Alternatives to Air Conditioning

Alternatives to Air Conditioning

SPECIAL ISSUE LAUNCH: A panel discussion explores future policies, design, technologies and behaviour

In an increasingly hotter world, can we halt a significant rise in the demand for air-conditioning (AC)? A recent Buildings and Cities special issue examined the impact of an increasing reliance on AC as well as potential alternatives through the lenses of policy, building design, technology and occupancy behaviour & wellbeing. Duncan Grassie and Daniel Godoy-Shimizu (University College London) present the highlights of a recent panel discussion held on 12.10.2022 to celebrate the launch of the special issue.

The special issue

The demand for cooling has increased dramatically over the past few decades, and this trend is projected to continue, with an estimated potential 700% rise globally by 2050. Such a change would have considerable impacts on society, healthcare and the economy, as well as the energy use and emissions associated with the building stock. Naturally, the magnitude of any impacts, as well as their significance, will vary globally reflecting differences in climate, the characteristics of the building stock, as well as wider societal factors.

Introducing the event, chair Dejan Mumovic (University College London) highlighted the breadth of research across the special issue’s 13 papers, reflecting the wide-ranging topics covered, as well as their international scope. The issue includes studies covering from New Zealand to the UAE, from the House of Lords in the UK to housing in India and China, and from the design of filters and ceiling fan nozzles to school retrofits. The papers can be loosely grouped around topics of policy, design, technology, and behaviour, and raise interesting questions around the sorts of policy changes that might be needed over the coming decades; how design teams and professional practice might respond; the technological improvements that might occur and how they might enter the market; as well as the potential for public engagement and the need to ensure that any changes do not increase heat exposure, especially for the most vulnerable members of society.

Introducing the four panelists, moderator Brian Ford (Nottingham University) asked each to provide their perspective on how to best approach the use of air-conditioning (AC), and comment on the important contemporary concerns. This was followed by a broader discussion with questions and comments from the audience. The panellists were:

  • Kevin Mitchell (CIBSE President and Global Practice Leader for Building Services Engineering at Mott MacDonald, UK)
  • Sheila Hayter (past ASHRAE President and NREL Laboratory Programme Manager for the  Department for Energy Federal Energy Management Program, US)
  • Rajan Rawal (CEPT University, IN)
  • Mike Davies (UK Climate Change Committee and University College London, UK)

Unintended consequences

The panelists noted the need to deal with overheating, particularly within the residential sector and in the context of rising global temperatures. Mike Davies presented a sobering assessment of the impact of exposure to heat within the UK, identified within the CCC’s “Risks to health, wellbeing and productivity from overheating in buildings” report. This points out impacts already being felt during recent periods of high temperatures, including reduced productivity as well as increased health issues and deaths. Along with climate change, these issues will potentially be magnified by demographic changes, such as an ageing population.

Since the risks are driven by the climate as well as the characteristics of the building stock, several panelists noted the importance of acknowledging differences across the international context. In certain climates, for example, cooling is not simply a luxury in the building stock, but a necessity. Local factors are also crucial for contextualizing the issue. Rajan Rawal noted, for example, that within India the current average household is only 5.2m2/person, but improvements to housing may result in this rising to 17-25m2/person. Thus, a significant focus will be on producing thermally comfortable new developments. In contrast, most of the building stock that will exist in the UK in 2050 has already been constructed, and so the need to deal with retrofitting existing buildings is of greater importance.

Moving the needle

The panelists, as well as members of the audience, highlighted the need to consider, and address, alternatives to AC within the context wider issues. For example, measures to reduce the demand for space heating in winter -such as increased insulation and air tightness- can inadvertently also increase the potential for overheating in summer. Mike Davies pointed out, therefore, that policies to reduce building emissions should be developed with appropriate consideration of unintended consequences such as increasing overheating. Similarly, Rajan Rawal pointed out the potential for the public’s expectations of their internal thermal environment to change over time. AC currently remains very rare within UK housing, however, if the decarbonization of heating involves a widescale transition to heat pumps (especially if this also involves changing from water- to air-based distribution systems), could this encourage an increase in domestic cooling?

The need to consider economic factors when planning long-term changes was pointed out by Sheila Hayter and Kevin Mitchell. This includes dealing with the fact that approaches to decarbonising the building stock will not necessarily align with the most financially preferable options, but also because of the different motivations across the stakeholders. While overheating in owner-occupied dwellings might be expected to be addressed ‘naturally’, the incentive for landlords to improve rental accommodations may be lower.

