Martin Liddament is the Chairman of CIBSE’s Natural Ventilation Group.
At the Club’s April 2017 meeting, Martin answered the same question that was discussed 70 years previously at the very first Rumford club meeting: is air conditioning, as practiced in 2017, a menace or a benefit to mankind?
Traditional approaches to environmental control within urban areas require heating, ventilation and air conditioning systems that consume energy and emit carbon dioxide.
These approaches result in high energy use, the release of greenhouse gases and pollutants leading to rising temperatures, which then results in the still greater use of HVAC systems.
To break this cycle, we require fresh engineering solutions – ones that make use of natural solutions as well as mechanical ones.
Outdoor air quality
The challenge is that “green infrastructure” (that is to say, using alternatives to air conditioning) is far less efficient than mechanical filtration solutions when it comes to improving indoor air quality. Without exemplary levels of air quality monitoring and control, there may be an argument that natural and mixed mode strategies may be viewed as a poor choice compared to full mechanical ventilation systems with appropriate levels of filtration and purification.
This shows one major benefit of air conditioning. Indeed, over its 70 years of existence, air conditioning has provided high levels of comfort and high indoor air quality.
It’s outdoor air quality that provides the current challenge. A recent CIBSE Journal set out that nitrogen dioxide causes 6,000 deaths annually in London. And a recent article in the Sunday Times set out that air quality is so poor in some places that developers are to be forced to fit thousands of new homes with filtration systems to purify all the air entering them. https://www.thetimes.co.uk/article/air-tight-homes-to-block-toxic-fumes-xs6d5zhkv.
Such hermetically sealed homes have air tight doors and windows which cannot be opened, which aim to block any unfiltered fresh air.
The issues with outdoor air
The results of a major European study on the impacts of pollution on short term effects on levels of health, based on observations in 15 cities, were as follows.
There is a link between poor outside air quality and illness and death.
There were significant increases in daily admissions to hospitals for respiratory diseases (particularly for the elderly) where there were elevated levels of ozone. Essentially, ozone is generated by the photochemical reaction of solar radiation onto nitrous type compounds and these clouds will spread away from urban areas and cover quite large areas elsewhere.
As a standalone gas, there is no association between the levels of nitrogen dioxide and the level of hospital admissions. However, when combined with particles (PM10), there was a significant correlation: “black smoke” has a greater effect on days with high NO2 concentrations.
Sulphur dioxide did not seem to have significant adverse health effects.
When designing air conditioned buildings, we need to take account of:
- The need to maintain indoor air quality
- The volume of the building
- The amount of trapped heat
- The degree of solar radiation
- The degree of humidity
- The amount of incoming hot air
- The density of occupancy.
In commercial buildings, staff costs make up 90% of the business operating costs but energy costs only make up a mere 1%. However, if you do not manage that 1%, for example by regulating the quality of indoor air, the other 90% is heavily affected.
Improvements in design
Whether we like it or not, modern cities could not have evolved as far as they have without air conditioning.
Over the last 70 years efforts have been made to improve air conditioning, as the result of:
- Good understanding of how buildings “work” through simulations
- Mixed mode solutions
- Effective methods to reduce solar gain
- Effective methods to reduce internal heat gains
- Effective introduction of regulations that promote the use of best practice
- Improved mechanical and refrigeration systems.
In summary, we do need to improve urban outdoor air quality. The challenge is not dissimilar in scale to that faced by the Victorians when they introduced sewerage systems. This in turn will improve air quality inside the buildings in which we live and work.
So long as urban outdoor air quality is not significantly improved, air conditioning is here to stay.