Engineering Analysis: Ground Source Heat Pump Systems & Climate

This report provides an in-depth analysis of Ground Source Heat Pump (GSHP) systems, covering their operational principles, major components like ground loops, heat pumps, and distribution systems, and various types including closed-loop (vertical, horizontal, slinky, pond) and open-loop systems. It discusses factors affecting GSHP operations, such as Seasonal Performance Factor, and explores the application of these systems in hot and dry climates, referencing studies conducted in regions like Saudi Arabia. The report highlights the temperature profiles, soil properties, and cost analyses associated with GSHP implementation, emphasizing the potential for energy savings and the importance of considering geological and economic factors. It also notes the advantages and disadvantages of different loop configurations, providing a comprehensive overview of GSHP technology and its practical considerations.

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2.4 Principle of operation of GSHP
Ground Source Heat Pumps are systems that consist of three major elements; (a) the ground loop
major element that is includes in the GSHP system. A schematic representation of the operation
of the GSHP system is given in the figure 2.1. In detail, the GSHP contains a ground loop
(ground heat exchanger GHE), a heat pump unit and distribution system. In addition to this a
refrigeration system is also included in a GSHP system.
2.4.1 Ground Loop
The Ground loop is formed by a connection of network which is a closed loop and an outlet
structure known as open loop which is located underground or underwater. The entire set up of
the ground loop is always located outside the building footprint. Collecting the heat from the
ground water or the ground and disposing the heat to the ground or ground water is the main
function of ground loop (Bonin, 2015). This function of the ground loop is accomplished when
circulating a fluid through pipes. In the submerged pipes, working fluid is made to circulate and
the groundwater is also taken out of the ground loop.
2.4.2 Heat pump
Heat is transferred by a heat pump from a fluid with a low temperature and passes it at very high
temperature to another fluid; a heat pump may also be used. From low to high temperature; heat
is transferred a by heat pump that is Heat collected in the ground is transferred to the application
using refrigeration where the ground is used as the heat source. The discharged heat is
transferred from the building to the ground in the cooling mode (Ghosh, 2011).

2.4.3 Distribution System
The major function of a distribution system is to distribute heat to the application and the heat
from the application is also removed by a distribution system. Consider heating a swimming pool
which is the best example of the distribution system. A good example is heating the swimming
pool.
2.4 Factors effect GSHP operations
For the ground source heat pump, the Seasonal Performance Factor is always about 4 and ground
source heat pumps are much more efficient for the heating season.
2.5 Types of Geothermal Heat Pump Systems
Based on the set up or installation surface of the GSHP can be classified into several categories.
A GSPH can be installed above the surface of the ground about 20 meters from the surface the
ground. When a GSHP is installed below the ground surface and the distance is not more than 20
meter then it is said to be superficial shallow (Bonin, 2015). A GSHP be installed between 30
meter to 400 meter under the ground surface and this is defined as shallow ground. Ground
Source and Heat Pump can be installed in two ways which are termed as a closed loop and an
open loop.
2.5.1 Closed loop systems
Heat transfer in the closed loop systems does not have any direct contact with the ground and the
loop fluid for the heat transfer is enclosed. Further, There will is direct contact of the closed
loop system with the ground and Pipe is installed and it is only through the piping that the heat

transfer occurs (Rees, 2016). This closed loop is classified into different types, one is a vertically
closed loop, and the other one is horizontally closed loop. Slinky or spiral closed loops and in
addition to closed pond loops are other types of closed loop systems. For all these types the
configuration of the system and the space requirement varies and the installation depth varies
from one type to other type in closed loop systems.
2.5.1 .1 Vertical closed loop
A vertical closed loop, ground bores has to be constructed and it contains vertical oriented heat
exchange pipes. For residential application a bore hole ranging in size from 45 to 75 meter depth
is usually require but for industrial application then above 150 meter depth bore hole is usually
constructed (RSES, 2011). Thermal contact has to be maintained between the heat exchanger and
the borehole wall. Entire gap around the borehole is filled with enhanced cement or sand but
betonies can also be used to fill the gap. In the heat exchanger, the fluid is circulated and
transfers the heat from ground to the heat pump and again from heat pump heat is transferred to
the ground. This process exchanges heat in the ground surface. Based on the type of the heat
exchanger and grouting material employed, the thermal efficiency of BHE varies and
performance of the BHE is based on the initial ground temperature (Orio, 2013). The hydraulic
properties and ground properties also impact on the performance of the BHE. In general, vertical
loop system is more advantageous for large applications but it has the major disadvantage of the
large installation cost. Further in the installation cost is high in the vertical than horizontal closed
loop.
2.5.1.2 Horizontal closed loop

