m&e sustainability

Massive publicity about renewable technologies means m&e firms are faced with a host of choices and a barrage of questions from increasingly energy conscious customers.

Here Ewen Rose, a consultant to M&E Sustainability, looks at the background, some of the main technology choices available and what you should do next…

The background
Over the next few years, the UK will begin running out of its own supplies of increasingly expensive fossil fuels. For the first time since the 1970s, we are a now a net importer of natural gas and our nuclear energy industry is about to start shutting down the ageing reactors that currently provide around 20% of our electricity.

We are also going to lose a further 36% of our capacity when the country’s 14 coal-fired power stations are shut down because they are far too carbon intensive to meet the EU combustion directive.

The Government’s recent energy White Paper laid the groundwork for a whole new generation of nuclear power stations, but there are two major flaws in this strategy. Firstly, a new generation nuclear reactor takes up to 15 years to design, build and commission – and we don’t have that long before the gap in our fuel supply reaches critical point.

Secondly, even if all of the current nuclear generating capacity was replaced we would still have a large shortfall because of the closure of coal and gas-fired facilities.

Energy experts calculate that by 2020 we will be importing 90% of our gas and oil supplies and by 2023 only one of our current nuclear plants will still be operating.
The EU has set a target for 20% of the continent’s entire energy to be supplied by renewables, such as solar, wind and tidal power, by 2020.

However, that alone will not secure our energy future. We have to go far further by tackling demand. If we are going to be importing 90% of our fossil fuels from increasingly unstable sources such as Russia and Afghanistan, we have to make sure it is 90% of a falling amount. This means tackling demand and the methods of energy distribution.

According to the Department of Trade and Industry, 60% of the gas we use in the UK is to provide heat. Heating the 25 million homes in this country accounts for one quarter of the UK’s entire energy consumption. This is primarily gas, but there are still over 4 million homes not connected to the gas network and they, largely, rely on oil.
Added to these rather sobering facts is the dramatic increase in prices. The average British gas bill has gone up by 35% since 2003 doubling the number of people in fuel poverty, also according to the DTI, to two million.

This is the background to a surge in interest in alternative heating systems that can reduce our reliance on fossil fuels such as solar panels and heat pumps, or that burn them more efficiently such as combined heat and power (CHP).

Renewable microgeneration technologies have the added benefit of producing energy at or close to the point of use so avoiding the incredibly wasteful transmission losses experienced by central power generation. The environmental pressure group Greenpeace estimates that for every 100 units of fossil fuel energy put into a conventional power station, only 22 are actually used – the rest is wasted in the generation and distribution processes.

Former Energy Minister Lord Truscott claimed that the microgeneration industry could provide between 30% and 40% of the UK’s electricity by 2050 and reduce household carbon emissions by 15%. He also said that the renewables industry was already benefiting from £1 billion worth of investment through giving businesses exemption from the Climate Change Levy (carbon tax) if they installed renewable systems and the creating of an Energy Technologies Institute that would have £500 million to spend on developing low carbon technologies.

The Government has also stated that all new homes will have to be “zero carbon” (more likely “carbon neutral”) by 2016 and this will depend heavily on their use of renewable systems to offset other systems where carbon emissions are unavoidable. The Code for Sustainable Homes has been developed to guide the housebuilding industry towards this goal and its measures will become enshrined in law by the next revision to the Building Regulations.

This background makes the argument for on site renewables ever more attractive, but despite all the press coverage and hours of learned debate, the renewable market still only accounts for less than 2% of domestic heating. There is a long way to go, but the potential is huge and more consumers are looking at the options available to them.

The Chancellor reduced the rate of VAT on many low carbon technologies and installation grants are available through the Low Carbon Buildings Programme (www.lowcarbonbuildings.org.uk) although these are proving incredibly difficult for many people to get their hands on and will come to an end in 2008.

A growing number of local authorities are also offering council tax rebates to residents who fit renewable energy systems in their homes. British Gas is running a scheme with 44 local authorities covering 2.5 million homes to offer householders up to £500 off their council tax bills if they fit solar water heating and photovoltaic systems.

They estimate that each homeowner could save £1,000 over five years via the combination of council tax rebate and reduced energy bills. And, under the same scheme, householders receive rebates for fitting cavity wall and loft insulation to further reduce energy demand for heating.

So what is it to be? Solar panels or wind turbines, heat pumps or fuel cells, or should you just concentrate on improving the basic efficiency of the already installed system? So many choices, so much to think about.

The following guide outlines the main points surrounding the technologies with pluses and minuses for all.

