Renewable Heating Systems Ground Source Heat Pumps Cernunnos Homes Version 1.0 The set of documents under the “Renewable Heating Systems” header are intended to be an “A to Z” educational set of brochures to help you choose your heating system. Some parts may be outside of what you need and some details too technical, but you should find everything you need within these documents. They have been split into separate documents due to their size and range of topics covered. We start by looking at how you measure and design heating systems suitable for your property. We then move onto traditional boiler systems that currently exist in the UK. Finally, and only then, do we start to look at renewable heating systems and how they can be integrated into your property. As ever at Cernunnos we have a very technical and financial viewpoint, and want to explain all the options through facts and figures rather than “heresy”. If you have further questions after reading this, then why not contact Cernunnos Homes on 0845 680 2183 or via [email protected], and we will be more than happy to help. Alternatively you could arrange a free, no-obligation site survey. We don’t have pushy sales people that turn up at your house. We have qualified technicians who are on hand to answer your questions and help you chose the right system for you.

Documents in this section include: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Renewable Heating Systems: An Introduction to Heating Systems Renewable Heating Systems: Solar Thermal Systems Renewable Heating Systems: Ground Source Heat Pumps Renewable Heating Systems: Air Source Heat Pumps Renewable Heating Systems: Biomass boilers and Log burners Renewable Heating Systems: The next generation – Solar Thermal with ASHP Renewable Heating Systems: The Renewable Heat Incentive Renewable Heating Systems: Commercial Heating Systems Renewable Heating Systems: Community Heating Systems Renewable Heating Systems: Swimming Pools

Introduction: Renewable Electricity systems, such as Solar PV, are much simpler compared to heating systems. For example, heating systems must be designed specifically for the property it is to be installed within, whereas with electrical systems you can easily over generate power and simply supply this excess power to the grid who then distributes it to those that have excess electricity demand (and vice versa, if you don’t generate enough power you can simply pull extra in from the grid). This cannot be done for heating as it cannot be transported, and thus excess heat must be “dumped” (i.e. the building is cooled by simply opening the window etc). Heat dumping can be a very serious matter as an incentive scheme such as the FiT, can and would incentivize consumers to pursue this action. Additionally, you do not want a heating system that is too small for your property as then you would be very cold and cannot easily import heat from another source. Correctly sized boilers/heating systems are extremely important as they run more efficiently and are cheaper to install. A boiler or heating system that is too small will have to work overtime to get the property to the desired temperature. This will be very costly to run as the efficiency of the boiler is decreased. Meanwhile, a boiler that is oversized will be more expensive to purchase and install compared to a correctly sized boiler. Additionally, a boiler working at only 70 or 80% of capacity will be running below peak efficiency levels. Before we start to look at Renewable Heating Systems, we must first learn about how traditional heating systems work.

1. What are Ground Source Heat Pumps? The seasonal variations in the earths’ ground temperature disappear at a depth of below 10 meters, whilst the upper most 10 feet of the earth maintains a relatively stable temperature all year round – between 10 and 15 degrees Celsius, meaning that heat can be extracted from this level during the winter months and cooler air during the summer months. This extraction is done through a Geothermal Heat Pump (GHP – also known as a Ground Source Heat Pump or GSHP) and these can be used anywhere in the world, in essence providing a household with its domestic heating during the winter months. A Geothermal Heat Pump consists of pipes buried in relatively shallow ground within the proximity of the property for which they apply. In winter the heat from below the surface is pumped directly into the house via a heat exchanger, whilst in the summer months the heat from the house is pulled into the heat exchanger and pumped back into the ground (or used to heat water). Thus the GSHP helps heat the house in the winter and cool the house in the summer. This is a very efficient and green source of obtaining heating for households and businesses. However, the GSHP’s do need to use electricity to operate the pumps and therefore the efficiency of the heat pump is essential. A mid-range pump with good ground conditions will generally provide 3 to 4kW of heat energy for every 1kW of electricity used to generate the heat (a Coefficient of Performance of around 4:1). Therefore it has an energy efficiency of some 400%. The advantages of geothermal energy are that it is efficient and available 24 hours a day, 365 days a year, anywhere in the world (even in snowy regions such as Sweden and Norway). Meanwhile, GSHP’s are easily installed, reliable with little maintenance requirements, and make next to no noise in energy production. However, the disadvantages of GSHP’s are that they can be costly to install and will be needed to run alongside traditional boiler systems (although reduced energy bills will mean that the system pays for itself over future years), and they do require a lot of land mass for the pipe network to be laid (more on this later). The temperature at a depth of 1 meter below the ground surface is affected by the outside air temperature that prevailed approximately 6 months previous. That is, the temperature of the ground at a depth of meter below the surface is actually a factor of the outside air temperature that prevailed in the previous July. The ground temperature at a depth of 1 meter in July will be a result of the air temperature at the surface in the previous December! The added advantage of this is that when you are trying to extract the most heat from the ground (i.e. during winter) you are actually extracting it from a source that has been determined by the summer weather! That said, the temperature at a depth of 1 meter only ever varied by 1 or 2 degrees! Hence the variation between summer and winter is actually minimal!

