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Tag Archives: CHP

ETI on energy saving in buildings

By Dave Elliott

The UK Energy Technologies Institute’s report by Jeff Douglas on Decarbonising Heat for UK Homes notes that ~20% of CO2 emissions are from domestic heating, but says insulation/upgrades won’t cut that enough: ‘the scope for cost effectively reducing the energy demand of existing buildings to the great extent required to meet emissions targets is limited as comprehensive insulation and improvement measures are expensive and intrusive. A several hundred billion pound investment in demand reduction for the entire building stock might deliver less than half of the emissions abatement needed. The most cost effective solutions therefore involve the decarbonisation of the energy supply combined with efficiency improvements that are selectively rather than universally applied, as part of a composite package’.

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The RHI to be ‘reformed and refocused’

By Dave Elliott

The UK’s Renewable Heat Incentive (RHI) was introduced to support households, businesses, public bodies and charities in moving from conventional forms of heating to renewable, low carbon sources of heat. It has escaped cuts so far, indeed it is set to expand, but the government wants to restructure it to keep energy costs down for consumers and get better value for money. It expects spending on the RHI to rise from £430m in 2015/16 to £1.15bn in 2020/21, but says it wants to promote wider access and make project more affordable, ‘by firmly controlling costs’.

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Why get rid of gas heating?

By Dave Elliott

The current decarbonisation plan in the UK is to replace the use of fossil gas for domestic heating by the use of electricity. That may have been slowed by the abolition of the Zero Carbon Homes policy for new build, with its 2016 deadline, but there is still a strong push in that direction, with a ‘Near Zero Energy in Buildings’ concept and specific programmes for roll-out of technologies like electric heat pumps, apparently one of the government’s favoured heat supply options, along of course with insulation and improved building design to reduce demand. The latter makes sense, the former, well that is debatable.

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Small modular nuclear – is small beautiful?

By Dave Elliott

A new report ‘The role for nuclear within a low carbon energy system’ from the Energy Technologies Institute, claims that the UK could have 50GW of nuclear power plants by 2050, including Small Modular Reactors (SMRs). Although it says, due to basic economies of construction and operational scale, ‘large reactors are best suited for baseload electricity production’, it notes that, based on using existing sites, there is ‘an upper capacity limit in England and Wales to 2050 from site availability of around 35 GWe’, and it could be less (e.g. if CCS plants need some of the sites). However, there could be more room for small nuclear plants (under 300kW) on new sites, at least 21GW and in theory up to 63GW.

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What a waste: an end of year lament

By Dave Elliott

In a post-Xmas pre-new year Scrooge-type austerity mood, I worry about the money we are wasting on energy. If you look at Sankey diagrams of energy flows from primary resources to final end use, you will see that for many countries around half the raw energy input is wasted in the conversion process, most of it being rejected into the atmosphere as heat, for example from steam-based fossil and nuclear generation systems.

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Devolving power

By Dave Elliott

‘Distributing Power: A transition to a civic energy future’, a report on research by the EPSRC-funded Realising Transition Pathways Research Consortium of 9 UK universities, argues that up to 50% of electricity demand in the UK could be met by distributed and low carbon sources by 2050. The report assesses the technological feasibility of a move from the current traditional business models of the ‘Big Six’ energy providers to a model where greater ownership is met by devolved governments, municipalities, co-ops and communities. And it looks in details at what types of governance, ownership and control a distributed future would need. (more…)

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Water source and gas fired heat pumps

By Dave Elliott

Heat pumps are seen as a clever way to get an energy upgrade, with the input energy driving a compression cycle, pumping heat collected from outside a building into radiators inside, like a fridge working in reverse. Most systems use heat from the air or from the ground, but there are also some water-source systems. For example there are large water-source heat pump schemes in Scandinavia, feeding heat to district heating networks. About 60% of the total energy input for Stockholm’s Central Network is provided by a district heating plant with six large heat pumps using the sea as a heat source. Warm surface water is taken during summer, while in winter, the water inlet is in 15m depth where the temperature is at constant +3°C. Helsinki in Finland also has large heat pump plant producing district heating with capacity of 90 MW, as well as cooling, with capacity of 60 MW, using heat from the sea and from wastewater led into the sea from a central wastewater treatment plant.