The Heat exchange well contains a loop of piping which is horizontally installed and usually
within 15 feet below the ground surface. A Horizontal closed loop is considerably about 30
percent in a vertical closed loop and several factors have an impact on the cost, namely.
 Poor (geology): a larger collector field is required if the geology is poor.
 Collector protection: Protection has to be given for the horizontal collector against
sharp stocks (Chiasson, 2016).
 Excavation trenches the amount of time spent must be considered.
 Landscaping; the ground is a factor.
These factors reduce the cost of the installation of horizontal closed loops; however the exact
costs can only be calculated after a thorough geological investigation the area undertaken.
2.5.1.3 Slinky closed loop
A slinky closed loop, or spiral loop, is horizontal oriented loop within shallow trenches and
therefore resembles to a conventional horizontal loop. The piping in the slinky closed loop is laid
out as circular loops and therefore requires a smaller area when compared to a horizontal closed
loop and in slinky loop at the end return pipe is attached to the heat pump and the system
requires a huge amount of piping in order to carry on with the load. A spiral GHE can either be
fixed vertically or horizontally (Silberstein, 2015). The heat transfer is low in spiral GHE which
is the major disadvantage of using that system. However slinky supports high pumping, due to
the added pipe length and this is the main advantage of using the system.
2.5.1.4 Closed pond loop
A geothermal long pipe is defined as a closed pond loop and this pipe is attached and placed
inside a lake or a water source. The loop has to be completely immersed in the water and

installed in such a way that it is about 8 feet above the pond loop. Further, the pond or lake,
which has larger volume, can only be used for the installation of the closed pond loop. The coils
of pond loop are connected to the skid and installed under the water in order to prevent from
freezing.
2.5.2 Open loop systems
In general for large commercial applications an open loop system is used as the system directly
interacts with the ground (Kavanaugh, 2014). Groundwater or surface water is used as a direct
heat transfer medium in open loop systems and system requires a huge groundwater source for
its operation and as the result it is not suitable for all locations. The water from the lake or
groundwater is directly extracted and sent to the heat exchange pipe and after the heat exchange
is achieved then discharged back to the source of water the through a separate pipe. The issue
that has to be investigated in the installation of an open loop system is if there is sufficient
groundwater available. Thus installation cost of an open loop system is very low when sufficient
ground water is availability (Kavanaugh, 2014). An open loop system has a high coefficient of
performance and the system is considered to be an environment friendly system since the heat
carrying medium is in direct contact with the ground.
2.6 Ground source heat pumps in hot and dry climates
As part of the assessment, a literature review of hot and dry climates where ground coupled heat
exchangers have been used is investigated in order to determine the temperature profiles and soil
properties required for the performance of these heat exchangers. Hot and dry climates are
encountered in vast regions across the globe but, unfortunately, not much data exists in terms of
borehole temperatures at various depths in hot and dry climates. The following studies have been

assessed in order to qualitatively assess the available literature such that it may form part of the
assessment (Lloyd, 2016). A synopsis of how this is relevant in investigation has also been
evaluated.
2.6.1 Saudi Arabia
An assessment into the feasibility of using ground-coupled condensers for air-conditioning (A/C)
systems in Saudi Arabia was investigated (Said et al., 2010). The temperatures and soil
properties required for the performance analysis of one of these condensers was determined
experimentally and thermal response tests were conducted to evaluate the effective thermal
conductivity of the ground. The measurements undertaken as part of this investigation revealed
significant differences between the ambient air and the ground temperatures, which results in an
increase in the coefficient of performance and in a reduction in the energy consumption of an
A/C unit when using a vertical ground heat exchanger rather than an air-cooled condenser which
is the existing norm in the country (Ghosh, 2011). A maximum difference of about 12oC was
observed between the ground temperature and the dry bulb temperature of the ambient air. A
steady-state value of 32.5oC for the mean borehole temperature was reached.
A cost analysis was also undertaken by investigators and this indicated that the use of ground-
source heat pumps in Saudi Arabia would result in about 28% energy savings should ground
coupled heat pumps be utilized over the use of the ambient air. However it was deemed not
economically viable due to the low electricity prices that were prevalent in the country due to
government subsidies and high drilling costs.

The study highlighted some salient aspects to note which are relevant in our study
I. There is a significant temperature difference between the ambient air and the ground that
will favors the performance of GHXs over that of air-cooled condensers.
II. The ground temperature in the KSA does not change significantly below about 30m
depth throughout the year.
III. A performance analysis indicated an increase in the COP, and a reduction in the energy
consumption of an A/C unit, when using a vertical GHX instead of an air-cooled
condenser and this resulting in energy savings of about 28%.
Another study, Sharqawy et al., (2009) deals with the in situ experimental determination of the
thermal properties of the underground soil for use in the design of borehole heat exchangers
(BHE). The approach is based on recording the unsteady thermal response of a BHE and this
was, installed for the first time in Saudi Arabia.
In this approach, the temperature of the circulating fluid was recorded at the inlet and outlet
sections of the BHE with time as bellow.

The survey revealed typical costs of a drilling of oil borehole drillers and this can be as high as
$300 per meter of borehole depth but for water well drilling cost much less since it used a rotary
drilling rig and the averaged cost is about at $50 per meter.
The recorded thermal responses, together with the development of a simple line source theory,
were used to determine the thermal conductivity, thermal diffusivity and the steady-state
equivalent thermal resistance of the underground soil.