Back to basics – an introduction
Amid all the excitement about the emerging technologies designed to reduce our impact on climate change, it is important not to forget the basics. Before considering installing any new sustainable heating or cooling technologies, we must look at first reducing the demand for heating and cooling in our occupied spaces and cutting energy consumption by conventional means.

The new Building Regulations have been designed to ensure that building services professionals address the airtightness and insulation levels of buildings; how the energy consuming systems are controlled and what basic improvements can be made to existing systems including things like fitting thermostatic radiator valves and replacing old hot water cylinders.

We must first look at recommissioning what we already have before even thinking about adding new technologies.

The temperature inside our buildings has risen steadily since the advent of central heating. In 1970 the average temperature in a UK house was 13degC. Today it is 18degC, and that extra five degrees takes around 50% more energy to achieve.

Cavity wall and loft insulation, lagging pipes and double and triple glazing all dramatically reduce the need for space heating. Around a third of all the heat produced in British homes is lost through the walls and roof including 70% of the heat from radiators, which goes straight out through the wall.

The DTI calculates that loft insulation could cut our carbon emissions by 1.2 million tonnes and offers a great payback to the homeowner of less than two years – considerably quicker than many renewable technologies.

British Gas calculates that installing 250mm of loft and cavity wall insulation in an un-insulated three bedroom semi-detached property with gas central heating would cut the householders annual energy bill by £239. The participating councils are offering either £50 or £100 rebates on top of this.

The same principles apply to commercial buildings, although the methods of achieving the results may require different measures.

The message in both domestic and commercial buildings is, however, look at the basics first to make sure you get the full benefit of any retrofitted renewable system.

High efficiency central heating
Although not a renewable technology, high efficiency condensing gas and oil boilers are now being specified for a much wider range of applications due to changes to the Building Regulations and recognition of their ability to extract more heat from the combustion process than conventional boilers.

They are also better placed than any other available energy efficient technology because of the huge installed base of standard efficiency boilers, which can be replaced on an almost like-for-like basis with no major, expensive changes to the existing heat distribution system.

There are still five million permanent pilot low efficiency gas boilers installed in UK homes and if these were all replaced by high efficiency condensing alternatives, the overall efficiency of our central heating market would be transformed quickly and for a relatively small investment.

Condensing boilers make full use of heat from the exhaust gas created by the combustion process. With conventional boilers, a lot of usable heat energy disappears out of the flue with the waste gases from the combustion process. A condensing boiler has additional heat exchanger surfaces, which extract more heat from the exhaust gases converting that energy to pre-heat the water in the boiler system. The water vapour is then at a lower temperature than it would be in a conventional boiler and so condenses back into liquid form releasing further ‘latent’ heat.

At peak load this means they will extract 90% or more of the available heat energy, which means that overall they should work out 30% more cost-effective to run than conventional boilers of ten years old or more and are 10% more efficient than even the most up-to-date conventional alternatives.

Condensing systems are now being regularly twinned with solar water heating systems to deliver a highly efficient way of producing the complete needs of a home or commercial premises.

This technology should also be twinned with improved controls to ensure maximum benefit is extracted and waste is minimised. As well as upgrading programmers and fitting thermostatic radiator valves, installers could also consider using weather compensation controls to ensure the system always runs at the optimum temperature for the prevailing conditions and that the boiler remains in condensing mode for most of its operating time.

Key points:
The radiators and pipework may need to be re-designed to ensure that water returns to the boiler at as low a temperature as possible to deliver maximum efficiency by keeping the system in condensing mode.

The condensate produced by the boiler must be removed by an extra pipe or condensate drain and then disposed of sensitively via a ‘sink’ system.

Condensing boilers will produce a fairly dramatic plume of steam from their flues so the position of the flue is important to avoid nuisance to neighbours and passers-by as well as preventing this ‘mist’ from drifting through windows.

The flues must also be resistant to corrosion, which might be caused by the condensing process, so it is usually not possible to use an existing flue when upgrading to condensing.

Heating with biomass and biofuel

Biomass and biofuel (oil and gas) are carbon neutral because the plants grown to produce these fuels also absorb the C0₂ emitted when they are burned – it is a virtuous circle. Or so we thought until the full impact on global food prices of turning over farm land to biofuel crops hit home this year.

Any long-term thinking about biomass must be tempered with some consideration for the big picture and whether farmers may be causing more environmental damage through de-forestation to clear the way for biofuel crops.

Biomass wood pellets are a renewable source of heating fuel as they are often sourced from waste wood that would otherwise be discarded at the end of timber processing. The pellets are formed from natural, untreated wood collected from wood shavings, sawdust or forestry offcuts – two kilograms can produce about the same amount of heat as a litre of heating oil.

