Effect of parameters on Earth Air Heat Exchanger in Hot- dry climate

 

Baljit Singh¹*, A. K. Asati², Rakesh Kumar³

¹Ph.D Research Scholar, IKG Punjab Technical University, Jalandhar-Kapurthala Highway, Kapurthala, Punjab,

²Associate Professor, SBS STC Ferozepur, Punjab,

³Associate Professor and IET Bhaddal, Ropar- 140108 Punjab,

 

ABSTRACT:

Now days “save electricity and save high grade energy” are major concerns for societal needs. Various cooling methods are used to save energy as well as environment. To achieve comfort environment many techniques are used. The use of geothermal energy is one of the attractive ways to make environment healthy for mankind and to reduce the demand of electricity, which is increasing day by day. The Earth Air Heat Exchanger system is a better passive technology to the use of geothermal energy. In this research paper efforts are made to analyse the accomplishment umidityHhof low cost cooling system of outdoor air for hot-dry climate. The effect of velocity, length and drop in temperature of air is studied at inlet and outlet of the pipe. The results of velocity variation reveal that for length of pipe 15 m and 1.5 m depth at velocities 4.8 m/s, 3.4 m/s and 2.5 m/s, the temperature drop is 4.2 °C, 7.5 °C and 9.2 °C respectively. The effect of variation in length of pipe has been studied and as per the measurements the temperature drops of 9.2 °C, 10.6 °C and 11.9 °C corresponding to length of 15 m, 30 m and 45 m for air velocity of 2.5 m/s and depth of 1.5 m. The maximum average temperature fall corresponding to 45 m length, at 1.5 m depth and at 2.5 m/s velocity is 8.6 °C. The results show that maximum temperature drop available at low velocities because air gets larger time to get heat transfer in the underground pipe in soil.

 

 

 

1. INTRODUCTION:

Earth air heat exchanger is a good method of cooling of air for making the comfort environment for human beings. It uses the temperature of earth at a certain depth of earth for cooling of air. The undisturbed temperature in the deep of earth remains approximately constant throughout the year. In this system the number of pipes are connected in parallel and buried at a certain depth inside the earth.

 

The air from the blower is forced through the pipes. The pipes are made of materials i.e. Poly vinyl chloride (PVC), GI, mild steel and concrete etc. by which heat exchange between earth and air is possible [1].

 

In this research paper the Earth Air Heat Exchanger (EAHE) is studied for hot-dry climate. Air-conditioning systems consume huge high grade energy and reduction of the same is big challenge is in the present scenario. The challenge can be overcome by the use of ground coupled heat exchanger in air conditioning system [2]. It may suitably meet the heating and cooling energy loads of any space. Its performance is based upon the seasonally varying inlet temperature of air which further depends on the under ground temperature [3].

The thermal analysis of air conditioning system have been done with its different components like desiccant wheel, solar collector, heat exchanger, ground heat exchanger and water spray evaporative cooler gives the prediction about the thermal performance of the EAHE system. The simulation is conducted for three different zones i.e. hot-dry zone, warm-dry zone and hot-humid zone. The experiment shows that the EAHE system using desiccant system provides a better thermal comfort for human beings in different climates. The combined system significantly decreases the inlet air temperature from 12.7 to 21.7^°C at different climate zones and the highest COP value for the EAHE system using the desiccant  for air conditioning is about 1.03 while the lowest value is about 0.15 [4]. Polypropylene capillary heat exchangers are used for absorbing and dissipating solar energy in excess value. During the day time, the air-suspended exchangers store the solar energy and during night time the stored thermal energy is brought back to heat the greenhouse air [5]. The EAHE system calculated the overall energy efficiency value is 72.10% and the overall exergy efficiency value is calculated to be 19.18% at a reference state temperature of 0°C. As the environment temperature increase from 0 to 18^°C the exergy efficiency of the whole EAHE system decreases from 19.18% to 0.77% [6]. EAHE is a passive technique of cooling which is used for air heating or cooling for reducing ventilation heat losses and maintains a comfort environment in buildings. A literature review was carried in order to determine the design and various parameters related to earth air heat exchangers [7]. With the integration of Earth air tunnel heat exchanger system with conventional vapour compression system the air conditioning capacity is improved. The results analyse that the power consumption of conventional 1.5 Tonnes of refrigeration window type of air conditioner is reduced by 18.1% when cold air from EATHE is completely used for condenser cooling of the air-conditioner [8].

