CIBSE Energy Performance Group

Dynamic Simulation Modelling (DSM) packages use actual building geometry, details of construction materials, HVAC design strategies (including renewables), solar gain, occupancy data and hourly (or even sub-hourly) weather data to enable the performance of the building to be modelled for a wide range of purposes, from design development through to Building Regulations compliance. The ‘performance’ of the building can be quantified in a number of different ways, including energy consumption, peak summer time temperatures and the adequacy of ‘passive’ engineering solutions, such as thermal mass, solar shading and natural ventilation.

DSM packages therefore offer a way of assessing how a building might perform and the impact of making modifications to the design all through the design process. For instance, at the initial stages of a project, a simple model can be produced to inform key architectural or servicing decisions. As the design becomes more developed, so the model can be refined to monitor compliance with the Building Regulations and fine-tune the scheme as a whole.

DSM packages therefore have many advantages as a design tool over compliance only ‘steady state’ software such as iSBEM which can only usefully assess compliance with the Building Regulations and are not appropriate as a design tool. However, DSM packages should be used appropriately and with caution, particularly where ‘automated’ control of systems is assumed.

As with any model using weather data and anticipated occupant behaviour, a DSM package is not able to provide a guarantee of future performance, but instead can be used to compare alternative designs and/or other buildings on a regulated, like for like basis.

For building design purposes, a number of packages can be used. However, where the packages need also to provide Building Regulations compliance, only accredited software can be used. A list of approved software can be found through the Building Energy Calculation Software Approval Scheme. Refer to the weblink below.

Key issues

• DSM allows dynamic aspects of a buildings performance to be modelled and compared
• DSM offers a more refined analysis of energy consumption over similar ‘steady state’ software
• DSM software can allow design strategies and building compliance to be assessed relatively quickly, depending on the scale and complexity of the building and accuracy required
• Problems can occur when switching models between different software versions
• DSM training is essential – as with any software package DSM can suffer from "rubbish in, rubbish out"
• Only accredited software packages can be used for Building Regulations compliance
• Only accredited Energy Assessors are able to produce the final compliance certificate for Building Regulations and EPC purposes

Links to further information...

There is significant evidence to suggest that buildings do not perform as well as anticipated at design stage. Findings from the PROBE studies (Post Occupancy Review of Buildings and their Engineering) demonstrated that actual energy consumption in buildings will usually be twice as much as predicted. This was based on post-occupancy reviews of 23 buildings previously featured as ‘exemplar designs’ in the Building Services Journal (BSJ) between 1995 and 2002. More recent findings from the Carbon Trust‘s Low Carbon Buildings Accelerator and the Low Carbon Buildings Programme have demonstrated that in-use energy consumption can be 5 times higher that compliance calculations. Both studies suggest that lack of feedback following occupancy is one of the biggest contributors to this gap. Another key factor is that calculations for regulatory compliance do not account for all energy uses in buildings. These calculations are commonly misinterpreted as predictions of in-use energy consumption, when in fact they are simply mechanisms for compliance with Building Regulations. Unregulated sources of energy consumption such as small power loads, server rooms, external lighting, etc, are rarely considered at design stage. Yet these typically account for more than 30% of the energy consumption in office buildings, for example.

In essence, the performance gap can be regarded as a combination of poor assumptions when predicting energy consumption at design stage (e.g. non-inclusion of unregulated loads, standardised assumptions for occupancy hours and controls) followed by a lack of monitoring post occupation. In other words, current predictions tend to be unrealistically low whilst actual energy demand is typically unnecessarily high (but this is rarely flagged up due to lack of monitoring).

Key issues

• Buildings typically consume 2 to 5 times more energy than predicted at design stage
• Compliance modelling does not account for all energy uses in the building, dealing solely with ‘regulated’ energy loads (i.e.: fixed building services and internal lighting)
• Designers are rarely required to predict in-use energy consumption
• Lack of guidance for modelling unregulated energy loads makes it harder for designers to consider these at design stage
• Lack of feedback regarding the in-use energy performance of buildings is likely to result in an increase in the performance gap
• Discrepancies between design specification and as-built are also observed to significantly contribute to the gap in performance
• In order to obtain more accurate predictions, design assumptions must reflect in-use performance of buildings

Links to further information...