Pellets are burned in stoves, central heating boilers and large district heating schemes. They are delivered by tanker and kept in a silo or underground storage bunker. The system for delivering the pellets to the boiler requires fairly sophisticated engineering and high safety standards.

The transport industry is investing massive sums in biofuels because of the obvious environmental and security benefits of moving away from an oil-based economy. The heating industry is moving quickly to take advantage of this development.

Existing oil-fired heating systems can be easily converted to work with bio-fuel and this process is already underway in Germany where over 6 million oil systems could be converted. Modern burners are able to cope with the new generation of biofuels and the existing storage and transportation systems can be retrofitted to accommodate this new approach.

Biofuels are derived from rapeseed, sunflower and palm and when processed with has very similar properties to heating oil and diesel. A second generation of synthetically created bio-fuel is also under development and this might be the key to avoiding long-term problems with farm land being converted from food production.

Biogas is produced in a process very similar to fermentation and is ideal for use in rural areas. Decomposed vegetation, manure and organic waste is treated to produce a mixture that is largely methane and CO2. It is already being mixed with natural gas in several European countries to reduce carbon emissions and extend the life of gas reserves. It can be used with a condensing boiler or Combined Heat and Power (CHP) – see later page – as the use of more efficient technologies helps to offset the currently higher cost of producing this fuel.

Key points:
Is there a local source or will the fuel have to be transported from great distances so rather negating the point by adding to transport emissions?

Does the property have adequate space for the substantial storage facilities required?

Wood burning systems require special fire safety measures and are subject to fire safety inspection.

Heat pumps – air, ground and water source
Heat pumps make full use of heat naturally stored in the ground, water and even the air to reduce the amount of fossil fuels we need to burn to heat or cool our buildings.

The ground is continually soaking up and retaining warmth from the sun. Heat pumps extract that heat and use it to pre-heat water for space and water heating so reducing the amount of gas, oil or electricity consumed.

A heat pump works like a fridge in reverse. While a fridge takes heat out of the food stored inside and releases it into the room, the heat pump extracts heat from cold surroundings. It then brings this heat up to a temperature sufficient for central heating (between 55 and 60degC).

This works in the summer as well as in the winter 24 hours a day. As it is a low temperature heat source – unlike conventional central heating, which operates at high temperatures – larger heating surfaces such as underfloor heating and low surface temperature radiators are the best way to extract maximum efficiency.

Depending on the plot size and ground conditions, ‘slinky’ loops can be buried a metre or two below the surface in horizontal trenches or in vertical boreholes drilled down to around 80 metres.

The higher the temperature of the heat source, the more efficiently the heat pump will operate, but the key thing is having a constant temperature. The earth around UK buildings is on average a constant 10degC, which is ideal.

The heat is collected by polyethylene pipes filled with a water and anti-freeze mixture that extract about 50 watts of heating energy per metre in a borehole or one kilowatt per 25 square metres with the horizontal coils. This temperature is ideal as a pre-heated source of water for heating or as a cool water source for cooling in summer.

Air source heat pumps are not as efficient, but are easier to apply as they do not require any groundworks and can be used in properties without much surrounding land. They extract heat from the air and can be installed either inside or outside.

Open loop water source heat pumps can be the most efficient of all as they use heat extracted from a body of water. In this case the water from the source itself is pumped directly through the system. This source water is also proving highly effective in air conditioning systems and is particularly well suited for chilled ceiling systems providing, in theory, full building cooling with no mechanical systems at all.

Key points:
Ground source heat pumps require adequate land for the ‘slinky’ approach or a borehole and groundworks can be expensive and disruptive.

If the system is not properly sized it may freeze the ground - permanently!

Air source systems are less efficient and can be unsightly as they are relatively large units installed either inside or outside the property.

Water source heat pumps require a standing body of water and also care must be taken to ensure components are rust and corrosion proof.

Solar water heating
Improved insulation levels in British buildings have reduced the amount of energy required to heat occupied space. As a result, generation of hot water is taking up a higher proportion of our energy consumption and solar panels are increasingly being adopted to address this aspect of our contribution to global warming.

Once solar heating is installed it is almost entirely maintenance free and a 4m2 array will provide half of an average family’s hot water needs for the year. Normally used to supplement a conventional water heating system, solar panels will cut the amount of heating fuel used by between 40% and 60% - which is about 1,500 kilowatt hours (kWh) per year, according to the Solar Trade Association.

