Developers are up against two forces in house construction that can be contradictory – the need to increase energy efficiency and the need to improve indoor air quality. Against the backdrop of the hike in energy prices and the growing push to increase sustainability, maximising energy efficiency is important. However, at the same time, building regulation uplifts are driving a rethink about ventilation. On the one hand, energy efficiency advocates a sealed home, but on the other, health needs and regulations require that the home environment has a good airflow from the outside to ensure high standards of indoor air quality.
Can these forces be balanced? What’s the best path for specifiers and developers to tread?
The key to creating a well-ventilated, energy-efficient house is to look at heating and ventilation as two halves of a whole.
For too long, the construction industry has seen the next generation of heating systems as separate, unrelated parts. Ventilation, underfloor heating or radiators, and heat pumps have been specified individually – and the resulting combinations haven’t always delivered the energy savings and warm, safe homes that buyers expect. What’s more, developers have prioritised spending on heat pumps, meaning they have to make more cost-conscious choices for the rest of the heating and ventilation systems, leading to less-than-optimal results.
Tightening regulations are adding pressure to this situation. An uplift to Part L of the building regulations now caps the temperature of water leaving heating systems at 55°C - where previously 60 to 80°C was common. This cap sits well with the move to heat pumps that run at around 45°C and, if combined with large, heated surface areas via underfloor heating (rather than giant, inconvenient radiators), heat pumps can generate a comfortable temperature throughout the house.
However, this all depends on a relatively air-tight house. To achieve this, ventilation must be taken into account, too. Ventilation is vital for removing toxic substances from the dwelling and for preventing the dampness that can trigger mould. However, this often means letting valuable warm air out of the house – and this can drop the internal temperature, leading to dissatisfied residents.
New uplifts to Part F of the building regulations dictate that new build homes must have a mechanical ventilation flow rate of approximately 6 litres per second in each room. This is a steep increase in ventilation rates, and will potentially have a significant impact on comfort levels within leakier homes, or ones that have poorly aligned ventilation strategies.
Anthony Croke, Territory Product Manager for Indoor Climate Solutions at Wavin sums up the developer’s dilemma: “No single heating or ventilation product can solve these issues. The smart developer is looking at this as a whole, so they can hit the sweet spot of sustainable, energy-efficient heating combined with health-giving ventilation. This is critical to meeting regulations, keeping home buyers comfortably warm and creating efficient, future-proofed homes.”
To hit this heating and ventilation ‘sweet spot’, the ventilation system chosen must be controllable so that it can maintain reasonable indoor air quality and avoid wasting energy. Developers need to think about sustainability (in terms of lowering the Dwelling Emission Rate) and reducing the overall energy usage of the house by incorporating heat recovery into the solution.
This rules out the background ventilators and intermittent extractor fans approach, as well as the continuous mechanical extraction approach since neither offers heat recovery. Relying on these methods, the energy used to heat the house is lost quickly. Plus, window vents must now be double in size if these approaches are to meet Part F specifications (increasing from 2500 mm2 to 5000 mm2 for extract-only systems) – which further increases the rate of heat loss.
Mechanical ventilation heat recovery (MVHR) systems have emerged as a highly efficient way to transfer the heat contained in the outgoing air to the cold, fresh air coming in.
Typically, such a system quietly moves the heat from rooms that produce the most heat (bathrooms, kitchens and utility rooms) to cooler rooms such as living areas and bedrooms – without transferring any of the fumes from those rooms. Filters provide further protection from external environmental air pollutants, significantly benefiting those with breathing difficulties, allergies or susceptibility to dampness. In the summer months, the heat recovery element of MVHR systems can be switched off without affecting its ventilation abilities, keeping the house cool.
Anthony Croke explains, “The continuous and controlled ventilation rates of MVHR reduce heating demand as well as meeting all regulations. By reducing heating demand, MVHR makes a heat pump combined with underfloor heating a viable way of providing a level of heat that today’s home buyers will find comfortable. It’s a heating ecosystem approach that boosts sustainability and is fit for the future.”
Calculations run by Wavin show that lower temperature underfloor heating solutions, combined with heat pumps as a replacement for gas boilers, provide a vastly more efficient heating strategy when used alongside MVHR - particularly when they are controlled together to optimum efficiency. During a heating season, a typical four-bedroom house of 120m experienced a ventilation heat loss of 3,679kWh without MVHR. However, the same set-up with MVHR experienced a ventilation heat loss of only 405kWh. Combining MVHR with an air source heat pump equated to a saving of almost £300 during the heating season.
Can your development afford to overlook MVHR?
At Wavin, our purpose is to build healthy sustainable environments. Our tailored indoor climate solutions feature our market-leading systems and products including underfloor heating, heat interface units, MVHR and single controls (interfacing with all of these technologies). They provide the following benefits: