Airing the issues
There is much debate on trends in natural ventilation, but is it all hot air? Roy Jones of Gilberts of Blackpool shares some thoughts.
Resource efficiency/heat recovery, noise and perceptive ventilation are all generating much discussion, but actually bring little or nothing new to the table.
Reducing our emissions and minimising heat loss have long been targets. We are driven to minimise air leakage and almost seal the building envelope. But if we achieve the ultimate — a sealed building with no air leakage — how do the occupants function?
We need fresh air to breathe, so air has to get out of the building somehow to enable fresh air to be introduced.
The key is for it to be controlled within ‘acceptable’ parameters. And even then, the human factor needs to be considered; I won’t say addressed because we all know it is impossible to please all of the people, all of the time….and, being human, we all have different ideas and methods for addressing how we feel. Whatever ethereal targets are set, it all blows out the window the moment an occupant opens one.
There has been a vast amount of research lately into perceptive ventilation — i.e. when/whether building occupants feel hot or cold, and what is the ideal ambient rate of airflow. Despite significant time, effort and financial investment, the outcome has been what has been accepted for years — air velocity of 0.25 m/s will please most of the people, most of the time.
The effort therefore needs to be focused on ways of maintaining that rate of air-change condition alongside maximum conservation of heat from within.
The domestic market has responded to minimising heat loss with the development of systems based on natural ventilation and incorporating heat recovery technology, (removing the heat from the ‘used’ air being exhausted and transferring it to the cooler incoming fresh air) or geothermal solutions that warm the incoming air first by passing it through the ground.
While, energy is saved through re-use of that warmth, there can be a corresponding increase in energy consumption through the electricity used to power the heat exchangers and fans.
However, technology is catching up. Solar arrays and low-energy fans that cost as little as £1 per annum to run can be employed. Recirculating air can blend the fresh incoming air with the internal atmosphere, reducing the load on heating systems to maintain the ambient temperature.
But fans create noise, even if ‘whisper quiet’. In the education sector, the Department for Education has published its new BB93, which in essence only consolidates what guidelines have been applied and still sets an acceptable acoustic modulation level for the majority of occupied spaces at 35 dB(A).
The issues do need to be discussed, as it is only brain-storming in this way that we achieve a eureka moment, but as yet that hasn’t arrived.
Manufacturers are refining systems to achieve ever better performance. Coupled with good architectural and building-services designs and thorough testing with technology such as computational fluid dynamics, the best possible, compliant solution for the building purpose and budget can be achieved that ensures a comfortable internal ambience with as little energy consumption as possible.
Roy Jones is senior technical manager with Gilberts of Blackpool.