There are two main types of system:
Flat plate collectors consist of a metal sheet embedded in an insulated box covered by glass or clear plastic. The solar energy absorbed by the sheet is trapped by the glazing above and insulation behind the panel. The heat energy is then transferred via circulating copper pipes containing a mixture of water and glycol and through a heat exchanger in the hot water cylinder. On average, this ‘indirect’ approach will convert about 50% of the energy received into useful heat.

Evacuated tube collectors are generally considered to be about 20% more efficient because of their ability to capture energy from low levels of sunlight. Being cylindrical, they have a 180 degree absorbing surface facing the sun for most of the day whereas flat plates are only in an ideal absorbing position for a short period.

The cost of installing a solar hot water system ranges between £2,500 and £4,000 dependent on the size of the system – grants are available from the DTI’s Low Carbon Buildings Programme as they are for most renewable type technologies.

A typical domestic installation in the UK would have a panel area between 3 and 4m² when using flat panels and about 2m² with evacuated tubes. The storage cylinder will typically have capacity for between 200 and 300 litres depending on usage patterns in the building.

Key points:
The solar installation must be carefully integrated with any existing heating system to provide the full benefits to the end user – only fully trained and experienced heating engineers should be employed to carry this out.

The position of the installation is important both from an aesthetic and performance point-of-view – is the user happy to have solar panels on their roof?

Planning permission is still required in many areas although this restriction may soon be relaxed.

Anti-freeze must be applied to the collector loop to avoid the system freezing in cold weather

These systems do also have the potential to provide low temperature space heating as well as hot water via a triple coil cylinder. Solar thermal collectors feeding underfloor heating, in particular, is becoming more common across continental Europe and may eventually make an appearance in the UK.

Photovoltaics (PV) – power from the sun
As well as heating water, the sun can be harnessed to produce electricity by solar photovoltaic (PV) modules.

It is estimated that were we able to capture all of the potential power provided by solar radiation to the earth we could deliver 15,000 times the whole world’s power needs. Around 1,000 watts falls on each square metre of the earth’s surface in a Northern latitude country like the UK, although on a dull day this will drop to only 20 watts.

PV modules are a network of solar cells built from silicon or similar semi-conductor materials that generate electricity when exposed to light. This power is then transferred into a row of batteries for storage and later use.  The modules must face south and be at an angle of 30 degrees for optimum performance in the UK.

In a number of European countries, but not the UK so far, most PV systems are tied to the national grid and owners receive a guaranteed price for the power they produce. 

Key points:
PV is extremely expensive at the moment due to the global shortage of silicon and extreme competition for this resource.

The UK national grid is not geared up to receiving electricity back from microgenerators so currently PV is only used to provide on site power. This means the payback period is extremely long making PV rarely a sensible investment at the moment.

Combined Heat and Power
CHP is not classified as a renewable technology as it needs a fossil fuel source, but it is an extremely efficient way of generating both heating and electricity in a single piece of equipment so it is a genuinely low carbon solution.

It converts up to 85% if the fuel it receives into useful energy i.e. heat and electricity compared with the 22% to 25% delivered by conventional ‘centralised’ power generation so cutting carbon emissions by around 30%.

It has the added benefit of making the user largely self-sufficient because they are able to generate their own electricity where they need it i.e. on site. As well as providing security of supply, this also avoids the transmission losses experienced by mains generated power - as much as two thirds of all centrally generated power is lost either as waste heat or in transmission.

A number of varieties are available including internal and external combustion engines (Otto or Stirling) and steam-based turbine systems. In the future, it is expected that CHP plant will also be fired by hydrogen fuel cells providing a truly sustainable solution.

The ‘primary’ fuel – oil or gas – drives a generator that produces electricity. The process creates heat as a by-product and this is captured and used to heat occupied areas and water. Originally, CHP units were normally deployed in large buildings or industrial complexes like waste incineration plants, but the technology is now available in ‘mini’ systems for domestic and small commercial premises. Eventually, CHP units could provide 100% of the heating and 80% of the electricity needs of many buildings so reducing their carbon emissions by 40%.

Key points:
The vagaries of the UK energy supply market means selling microgenerated electricity back to the grid remains difficult and complex.

Installation of CHP systems is not inherently complicated, but does require an engineer with sound understanding of the technology and how it can be applied to provide a balanced heating and power solution.

Community/district heating schemes
CHP and biomass boilers are now being regularly used to provide renewable community heating schemes to maximise efficiency. This is more common in the rest of Europe, but a number of schemes are already being run successfully in the UK and many more are planned.

