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Transcript of Heat
Domestic & Non-Domestic
Energy sources of Heat
What is heat?
Heat is defined as the net exchange of thermal energy between two systems in thermal contact, only if the systems are at different temperatures i.e. net exchange is non-zero.
In other words, heat naturally flows spontaneously from hot to cold. This occurs until thermal equilibrium is reached i.e. net exchange is zero.
Temperature is a measure of thermal energy. The more thermal energy a body has, the hotter it is and the higher its temperature.
A thermometer is a device calibrated to measure temperature
Commonly 3 temperature scales are used: Fahrenheit, Celsius and Kelvin
Kelvin is an absolute scale i.e. it begins at absolute zero
The exchange of thermal energy can occur in 3 ways:
Conduction – transfer of heat from one body to another through direct contact due to a temperature gradient , with no transfer of matter.
Typically conductors are solids and generally good conductors of electricity are also good conductors of heat.
Convection - transfer of heat through the motion of matter i.e. fluids (liquids and gases e.g. water and air); the heated fluid is caused to move away from the heat source carrying energy with it.
e.g. Warm air rises away from the heat source and cooler air drops to replace the warmer air creating a convection cycle.
Radiation - transfer of heat by the emission of electromagnetic waves that carry energy away from the emitting body and does not need a medium of transfer.
e.g. The Sun emits radiation through the vacuum of space that heats the Earth.
These systems delivers heat to both Domestic and Non-domestic sectors:
Typically a central heating system that provides heat to the interior of a building from a source such a gas boiler distributed through pipes and radiators. Other forms include heat pumps and micro-CHP (combined heat and power)
Gas and electricity distributed to the site provides fuel to the heating systems.
Heat networks (aka District heating) involve producing heat in a centralized facility/location and distributing this heat to more than one building through a network of insulated pipes using water or steam a medium.
Sources of heat include combined heat and power (CHP), Large Heat Pumps, gas/biomass boilers or waste industrial heat.
Heat storage enables excess thermal energy to be stored for use at a later date which could be hours or days at individual buildings, towns or districts depending on the technology implemented.
Storage mediums include: water, native earth or bed rock, lined pits filled with gravel, concrete and pebbles or molten salt.
UK has one of the most developed Gas networks in the world with 81% of all homes and UK industry connected to the gas grid.
Nearly half the energy in UK is used for heating , with gas as its main source accounting for 70% of all heat.
95% of UK homes are heated by a boiler, typically powered by gas (others include oil boilers)
Government aims to reduce in the roles of gas to almost zero by 2050, however it has been pointed out that gas will still play a major role until 2030.
Gas grid will still need major development (capacity and source). In March 2013, the coldest since 1962, natural gas saw a huge price spike, as storage stocks were almost depleted. Eventually shipments of LNG arrived to replenished stocks, alleviating prices in April.
Since natural gas will be here to stay to deliver energy well at least until 2030, there are attempts to explore shale gas as an alternative source to secure supply. Currently there is an estimated 1,300 tcf of shale gas resource available in the UK.
33% of the total amount of electricity consumed in the UK was to produce heat.
Electricity can be generated through nuclear, renewables such as wind farms or in power plants using fossil fuels, predominantly coal and gas - 40% of electricity generated in power stations was fuelled by gas in 2011, thus it could be argued that gas provides heat indirectly through electricity.
Electricity can be converted into useful heat via several routes, such as heat pumps or electrical heaters – resistive heaters and storage heaters.
Typically used in rural areas to fuel boilers where homes are not connected to the gas grid. However it is more expensive and costs 50% higher than with mains gas.
Another major consumer of oil is industry in order to fuel industrial heat processes. For example it is used refineries to heat boilers and ovens.
Heating technologies available to the Domestic and Non-Domestic sectors
34.26% of gas boilers are condensing boilers by 2010
Condensing boilers in comparison to a conventional boiler extracts additional heat from the unit's exhaust gases to supplement the heat normally provided by burning fuel. They are around 90% efficient.
Benefits: 10- 20% more efficient than a conventional boiler
Challenges: Dependent on gas, a fossil fuel
Resistive heating passes an electrical current through a metal in order to produce heat through friction between the electrons and the metal atoms. Analogous to a light bulb but produces more heat instead of light.
Benefits: Quick to heat; easy to transport; doesn’t rely on gas
Challenges: Low efficiency; poor temperature control; need multiple heaters for multiple rooms
Approximately 25,897 installed since 1991
Fewer than 1,000 micro-CHP by 2010
A typical conventional power station converts thermal energy (steam) to electricity by means of a turbine. In this process the heat has to be dumped into a cold place, usually the sea or a cooling tower. The concept of CHP is to harness this heat by-produce for useful purposes such as heating buildings and water.
Benefits: Produces electricity and heat simultaneously; More efficient use of fuel - 80% efficient; Flexible energy supply.
Challenges: Electricity produced is more valuable than heat; Harnessing heat hampers electricity production.
