Commercial Buildings and Operational Energy

Commercial buildings use energy primarily for space and water heating, lighting, cooling, ventilation and small power. In order to reduce operational energy, buildings should be designed to provide maximum occupant comfort throughout the year with minimum energy requirements. The charts in Fig. 8.2 show typical energy requirements and carbon dioxide emissions for two types of commercial building.

Comparison of operational energy requirements and resulting carbon emissions for a typical air conditioned office and a good practice naturally ventilated open plan office (source: Econ 19, Energy use in offices, Energy Efficiency Best Practice Programme)
Fig. 8.2 Comparison of operational energy requirements and resulting carbon emissions for
a typical air conditioned office and a good practice naturally ventilated open plan
office (source: Econ 19, Energy use in offices, Energy Efficiency Best Practice
Programme)
Although heating accounts for a significant part of the annual operational energy use, it produces a relatively small proportion of the overall carbon emissions since it is generally provided by burning natural gas. In the UK, gas produces only 41% of the carbon dioxide emissions per kilowatt hour that are produced by electricity.

Therefore the greatest scope for reducing carbon emissions from commercial buildings is in reducing the energy required for cooling, mechanical ventilation and artificial lighting.

Energy use is heavily dependent upon building design, including such factors as layout, orientation, thermal capacity, glazing arrangements, solar  shading, cooling and ventilation.The choice of structural system (steel or concrete frame4 ) has been found to have very little effect on operational energy requirements, so the follow- ing notes apply in general to all commercial buildings.

Structural steel gives the design team the flexibility it needs  to exploit these factors to the full.

One of the major ways of providing the necessary comfort levels is to make use of fabric energy storage.

This involves using the floor plate to absorb heat during the period when the building is occupied during the day and then purging it at night as shown in Fig. 8.3.

Initially there was a perception that thick concrete floors were needed for the system to be effective. However, it has been shown that, with a 24-hour cycle of heating and cooling, the necessary volume and disposition of concrete can be provided by composite construction.

Perforated permeable ceilings can be used to permit the necessary contact between the warm air and the floor. Enhancements can be achieved by ducting air immediately above or below the slab. Examples are illustrated in the SCI publication Environmental Floor Systems.

Diurnal cycle for fabric energy storage
Fig. 8.3 Diurnal cycle for fabric energy storage

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