Overheating in homes

This post was written by BSRIA's Saryu Vatal

This post was written by Saryu Vatal, Senior Consultant of BSRIA’s Sustainable Construction Group

BSRIA’s Residential Network organised an event on the 22nd of July focussing on the issue of overheating in homes with an excellent line up of speakers. Nicola O’Connor started the day summarising an extensive research project by the Zero Carbon Hub that brought together input from government, industry and academic experts to understand the challenges around tackling the risk of overheating in homes (http://www.zerocarbonhub.org/current-projects/tackling-overheating-buildings). Chris Yates from Johnson and Starley made an appraisal of the assumptions and requirements within the Building Regulations and associated guidance as well as the implications for mechanical ventilation system manufacturers. Neil Witney from DECC explained the challenges around defining and regulating of overheating within homes, current policies and mechanisms that may be introduced in the future in response to the growing body of evidence highlighting the issue. Paul Ciniglio from First Wessex shared the organisation’s findings from several research projects and experience from their own developments, which resonated with issues highlighted by members of the audience. Bill Gething of Sustainability + Architecture and professor at the University of West England brought into perspective how changes in the way homes have been designed and built over the recent years has led to a shift in the performance of homes. James Ford, partner at Hoare Lea discussed some key considerations for designers to address the issue at early stages, to help minimise risk and dependence on active cooling solutions.

Extent of overheating

Evidence indicates that up to 20% of homes in England may already be overheating. Areas where additional risks have been highlighted include:

  • Common areas in apartment blocks, especially where community heating is installed – these areas are not assessed using SAP as they are outside the dwelling envelope. In reality, being unoccupied spaces these are often not modelled for their thermal performance (and energy use) at all. Community heating is being incorporated in an increasing number of projects and the supply network remains live even in the summer to meet the domestic hot water demand. Ensuring that the specification and installation of insulation for the distribution pipework is adequate is becoming increasingly important as buildings are made more airtight. Often stairwells and circulation areas have a high proportion of glazing and, with recent improvements in the general standard of construction and materials, tend to retain a large proportion of the heat gains. It is now important to incorporate a ventilation strategy for these spaces so that the accumulated heat can escape.
  • Urban areas – the average temperatures in city centres can be more than 4°C higher than rural areas. Flats are more common to city centres and these are often close to sources of noise and air pollution and have limited, if any, potential for cross ventilation. All these factors can combine to limit the effectiveness of natural ventilation in addressing the build-up of heat and not just in the summer. Building designs that incorporate large proportions of glazing in their facades, such as penthouses, if not carefully designed, can require air change rates that are unrealistic to achieve, using natural or mechanical ventilation systems.

Need for a definition

A number of sources and definitions are being referred to currently when evaluating for the risk of overheating in homes. These include CIBSE’s Environmental Design Guide A (2006) which sets standards for comfort, although it is not mandatory to use this to demonstrate compliance with the Building Regulations. Dynamic modelling through tools such as TAS and IES offer the opportunity of making a more comprehensive evaluation than SAP, but this option is skill, time and cost intensive. Building Regulations do not relate to limiting overheating for thermal comfort, just limiting the use of fuel and power for air-conditioning. The minimum evaluation for demonstrating compliance with Criterion 3 of Approved Document Part L of the Building Regulations needs to be carried out using SAP. While SAP is not intended to be a design tool, it is accepted that it is the default tool the industry uses widely.

Research projects have highlighted that dwellings can demonstrate a risk of overheating when evaluated against the CIBSE standard but not when modelled in SAP. Surveys from the Zero Carbon Hub study showed that nearly 60% of the housing providers surveyed had checks in place to assess the risk of overheating. However, only 30% of these housing providers explicitly included the requirement for considering the risk of overheating as part of their employees’ requirements to architects and designers. This suggests a missed opportunity for the issue to be addressed early on in the process, when cost and energy efficient measures may be effectively incorporated.

