‘O’ for a balance between thermal comfort and health

Meeting Part O means achieving a balance between thermal comfort and healthy indoor air quality for residents; as James Fisher from Titon Ventilation explains

Ventilation plays a crucial role in maintaining a healthy and comfortable indoor environment in residential applications. It helps to remove indoor air pollutants, excess moisture, and unpleasant odours, ensuring better air quality for occupants. Additionally, ventilation supports the maintaining of good indoor air quality, preventing the build-up of heat that can lead to discomfort and health issues.

Overheating in homes can also pose various risks, including heat stress, dehydration, and an increase of health conditions. It is estimated over 4,500 people died in the UK in 2022 due to high temperatures, the largest on record in recent years. Effective ventilation systems, such as mechanical fans or natural ventilation are essential in alleviating overheating by promoting air circulation and cooling indoor space.

As dwellings become more airtight and the summers become warmer, ventilation choice is vital to provide the occupants with effective ventilation. The latest Building Regulations of Approved Document F (ADF) ‘means of ventilation’ and Approved Document L (ADL) ‘conservation of fuel and power in existing dwellings’ mean a continuous mechanical ventilation system is often required. Mechanical ventilation with heat recovery (MVHR) is the ultimate system – reliable, continuous ventilation providing balanced extract and supply air flow. MVHR systems not only recover heat from extract airflow during winter but also incorporate a summer bypass to mitigate heat gains. However, it’s important to note that warm air from these systems can still enter dwellings during summer months; incorporating a cooling module enhances control over indoor temperatures. Additionally, MVHR systems effectively reduce the infiltration of unwanted air particles into dwellings, thereby enhancing indoor air quality. By incorporating high-grade filters, homeowners can alleviate pollution from outdoor sources while ensuring a continuous supply of fresh air within the dwelling.

Further Building Regulations were introduced to support indoor comfort with the addition of Approved Document Part O (ADO) released in June 2022. The new Building Regulation looks at overheating in new dwellings where people sleep overnight with the aim of ensuring ‘habitable comfort.’ The regulation does not affect pre-existing and commercial buildings.

ADO highlights two approaches for compliance; the simplified method and thermal dynamic modelling. The simplified method – considers factors such as dwelling location, orientation, window dimensions, solar gains, removing excess heat and cross-ventilation for residential properties.

Secondly, thermal dynamic modelling is a method of building modelling that predicts the internal conditions and energy demands of a building at short time intervals using weather data and building characteristics and follows CIBSE TM59 (to an extent).

ADO states a preference for passive ventilation, if possible, but once natural ventilation solutions cannot be applied, then mechanical ventilation will be required. This means a change in TM59 which no longer uses adaptive thermal comfort and the required dwelling rooms will now not exceed a fixed threshold of 26°C for more than 3% of occupied hours.

Integrated cooling solutions

External considerations such as noise and solar gains can affect the selection process of trying to remove excess heat from a dwelling. If passive ventilation is not an option, then an alternative option needs to be considered; one alternative is an integrated cooling system which fits on top of a MVHR system.

An integrated cooling system will assist in removing heat from a dwelling and can further enhance a MVHR performance by pre-cooling the incoming fresh air during warmer months. By combining the benefits of improved air quality and energy efficiency, MVHR systems with cooling modules contribute significantly to creating more comfortable indoor spaces and supports ADO compliance, whilst recycling energy within a home.

As an example, Titon offers a matched cooling module that is a mechanical solution to provide filtered and tempered air during periods of warm weather for user comfort, as part of an overall heat recovery ventilation system that is easy to install and control. Combined with its HRV.25 MVHR, this solution has the ability to enable a perfect combination for mitigating overheating.

James Fisher is commercial director at Titon