Passively achieving excellence
Wayne Aston looks at how natural ventilation and daylighting can help achieve excellent high BREEAM standards — and deliver lifecycle benefits
Today, 50% of CO2 emissions in the UK derive from buildings, and heating and cooling can account for more than 50% of a commercial building’s energy consumption. The standards for reducing energy consumption continue to evolve, potentially putting greater pressure on building-component manufacturers to develop new technologies to meet the criteria. In reality, the core technology already exists, naturally; to take natural ventilation into the 21st century, modern techniques are applied to ensure the buildings of today, and tomorrow — whether new build or refurbishments, are effectively and efficiently aired.
Natural ventilation is as old as the planet itself, utilising natural pressure differential to promote natural air movement. Properly harnessed, it can help buildings achieve the highest possible BREEAM rating, an A rated Energy Performance Certificate, and is already proven in practice to contribute towards a zero-carbon commercial building.
Warm air naturally rises in a building, and cool air is drawn in to replace it. Air moves more quickly with height. These basic principles of physics have been utilised by mankind since we first learnt how to make fire, with the creation of chimneys. Today, they are at the foundation of natural-ventilation strategies — but coupled with modern technology to achieve appropriate flow of fresh air for occupant comfort with minimal heat loss and energy consumption.
Natural ventilation reduces energy consumption over air-conditioned buildings by up to 50%. It can also yield up to 15% savings on capital costs, 75% savings on maintenance costs and can eliminate the need for a separate plant room. It thus has a positive impact on life-cycle costs, another issue often overlooked in new-build and refurbishment with the latest Energy Efficient Building (EeB) Initiative.
The savings come because the only electricity consumption is to occasionally actuate louvres to control inlets and extracts, and to power the control systems which enable precise adjustment depending on temperature and/or CO2 levels depending on application. The lack of fans to drive the system means there is no distracting background noise as ‘machinery’ switches on and off, there are fewer moving parts to go wrong, wear out, need replacing, and less plant to house and maintain.
As the forces driving the system are naturally present, natural ventilation functions 24/7 and can provide effective night cooling. The difference between internal and external temperatures is greater at night, increasing convection and removal of surplus heat gain within the building, minimising energy consumption to reduce the temperature in the building.
|Natural ventilation was provided in the refurbishment of this 1960s office block in Sheffield using Passivent systems to reduce energy consumption. The system also cools the building overnight.|
The latest technology is ‘mixed mode’, combining natural ventilation supported by air conditioning when needed, enabling larger and deeper buildings to benefit from natural ventilation where otherwise the simple distances involved might have made it impractical as an effective solution in extreme weather.
Studies have shown that energy consumption over traditional mechanical ventilation is reduced by 41%. Because the building is primarily aired naturally, incidence of sick building syndrome is reduced, thus improving occupant performance. There is a reduced requirement for plant space, optimising useable floor space.
The system can be retrofitted as well as incorporated into new-build schemes and can adapt to the building’s changing use over time. Passivent and Mitsubishi have both retro-fitted the mixed-mode system in their office headquarters, and reduced energy bills by over 40% as a result.
BREEAM is not just about reducing energy usage. It is also about people; the categories for health and wellbeing score higher credits than other sections. Research shows people’s performance — be it worker output, student learning or patient recovery— is improved in buildings with natural ventilation, and natural daylight. The night cooling of natural ventilation helps ensure a pleasant, fresh environment within the next day, reducing incidence of ‘sick building syndrome’, and we all know how much brighter we feel when the Sun is shining!
Natural daylight also reduces the need for artificial light. Rooflights allow up to three times the amount of daylight into a building than a vertical window of comparable size. Technologies such as tubular rooflights have advanced to the extent that the amount, quality and type of natural light can all be influenced. As a result, rooflights, especially tubular versions, are recognised under BREEAM. A 530 mm-diameter Sunscoop tubular rooflight, for example, yields up to eight times more light than a single 13 W low-energy lamp (60 W bulb) without a shade on a clear Summer day with direct sunlight. Further, modern devices such as dampers enable finite control over the light, making tubular rooflights a practical solution in many of today’s buildings.
Usefully, support systems have developed alongside the product technologies. Dynamic simulation modelling software tools means designers can theoretically test the building before it is physically constructed or refurbished to verify the impact of the natural ventilation and/ or natural daylight on the overall building performance.
Tesco is a prime example of how to implement such strategies. The chain aims to be zero carbon by 2050. It has already built new zero-carbon stores and is now trialling modular building. At the first store to use the faster construction technique, at Southam, Tesco has used Passivent natural-ventilation and natural-daylight strategies to reduce the store’s energy consumption in line with its corporate target.
Wayne Aston is technical director with Passivent.