There are several challenges around the definition of conditions under which overheating can be said to occur as several factors contribute to this, including but not limited to air and radiant temperatures, humidity, air velocity, level of activity the adaptability of the individual. There are several checks that can be built into the design process which can help identify the risk at an early stage and allow for a method for mitigating these to be set up and followed through.

Contributing factors
The energy efficiency of homes in the UK has improved significantly in terms of reduction of space heating loads. This has come about in new homes through Approved Document Part L 1A of the Building Regulations and in existing homes through schemes such as the Green Deal. Homes are now less leaky and better insulated to keep warmth in but attention and emphasis is needed on measures to facilitate the expelling excess heat adequately when temperatures rise.

Homes are expected to provide comfortable conditions for occupants all year round and through a range of different occupancy patterns, which may in reality be considerably different to the standard assumptions made in modelling tools like SAP. It is possible that if modelling for thermal comfort is carried out assuming worst case assumptions for occupant density, external conditions and hours of occupancy, many homes would require mechanical cooling. There are, however a number of common sense measures that can be applied to ensure the impact of key contributing factors are minimised. These include controlling solar gains from south and west facing glazing and making provisions for adequate, secure ventilation especially when thermal mass has been incorporated in the structure.
The current extent of overheating in homes must be seen in the context of the anticipated changes in climate. With external temperatures expected to rise with an increased frequency of extreme weather conditions, homes built today must be fit for purpose for warmer summers.

Mechanical cooling?
There has been a rise reported in the installation of mechanical cooling systems in homes in the UK, more noticeably so in the south. While this may be an expected feature in high end homes, the cost of running these systems can be prohibitive, or at least perceived as so, for households where minimising expenditure on energy and fuel is a priority.
There is potential to develop low carbon mechanical cooling systems such as reversible heat pumps. The large scale uptake of these can however have some serious implications for energy supply and the capacity of the grid to accommodate a draw in peak summer months.

Way forward
In addition to affecting comfort, exposure to high temperatures over prolonged periods can have a significant impact on the health and well-being of residents. It is critical therefore to agree on a set of parameters that can help define overheating in homes and this should be carried out with input from bodies such as Public Health England.
Until a definition and modelling strategy is developed, designers and housing providers can refer to several good practice guides and research studies that help embed a common sense approach to design. There is significant potential to mitigate the risk of overheating in homes if early stage design decisions are taken with due consideration for the issue. The limitations of mechanical ventilation systems to help achieve comfort in homes must be acknowledged so that the final burden of an ill-considered design does not rest with the occupants.

References and further reading
http://www.zerocarbonhub.org/sites/default/files/resources/reports/ZCH-OverheatingInHomes-TheBigPicture-01.1.pdf
Design for Climate Change, Bill Gething and Katie Puckett, RIBA Publishing Feb 2013
http://www.arcc-network.org.uk/wordpress/wp-content/D4FC/01_Design-for-Future-Climate-Bill-Gething-report.pdf
http://www.zerocarbonhub.org/sites/default/files/resources/reports/Understanding_Overheating-Where_to_Start_NF44.pdf

To find out more about our Residential Network and to download the presentations from this meeting check out BSRIA’s Network pages.  To find out more about all of BSRIA’s networks contact tracey.tilbry@bsria.co.uk.

Think in £s not kWhs and Start Reaping the Rewards

Steve Browning is Marketing Manager of Trend Controls, a BSRIA member company

Steve Browning is Marketing Manager of Trend Controls, a BSRIA member company

Often considered an unwelcome expense, the truth is that investing in energy saving initiatives offers significant financial benefits, as well as enhancing an organisation’s environmental credentials. I’m Steve Browning, marketing manager of Trend Control Systems and in this blog I will explain how a Building Energy Management System (BEMS) can increase the bottom line.

Although better energy management and the need to reduce carbon emissions are both moving to the forefront of the corporate agenda, they are doing so far too slowly. Rising prices, combined with the increasing scarcity of resources and a growing raft of environmental legislation, means that addressing the issue of how energy is used is no longer just an option, but something that requires serious attention by all businesses.