One of the mandatory credit requirements introduced under the Abu Dhabi Estidama Pearl Rating System is that all developers must appoint an independent consultant to ensure robust commissioning and handover is both prepared for and then takes place, prior to practical completion. It is a monitoring role where an independent consultant is appointed by, and reports to, the client. This ensures that

1. Projects can be commissioned
2. Projects are commissioned
3. Projects are handed over

The independent commissioning consultant must be appointed and integrated into the project team at an early stage in the project, around RIBA Stage C, to allow the project to gain planning consent with The Abu Dhabi Urban Planning Council (UPC). The UPC recognises the need for an independent consultant to monitor commissioning and handover because designing an efficient building is just the first step in ensuring a building is on track to being efficient. Buildings must also be commissioned and handed over correctly if operational energy and CO2 emissions are to be managed.

The engineering part of Estidama takes the best elements from Part L, LEED, ASHRAE, CIBSE and BREEAM and combines these in a common-sense methodology that can be implemented in practise. If the UK had a regulatory framework similar to Estidama, the UK’s CO2 targets would be more likely to become a reality.

Key issues

• ‘Estidama’ means ‘sustainability’ in Arabic
• It is an initiative of the Abu Dhabi Urban Planning Council and a key aspect of Abu Dhabi’s ‘Plan 2030’
• It is a mandatory framework for development based on four ‘pillars’ of sustainability: social, cultural , economic and environmental and is tailored to the local environment and culture of Abu Dhabi
• The Pearl rating system is organized into seven categories; within each category there are mandatory and optional credits. Ratings range from a minimum of one Pearl to an exemplar level of five Pearls
• To achieve a one Pearl rating all the required credits must be met
• To achieve a rating above on Pearl a minimum number of credit points must also be achieved
• Government-funded projects must achieve a minimum of two Pearls

Links to further information...

What is embodied energy?

Embodied energy is defined as the commercial energy (fossil fuels, nuclear, etc.) that was used to make a product, bring it to market, and dispose of it. It is an accounting methodology that aims to find the sum total of the energy necessary for an entire product lifecycle. A ‘product’ could, for example, be a building, a boiler or a lighting system. Embodied carbon is the carbon dioxide (and the equivalent GWP of other gases) emitted as a result of the embodied energy.

In existing buildings, embodied energy is typically equivalent to only a few years of operating energy. It is a ‘sunk cost’ that cannot subsequently be reduced. In new buildings, the operating energy is lower and so the embodied energy is proportionately higher (but in absolute terms much the same) – perhaps of the order of 15 to 25 years of operating energy.

Building services products are typically constructed of high energy content materials (notably metals) and have shorter life times than buildings (and contribute additional embodied energy each time they are replaced). It has been estimated that over the lifetime of an office building, the building services typically account for ~20% of the embodied energy but not much work has been done on this; for dwellings a figure of ~10% seems probable. It has also been estimated that between 30% and 60% of the embodied energy associated with refurbishment is due to building services.

Key issues

• There are several conventions for calculating embodied energy and carbon (the use of AS 2050 and the ICE materials database – see links below - seem to be de facto UK common practice, but these may not agree with conventions used in EU Eco-design procedures)
• The importance of building services systems is uncertain, as is the degree of influence that designers can have on embodied energy.

Links to further information...

Voltage optimization is sold as a technique for saving energy on the basis that a lower voltage should mean a lower current and therefore less power consumption. This concept is superficially correct and generally produces savings, but take care; the payback may be longer and the hassle greater than you expect!

A number of approaches are possible – depending on what you mean by "voltage optimization"...

