This write-up describes the development and some applications of earth tube heat exchangers in Gujarat. Work outlined here was delivered as Nanubhai Amin Memorial Lecture at Electrical Research and Development Association, Vadodara as part of Technology Day, 11 May 2004.

Girja Sharan

English

Research Papers in Economics

 
Development and Some Applications of 
Earth Tube Heat Exchanger in Gujarat
♣ 
 
Girja Sharan   Ph.D. (Cornell) 
Agricultural Engineering [Farm Machinery & Power] 
Coordinator,  Cummins-IIMA Lab for  
Environmental Technologies in  Arid Areas,    
Indian Institute of Management, Ahmedabad 380 015 
Email :   gsharan@iimahd.ernet.in 
 
 
Abstract 
 
This write-up describes the development and some applications of 
earth tube heat exchangers in Gujarat.  Work outlined here was 
delivered as Nanubhai Amin Memorial Lecture at Electrical 
Research and Development Association, Vadodara as part of   
`Technology Day’,  11 May 2004. 
 
 
Earth Tube Heat Exchanger  
 
Earth Tube Heat Exchanger (ETHE) is a device that permits transfer of heat 
from ambient air to deeper layers of soil and vice-versa.  ETHE  usually  
consist of  loop(s) of  pipe buried in the ground  horizontally or vertically.  
Vertical  loops  go  deeper .  Horizontal  loops  are usually  buried at one 
to four meter depth.  Temperature regime at this depth and beyond is 
stable, with no diurnal fluctuation and with only a small seasonal or annual 
variation. 
 
This  stab ility is result of  a natural   physical phenomena.  Temperature 
waves dampen as they penetrate through layers of soil. High frequency 
waves do so more rapidly.  Accordingly   diurnal  fluctuations  ( one cycle 
                                                 
♣    Work on development and application of earth tube heat exchanger was  
supported by Gujarat Energy Development Agency (GEDA);   Cummins Diesel 
India Foundation;  and  Sir Ratan Tata Trust.   2
per day)   diminish  within less than a meter .  But  the annual wave (one 
cycle per year) penetrates deeper.  Its amplitude of  fluctuation is much 
smaller.  Large  mass of soil   at  a  stable  , near constant,  temperature  
permits its use as sink and source of heat.  
 
Ambient air is pumped through buried pipes at moderate velocities.   
When it is warmer (as in summers) than the basic temperature of soil 
surrounding the pipes, heat is transferred from air to soil resulting in 
cooling.  In winters or at nights the reverse takes place.  Thus, ETHE can be 
used for cooling  in summer and  heating  in winter.  
 
ETHE based systems are increasingly being used to condition the air in 
commercial livestock buildings, greenhouses.  Ground source heat pumps 
(GSHP) are used in North America, Europe to heat and cool houses, 
commercial complexes and offices.  Over 550,000 units are reported to be 
in operation worldwide and some 66,000 are added annually 
(Geoscience Ltd,   United Kingdom). 
 
Advantages and Disadvantages 
Being  result of a   natural phenomena deep ground as source and sink is 
available  easily in most places in the world. Such a use  is sustainable and 
equivalent to having a renewable energy source. 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.   However, initial 
installation costs are likely to be higher than the comparable conventional   3
(refrigerant based) systems.  Conventional systems can be customised 
easily for varied applications and industry is well developed. This is not yet 
the case for ground coupled systems.   
 
Development in Gujarat 
Cummins Foundation-IIMA Laboratory for Environmental Technology in 
Arid Areas    has been engaged in development of ETHE in the recent 
y e a r s .   A s  s t a t e d ,  t h i s  w a s  m o t i v a t e d  b y   n e e d  t o  f i n d  w a y s  t o  c o o l  
greenhouses in hot-arid Kutch, with minimal  or no use of water. Good 
quality water is chronically scarce there.   
 
Year-long measurements of deep soil temperature  in Ahmedabad 
indicated that mean temperature of ground is 27oC  [1].  T e m p e r a t u r e  
regime at Ahmedabad can be described  by equation (1).  
 