2. How do Ground Source Heat Pumps work? Heat pumps work on the basis of constant temperature households. In this, they initially heat the house and then top-up any heat loss on a constant flow basis. They have many sensors that monitor the house, ground loops and outside temperatures. By monitoring outside temperatures they try and predict how much heat the house will require and start supplying that heat before the natural heat loss occurs. 1. The system extracts the natural heat from the earth by pumping a water and glycol mixture through a series of Pipes buried beneath the earth. The warmer temperature underground (typically around 10 degrees Celsius) heats the mixture making it hotter when it comes out of the ground than it was when it went in. The mixture only needs to be heated by 3 or 4 degrees Celsius for the Heat Pump to work. 2. The heated water mixture is then passed to an Evaporator. This uses the warm water mixture to heat a refrigerant liquid. The refrigerant liquid boils at temperatures as low as minus ten (-10) degrees Celsius. The refrigerant liquid then boils into a gas which is passed to a Compressor. 3. The Compressor compresses the gas (law of Thermodynamics) creating heat. Temperatures achieved in the gas can now reach between 75 and 100 degrees Celsius. The gas is then fed through a heat exchanger. 4. The Heat Exchanger then warms the surrounding water, which is part of the central heating/domestic hot water system, thereby providing central heating. As the gas goes through the heat exchanger it slowly cools and condenses back into a liquid. It is then passed back into the ground loop to repeat the process.

There are 3 main parts to the ground source heat pump: 1. The Ground loop piping 2. The Heat pump which incorporates: 1. Evaporator: takes the heat from the water mixture and transfers it into a gas 2. Compressor: compresses the gas to get higher temperatures 3. Condenser/heat exchanger: gives the heat to the hot water tank for distribution 3. The Distribution System: under-floor heating or radiators

3. Types of Ground Source Heat Pump: There are 4 main types of pipe installation: 1. Horizontal piping: this is where the piping is laid flat, often in a loop pattern, at a depth of at least 1 meter and is the most cost effective. However, a lot of land is required for excavation.

If more than one pipe run is being buried and run into the heat pump, each run of piping MUST be the same length and each trench must be 5 meters apart.

2. Vertical piping: the piping is dug deeper into the ground and installed vertically, with the top section 1 meter under the surface. This is in case there is not enough ground surface for horizontal piping and is often used for commercial buildings where the heat requirement means the horizontal piping system is not feasible. 3. Bore holes: for areas with minimal space two vertical holes can be drilled. The type of earth you are drilling into will determine how far down you will need to drill. Some materials, such as granite, will have a high heat extraction rate such as 65 Watts per meter (65 W/m). Granite has a high thermal conductivity, which means you can extract more heat out of a smaller area than in other materials. Others, such as simple dirt, will have a low heat extraction rate of just 15 Watts per meter (15W/m), meaning you will have to dig a lot deeper to get the desired heat output. How far down you need to dig will depend on both the amount of heat you require (i.e. the GSHP system size for the property), and the material you are drilling into. A typical small scale system of 5kWp will require a depth of 100 meters. The bore-hole width would be just 150mm with the pipe that carried the heat transfer mixture being around 40mm in width. Once the fluid pipe is inserted into the bore hole, it is filled with a Grout that helps keep the shape of the hole. This grout also helps the fluid in the pipes extract heat from the ground more efficiently.

The cost of drilling a bore hole will depend on what material is being drilled through (i.e. granite or soil) and the location of the bore hole (i.e. in a built up area or field). Typically the costs of bore-holes will range between £35 and £70 per meter drilled. This does not include the cost of the grout, piping, pressurizing and capping of the hole, which could in total add another £20 to £25 per linear meter. 4. Rivers/Ponds/Lakes: pipes can also be laid at the bottom of river/ponds/lake beds where the surface temperature is the same as that under the earths’ surface. Water is a better conductor of heat than the ground, making the heat transfer more efficient. Also, the lack of

need for digging/drilling, means reduced costs. However, there will be very few locations where the situations are ideal for such an installation as you must have a property that is very close to a deep water source. The water depth must be AT LEAST 1m, ideally more.

