EXPERIMENTAL SETUP FOR THE DETERMINATION OF HEAT …

Proceedings of 2nd International Conference on Mechanical and Aeronautical Engineering

Held on 13th – 14th July 2016, in Bangkok, ISBN: 9788193137352

79

EXPERIMENTAL SETUP FOR THE DETERMINATION

OF HEAT TRANSFER INSIDE THE SOIL REGION IN

GROUND SOURCE HEAT PUMP (GSHP)

Nurullah Kayacı

Heat and Thermodynamics Division,

Department of Mechanical Engineering, Yildiz

Technical University (YTU), Yildiz, Besiktas,

Istanbul 34349, Turkey

Hakan Demir

Heat and Thermodynamics Division,

Department of Mechanical Engineering, Yildiz



S. Ozgur Atayılmaz

Heat and Thermodynamics Division, Department of Mechanical Engineering, Yildiz



Ozden Agra

Heat and Thermodynamics Division, Department of Mechanical Engineering, Yildiz



Abstract- The earth is an energy resource which has

more suitable and stable temperatures than air.

Ground Source Heat Pumps (GSHPs) were

developed to use ground energy for residential

heating. The most important part of a GSHP is the

Ground Heat Exchanger (GHE) that consists of

pipes buried in the soil and is used for transferring

heat between the soil and the heat exchanger of the

GSHP. Two important parameters of selection and

sizing of soil heat exchanger other than properties

of the soil are the depth of burying and distance

between buried pipes. It is also important to

determine different ways of arrangement under the

ground. Slinky, horizontal straight pipes and

horizontal U-type soil pipe were buried to ground

under the building foundation. Also, horizontal

straight pipes were buried into concrete section of

the building foundation. Thermocouples were

connected on these pipes to measure ground

temperature distribution in horizontal and vertical

axes. The experimental setup is designed for

capable of changing the different operating

parameters. The detailed description of design and

development of the experimental setup for ground

source heat pump system has been explained in

detail depending on our project. It experimental

setup, control devices, instrumentation and the

experimental procedure are reported and the study

of experimental setups from the available literature

survey with the existing one are compared in this

paper. The determination of heat transfer and

temperature distribution of two different types of

buried pipes which were U-type and straight pipe in

soil by means of Ansys Fluent program are shown

in this study.

Keywords: Ground source heat pump, Ground heat

exchanger, slinky heat exchanger, heat transfer

I. INTRODUCTION

Humankind have directed to investigate more

efficiently use of available energy sources and use of

renewable energy systems because of growing energy

demands and decreasing energy sources as well as

harm of fossil fuels to world. Heating and cooling

systems demanding low energy for building have been

developed like the other application used energy. Heat

pump systems which can be provided high heating



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and/or cooling demands as well as with low energy

consumption have quite importance for these aims.

The principles work of the heat pump is a loop of

refrigerant that is pumped through a vapor-

compression refrigeration cycle moving heat. Thus,

heat pumps can transfer heat from a cool medium to a

warm medium against the natural direction of flow.

Also, they can be used to enhance the natural flow of

heat from a warm medium to a cool medium.

There are different heat pump systems called such as

ground source, air source, water source and etc.

Ground source heat pump (GSHP) has been considered

with this study. A ground source heat pump is a central

heating and/or cooling system transferring heat from

ground or to ground depending on purpose of condition

of building. It uses the earth as a heat source in the

heating season or a heat sink in the cooling season.

This design takes advantage of the moderate

temperatures in the ground to increase efficiency and

reduce the operational costs of heating and cooling

systems. Also, it may be combined with different

systems like solar heating with even greater efficiency.

