Low carbon air conditioning

As managers come under increasing pressure to cut carbon emissions, air conditioning purchasing is coming under close scrutiny, explains Daikin UK’s Simon Keel

16 June 2011
Large-scale users of energy are under pressure to reduce CO2 emissions and meet government targets. This pressure has manifested itself in a constant stream of legislation, standards and regulations. This article looks at several issues that FMs will face when accommodating carbon reduction legislation for air conditioning, and how these challenges can best be met.

Building managers could be forgiven for feeling bogged down by the raft of constantly changing carbon reduction legislation, which needs to be understood and addressed in order to reduce the energy used in, and the carbon produced by, our buildings. However, by taking a little time to understand the legislation, significant energy savings can be made.

Take, for example, the requirement for air conditioning systems to be inspected. This can be viewed as a route by which thermal efficiency can be improved and significant energy performance improvements can be achieved.
However, as well as assessing how an air conditioning system is functioning at the point of inspection, the role of the inspector is to offer advice on how improvements in performance can be made going forward. This is vital information which will help mangers to create a coherent energy plan providing even higher reductions in a building’s energy usage.
In the race for sustainability it is all too easy to look at headlines and forget the facts behind the news. For example, refrigerant gasses such as R410A (which may have a high global warming potential) come under serious and sustained criticism, despite the fact that there are other parts of a system that could be doing worse damage.

A key component in most refrigeration systems, refrigerant gasses allow the movement of renewable heat from one source to another. In a domestic fridge, the refrigerant expels heat from the ice box to the kitchen. A commercial air-to-air heat pump works in the opposite way, extracting heat from the solar heated air outside – even when the weather is at sub zero temperatures – and using it to warm the building.

Various refrigerants can be used for this; the one major difference being the efficiency with which they perform the task. Each one has its own characteristics. In an ideal world, the perfect refrigerant would be highly efficient, non-flammable, non-toxic, plentiful, cheap – and have a low Global Warming Property (GWP). Unfortunately, no single gas ticks all these boxes. This leaves a choice to 
be made, and an inevitable compromise.

Sustainable thinking asks that we minimise the damage we do to the environment. In the developed world at least, any future building or operation under proposal is now specified with the aim of minimising global warming gasses. This inevitably calls for compromise. When electricity is generated, it releases CO2 at the power stations. Thus when a heat pump operates, it uses electricity and is therefore responsible for some CO2 being released. If that system is highly efficient, it will release less CO2 than a less efficient model. But if that heat pump leaks refrigerant, this will also contribute to global warming. A refrigerant with a high GWP will be worse than one with a low GWP.

Thus there are two sums that must be done: one is to assess the quantity of CO2 being released as a result of the electrical consumption; and the other is the equivalent quantity of CO2 predicted to be released by any potential gas leakage. The first uses a set quantity of CO2 for each kW of electricity; the second multiplies the weight of released gas by its GWP number. This gives the total equivalent warming impact or TEWI.

The updated Breeam regulations for 2011 will be backing this assessment of emissions and will reward low energy-using products as well as encouraging use of low-GWP refrigerants. Unfortunately, the ideal refrigerant is not yet on the market and most refrigerants are less damaging and more economical than their headline GWP figure might suggest.

The conclusion for facilities managers is that a multitude of factors need be taken into account to reach the ideal solution. Looking at one figure in isolation may result in an unintended consequence and create greater carbon emissions in the long run. Using energy efficient heat pumps, which 
use the correct refrigerant and are properly designed to maximise all heat reclamation opportunities, is the only way to create a truly sustainable, renewable heating system.


Simon Keel is product executive at air conditioning manufacturer Daiken UK