The importance of addressing the political and technical barriers to technological change were also noted by several panelists. As a panel member for the Global Cooling Prize, Rajan Rawal identified the significant challenge of bringing advancements in HVAC technology into the market, especially in the context of small-scale residential systems. Similarly, Peter Little, from the audience, noted the need for new standard design solutions to be developed for dealing with overheating without cooling, especially in the existing stock. Kevin Mitchell noted that this represents an opportunity for greater collaboration between academia, practice, and industry.

A holistic approach

Addressing several comments & questions from audience members, a key issue discussed at length by the panelists was the potential for policy and regulations. Could (and should) policy limit the inclusion of AC within the design of new buildings, for example? And for existing buildings, should homeowners be prevented from purchasing and installing AC systems, or could caps be applied to limit cooling use?

In the UK context, the panel highlighted a number of recent developments in regulation and industry, including Building Regulations Part O, guidance documents from CIBSE as well as a move away from temporary refrigerants through the Kigali Agreement to permanent shading and thermal mass solutions. It was noted that, to date, policy and guidance has largely focused on new builds rather than providing alternatives to cooling in the existing stock. Looking further ahead, regulation could mandate reduced use of AC in building design, or at least ensure that alternative thermal options have been properly considered within the design process; and examples were given where local authorities are moving in this direction. However, in the context of the general public installing cooling in existing homes, it may be preferable to provide greater awareness of, and access to, alternative solutions and possible savings; potentially with some involvement of local government through the planning and regulatory system.

The need for the development of any policy or regulatory framework to carefully consider the issue of equity was pointed out by Rajan Rawal and Kevin Mitchell. They described the differences in the vulnerability across the population to overheating risks, and the fact that cooling cannot simply be treated as a luxury in all contexts. In order for any policy to be successfully implemented, Mike Davies highlighted the need for a framework for monitoring and enforcing compliance. This will require demonstrations of what a well-adapted building stock looks like, clear design/performance guidance & targets, as well as measurable indicators (e.g. based around the percentage of the year in which a building can operate without mechanical cooling, calculated on an annual, or a monthly basis). While some buildings may preclude the full use of natural ventilation (e.g. due to noise, outdoor air quality, or internal requirements), successful hybrid solutions have been demonstrated, for example through traffic lighting in the White Collar Factory in London’s Tech City (where a simple green/red light system is used to inform building occupants when opening windows for natural ventilation would be most suitable).

The question of how theory & research can successfully be put into practice was addressed by Sheila Hayter. She introduced the US Department of Energy’s recently launched Net Zero Labs Initiative that aims for 4 federal campuses to achieve complete decarbonization. Such changes require a holistic approach to consider the wider context alongside building operation e.g. that an increase of electricity use within the buildings requires a corresponding decarbonisation of the grid to achieve significant emissions reductions. Another key factor, noted by Kevin Mitchell is careful documentation to aid eventual building users, as well as the importance of strong collaboration and multi-disciplinary teams within the design process. In the context of the Net Zero Labs, the first campus is expected to reach net zero in late 2023, through measures such as complete electrification, the use of carbon capture and storage and microgrids.

Challenging the orthodoxy

Asked to provide advice for young building professionals, Kevin Mitchell, the current President of CIBSE, noted that the main theme for this year’s 125th anniversary celebration for CIBSE is to “inspire the next generation”. During the design process, he suggested that new & future buildings professionals should:

  • aim to understand the underlying goals of construction projects (e.g. what is the facility being designed, why is it required, and how might these factors inform the design process?)
  • challenge the orthodoxy in terms of assumed design requirements (e.g. does this type of facility require very strict internal conditions?)
  • be open to new ideas (noting the benefit of open, multi-disciplinary brainstorming workshops in the early stages of design)
  • develop greater collaboration for successful projects.

Final thoughts

The panel discussion, and the special issue that it accompanied, explored a variety of interesting ideas and concerns around the topics of overheating & cooling, and how these might be addressed over the short and medium term to meet the targets for rapid decarbonisation. Reflecting its size and complexity, any large-scale and long-term improvement of the building stock will require careful consideration of a wide range of issues including carbon emissions, costs, health, and societal equity. The panel agreed that in this 125th year of CIBSE there was a greater need than ever for future academic and industry architects and engineers to have a firm grasp of building physics and to be able to integrate these both in addressing the consequences of design and providing holistic solutions.


Special issue editorial:
Ford, B., Mumovic, D., & Rawal, R. (2022). Alternatives to air-conditioning: policies, design, technologies, behaviours. Buildings and Cities, 3(1), pp. 433–447. DOI:

Link to the Buildings & Cities special issue

Watch the event (recordings on YouTube):

1-2-5 challenge

Committee on Climate Change report
Risks to health, wellbeing and productivity from overheating in buildings

Global Cooling Prize

The Net Zero Labs

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