 

A simulation model has been developed to predict the performance of greenhouse that is heated with a heat-pipe system. The model is validated with the results obtained from experiment and is found to be in close agreement. The simulation model can provide predictions of the effect of the maximum height, the heating capacity required in cold climate and the different heat losses from the green house [9]. The number of studies has been conducted by various researchers in the design, modelling and testing of various parameters related to EAHE systems. The research studies undertaken on these systems are categorized into two groups as follows: (i) open loop for space heating/cooling (ii) closed loop for space heating/cooling systems [10].

 

The EAHE is effectively used to achieve cooling energy demand of buildings in hot and dry climate system in Bhopal (India) [11]. The velocity of air varies from 2 m/s to 5 m/s and for PVC pipes the corresponding change in air temperature varies from 11.3^°C - 12.9 ^°C obtained with the experimental set-up of EAHE varies from 11.3^°C - 12.9 ^°C. The study reveals that diameter of the pipe and air velocity greatly affects the performance of EAHE system.

 

The EAHE system is installed in a school of Imola, Italy and it is effectively utilised for the long term analysis. It is monitored for 12 months and the length of the buried pipes kept is 2 km. A huge drop in temperature of air between inlet and outlet has been observed both in hot and in cold climates. The relative humidity has been determined and the air temperature has also been calculated [12]. The EAHE was placed in Viamao, city located in the south of Brazil for determining the thermal performance of the complete system experimentally. The ducts A and B are installed at a depth of 1.60 m and 0.60 m apart but the duct C is installed at a depth of 0.50 m inside the earth. The results show that the months of May and February were the best for heating and cooling respectively [13]. An investigation of Earth pipe cooling technology, conducted in a university campus in Malaysia. EAHE is a passive cooling alternative to simple air-conditioning systems. Polyethylene pipes were buried around 1.0 m in the earth and temperature fall of air between pipe inlet and outlet of the pipe were compared and analysed. A significant air temperature fall from 6.4^°C and 6.9^°C was determined, depending on the season of the year in these pipes [14]. The parameters like design and analysis of EAHE systems are well established by engineering knowledge and optimization techniques. A prototype of this system is established and is monitored for thermo-economic parameters. The use of this heat exchanger in residential and agricultural buildings is a new concept in Turkey [15].  The effectiveness and performance of simple earth–air-tunnel heat exchanger (EATHE) is boosted by integrating an evaporative cooler at the outlet of the pipe. The experiment has been carried out in the city of Ajmer (India) individually for all 8760 h.  The experimental  result show in the summer months a simple EATHE system provides 4500 MJ of cooling effect, whereas by integrating evaporative cooler with the same system 3109 MJ of more cooling effect can be achieved [16]. The analysis of an EAHE requires knowledge of its total thermal resistance for heating and cooling applications. A galvanized pipe of 0.56 m nominal diameter and 47 m length is used for the determination and evaluation of thermal performance of Earth air heat exchanger. This system was designed and installed in the Solar Energy Institute, Ege University, Izmir, Turkey. The thermal resistance for both the purposes i.e. heating and cooling has determined from generalized relationships [17].

2. OBJECTIVES OF THE STUDY:

In reference to cooling of hot and dry air, the objectives of the current study are

(a) To study variation of the inlet and outlet temperatures from morning to evening.

(b) To study the effect of velocity on temperature drop.

(c) To study the effect of length on temperature drop.

 

3. EXPERIMENTAL SET-UP AND INSTRUMENTATIONS:

The EAHE is installed in the village Bazidpur, which is in district and tehsil Ferozepur (Punjab), India. Most of the time the climatic conditions are hot in this region and in month of June temperature reaches upto 45 °C.  Therefore cooled air is need of the people of the area to live healthy life with their good physical and mental health.

 

A testing room of dimensions 3.4 m × 3.3 m × 2.3 m has been taken as a test space to be cooled. The experiment setup consists of concrete pipes of diameter 0.224 m connected in series to have length of 15 m, 30 m and 45 m and are buried in the soil at a depth of 1.5 m. The one end of the series of pipes open outside at ambient conditions and other end of the pipe opens to the space, which is to be cooled. A blower with variac is connected to the open end of pipes which delievers air to the room for study. The temperature is measured with the help of mercury thermometers/RTDs (0.5°C accuracy and least count 0.1 °C, range 0-100 °C) at the inlet and outlet of pipe. The air velocity is measured by a portable, digital vane typeanemometer (Thermo-Anemometer, PROVA Instruments, velocity range 0.3 to 45 m/s ) The arrangement of different instruments used in the current investigation is shown in fig 1.

