Thursday, September 08, 2005

Energy efficiency vs small scale renewables.

Climate Change is the biggest challenge facing the world today. Civilization has developed in what is now recognised and an unusually stable climatic period. We may be about to change all that. The climate change when initially responding to changes in greenhouse gases does so in a fairly predictable manner, and the consequences of this alone will be devastating. More abrupt changes are however possible when the climate system changes state i.e ocean circulation patters change. The climate system has been described as a drunk: leave it alone and it is likely to gently wobble around but push it and you increase the likelihood that it will collapse. We are performing this experiment by releasing vast quantities of greenhouse gases, preeminent of which is carbon dioxide. The harder we push and the more sudden the jolt, the more likely the climate system is to change dramatically. Many people think we should stop pushing!

Govornments have responsibility to act, but so do individuals, what can we do? Many things: restrict the distance we travel, use energy efficient cars, and, importantly, reduce use of fossil fuel derived energy for running our homes.

In the domestic setting is it more cost effective to reduce energy usage or produce your own green energy? Unfortunately this question doesn't have a simple answer.

Case A When the 'domestic setting' is a yet to be built house there is great potential to save all the energy associated with heating. However the cost of several renewable energies is also reduced at this stage.
Case B When the 'domestic setting' is an already built house built up to modern building regulation standards the opportunities for energy efficiency improvements are significant but poor when compared to the opportunities for renwables.
Case C When the 'domestic setting' is an old house with little in the way of insulation there are often several cheap energy efficiency measures which are worth looking at.

Case A: The Details

The physical structure of a house has an impact on two main energy requirements, energy for heating (or cooling) spaces and energy for lighting. Energy for heat is by far the most significant of these requirements in most situations.
  • In order to keep a property at a suitable temperature the design should consider the proportion of windows on the northern and the southern side of the building, it is advisable to glaze the southern side with 70% of the total glazing when in a cold environment. This maximises 'solar gain' and minimises energy losses.
  • In hot areas it may be worthwhile considering 'thermal mass' i.e rock/concrete as a significant structural element it living areas. Thermal mass stores heat but also takes a long time to warm up: during the night the living areas have time to cool down so during the day much of the heat in the air is removed warming up the mass again. If any of you have ever been in a castle before then you will know they tend to remain just cool, roughly the same temperature at mid day as at mid night.
  • More traditional methods of insulation have two important factors: thermal conductivity and air tightness. In new houses both of these are important but air-tightness is a particular feature of top-end eco-homes . Reducing the number of air changes per hour down to very low levels has enabled the design of buildings that need no heating, or only very occasional heating, even as far north as Norway and Sweden! One of the best ways to achieve this air tightness is through use of structurally integrated panels (SIP). This building method involves using a layer of insulating material sandwiched between two pieces of composite board and allows very tight sealing of these components to give a more or less air tight 3D jigsaw. These building if done correctly actually need a ventilation system to be included to remove stale air! This ventilation system can be fitted with a heat exchanger so that around 75% of the warmth in outgoing air is used to heats the incoming air.
  • Preventing the usual types of heat loss through thermal conduction is relatively inexpensive whatever system of building is used. There are a wide variety of alternative insulation techniques such as using straw bales, wool or recycled news paper. All of these materials however require careful consideration and there use requires consideration at an early stage of the design process. In the UK the traditional form of insulation is mineral wool, increasingly a layer of sprayed cellulose is used, this having similar thermal properties. These materials if applied to sufficient depth (>300mm for a low carbon home) do provide a good level on insulation, this thickness insulation is however not possible in all areas of buildings. Several high performance alternatives exist, including foil backed PU, this can be used at a thickness of 100mm to give the same insulating properties as 250mm mineral wool. Particular attention has to be paid to dormer windows which are often poorly insulated due to the lack of space. A specific warning should be given with regards multi-foil insulation (typically 20mm thick with numerous layer of foil) don't use it! The national physical laboratory just revealed its performance is about a qaurter what is claimed! Use foil faced PU instead
This table gives the performance of insulating materials per thickness. Materials father to the left have lower energy losses per square meter of exposed surface at a given thickness. These are generic types of materials but catalogues usually give the proprietary names along with the material type, for example kingspan as both foil faced PU and PF products.

  • The main types of renewables which can be installed at reduced cost during the construction phase are photovoltaics(PV) and ground heat. The reduced cost of installing PV is due to the fact that PV tiles can be used instead of regular tiles or slates. For this reason there is some gain from PVs as you need less regular building materials. Ground heat (as apposed to geothermal) is an increasingly common way of getting cool but not cold water out of the ground. During the winter at mid latitudes water used in households has to be heated from around 0 degrees celcius up to usable temperature. Ground heat utilises the fact that below about 1m in depth the ground is at a just about constant temperature all year round and therefore water has to be heated less. This system needs quite a bit of room and installation under the floor of buldings is ideal.
Case B: The Details

Modifications of buildings are expensive, alterations therefore have to have significant advantages over the status quo for them to be viable when compared to micro-generation. The main modifications which can be easily carried out on new buildings are 1.The fitting of a condensing boiler.2. Draught proofing 3.Increased loft insulation and 4. improved glazing (perticularly softwood argon filled low-emmisive glass double glazing).

Because of the limitations of affordable modifications in this case i will take this opportunity to give a rough guide to micro-generation. The suitability of these power sources varies enormously with site but one or other of them will be practicle for most sites.

