Whats Building Energy Simulation Construction Essay

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Building design has almost come full circle; from when buildings were built in the vernacular and represented the most efficient response to the local environment and resources. With advances in technology, and materials that permitted isolation from the local climate, the potential for design became boundless. In the new era of sustainability however, the focus of design may not be to the same extent or indeed the same 'fashion'; environmental factors shall begin to heavily influence the outcome of designs. The aim, as defined by Brundtland, is towards

Designers are now required to provide estimates of energy use in buildings (Augenbroe & Hensen, 2004). Buildings however, are a complex mix of variables that combine to form multiple systems; all of which are interdependent and impact on the internal environment, energy demand and ecology of the building. Building Environmental Simulation (BES) provides a method of evaluating the interaction of the numerous variables from a wide range of sources, including physics, human behavioural, environmental and computational sciences (Demanuelle, Tweddell, & Davies, 2010). As a human being, the relationship between the individual and the environment is an ever evolving process; this interaction also forms an important part of the system (Markus, 1980).

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Clarke (2001) amongst others has noted the potential for BES as a tool for evaluating the wide range of responses of the systems involved. Selkowitz et al. (1992) provides well documented reasons for use of simulation in the design process. It can provide an invaluable source of information on the future performance of buildings, allowing for the evaluation of different climatic scenarios (UKCIP & Engineering and Physical Sciences Research Council).

It is an ever more accepted fact that that human activity is having a dramatic impact on global climate (Doran & Zimmerman, 2009). Global temperatures have risen by 0.6°C since the start of the 20th Century, with approximately 60% of that rise occurring since the 1970s. Hulme, Turnpenny and Jenkins (2003) have attributed this rise to a combination of natural and human factors; however only the human factor has caused an accelerated increase in temperature. The impacts of the changing global climate will affect many aspects of the climate in the United Kingdom, resulting in a minimum 2°C increase by the 2080s, with wetter winters and drier summers (Hulme, Jenkins, &Turnpenny, 2003).The use of Building environmental modelling has developed rapidly in recent years in response to the factors described above.

The consequences of a changing climate are likely to impact on the built environment in terms of thermal comfort, security of energy supply, and/or durability of design. The built environment alone is responsible for 47% of total CO2 emissions in the UK (Morrel, 2010), a contribution it is essential to work towards mitigating. The long life cycles of buildings shall bring further implications for future generations; refinement in BES is needed to incorporate the full range of future climatic scenarios (UKCIP & Engineering and Physical Sciences Research Council).

Research and experience (Norford, Socolow, Hsieh, & Spadaro, 1994) have indicated a shortfall in the delivery of low carbon, energy efficient buildings. Whereas the outputs of different simulation software packages are comparable (Karlsson, Rohdin, & Persson, 2007), BES results were found to be highly dependent on the accuracy of inputs, including component data such as heat exchanger efficiency. A study carried out in Sweden (Karlsson, Rohdin, & Persson, 2007) found that the influence of heat exchanger efficiency had the greatest impact on space heating in a 'low energy' building.

This is not to say that the predictions are wrong; other factors may be contributing to this short fall. The design approach to achieving technologically advanced, highly efficient buildings requires early involvement of all contributing parties from the design stage (McElroy 2009); increasing responsibilities of the construction professionals (Latham 1994). Sir John Egan (2002) also identifies integration as one of the key drivers to realising the true value of the professional's knowledge; changing the way the construction industry does business. Carbon reduction can be delivered through effective procurement (Morrel, 2010) from project appraisal to the routine adoption of post occupancy evaluation.

Since the Kyoto Protocol in 1998 which acknowledged the need for adaptation and limitation in a bit to deal with the impending threat of climate change; there has since been a greater shift towards mitigation of greenhouse gases (GHG). This change in strategy acknowledges the importance that climate change shall play in the 21st Century (United nations Framework Convention on Climate Change, 2010), with the UN identifying it as one of the greatest challenges of our time.

