Cost-effective carbon reduction
With the Coalition Government set on cutting the UK’s carbon emissions, James Parkinson explains how boiler plant has a key role to play in reducing the carbon footprint of existing building stock cost effectively.
Businesses face a tricky balancing act. The coalition Government is committed to reducing the UK’s carbon footprint and is pressing the EU to tighten its own targets, suggesting that CO2 emissions should be reduced by 30%, not 20%, by 2020. The buildings sector accounts for 40% of the EU’s energy use and is the single largest area in which energy efficiency gains can be made.
In the current financial climate, however, it is the bottom line rather than environmental issues that is driving businesses to take an energy-saving approach. It is vital for the UK to maximise the carbon-saving opportunities offered by retrofits, since around 60% of the buildings that will be standing in 2050 have already been built.
During the last few years renewable technologies have proved a fashionable way to cut carbon and show off a company’s environmental credibility, but renewables do not provide an economic total solution for the commercial sector. As a result, replacing old and inefficient boiler plant still has a crucial role to play in cost-effective energy saving and carbon reduction.
Replacing an old, heavyweight boiler with a modern high-efficiency unit, coupled with heating controls that comply with Building Regulations Part L2B, has the potential to significantly increase seasonal boiler efficiency from around 50 to over 80%. (Part L2 2010 increases the required seasonal efficiency of boilers to 84%.) If a condensing unit is specified, fitted with system controls that ensure an optimum level of condensing operation, seasonal boiler efficiency can be increased to more than 90%.
To reduce building running costs and improve carbon savings, the latest condensing boilers tick all the right boxes for businesses. Ultra-high-efficiency wall-hung condensing boilers, such as Ideal’s Evomax, offer ease of installation, service, maintenance and operation. Boasting superb environmental performance with seasonal efficiencies of up to 97.9% and NOx emissions of less than 40 mg/kWh, the Evomax gives specifying consultants maximum BREEAM points. The Evomax is available for use in cascade format with an easy-to-use sequence controller and features wide output modulation, giving closer load-matching and more efficient system operation.
To maximise condensing boiler efficiency, a number of steps should be taken when specifying and installing new boiler plant.
The first step is sizing.
In the past it was common to oversize boiler plant relative to design conditions to ensure heat was available under many circumstances. Quite high levels of additional boiler plant were often specified to cater for servicing and maintenance situations. Unfortunately, oversized boiler plant wastes energy for large parts of the year.
Matching boiler size to building load is key to efficiency. Multiple boilers provide closer load matching than a large single boiler, the most sensible and efficient option being to use a cascade boiler system, with a mixing header employed to deliver both central heating and hot-water loads. Multiple boilers also provide the solution to servicing issues, ensuring continuous heat availability.
The next step in increasing energy efficiency is to ensure a condensing unit actually condenses! The system therefore needs to be designed to maximise the time the boiler operates below the flue-gas dewpoint temperature, which is about 54°C for natural gas. Optimum efficiency is achieved through designing a low-temperature system, and increasing the heating flow and return differential from the typical 11 K to 20 K will help as a starting point. To complement the system, heat emitters should be specified that operate at lower system temperatures.
With condensing-boiler technology having reached the pinnacle of efficiency, it is controls that are central to ensuring a system’s performance and making further energy savings. For instance, optimisation ensures the boiler system starts at the last moment so no energy is wasted by achieving the set temperature before it is needed.
System controls are also key to optimising the performance of a large commercial heating system where part of the building is unused or does not require heating at all times. Adequate zoning is essential to ensure cost-efficient operation, allowing spaces to benefit from individual time and room-temperature control tailored to their needs. Meanwhile, weather compensation ensures boiler plant only raises system temperatures to the minimum required to meet the building loss, relative to the outside temperature that day, thus making further CO2 savings.
Finally, to achieve maximum boiler efficiency in retrofit projects, the existing system needs to be cleaned and flushed before installing the new condensing unit. This helps prevent any dirt being dislodged or carried into the new system. Once installed, a water-treatment regime must be in place, a mandatory requirement of the Building Regulations, since hard water can cause scaling — resulting in a loss of efficiency of heat transfer to system water. Just 1 mm of limescale on the surface of a heat exchanger can reduce heat transfer by as much as 10%.
With the current financial squeeze now starting to bite, businesses want to reduce running costs while making the right environmental choices. Replacing old inefficient boiler plant with new energy-saving boilers is a simple and cost effective way to do both. So despite the rise of renewables the role of the commercial boiler is still key to reducing the UK’s carbon footprint.
James Parkinson is managing director of Ideal Commercial Heating.