4. How efficient are Ground Source Heat Pumps? As mentioned earlier, Ground Source Heat Pumps require electricity to operate. However, for every unit of electricity that is used to operate the system, on average, 4 units of heating are generated by the system. This means that the system has a Coefficient of Performance (CoP) of 4 to 1. The CoP of any single system will vary as each installation is different. Some will be installed in more conductive land materials, whilst others may be installed in water. However, when designing a system the CoP should never be less than 3. Similarly, the CoP of any single system will vary throughout the year as it is affected by how much energy you need the heat pump to produce. If you require the heat pump to heat the water in the house to around 60 degrees (i.e. in winter), then the CoP is likely to be around 2, whilst heating the water to just 35 degrees (i.e. in Summer) will create a CoP of around 4+. This relationship can be seen in the following chart:

6

Coefficient of Performance

5 4 3 2 1 0 20

25

30

35

40

45

50

55

60

65

70

The CoP will also be affected by how warm the ground temperature is, and thus how warm the transfer liquid is when it comes back from the ground loops and into the Evaporator. This is because the warmer the liquid, the less work the Evaporator will have to do to boil the refrigerant liquid and thus the less electricity it will need to work. The relationship between ground temperature and CoP can be seen as:

Coefficient of Performance

6 5 4 3 2 1 0 0

1

2

3

4

5

6

7

8

9

10

Ground Temperature All GSHP’s are tested as standard with a ground temperature of zero and a heating requirement of 35 degrees Celsius, and it is this test that is used to give the official CoP that is described in the datahseets. 35 degrees Celsius should be more than enough heat for a well-insulated house that uses underfloor heating. Heat Pumps that are required to provide domestic hot water, which requires a higher temperature than domestic heating (at least 65 degrees Celsius in the UK), will have a lower CoP. That said, more traditional methods of heating, such as immersion heaters, have a CoP of 1 or even less than this (meaning more energy input is required than the outputted heat). For example, Gas and Oil boilers have efficiency ratios of 85%, equivalent to a CoP of 0.85. This is also why GSHP systems are more suited to under floor heating, a system that requires a lower temperature/more continuous flow of water through it (under floor heating generally requires a water temperature of 35 degrees, as opposed to 65 degrees for domestic hot water, and 75-80 degrees for radiator heating systems). This increases the CoP of the GSHP.

5. Sizing a Ground Source Heat Pump: The Heat Pump should be sized as to the heating requirement of the building (see “Renewable Heating Systems: An Introduction to Heating Systems” to see the calculation method for sizing a buildings heating requirement). For Space heating, a general rule of thumb is that 25 square meters of living space, in a well-insulated house, requires 1kW of thermal heating. However, this is only a generalisation. Let us assume that a property has a Space Heating requirement of 25kWp, then a 25kWp GSHP should be used. To work out how much ground looping is required for such a system, a general rule of thumb is that for every 1kWp required, there is a requirement for 10 meters of horizontal piping. Thus this property would need 250 meters of horizontal piping. For bore-hole piping, every 100 meters delivers around 3 to 5kWp of heat capacity, depending on the earth material you are drilling into (in our example we would need 5 identical bore-holes of 100 meters in depth).

For horizontal piping the bigger the piping area the better and wet areas are better than dry as they have higher conductivity properties. Following installation there should be very little maintenance and Ground Source Heat Pumps have a lifespan of over 25 years.

6. How much does a GSHP cost? A system for a domestic house (uses around 25kWh of heating a year for both space heating and domestic hot water), using a horizontal piping installation, will cost between £15,000 and £20,000 and will provide all the heating and hot water needs for an average household. However, if you do not have the land availability for a horizontal piping network then costs can increase significantly for vertical piping and bore holes. The cost of installation and the efficiency of the system can also be more viable on new builds or complete renovations, when ground work and under floor heating can both be installed whilst other work is being done. For more specific costing you need to have a site survey by Cernunnos-Homes. This is because the efficiency and size of any system that may be needed depends on so many factors. The SAP appraisal will be a starting point, but it may also be that your property is not suited to a GSHP. However, never fear, Cernunnos-Homes can find the renewable energy system that is most suited for your property and finances!

7. Planning Permission: Heat pumps generally do not need planning permission, although this may be different for listed buildings. However, due to some excavation works to bury the piping network (or indeed to drill deep bore holes) you will need to comply with building regulations.

