Engineered solutions to meet environmental demands
Energy regulations have become progressively tougher in response to European and UK government targets. On 25 October 2012, the EU adopted the Directive 2012/27/EU on energy efficiency. This Directive establishes a common framework of measures for the promotion of energy efficiency in order to ensure the achievement of the Union’s 2020 20% headline target on energy efficiency and to pave the way for further energy efficiency improvements beyond that date.
Buildings of course have a large role to play in this. The Chartered Institution of Building Services Engineers (CIBSE) estimates that buildings use almost 50% of the UK’s energy and that 20% of energy used in buildings is needlessly wasted.
As part of the EU Energy Efficiency Directive, Member States must develop high quality energy auditing systems aimed at determining which measures can be taken to improve energy efficiency. They must also ensure that end-users are provided with competitively priced individual metering and informative billing that shows their actual energy consumption. As far as possible, bills must be based on actual energy consumption.
In the UK to date Part L of the Building Regulations has been the key vehicle for implementing energy and carbon reduction requirements for new builds, and for the refurbishment of existing buildings through a requirement for consequential improvements.
Further announcements to changes to Part L 2013 for non-domestic buildings have been delayed, but government policy remains a key driver for energy efficiency.
Assessment systems can help achieve low carbon buildings. The BREEAM design and assessment method sets a standard for best practice in sustainable building design and offers a range of assessment systems including new construction and buildings in use. Originally developed for the US, LEED is gaining popularity with many multi-national property owners worldwide.
Spiralling energy costs are also a critical factor; in the current economic climate saving energy fundamentally means saving costs. This holds as true for a brand new low energy BREEAM or LEED accredited building as it does for a refurbishment project.
Reducing operating costs of buildings remains a primary driver of retrofit activity, whilst with new build, energy efficiencies can be taken into account from the design stage.
Designing for specifics
There is increasing concern about the cost and sustainability of energy, and as a result consumption is a fundamental part of choosing the most appropriate technologies for heating and air conditioning solutions.
As each building will have different requirement, it is the role of a design engineer to select the most cost effective and energy efficient solution for a particular application. The complexity of building services in commercial property is significant and designed to meet activity profiles at the time of construction or refurbishment.
Choosing a solution that is flexible as well as energy efficient is also crucial for many refurbishment projects with constraints within the building design or fabric to be considered.
Chilled ceiling systems can be installed within 100mm ceiling void and therefore useful for older buildings where minimal floor to ceiling heights need to be maintained.
Chilled ceilings incorporate a single piece copper or aluminium element into the rear of a standard suspended metal ceiling tile. Flow and return temperatures are typically between 14 and 17°C which means that they can also be linked to renewable options such as ground source heating and cooling systems.
Meanwhile, chilled beam technologies are a popular choice to achieve both M&E demands and match architectural aesthetics in new buildings.
There are two main types of chilled beam. The first is passive beams which use natural convection and as warm air rises in the occupied space, it is drawn through the beam, which is fitted with pipes carrying cooled water. The warm air is cooled before returning downwards into the space. Fresh air can be introduced to the space via a floor-based ventilation system or ceiling diffusers.
Passive chilled beams can also be used with a chilled ceiling at perimeters to combat higher loads such as solar gain.
Active chilled beams are induction engines and offer an effective air supply through their ability to recirculate air within a space. Primary air is supplied to the room at a high velocity via nozzles, which induce secondary room air over the water driven heat exchanger to produce required performance.
Operational savings are achieved because chilled beams can use higher water temperatures than traditional cooling systems. This has the advantage that it allows chillers to operate more efficiently and take advantage of free cooling for much of the year. The raised water temperatures also enable renewable solutions such as ground source water cooling to be considered.
Fewer air changes are needed so ductwork and air handling units can be smaller. This reduces construction costs while enabling exhaust fans and chillers to be downsized too, or run at a lower speed, to reduce emissions and cost.
Experience has now determined the quantity per person required in order to maintain good air quality to meet occupancy requirements and is laid out in the Chilled Beams and Ceilings Association’s Technical Fact Sheet – Thermal Comfort issued by the CBCA in January.
The CBCA provides technical detail on the Valuation of Thermal Comfort using BS EN ISO 7730, which can provide methods for predicting the general thermal sensation or degree of discomfort of moderate thermal environments. PMV (predicted mean vote for a large group of people subjected to the same environmental conditions) and PPD (predicted percentage of dissatisfied which determines how many occupants will fall outside the limits of comfort) can help determine good air quality to meet occupancy requirements. The CBCA details the maximum spatial operative temperatures and mean air velocities dependent upon the desired design category for a typical chilled beam application.
Refurbishment and new-build projects are challenging in different ways. In both types of project, choosing chilled ceilings or chilled beams options can satisfy the thermal, aural and visual comfort of occupants whilst providing a cost effective, energy efficient solution that will satisfy both occupants and developers.
A good example of this was in a recent project where SAS International worked closely with Cartwright Pickard Architects and Consulting Engineers, Buro Happold at Wakefield Civic Offices. The entire project took a holistic view of sustainable design so that structural, environmental and architectural elements all contribute in providing a low energy BREEAM ‘Excellent’ solution which according to the architects produces 30% less carbon than a conventional comfort cooled office.
By working closely with manufacturers, M&E consultants, architects and contractors can help realise project and client goals to achieve engineered solutions that meet environmental demands and provide long term value to the client.