Solar thermal collectors
About 100,000 solar thermal collectors installed by 2010
Solar thermal heating systems exploit the heat radiated by our Sun to provide heating for buildings. Water flowing through an outside heat exchanger (known as a solar collector - the 'pipes' in the picture) is irradiated by the sun that is positioned to maximise sun exposure.
Benefits: Free energy to heat water
Challenges: Depends on weather – limited use in the UK; Needs another technology to supplement it.
This utilises the heat generated by the Earth’s core and radioactive decay that heats the crust. A method to harnesses this heat would be to bore holes several kilometres into the Earth’s crust, depending on the temperature gradient – typically want ‘hot spots’, where it is hot enough to boil water. Cold water is pumped down one hole, heated up as it moves through fractures in hot rocks, and the steam generated is extracted from another hole
Benefits: Independent of weather - heat is consistent; Opportunity to create geothermal power stations; Can be used for heat networks; Can make use of fracking techniques
Challenges: Picking location – Depends on temperature gradient, Not many opportunities for this in the UK; Drilling at large depths is difficult; Heat depletion if extracted too quickly; Pumping water into ground may cause earthquakes
Renewable heat incentive (RHI)
The RHI is a financial incentive to install renewable technology.
Provides payment of a certain amount (X pence) per kWh of heat produced depending on the technology.
2 phases: 1) Non- Domestic scheme
2) Domestic scheme
Non-domestic scheme launched in Autumn 2011.
Domestic scheme was aimed for launch in March 2012. However, the launch has been delayed until March 2014, as the government wants review details over how the scheme will work such as final eligibility requirements and final tariffs. Progression of this has been reported in recent news, with the release of final tariff details on 12th July 2013.
Technologies supported are: biomass, heat pumps, geothermal and solar thermal collectors.
Renewable heat payment premium (RHPP)
RHPP scheme provides one-off grants to householders to help them buy and install renewable heating technologies in particular solar thermal panels, heat pumps and biomass boilers.
The RHPP scheme has been extended until March 2014, covering for the delay in the domestic RHI expected to launch on that date.
Launched in January 2013, the green deal provides loans to householders or businesses wishing to install energy efficiency improvements such as insulation and double glazing and renewable heating technologies.
– Concept that repayments on the loan will be covered by expected financial savings. However no guarantee that savings will match the cost of the loan taken out.
Paid through electricity bill so that loan is tied to house not borrower.
Scheme can be used in tandem with the RHI or RHPP.
Initial cash-back incentive scheme to encourage people to take advantage of the deal by being able to claim money back (£125m put aside).
Interest rates are high – Consumers may find a better deal elsewhere
On March 2012 DECC released its first heat strategy:
‘The future of heating: A strategic framework’
General review of current heating situation in the UK and does not focus on policy.
In March 2013 DECC followed up with another heat strategy after gaining responses from the previous:
‘The future of heating: meeting the challenge’
‘The future of heating: meeting the challenge’
DECC has prioritised:
Efficient low carbon heat in industry
Heat and cooling for buildings
The main issues they identified were:
High upfront costs
– funds are required to implement and progress projects to positions for attracting financing. In addition, the scale of investments required for large projects, e.g. heat networks, compounds this challenge.
– training is needed for installers and heat engineers.
– there is a need to develop standardised design, installation, maintenance and legal requirements for existing technologies.
Enhancing consumer understanding and awareness
– promoting the role and importance of heat to the energy system and ensuring the incentives to shift to new technologies are understood.
They have produced various policies in an attempt to tackle these challenges such as a
to provide financial incentives for heating engineers to train in handling renewable heating technologies or the
Heat network delivery unit (HNDU)
to help local authorities build heat networks.
Other policies like the
could either can be used in conjunction or have a knock-on effect with heat policies. These examples could affect technologies such as heat pumps that operate using electricity.
Information and advice is disparate and complex – need to clarify and narrow it down for ease of consumer understanding of heat.
Wider energy policy and factors – this includes other policy affecting low carbon heating technologies indirectly. Extending from the EMR, to the weather affecting renewable energy that will complicate the development of strategies for heat.
Maintenance and installer base – increasing demand for low carbon technology will require a bigger specialist base, that requires more development.
- Content with gas heating and lack of awareness of low carbon technologies
- Lack of confidence in low carbon technologies
- Lifespan of low carbon technologies
- Cost, frequency and ease of maintenance
- Affect on house price
Competitive market – Gas boiler technology is mature compared to the relatively new low carbon alternative. This makes it difficult for low carbon technology to penetrate the market.
Skills shortage – takes time and money to train and earn a certification for a particular technology, only to install relatively few compared to boilers.
Most homes that will exist in 2050 have already been built – major improvements i.e. retrofitting will have to made to ensure they are energy efficient. This will require a workforce of skilled people relating to the above point and the need to create a specialist base.
Fuel poverty – high initial capital cost of low carbon heating technologies is a major barrier.