  • Solar Panels (provide hot water). The average UK emmits around 5tonnes of co2 per year. Of this around 27% is due to heating water. A typical solar panel system may aim to provide 60-70% of this hot water requirement. 100% of the hot water requirements in the summer but no more than about 25% in the winter. carbon resuctions are therefore 5 tonnes*0.27*0.65, giving an anuual saving of around 0.9 tonnes of carbon a year. The price of solar heating varies but is typically in the range of 2500-3500 pounds, in the UK grants of 400 pounds are available for these systems so the cost to the consumer is from 2100 pounds. Solar is currently the most affordable small scale renewable. In spain it has just become compulsory to install solar pannels on all new buildings, the carbon saving produced by this plan will be huge, bearing in mind the hundreds of thousands of new homes built each year. Two UK suppliers are Solar Twin and Genersys.
  • Small Scale Wind (feeds directly into power supply, or used to heat water). Wind turbines intended for domestic use typically have a maximum rated value of 0.6 KW to 1.5 KW. The average UK home uses 3300KWh electricity a year (and a greater amount of gass for heating needs). Over a year these systems will generally generate as little as 800KWh and as much as 2500KWh, these values may however be radically imporved upon given an ideal location. Wind power on the west coast of scotland for example is likely to be by far the most affordable small scale renewable. The small units are designed to feed directly in to the power supply of the house, they provide the base load and less electricty is drawn from the grid. Larger units often have an optional heating element so the all the energy captured is utilised even if more energy is produced than immediately required by the household. Costs are fairly high, but significant grants are available.Two very competative systems are the 1Kw windsave and the 1.5 Kw Swift . Windsave have an agreement with scottish power that they will carry out installation. Another manufacturer that supplies 0.6 to 5kw turbines is proven energy.

These tables give a good guide to the amounts of energy that can be harnesed from affordable ammounts of wind power, 1-3Kw of gnerating capacity will generate from a qauter to a significant excess of power, depending largely on location.
  • Photovoltaic (PV) is a new and still rapdily developing technology which faces significant economic problems in the UK but which has great potential in warm climates. A typical instalation would consist of two modules and produce a maximum of 2KW of power. A 2KWp system in the uk will produce atleast 1500KWhr (about half the average household consumption) and would save around 0.65Kg of carbon dioxide emmisions a year. In the lifetime of a solar cell (atleast 25 years) the saving would be more than 16 tonnes of carbon, from around 37'500 KWhr of electricity. Factors currently encouraging the uptake of PV include govornment grants of around 3500 pounds per KWp of installed capacity and the dramatic increases of oil prices (from 60 dollars a barrel when i started researching this article to around 70 now!). Like large scale wind which has reduced its prices per KWhr dramatically since the 1980s it is expexted that innovation and market scaling will cut prices drastically in the long term.
Case C: The Details

In old houses with poor insulation, and, of a design which dosent consider energy needs, the gains that can be made from energy efficency and renewables are largest of all. In this case i will focus on renovation.The cheapest gains are likely to come from improvements in energy efficency but investment in renwables is also required to reduce the carbon footprint of these buildings to sustainable levels.
  • Energy efficency of households can be improved by changeing the appliances and heating systems being used. Use of A rated white goods and energy efficeint light bulbs are the first steps to be taken.
  • More significant investment and savings can be made by using a A rated condensing boiler.
  • In terms of reducing the requirement for heating the two biggest and least expensive gains can be made by increasing loft insulation and adding insulation to cavity walls. There are numerous types of cavity wall insulation that can be applied without major disruption to the house. Injected resins and foam beads are commonly used.
  • Many old houses are single glazed and good qaulity double glazing achieves a U-Value of around 1.4 to 1.6 which compares favourably to 5.0 for single glazing. Secondary glazing, when appropriately fitted can be a cheaper option that results in similar improvements in energy efficiency.
  • Somewhat suprisingly one of the best value investments in old houding stock is the purchase of a good central heating system which is easy to use and programable. Being able to set individual rooms at the desired temperature and at the desired times has been found to reduce the total amount of heating used drastically.
  • Finally a bit of simple DIY is often very usefull, draught stripping and other improvments to air tightness can make an enormous difference to old houses.
As an example of what can be achieved Kirklees Metropolitain Council managed to upgrade 19 houses built in 1946 to a SAP (Standars Assesment Procedure) rating of 76 from 35 by simply installing a well insulated and efficient heating system with 3-4 sqaure meters of solar panels. This resulted in avergage yearly savings of 1.4 tonnes of carbon dioxide.

To conclude: there are many renewable energy options and they tend to be locations specific. Basic imporvements in energy efficency of old housing should however be the first consideration. The reason for bothering is Climate Change, many of the measures will have long terms of payback but increases in comfort levels are also important. According to the latest science we each have about half a tonne of carbon dioxide to emmit a year! The earth can remove around 3 billion tones from the atmosphere and there are six billion people on the plannet and rising. So the message is get on to it, do your bit renewables and energy efficency measures will be needed (if you still want your tv/pc/washing machine/dvd player/dish washer etc...) The tables below show how much the average UK household emits (various types of housing).

Climate Change Action

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At 10:06 AM, Anonymous Kevin Heath said...

I would like to point you in the direction of a third UK supplier of Solar Water Heating Systems.

I recently used Aztec Solar Water Heating and was very impressed.

At 9:43 AM, Anonymous Beth Trevellis said...

I have recently embarked on a re vamp of my house in Cornwall with the help of an excellent company. They deal with many technologies and have installed a Proven wind turbine for me and solar heating panels.
I would highly recommend them.


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