The use of these fuels is damaging to the planet and their resource is finite, increased demand coupled with an ever dwindling supply is pushing up energy prices.
Renewable feed-stocks are presenting a viable low/zero carbon alternative to conventional fossil fuel based methods of space/water heating and electricity generation.
Oil prices
Crude oil prices have reached record highs in 2008. In London prices have advanced 36 % this year and reached a record $135.14 a barrel by May 22. Prices are currently $122.61/£62.10 a barrel as of August 1 2008.
Crude Oil price ($/barrel)
Gas Prices
Offshore gas production from UK fields in the North Sea fell by around 10% last year. The UK increasingly has to compete for imported gas supplies with buyers in Europe and Asia, as its own production begins to dwindle. The price of gas peaked this March as the closure of the UK’s main gas storage facility raised fears of a shortage. Prices on the 13th of March quadrupled to as much as 255 pence a therm.
The gas price in Europe is assumed to remain linked to oil prices, and UK gas prices are assumed to be similar to continental prices plus the transport cost differential.
Gas prices for U.K. households more than doubled since 2003 to an average £646 a year, while electricity bills are 69 percent higher. The average household now spends £1,058 a year on power and fuel. [3] Many forecast a rise of up to 40% in energy bills this year, meaning this figure could rise to £1,467 within seven months.
Forward gas contracts for delivery this winter reached a record 94.75 pence a therm (3.2215p/kWh) on May 27 and traded at 94.25 pence (3.2045p/kWh) June 6, according to ICAP. Gas for the 2009-2010 winter rose to a record 95.80 pence on May 27.
Gas bills are priced in kWh rather than pence per therm, therefore the conversion is for 1 therm being equal to 29.31 kWh., thus 1 kWh is equal to 0.034 therm's.
Therefore the a market price of 85p a therm for winter delivery is equal to 2.9p per kWh
The actual price British Gas customers pay is estimated at 29p per kWh - Or TEN TIMES the market price.
From today, British Gas is raising the price of its gas by 35 per cent, while customers buying electricity from it will pay 9.4 per cent more. Households who buy both services from the utility will see their dual fuel bills rise by 25 per cent.
Therefore a 35% price hike would equate to a price rise of 10p kWh from 29p (85p a therm) to 39p against a market price rise rise of 1.4p kWh to 4.3p kWh
Future projections gas prices for domestic heating are dependant on numerous factors and therefore vary considerably. Most estimates describe gas price increases to be congruent with oil price fluctuations until at least 2010.
Many speculate that oil prices may rise to $200 a barrel by the end of the year and evidence suggest that these increases will continue into the next decade.
The use of natural gas is loosing its edge as the cheapest means of space and water heating, the use of the fuel also carries obvious environmental problems associated with the combustion of a finite fossil fuel.
Electrical space heating
The use later heating. The idea being that the occupier would subscribe to a renewable energy supplier and therefore the carbon dioxide debt from heating
the home would be zero. Clearly in today’s energy market this is incorrect as all energy suppliers still rely on non-renewable sources to provide at least their base load.
The concept is attractive as installation costs for standard electric radiators and hot water systems are low. This is beneficial for landlords and developers installing housing in places such as converted warehouses where there is no existing gas supply.
However the costs on the consumer are high, with higher tariffs and less controllability than gas central heating. The loss of efficiency in electric space heating arises from the long energy chain in its development. This involves; The transfer from heat energy into kinetic energy in the turbines of a power station, then the transfer of kinetic energy to electrical energy in a generator, then losses in distribution of electricity then the conversion of this to electrical energy in the home.
This results in almost double the carbon emissions per kWh delivered energy. In a dwelling built to the proposed 2006 Part L amendments, the hot water load will be greater than the heating load. For a family of four heating the hot water using a gas condensing boiler will produce 1 tonne of CO2 emissions. Heating the hot water using electricity will produce 2 tonnes of CO2. That extra 1 tone of CO2 will not be offset by improving the insulation standards of the dwelling beyond the statutory requirements.
Providing space heating and hot water through sustainable and low/zero carbon means is an essential component of the construction of homes that are to meet the higher codes for sustainable homes.
The conventional methods of natural gas and standard electric space heating are carbon intensive and rely on non-renewable energy sources that are becoming increasingly expensive.
The demand for space heating in highly insulated sustainable homes is significantly reduced. There are numerous options on the market to provide low or zero carbon alternatives to space heating and hot water generation.