These are large projects, but a medium-scale system is being developed in the UK, using Mitsubishi’s Ecodan pump, which was voted the best new product or technology at the 2014 Climate Week Awards. It’s the first application of a system of its kind in the UK, and is backed Mike Spenser-Morris, a local developer and director of the Zero Carbon Partnership. The heat pump will use the Thames to provide hot water for radiators, showers and taps in nearly 150 homes and a 140-room hotel and conference centre at Kingston Heights in Richmond Park, cutting heating bills, it’s claimed, by up to 20%. It’s based on using water drawn from two metres below the surface of the Thames, where the ambient temperature, sustained by ambient heat from the sun, stays at around 8C to 10C all year round. A system of heat exchangers, pumps and condensers boost that to 45C. The electricity used to power the system is supplied by Ecotricity, which makes it zero carbon. According to a report in the Independent on Sunday, the system is thought to have cost about £2.5m, though this is for a ‘first of a kind’ project. The cost of future systems should be lower, and the Renewable Heat Incentive can offset supply costs.

Energy Secretary Ed Davey told the Independent on Sunday: ‘This is at a really early stage, but it is showing what is possible. You never have to buy any gas- there are upfront costs but relatively low running costs. I think this exemplifies that there are technological answers which will mean our reliance on gas in future decades can be reduced. Here you have over 100 homes, you have a hotel with nearly 200 bedrooms and a conference centre that won’t be using gas. It will be using renewable heat from the nearby River Thames. This is a fantastic development. My department is exploring the potential for this sort of water-source heat pump across the UK, so we’re going to map the whole of the UK for the potential’: www.independent.co.uk/environment/climate-change/exclusive-renewable-energy-from-rivers-and-lakes-could-replace-gas-in-homes-9210277.html

As the Independent noted, in theory, any body of water, including tidal rivers as well as standing water such as reservoirs and lakes, can be used as long as they are in the open and heated by the sun. The Government has a target of 4.5 million heat pumps across the UK, though most will be using heat from air or ground and will be small domestic units. Prof. David MacKay, until recently DECC’s chief scientific adviser, has described a combination of heat pumps and low carbon electricity as the future of building heating. However, as I’ve noted before, there are limits to the viability of small domestic systems: they make most sense in off gas-grid areas. Larger units, feeding district heating networks, are more efficient, and make more sense in urban areas, where there are large heat loads. Operation at the larger scale also make it easier to provide an effective maintenance regime, important for heat pumps, which need careful adjustment and servicing to maintain optimal performance. Otherwise the coefficient of performance (CoP), usually expected to be around 3, can fall dramatically. For example, in winter in damp cold countries like the UK, the external heat absorption pipes of air source heat pumps can develop a film of frost, reducing the heat flow. Without regular de-icing, the pump then has to work harder, potentially, in the extreme, reducing the CoP to perhaps 1 or less- making it less efficient than a simple one bar electric fire.

Moreover, large or small, the current type of heat pump run on electricity, and it’s been argued that the idea of shifting to heat pumps instead of gas for home heating on a national scale may be suboptimal, since using heat pumps run on mains electricity generated in large gas fired-plants, may be no more efficient than using gas direct in a domestic scale condensing boiler. It’s also argued that the wide-scale use of electric heat pumps is impractical, since the electricity network could not supply the large amount of power needed – the gas grid carries 4 time more energy than the power grid. It’s perhaps worth noting in this context that in the 1950’s, Southbank’s Festival Hall was heated by a large 7.5MW gas fired heat pump using the Thames as a heat source, although it seems it was taken out mainly as it produced too much heat: it was oversized www.architectsjournal.co.uk/home/rolls-royce-performance/181204.article#

