Ian Ellis, marketing & sales specialist manager, Siemens, looks at the importance of energy efficiency in buildings.

Much has been written and talked about the role that building automation and control systems (BACS) can make to the energy efficiency of a building. But how can such efficiencies be quantified? It is all very well to say that introducing a BACS (or building management system (BMS) as they are sometimes known) is a good idea and will have a positive impact in terms of reducing a building’s energy use, but by how much? Do the benefits outweigh the cost? Is the payback actually worth the initial investment? How long will the payback be on that investment?

Well, a good place to start is to appreciate just how big a contributor buildings are in terms of energy consumption. According to the European Commission, buildings are responsible for approximately 40% of all energy consumed and 36% of CO2 emissions in the EU (while the UK is obviously no longer a member of the EU, these figures were calculated when it still was.) So, in heating, lighting, cooling and powering our buildings we are using almost half of all Europe’s energy. It is also important to understand the make-up of the building stock. Some 35% of buildings within the EU are more than 50 years old. While there are obviously many new-build and recently built projects throughout the EU which have followed current building regulations, the older buildings certainly make up a sizeable proportion of the estimated 75% of building stock which is deemed to be energy inefficient.

So, from those headline figures it is reasonable to assume that being the largest single energy consumer in the EU, addressing the building sector is likely to reap significant energy efficiency gains. But again, just how significant?

EPBD Directive

This is where the Energy Performance of Buildings Directive (EPBD) comes in. This saw the EU mandate CEN to standardise calculation methods for improved energy savings. This covered a range of energy related topics including construction materials, plant within buildings such as boilers and chillers, and design codes. One of the sub-groups within the various committees tasked with the new Directive was a technical committee which specifically considered how energy is controlled within buildings. The results of that committee saw the introduction of the EN 15232 standard, which subsequently morphed into ISO 52120. This standard covers the role of building automation and control systems (BACS). Despite the change in name and the fact that from the prefix it is evident that ISO 52120 is an international standard, the UK becoming devolved from the EU does not change the fact that it is still applicable as a British Standard and is referenced in the English Building Regulations (Part L) and the Scottish version.

In terms of the EPBD, the headline definition of energy performance of a building is “…the amount of energy actually consumed or estimated to meet the different needs associated with a standardised use of the building…”. This is effectively split into six categories:

  • Heating - this relates to how the building is kept warm
  • Domestic Hot Water
  • Cooling – air conditioning, for example, is more widely used in certain countries depending on the prevailing weather
  • Ventilation – energy is consumed by methods of moving air around a building
  • Lighting
  • Auxiliary energy – this is anything which is not covered by the above five categories

A BACS can manage all of those areas or selected areas, depending on its design.

Levels of control

This is reflected in the standard which recognises that there is more than one way to control a building and that there are different degrees of control that can be applied. It offers guidance on how to control different elements. Using the simple example of a boiler, the easiest method of control is to just turn it on or off based on a thermostat. If the thermostat is set at, say 70°C, then the boiler comes on at any point below that temperature. However, this does not take into account the fact that this might not be required 24 hours a day. So, while there is a level of control applied, it may not be particularly efficient. Adding an element of time control can address this issue. In an office environment, for example, running the boiler may only be required from 8.00am to 6.00pm. That represents 14 hours of energy savings per day.

Taking that a stage further, in multi-room buildings you can consider if a particular room requires heating, even during the designated 10-hour operating period. If there is some form of temperature measurement in a given room and the sensor is set at 20°C, then if it is above that temperature then a signal is sent back to the boiler controller indicating that heating is not required: more energy savings. But what if the boiler control is informed when people actually enter the room. Through a demand-based control approach, the boiler can then be activated only when there are people present. In many buildings, rooms are unoccupied for a significant proportion of the time, meeting rooms being a prime example. Controlling energy supply based on room demand can bring even greater energy savings.

A to D classifications

This is a simple example of how the calculation procedures based on BACS efficiency factors are derived in ISO 52120. It identifies four classes - from Class D which is the most inefficient through to Class A which is high performance and the most efficient. The assumption is most buildings actually have a Class C system installed.

Achieving a Class A rating understandably requires more equipment – more controllers, more sensors – and is therefore a higher initial investment in terms of capital expenditure. This is where the cost:benefit analysis can be invaluable. The standard provides the means through which the actual cost savings of moving from a Class D to a Class A rating or from a Class C to a Class B rating etc can be calculated.

If a value engineering approach has been adopted and a BACS solutions company has designed a system to a Class A rating which is coming in at £X,000, the client may well say ‘is it possible to reduce the cost by £Y,000?’ The answer is normally ‘yes’. But, using the standard, you can actually calculate what this initial capital cost saving will mean in terms of reducing the energy efficiency and what this actually represents in terms of operating cost. It also provides guidance regarding what you can do in terms of control for each of the six categories we spoke of earlier to achieve a Class A, B, C or D rating. The differences in buildings are also covered – for example, while an office environment may function well based on an 8.00am to 6.00pm occupancy model, this would not be applicable for something like a hospital ward which is occupied 24 hours a day. The occupancy profile will have a direct impact and should be a fundamental consideration in calculating how much energy is going to be saved by moving from one Class to another.

Typical energy savings

Having said that one of the real benefits of the standard is to offer the capability to calculate precisely the energy (and therefore cost) savings for a specific application, I am now going to generalise. Taking a mean average, a saving of approximately 30% is achieved by a building moving from a Class C to a Class A rating. This changes slightly by application:

  • Hotels – 25%
  • Education – 34%
  • Hospitals – 18%
  • Residential – 27%
  • Restaurants – 31%
  • Shopping Centres – 49%
  • Office – 39%

The average saving of 30% as been substantiated by independent research which illustrates that just by adopting the intelligent use of building automation, savings of around a third can typically be realised.

The calculations split the savings across two categories: thermal energy (in simplistic terms, this relates to wet systems i.e. anything that has water running through it) and electrical energy.

A quantifiable contribution to sustainability

In conclusion, it is important to appreciate that with buildings being responsible for some 40% of the EU’s energy consumption and 36% of its CO2 emissions, a focus on reducing energy use is crucial in meeting the commitment to a more sustainable future. Well designed and effectively implemented BACS can contribute significantly to a reduction in energy consumption, as well as enhancing comfort and convenience for the occupants. However, there is, understandably, a need to quantify the potential impacts of implementing BACS, especially in terms of their capacity for reducing the operational energy demand of a building. Rather than simply claiming that BACS is ‘a good idea’, ISO 52120 provides the means to calculate the actual savings that will be made. One of the important points to recognise is that this standard is completely independent and can be used to analyse any BACS, irrespective of the system supplier.