Exploiting the benefits of renewable energy
Is solar energy far too valuable just to enjoy?
Before going for renewable-energy sources to improve a building’s energy certificate, make sure your building is ready first, says John Bailey.The secret of reducing the carbon footprint of an existing building is to get back to the design principles that should have been applied when it was first built. There is no culture of energy efficiency in this country. The liberalisation of the energy markets in the 1980s has meant gas and electricity prices have been kept artificially low for most of the working lives of many facilities managers. We also have a damaging communication breakdown between those who designed and installed the original building services and the people operating the building today. O&M manuals are no substitute for clear design guidance and understanding of the designer’s intentions for a building. The Building Regulations have tried to address this aspect with their requirement for log books, but these are not being applied retrospectively so they are still unavailable in the vast majority of buildings.
Regulatory drivers However, there are a couple of regulatory drivers that could start to make the building-services engineer’s life easier. The requirement, under the European Energy Performance of Buildings Directive (EPBD) for Energy Performance and Display Energy Certificates (EPCs and DECs) as well as air-conditioning inspections, will make it possible to tie the value of a building to its energy efficiency. While chaos still surrounds the implementation of the certificates, they are coming, and they will drive the market. A number of end users are opting into the scheme voluntarily — particularly in the retail sector — because they view it as a potential marketing tool. ‘My building is greener than your building,’ and we can expect a level of competition to emerge between local authorities as well. Lawyers are also likely to get involved (when are they not?) as the certificates must be available on sale or rent of the buildings, so could be directly tied to the offer price. The Government has recently adjusted the timetable so that by 6 April 2008, EPCs will be required for all new homes and for all commercial buildings with a floor area over 10 000 m2 when they are either built, sold or rented. By 1 October, EPCs will be required on the sale or rent of all remaining domestic and commercial buildings, with DECs required for all public buildings over 1000m2. By January 2009 the first mandatory inspections of air-conditioning systems over 250 kW of cooling should have taken place, to be followed two years later by inspections for all air-conditioning systems over 12 kW.
Using renewable energy So how can a building be prepared for scrutiny? And how can a building operator use renewable energy to improve the A to G rating of their building? The first thing to recognise is that making savings does not require big expense. There are a series of basic things that can be tackled long before getting onto renewables — the most basic of which is measuring energy consumption. Currently, we are largely dependent on utility companies to give us our energy consumption figures via quarterly bills, but far too many of these are estimated for us to get a truly accurate picture. It is far better for building operators to introduce sub-metering to get a clear picture of how energy is being used and where it is going. Smart meters are appearing in greater numbers too, and these are ideal for giving a real-time picture of actual energy consumption and how much it is costing the building owner. Having measured energy consumption, the facilities manager can draw up a re-commissioning plan. Smart meters will identify anomalies like energy spikes in the middle of the night, perhaps if the boiler plant is firing up because the controls are wrongly set. An energy audit often reveals that services were never commissioned in the first place, and this is an obvious place to start. Auditors also reveal that the boilers will are not regularly serviced, controls are stuck with thermostat set on high and filters and ductwork are clogged with dust and dirt — all of which have a huge impact on energy consumption. We must also take the building fabric into account. Leaky buildings will never deliver good energy performance because it is almost impossible to correctly balance the building-services systems. Plugging gaps around doors and windows as well as upgrading glazing where necessary are fundamental first steps, but are often overlooked.
Replacing equipment Having addressed the underlying problems, it is time to consider equipment replacement. This can be carried out on a phased basis to keep capital costs down. There is good payback on energy-saving equipment, but only if it is fitted properly and integrated with the existing systems. Tax breaks are available through the Enhanced Capital Allowances scheme, and it is very important that contractors can talk knowledgeably to their clients about this. Having made the improvements and trained building staff to monitor and assess the energy-consuming systems, we are ready to consider the renewable option. They can now deliver even greater and more cost-effective savings thanks to the lower base load of our re-commissioned building. When considering adding renewables to existing plant, the engineer needs to take a number of factors into account. Depending on the system chosen, the installation may be subject to planning rules. Structural issues may need to be considered, so a survey may be required. If there is an element of micro-generation in the chosen solution, arrangements with the electricity supplier to the premises will need to be examined. An onsite micro-generator (CHP or photo-voltaic system, for example) that produces more electricity than is being consumed will create a reverse flow into the grid. Not all meters are set up to accept this, and the client will not receive any benefit — so this bridge needs to be crossed in advance and a buy-back tariff negotiated. However, in the case of solar heating for hot water, the task of the design engineer is relatively simple, and this is an area that is growing fast, in both commercial and residential retrofit applications. Control of the system is the critical area, so engineers need to make sure they are comfortable with the layout of the existing services and are able to fully integrate the new solar array. This must be sized properly and set at an angle of 30 to 60° to the horizontal. A second hot-water cylinder, alongside the standard one served by the boiler plant, is normally installed and receives pre-heated water from the solar array. The two cylinders improve energy recovery by increasing the temperature difference between the water in the store and the water leaving the solar panels. It is also possible to retrofit using a single cylinder, although this is more disruptive and, of course, requires the use of a specialised split cylinder. Ground- and air-source heat pumps are also being fitted in greater numbers to improve the coefficient of performance (CoP) of existing services. In this case, the refrigeration cycle in the heat pump is set up to deliver space heating, with the boiler then made redundant for certain periods to reduce energy consumption.
Expertly integrated The principle with any project to add renewables to existing heating plant is that the two should be fully and expertly integrated. Most important, the existing plant must first be optimised or any gains from the renewable will be wasted.
John Bailey is technical sales manager for Vaillant Applied Systems.
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