There is now renewed interest in gas-fired absorption cycle heat pumps. They are less efficient than the electric motor driven compression-cycle variant, but gas is cheaper/kWh than electricity, much of which, after all, is made inefficiently by burning gas (and coal), so a 50% net fuel saving is claimed. At the World Renewable Energy Congress in London in August, Prof. Bob Critoph from the University of Warwick noted that there were now three domestic gas-fired systems on or very near to market (Robur, Vaillant, and Viessmann) with others under development. He proposed a mixed heating solution with both gas-fired and electric heat pumps, and also the use of hybrid electric heat pump-gas boiler systems, e.g. for older properties. He felt that the proposed mix, whilst not being the minimal emission route, was an affordable and pragmatic solution to domestic heating. There are of course other novel ideas, for example solar thermal fired absorption cycle heat pumps, which may have relevance even in the UK, with the combined air source/solar Solaris system claimed to be 25% more efficient than standard air-source electricity-powered units depending on location: www.uk-isri.org/case-studies/solaris and http://cordis.europa.eu/publication/rcn/16280_en.html

Whatever the heat and power source, are heat pumps the way ahead? Some say that large community scaled gas-fired combined heat and power (CHP) plants, with CoP equivalents of up to 20, are better in energy efficiency and carbon emission terms than heat pumps of any scale or type. That may be true at present, but, longer term, if electric heat pumps use green electricity, or gas fired heat pumps use green gas (biogas or stored gas produced using surplus wind/solar-derived power), then net emissions would be near zero. Although the same would be true for green gas fired CHP.

In the final analysis, given its high CoP, CHP seems to have the edge for the moment, but, in economic terms, the optimal systems choice may depend on the location and the size of the load. One of the largest gas-fired heat pump systems so far is the 140kW unit at Open University: http://www.modern-building-services.co.uk/news/archivestory.php/aid/9841/__65279;Ener-G_teams_up_boreholes_with_absorption_heat_pumps_.html

In some locations, large water sourced units may make sense, but large gas-fired units might have even wider applications. But then so may CHP, linked to district heating networks. However, to complicate matters further, it may not be a straight choice between CHP and heat pumps: e.g. a heat pump can be run using electricity from a CHP plant, while using the heat from the CHP plant as its heat source, thereby upgrading the heat output. Plenty of room for innovation! http://setis.ec.europa.eu/system/files/JRCDistrictheatingandcooling.pdf

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Sustainable heating and cooling for buildings

by Dave Elliott

 ‘40% of Europe’s energy use and a third of the greenhouse gas emissions can be attributed to buildings and much of this relates to heating and cooling. For example in the UK, 38% of all CO2 emissions are related to space heating. These emissions can be avoided or significantly reduced through a combination of holistic design, integrated renewable energy and high efficiency.’  So says a report on Sustainable Heating and Cooling of Buildings from Leonardo Energy, the European Copper Institute’s think tank, offering a good analysis of the options for reducing buildings’ energy consumption  and carbon emissions. (more…)

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Green Heat 2

By Dave Elliott

The governments new Heat Strategy review took on board many of the arguments for district heating, and even the use of solar, that previously had been rather marginalised. It identified pathways for the transition of the UK’s heat supply to low- and zero-carbon energy sources in the domestic and industrial sectors.

The Combined Heat and Power Association (CHPA) was delighted. It said that ‘the Strategy points the way to a major expansion of new district heating networks in towns and cities, driving a multi-billion pound investment programme in green infrastructure and creating an additional 40,000 jobs in construction and engineering’.

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Green Heat 1

I have often been less than impressed by reports from the Royal Academy of Engineering (RAE) , which usually seems to take a conservative line on energy issues, but their new report on heating for buildings seems overall very well done, although with lapses. It makes the sensible point that we need to deal with the building envelop first, but also notes that most of the houses that will be lived in by 2050 have already been built, so we must look to remedial measures. It also notes that ‘Manchester isn’t Leipzig’, and looks at patterns of heating need and perceptions of comfort. It assumes we are talking about well insulated buildings, and familiar levels of comfort, and it reviews the energy supply options for supporting that.