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At a national level the British government introduced the first long-term, legally binding framework to deal with the dangers of climate change. Setting emission reductions targets of at least 34% by 2020 and 80% by 2050 against a 1990 baseline (Offices of Public Sector Information, 2008), The Climate Change Act 2008 adopts a new approach to managing and responding to climate change in the UK. With an additional aim for achieving 'zero carbon' domestic buildings by 2016 and 2019 for non-domestic buildings Building Regulations have been brought up-to-date. Part L now stipulates acceptable levels of CO2 emissions, minimum standards of thermal criteria and quality control; setting performance standards for a whole building, rather than for construction and service elements as components.

Effective policy is essential; Boardman (2007) indentifies the need for a policy that brings together all standards that contribute CO2 in building operation and construction. From planning permission, through construction to proper commissioning to ensure appropriate performance; by implementing a range of policies the government has the potential to influence consumer behaviour. Economies of scale can be achieved with widespread up take of low energy further promoting up take. One very positive step the government has taken is the proposal for a 'Green Deal', which shall help homes and businesses reduce energy consumption in existing buildings.

It has been recognised that behavioural changes need to be brought about to ensure carbon reduction (Barrett, Lowe, Oreszczyn, & Steadman, 2008); implementation remains one of the hardest aspects of policy. The trend in increased comfort levels ((Domestic energy fact file 2008, 2008)Figure Standards of comfort - mean internal and average winter external temperatures Source: Domestic Energy Fact File (Domestic energy fact file 2008)) is a key problem of any energy saving measures, resulting in 'take back' of an increased level of comfort negating any saving in energy. However it is expected that average internal temperature will begin to stabilise as the optimum comfort level is reached; a study carried out in Germany (Schnieders & Hermelink, 2006) found 22°C to be the optimal average temperature for thermal comfort.

There are however many contributing factors to comfort, not simply mean internal temperature. Perception plays an important role in determining comfort levels; much research has been done on the differences in perceptions of those in a naturally ventilated building, compared to a fully air conditioned. Research carried out on behalf of ASHRAE showed greater acceptance of higher internal temperatures in naturally ventilated buildings. The research follows the theory of adaptive comfort (Nicol, 2011), which suggests that thermal expectations are also influenced by outdoor temperature, psychological factors as well as user control. Accounting for comfort in this way would ultimately allow for greater acceptance of design temperatures and ensure that energy use would be greatly reduced.

The price of energy is a key driver of behaviour, due to the lack of a definitive agreement at the G8 summit in December 2009 the price of carbon fell undermining the importance of the issue. The Economist (2010) gave one explanation for this being due to the "long- term prospects still remaining reasonable, if humble". A high price of carbon would promote greater investment in alternatives, whether motives are economical or ecological.

To help engage the population in their behaviour in buildings the Energy Performance of Buildings Directive (EPBD) was established in 2002 to advise the government on the energy performance of buildings, this led to the introduction of Display Energy Certificates (DECs) and Energy Performance Certificates (EPCs). EPCs are now required for all domestic and non-domestic, with DECs needed for just non-domestic and public buildings

Currently in use to identify building performance, DECs and EPCs aim to make energy performance more accessible and transparent (Field, 2008). The DECs indicate the operational CO2 emissions for a building, while the EPCs indicate the 'as designed' energy performance (The Carbon Trust, 2009). EPCs highlight the influence of building quality separate to other influences such as occupant behaviour. DECs incorporate total emissions for a building and are considered more important, reflecting the highly influential impact of user behaviour. EPCs and DECs are therefore measuring two very different aspect of building performance; managing the expectations when comparing the two would go some way to addressing the credibility gap between prediction and delivery.