• Tap down an existing transformer to the correct voltage
• Add a secondary transformer to step down to the correct voltage
• Add automatic voltage regulation to maintain the correct voltage

The difference in cost between these options is considerable and to make a choice you will have to understand your electrical distribution. Consider the key issues set out below – then investigate further on the web sites listed.

There is considerable debate about how effective these devices can be – both for energy saving and for other claims on harmonics and phase balancing - the web sites listed have more detail.

You should also consider whether proper consideration of each energy consuming system (particularly lighting) might be more productive – the "site wide quick fix" is attractive – but a step-by-step approach is likely to be better overall.

Key issues

• What is the size of your demand – is your existing transformer right ? (Losses on older transformers can be 8% of rating -and do not reduce with lower loads – get this right before moving on)
• What is the nature of your load – reactive or inductive ? (Lighting is reactive and may reduce as planned – motors are inductive and may not)
• What voltage is your equipment designed for – is the current sale pitch assumption of 240V/440V supplied and 220V/400V optimum correct for you ? (Older motors and control gear may require 440v – equipment is most efficient at its design voltage – whatever that is)
• What voltage drops do you experience – would your longer runs drop too far ? (inductive loads will draw more current, under sized cables will run hotter, motor losses will increase and switch mode power supplies may start to give trouble)
• What load fluctuations do you experience – is a general reduction suitable or do you need voltage regulation ? (watch out for summer / winter variation – winter may place a higher load on a reduced grid voltage)
• Do you have UPS or standby generation; will they need re-commissioning ? (controls and fault protection will need to be re-set – expect problems)
• Should you optimise the whole installation – is lighting your real target ? (Up to 30% for discharge and switch start fluorescent – 5% for high frequency - nil for LED)
• Can you afford the downtime ? A distributed approach is less intrusive. (Major surgery on your LV incomer and a single point of failure – against a distributed risk on less vital circuits with cheaper equipment)

Links to further information...

BREEAM (Building Research Establishment Environmental Assessment Method) addresses wide-ranging environmental and sustainability issues and enables, including energy and carbon, and is now a common place requirement imposed on UK buildings by Planning Authorities, clients or as a pre-requisite for funding.

Carbon issues play a central role in the BREEAM score, and for BREEAM 2008, as well as the up-coming BREEAM 2011 criteria, this includes mandatory requirements which must be met in order to achieve higher ratings. Therefore it is important to understand the issues at the outset of a building’s design.

In a BREEAM 2008 Assessment, Ene1 accounts for up to 15 credits so forms a significant portion of the assessment, with points for the CO2 reductions credit awarded on EPC ratings rather than percentage reductions. Alongside this, minimum requirements have been put in place for this credit to ensure that buildings being awarded the ‘Excellent’ or ‘Outstanding’ rating are performing to a suitably high level on their energy use, needing to achieve an EPC Carbon Index of 40 and 25 respectively. These targets are not easy to achieve and are chosen to stretch design teams and force them to seriously consider the energy efficiency of the building and their design process.

Carbon also has a key role in Ene5 where credits are awarded for a feasibility study being carried out to determine carbon emission reductions from low and zero carbon technologies. This feasibility study is mandatory for BREEAM ‘Excellent’ or ‘Outstanding’ and there are further credits for a 10% or 15 % reduction in carbon emissions as a result. This encourages the team to look at renewable sources of energy early on (no later than RIBA Stage C) of the design process in a bid for renewable energy to become a real option in terms of energy generation rather than being seen as an add on for public image or as a last resort.

In the upcoming BREEAM 2011 version, Ene1 will be modified so credits can be achieved for a) energy demand, b) energy consumption and c) actual carbon emissions of the development. There will still be mandatory requirements for ‘Excellent’ and ‘Outstanding’ targets. Under Ene5 there will be a further credit for investigating and achieving a reduction in the life cycle carbon emissions of a renewable technology.

Carbon is a key driver for other credits as part of the BREEAM assessment, for example: daylighting and lighting performance and controls, natural ventilation, thermal comfort and free cooling credits, transport credits encouraging the use of public transport and cycles and green guide ratings of materials.

