What is TM52? Thermal Comfort in Buildings

Overheating is a growing risk due to climate change and shifting weather patterns. It can occur as a result of poor design, inadequate management, or ineffective building services, with features intended to reduce winter heating demands sometimes leading to excessive summer temperatures. To address this, the CIBSE developed TM52, a thermal comfort analysis methodology that helps to assess and mitigate overheating risks in buildings.

In this blog, you’ll learn:

• What TM52 is and how it works
• Why thermal comfort is essential in new and existing building design
• How TM52 helps mitigate overheating risks and enhance building performance
• How TM52 can be applied to existing buildings, including a test example, to assess and improve thermal comfort

What is TM52?

TM52 The limits of thermal comfort: avoiding overheating (2013) is a methodology developed by the Chartered Institution of Building Services Engineers (CIBSE) to assess the thermal comfort of non-domestic buildings and predict their overheating risk. It focuses on the indoor temperature conditions that occupants experience in these types of buildings, such as offices, schools, hospitals, and other public or commercial buildings.

The methodology applies to “free-running” buildings, meaning those where the peak internal temperature is not controlled by air conditioning, with means for the occupants to locally alter conditions. It evaluates both the frequency and severity of temperature exceedance over the warmer months, specifically from May to September.

TM52 sets out three key criteria that help determine whether a building is at risk of overheating:

1. Hours of Exceedance: Limits the number of hours during which the internal temperature can exceed a specific threshold (Tmax) by 1°C or more. This is set at a maximum of 3% of occupied hours from May to September.
2. Daily Weighted Exceedance: Accounts for both the degree and duration of temperature exceedance in a given day, ensuring that extreme heat exposure is not prolonged.
3. Upper Limit Temperature: Establishes an absolute maximum temperature limit of Tmax + 4°C. If a building exceeds this limit, it is considered at an unacceptable overheating risk.

If a building fails to meet two or more criteria, it is considered at high risk of overheating and requires intervention to mitigate the issue.

Why is Thermal Comfort Important?

Thermal comfort directly impacts occupant health and well-being. Prolonged exposure to uncomfortable temperatures can lead to heat stress, poor air quality, and a reduction in productivity. In terms of energy efficiency, buildings that lack proper thermal comfort often result in an increased reliance on energy-intensive cooling systems, which can drive up energy costs and contribute to carbon emissions.

In the context of modern building regulations and sustainability goals, ensuring thermal comfort is now considered just as important as optimising energy efficiency. TM52 provides a data-driven, scientifically backed methodology to assess a building’s ability to maintain comfortable temperatures and reduce overheating risk.

How Does TM52 Work and Mitigate Overheating Risk?

TM52 works by assessing a building’s thermal performance based on the three criteria mentioned earlier. This is done by running simulations that test whether internal temperatures exceed acceptable limits under normal use and summer conditions. By modeling the building’s thermal behavior and identifying any areas where that may surpass thresholds, TM52 analysis can highlight where improvements are needed.

The results of a TM52 assessment can inform practical design and retrofit strategies to help mitigate overheating risks. Some common strategies to mitigate overheating risks include: 

• Shading: Adding external shading devices or solar control glazing to limit solar heat gain.
• Insulation: Improve insulation and thermal mass to maintain stable indoor temperatures.
• Ventilation: Enhancing natural or mechanical ventilation to facilitate effective heat removal.
• Passive cooling: Use techniques like night-time cooling to lower internal temperatures after hot days.

These measures reduce reliance on energy-intensive cooling systems, improving both comfort and sustainability. By identifying problem areas and guiding targeted improvements, TM52 analysis supports better thermal comfort and more energy efficient buildings.

TM52 in Practice: Test on an Existing Building

Overheating isn’t just a concern for new buildings – it’s equally useful for existing buildings, especially those not originally designed to handle today’s warmer climate. Older buildings often lack sufficient insulation, shading, and ventilation, making them more prone to overheating during summer months. Our TM52 analysis can help identify these vulnerabilities and guide improvement strategies.

The following test example illustrates how TM52 can be used to assess an existing building. After conducting an onsite survey, we developed a dynamic thermal model to simulate the building’s performance. The results revealed that the building is at significant risk of overheating in its current condition, highlighting the importance of targeted interventions.

What’s Next?

As the risk of overheating increases with climate change, considering thermal comfort and overheating risk is essential for ensuring that buildings remain comfortable, efficient, and healthy. Whether designing new buildings or retrofitting older ones, TM52 analysis provides valuable insights into a building’s thermal behaviour and offers practical solutions to prevent overheating.

Are you are looking to ensure your building meets the latest standards for thermal comfort and energy efficiency? Contact us today for a comprehensive TM52 Thermal Comfort Analysis assessment. Our experts can help you identify and mitigate overheating risks to create a more sustainable, comfortable, and energy-efficient building.

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TM52: Thermal Comfort Analysis

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