Steve Hunt from building services engineering firm Steven Hunt & Associates on a loophole in the Simplified Building Energy Model calculation that is leading to inappropriate specification of combined heat and power systems.
Over the past 20 years, the low carbon agenda has precipitated a clear regulatory framework for the construction of new buildings, with increasingly stringent Part L Building Regulations and both target emission rate (TER) and Energy Performance Certificate (EPC) requirements for non-domestic buildings.
The Simplified Building Energy Model (SBEM) is designed to ensure that compliance with Part L, TER requirements and EPC certification are all measured using a single, accountable methodology. The model scores elements of the specification to ensure that the energy a building requires is delivered in the most efficient way possible and in a manner that fits the building’s design and use.
It has been very successful in simplifying the process of assessing the energy that a building will use. However, there is a major flaw in the model which is already starting to have a negative impact on the progress made in driving a greener, more efficient built environment. That flaw concerns a loophole relating to the specification of Combined Heat and Power (CHP) systems.
CHP systems may not fit neatly under the banner of “renewable” or “sustainable” like many of the high scorers in the SBEM calculation, but they are championed by the government as a beneficial solution to the heating and power needs of larger buildings. This is because enabling buildings to generate their own heat and power takes pressure off the grid. At a time when the UK’s generating capacity is low due to the decommissioning of coal-fired power stations, that’s particularly beneficial.
"There is no actual legislative requirement for the CHP to be commissioned or used once the build programme is completed, which enables specifiers to pass SBEM on the back of installing a CHP without delivering any of the grid capacity benefits."
As a result of this drive to encourage more CHPs, SBEM has been designed to offer a “golden ticket” to buildings that include them, ensuring that the overall building passes the calculation automatically, regardless of any other heating or power systems that are also or subsequently specified.
Therein lies the loophole: there is nothing in the SBEM calculation that prevents a CHP from being specified with inefficient electric heating systems, which are both costly for the end user and are power hungry carbon emitters. Worse still, there is no actual legislative requirement for the CHP to be commissioned or used once the build programme is completed, which enables specifiers to pass SBEM on the back of installing a CHP without delivering any of the grid capacity benefits that the golden ticket approach was designed to provide.
While specifying the right combination of energy sources to meet the layout, use and requirements of a building should always lie at the heart of the building services design, the temptation to take a short cut is attractive to both specifiers and developers. As a result, CHPs are often being specified without good engineering reasons as a guaranteed SBEM pass. In this scenario, the CHP may be commissioned and put into use but the specification may not be the most cost-effective or energy-efficient approach to meeting the building’s needs.
The biggest issue this loophole has created, however, is with the buildings where CHPs are being specified as a cynical ploy to avoid the additional build costs of a more environmentally progressive approach.
Installing a CHP without any intention of running it avoids the capital costs of putting in the pipework infrastructure of a more traditional system and allows the building to pass Building Regulations, but fails to deliver the promised energy efficiency.
Unfortunately, some specifiers are more concerned with the SBEM pass than they are with genuine environmental performance and, as a result, I know of several projects where a CHP has been installed but not commissioned.
In principle both SBEM and the drive to encourage increased use of CHPs are positive developments. But CHPs must only be specified as a best fit solution, not as a value engineering short cut or a cynical tactic for under-the-radar specification of inefficient systems.
When it comes to specification of CHPs, the Simplified Building Energy Model is just too simple. The Department for Communities and Local Government and the BRE, which developed the SBEM software tool, need to look again at how the calculation can be changed to encourage appropriate CHP specification without enabling corners to be cut.
Steven Hunt can be contacted on 0151 427 8009 or at www.stevenhunt.com
