Reducing carbon emissions as part of building refurbishment
Published: 07 May, 2007
Reducing, or even eliminating, carbon emissions from new buildings cannot by itself meet Government targets for reducing emissions. The refurbishment of existing buildings has an even greater role to play.
Just as the latest Building Regulations take a fundamentally different approach to new buildings, they also embrace a fundamentally new approach to the refurbishment of commercial and industrial buildings (non-dwellings in the vocabulary of the regulations).
As Ant Wilson, a director of Faber Maunsell, has explained in various presentations around the country on the new Building Regulations, the rate of replacement of the UK’s building stock is so slow that it would take far too long to make a significant dent on the UK’s carbon emissions if higher standards were only to apply to new buildings. That is why the latest regulations require a range of consequential improvements to be made when buildings are refurbished. These requirements apply to buildings with a useful floor area exceeding 1000 m2.
Historic buildings are not excluded, though it is acknowledged that the character of such buildings should not suffer as a result of work to reduce their carbon footprint and nor should the risk of long-term deterioration be increased.
In his presentations, Ant Wilson highlights a range consequential improvements set out in the Building Regulations. Not all of these improvements have to be made — only those that are appropriate to the project.
Heating systems, cooling systems and air-handling systems that are more than 15 years old should be upgraded by replacing the plant or improving controls.
There is also a focus on lighting. Areas larger than 100 m2 with an average lamp efficacy of less than 40 lamp lumens per circuit watt should be upgraded by installing new luminaires or upgrading controls. Not only will the lighting load be reduced, but so too will the space cooling demand.
Not only should the lamps themselves be more efficient, but they should be controlled to avoid unnecessary lighting when there is enough daylight or when areas are not occupied. Lights can also be dimmed by reducing, rather than diverting, the energy supply.
Cost effectiveness enters into the equation, and improvements should be made if the simple payback is 15 years or less. The simple payback is calculated by dividing the capital cost by the annual saving in fuel cost. If that seems a very long payback, the energy prices to be used are very low: mains gas 1.45 p/kWh; electricity 5.0 p/kWh; heating oil 1.9 p/kWh and LPG 3.39 p/kWh. With up-to-date fuel prices, the payback will be rather shorter.
To help monitor energy usage, another consequential improvement is to install energy metering following guidance given by the Chartered Institution of Building Services Engineers in TM 39.
Increasing the capacity of plant already on site to generate low- and zero-carbon energy is encouraged if it provides less than 10% of on-site energy demand — but only if a simple payback of seven years or less can be achieved.
Part L2B of the latest Building Regulations is not just concerned with the efficiency of plant such as boilers but also how it is controlled and the thermal performance of the building.
Minimum controls for replacement boilers in existing buildings are prescribed. They include a time clock, zone controls and demand controls such as, for a boiler with constant flow temperature, a room thermostat and diverter valve — although this method is not suitable for use with condensing boilers.
For buildings with a floor area greater than 150 m2, zone control is required. The minimum requirement is on/off control using an isolation valve.
Measures to improve the energy efficiency of existing buildings when the installed capacity per unit area of building-services plant is increased or a new fixed building service is first installed are encouraged. That quite simply means paying attention to making cost-effective improvements to the fabric of those parts of the building served by the service to reduce the installed capacity — and cost — of the new plant. At the same time, the energy used by the new plant will also be reduced.
If only these improvements were made to the building fabric, carbon-dioxide emissions might well increase because of the higher level of servicing. For that reason, further improvements of 10% or more of the main work should be made — but this cost cannot include the economically feasible measures taken to reduce the capital cost of the plant.
Similar thinking applies to the replacement of cooling plant such as a chiller. Accordingly, the regulations encourage practical and cost-effective measures to reduce cooling loads — such as improved solar control or more efficient lighting. The idea is to reduce the size of chiller required, and its capital cost and running costs.
There is also guidance on factors to be considered if an existing vapour-compression chiller is replaced with an absorption chiller powered by waste heat from, for example, a CHP unit.
Superficially, an absorption chiller with a COP of 0.8 cannot compete with a vapour-compression chiller with a COP of 2.5. However, carbon-dioxide emissions for electricity are 422 g/kWh but only 18 g/kWh for waste heat, according to the Building Regulation. For the same amount of cooling delivered, a vapour-compression chiller is therefore responsible for 7.5 times more carbon-dioxide emissions than an absorption chiller.
Since, unlike new build, there is limited scope for improving the fabric of existing buildings, reductions in carbon emissions must come from more efficient plant being used more efficiently.
Reducing carbon-dioxide emissions from existing buildings is crucial to the meeting of Government targets — so refurbishment must not only deliver better-serviced buildings but also lower carbon emissions.