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This research project represents an investigation into the energy efficiency and cost effectiveness of a Ground Source Heat Pump used in a domestic dwelling, with a view to attempting to prove that a Ground Source Heat Pump is viable form of home heating. With the demand and escalation in oil and gas prices, and predictions that they will continue, house heating is now becoming a more and more expensive part of our lives we take for granted. Being environmentally friendly and offering cheaper home heating costs, a GSHP is becoming increasingly attractive for home owners.
An interview was conducted with the owner of the GSHP with an aim to establish the efficiency and cost effectiveness of the GSHP.
It was calculated that the ground coil in the sample GSHP was oversized by 750 metres, whereas the heat pump was slightly undersized. It was judged that these two factors increased the efficiency of the GSHP although at the cost of a more expensive installation for the extra ground coil.
The study proved a GSHP to be a cleaner house heating method in comparison to other more commonly used house heating methods. The result was that a GSHP emits 66% less carbon dioxide per year than oil heating as well as 43% less carbon dioxide than gas heating.
In regard to pricing it was proved that GSHP's are a cheaper form of house heating in comparison to gas and oil heating. A GSHP offered savings of £400 and £300 respectively, in a four bedroom detached house.
I would like to take this opportunity to express my gratitude to the people who gave me guidance, continuous help and patience throughout the year who without them this dissertation could not have happened.
The following chapter will introduce the background to this study, detailing areas which the study is related to. The aims and objectives will be stated and the methodology of how these objectives are to carried out will be stated.
1.2Â Research Introduction
It is safe to say that we live in a hugely wasteful world with regards to our energy consumption. We live in a world where apparently bigger is better in regards to cars and houses, but with little thought spared for efficiency or value. If we are to believe countless energy analysts and scientists then we are approaching an age where we need to drastically change how we produce and consume our energy. It is generally thought that our current energy system, and it's attendant waste, is fuelling our increasingly destructive weather patterns and in addition due to the finite nature of fossil fuels is increasingly at risk of economically devastating energy shortages.
Since the beginning of our worlds current major energy system in the 1800's (i.e. fossil fuels), our society has gone under vast changes of great size and speed that no other era has ever witnessed. The massive growth and development in our world also has a huge wastefulness in the everyday usage of our energy and has caused major damage to our environment. It has been said for years how the emissions from burning fossil fuels is damaging our environment and will eventually devastate our planet through climate change. These environmental problems have been well documented and many would say have been largely ignored. Our world needs a cleaner energy supply if we are to have any chance of preventing the consequences of global warming. But as they created massive development on our planet, while fossil fuels can still burn cheaply they remain the most attractive option to fuel society as unfortunately in this industrial age it is often said that economics will have the priority over the environment. But today the world is, according to many energy analysts, on the brink of a major energy crisis.
There seems to be one option to our problem which stands out more than any other at this time. The sun, wind, earth, rivers and oceans can provide clean and unlimited energy which could provide the answer to our predicted environmental and available energy related problems of the future. Environmental scientists and energy analysts believe that the time is now to begin to reduce our energy consumption and convert to renewable energy if we are to come through such an energy crisis.
This dissertation will be a study on Ground Source Heat Pumps (GSHP) used in domestic dwellings in the UK. According to a report titled 'Domestic energy fact file 2003' by L D Shorrock, domestic energy usage has risen from 25% to 30% of the total national energy usage since 1970. Given a rise of 5% this would indicate that household energy consumption is an area which could be reduced to help ease our energy problems. The Energy Savings Trust (EST) states that of the total energy consumption for each household in the UK, 52% is used for space heating and 22% for water heating, both of which a GSHP can provide. For these reasons I have chosen to study the operation of a GSHP to try and determine if it is a more energy efficient form of space and water heating in a domestic building and also if it is economically viable for a home owner in terms of installation and running costs.
'As a mean to mitigate global human linked environmental pollution and to achieve sustainability, renewable energies must become not just a part of but THE primary energy source for the world. Heat pumps, as a process recirculating environmental heat back into useful heat production, fit the environmental requirements of this global policy' (A.C. Gillet - Heat Pumps and Renewable Energies)
The reason for this study came when the author first heard of ground source heat pumps during research for a live project at university. This was a project to implement sustainable technologies. The fact that there is a heating and cooling system which somehow takes heat from pipes buried beneath the ground sparked the authors interest in this subject and wanted to learn more about it.
The first documented use of a ground source heat pump was in 1912 in Switzerland by H Zolly (Wirth 1955). This was during a period of time when energy prices were low and the efficiency of these pumps were very poor and therefore the initial idea was not followed up. However, the theory remained and in the 1940's it was reinvestigated. During this time in the UK a heat pump used for a single storey house achieved a CoP of 2.8 (Sumner 1976). However, it was not until the oil shock of the seventies that GSHP were considered as a realistic alternative for space or water heating. Since then they have been very gradually becoming more and more recognised and attractive as their costs have gone down and there systems have improved.
'Today ground source heat pumps are an established technology with over 400,000 units installed worldwide (around 62% are in the US) and about 45,000 units installed annually. Studies carried out for the Department of Energy in the US identified ground source heat pumps as the technology for space heating which had the highest potential energy efficiency.'
(Rawlings 1999 page 1)
It is the author's belief that the way we produce and use our energy needs to change and it will in the coming future. Whether it will be by the most depressing predictions of environmental disaster or economic collapse or simply by a gradual systematic adaptation, the author believes that renewable energy technologies will be not just part, but the main form of how we produce energy to live our day to day lives. The author hopes to spread the word about renewable technology but specifically GSHP since he feels most people do not tend to know about this technology. As the authors family is preparing to move homes he intends to bring the idea forward to incorporate renewable technologies which he feels will not only help the environment but be the most cost effective for his needs. From this dissertation the author wishes to gain knowledge of GSHP that will help him determine whether they are a viable form of domestic space and water heating in the UK.
1.3 Aim of Study
Determine the efficiency and cost effectiveness of a Ground Source Heat Pump used in a domestic dwelling in the UK today.
In order to achieve the aim of the study, the following objectives have been identified.
- Compare performance of heat pump installed at a domestic dwelling with the performance rating specified by the heat pump manufacturer
- Determine running costs of a GSHP and compare with running costs of different heating systems in similar houses
- Calculate the length required for the ground coil of a heat pump and compare with the length actually installed.
- Calculate the heating load of a house with a heat pump installed and compare with the heat pump installed.
- Establish CO2 emissions associated with a GSHP and compare to other methods of house heating.
- Outline ways of improvement for the GSHP in the case of underperformance or establish reasons for possible over performance
1.5.1Â Aim of the Research
The basis of the research will concentrate on the performance and sizing of a domestic GSHP in the UK. In order to achieve this, there will be information provided by a owner who has installed a GSHP to his home. A structured interview will take place with the owner of the GSHP to gather information on its performance and its cost.
1.5.2Â Literature Review
The key purpose of the Literature Review in this study is to gather all available information and data relating to the chosen subject area in order to establish a quality understanding of all previous studies and research carried out in areas of similar interest.
While the literature review can be presented in several different forms, the basic requirement of the review will remain constant. In general, a literature review should:
- Provide context for the research
- Justify the research
- Show where the research fits into the existing body of knowledge
- Understand and learn from previous theory on the subject
- Illustrate how the subject has been studied previously
- Show that the work is adding to the understanding and knowledge of the field
1.5.3Â Structured interview with GSHP owner
The interview with the GSHP owner, Brian Murray, is vital in obtaining knowledge about the workings of a GSHP that testing and literature will not provide. The owner will provide experienced knowledge regarding a GSHP and will allow him to offer his perceptions, views and attitude towards the topic. The strengths of using an interview in the research are the validity of the knowledge that is provided from a firsthand basis and it allows the interviewee to expand on their thoughts of the subject which may not be permitted in a questionnaire.
The interview is structured so as to obtain the maximum amount of useful information that the owner can provide. The layout of this interview will be shown in a later chapter.
The following chapter details information on previous and current research in the topic related to the dissertation.
2.2 Literature Review
According to countless oil analysts and energy experts the world today is on the brink of a major energy crisis which is sure to affect the everyday lives of all of us. This problem will only increase and is one which requires action and careful planning for the future. Currently we rely heavily upon fossil fuels (oil, coal, natural gas) to provide energy for our society. To continue choosing fossil fuels as our main energy source would spell economical and environmental disaster.
'The world is changing before our eyes dramatically, inevitably and irreversibly. The change we are seeing is affecting more people, and more profoundly, than any that human beings have ever witnessed. I am not referring to a war or terrorist incident, a stock market crash, or global warming, but to a more fundamental reality that is driving terrorism, war, economic swings, climate change, and more: the discovery and exhaustion of fossil energy resources'
(Heinberg 2004 page 1)
According to the International Energy Agency the world will need almost 60% more energy in 2030 than it did in 2002. (www.bbc.co.uk) The planet now faces a major challenge to meet this growing energy demand without causing catastrophic damage to our environment.
There are three key questions to the energy crisis:
- What effect does our current energy system have on our environment?
- Can the world meet a soaring increase in energy demand?
- What form of energy is the best option for the future?
What effect does our current energy system have on our environment?
The world's current energy system started in the 1800's and is largely based on fossil fuels. At the beginning no one foresaw the long term effects that fossil fuels would have on our world. The discovery of oil, coal and gas has fuelled the creation of our modern industrial society. However it has become increasingly clear from the latter part of the twentieth century onwards that our current fossil based energy system is profoundly unsustainable from both a resource depletion and environmental degradation point of view. Perhaps the starkest threat from an environmental point of view is the emergence of fossil emission driven global warming, which holds out the potential of devastating consequences for both man-kind and the thousands of other species which depend on a relatively stable climatic regime for their survival.
'During the last century, increases in human activity have lead to an increase in the emissions of greenhouse gases being released into the earth's atmosphere, primarily carbon dioxide from the burning of fossil fuels. This rise is expected to increase the greenhouse effect, in turn forcing average global temperatures to rise'
'The global average surface temperature has risen by over 0.7oC in the last 300 years. The twentieth century has seen the largest increases of 0.5oC'
(BBC Weather Centre, 2005)
Most scientists believe that dramatic shifts in our average global temperature will have devastating effect to mankind if as predicted they continue. IPCC (Intergovernmental Panel on Climate Change) predicted in 2001 that global temperature will rise by between 1.4oC - 5.8oC by the end of the 21st century. They also note that in all cases the average rate of warming would probably be greater than any seen in the last 10,000 years (www.ongcindia.com/techpaper1).
Such temperature rises would affect our climate across the globe bringing more frequent extreme weather conditions. Effects of such extreme weather conditions include more powerful flooding and hurricanes in some parts of the globe with, more extreme droughts and forest fires in other areas. In addition polar ice melting may both weaken the Gulf Stream and eventually lead to dramatic rises in sea-level. It is worth noting that to some extent many of these predicted effects are already being observed.Â
It is clear that our reliance upon fossil fuels as our main energy system is having extremely damaging effects on our environment and to continue to do so will only increase these problems.Â
Can the world meet a soaring increase in energy demand?
During the industrial era of the past 150 years living standards have improved dramatically with vast improvements in economic productivity, agricultural yields, transport systems etc. Fossil energy has fuelled economic development and technical innovation in a way previously only dreamt of. However nearly all of the modern comforts with which we have become familiar are either directly or indirectly dependent on a cheap and plentiful supply of oil, natural gas and coal. But is this all to come to an end?
When reviewing information and opinions available on the reasons for an upcoming energy crisis the main question that stands out is 'Are we running out of oil?' Many believe that the earth still boasts vast amounts of oil reserves which are enough to meet our energy needs for many years to come. According to John Felmy, economist for the American Petroleum Institute, mankind consumes 1.2 cubic miles of oil per year and estimated world oil reserves at the beginning of 2005 were 33 cubic miles. (www.healthandenergy.com) From these figures one would assume that the earth still has enough oil to fuel society for many generations but is that really the case?
'From an economic perspective, when the world runs completely out of oil is not directly relevant. What matters is when production begins to taper off. Beyond that point, prices will rise unless demand declines commensurately.'
(Heinberg 2004 page 93)
'We started running out of oil when we produced the first barrel. But running out is not the main issue, as the tail end of production can drag on for a very long time. What matters much more are the dates of the peak and the onset of the decline, which are likely to constitute a historic discontinuity as the growth of the past gives way'
(Heinberg 2004 Foreword ix)
So it would seem that it is not 'running out of oil' that is the real issue of an energy crisis rather just plain old supply and demand. According to Colin J. Campbell (Petroleum Geologist) around 80% of oil produced today comes from fields that were discovered before 1973 (Heinberg 2004). He also states that in the 1990's oil companies have discovered an average of 7 billion barrels of oil yet in 2003 alone they drained 3 times that amount. Such figures would suggest that our oil reserves are decreasing at an alarming rate. This may not be due strictly to oil running out but rather drastic increases in global energy demand at a rate that oil companies cannot meet.
So why is there such a drastic increase in global demand for energy?
'The surge in demand is coming primarily from two of the fastest growing countries on Earth: China and India. As people move into the middle class, they want to buy cars, TVs, air conditioners and other products that use oil and electricity. If mankind continues to increase oil consumption more than 2% each year, then a more realistic estimate for the useful life of existing oil reserves may be a paltry 24 years'
'There is no esoteric reason. It is plain old supply and demand. With the economies of huge nations like China and India developing more rapidly, now that they have freed their markets from many stifling government controls, more oil is being demanded in the world market and there are few new sources of supply.'
It's clear that the world faces a major challenge in reviewing and re-launching its major energy system. With such a surge in energy demand coupled with the peak production of oil it's clear that we must harbour alternative sources of energy which can fuel future society.
What form of energy is the best option for the future?
'Continuing to increase our dependency on petroleum consumption is clearly a suicidal course of action. The only intelligent alternative is to begin reducing energy consumption and finding alternative energy sources to substitute for petroleum. Non-renewable resources should be exploited, but at a rate equal to the creation of renewable sources.'
(Heinberg 2004 page 123)
'The European Renewable Energy Council says that there is potential for nearly 48% of global energy demand by 2040 to be met by economically feasible renewables'
Renewables it would appear offer a possible way out of both an energy and environmental crisis. They represent an infinite source of energy and are all around us in the oceans, sun, wind, water and earth. They can help us meet the demands of our future energy needs while causing minimal damage to the environment around us. In short they may be something which fossil fuels are emphatically not i.e. economically and environmentally sustainable in the long term.
'The good thing about renewable sources is that they are infinite, meaning we will never run out of them. We will always have access to the oceans, sun, wind, water and heat from the earth. Renewable sources also do not have the damaging effect on the environment that fossil fuels do.'
Whilst renewables stand out as a possible alternative to a fossil fuelled economy the question remains, is it economically feasible to move our economy onto a renewable footing. In short renewables must become economically attractive for homes and businesses for it to be possible for them to form the core of our energy system. With a looming shortage of oil, its price will inevitably rise which will lead consumers to look elsewhere for their energy supplies. Technological advances coupled with economies of scale achieved through increased take up of renewable technologies, could potentially in such a situationÂ trigger aÂ wholesale transition to renewables based economy.
'This is an exciting time for the renewables industry and an opportunity for it to move from being a fledging industry to a mainstream business activity'
'These energy sources (renewables) are rapidly becoming as cost-effective as fossil fuels. Their cost will continue to decline while the prices of fossil fuels and their environmental costs move higher.'
The different types of renewables are given below:
'The sun radiates huge quantities of energy into space. Earth intercepts a small proportion of this energy. The earth's atmosphere absorbs some of this energy and about 30% is reflected back into space without reaching the earth's surface. The energy absorbed is estimated to be equivalent to 10,000 times humanities rate of consumption of conventional fuels.' (Boyle 2004)
There are several different types of solar power:
- Passive Solar Design
- Solar Water Heating
- Solar Photovoltaic (PV)
'Wind energy has been used for thousands of years for milling grain, pumping water, etc. Today, the use of wind energy to produce pollution free electricity has become the most common use. Northern Ireland has some of the best wind profiles in Europe making it suitable for wind energy development' (BBC Weather Centre 2005)
'Hydropower is obtained by allowing water to fall through a turbine to turn a shaft. This is done by converting the potential energy of water stored at a height into kinetic energy which turns the turbine and produces the electricity' (Langston and Ding 2001)
'The main method of harnessing this power is by building a low dam or barrage across an estuary of a suitable river. Inlets allow the rising tide to build up behind the dam or barrage. These are closed when the tide has reached full height and the stored water released back into the sea via a turbine generator.' (Boyle 2004)
'Wind blowing over the earth's oceans produces waves. The power that builds up in such waves is immense. This power potential can be harnessed to produce electricity.' (Boyle 2004)
'Bio energy is derived from materials known as biomass. Biomass materials are organic matter that has stored energy from the sun through photosynthesis, such as wood, dried vegetation, crop residues, etc. In recent years bio energy has become the largest renewable energy source in the UK. In 2000 organic waste accounted for 80% of the renewables total for the UK' (Boyle 2004)
'The concept behind geothermal energy is to use earth's constant temperature beneath the surface to generate power and transfer heat. Geothermal systems circulate a water based solution through a loop of underground pipes. The heating process involves the extraction of heat energy from the ground, and moving it into the building. A refrigerant is used as the heat transfer medium. The cycle starts as cold, liquid refrigerant passes through a water-to-refrigerant heat exchanger and absorbs heat from the low temperature source.'
In order to speculate what area of energy use renewables will be attractive to consumers, it is important to study our current energy consumption and more importantly areas where we waste energy. With available energy soon to become scarce it will become more and more important to be maximise efficiency with our energy use. As oil prices continue to raise people will look for a less expensive alternative energy source, this will make renewables more competitive and marketable.
According to L D Shorrock and J I Utley in a report titled 'Domestic energy fact file 2003' domestic energy use have risen from 25% of the total national energy usage in 1970 to 30% in 2001. This is clearly a large and growing slice of our total energy demand and as such will form an important area to be targeted in any future reform of our energy system.Â Â Â
Figure 4 displays information provided by the Energy Savings Trust. As the chart shows the main contributor to CO2 emissions in an average UK household is Room Heating at 52% of the total CO2 emissions. With the rest resulting from Lighting & other appliances at 23%, Water Heating at 22% and then Cooking at 3%.
Similar figures on household energy consumption can be obtained from other sources.
'Currently in the US, according to the EIA, residential energy use accounts for 21% of the total national energy consumption. Of this, 51% is consumed for space heating, 19% for water heating and 4% for air conditioning. The rest powers lights and other appliances, including refrigerators.' (Heinberg 2004 page 179)
These figures given above both indicate that Room Heating in a household is the biggest area where home energy usage can be saved by heating rooms more efficiently and/or with alternative methods for heating.
Electricity emits 0.414 kg of CO2 for every kW of heat energy it delivers. This appears to be of low efficiency in comparison to that of Oil heating which emits 0.271 kg of CO2 for every kW of heat delivered. Of the three Gases is the most efficient emitting just 0.194 kg of CO2 per kW of heat delivered which is a 53% reduction in CO2 emitted for heat delivered in comparison to that of electricity.
So how does a GSHP compare to the fuels above in terms of CO2 emitted for heat delivered? According to the 'Housing Energy Efficiency Good Practice Guide' a heat pump emits 0.12kg of CO2 for every kW of heat it delivers. This shows that a GSHP is the most efficient out of the above three most common methods of house heating. A GSHP emits 71% less CO2 than electricity, 55% less than oil heating and 38% less than gas. This clearly shows a GSHP to be extremely advantageous in terms of efficiency.
With greater fuel efficiency of a GSHP a consumer will achieve savings in comparison to the most common house heating fuels. In fact, according to the Energy Savings Trust, at least 65% savings can be achieved by installing a GSHP for house heating and/or water heating. So it would appear that GSHPs offer an economically and environmentally feasible method of house heating.
Potential for GSHPs and other forms of geothermal energy are apparent in countries such as Iceland. Unlike most countries, a vast amount of Iceland's energy requirements are met through renewable energy, particularly geothermal energy. In a report titled 'Geothermal Energy In Iceland' it is stated that the annual primary energy supply in Iceland, which has a population of 268,000, is 98,000 TJ or 366GJ per capita, which is amongst the highest in the world. Of this Geothermal energy provides about 48.8% of the total, with the rest supplied by hydropower at 17.2%, oil 31.5% and coal 2.5%. This is shown in figure 7.
The report also states that main use of geothermal energy is for space heating, with around 85% of all houses heated in this way. According to the report replacing imported oil with indigenous energy sources received high priority after the oil crisis in the 1970s. As Iceland is a country with a cold climate house heating is of great importance and is needed all year round. By switching from oil and other fossil fuels to geothermal energy for house heating the country has experienced huge economical benefits, according to the report it saves annually around 100 million US$ in imported oil. The report does not mention the undoubted beneficial effects for the environment for a country to have such a high percentage of its energy supply from renewable sources.
Although Iceland is a country much smaller than the UK and one with a climate completely different it still provides firm proof that such technology has potential to expand in the UK as we desperately seek alternatives for our energy supply. It took the oil crisis of the 1970s for countries such as Iceland to begin a transition to make Geothermal and Hydropower their main sources of energy. If we are to believe oil analysts mentioned earlier then we have less time than Iceland here in the UK to begin such a transition.
What is a Ground Source Heat Pump?