To put the issue into perspective, the long-term framework outlined by the Department of Energy and Climate Change (DECC) sets out plans for achieving the reductions stated in the Climate Change Act 2008. When compared to 1990 levels, this equates to a reduction of at least 34 per cent by 2020 and at least 80 per cent by 2050. As they are responsible for 17 per cent of the UK’s carbon emissions, the nation’s 1.8 million non-domestic buildings are at the very heart of meeting this challenge.

The government is also ramping up the pressure to comply. In addition to the CRC Energy Efficiency Scheme, the Climate Change Levy (CCL), Air Conditioning Assessments, Display Energy Certificates (DECs) and Energy Performance Certificates (EPCs), earlier this year the Energy Savings Opportunity Scheme (ESOS) was introduced to address the requirements laid out in Article 8 of the European Union (EU) Energy Efficiency Directive.

It means that ‘large enterprises’ employing 250 or more staff, or that have an annual turnover of in excess of around £42m and an annual balance sheet total of around £36m, must complete regular energy audits. The first must be undertaken by 5th December 2015, and then at least every four years.

The government hopes that ESOS will drive the take-up of energy efficiency measures amongst businesses, enhancing their competitiveness and contributing to the wider growth agenda. Furthermore, for organisations wishing to comply with increasingly popular international standards such as ISO 50001, a certified energy management system (EnMS) must be in place.

It is therefore a constant source of bemusement and irritation to me that some organisations aren’t making the obvious correlation between investing in technology that can reduce energy use and saving money. By failing to ensure that energy is being used as well as it could be they are, quite literally, paying the price.

One reason for this could be that for energy bills are often low compared to items such as wages, research and development, and property rental. However, companies must consider other issues such as brand reputation, employee expectations and competitive positioning, while customers expect them to play an active role in reducing the carbon footprint of their operations and products.

Even more frustrating is that in many circumstances it doesn’t even involve a vast capital outlay on new technology – for example, by simply maximising the potential of an existing BEMS energy savings of 10-20 per cent are easily achievable. This could equate to a 0.1-0.4 per cent saving on a company’s total cost base, instantly increasing profitability.

When a BEMS is first commissioned it is configured around an existing building layout and occupancy patterns. These can change over time and incorrectly configured time clocks and setpoints, new layouts, and repartitioning can all lead to poor control and energy wastage.

Failure to maintain a BEMS on an ongoing basis will result in degradation of the building’s energy performance. In order to rectify this, it is advisable to undertake an audit that ascertains what can be achieved and identify any energy saving opportunities. While items such as boilers, chillers, air conditioning, and pumps can be checked to make sure they are working correctly, any maintenance issues to do with the BEMS itself or the building services equipment use can also be addressed.

BEMS providers will be able to offer expert advice on how to enhance the operation of plant by installing items such as variable speed drives. The investment can pay for itself in a matter of months – for instance a centrifugal pump or fan running at 80 per cent speed consumes only half of the energy compared to one running at full speed.

It is critical to achieve stakeholder buy-in for any business enhancement programme and by using a standard Internet browser, software based packages are available that act as a window to a BEMS. It is also possible to access utility meter readings from a BEMS and present a continually updated record of a building’s energy consumption and carbon emissions – showing employees and visitors whether they are on, below or above performance targets.

Hopefully, I have demonstrated that reducing carbon emissions and lowering energy expenditure are closely linked. The savings that can be made through the use of a correctly specified and maintained BEMS are considerable and will help achieve compliance with environmental legislation. My advice is to take action before it is no longer a choice!Trend_RGB SMALL

For further information please call Trend Marketing on 01403 211888 or email marketing@trendcontrols.com. Trend are the main sponsors of this year’s BSRIA Briefing – Smarter ways to better buildings.

You can read more BSRIA blogs about BEMS here.  BSRIA’s WMI team also produce a BEMS market report –Building Energy Management Systems (BEMS) in Europe and the USA – which is available to buy from the BSRIA website. 

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