Electricity price
Energy saving trust figures (2008) place estimates of average electricity price of 12.12p/kWh [5] price increases of 9.4% as announced by British Gas could see this rise to 13.26p/kWh.
Heating means, new and old
Biomass
Biomass heating in the form of woody materials and peat has been used in conjunction with coal as a means to heat water and homes for centuries. A traditional wood or coal fired Aga would be used for cooking, hot water and heating.
Modern Biomass heating falls into two categories depending on the feed-stock:
Woody biomass includes forest products, untreated wood products, energy crops and short rotation coppice (SRC), which are quick-growing trees like willow.
Non-woody biomass includes animal waste, industrial and biodegradable municipal products from food processing and high energy crops. Examples are rape, sugar cane, maize.
For small-scale domestic applications of biomass the fuel usually takes the form of wood pellets, wood chips or wood logs.
Domestic biomass stoves can be used for space heating in an individual room, they can also provide a desirable aesthetic component to a living space. They can run on logs or wood chips and wood waste, automatic feeding systems run on pellets only. Such stoves are generally 5-11 kW in output, and some models can be fitted with a back boiler to provide water heating, these stoves can be up to 80% efficient.
Larger boilers can be connected to hot water and heating systems providing full space and hot water heating for a home. These systems are generally larger than 15kW in size.
Many systems exist with automatic feed systems, using wood chips or pellets being more efficient, but also more expensive. Log fed systems have the disadvantage of needing to be fed by hand. One of the obvious considerations of these systems is storage of the feed-stock. Automatic chip or pellet fed systems are usually designed with a large storage hopper. This can be a problem where storage space is limited. Economies of scale generally mean that a system that has fewer but larger deliveries of feed-stocks is most efficient both financially and in terms of energy expended in the delivery process. Although feed-stock may be generated on site as part of agricultural waste or waste from wood turning, sawing, milling etc. or generated from other plant wastes.
Most systems are versatile in the fuel from which they can operate; in terms of sustainability it is preferential to use locally sourced sustainably produced fuels. Boilers are often designed with an integral hot water energy storage or accumulator tank that stores water up to 90ยบ C, this enables the supply of heat to be further de-coupled from the combustion of the fuel. This is particularly helpful with log boilers where systems operate at full load and the matching of demand with load is performed by the accumulator.
Costs
A stand alone room heater or stove costs between £2,000-£4,000 including installation for larger boilers that incorporate space heating for the entire home there is greater variation between £5,000 and £14,000 depending on the nature of the boiler and the feed-stock used. Manually fed log boilers are generally cheaper than auto pellet boilers. The cost of fuel is a significant consideration. This depends often on the distance from the supplier, as a general rule fuel is cheaper in areas that don’t have a mains gas supply. A relationship with local farms or forestry industry could provide fuel for a housing development utilising biomass heating. This relationship would obviously have to be worked out at a local level and be dependent on availability of different fuel materials.
Wood chip
1.65p/kWh (£45/ton 85% efficiency) – 2.56/kWh (£70 /ton 85% efficiency)
Wood pellet
2.66p/kWh (£110/ton 85% efficiency) -3.87p/kWh (£160/ton 85% efficiency)
1.4-2.8p kWh mains gas (BIOHEAT has grown up)
Woodchips occupy a greater volume by weight (0.3 tons/1m3) when compared to pellets (0.7 tons/1m3). Wood pellets have a higher energy density than chips, are easier to handle and more reliable in feed mechanisms, they also have uniform lower moisture levels and have no degradation, unlike chips.
Installation of biomass heating systems is considered to be in the region of £200-450/kW for the UK, This can be 2-3 times the installation cost of traditional fossil fuel heating systems.
The energy saving trust (2005) places the cost of a 20kW domestic installation at around £5000, compared with an installed cost of £2500-£3500 for a new installed condensing boiler. The capital cost biomass boilers is decreasing as the market increases larger community sized systems sees this capital cost per unit of energy reduced still further.
Environmental considerations
The principle of the combustion of biomass as carbon neutral fuels is based on the concept that all carbon dioxide released has first been sequestered during the growth/photosynthetic activity of the plant. The length of this cycle with energy crops is very short with growing times of only a few years or so. However the combustion of fossil fuels releases CO2 in a fraction of the time in which it was divulged from the atmosphere, this results in a net atmospheric increase.