A basic definition from the UK Heat Pump Network describes a heat pump as a device which moves heat energy from one place to another and from a lower temperature to a higher temperature. A domestic refrigerator is a heat pump. Heat is removed from the inside of the refrigerator and discharged leaving the contents cool. In the case of domestic space heating we should think a heat pump working in the same way as a refrigerator but in reverse.
In a journal titled 'Ground Source Heat Pumps - A Technology Review by Rosie Rawlings' the term ground source heat pump is applied to a variety of systems that use the ground, groundwater and surface water as a heat source. The journal states that until recently ground water heat pump systems were the most widely used as they were attractive, especially for commercial applications, because they could deliver and return large amounts of water using relatively inexpensive wells that required very little ground area. The disadvantages of such a system however are that sometimes the availability of water can be limited, fouling and environmental regulations covering the use of ground water becoming increasingly restrictive. These limitations mean that interest is now growing on ground coupled systems which, although are more expensive, are much more applicable.
From the authors experience of discussing the subject with people it seems to be a common misconception that ground source heat pumps take heat energy from the core of the earth. The heat is actually taken from the soil which acts like a huge solar collector by absorbing energy from the sun.
'Ground source heat pumps make use of the energy stored in the earth's crust. Energy is transferred to and from the earth's surface by solar radiation, rainfall, wind, etc. Only a small part (less than 3%) of the stored energy in the earth's crust comes from its core.
(Ground Source Heat Pumps - A Technology Review)
How does a GSHP work?
The process of extracting heat from the ground and distributing it to a house using the various components begins at the Ground Loop. The Ground Loop comprises lengths of pipe buried in the ground, either in a borehole or a horizontal trench. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe absorbing heat from the ground. As the fluid passes up the pipe it evaporates through the evaporator 'by extracting heat from a low temperature source, the vapour is compressed mechanically (compressor) and condenses back into a liquid state (condenser) giving up its latent heat as useful heat. The liquid then expands through the expansion valve causing a drop in pressure and partial vaporisation before re-entering the evaporator for the cycle to be repeated.' (Rawlings 1999)
Figure 8 shows an example of a borehole installation GSHP or a horizontal closed loop. A form of closed loop system tends to be the most common installation of a GSHP but there are also various configurations of typical GSHP Loops.
Closed Loop - Most GSHP would be a closed loop configuration like the one shown in the diagram above where water mixed with an anti-freeze solution is circulated through the buried pipe. 'The diameter and length of the pipe depends on the amount of heating or cooling required for adequate space conditioning and on the ground temperature, the degree of ground moisture, the thermal conductivity of the ground and the basic design of the system.'
(Geothermal Heat Pumps - An Increasingly Successful Technology 1996)
Horizontal Closed Loops - This system is used where space is plentiful and inexpensive. Perhaps more convenient in rural areas rather than in a city or town. 'Pipes are buried in trenches dug about 5 feet deep. As many as six pipes can be buried in one trench, with about a foot separating the pipes and trenches typically being twelve to fifteen feet apart. The Slinky, a loop comprising overlapping coils of pipe, can be used to maximise the number of feet of pipe buried per foot of trench.' (Geothermal Heat Pumps - An Increasingly Successful Technology 1996)
Vertical Closed Loops - This system is more commonly used in situation where space is less plentiful or at sites where the soil layer is thin. This type of system is commonly used for commercial and school installations. 'The depth of the boreholes ranges between 100 and 400 feet. Hole diameters range from 4 to 6 inches.'
(Geothermal Heat Pumps - An Increasingly Successful Technology 1996)
Surface Water Closed Loops - This system is installed 'at sites where there is a body of water that is deep enough and which has significant flow, closed loops can be positioned on the bottom. The circulating fluids effect excellent heat exchange with the surrounding water while limiting the need for excavation to that required on dry land to bury the pipes leading to and from the water body' (Geothermal Heat Pumps - An Increasingly Successful Technology 1996) This type of system would be fairly rare but it is known to be inexpensive, efficient and has no effect on aquatic ecosystems.
Open Loops - This system is generally very simple. It works by pumping water from a well or surface water body, passing this water through the heat pump heat exchanger and then sending it back to the source. 'Typical pumping rates are only 2-3 gallons per minute and, since water temperatures remain relatively constant year-round, these systems are favoured in places where their use is allowed.' (Geothermal Heat Pumps - An Increasingly Successful Technology 1996)Â Although open loop systems are most inexpensive and efficient they are reported to require frequent cleaning, particularly the heat exchanger. They also require the addition of chemical inhibitors to prevent fouling of loops by organic matter and they need a suitable site for discharge.
Standing Column Wells - 'These are used primarily in those parts of the country where bedrock and the ground water table are near the ground surface. SCW's can be up to 1500 feet deep and have diameters of 6-8 inches.' (Geothermal Heat Pumps - An Increasingly Successful Technology 1996) As SCWs are usually drilled into hard rock they are more expensive than a typical vertical closed loop system. However, they make up for this as they have greater heat exchange capabilities which make them more competitive.
Data & Methods
Chapter 3 highlights the chosen research methods employed for this study as well as the information collected from the research carried out in the study.
3.2 Structured Interview
The interview will be structured around discussing installation costs, running costs, the type and performance of the GSHP and details of the house to determine its heating requirements. The interview should be structured so that it is free flowing, to the point and encourages the opinion of the owner. A structure will be in place but flexibility will be allowed for the interviewee's answers so as to encourage the true opinion of the interviewee regarding the heat pump. All information given which the interviewer feels is relevant to the subject should be noted.