Key issues

• Ene1 mandatory requirement of at least 6 credits (EPC of 40) for BREEAM Excellent
• Ene1 mandatory requirement of at least 10 credits (EPC of 25) for BREEAM Outstanding
• Ene5 minimum of 1 credit (a LZC feasibility study) for Excellent and Outstanding
• Early assessment of the above bullets by a low carbon consultant

Links to further information...

Photovoltaic (PV) panels convert solar energy into direct current (DC) electricity. This can either power DC loads or be converted into alternating current (AC) by an inverter. AC electricity not consumed onsite can be fed into the local grid. PV installations can be ground-mounted, mounted onto the roof or walls of a building, or built into the roof or walls of a building (known as Building Integrated Photovoltaics - BIPV). Essential design considerations include:

• Avoid shading of the panels (partial or full shading of PV can lead to a 90% drop in output)
• Orientate and mount panels so they are angled (30-35 degree optimum in the UK) to face the southern solar radiation
• Design in adaptability for future expansion
• Ensure the structural integrity of the mounting surface can support the PV installation over the planned lifetime (usually a minimum of 25 years), and
• Model the electrical output on the annual solar irradiation of the location (kWh) rather than the peak (kWp).

As a rule of thumb a well designed PV installation sized at 1kWp (~7-14 m² and £3k-4k per kWp) can generate between 780-850 kWh per year (depending on solar irradiation available). This can offset 445-485 kg CO2 per year. The most common PV panels are made from silicon. Their efficiency at converting solar irradiation into DC electricity under standard test conditions are approximately:

• Mono-crystalline silicon (15% - 18%)
• Poly-crystalline silicon (12% - 15%)
• "Thin film" technology; amorphous silicon, CdTe, CIGS (5% - 12%)

Key benefits include low operational costs, negligible maintenance and noiseless operation. The main drawback is high capital cost. However, the Government’s Feed-in Tariff (FiT) scheme, implemented in April 2010, has incentivised the adoption of PV as the owner of the installation can claim additional income for the electricity generated and exported. The expected rate of return can be as high as 8% over 25 years; however, this depends on factors including the ownership and management model, the cost of the offset energy and whether the generated electricity is consumed onsite or exported.

Key issues

• The system efficiency is the percentage of solar irradiation converted to electricity. Solar irradiation in the UK ranges from 1,200 kWh/m² in the south-west to 900 kWh/m² in Scotland.
• Design the installation so air can flow freely around the panel. A 1 °C rise in the temperature from ambient of the panel can lead to a 0.5% drop in efficiency.
• For PV installations below 50 kWp to qualify for the FiT the installer must be MCS accredited.

Links to further information...

The CRC Scheme, which became law in April 2010, requires businesses and organisations to report annually on their energy use and carbon emissions, and to buy carbon allowances for these emissions. The scheme applies to all primarily non-energy intensive large public and private sector organizations that used more than 6 million kWh (costing around £0.5 million) of half-hourly metered electricity in 2008 – it includes for example banks, supermarket chains, local authorities and central government.

The Government will publish national a League Table each year from October 2011 showing the performance of all the organisations in the Scheme. These League Tables generally reflect each organisation’s ability to reduce its energy use but in the first year the tables reflect whether Automatic Meter Reading equipment is voluntarily installed in 2010 and whether Carbon Trust Standard (or equivalent) accreditation has been achieved.

The first phase of the scheme extends from April 2010 to March 2014. In the second phase, the plan is to cap the total number of allowances available nationally and auction them at the beginning of each year – thus ensuring that the country does reduce its emissions in these very important sectors of the economy. So-called secondary trading (between participants) would be allowed so that benefit can be gained from reducing energy use.

The scheme has been the subject of substantial revision from the government spending review in October 2010 and consultations ending in December 2010 and March 2011 – the future of the scheme and especially the arrangements for the second phase and the timing of allowances payments is up for consideration and change.

