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Mixing It Up

Wednesday, 03 September 2008

Page 1 of 4

As Building Regulations tighten on carbon emissions, energy reduction and mandatory renewable energy targets, the task for designers becomes harder and harder. Bobby Gilbert of Bobby Gilbert and Associates explains how a new design tool is making sustainable design easier.

The process of calculating CO2 emissions for a development is one of first calculating energy demands (different buildings have different energy demands for heating, cooling, hot water, and power for electrical appliances), then selecting energy supply systems and calculating how much fuel these supply systems will use. It is the burning of fuel, directly or indirectly – such as at a power station to produce electricity – that results in CO2 emissions, with different fuels producing different quantities.

Whilst this process is not rocket science it requires a methodical approach if it is not to result in confusion. Consider a mixed use development with a range of building types each of which have different energy demands. The energy supply strategy could be based around a number of systems including solar hot water, photovoltaic power, ground source heat pumps, combined heat and power, and so on, as well as conventional gas boilers and grid sourced electricity. These systems will have varying efficiencies which, combined with the type of fuel they use, will result in a wide variety of levels of CO2 emissions. Now add in costs for the various components (both capital and running costs) as well as the cost of fuel and perhaps even the polluting cost of the CO2 emissions. The calculation of emissions and costs starts to become more complicated, though not insurmountable if you keep a cool head.

The complications really start with the “what if?” studies. What if we use ground source heat pumps instead of gas boilers? What if we put wind turbines on the site instead of photovoltaic panels? What if the price of fuel doubles in the next 10 years? These sorts of questions and many others should be asked right at the very start of a design process. The trouble is keeping track of all the assumptions you make when doing the different calculations, so that when asked what made option A better than option B in 12 months time you can give a clear and confident answer rather than have to wade through a mass of confusing spreadsheets.

Carbon Mixer is designed to make this process consistent, reliable and robust. It stores the characteristics of buildings, heating, cooling, power, and renewable systems in a database from which it is easy to mix and match combinations and find CO2 emissions and costs. Any interesting scenarios can be saved in a project file which can be archived with other project data, or emailed to a colleague for discussion, and at any time in the future can be easily reproduced. The strong use of graphics during the data input stage means that users can see instantly how a mix is working and where strengths and weaknesses lie. This aspect is particularly useful in discussions with clients and other professionals who can instantly see the impact of a proposed change to the energy strategy.