Passivhaus is gaining momentum as the UK’s net-zero target grows nearer, with the design approach increasingly being adopted for non-residential buildings. In turn, the increased air tightness of Passivhaus buildings means effective ventilation is vital to ensure good indoor air quality (IAQ) and to help mitigate overheating. Long established within the residential sector, Passivhaus principles are now being widely adopted across non-residential applications, including education, offices and healthcare, as specifiers seek proven methods to reduce operational carbon while improving building performance.
This growing momentum is particularly evident in the public sector. In Scotland, for example, around 60% of new schools are now being designed using Passivhaus methodology. As local authorities and developers look for reliable routes to deliver low-energy, future-proofed buildings, Passivhausoffers a robust, performance-based framework that aligns closely with wider decarbonisation goals.
However, as building fabric becomes more efficient and airtight, the importance of building services, and ventilation in particular, has moved firmly into focus.
PASSIVHAUS PERFORMANCE
Passivhaus is defined by rigorous performance benchmarks. To prevent unwanted heat loss and drafts, airtightness must be ≤0.6 air changes per hour at 50 Pascals to meet the standard Passivhaus benchmark. Space heating demand must not exceed 15kWh/m² per year, while summer performance is controlled either by limiting cooling demand to 15kWh/m² per year or by restricting peak cooling load to 10W/m², depending on climate and building use. This dramatically reduces reliance on conventional heating and cooling systems and significantly lowers operational carbon emissions. These targets create buildings that are exceptionally energy efficient, but also require a carefully integrated approach to ventilation.
INDOOR AIR QUALITY
High levels of airtightness are fundamental to Passivhaus performance, but without effective ventilation, airtight buildings risk poor IAQ, condensation, mould, and overheating, all of which affect occupant comfort and potentially health. In non-residential settings, varying occupancy patterns place even greater demands on indoor environments, maintaining a healthy IAQ to support wellbeing, concentration and productivity, making effective ventilation central to successful building design.
The increased air tightness of Passivhaus buildings means effective ventilation is vital for good indoor air quality and to mitigate overheating.
MVHR
As Passivhaus has become increasingly popular, so has mechanical ventilation with heat recovery (MVHR). By extracting stale air and recovering its thermal energy to pre-warm incoming fresh air, MVHR provides continuous ventilation and minimises heat loss. This allows buildings to maintain comfortable internal conditions with minimal additional heating. MVHR performance is considered an integral element of the primary Passivhaus heating demand calculation. This means MVHR specification can influence whether a building meets the required performance targets. For specifiers, selecting high-efficiency MVHR with verified performance data is essential.
As Passivhaus expands into larger and more complex building types, demand has grown for commercial MVHR systems capable of delivering high airflow rates with low specific fan power (SFP) and high heat recovery efficiency. This makes units like Vent-Axia’s Passivhauscertified Sentinel Apex commercial MVHRs the ideal choice, with a performance number of ≥11.5 combined with up to 80% thermal efficiency. Specifiers are increasingly opting for Passivhauscertified MVHR since it ensures the units meet performance criteria, saving time and helping ensure projects meet Passivhaus standards once operational.
OVERHEATING
Since a Passivhaus building features high levels of airtightness and thermal efficiency, it reduces the reliance on conventional heating and cooling systems. However, the combination of increasingly thermally efficient buildings and rising global temperatures, especially in urban areas, is leading to buildings overheating if not carefully ventilated.
The latest MVHR units, such as Vent-Axia’s Passivhaus-certified Sentinel Apex, deliver coolth or heat recovery efficiencies of up to 80%. Crucially for overheating mitigation, the latest MVHR comes with intelligent automatic 100% summer bypass capabilities, offering free cooling, allowing night-time air to flow through the home when conditions permit.
Demand-controlled ventilation is another MVHR feature that is gaining in popularity. These systems adjust ventilation rates in response to monitored parameters such as CO2 levels, occupancy, or humidity. By tailoring ventilation to actual needs, demand-controlled systems can ensure that fresh air is supplied exactly where it is needed, without wasting energy, to ensure optimal IAQ and thermal comfort.By incorporating high-performance MVHR early in the design process, specifiers can ensure buildings are not only energy efficient but also healthy, comfortable, and future-ready.
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