Also sometimes referred to as ‘district heating’, these systems produce heating for a number of buildings in a local area, for multiple use buildings such as tower blocks or even for entire cities as in the case of Southampton and Sheffield. They are often fed by heat from incinerating waste so creating a further environmental benefit.

Once a heat distribution network is in place to deliver the heat to the local buildings, the energy source can be flexible and the consumers receive hot water in a similar way to conventional systems via their radiators. The only noticeable difference for the end user is the lack of a boiler for each property.

Aberdeen City Council is providing 988 homes, a local swimming pool and a further education college with renewable heat from a district CHP scheme. This has been particularly welcome for a large proportion of tenants in the area who were suffering from fuel poverty as their energy bills have fallen by £574 a year. Aberdeen also estimates that it has cut its annual carbon emissions by 411 tonnes.

Key points:
This approach is only really effective for very large or multiple buildings projects

It requires a complex combination of factors including local political support; a suitable network of buildings or multi-occupancy facilities; and co-operation with waste disposal authorities

It is becoming a greater priority for planning authorities including London where all developers are expected to at least consider the option of linking their building to others before submitting a planning application

Wind power
Micro wind turbines enjoyed a surge of interest when various DIY retailers starting promoting them, but actual performance has been disappointing often due to inappropriate siting of the devices and unrealistic claims.

In theory, micro wind units can deliver a useful amount of supplementary electricity into a building, but this should only be regarded as minimal ‘top up’ supply. There have been claims that this technology can provide as much as 30% of a household electricity needs, but this is not a common return and normally assumes that the property is positioned at a high altitude in an area of constant wind – 10% is more realistic.

The most convenient approach plugs the turbine directly into the ring main of the building to reduce the amount of electricity extracted from the grid. However, payback periods are lengthy due to the relatively high installation costs and permission from the local authority planning department is required.

Wind power has a greater role to play in large-scale electricity generation from offshore wind farms where it will clearly make a big contribution to future national energy supplies rather than in individual buildings.

Key points:
Wind power is only relevant for a minority of properties

Long payback periods

Planning permission is likely to still be required even with the newly liberalised planning laws because turbines do have an impact on lines of sight

Bigger is better!

Low carbon cooling and ventilation
Ventilation systems are highly desirable because of their role in reducing humidity; smells and CO2 build up from everyday human indoor activity. However, there is a balance to be struck between the need for fresh outdoor air, the power required to drive the systems and the need to reduce heat losses through air leakage.

A number of automatic ventilation systems are available that deliver this balance and when combined with heat recovery can recapture much of the wasted heat from exhausted outgoing air to pre-warm the incoming fresh air and save energy.

Many engineers are now combining these systems with heat pumps to deliver a highly sustainable solution.

Individual room ventilators are usually installed in the wall and are fitted with a heat exchanger for the heat recovery function. They use fan power to move the treated air in and out of the room.

Centralised ventilation systems for whole buildings use ductwork built into the ceilings to move air around with grills providing air intake and extract for living rooms and bedrooms to tackle condensation and humidity. Built-in heat exchangers are capable of recovering up to 95% of the heat from outgoing air in such systems.

For full blown air conditioning systems, low speed fans; efficient motors and heat recovery mean that end users can now have the increased comfort without paying the energy penalty – if the systems are properly designed and installed.
The proliferation of portable units seen during British heatwaves is not a good development for the environment as this tends to be an extremely energy intensive way of cooling offices, homes and shops.

Manufacturers also offer air conditioning systems that use ‘natural’ refrigerants such as ammonia, hydrocarbons, water and CO2, however, it is important to ensure energy consumption is not compromised by the choice of refrigerant.

Key points:
Is there a potential energy cost from using mechanical ventilation i.e. fan power?

What are the likely heat losses?

Is air conditioning really necessary for this building?

European F-Gas (fluorinated) Regulation is placing tougher restrictions on contractors working with refrigerants

Fuel cells
The fuel cell is hardly new as it was invented by Sir William Grove in 1839, but it still remains a solution for future building services applications.

It is a bit like a battery that never goes flat because as long as there is a flow of hydrogen and oxygen into the cell it will continually produce electricity from the process of electrolysis i.e. it converts hydrogen and oxygen into water. The by-products of this never-ending power source are heat and water that can be captured and used by heating and/or cooling systems.

Several manufacturers are developing fuel cell heating and cooling products, but none are commercially available as yet. When they do appear they could provide the ultimate ‘trigeneration’ solution by delivering pollution, noise and waste free heating, clean water and electricity.

Key point:
Be patient. This could be the ultimate solution to our building energy crisis, but not yet

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