Key issues

• Participation is mandatory for qualifying organisations
• Organisations which used more than 6 million kWh of half hourly electricity in 2008 must participate
• Organisations which had even a single half hourly electricity supply in 2008 must make a registration – but do not need to report or buy allowances if usage in 2008 was below 6 million kWh
• Allowances must be bought every year – the cost in the first year (2011-12 to be paid in mid-2012) is set at £12/te CO2, which is around 7% of energy costs, and works out at 0.65 p/kWh of electricity and 0.22 p/kWh of gas.
• Allowances costs are retained by the government and not repaid to participants.
• Each year from July 2011 an Annual Report of energy use and emission for the previous year must be submitted. In the first year a Footprint Report of all emissions is required.
• The Scheme publishes a single League Table each year from October 2011 reflecting the performance of each participant – mainly the year-on-year reduction in carbon emission, although early action metrics apply in the first year.
• The Scheme has been subject to major modification and national consultation in its first year and so further changes are possible after the current consultation ending March 2011

Links to further information...

The UK Government sees domestic low carbon retrofit (retrofitting existing homes with energy efficiency measures and low carbon technologies) as a key instrument for achieving its target of an 80% reduction in CO2; emissions by 2050. However, the challenge is formidable, and equates to having to treat 12,500 homes for improved energy efficiency each week, every week, for the full 40 years to 2050.

Existing homes have hardly been impacted by climate change policy and regulation updates. However, with the Household Energy Management Strategy, published in early 2010, the government articulated its proposals for tackling climate change and energy security in the context of existing homes. The proposals outlined will largely be implemented through the Green Deal and a new micro-generation strategy. This should see extra advice provision, new standards for upgrades, installations and service providers, with further obligations on energy companies, and the introduction of Pay-As-You-Save financing; initiatives that are building upon the experience of a series of pilot and research projects that are helping to develop the necessary knowledge, skills, practical experience and market stimulus necessary for large scale implementation.

Projects such as the TSB’s Retrofit for the Future are proving that, of course, "the devil is in the detail". In seeking opportunities to minimise transmission and ventilation losses; manage internal and solar gains; supply energy efficiently; and control overheating and comfort, whilst accounting for a myriad of constraints, including: location; orientation; construction type and quality; layout; internal/external space; existing services; architectural/social context; and of course building occupants, retrofits present complex and multifaceted projects that require an appreciation of context as well as detailed technical understanding.

In seeking to achieve substantial, cost effective and long term carbon savings there is no one-size-fits-all solution. Whether delivered at community scale or on an individual home, adopting a whole-house or stepwise approach, if solutions are to be effective in saving carbon, and as a sound investment opportunity, they must be informed by practical experience and robust qualitative and quantitative performance data. Innovative technologies can play a role, but progress will depend on how effectively basic principles and current technologies can be presented in design, delivered in construction, and managed in operation.

Key issues

• Gain a good understanding of the dwelling, its context, and occupancy characteristics; accurate surveying and early engagement with planning authorities and occupants will help to realise effective solutions and avoid wasted design effort.
• Investigate scale-up opportunities; look to maximise time/resources on site, talk with neighbours, review neighbouring sites/developments for expansion of works or integration of infrastructure.
• Evaluate cost-optimal retrofit levels; review against "anyway-investments", use accurate life-time projections.
• Focus on simple, robust, and proven no-to-low maintenance solutions; overly complex options may be difficult to install and a burden to operate and maintain.
• Account for occupant comfort; ensure that retrofit measures don’t compromise wellbeing.

Links to further information...

Daylighting design is the practice of utilizing natural light within a building. By providing a direct link to the dynamic and perpetually evolving patterns of outdoor illumination, daylighting helps create a visually stimulating and productive environment for building occupants, while significantly reducing energy consumption and costs. It has been long established that access to daylight contributes to the health and well-being of building occupants, as well as having a positive effect on productivity, learning, attentiveness and recovery from illness. Successful daylighting design requires careful planning to balance heat gain and loss, control glare, and adjust for variations in daylight availability.