 
 
      ω        angular frequency   ( rad / day ) 
     k        thermal diffusivity      ( m2 / day ) 
      t        day of the year with  January 1 as origin ( numbers )  
      z        depth from surface (m) 
      T(t,z)  temperature  at depth  z,   day  t   ( oC ) 
  
Equation shows  what was stated earlier - that the amplitude   reduces 
with depth and that  higher frequencies dampen more rapidly.  Waves at 
k 2
ω
α =
1 .......... ) 105 (
365
2
cos 10 27 ) , (  

 
 − − + =
− z a t e z t T
z a π  4
deeper levels  are also out of phase ( lag )  with the one at the surface. At 
three-meter depth the fluctuations reduce to just  2.8oC.  This  suggested  
that a suitably designed ETHE  placed at this depth could cool the air 
close to what  ( evaporative) air coolers do.  
 
A    5 0  m   l o n g   s i n g l e  p a s s  E T H E  w a s   a c c o r d i n g l y  i n s t a l l e d  n e a r  
Ahmedabad to check this out [2] .   Figure-1 shows a schematic diagram 
of the installation. Diameter of the ms pipe used was 10 cm.  A blower of 
400 watt moved air  at 5.6 m3/min (200 cfm). The tube was buried at  3 m 
depth and was elaborately instrumented.  Performance tests were carried 
out each month for  one full year.  Tables (1) and  (2)  show the results 
respectively for the months of January when it was operated at night in 
heating mode and May in cooling mode. It is seen that the  ETHE could 
warm-up the cold air  by as much as 12 -13 oC.  It could cool the air in  
May  also by a similar amount, from  40.8oC to 27.2oC.  
 
Using the empirical results, a mathematical model was developed which 
permitted study by simulation of the effects of varying various parameters 
[3].  Simulations showed that increasing the length of pipe improves the 
performance. Reducing the air velocity , reducing the diameter of pipe 
also lead to improvement.  Use of metal pipes make for shorter transience 
or quicker response. Fixing fins to the outer surface of the pipe also 
appears to be beneficial.  Using these results, two working systems were 
built which are briefly described below. 
 
ETHE Based  airconditioning System Kamala Nehru  
Zoological Garden Ahmedabad 
 
This system was installed in the year 2000 at Kamala Nehru Zoological 
Garden,  Ahmedabad  to condition  ( cool in summer warm in winter)  the   5
air  in  the dwelling of tigers. The system configuration is given in detail in  
[4].  Figure-2 shows a schematic diagram. This system delivers  air at 44.4 
m3/min (1600 cfm).  It consists of two  20 cm diameter ms pipes  placed in 
parallel  at  two  meter  depth  in the  moat  near  the  dwelling .   Pipes 
are 27 m long each and are separated horizontally by 1.5 m.  Air is moved 
by a 1.2 kw blower. 
 
This system cools the ambient air in hot summer by about 80C and warms  
the cold air in winter by about 10oC.  System  was designed at the request 
of the zoo authorities and was preferred  because  it does not increase 
humidity in the dwelling as a desert cooler does.  It is economical and 
easy to maintain.   It was preferred also because it works as duel mode 
conditioner--cooling in summer  and  warming in winter. 
 
Greenhouse Coupled to  ETHE in Closed-Loop Mode  
at Kothara ( Kutch) 
 
This installation consists of a greenhouse  standing directly above a 
specially designed  large ETHE. Unlike the system in the Zoo, which is one 
way, here the greenhouse and ETHE are coupled  in closed-loop mode. A 
detailed description of the installation can be seen in [5].  Greenhouse is 
of   6 m  span,  20 m  length  and  3.5 m  height at the ridge. Ridge is east-
west oriented (figure-3). Cladding is 200 micron  UV  stabilized 
polyethylene sheet.  There are three vents - two on the sides and one at 
the ridge.   All vents are closeable. 
 
ETHE lies directly below the greenhouse at 2-3 m depth. It  consists of  eight 
pipes arranged in two tiers.  The first tier has four pipes placed at  3 m  
depth,  the second also has four pipes and is placed  1 m  above the first.  
Each pipe is 23 m  long and  20 cm in nominal diameter.  Thickness of pipe   6
wall is  3  mm.  Pipes are made of  mild steel,  and placed  1.5 m apart 
(Figure-4).  There is a common header at both ends of each tier.  Headers 
in turn are connected to specially fabricated ducting that rises above the 
ground to form inlet and outlet. Conditioned air is let into the greenhouse 
via a louvered opening,  6 m  wide and  0.45 m  high. Outlet on the 
opposite end is identical in construction to the inlet.  
 
