubic meter room volume per floor

            For 3 floor = 20,100 cubic meter room volume

ESTIMATION OF COOLING LOAD

Human load

            550 workers (80% female and 20% male) per floor

            Total for 3 floors=1650 workers

ESTIMATION OF COOLING LOAD

Internal machine heat generation load

ü       300 motor driven sewing machines

ü       500pcs of 40 watt tube lights

ü       50pcs of steam iron

ü       few heat generating fusing machines

ü       and miscellaneous equipments

ESTIMATION OF COOLING LOAD

ü       Considering total electrical load computed as 250 KW and fresh air intake and number of door opening as additional load.

ü       The calculated cooling load per floor=120 ton

ü       Total estimated cooling load for 3 floor = 360 ton

ü       The ground floor space was not included in the estimation due to its uses as storage purposes only

OUTLINE OF COOLING LOAD, ACTIVE AND PASSIVE COOLING CAPACITY, ENERGY EXPENSES AND ENERGY SAVING

●        Total requirement of the cooling load = 360 ton

●        Cooling load reduced by cavity wall = 60 tons

●        Cooling load reduced by EAT (300-180) = 120 tons

●        Balance 120 ton cooling should be covered by Active Cooling

OUTLINE OF COOLING LOAD, ACTIVE AND PASSIVE COOLING CAPACITY, ENERGY EXPENSES AND ENERGY SAVING

RUNNING COST OF ACTIVE COOLING SYSTEM

Tk 1,46,400 for AC + Tk 30,240 for large blower

      + Tk 4,032 for small blower + maintenance cost

      = Tk 2 lacs per month

Per unit cost of electricity in CEPZ = Tk 4.50

OUTLINE OF COOLING LOAD, ACTIVE AND PASSIVE COOLING CAPACITY, ENERGY EXPENSES AND ENERGY SAVING

ENERGY SAVING

60 ton from cavity wall construction for reduced heat gain

180 ton from EAT for reduction of room temperature

1 ton = 1.2 kW energy requirement, 8 hrs per day, 28 days per month

                = 1.2 kW x 8 hours x 28 days = 270 kW-h

Energy saving in case of 60 ton cooling load reduction

            by cavity wall = 13,440 kW-h

Total saving of electricity cost due to passive cooling

 = Tk 2,20,000 per month

INSTALLATION COST OF COOLING SYSTEM

●        Tk 70,00,000 (equivalent to US$ 1,00,000)

                                                            [1 US$=Tk 70 only]

●        Payback period in terms of energy saving = 3.5 years

Construction of custom-made Earth Air Tunnel (EAT)

Building construction underway

100 feet of 96 line 9” diameter R.C.C pipe round as EAT Tunnel

Construction of custom-made Earth Air Tunnel (EAT)

Earth removal

100 feet of 96 line 9” diameter R.C.C pipe round as EAT Tunnel

Construction of custom-made Earth Air Tunnel (EAT)

Earth removal – Block-by-Block

100 feet of 96 line 9” diameter R.C.C pipe round as EAT Tunnel

Construction of custom-made Earth Air Tunnel (EAT)

Round R.C.C pipe laying (1 meter bellow the ground floor)

100 feet of 96 line 9” diameter R.C.C pipe round as EAT Tunnel

Construction of custom-made Earth Air Tunnel (EAT)

Round R.C.C pipe laid in one Block

100 feet of 96 line 9” diameter R.C.C pipe round as EAT Tunnel

Construction of custom-made Earth Air Tunnel (EAT)

Filling with clay over R.C.C pipe

100 feet of 96 line 9” diameter R.C.C pipe round as EAT Tunnel

Construction of custom-made Earth Air Tunnel (EAT)

Water curing of clay

100 feet of 96 line 9” diameter R.C.C pipe round as EAT Tunnel

Construction of custom-made Earth Air Tunnel (EAT)

Construction of maintenance channel of R.C.C pipes (East)

100 feet of 96 line 9” diameter R.C.C pipe round as EAT Tunnel

Construction of custom-made Earth Air Tunnel (EAT)

Construction of maintenance channel of R.C.C pipes (West)

100 feet of 96 line 9” diameter R.C.C pipe round as EAT Tunnel

GI SHEET DUCT COUPLING FOR AIR SUPPLY AND DELIVERY FROM EAT

FORCED CIRCULATION OF AIR USING BLOWER

FORCED CIRCULATION OF AIR THROUGH EAT USING BLOWER

AC TO AC DUCT WITH AIR DISCHARGE SLITS INSIDE PRODUCTION FLOOR

AC TO AC DUCT INSIDE PRODUCTION FLOOR

WINDOW TYPE AC POSITION - FLOOR WISE

RECESSED WINDOW FILLED WITH TINTED GLASS

FRESH AIR INTAKE MECHANISM USING GI PIPE

FRESH AIR INTAKE MECHANISM USING GI PIPE

ROOM ENVIRONMENT WITH COOLING SYSTEM IN OPERATION

Light load = 550 nos 40 watt tube lights per floor

ROOM ENVIRONMENT WITH COOLING SYSTEM IN OPERATION

Light load = 550 nos 40 watt tube lights per floor

ROOM ENVIRONMENT WITH COOLING SYSTEM IN OPERATION

Noise free environment

PERFORMENCES OF COOLING SYSTEM

Room environment without any cooling system on and with all windows/doors open

Room environment with passive cooling (Blowers) on and active cooling (AC) off

Room environment with passive cooling (Blowers) off and active cooling (AC) on

Performance of cooling system-(Active and Passive on) - Data collection -incomplete

ASPECTS OF SUSTAINABILITY AND DEVELOPMENT

Control of demand, conservation, minimization of waste and conservation of natural resource

ACHIEVEMENTS

●        Power savings (energy conservation)

●        Reduced Green House Gas emission

●        Easy maintenance due to Modular Design

●        Low maintenance cost

●        Total shut-down (characteristics of central A/C system) may not happen.

●        Approximate running cost of designed system

●        Tk 2 lacs per month (US$ 2,857)

●        Energy saving per month = 50 MW-h due to reduction of cooling load by passive cooling

●        Equivalent amount of carbon emission saving 261 ton per year (RETSCREEN)

●        Electricity saved per year = 600 MW-h per year

●        Average production target per day = 11,000-12,000 pieces of gents shirt per day based on design, 90% achieved

INSTALLATION COST OF COOLING SYSTEM

●        Tk 70 lacs only (US$ 100,000)

●        Tk 50 lacs saved (US$ 71,429) due to  non-conventional cooling system design

OTHER FEATURES ADDED OR TO BE ADDED IN THE BUILDING

●        Rain water harvesting from rooftop to ground water reservoir tank as a source of iron free water for the boiler during rainy season (added)

●        Installation of small scale PV panel for power generation to operate LED security lighting (added)

●        Installation of solar water heater for boiler (proposed)

CONCLUSION

Since it is a recently installed project the collection of essential data are still ongoing. Necessary modification is also going on to optimize the designed system floor wise. Initial findings of various performances in terms of energy conservation and other associated factors are very encouraging. The detail performance results would be complete after one full year of operation on 15th June 2008.

This hybrid cooling system may continue to demonstrate a commercially preferable, environmentally benign, aesthetically pleasing way of reducing carbon emission through industrial, institutional energy conservation and many other kinds of buildings for sustainable development.

To serve every potential eco-aware consumer in such implementations trained human resources are essential, where the joint role of investor and academics could be enormous. Ultimately it could provide incentive for motivation, design innovation, integrity, efficacy, courage and reliability for the growing youth force of the country.