Refurbishing to improve energy efficiency and carbon emissions
Combined heat and power is a low-carbon technology that has been used in the refurbishment of the plant room of the Natural History Museum in London. This CHP unit has an electrical output of 1800 kW and provides heating and cooling using two absorption chillers.
The refurbishment of a building provides the opportunity to improve its energy efficiency and reduce carbon emissions. Kevin Pennycook explains how new guidance can help.With increased awareness of the importance of energy efficiency in buildings, not only to reduce carbon emissions but also to meet regulatory and planning requirements, the refurbishment of building services is currently an important subject. Whilst we build 1% of the stock new each year, 99% of the stock is already with us. Whenever a building is refurbished presents an opportunity for building-services engineers to add value and reduce energy costs and carbon emissions through energy efficient measures. Principal aim
Building-services systems are retrofitted for a variety of reasons, including replacing old and inefficient plant and in response to changes in the use or the extension of buildings. The principal aim when refurbishing building-services systems is to provide optimum system performance for minimum capital outlay, ensuring appropriate comfort conditions are maintained at the least possible rate of energy expenditure and consequent emissions of carbon dioxide.
The restoration of the Solarium in Blackpool includes a photo-voltaic roof and wind turbines that, together, can generate up to 35 kW of electricity. There is also a passive solar-heating panel on the roof to pre-warm water for the central-heating systems and a 5.5 kW(e) CHP unit.
In reality, these aims are not always fully realised, so CIBSE and BSRIA have published a joint publication that provides guidance to building-services engineers who are tasked with upgrading existing services.* It is also intended to help building occupiers and managers understand the minor refurbishment steps that can be taken to improve the energy efficiency of their building services. This ‘knowledge series’ publication is intended to provide a concise overview of building-services refurbishment. It is not intended to give an in-depth review of the various refurbishment issues and options; rather it is an introduction to the various topics along with sources of in-depth guidance. The publication starts with an overview of factors that relate to the question, ‘Why refurbish?’ They include reducing energy consumption and carbon-dioxide emissions, the impact of Building Regulations (e.g. consequential improvements), the EU Directive on Energy Performance of Buildings, the condition of existing building services and improved occupant comfort and productivity. Assessment procedure
Refurbishment challenges along with a recommended refurbishment assessment procedure are provided. The latter covers assessing the client requirements, energy benchmarks, assessing occupant satisfaction, building-services condition surveys, feedback from maintenance/ operational procedures, existing building constraints (e.g. slab-to-slab height, floor void size etc.) and a review of refurbishment options. Refurbishment options are split between lower-cost options and higher-cost options. Lower-cost options include steps such as changing space layout. This involves reviewing the location of office equipment in relation to the mechanical cooling systems to avoid hot spots where air conditioning cannot cope.
As part of the refurbishment of the tower of the Co-operative Insurance Society in Manchester, over 7000 photo-voltaic panels were installed on three sides of the facade to generate over 180 MWh of electricity each year.
For naturally ventilated buildings, checks can be made whether air flows are hindered by partitions or office furniture. Room layouts can be modified to enhance airflows. Improved zoning can also be considered, for example a single room for fax machines, photocopying and printing machines etc. can be provided — so only this room may require mechanical cooling, rather than the entire office space. Other lower-cost options include improved natural lighting, improved artificial lighting, reduced solar gain, improved controls, heat recovery, high-efficiency motors, variable-speed control of motors and improvements to domestic hot water systems. Higher-cost refurbishment options include alterations and improvements to the building fabric, avoiding the need for mechanical cooling, energy-efficient mechanical-cooling options, free-cooling strategies, passive cooling and ventilation techniques, adopting energy-efficient heating systems, improved daylight strategies and the use of lighting-management systems. Avoiding mechanical cooling
Steps that can be taken to avoid the need for mechanical cooling include the following. • Minimising heat gains to the space by improving the thermal performance of the fabric, solar shading and reduced air infiltration. • Minimising internal heat gains from lighting, office equipment etc. • Wherever practical, meeting the cooling requirements using passive cooling techniques such as natural ventilation, mixed-mode ventilation and night cooling. • Checking that controls will be able to match the cooling load efficiently.
The high heat content of wood pellets (about 3450 kW/m3) can help provide a biomass solution where storage space is limited in a refurbishment project.
As part of a refurbishment project it may be desirable to incorporate one or more low- or zero-carbon technologies. Low- or zero-carbon energy (LZC) is the term applied to renewable sources of energy and also to technologies which are either significantly more efficient than traditional solutions or which emit less carbon in providing heating, cooling or power. Seven LZC options summarised in the guide. • Solar thermal.
• Combined heat and power.
• Ground-source cooling.
• Ground-source heat pumps.
• Wind power.
• Biomass. The importance of commissioning and recommissioning existing building-services equipment is emphasised, along with key requirements for successful commissioning. Finally, handover is considered — covering the requirement for building logbooks, training of maintenance staff and building occupants, along with ongoing energy management/monitoring and targeting programmes. The guide emphasises that training of both those responsible for operating the building and the occupants should be undertaken to obtain the optimum operating conditions from the refurbished area or building. This is particularly important when staff have previously worked in a building that was previously a mechanically cooled and/or ventilated building but which has been refurbished to incorporate passive design techniques. In such a case, staff may be less likely to make effective use of vents and any adjustable solar shading unless they are made fully aware of the building’s operational strategy. Kevin Pennycook is a principal engineer with BSRIA.
* ‘Refurbishment for improved energy efficiency: an overview’ is part of the ‘knowledge series’ published by the Chartered Institution of Building services Engineers. It is available from the CIBSE Bookshop at www.cibse.org or 020 8772 3618.