The UK Government’s decision to move towards zero carbon buildings by 2019 has significantly increased the importance of daylighting design and in particular the role that daylight evaluation plays in the design process. There is now a greater need than ever to demonstrate compliance with new standards and performance indicators, including more accurate predictions of thermal, visual and environmental performance and energy consumption for various design options. Unlike the thermal performance of buildings where the standards are relatively simple to define and advanced modeling tools provide detailed analysis and a high level of predictability, the current standards for daylighting design are unhelpful to the designer in the pursuit of low/zero carbon design.

Most current evaluations of daylight performance are made using greatly simplified "snap-shot" or single-point-in-time methods that do not account for all the influences on daylight illumination levels nor the variation over time. Indeed, the most common method, the ‘Daylight Factor’, does not even include the contribution from sunlight, only skylight, and even then under the simplified assumptions of the International Commission on Illumination (CIE) standard overcast sky distribution. Alternatively, many practitioners try to understand the pattern of sunlight in a space via study of the sun-path diagram, or a dynamic solar shading analysis, but without analysis of resulting illumination levels or the contribution of light from the sky or reflected light from the sun. Both the UK building industry and the international day-lighting community are aware of the problem and are pursuing alternative more realistic evaluation methodologies such as climate-based daylight modeling, pioneered by John Mardaljevic and now the focus of development worldwide by researchers and practitioners [see links below]. An interesting paper on climate-based daylight modeling by Mardaljevic may be found in the Learning Zone of the EPG website. Whilst much of the new development in daylighting evaluation and the design methodologies are within the academic community they are being to emerge commercially so keep an eye out for developments.

Key issues

• Practitioners appreciate the reality of daylight, i.e. light from the sun and the sky acting together.
• Architects should strive for designs that achieve a "well-tempered" daylit environment, i.e. where the fixed architectural form provides both good daylighting and effective solar protection.
• Determine a sound basis for recommending solar control devices such as landscape features, overhangs or vertical fins, light shelves, SC glass, Venetian blinds and louvers.
• Compile an evidence base to demonstrate best-practise in daylighting design and evaluation.
• Facilitate the application of climate-based daylight modelling early in the design process.

Links to further information...

Do heat pumps as applied purely to space heating really contribute to a reduction in energy costs? Heating-only heat pumps, represented as low carbon and efficient heating solutions, have become positioned in market areas that are poorly serviced.

It is possible for us to be enticed into specifying heat pumps for heating-only applications despite having little real performance data. Irrespective of the heat exchange mechanism (air-to-air, air-to-water, ground-to-water) there are significant pitfalls to overcome in design, and where this is not appreciated many heating-only installations fail.

A large number of products claim to offer both high seasonal coefficient of performance (CoP) together with copious amounts of hot water delivered at over 60°C. In reality, heat pumps typically work most effectively when the leaving water temperature does not exceed 55°C, with lower leaving water temperatures producing superior energy efficiency.

With elevation in leaving water temperature seasonal CoP will suffer, or else leaving water must be kept low in order to maintain a good seasonal CoP. However, if the heat pump is used for both heating and cooling this problem can be overcome.

It is very easy to incorrectly size a heat pump; the application will fail, producing either higher running costs or installed costs.

Heat pumps have the best chance of success if they are designed as part of new, or well-constructed and thermally efficient, structures. Heat pumps require correct application, which takes skill in design, installation and commissioning. Perhaps more importantly the client should be made aware of all aspects of their use, both "pros" and "cons".

Key issues

• Don’t rely on questionable performance data
• Calculate carefully both heating and potential domestic hot water loads
• Identify noise issues in air-to-air units
• Carefully check out heat emitters in air-to-water units
• Execute a detailed examination of geographical issues in ground-to-water units
• Consider solar-thermal as an addition where domestic hot water is to be generated
• Choose suppliers/contractors who know their products well
• If possible, see a similar working system with decent operational data
• Consider whether supplementary heating will be required
• If possible, monitor operational running costs after final commissioning

Links to further information...