 
ETHE provides air at the rate of 194 m3/min (7000 cfm). This is equivalent to  
20 air changes in the greenhouse per hour.  Blower is powered by a  4.2 kw   
1440  rpm  motor.   Figure-5  shows the fully furnished greenhouse. 
 
First cropping trial commenced in December 2002.  Tomato, chilli and 
capsicum were grown in the first round. Second round of cropping is now 
on. Tomato yield in the first round was 2.7 times of the open field yield. 
Water required was nearly half of the open field. These are satisfactory 
results. 
 
ETHE system has been used in winter nights to warm the greenhouse. Night 
temperature in Kothara begin to drop below  18oC in December.  January 
nights were colder with temperature going down to  8oC  to  9oC.  ETHE 
was operated at night from December 15 to February 15 when 
temperature in greenhouse fell below  15oC. The house was always closed 
at night. Temperature inside closed greenhouse at night was observed to 
be virtually the same as the ambient. 
 
Operation of ETHE at night raised the greenhouse temperature to  22-23oC  
within about  30 minutes. An on/off schedule was adopted.  ETHE would 
be turned on when temperature reached about 15oC,  turned off when it 
reached  22oC.  It usually took  70 to 80 minutes for temperature to fall   7
back again below  15oC.  Figure-6 shows the temperatures inside 
greenhouse and the ambient on  one of the nights (January 14-15).   ETHE 
was able to meet the heating need easily, entirely and at only a small 
cost.   
 
This greenhouse gains as much as  15oC in winter over the ambient when 
closed and  20-21oC  in summer months.  Cooling  is  needed practically 
all through the year during the day. low.  The aim in the first cropping trial 
was to determine the cooling capabilities of three provisions, singly and in 
combination and the schedule of operation that could be feasible. 
 
Opening the two side vents reduced the temperature gain significantly 
(Table-3).  Opening the ridge vent together with side vents reduces it 
further.  Fogging for 60 seconds every half hour was able to reduce the 
temperature by two another degrees.  It also increased the humidity 
levels.  ETHE operation (with all vents closed) reduced the greenhouse 
temperature by 6 to 7oC below the ambient.  
 
Figures-7 and 8  show tomato and chili being picked in the greenhouse.  
ETHE appears to be satisfactory in cooling mode as well. This is a 
significant achievement in Kutch. Our effort now is to reduce the cost of 
installation and of running. 
 
 
 
 
 
 
 
 
 
 
   8
 
 
 
Summary 
 
Gujarat is hot and arid in most parts.  Earth tube heat exchangers 
appear to be especially appropriate to  regions like Gujarat.  Unlike 
evaporative cooling procedures these do not use water.  These can be 
used both for cooling and warming. 
 
Our experience has demonstrated that these systems are easy to build 
and maintain. The fact that space could be cooled without the use of 
water in Kutch  promises to remove or at least greatly ease  a major 
impediment in introduction of greenhousing in hot arid areas.   
 
Experience has also shown that environmental control in the dwellings 
of animals in zoo can be done using ground coupled systems.   
Commercial livestock buildings--dairy cattle,  poultry-- offer further 
opportunities for application.  Improved comfort is known to lead to 
better health and productivity. 
 
   9
 
 
 
Table-1 :  Air Temperature inside ETHE and  
             Soil Temperature ( JANUARY ) 
 
Hour of 
day 
Ta 
(oC) 
Ts 
(oC) 
Tm/d 
(oC) 
To 
(oC) 
COP 
18:00 19.8  24.2 22.3  23.4  1.5 
19:00 17.6  24.2 22.2  23.4  2.6 
20:00 13.3  24.2 22.1  23.3  3.5 
21:00 11.9  24.2 21.9  23.3  3.4 
22:00 10.4  24.2 21.8  23.3  4.3 
23:00 9.6  24.2 21.7  23.3  4.5 
0:00 9.1  24.2  21.6 23.2  4.6 
1:00 8.7  24.2  21.5 23.2  4.7 
2:00 8.3  24.2  21.5 23.0  5.0 
3:00 8.7  24.2  21.4 23.0  4.5 
4:00 9.1  24.2  21.3 22.9  4.4 
5:00 9.6  24.2  21.2 22.9  4.3 
6:00 9.8  24.2  21.2 22.8  4.2 
 
  Ta      Ambient air temperature 
 
  Ts        Soil temperature at  3 m  depth 
 
  To       Temperature of air coming out of the tube 
 
  Tmd    Temperature of air  at 25 m along the tube 
 
 
 