 

 

Fig. 1: The complete setup for system

 

4. METHODOLOGY:

The blower is started, which cause flow of air through the EAHE which are underground concrete pipes. The recording of the temperatures are done after regular interval of time i.e. each half an hour when EAHE is in use for the cooling of the air. The dry bulb and wet bulb temperatures of air are recorded at inlet and outlet of the pipe by RTDs along with digital indicators. The temperatures at various locations of EAHE are cross checked by mercury thermometers. Specific humidity of the air is also checked at inlet and outlet of the EAHE to verify that only the sensible cooling of the air is handled by it or latent cooling also. Velocity of the air is set by variac by controlling speed of the blower.

 

The EAHE has been studied for cooling of air that how the cooling process is effective throughout the day on number of days in respect of observation of the inlet and outlet temperatures.

The EAHE is studied to determine the effect of varying velocity of the air and varying length of it for result in temperature drop of the air across it.

 

To study the effect of velocity, the system is operated at velocities 4.8 m/s, 3.4 m/s and 2.5 m/s on 29^th April 2017, 1^st May 2017 and 3^rd May 2017 respectively for the EAHE length of 15 m and buried at depth of 1.5 m.

Similarly to study the effect of length, the EAHE is kept for lengths 15 m, 30 m and 45 m on 18^th May 2017, 22^nd May 2017 and 24^th May 2017 respectively, keeping air velocity 2.5 m/s and the depth 1.5 m.

 

5. RESULTS AND DISCUSSIONS:

5.1. Day based observations :

Day based observations of the temperatures for the EAHE are recorded from morning 8 am to 4 pm on 29/04/2017, 01/05/2017, 03/05/2017, 18/05/2017, 22/05/2017 and 24/05/2017 as shown in figure 2 - 7. It has been found that initially in beginning of day, the temperature drop of the air is small i.e. approximately 0.5 ^oC at 8 am on 29/04/2017 corresponding to velocity 4.8 m/s, length 15 m and depth 1.5 m with the air inlet temperature 28.2 ^oC. But as soon as the outdoor air temperature increases, the temperature difference between air and the underground soil is also increases, which gives rise to heat transfer rate result in the temperature drop/ cooling of the air also increase. On the same day, 29/04/2017, the maximum temperature drop of 5.2^oC has been observed with the air inlet temperature 43.4^oC at 1.30 pm. The maximum temperature drop of the air is found, when the outdoor temperature reaches to maximum. Thereafter the temperature drop of the air in EAHE is starts decreasing due fall in the outdoor temperature.

 

5.2. Effect of velocity:

The measurements are done on day basis for EAHE corresponding to its length 15 m and depth 1.5 m. It is observed that the velocity of the air in the EAHE increases, the temperature drop across it decreases as shown in figures 2, 3 and 4.

 

The maximum temperature drop at velocities 4.8 m/s, 3.4 m/s and 2.5 m/s are found 4.2 °C (T_in = 43.4^oC), 7.5 ^oC (T_in = 44.2^oC),  and 9.2 ^oC (T_in = 44.2^oC) respectively. As velocity of the air decreases then the presence time of the air in the EAHE i.e. duration of heat transfer from air to ground/soil increases. Perhaps the heat transfer from air to soil is multiple of heat transfer rate and duration heat transfer, therefore temperature drop of the air in EAHE is found higher at lower velocities. It seems that increase in heat transfer rate due to increase in heat transfer coefficient at higher velocities is not much to counter the air presence time in the EAHE. The trends of variation of the temperature drop for day wise run of the EAHE at different velocities are found same.

 

 

Fig. 2: Time vs. temperature plots for an air velocity = 4.8 m/s, pipe length = 15 m, depth = 1.5 m of 29 April 2017

 

 

Fig. 3: Time vs. temperature plots for air velocity = 3.4 m/s, pipe length = 15 m, depth = 1.5 m of 1 May 2017

 

 

Fig. 4: Time vs. temperature plots for an air velocity = 2.5 m/s, pipe length = 15 m, depth = 1.5 m of 3 May 2017

 

5.3. Effect of length:

The measurements are done on day basis for EAHE corresponding to its depth 1.5 m and velocity of the air 2.5 m/s. The temperature drop across the EAHE is shown in figures 5, 6 and 7.

The maximum temperature drop found at lengths 15 m, 30 m and 45 m, are  9.2 ^oC (T_in = 44.4^oC), 10.6 ^oC (T_in = 40.0^oC) and 11.9 ^oC (T_in = 45.9^oC)  respectively. It has been observed that the length of the EAHE increases the temperature drop of the air moderately. Increasing the length means increase in surface area of heat transfer of the EAHE. Although the air moves towards the outlet, the difference of temperature of air and soil decreases, hence slow down the increase in heat transfer rate due to increase in area of heat flow. It seems that selecting length in between 15 m to 30 m may be suitable in design of the EAHE for the taken input parameters. The trend of variation of the temperature drop for day wise run of the EAHE at different length is found same.