It sets the scene by pointing out that ‘If space heating could be decoupled from water heating it would change the selection criteria for heating appliances and boilers. There would no longer be a need for the heating system (as opposed to the hot water system) to be on standby during summer months or to be capable of operating at a sufficiently high temperature to prevent Legionella developing in water systems. All domestic heating is currently thought of as low-grade heat requirement, but there is a case for distinguishing space heating as low grade and hot water as medium grade. A policy for heat should separate these two different uses’.

It looks at heat pumps as a possibility, but is not too convinced. ‘While the general reduction in carbon intensity of grid electricity makes the use of electric heating (direct or via a heat pump) more attractive, peak heat loads tend to coincide with peak electricity loads. There is, therefore, a significant likelihood of heating demand being met by high carbon electricity generation brought onto the system to meet peak loads over and above the capacity of low carbon generators’.

It goes on ‘Air source heat pumps have been rising in popularity for new build in the UK, but this is partly an effect of the way in which electrical energy is treated in the regulations that makes CO2 targets more lenient than for gas systems.’ While it admits that ‘Air source heat pumps integrate well with well insulated dwellings, if properly sized and installed,’ and it suggests that ‘micro-CHP complements and could balance some of the properties of heat pumps’, it also notes that ‘several reports discuss inadequacies of the application or system engineering in heat pump installations. It is clear that heat pumps are not forgiving if installed inappropriately.’

By contrast, it’s much happier will larger-scale communal system. ‘Communal air source heat pumps are an interesting area of development with some new configurations of systems coming to market. Central systems may be more efficient and are likely to offer much greater energy storage than do systems designed for individual household’.

It adds ‘Larger district systems, incorporating a CHP facility and providing heating are significantly more efficient than domestic level installations. This is because waste heat can be used in district heating after it has generated an element of electricity. Such district heat is therefore always of significantly lower CO2 emissions than any heat only production utilising the same fuel’. And that, it seems, includes domestic scale heat pumps.

The RAE does seem to been moving towards community- scaled system across the board. However, it is less happy with renewables. Although it sees some potential for bioenergy e.g for CHP/District Heating , it is not very impressed with solar, and overall treats renewables as problematic in terms of grid power supply, reverting to the traditional RAE line on the problems of intermittency and the delights of nuclear: ‘During the summer months, most of the night-time load could be provided by nuclear power with renewables providing additional power during the day’, while in winter ‘we would need sufficient renewables to guarantee 40GW during the evening peak. As wind, tides and the sun are intermittent, that would require significantly higher installed capacity of renewables or thermal back-up capacity, much of which would be unused for long periods in the summer’ making renewables uneconomic.

Nevertheless, it does look at smart grid /load management options which might change the situation radically, helping to deal with intermittency. A bit grudging, but at least there is now some recognition that a new interactive supply and demand system might be viable. It’s taken decades to get the community CHP/DH message across to the traditionalist engineers, so maybe it’s too early for idea of smart dynamic grids to have got through! And it may take even longer for them to give up on ‘baseload’ nuclear, which they still see as essential, rather than as getting in the way of a more interactive flexible system based on renewables ( which is the view emerging from Germany) .

However, as far as CHP/DH in concerned, the RAE is now full of praise. It says that ‘CHP plants, biomass combustion, and heat pumps are more efficient, reliable and cheaper at scales larger than a single dwelling. The costs of large scale heat pump installations per kW are a quarter of that for domestic-scale installations.’ It adds that ‘it is more efficient to use the available skills for fewer large systems than for many individual units’, and that, since energy storage will be needed ‘district heating systems have another important benefit – the mass of water in the underground pipes provides a heat store that evens out daily peaks and troughs in demand. This can be supplemented by hot water tanks to increase energy storage’. And taking it one step further, it points out that ‘well insulated hot water tanks or underground inter-seasonal thermal stores will be simpler to provide on a community basis given the small (and reducing) size of most UK homes’.

Some sense last! And DECC seem to be taking notice, in their new Heat strategy- see my next Blog.

‘Heat: degrees of comfort?’ Royal Academy of Engineering www.raeng.org.uk/heat

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