Supply and Demand of heat
Innovation and research in low carbon technologies and new sources such as shale gas and hydrogen will help supply
Capacity market detailed in the EMR will ensure supply and capacity of electricity
Storage technology will support supply at peak time
Development of heat networks
Residential sector – Houses, flats and tower blocks or estates.
Heat was responsible for 82% of energy consumption
85% of homes are connected to the gas grid and produce heat through gas boilers.
Mainly used for space heating and hot water (some used for cooking and catering)
Consists of the
Gas boilers are the predominant method of heating.
i.e. offices, shops, hospitals, airports etc.
64% of energy demand in the commercial sector was for heat.
Similar to domestic sector, commercial heat is mainly used for space and water heating with a small amount for cooking and catering.
73% of industrial energy demand is for heat.
The majority of this heat demand is concentrated among six key industrial sectors consuming 67% of industrial heat.
4 categories of industrial heat use: space heating, high temperature processes, low temperature processes and heat for drying and separation.
Overall, a move towards greater electrification of our heating supply will cause a greater strain on the UK’s electricity generation.
Air-source heat pump
Around 28,000 heat pumps installed by 2010
Heat pumps are often seen as refrigerators in reverse. They operate by transferring outdoor heat into buildings against a temperature gradient (opposite direction of natural heat flow i.e. from colder to hotter) and employs electricity to drive this process. The process manipulates a refrigerant as a medium for transferring heat through a cycle of vaporising and condensing. The refrigerant vaporises as it absorbs heat in the evaporator, which is followed by the dissipation of this heat as it condenses in the condenser.
There are two main types of heat pumps, these are:
- Air source heat pumps (ASHP) extracts ambient heat from the outside air, drawn into the heat pump through large fans.
- Ground source heat pumps (GSHP) passes fluid through coils installed beneath the ground, at depths of between six to fifteen meters where the ambient temperature is fairly constant throughout the year, to extract heat.
Efficiency depends on the weather, but typically achieves a coefficient of performance (CoP) of 4.
Benefits: Uses Electricity – Decreases pressure off gas grid; Very efficient; Can be used as an air-condition in the summer.
Challenges: High initial cost of capital. Heat depletion; Units are large; Installation can be sophisticated.
Note: CHP and Heat pumps are classified as renewable heating technology depending on efficiency and energy source. Badly installed heat pumps may not be efficient enough to be classified as renewable.
Ground-source heat pump
- Homes insulated under the green deal scheme could be at risk of overheating in the
- Conmen posing as Green deal assessors – charging ‘administration fees’
- Total of 38,259 assessments have taken place. Only 4 people have actually signed up so far since launch 6 months ago.
Majority of the news are negative and critical of the scheme. However, the Green deal demonstrates that the government is taking the initiative, to tackle the issue that home improvements and heating technology is expensive, with high upfront costs; in order to encourage consumers and those who cannot afford these expenses, so that they may take advantage of the RHI as well.
Around 1,500 biomass boilers installed by 2010
Bioenergy is generated through the combustion of biofuels which acts as a substitute for fossil fuel. Biofuels such as biogas and biomass are produced by refining organic material such as agricultural crops and waste material.
Benefits: Cheaper fuels; Reduced green house gas emission; Can be produced locally; Bio-methane can be injected into the gas grid.
Challenges: Requires large areas of land; Time to grow crops; Ability to produce sufficient quantity to meet demand.
The quality of heat can be graded. There is no unified specification on the temperature range of these grades, but generally:
– ‘Useful heat’ that can be used in many processes (mainly in industry) and typically class's heat above 400 C.
– Ranging anywhere from below 370 C and includes ‘waste heat’ from e.g. industry and space heating and hot water for domestic purposes.
Guideline Room temperature
- minimum of 16 C with comfort levels at around 18-25 C.
Usually heat is generated in homes and industry through electricity or combustion of fossil fuels such as gas, oil ,and coal and biofuels such as wood and methane.
Stone pellets as heat storage medium
by Matthew Wong
Moving the majority of our heating to electricity will induce greater loads on the electricity grid.
However, the electricity grid cannot handle the large peaks in heat demand that varies widely over the day. It will need significant storage, for example in the form of hydroelectric generation - already employed to meet peaks in electricity demand now.
The following graph compares heat demand fluctuations of gas and electricity, notice the sharp, high peaks in gas demand compared with the relatively low, dull peaks in electricity demand:
RHI, RHPP and other financial incentives will increase demand for renewable heating technologies (relates to the above point)
Installing Smart meters and thermostats to reduce demand for heat
Insulation will reduce demand of heat
Using multiple low carbon technologies in tandem to meet demand for heat
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/190149/16_04-DECC-The_Future_of_Heating_Accessible-10.pdf [See 3.48]
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/48574/4805-future-heating-strategic-framework.pdf [See 2.6]
Solar thermal collector
Process for extracting geothermal heat
Sources of biomass
Process of Biogas production
Zoom in on pictures to view
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/48574/4805-future-heating-strategic-framework.pdf [Box 4]