Because the temperature beneath the upper 6 meters of

Earth's surface maintains a nearly constant temperature

between 10 and 16 °C depending on latitude [1],

ground is quite good at a heat source for systems

working main vapor-compression cycle. Ground heat

exchangers mainly are settled horizontal and vertical

into ground. Horizontal settlement of GHE can be

designed such as single-pipe, multiple-pipe, and spiral-

type systems and etc. A typical heat pump has a COP

of around 4 which indicates that the heat pump

produces four units of heating energy for every unit of

electrical energy input. The COP of the GSHP depends

on the soil type at the installation [2]. But these

systems have still high initial cost, since ground heat

exchangers can be constructed using common

excavation machines [3].

In literature, there are many studies on ground source

heat pump (GSHP) as experimental, numerical and

analytical studies especially for ground heat

exchangers. Li et al. worked on experimental and

theoretical methodology with which a designer can

determine the size of a spiral heat exchanger. They

suggested that their methodology can be applied

effectively to different spiral heat exchanger

configurations [4]. Wu et al. studied on slinky ground

heat exchangers in term of both experimental and

numerical studies. After validation of experimental

studies for two months with 3D model numerical

studies, they declared there was no significant

difference in the specific heat extraction of the slinky

heat exchanger at different coil diameters. Also, they

concluded that the larger the diameter of coil, the

higher the heat extraction per meter length of soil.

They used 4 parallel horizontal slinky heat exchanger

loops placed in 80 m long by 20 m wide paddock area

at a depth of around 1.2 m below ground surface [2].

Esen et al. investigated of energetic and exergetic

efficiencies of ground-coupled heat pump (GCHP)

system as a function of depth trenches for heating

season. They settled horizontal GHEs consisting of a

high density polyethylene tube, 16mm diameter in 1 m

from ground surface [5]. Demir et al. carried out

experimentally on GHEs consisting of three parallel

pipes which have 40 m length and 1/2" diameter buried

in soil. Also, they suggested a new numerical models

by means of energy balance equation to estimate the

fluid outlet temperatures with a small error can be used

for calculating optimum ground heat exchanger

dimensions and burial depth for a given location if

meteorological data are available [6].

In this study, experimental setup for ground source heat

pump system has been explained in detail depending

on our project. It has been placed three different

configuration of horizontal ground heat exchangers and

a horizontal heat exchanger in concrete as shown in

Figure 3. They are respectively called as U-pipe heat

exchanger in soil, straight pipe heat exchanger in soil,

slinky heat exchanger and straight pipe heat exchanger

in concrete. It has been expressed how to prepare

ground source heat pump systems. For this purpose,

measurement devices have been elucidated how to be

calibrated and inserted. Also, ground heat exchangers

gradually have been informed how to be buried and the

last case of project with plan to future has been

commentated. Also, numerical analysis has been

applied to straight pipe heat exchanger in soil and U-

pipe heat exchanger in soil to determine heat fluxes and

temperature contours depending on different pitch

spaces. Also, material of pipes were investigated on



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provided heat fluxes at different pitch spaces for U-

pipe heat exchangers in soil.

II. EXPERIMENTAL SETUP

Experimental system has been applied to Central

Laboratory of Yıldız Technical University, which has

been built newly in YTU Davutpaşa Campus. The

building has 4 store and 84 m x 30 m settlement area.

Figure 1 shows the building plan of Central Laboratory

of Yıldız Technical University.

Figure 1. The plan and real photo of Central Laboratory of Yıldız Technical University

Experimental system basically has been contained

three stages involving the calibration and insertion of

measurement device, settlement of heat exchanger in

soil and concrete, settlement of heating and cooling

panels to indoor building.

a) Settlement of Heat Exchanger in Soil and

Concrete

To set up the system, firstly heat exchanger soil side

was properly buried to area of building foundation after

the abolition of excavation as seen on Figure 2.



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Figure 2. Abolition of excavation and settlement of heat exchangers

These heat exchangers are U-pipe, straight pipe in soil,

slinky. Also, there is a heat exchanger buried in

building foundation, which is called as straight pipe in

concrete. The planned design of settlement of heat

exchanger both soil and concrete of building

foundation can be seen on Figure 3.

