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SIZING UP THE BENEFITS OF CHP Why it’s all about getting the perfect fit


Whilst the installation of CHP has the potential to provide impressive savings, specifying an inappropriately sized unit can drastically limit the cost and efficiency benefits. Gary Stoddart (pictured), Technical Sales Director at Remeha CHP, explains the importance of always choosing a system which meets a building’s heating and hot water needs.


installation growing by an average of 6 per cent annually since 2006. According to a recent study, this rise is only likely to continue, with current estimates putting installed CHP capacity at a global total approaching 972 GW by 2025. This is due to increasing awareness of the significant energy savings and green credentials that this innovative technology can offer, particularly to premises which have a high requirement for heating and hot water. These savings are provided in two ways – firstly, by producing electricity using natural gas, rather than purchasing it from the grid. When electricity is transferred from the grid, especially when moved over large distances, a certain amount of power is lost – CHP not only negates this issue, but also costs three to four times less. Secondly, further savings are provided by the generation of heat. At gas power stations, the heat produced via the generation process is lost. By contrast, the heat created by on-site CHP can be reused in the hot water and heating systems. Whether CHP is part of a heat network or an independent heating system, it can achieve carbon reduction, especially when it is the lead heat source. With an energy cost ratio of around 3.5:1, the savings are calculated using the cost of energy input to the unit (natural gas), the value of the heat output (thermal) and the electricity produced. Overall, it means CHP can be approximately 30 per cent more efficient than traditional electricity. Typical payback periods are around seven to 10 years, but five is possible. Before specifying a CHP system, it is essential to assess the requirements and average usage levels of the building, and size on this basis, to reap the full benefits.


C The perfect fit


There is still a tendency to ‘size up’ during specification, with some professionals applying the old adage ‘add ten per cent for luck’ when it comes to calculating the size of a unit. But, by fitting an oversized CHP, not only is the capital expenditure increased unnecessarily, but the unit will operate less efficiently too. Oversized CHP units will not run if the heat demand is not present, and as a


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The rule of thumb for sizing CHP is to use the smallest sized unit possible, to cover baseload heating requirements. If additional heat and/or hot water is needed at peak times, consider an energy‐efficient condensing boiler or water heater to supplement supply rather than a too‐large CHP unit.


’ 22 BUILDING SERVICES & ENVIRONMENTAL ENGINEER APRIL 2017


ommercial interest in Combined Heat and Power (CHP) has been rising steadily over the last decade, with


result the anticipated electricity will not be generated, leaving building owners with higher operating costs and ultimately disappointed with the performance of their equipment. The rule of thumb for sizing CHP is to use the smallest sized unit possible, to cover baseload heating requirements. If additional heat and/or hot water is needed at peak times, consider an energy-efficient condensing boiler or water heater to supplement supply rather than a too-large CHP unit. This approach ensures that the unit is running constantly and, as such, is generating low cost, low carbon electricity as a by-product of producing base load heating. Sourcing both the boiler and the CHP unit from the same manufacturer has a number of benefits in terms of compatibility and assistance with system design. Indeed, Remeha offers a comprehensive commissioning and aftercare service, based upon extensive experience of both technologies.


When calculating the size of the system, the Building Regulations state that CHP must be sized to provide ‘not less than 45 per cent of the annual total heating demand’, which includes space heating and domestic hot water. This is critical for CHP as oversizing for summertime loads can result in either non-operation of the CHP or the heat produced being ‘dumped’ in order to continue generating electricity.


A cascade arrangement can be a way to meet fluctuating demands, as this can respond quickly to changes in usage patterns. Cascading CHP units also mean that when one unit requires maintenance or repair, there is no interruption to the building’s heating, as an additional unit/s can take on the base load.


Keep running


There are many benefits to sizing CHP so that it runs constantly, not least that ROI is achieved much faster. By never powering down the CHP, the power required for start-up isn’t used, thus minimising costs and enhancing savings. What’s more, constant use also prolongs the life of the unit, as repeated starting and stopping eventually wears down the engine and starter motor, whilst using more oil than the alternative.


To run continuously, the CHP unit stores hot water generated during low- demand periods in storage cylinders, to supplement supply during peak times. As soon as the stored water begins to be drawn off, the CHP unit detects cold water coming into the system and continues firing, creating more hot water to satisfy the demand. The unit remains firing throughout the day, refilling the tank to meet the next rush period.


Collaboration


To get the most from a CHP unit, in terms of longevity and maximum delivery of savings, it is crucial that all relevant parties collaborate from the very beginning of a project. By involving heating engineers at the early


stages of the conversation, the project is supported by all of the necessary information and expertise, which is key to identifying the right solution. Equally, it’s important that the CHP supplier remains involved with the project beyond the commissioning process, to make certain that the system is being used as intended and is performing to the highest levels of efficiency. Remeha offers a range of maintenance and monitoring solutions, meaning we can work with the building operator to ensure the system runs efficiently.


Although there can be a temptation to factor in a little extra capacity, choosing an oversized CHP can undermine the inherent advantages of the unit. By carefully assessing the exact needs of a building, users can choose a unit which not only meets heat and hot water requirements, but also delivers lower energy bills and reduced carbon emissions.


www.remeha.co.uk References:


http://finance.yahoo.com/news/ combined-heat-power-chp-market- 124500142.html


The average cost of electricity from the grid is 14p per kWh, however the gas used to generate electricity on site costs an average of just 4p per kWh


(www.energysavingtrust.org.uk/domestic/co ntent/our-calculations)


VISIT OUR WEBSITE: www.bsee.co.uk


uThe rule of thumb for sizing CHP is to use the smallest sized unit possible, to cover baseload heating requirements.


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