Since the 2006 update of Part L REF## of Building Regulations; stipulating the need for energy predictions for compliance, the use of BES has increased. The BRE also developed the Simplified Building Energy Model (SBEM) using steady- state calculations to provide monthly energy use and CO2 predictions, both methods are used; using the same base data provided by the National Calculation Method (NCM). Obviously SBEM was developed purely for compliance purposes; however the capabilities of its application are limited to more simple building forms. BES allows the flexibility to model larger, more complex buildings, with the potential to provide more accurate predictions. Both SBEM and BES are used for non-domestic predictions, whereas Standard Assessment Procedure (SAP) 2005 is used for domestic buildings.

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At present the indicators of building energy use are positive, since 2005 the fall in energy consumption has been due to a combination of energy prices, improved efficiencies and weather (Department of Energy & Climate Change, 2010). However any energy efficiency measures have been counteracted by an increase in space heating of 20% and 175% for lighting and appliances (see Fig 3)(Department of Energy & Climate Change, 2010). Following on from the introduction of DECs and EPCs as previously mentioned, Figure 4 indicates a lack of correlation between energy performance of buildings and their corresponding SAP rating. Despite the SAP rating being only a measure of the asset, (not accounting for 'in use' energy use) unlike the average consumption per dwelling a better correlation should still be expected. These results highlight the short fall in delivery (Summerfield, Lowe, Firth, Wall, & Oreszczyn), identifying a need for a better understanding of occupant behaviour influencing energy demand.

Much information*REF. PREDICTION TO DELIVERY*is available providing reasoning for the lack of performance delivery of buildings. Bordass, Cohen, & Field (2004) identify both the simulation process and the building's physical characteristics as causes for inconsistency. This problem is amplified by the expectations which are built up by designers, when making direct comparisons between their asset predictions and benchmarks that are based on actual energy performance. These benchmarks incorporate all energy uses in the complete building. This leads to a significant credibility gap, when buildings eventually fail to deliver on the unrealistic predictions (Bordass, Cohen, & Field, 2004).

Problems indicative of model simulations are partially down to the complex nature of the building systems involved. To model the systems accurately means incorporating a large number of parameters, and thus introducing numerous estimates and notional values. In addition to the unknown contributions from external, uncontrolled parties e.g. contractors and occupants, all are contributing to the element of uncertainty that is inherent in predictions (Frenklach, Packard, & Seiler, 2002).

The impact of external systems becomes more important with the increasing need for passively designed buildings that rely on air movement and other physical phenomena to provide a comfortable environment. Computational fluid dynamics*REF. CFD in simulation*and the simulation of air movement has become an effective tool in predicting air movement through a building.

Buildings represent 40-50% of UK carbon emissions; this figure is the 'in use' value, namely the building occupant. Therefore the importance of peoples' behaviour in buildings shall play a vital role in achieving targets (Innovation & Growth Team, 2010). This begs the question of whether the occupants are aware of the important role they play in delivering low energy buildings. This issue highlights the importance the commissioning process and feedback. Standard practice means that commissioning rarely goes beyond finding out wither the mechanical and occasionally other system equipment are functioning as purchased and installed, the question of appropriateness is seldom asked(Zimmerman & Martin, 2001).

'Soft Landings'(Way & Bordass, 2005) was developed to address the issues at handover and help avoid the ensuing problems; helping close the loop between design, construction, operation, and providing feedback into design. This is especially important with innovation, where new techniques often have unintended consequences. Knowledge of how to operate low energy buildings has been identified as one of the barriers to the development and uptake of such buildings (The Carbon Trust, 2009). In recognition of the potential benefits of a graduated handover, Soft Landings has now become a recognised credit on BREEAM 2011

The importance of human behaviour in buildings is supported by a number of studies e.g.(Demanuelle, Tweddell, & Davies, 2010)&(Hinnells, 2008).Both of which identify occupants to having one of the greatest influences on energy use. Thus changes in behaviour have the potential to be as effective as technological advances in reducing energy use in buildings (Barrett, Lowe, Oreszczyn, & Steadman, 2008).