Figure 3. Design of settlement of heat exchanger both soil and concrete of building foundation

Due to project, the heat exchangers were placed as seen

on Figure 4. About 370 meters pipe which is produced

from polyethylene and has 32 mm outer diameter were

used for slinky pipe implementation. Distance between

pipes were determined as 50 cm.

About 850 meters of PE32 pipe was placed for U-pipe

implementation, straight pipe in soil and straight pipe

in concrete.

Figure 4. shows implementation of settlement of heat

exchanger both soil and concrete of building

foundation. After settlement of heat exchangers in

ground, the special sand which does not include rock

etc. spread over pipes to protect them.



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Figure 4. Implementation of settlement of heat exchanger both soil and concrete of building foundation

After the heat exchanger in soil and concrete were

settled, each of them connected heat pumps. There are

four heat pumps having 11 kW power on the system.

The thermocouples were properly placed to soil and

pipes.

Figure 5. Heat pump used in project and its connection chart

b) Calibration and Insertion of Measurement

Device

Many measurement devices consisting thermocouples,

RTDs, differential pressure transmitters, turbine type

flowmeters have been used so as to measure

performance of systems. Thermocouples used in the

project are T*-type and have 2 x 0.3 mm diameter.

Firstly, the thermocouples cut as 6 - 7 meters by

thinking different configurations and their tips were

connected with a thermocouple welding placed in the



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University laboratory. Cutting and welding process can be seen on Figure 6.

Figure 6. Cutting and welding of thermocouples

Then, each of them were numbered and connected to

datalogger cards as seen on Figure 7. After that

process, the screw terminal cards were inserted to data

logger and they were calibrated with a RTD type

thermometer in a constant temperature bath which

maintains the temperature as desired. Data loggers used

for experimental study are Agilent 34972A brand for

both calibration and measurement of systems.

Figure 7. Calibration of thermocouples

After calibration of thermocouples, their calibration

curves and equations were obtained for each of

thermocouples. Figure 8 illustrates the screenshot of

computer program during the calibration of a

thermocouples.



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Figure 8. Calibration curve and screenshot of computer program for a thermocouple

After all those processes, the calibrated thermocouples

were precisely placed into soil and concrete. The

thermocouples were inserted at 10 cm intervals into

ground and building foundation to see variation of soil

temperature during working conditions as seen on

Figure 9.

Figure 9. Insertion of thermocouples to ground

In addition to that processes, RTD type temperature

measurement devices have been used to determine

water temperature in ground heat exchangers by

inserting to stream and return of heat pumps. Each of

heat pump systems have been used two RTD.

Similarly, differential pressure measurement devices

have been inserted to each of heat pump systems to

determine pressure drop of ground heat exchangers. At

the same time, flow meters have been inserted to

systems to be indicated flowrates during working

conditions.

c) Installation of Heating and Cooling Panels to

Indoor of Building

This stage of project is under construction, because the

building has not completed yet. But, settlement of

panels have been planned as seen on Figure 10. The

administration of university has been provided 7 rooms

for indoor panel applications whose total areas are

about 210 m2. The panels have been produced and will

be applied to the building by Dizayn Group

Corporation being our project partner. The area

numbered as 1 in Figure 10 is going to be conditioned



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by both wall and ceiling panels working with a heat

pump connected to U-pipe ground heat exchanger. The

areas numbered as 2, 3 and 4 in Figure 10 are

approximately 52 m2 and each of them are going to be

conditioned just wall panels working with a heat

pumps connected to straight pipe in soil, straight pipe

in concrete and slinky type heat exchangers

respectively.

Figure 10. Plan of wall and ceiling panels settlement

III. DETERMINATION OF HEAT TRANSFER

AND TEMPERATURE DISTRIBUTION OF TWO

DIFFERENT TYPES OF BURIED PIPES

Analytical studies has been done and will be done

during project as well as experimental studies by Ansys

Fluent®. It was started analyzing U type heat

exchanger in soil according to different pitch space of

pipes and different material of pipe conditions. The

pitch spaces have been selected as 25 cm, 50 cm and

75 cm.