 

 

Fig. 5: Time vs. Temperature plots for pipe length = 15 m, air velocity = 2.5 m/s, depth = 1.5 m of 18 May 2017

 

Fig. 6: Time vs. Temperature plots for pipe length = 30 m, air velocity = 2.5 m/s, depth = 1.5 m of 22 May 2017

 

 

Fig. 7: Time vs. Temperature plots for pipe length = 45 m, air velocity = 2.5 m/s, depth = 1.5 m of 24 May 2017

 

5.4. Average day wise temperature fall variation:

Figure 8 shows the average temperature drop of the air versus it’s velocity in the EAHE, at the depth of 1.5 m and for the length 15 m. As per the day wise observations with respect to the velocity 2.5 m/s (T_in average = 39.0 °C), 3.8 m/s (T_in average = 38 °C) and 4.8 m/s (T_in average = 40.9 °C), the average temperature drop have been found of 7.3 °C, 5.3 °C and 2.9 °C respectively. It is obvious that effect of the velocity for the given EAHE is quite significant.

 

Figure 9 shows the average temperature drop of the air versus length of the EAHE, keeping the depth 1.5 m and the air velocity 2.5 m/s. As per the day wise observations for the length 15 m, 30 m and 45 m on days 18/05/2017, 22/05/2017 and 24/05/2017 respectively.

 

The average temperature drop has been calculated from the temperature drop observed across the EAHE for entire run during a day, which were found 6.0 °C (T_in average), 7.3 °C (T_in average) and 8.1 °C (T_in average) for the lengths 15 m, 30 m and 45 m respectively. It is understandable that the major part of average temperature drop is in first 15 m length of the EAHE.

 

 

Fig. 8: Average Temperature vs. velocity plots for 29 April, 1 May and 3 May 2017

 

Fig. 9: Average Temperature vs. length plots for 18 May, 22 May and 24 May 2017

 

6. CONCLUSIONS:

The findings from EAHE system brings us that technology of varying temperature with the soil temperature found many benefits like energy saving and environment saving. These benefits may help us lot in future in the field of renewable energy resources which is peak demand of the society. The loss of energy can be minimized with the help such type of systems.  The use of EAHE is very limited in the state of Punjab and it becomes an energy crisis state in few years; if renewable energy resources not implemented at state level. The results of velocity variation reveal that for length of pipe 15 m and 1.5 m depth at velocities 4.8 m/s, 3.4 m/s and 2.5 m/s, the temperature drop is 4.2 °C, 7.5 °C and 9.2 °C respectively. Similarly the effect of variation in length of pipe has also been studied. As per the measurements the temperature drops of 9.2 °C, 10.6 °C and 11.9 °C corresponding to length of 15 m, 30 m and 45 m for air velocity of 2.5 m/s and depth of 1.5 m. The maximum average temperature fall corresponding to 2.5 m/s velocity, 1.5 m depth and 15 m length is 7.3 °C. The maximum average temperature fall corresponding to 45 m length, at 1.5 m depth and at 2.5 m/s velocity is 8.6 °C. The results show that maximum temperature drop available at low velocities because air gets larger time to get heat transfer in the underground pipe in soil. The best advantage of EAHE system is that it does not require water for cooling which is valuable feature in arid areas. It is that feature that motivated our work on EAHE development.

 

7. ACKNOWLEDGEMENT:

I would like to thanks to IKGPTU, Kapurthala who gives us opportunity to perform on Earth Air Heat Exchanger to found a low cost cooling system. The Investigations of Earth Air Heat Exchanger may not be fulfilling with the kind help of Dr Arun Kumar Asati, Associate Professor at Shaheed Bhagat Singh State Technical Campus, Ferozepur. I also thank Dr Rakesh Kumar Associate Professor and Head in the Department of Mechanical Engineering at IET, Bhaddal who helped me a lot at every step of my research.

 

8. CONFLICT OF INTEREST:

The authors declare no conflict of interest.

 

9. ABBREVIATIONS:

Subscripts

In:Inlet 

Out: Outlet           

EAHE: Earth air heat exchanger

T_in: Inlet temperature of air

T_out: Outlet temperature of air

 

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Received on 14.09.2017            Accepted on 13.02.2017       ©A&V Publications all right reserved Research J. Engineering and Tech. 2018;9(1): 59-66 DOI: 10.5958/2321-581X.2018.00009.0