 
 
 
 
 
   10
 
 
 
 
            Table 2:  Air Temperature inside ETHE and  
                            Soil Temperature  ( MAY )  
 
Hour of 
day 
Ta 
(oC) 
Ts 
(oC) 
Tm/d 
(oC) 
To 
(oC) 
 
COP 
10:00 31.3  26.6  29.1  26.8  1.73 
11:00 33.7  26.6  29.2  26.8  2.6 
12:00 36.4  26.6  29.5  27.2  3.2 
13:00 37.8  26.6  29.5  27.2  3.9 
14:00 40.8  26.6  29.7  27.2  4.4 
15:00 40.4  26.6  29.7  27.2  4.2 
16:00 39.8  26.6  29.8  27.2  4.1 
17.00 39.6  26.5  30  27.2  4.0 
 
  Ta      Ambient air temperature 
 
  Ts        Soil temperature at  3 m  depth 
 
  To       Temperature of air coming out of the tube 
 
  Tmd    Temperature of air  at 25 m along the tube 
 
 
 
 
 
 
 
 
 
 
 
   11
 
 
 
 
 
 
 
 
 
Table-3   :  Difference between empty greenhouse 
  temperature and the ambient 
 
Details February 
2002 
( oC ) 
April 2002 
( oC ) 
June 2002 
( oC ) 
 
All  vents  
closed 
 
15.4 20.0 21.3 
Only the side 
vents open 
 
5.5 6.7 7.9 
Side and 
ridge  vents 
open 
4.9 - 2.6 
 
 
 
 
 
   12
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure-1   
      Single Pass 
 installed at Thor  for  R&D  
 
 
 
 
         2  14
 
 
 
Figure 3:  Greenhouse Coupled to Earth Tube Heat Exchanger (ETHE)  
         at  Kothara (Kutch-Gujarat)  -   Schematic 
 
 
 
Louvr
Greenhouse  Roll-
up 
ETHE   15
 
  
Figure-4:  ETHE before being covered 
 
 
   16
 
 
Figure-5:  Fully Furnished Greenhouse, Kothara-Kutch Showing 
Blower and Suction Duct 
 
   17
 
 
 
 
 
Figure-6:  Greenhouse and ambient temperature  
                  (Night of 14-15 January). 
Greenhouse 
Ambient   18
 
 
 
 
 
 
    Figure-7:   Tomato being picked from  
                       Greenhouse   19
 
Figure-6:    Chili  being picked  
 
 
 
 
 
   20
 
References 
1.  Sharan G.  and  Jadhav R. (2002).  Soil temperature regime at Ahmedabad. 
Journal of Agricultural Engineering,   39:1,  January-March). 
 
2.  Sharan G. and  Jadhav R. (2003). Performance of single pass earth-tube heat 
exchanger: An experimental study. Journal of Agricultural Engineering 
[forthcoming]. 
 
3.  Sharan G. and  Madhavan T. (2003). Mathematical Simulation of Thermal 
Performance of a Single Pass Earth-Tube Heat Exchanger.  Journal of Agricultural 
Engineering [forthcoming]. 
 
4.  Sharan G., Sahu R.K. and Jadhav R. (2001).  "Earth Tube Heat Exchanger Based 
Air-conditioning for Tiger Dwellings."  Zoos' Print,  16:5,  May,  (RNI 2:8). 
 
5.  Sharan G.,  Prakash H. and Jadhav R. (2003). Performance of greenhouse 
coupled to earth tube heat exchanger in closed-loop mode.   XXX CIOSTA-
CIGR V Congress Proceedings of `Management and Technology Applications 
to Empower Agriculture and Agro-food Systems,'  Turin, Italy,  Vol.2,   September 
22-24,    pp.865-873.  
 
 
 
 
 
 
 

Earth Tube Heat Exchanger Based Air-conditioning for Tiger Dwellings.&quot; Zoos'

Mathematical Simulation of Thermal Performance of a Single Pass Earth-Tube Heat Exchanger.

Performance of greenhouse coupled to earth tube heat exchanger in closed-loop mode.

Performance of single pass earth-tube heat exchanger: An experimental study.

Soil temperature regime at Ahmedabad.

Development and Some Applications of Earth Tube Heat Exchanger in Gujarat

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Development and Some Applications of Earth Tube Heat Exchanger in Gujarat

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Research Papers in Economics