This was the first experience at representing a step towards a more detailed study on the effective
thermal properties of soil in different location in Saudi Arabia with a view to possible practical
applications of geothermal energy in the region.
From the experience accumulated from the results obtained by the report the following
conclusions may be
(a) A new approach was introduced in the assessment of a thermal response test data. In this
approach, it was possible to determine the time before which some experimental data could be
excluded to minimize the error associated with the line source model without knowing the value
of the thermal diffusivity v. In addition, the value of soil thermal diffusivity could be obtained as
well as the thermal conductivity and thermal resistance (Energy, 2014).
(b) For the selected site, the BHE effective values of 2.154 (W/m K), 6.252 x 10-6 (m2/s) and
0.315 (m K/W) were determined for the soil thermal conductivity, thermal diffusivity and
thermal resistance, respectively.
2.6.2 Erbil, Iraq
Due to the wide and varied climatic and soil conditions encountered in Saudi Arabia, a literature
review of hence conditions in Erbil, Iraq was performed. This area has more northern latitude
than Saudi Arabia but it closely resembles the dry mountainous region of Hejaz which forms a
natural barrier running parallel to the Saudi coastline from Yemen in the south to Jordan in the
North (CHUN-KWONG, 2017).
Investigate the storage technology used to save energy for a school building in Erbil, Iraq and
this covers different storage methods that are used in Iraq for energy storage. The assessment

covered a borehole thermal energy storage system in an underground structure for large
quantities of heat and cooled energy in the soil and rocks. The Earth energy design 2.0 PC-
Program was used for the borehole design and test building consisted of six class rooms within
the school with a total build area of about 1200m2, a height was 3m and a total volume 0f
3600m3. The annual mean temperature was calculated at 20.95OC and a degree hour method was
used to calculate the energy demand above the base temperature 17OC for heating and 20OC for
cooling (Ochsner, 2012). The required maximum power demand for heating was calculated at
158.4kW and the maximum power demand for cooling the building is 211.2kW based on the
climatic yearly extremes experienced in Erbil. The months from November until April were used
for calculating the total heating demand for the school building, and this was calculated to be
254,52MWh.
The months of May until September were used for calculating the total cooling demand for the
building, and it was calculated to be 10MWh. The month of October had a mild climate which
required no heating or cooling.
Erbil has been selected in our study due to a pervasive mountainous terrain which is similar to
the dry mountainous region in Hejaz which forms part of eastern Saudi Arabia. It is envisaged
that a similar borehole thermal energy storage system could be adopted in eastern Saudi Arabia.
2.6.3 Tunisia
The aim of this study by Naili et al., (2012) was first to evaluate the Tunisian geothermal energy
potential and to test the performance of a horizontal ground heat exchanger.

An experimental set-up was constructed for the climatic conditions in the Bork Cedria region
which is located in the north of Tunisia. The ground temperature at several depths was measured,
and the overall heat transfer coefficient (U) was determined.
The heat exchange rate was quantified, and the pressure losses were calculated. The total heat
rejected by using the ground heat exchanger (GHE) system was compared to the total
requirements of a tested room with a 12 m2 surface. The results showed that the GHE, with a 25
m of length buried at 1 m depth and this covered about 38% of the total cooling requirement of
the tested room.
This study showed that the ground heat exchanger could provide a new way of cooling buildings,
and also showed it that Tunisia has an important geothermal potential which could allow Tunisia
to be a pioneer in the exploitation of geothermal energy for the installation of ground source heat
pump systems (Chiasson, 2016).
While Tunisia is at more northern latitude than Saudi Arabia, it does but share similar climatic
conditions. The feasibility of horizontal borehole heat pumps can be utilized as a cooling
requirement of up to 38% can be realized at shallow depths of 1m and this could be considered
for standalone borehole heat pump applications (Orio, 2013).
Chapter 3: Ground Source Heat Pump Modeling
3.1 Introduction
One of the fundamental tasks in the design of a reliable ground-coupled heat pump system is the
proper sizing of the ground-coupled heat exchanger length i.e. the depth of borehole. Recent

research report has produced several methods and commercially available design software tools
for this purpose (Ingersoll, 1954; Kavanagh and Rafferty1997).
Al these design tools are based on the principle of heat conduction and rely on some estimate of
the ground thermal conductivity and volumetric specific heat. These parameters are perhaps the
most critical in the system design, yet adequately determining them is often the most difficult
task in the design phase. The objective os this chapter deals with the development and/or
application of a model, such that the principle of heat conduction can be accurately predicted.
3.2 Modeling
A “model” can defined as a physical or a mathematical representation of an actual system. A
model may help to explain a system and to study the effect of different component, and to make
predictions about different models (Bonin, 2015). A numerical model is the best way to break
everything down to an elemental level with a view to reconstruct and predict how the system
would behave under different conditions .This study deals only with mathematical
representations of system. The American Society for Testing and Materials (ASTM) defines a
mathematical model as “mathematical questions expressing the physical system behavior and
including simplifying assumption”. Mathematical models are solved analytically or using manual
or computer methods
The modeling approach consists of six stages:

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