8. GSHP’s versus Air Source Heat Pumps (ASHP’s): GSHP’s are much more efficient than ASHP’s as the ground is warmer than the Air in winter and cooler in summer. However, ASHP’s are much cheaper to install than GSHP’s as they are a single unit that can be simply fitted whilst GSHP’s need numerous operating parts and heavy ground work. Therefore, the trade-off between the efficiency of the GSHP versus its increased cost needs to be considered. This consideration can only be taken on a case-by-case basis. Each property is very different and will require different solutions, with each solution unique to that property. That said, ASHP’s work down to -10 degrees, although at this level the output produced is negligible. The performance of ASHP’s decreases just when it is needed for heat. Additionally, ASHP’s are located on the outside of a building and thus require planning permission, subject to noise constraints as they can be quite noisy (around 50 decibels without noise reduction measures and 25 decibels with them).

9. GSHP’s with Solar PV: Obviously Heat pumps, both Ground Source and Air Source, need electricity to help them generate heat. Thus a lot of emphasis is put on the coefficient of performances (CoP) that they can produce. However, we can also generate the electricity they need through renewable energy sources such as Solar PV:

10. GSHP’s: The Energy Saving Trust Field Trial: The Energy Saving Trust has conducted a field trial of Ground and Air Source Heat Pumps, the results of which were published in September 2010. The complete report can be found here: http://www.energysavingtrust.org.uk/Publication-Download/?oid=1801485&aid=4898250 A summary of their findings (taken directly from their report) are summarised here: Given the lack of data on heat pump performance in customers’ homes, the Energy Saving Trust undertook the first large-scale heat pump field trial in the UK to determine how heat pumps perform in real-life conditions. The year-long field trial monitored technical performance and customer behaviour observed at 83 sites across the UK. The findings provide valuable information about the factors that affect the success of a domestic heat pump installation. Instead of revealing outcomes along statistical grounds, or acting as a “brand-vs-brand” competition, the field trial findings provide a discussion of key points of interest to potential consumers, including: • • • • •

Measured coefficient of performance (COP) and system efficiency Installation practices (both system design and performance) Customer behaviour Heating patterns and average internal temperatures Economics

Key findings: 1. The performance values we monitored in the sample heat pumps varied widely; the best performing systems show that well-designed and installed heat pumps can operate well in the UK. 2. The sample of ground source heat pumps had slightly higher measured system efficiencies than the air source heat pumps. The ‘mid-range’ ground source system efficiencies were between 2.3 and 2.5, with the highest figures above 3.0. 3. The system efficiency figures for the sample of ground source heat pumps were lower than those monitored in similar European field trials. 4. The ‘mid-range’ of measured system efficiencies for air source heat pumps was near 2.2 and the highest figures in excess of 3.0. 5. Heat pump performance is sensitive to installation and commissioning practices. 6. The householders in our field trial sample reported good levels of satisfaction with both space heating and hot water provision. There was no significant difference between users’ satisfaction with ground and air source systems. 7. Heat pump performance can vary considerably from one installation to another and customer behaviour is a variable that was shown to impact performance.

8. Many householders said that they had difficulties understanding the instructions for operating and using their heat pump. This highlights a need for clearer and simpler customer advice. 9. A comparison between carbon emissions from heat pump installations and electric or gas heating (based on the UK government’s current predictions for grid decarbonisation) shows that a well installed heat pump can lead to carbon savings, both at present and over the lifetime of the pump. 10. The field trial shows that heat pumps have achieved reductions in heating bills for some customers – especially those whose installations are off the gas grid and are therefore replacing heating fuels such as electricity, LPG and oil. Further findings: As well as the key findings above, the field trial has revealed some secondary findings which will also help us to understand what factors determine heat pump performance: • • • • •

•

The wide-ranging performance values can be attributed to a number of observed factors, namely the system design and installation and the customers’ use of controls. Efficiencies for domestic hot water production were lower than expected in a number of cases, mainly in systems producing domestic hot water in the summer. Control systems were generally too complicated for the householders to understand. Some householders found it difficult to control the ambient room temperature. Many systems appeared to be installed incorrectly. Often there was no single contractor responsible for the installation, which might involve a ground works contractor, a plumber, a heat pump installer and an electrician. This meant that there was often no single point of responsibility or any liability for the eventual performance of the whole installation. Running costs are one of the main negative factors affecting user satisfaction. Dissatisfaction may be related to the substantial increases in fuel costs which occurred just before and during the project; however such feedback is subjective. There were many more dissatisfied social housing residents (42%) than private householders (13%).

