School of Geography and the Environment

Building Market Transformation

Residential Energy modelling

Key conclusions from our modelling work are as follows. The full report from BMT is now available on the RCEP website.

• Carbon emissions vary under the three scenarios modelled. In Scenario A (current policies and technologies continued into the future, with incremental change in policies in line with current trends), emissions continue to rise and do not fall below 1996 levels for another three decades. In Scenario B, emissions in 2050 fall to 44% of those in 1996 (equivalent to the scenario modeled in the 40% House report). In Scenario C, emissions in 2050 fall to 25% of 1996 levels.
• In all three scenarios it is assumed that there is no dramatic shift in the carbon content of electricity supplied by the national grid. The model and report focus on reducing energy demand within homes and decentralised local energy generation.
• If no action was taken on the housing stock, total decarbonisation of electricity supplied from the grid would not be sufficient to achieve a 60% reduction in carbon emissions and would not even result in a halving of carbon emissions.
• A combination of approaches eg refurbishment, demolition, energy-efficiency, building-integrated Combine Heat and Power and renewables, is necessary to deliver low-carbon housing, framed within a clear and co-ordinated strategy, with responsibility at a Local Authority level. There are important regional considerations in terms of the associated environmental impacts eg water, availability of energy sources (especially renewables), land availability, landfill resources.
• The emphasis must be on demand reduction first, as the least cost strategy, followed by considerable installation of LZC, so that residual demand has a minimal carbon impact.
• Significant refurbishment of the existing stock is the key factor in reducing overall emissions, with existing houses brought to a level beyond current Building Regulations. Programmes and policy need to focus on whole-house refurbishment.
• Point of sale or rental is a target for fiscal incentives, eg stamp duty rebates, to encourage investment in the energyefficiency of the housing stock. Fiscal incentives should be launched alongside the Home Information Pack.
• New buildings must be constructed to ultra-low energy standards (eg BedZED or Passive House standards), with Building Regulations set to achieve zero carbon emissions (for space heating) by 2016 in line with EU and Government objectives.
• There needs to be a move towards standards based on monitored performance and energy in use.
• Communal energy solutions and distributed generation can deliver carbon savings but require appropriate policy to support the development of new infrastructure eg district heating networks.
• Combined Heat and Power (CHP) and renewables integrated into buildings provide 30-85% of heat and 23-100% of electricity in the different scenarios. The appropriate technology depends on house type and fuel availability: communal systems are appropriate for dense housing, micro-CHP is appropriate for suburban areas, and biomass and heat pumps are appropriate where there is no gas network. Roof based technologies (PV, solar thermal and micro-wind) can make a contribution throughout the housing stock
• High uptake of CHP and renewables by 2050 could imply significant commercial opportunity for Energy Services Companies (ESCos), particularly in social housing and in new build.
• The high level of LZC uptake under Scenarios B & C requires major changes over a relatively short timescale for both new build and refurbishment and therefore needs policy support.
• Significant savings can be made in lights and appliances, but this depends on EU-level action, supported by national governments. The EU has been slower than other jurisdictions to make use of mandatory standards. New technologies need introduction to market including Vacuum Insulated Panels (eg for refrigeration) and Light Emitting Diode (LED) lighting.
• There is also a risk of significant increases in ownership (eg of space cooling) that could increase energy consumption.
• Estimates for the embodied energy of new build and refurbished dwellings vary widely, but in all cases the embodied energy implied is significantly outweighed by the potential for savings from energy in use (assuming a 60 year lifespan as a minimum) provided the refurbished or replacement dwelling is delivered to an extremely high standard.

About the UKDCM2 Model

To find out more about how these conclusions have been arrived at, read the ECI report to RCEP. The modelling work that supported this report was undertaken by BMT.

A model of the UK housing stock has been constructed using data from the various housing condition surveys (English, Scottish and Northern Irish). This stock model contains a number of categories of buildings, each category representing a number of real world dwellings such that the sum of the dwellings in the stock model equals the number of dwellings in the country in 1996. In each building category is information about the building fabric (windows, walls, lofts, storey heights, air change rates etc.) and internal demanded temperatures. The majority of the information was taken from the English House Condition Survey (EHCS) 1996 which contains structural information for almost 30,000 representative dwellings. The 1996 EHCS contained an energy sub-module which later surveys have lacked.

Using the mean UK external temperature (1970-2000), BREDEM-8 monthly energy balance equations were constructed which calculated the mean energy flows and therefore energy demands from the heating system necessary to keep a given mean internal temperature. These energy flows take account of gains from cooking, metabolism, solar and waste heat from hot water and lights and appliances. The heat demand over the stock is satisfied by a specific breakdown of heating systems that includes gas boilers, electric heating, solar thermal and solid fuels, and in future years such technologies as CHP (stirling cycle, fuel cell, district heating), heat pumps and biomass heating.

Electricity demands in future years can be offset by on-site generation (CHP and solar PV). The calculations result in monthly fuel demands (gas, electricity, coal/oil, biomass) from the UK housing stock. These calculations are repeated for all months over one year. At the end of each year, the housing stock is updated (new build, demolition and retrofits) and the process is repeated for each month of the next year. Within each year are defined the heating system breakdown, demand for hot water, demand for lights and appliances, internal temperatures etc. The result, when aggregated, is the end use demand (space heating, cooking, lights and appliances, hot water), the fuel demand (gas, electricity, coal/oil, and biomass) and the carbon footprint (using historical and predicted carbon emissions factors) of the UK housing stock on a yearly basis from 1996 to 2050.

Scenarios have been constructed of alternative build and demolition rates, fabric improvements, microgeneration installation rates and efficiencies, improved efficiency in lights and appliances, as well as changes in human behaviour. The scenarios explore the potential for carbon reduction in 2050 in comparison to 1996 (or 2005) using external monthly mean temperatures given by the climate in the UK 1970-2000. This takes out the effect of weather events, either historical or predicted (comparison between an uncharacteristic 1996 and an uncharacteristic 2050 will affect the results considerably). Climate change can be modelled by applying a shift in external monthly temperatures.

The model can also be run in validation mode where real external temperatures are used 1996-2004 and the results have been compared to quarterly measured fuel supplied to the domestic sector, as recoded by DTI in Energy Trends. Modelled energy use is very close to energy supplied.

In order to aid transparency of the modeling and results, a package of materials is available, including

• A spreadsheet of results from Scenarios A, B and C.
• The UK Housing Stock 2005 to 2050: Assumptions used in Scenarios and Sensitivity Analysis in UKDCM2. The basis for all assumptions in all three scenarios and the sensitivity analysis 2005-2050. Includes discussion of the socio-technical interactions and economic implications, and discussion of the policy framework that might bring about these scenarios.
• The UKDCM2 model, together with a Manual on how to install and run UKDCM2 is provided. For many users, the above outputs may be sufficient. Some users may want to explore their own scenarios and assumptions, However, in order to run the model you will need install and run IDL, Exceed and Putty (see Manual). IDL Single user licenses are available from £299, but most universities and large consultancies may already have a license. It should also be possible to run the code in PV-WAVE which is an almost identical commercially available software package. IDL is available for both Unix, Windows and MAC machines and is installed using a CD with a license key supplied by the company. PV-WAVE is usually available as a 6 month trial from www.vni.com. Please note, the model is available but we do not have the resources to support users.

Please contact mark.hinnells@eci.ox.ac.uk if you would like a copy of the model.

The non- residential model

A series of sector reports will be released in October 2007, with an open source model released in December 2007. Between then and the end of the project in September 2008, the model will be refined, with a further suite of scenarios released.