3.3Â Results of Interview with GSHP owner Brian Murray
The interview was carried out after the testing of the heat pump on Friday evening 24th March 2006. After taking temperature readings from the heat pump in a small store outside the house Brian invited the interviewer into his house to carry out the discussion. It should be noted that some questions that were included in the planned interview were answered during the testing phase. Below is the information which was obtained during the interview.
Q1 How did you hear about Ground Source Heat Pumps and what made you decide to install one?
Brian said that he first heard about heat pumps in a DIY television programme. He explained that he was always keen on energy efficient technology in the home and when he first heard about a ground source heat pump he was immediately interested. As it came at a time when Brian was proposing on building his new house he thought that he should explore the technology in more detail. He found useful information available on the internet regarding how a GSHP operates and also companies which carry out domestic installations.
Q2 What type of GSHP do you have installed? i.e. borehole, trench installation etc
The GSHP installed is a trench installation. Brian said he felt himself and heard from other sources that a trench installation performed with greater efficiency than a borehole installation as it required more energy to carry the fluid up the heat exchanger from the depth it is buried than around a trench installation.
Q3 Is the heat pump used for space heating, water heating or both?
The heat pump is used for both space heating and water heating.
Q4 What type of heat distribution system is used in the GSHP system?
Under floor heating is used in the house for space heating and a hot water tank is provided for hot water use.
Q5 Is there any form of back-up heating for the heating system?
The only other form of heating in the house is from an oil fuelled stove located in the kitchen/dining room area. Brian explained that the stove had to be turned off after only its first week in the house. This was because it was too warm.
Q6 Where were the GSHP system components purchased from?
Brian does not know where the components where purchased directly from but that the GSHP was installed by a company called PowerTech.
Q7 Have you any idea of the length of piping which was installed for the system and at what depth it is in the ground?
Brian had documentation from when the GSHP was installed. It read that 1200m of 2 inch pipe was installed at a depth of around 2.5 metres.
Q8 What size is the heat pump?
The heat pump is a 15kW Transen Alpha with electronic control
Q9 How long has it been since the heat pump was installed?
The heat pump was installed 2 years and 1 month previous to the date of the interview at Feb 2004.
Details of the heating requirements
Q1 How many rooms are in the house? Please specify.
10 Rooms:- Kitchen, Dining Room, Living Room, Sitting Room, Utility Room, 4 Bedrooms, Bathroom
Q2 Do you have any idea of the Gross Floor Area of the house?
This information was shown on the documentation given with the heat pump.
Total Floor Area:- 209m2Â Â Ground Floor:- 115m2Â Â First Floor:- 94m2
Q3 How many people live in the house?
7:-Â Brian, his wife Anne and 5 children
Q4 Could you give me details of roughly the house occupancy during the week and weekend periods?
During the week and on most Saturdays Brian would be out of the house during the day until the evening time. Two of the children are in school on weekdays until the afternoon. Brian's wife Anne and three of the children are in the house all day every day.
Q5 What is the usual output temperature for space heating?
As there are thermostats in every room the temperature output for the space heating could change all the time. However, Brian and Anne agreed that the usual temperature each thermostat is set to is 24oC.
Cost of the GSHP
Q1 How much was the cost of installation of the GSHP system? If possible try and break down to excavating work, heat pump installation and trade prices for components
As Brian is an excavator operator by trade he was able to carry out the excavation work himself which saved him a considerable amount on the installation costs. A breakdown of the rest of the costing was available from the documentation supplied by the installer.
The owner received a grant of £1,200 from Clear Skies. Information on Clear Skies is available at www.clearskies.org. Grants are available to fund various renewable technology installations including a GSHP. £1,200 is a fixed sum which is awarded for GSHP installations regardless of the size of the installation.Â
Q2 How much would your typical electricity bill be each quarter?
Brian said that with the use of his heat pump his electricity would be a maximum of £80 extra and sometimes as little as £30 per quarter extra than his normal bill without the heat pump.
Q3 Has there been any necessary maintenance work to the heat pump?
There has been no maintenance work at all necessary in the two years since it has been installed.
Q1 How happy are you with the overall performance and cost of a GSHP?
Brian said that he is extremely happy with how the GSHP has performed. He explained that he initially had fears as to whether the GSHP would be worth the money for the installation but that these were quickly squashed after the system was up and running.
Q2 How do you feel it compares with your previous heating system? Or if this has been the only heating system for this house, how do you compare a GSHP to your experience of other heating systems?
Brian informed the interviewer that in his previous house he had a heating system of an oil boiler and radiators and an immersion heater for water heating. He said at the time he was fairly happy with the system but when he looks back he feels it does not compare to a GSHP in terms of overall performance and running costs. He said that the oil tank in the house would be filled with 300 gallons roughly four times a year and possibly even more.
Q3 Have you any other information regarding your GSHP or just general information on the subject that you feel is useful to this study?
The interviewer remarked that it seemed unusual for the heat pump to provide both space heating and water heating and for there to be no form of back up heating. Brian explained that he felt the fact that there are thermostats in every room in the house mean that when the heating is on its only load is where the heating is required in whatever room an individual adjusts the thermostat.
Analysis & Evaluation
Chapter 4 presents data analysis of all the information included in the previous chapter and will discuss relevant findings from the data analysis.
4.2Sizing of the system
Sizing of the ground coil
As discussed in previous chapters the sizing of the ground coil is a key issue in relation to the heat pump performance.