Conclusions: 1. Heat pumps are sensitive to design and commissioning. The field trial covered a variety of early installations, many of which failed to correctly apply the heat pump. This result emphasises the need for improved training. 2. Keep it simple. There were many system configurations monitored in the field trial. In most cases, the simplest designed systems performed with higher efficiencies. 3. The impact of domestic hot water production on system performance is unclear. Heat pumps can be designed to provide domestic hot water at appropriate temperatures, but more investigation is needed to determine the factors which impact system efficiency. 4. Heating controls for heat pump installations have to be comprehensively reviewed. There has been a failure to explain proper control requirements to both installers and heat pump customers. 5. Responsibility for the installation should be with one company, and ideally be contractually guaranteed to ensure consistency in after-sales service.

6. Further study needs to be undertaken on an installation-by-installation basis, to record what has been done wrong (or well), what could be done better, and what exactly should be done in the future. Although every home is unique, it has been shown that a well-performing heat pump can produce a COP and system efficiency ratio of at least 3.0. This means that for every input unit of electricity there is a useful output of three equivalent heat energy units. These best-performing installations should give consumers confidence that heat pumps can provide good levels of internal heating, lower carbon emissions, and reduce fuel bills when installed properly. Approximately 13% of all sites in the trial achieved system efficiencies in excess of 3.0. The worst-performing sites we monitored illustrate the need for customers to be vigilant when purchasing a heat pump, to be sure that they are buying the best system for their property and their lifestyle. Manufacturers and installers should also take care to ensure that heat pumps are specified and installed properly. Measured coefficient of performance (COP) and system efficiency: 1. The performance values we monitored in the sample heat pumps varied widely, as shown in the table below. The best-performing systems show that well-designed and installed heat pumps can operate well in the UK, and that the technology has real potential to help the UK meet its carbon reduction targets. 2. The sample of ground source heat pumps had slightly higher measured system efficiencies than the air source heat pumps. The ‘mid-range’ ground source system efficiencies were between 2.3 and 2.5, with the highest figures reaching over 3.0. 3. The system efficiency figures for the sample of ground source heat pumps were lower than those monitored in similar European field trials. 4. The ‘mid-range’ of measured system efficiencies for air source heat pumps was near 2.2 and the highest figures were above 3.0. The sample of air source heat pumps performed comparably with other European studies Installation practices: 5. Heat pump performance is sensitive to installation and commissioning practices. A thorough review of installation guidelines and training should be undertaken. User perceptions and behaviour: 6. Heat pump performance can vary considerably from one installation to another and customer behaviour is a variable that was shown to impact performance. 7. The householders in our field trial sample reported, overall, good levels of satisfaction with both space heating and hot water provision. There was no significant difference between users’ satisfaction with ground and air source systems.

8. Many householders said that they had difficulties understanding the instructions for operating and using their heat pump. This highlights a need for clearer and simpler customer advice. 9. A comparison between carbon emissions from heat pump installations and electric or gas heating (based on the UK government’s current predictions for grid decarbonisation) shows that a well installed heat pump can lead to carbon savings, both at present and over the lifetime of the pump. Summary: 1. Heat pumps are sensitive to design and commissioning. The field trial covered a variety of early installations, many of which failed to apply the heat pump correctly. This result emphasises the need for improved training. 2. Keep it simple. There were many system configurations monitored in the field trial. In most cases, the simplest designed systems performed with higher efficiencies. 3. The impact of domestic hot water production on system performance is unclear. Heat pumps can be designed to provide domestic hot water at appropriate temperatures, but more investigation is required to determine the factors which impact system efficiency. 4. Heating controls for heat pump installations have to be comprehensively reviewed. There has been a failure to explain proper control requirements to both installers and heat pump customers. 5. Responsibility for the installation should be with one company, and ideally be contractually guaranteed to ensure consistency in after-sales service. 6. Further study needs to be undertaken on an installation-by-installation basis, to record what has been done wrong (or correctly), what could be done better, and what exactly should be done in the future. Results of the field trial show that well-designed and well-installed heat pump systems can perform well in the UK. Among the 83 sites we monitored, there were good, average, and poor performing sites. This variation in performance has been influenced by a number of factors, including system design (sizing of the pump, and type and size of heat source and heat sink), system installation, and customer behaviour In order to get the best performance from a heat pump, it is essential that installation and system design meet the heat demand of the building. The Energy Saving Trust is actively working with relevant stakeholders, including the trade associations, heat pump manufacturers, the Department of Energy and Climate Change, the Scottish Government, and the Microgeneration Certification Scheme (MCS), to identify improvements to heat pump installation guidelines and installer training.