Whilst this principle is upheld there is still a carbon input from the production in the felling processing and transport of the biomass fuel. Although this is a consideration, in reality the emissions from the overall process of producing the fuel are very low when compared to natural gas, the lowest fossil fuel emitter.
The most significant environmental concern arises from the potential for the cultivation of energy crops to compete with food crops for agricultural land. This is the greatest single criticism of the liquid bio-fuel industry. On a small scale the concept does not present a threat, but if the whole of the UK was to use short rotation willow coppice as a means of space and water heating this would equate to a huge percentage of our agricultural land. Research estimates that over 100% of the UK’s current agricultural land would be needed to convert all UK road transport to domestically cultivated Biodiesel. A change to bioheat of this scale would present ecological problems relating to change in habitat type of a huge portion of the countryside, many believe the wide scale switch to bio fuels will, and is, contributing to global food price increases.
Changes in heating efficiency, through insulation, mean that this change to bioheat would not present as a significant demand on the agricultural space in the UK, equally much of the biomass fuel is divulged from wastes from industry: the commercial sector and agriculture. However these issues are still of valid consideration even in light of the current small share bioheat has in the UK market.
Ground source heat pumps
A few meters below the soil surface the temperature of the ground remains at a near constant of around 11-12°c in the UK. The ground retains heat from the summer due to its high thermal mass. Ground source heat pumps can transfer this heat as a means for space heating or hot water in buildings.
The system consists of;
Ground loop – this a long length of piping buried in the ground, either in a vertical bore-hole or a horizontal trench. The tubes are filled with a mixture of water and antifreeze, this is pumped around the pipes absorbing heat from the ground.
Heat pump - this is similar in principle to the heat pumps in air conditioners and refrigerators.
Evaporator - takes the heat from the water in the ground loop.
Compressor - moves the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit.
Condenser - gives up heat to a hot water tank which feeds the distribution system.
This heat is transferred to the space heating system within a house such as under floor heating or a conventional radiator system.
Horizontal systems are generally cheaper than those employing a deep bore-hole, however they require a far greater area for the excavation of a trench.
As with other technologies such as CHP and Biomass, costs are brought down if a wet heating system is already installed or is part of a new build.
The energy required for the pump is considered to be around 25% of the total energy in the system, as in for every unit of electricity used to pump the heat, 3-4 units of heat are produced.
The Coefficient of Performance (CoP) is the ratio of the number of units of heat output for each unit of electricity input used for GSHP. cops range between 2.5-4, the higher values are achieved from an efficient space heating system such as under floor heating, as it operates at a lower temperature (35°c -40°c) than conventional radiators.
A typical 8 - 12kW system costs £6,000 - £12,000 (not including the price of distribution system).
With running costs dependant on electricity price and heating efficiency.
Employing a 9 kilowatt (kW) (peak heat output) ground source heat pump with a coefficient of performance (CoP) of 3.5 and costing around £9,000 would require 8,570 kWh of electricity to operate the pump. Assuming a 12.12p/kWh this would equate to £1038.68 a year, and heating costs of 3.46kWh (assuming a CoP of 3.5).
Air source heat pumps
An ASHP system consists of a compressor and a carefully matched evaporator coil and heat exchanger. A refrigerant liquid which circulates within the system has a boiling point as low as minus 40°C and evaporates when absorbing heat from the outside air. It is possible to extract considerable heat from the air at temperatures as low as minus 15°C. The resulting refrigerant gas is then compressed adding more heat energy and raising its temperature to around 75°C. This heat is then passed via the heat exchanger into water and used to provide space heating through radiators as for conventional heating systems, or via underfloor heating systems.
As external temperature is more variable than in the ground, coefficients of performance are likely to be lower, but so too are installation costs as no trenching or ground drilling is required. GSHPs are far more efficient at cooling than air-source (since the ground is cold) and GSHPs are quieter and have a longer life than air source pumps since they are not outside exposed to the elements.
An ASHP typically costs in the region of £3,500 (6kW) and £6,000 (12kW), (not including the price of distribution system) Assuming a 12.12p/kWh this would equate to heating costs of 4.85kWh (assuming a CoP of 2.5).
[1] http://www.berr.gov.uk/files/file39577.pdf
[2]http://www.forecasts.org/oil.htm
[3] http://www.energywatch.org.uk
[4] microgen report
[5] http://www.energysavingtrust.org.uk/energy_saving_assumptions
[6] http://www.lowcarbonbuildings.org.uk/micro/biomass/
© Donal Liam Kinnear Brown, July 2008
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