BRE DG457 PDF

Introduction

Changes to Approved Document L of the Building Regulations planned for 2002 (AD L2 (2002)[1]) introduce a new ‘wholebuilding method' for offices as a way of showing that the likely consumption of energy, or emissions of carbon, of new or refurbished office design will be reasonable for the purpose of the conservation of fuel and power.

The Carbon Performance Rating (CPR) is intended to provide one such method of assessing the likely level of emissions of carbon due to the use of air conditioning and mechanical ventilation (ACMV), space heating and lighting services. The CPR is a simple calculation that uses information available at the design stage, and that can be applied to both new and refurbished office building design.

The advantages expected of the CPR are comparative simplicity in use and the potential to accommodate flexibility in the design. Working to achieve an overall design target would also encourage early dialogue between the architectural and building services design professions and the client. The method extends a CPR assessment method that addresses ACMV systems only, also introduced in AD L2 (2002).

Both CPR methods are refinements of an earlier Energy Performance Index Method[2,3,4], which BRE developed in consultation with an Industry Advisory Group representing interests including the British Property Federation, the Federation of Environmental Trades Associations, the Heating and Ventilating Contractors' Association, and the Chartered Institution of Building Services Engineers.

The Carbon Performance Rating is the result of a calculation that uses the input power ratings of the installed building services plant together with factors related to the provisions made to control and manage the plant. The input power ratings of plant are seen as reflecting a wide range of decisions and assumptions made during the design and specification process of the building and its services systems. Plant size may be influenced by such factors as the building orientation and plan form, the levels of fabric and internally generated heat gain, any oversizing allowances, and the efficiencies of the services systems and of the plant itself.

The CPR calculation assesses the potential of systems to cause the release of carbon through their use of energy when operated to a notional typical usage pattern. This allows design and installation parameters to be compared on an equal basis between buildings. For example, for air conditioning in offices, the usage pattern of the notional ‘base case' system is considered to comprise 1000 hours per year (full load equivalent) operation of the refrigeration plant and 3700 hours per year (approximately equivalent to all-year operation, 13 hours a day, 5.5 days a week) operation of the distribution system fans and pumps.

The provisions made to control and manage the operation of the services have the potential to influence their periods of operation and efficiency. For simplicity in visualising their effect, it could be assumed that the combined effect is to reduce or increase the annual full load equivalent hours of use from the base case usage pattern.