'The more pipe used in the ground collector loop, the greater the output of the system, but as the costs associated with the ground coil typically form 30% to 50% of the total system costs, over sizing will be uneconomic. Conversely, under sizing, would lead to the ground loop running colder and could, at worst, result in ground temperatures not being able to recover and heat extraction from the ground being unsustainable.'
During the interview the heat pump owner, Brian, said he could remember that he installed the piping himself using his own excavator. He said that when the heat pump specialists came to install the GSHP they commented that he had installed too much piping in relation to the heating requirements of the house but at this stage it was too late to change and the installation went ahead as planned with what the specialists thought was too much, in terms of the installation cost of the system and not its efficiency.
It was known that 450 metres of piping would be required for the system to meet the heating load of the house. The documentation relating to the installation of the system, which Brian provided the interviewer, indicated that 1200 metres of piping was used. This shows that the piping was oversized by 750 metres. According to Rawlings 2003 this should mean that the system will be perform more efficiently with such over sizing of the ground coil but would have resulted in much greater installation costs.
Heat Pump Sizing
The heat pump is critical in terms of the operating efficiency where it was stated that a slightly undersized heat pump is the most efficient system.
The heat load of the house was 12.2 kW which was indicated that the heat pump was oversized at 15kW. In this instance it was predicted that a buffer tank would be installed in the house acting as a false load to prevent the heat pump cycling on and off and decreasing the efficiency of the heat pump and this was the case. A second calculation was therefore required to determine the heating load of the buffer tank. This indicated that the buffer tank had a heating load of 15.6 kW every 15 minutes which would mean the system is slightly undersized which according to Rawlings 2003 allows a GSHP system to work more efficiently. Therefore it could be said that the heat pump installed in the house is of good sizing in terms of maximising the operating efficiency of the system.
The calculations based on estimated annual heating requirements of a house similar to the one in chosen on the study and local fuel rates, provided annual running costs of a GSHP, oil heating and gas heating. They were as follows: GSHP = £584 per year, Oil Heating = £882 per year, Gas Heating = £986 per year. These results are shown in the graph below.
This shows that gas is the most expensive option for heating at £986 per year with Oil the second most expensive at £882 per year. A GSHP is 41% cheaper than Gas Heating and 34% cheaper than oil heating at £584 per year. This shows significant savings and with predicted increases in the price of both gas and oil the savings involved with a GSHP could become even greater.
However, it is worth noting that during the interview Brian claimed that he estimated that his electricity bill per quarter has increased between £30 - £80, i.e. his estimated running cost of the heat pump. Taking an average of £55 per quarter this would indicate that the heat pump would cost £220 per year to run. This shows a significant difference in the calculated estimate discussed above. It is of the author's opinion that Brian's estimate is incorrect, As it is based on a rough estimate which leaves room for error.
Brian's previous electricity usage could have been greater before the heat pump from his usage apart from the heat pump now. Brian stated that he had even "pulled the fuse out from the immersion heater switch." Without the use of the immersion heater throughout the year the electricity usage would be significantly reduced. Therefore it is fairly inaccurate to estimate the running cost of the heat pump based on the extra pounds thought to be on the electricity bill compared to the electricity bill without the heat pump.
It is also interesting that Brian commented that his previous oil heating system which he claims he purchased 400 gallons of oil four times a year to supply his house for space heating alone. A local oil company provided a price for 400 gallons or 1350 litres which was £496. This multiplied by four times a year means that Brian's estimated heating costs in his previous house were a £1,984. This is over £1000 more expensive than the calculated method discussed above. Again the compared running costs show substantial differences.
It could be possible in this case that Brian's estimate is incorrect. However, it may be the case that although Brian's previous house was similar in size in terms of floor area it may have a greater heating requirement. For example, Brian's previous house may have had a much greater heat loss in terms of insulation and glazing etc. This would therefore increase the heating load. It could also be possible that Brian's previous house was a bungalow which will have a greater heating load than his two storey house.
It is therefore difficult to fully analyse and compare the running costs of Brian's estimated costs for the heat pump and his previous oil running costs with those which were calculated.
The calculations based on the annual CO2 emissions of different heating methods for a four bedroom detached house, similar to Brian's, produced the following results: GSHP 2279 kg CO2 per year, Oil Heating 6625 kg CO2 per year, Gas Heating 4028 kg CO2 per year. These results are displayed in graph form on figure 14.
The results show that a GSHP is clearly the cleanest, most environmentally friendly form of house heating in terms of CO2 emissions. A GSHP has 66% less CO2 emissions than oil heating and 43% less emissions than gas heating. It is clearly without any question the most efficient house heating method from the three in terms of CO2 emissions.
4.5Â Hot Water
In the interview Brian commented that there is never any need for back up heating for space heating or water heating at any time since the installation two years ago. For this reason it can be said that the system is running very efficiently as it is meeting the required heating load of the house. However it is worth noting that the temperature reading taken from running hot water read 45oC. According to EHPA 2002, Legionella is a bacteria which exists in fresh water and if inhaled can cause pneumonia, Legionnaire's disease or a strain of flu. At temperatures below 20°C the bacteria does not reproduce but at temperatures between 20 and 45°C its reproduction accelerates. As Brian's water was running at 45oC this would indicate that his hot water supply is under threat of legionella. According to EHPA 2002, the bacteria begins to die at 50°C but takes several hours whereas at 60Â°C it takes just 10 minutes. From this evidence it is apparent that the hot water supply may need to be increased in temperature to avoid the existence of Legionella in the water. This may mean that some sort of auxiliary heating be required in order to avoid the bacteria which ultimately may affect the efficiency of the GSHP.
4.6 Â Factors which may affect the heat pump performance
It is clear from the results of the interview that the GSHP system is performing extremely well as Brian stated in two years it has provided sufficient heating and hot water for all seven occupants of the house without any requirement for a form auxiliary heating. There are several factors which were discovered during the study that may have contributed to the GSHP system running so efficiently.
It was calculated in the study that the length of piping for the ground coil was oversized by 750 metres. Although this will have significantly increased the installation cost of the system it is said (Rawlings 2003) that over sizing of the ground coil will increase the output of the system. Therefore it can be stated that the over sizing of the ground coil has lead to greater installation costs but has increased the efficiency of the system.
It was also calculated that the heating load of the buffer tank was 15.6 kW every 15minutes which meant the heat pump was slightly undersized. As discussed earlier in the study it is generally agreed that a slightly undersized heat pump will perform most efficiently as it prevents the heat pump from cycling on and off which according to EHPA 2002 will decrease the operational life of the system. Therefore, it can be stated that the sizing of the heat pump has increased the efficiency of the GSHP system.
During the interview Brian noted that he felt himself and had heard from other sources that the fact he had thermostats located in every room throughout the house meant that the heating load would vary in order with the occupants comfort levels. Therefore, rooms which no one was occupying were not heated which ultimately reduced the heating load of the building. This could also be a factor which influenced the performance of the system.
Conclusion & Recommendations
Chapter 5 presents the conclusions of the dissertation in relation to the research findings, with recommendations made by the author for further research in the topic area.
In order to appropriately conclude the dissertation it is necessary to look back to what the initial aims of the study were and the objectives proposed to achieve this aim. The aim of the study was:
"To determine the efficiency and cost effectiveness of a Ground Source Heat Pump used in a domestic dwelling in the UK today."
This study has identified a domestic a Ground Source Heat Pump is proven it to be not just an environmentally friendly form of house heating but a cost effective one which to most people in today's world is the most attractive benefit of the two. A number of conclusions can be made from the study.
The study has shown that running costs of a GSHP in comparison to the other more common forms of house heating in the UK to be extremely advantageous. In a four bedroom detached house it was calculated that the running cost of a GSHP would be £584 per year. With gas heating being the most expensive at £986 per year and then oil heating at £882 per year, a GSHP offers savings over gas heating and oil heating of £400 and £300 per year respectively, this represents significant savings. Despite the GSHP sampled in the study having expensive installation costs of £6,000 (£14,000 including plumbing), with its low running costs, reported minimal maintenance and predicted escalation in gas and oil prices, it offers significant long term financial benefits.
The study calculated the required length of piping for ground coil to be used in a GSHP in the house sampled to be 450 metres. The actual length of piping installed for the GSHP was in fact 1200 metres. This showed an over sizing of 750 metres for the ground coil. Such an over sizing would have affected the total cost of installation as the ground coil represents 30% to 50% of the total cost of the heat pump. However, this over sizing will have increased the efficiency of the system which will in turn decrease the running costs.
The author was able calculate the heat loss of the house where the heat pump was installed and from this determine the heat load which the heat pump would be required to meet. In terms of the heat load of the house, the heat pump was found to be oversized at 15 kW as the heat load was only 12.2 kW. It was then predicted and proved to be the case that a buffer tank was installed in the house to provide a 'false load' to the heat pump. The author was then able to calculate the heat load of the buffer tank to be 15.6 kW which was judged to be a good sizing as it was slightly over sized, which as discussed in the study is agreed to be the most efficient way of running a heat pump.
The study demonstrated that the CO2 emissions of a GSHP were extremely low in comparison to other more commonly used heating methods. It was calculated that in a four bedroom detached house, similar to the sampled house, a GSHP would have annual CO2 emissions of 2279 kg. In contrast, oil heating would have emitted 6625 kg of CO2 per year and gas heating would produce 4028 kg of CO2 per year. These calculations have proved that a GSHP is by far superior to today's common house heating methods in terms of environmental friendliness.
In conclusion, it is clear that the GSHP involved in the study performed efficiently and proved to be cost effective in terms of running costs. Over sizing of the ground coil and good sizing of the heat pump are the two key areas which have attributed to the performance of the heat pump. This study has provided constructive information on a GSHP based on an actual GSHP installed in a domestic dwelling. The study has completed its main aim and proven a GSHP is both energy efficient and cost effective.
5.3Limitations in the research
One of the objectives was to compare the performance of the GSHP to the performance rating specified by the manufacturer of the heat pump. Unfortunately, the manufacturers of the sampled heat pump were unable to provide a performance rating of any kind. For this reason this particular objective of the study was unable to be fulfilled.
Some of the information received in the interview regarding running costs of house heating proved to be conflicting with the calculated data. No conclusive analysis of the two conflicting running costs could be achieved. This was because the information given was too vague and not taking into account other factors which may have been involved.
5.4 Recommendations for further research
The following areas have been identified as possibilities for further research in the area highlighted by this study.
- Establish a Coefficient of Performance of a suitably sized domestic Ground Source Heat Pump under laboratory conditions and compare with a real life Ground Source Heat Pump. Establish reasoning's for any differences in results.
- Identify two domestic Ground Source Heat Pumps in the UK and establish rating points and running costs. Establish reasons for any conflicting results.
- Determine the maximum efficiency of a Ground Source Heat Pump under laboratory conditions through sizing of the ground coil and the heat pump relative to the heat load.