With the increased volume becoming available due to sub-metering, half hourly energy metering data provides detailed information of variations in energy use daily, seasonally and yearly However with such high volumes of raw data manual evaluation is no longer feasible. Brown & Wright (2007) go on to identify systems to automatically extract useful information, ensuring effective energy management.

Roaf et al. (2004)also promote the use of feedback to promote more accurate benchmarks, against which more accurate predictions can be made and performance measured. Carbon Buzz (CIBSE & RIBA) has been developed to promote up to date benchmarking of operational energy performance, providing feedback on low energy designs. The platform also compares design predictions with the operational performance furthering helping to inform design predictions, developing upon the idea of DECs and EPCs methodology to establish an understanding of end use energy consumption.

All these measures feedback to more provide more accurate assumptions and notional values that can be used in energy simulation, providing more accurate predictions that help to deliver truly low energy buildings that are used correctly.

'Soft Landings' (Way & Bordass, 2005) has been developed to close the loop between design, construction, operation, providing feedback into design. This is especially important with innovation, where new techniques often have unintended consequences. Knowledge of how to operate low energy buildings has been identified as one of the barriers to the development and uptake of such buildings (The Carbon Trust, 2009).

The importance of human behaviour in buildings is supported by a number of studies e.g.Demanuelle, Tweddell, & Davies(2010)&Hinnells(2008).Both of which identify occupants to having one of the greatest influences on energy use. Thus changes in behaviour have the potential to be as effective as technological advances in reducing energy use in buildings (Barrett, Lowe, Oreszczyn, & Steadman, 2008).

As well as occupancy feedback, energy monitoring is a vital method of feedback, providing opportunities for effective management (Brown & Wright, 2007) and improved understanding of end use (Hinnells, 2008).

With the increased volume becoming available due to sub-metering, half hourly energy metering data provides detailed information of variations in energy use daily, seasonally and yearly However with such high volumes of raw data manual evaluation is no longer feasible. Brown & Wright (2007) go on to identify systems to automatically extract useful information, ensuring effective energy management.

Roaf et al. (2004)also promote the use of feedback to promote more accurate benchmarks, against which more accurate predictions can be made and performance measured. Carbon Buzz (CIBSE & RIBA) has been developed to promote up to date benchmarking of operational energy performance, providing feedback on low energy designs. The platform also compares design predictions with the operational performance furthering helping to inform design predictions, developing upon the idea of DECs and EPCs methodology to establish an understanding of end use energy consumption.

Benchmarks and yardsticks have always been used to provide initial figures and targets for designers, while also providing a standardised comparison to assess performance. An energy benchmark is simply a performance value between a building performing badly and a building performing well. As building performance comes under more scrutiny, use of benchmarks becomes more important to provide relative indications. Benchmarks provide the opportunity to answers questions on whether improvements can be made, or whether the delivery was as intended; as highlighted in the benchmarks and targets set for GHGs in the Kyoto ProtocolREFF##.

TM46: 2008 (Field, 2008) provides 'in use' benchmarks for many building and in used to determine DEC ratings. At present there are 29 different benchmark categories, each representing a group of buildings with similar functions. To ensure direct comparison between buildings, benchmarks are expressed as kWh/m2. Even this measure is open to interpretation however; consolidated, high intensity buildings may appear to be less efficient compared to the same operational use spread through a number of buildings. The result however, would appear to be more efficient, whereas in reality more energy is being used due to the greater floor area.

Conversion factors are also applied to energy consumption to assess the carbon emissions of the buildings. As defined by the Department for Communities and Local Government; delivered electricity and natural gas have different carbon intensities, therefore conversion factors are 0.55 kgCO2/kWh and 0.19 kgCO2/kWh respectfully. The use of 0.55 kgCO2/kWh differs from the value given in CIBSE guide F of 0.43 kgCO2/kWh, this could potentially lead to confusion and distorted results in CO2 emissions.