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JUNE 10 - BUILD TIGHT, VENTILATE RIGHT!



New research has revealed that Passivent passive stack ventilation not only ensures more than adequate ventilation in airtight homes, but optimizes energy efficiency…..

The company, the UK's leading supplier of domestic and commercial natural and assisted ventilation solutions, has published data from a research study by the Institute of Energy and Sustainable Development at De Montfort University.

The results showed that Passivent's Passive Stack Ventilation (PSV)- which harnesses natural variations in air movement and convection only to function- yielded an average ventilation rate 40% more than the required minimum boost rate for a conventional mechanical system, with none of the electrical consumption or unnecessary heat loss. Further, the Passivent system showed a 9% saving in carbon emissions against a MVHR (mechanical ventilation with heat recovery) system. This is excluding the additional savings in capital, maintenance and lifecycle costs of Passivent PSV.

The research reinforces 'in practice' scenarios already experienced by Passivent; it was carried out in a completely airtight (0m3/hr/m2@50Pa) house. The average ventilation rate for the Passivent PSV was 11.39l/s, compared to the minimum high rate (ie boost) for a mechanical ventilation system of 8l/s, with a maximum humidity level of 68%- below the 70% maximum limit.

In addition to the research carried out by the Institute of Energy & Sustainable Development, PSV has also been used in many projects featuring airtight homes. One key example is that of Angela Carter Close which won the award for Sustainable Housing Project of the Year for new developments of less than 25 homes. The dwellings were built to an airtightness of 2m3/hr/m2@50Pa and have been the subject of ongoing studies by UCL to monitor energy use and indoor air quality. Research showed that the maximum humidity level was 68%- below the 70% maximum limit to prevent condensation and mould growth.

Stephen Smith, Passivent Product Manager, adds, "The newly published Approved Document L will make even more airtight homes a necessity. But the more airtight a building, the more vital it is to provide adequate ventilation, to avoid health issues affecting the building fabric and occupant's health. We are in effect expecting people to live in a sealed box- and then removing their fresh air! Day to day living generates up to 8litres of water vapour within the home every day: moisture that must be removed to avoid health issues for people and the building caused by damp, condensation. And a constant supply of fresh air is needed to remove build-up of carbon dioxide and other airborne pollutants.

"It is worth noting that a conventional mechanical system will work only when, and as long as, it is switched on, so is entirely occupier dependant. Mechanical fans can be noisy, and use energy, tempting the occupants to turn the ventilation off.

"Passivent PSV monitors the air quality 24/7, and our 'intelligent' iPSV system function as a typical PSV but with humidity sensitive extracts which open and close as appropriate to control the airflow and ensure the room is adequately, but not over-, ventilated, and there is no unnecessary heat loss. Because it uses natural air movement to function, it requires no energy, so incurs no operating costs. There is too the additional, often missed, benefit that our iPSV is silent, so eliminates the temptation to occupants to turn the ventilation off."

Passivent PSV and iPSV are'fit and forget' solutions. The systems use NO electricity, power source or fans to function, and have no moving parts to wear out or develop faults over time, requiring maintenance and/or replacement. They work automatically, and silently, by harnessing natural variations in air temperature and pressure- convection and the venturi effect. Moisture-laden air is warmer, so rises due to convection. Strategic ceiling extracts extract the stale, moist air through ducting to a roof terminal, whilst strategic inlets allow gentle replacement air in without draughts. Wind blowing across the roof enhances extraction (also known as the venturi effect).

In comparative 'lifetime' costings of ventilation in an individual dwelling over 60 years, covering initial purchase, installation and on-going maintenance, Passivent PSV costs under £1000; by contrast, MVHR can cost £27,945 at today's prices.

Passivent's range for domestic buildings further includes assisted and mechanical ventilation solutions for single person to multi-occupancy properties, plus a range of background window and through-wall ventilation solutions. Passivent is part of the Building Product Design Group which incorporates Glidevale (roofing and ventilation), Z-Led (damp-proofing solutions), and Kingfisher Louvre Systems (ventilation and solar shading louvre systems), all of which aim to bring to market innovative yet practical products in line with changing requirements.

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