Figure 11. Creating meshes depending on U pipe heat exchangers

Figure 11 (a) shows design of U pipe heat exchanger

in soil, (b) and (c) illustrates creating meshes

depending on U pipe heat exchangers. 3D meshes were

applied to design, also relevance center was kept high

for analyses, because the pipe diameter was quite small

compared soil. There are 1581622, 1692663 and

16992801 nodes and 7747120, 8193642 and 8352972

elements for 25cm, 50 cm and 75 cm pitch spaces

respectively.

Figure 12 (a), (b), (c) illustrates pitch spaces as 25 cm,

50 cm and 75 cm, respectively.



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Figure 12. Temperature contours of U-pipe heat exchangers in soil according to different pitch spacing of pipes

Analyses have been conducted for 6 months period. It

has been determined that the ground temperatures

changed between 274 K and 278.2 K at the end of 6

months for three different configurations (25 cm, 50

cm and 75 cm), when the initial temperature of ground

289 K. Also, polyethylene and copper pipes have been

compared in terms of heat provided heat quantity per

meter for each configurations. The results shows that

there is no big differences provided heat per meter for

25 cm pitch spaces between copper and polyethylene

pipes. However, material of pipes has been become

important with increased pitch spaces as seen on Figure

12.

Figure 13. The comparison of provided mean heat fluxes per meter in terms of material of pipe: copper and

polyethylene (W/m)

The average heat fluxes provided from ground with

polyethylene pipes according to 25, 50, 75 cm pitch

spacing became 3.30 W/m, 5.82 W/m and 7.65 W/m,

respectively. The provided heat fluxes by means of

copper pipes were determined as 3.41 W/m, 6.21 W/m

and 8.35 W/m under similar conditions respectively.



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VI. CONCLUSIONS

In this study, experimental for ground source heat

pump system setup and numerical analysis U pipe

GHEs has been explained in detail depending on our

project.

- Calibration and insertion of measurement

devices have been explained.

-

- Settlement stages of GHEs have been

elucidated for each GHEs: U pipe, straight

pipe in soil, slinky and straight pipe in

concrete.

-

- It has been commentated how to be installed

panels to indoor building in future

- .

- Numerical analyses have been conducted

according to different pitch spaces and

different pipe materials for U pipe heat

exchangers.

V. ACKNOWLEDGEMENT

This work was supported by Ministry of Science,

Industry and Technology of Turkey under SAN-TEZ

program with Grant No. 0472.STZ.2013-2 and partly

supported by MIR R&D. We gratefully acknowledge

these supports.

REFERENCES

1. "Geothermal Technologies Program:

Geothermal Basics". US Department of

Energy. Retrieved 2011-03-30.

2. Y. Wu, G. Gan, A. Verhoef, P. L. Vidale, R.

G. Gonzalez, Experimental measurement and

numerical simulation of horizontal-coupled

slinky ground source heat exchangers,

Applied Thermal Engineering 30 (2010)

2574-2583.

3. H.Fujii, S.Yamasakia, T. Maeharaa, T.

Ishikamib, N. Chouc, Numerical simulation

and sensitivity study of double-layer Slinky-

coil horizontal ground heat exchangers,

Geothermics 47 (2013) 61– 68

4. H. Li, K. Nagano, Y. Lai, A new model and

solutions for a spiral heat exchanger and its

experimental validation, International Journal

of Heat and Mass Transfer 55 (2012) 4404–

4414.

5. H. Esen, M. İnallı, M. Esen, K. Pihtili, Energy

and exergy analysis of a ground-coupled heat

pump system with two horizontal ground heat

exchangers, Building and Environment 42

(2007) 3606-3615.

6. H. Demir, A. Koyun, G. Temir, Heat transfer

of horizontal parallel pipe ground heat

exchanger and experimental verification,

Applied Thermal Engineering 29 (2009) 224-

233.

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EXPERIMENTAL SETUP FOR THE DETERMINATION OF HEAT …