www.heatingandventilating.net Why? One explanation could be due to the


interpretation of the CHP contribution for compliance with Part L. The advice offered by the Non-Domestic Building


Services Compliance Guide is that ‘a CHP plant should be sized to supply not less than 45% of the annual total heating demand (i.e. space heating, domestic hot water heating and process heating) unless there are overriding practical or economic constraints’. This leaves scope for varying interpretations


which can produce dramatically different energy calculations – and potentially encourage oversizing of CHP for compliance.


Another cause might be the counterproductive


tendency, when estimating the load profile, to increase – even double – the calculation to ensure that the demand is met.


And yet as we know, if oversized, the unit will


struggle to operate efficiently, reducing financial returns and emissions savings, as well as leading to


maintenance and warranty issues. So how to avoid oversizing? Our recommendation


to those looking to use CHP echoes that of the CIBSE Applications Manual AM 12: seek advice from experienced suppliers at an early stage of design. Let’s consider two real world examples where


interpretation of the compliance guidelines could have led to specification of a larger CHP unit when in fact a micro-CHP unit has provided the best solution.


Reap lifetime benefits


Of course, sizing the CHP is just the starting point. Good CHP suppliers will provide support at all stages of a project, from initial design advice and on-site commissioning to ongoing monitoring and maintenance to optimise performance throughout the life of the installation. A support service providing regular scheduled maintenance and remote monitoring has been set up


Combined heat & power


at all three of the above sites. This ensures that CHP services are carried out when required and also enables any faults to be corrected and reset remotely, reducing downtime, inconvenience and unnecessary costs. “Having remote access is extremely useful for me


at weekends so that I can monitor temperatures or reset the unit remotely if necessary,” explained Mr Carrington. “But equally it means that the Baxi Heating CHP


team can dial in and offer advice or correct any faults, often without the need to visit site,” he continued. “It’s reassuring to know that there’s always someone at the end of the phone to help answer any of my queries.”


At the end of the day, nobody wants to be left with


an oversized CHP that sits in the plant room unable to run. And, as identified, big buildings don’t always need big CHPs. So, when considering CHP, it pays to work with the experts to get the energy balance – and then keep it right.


EFFICIENCY SOLUTION FOR CARE HOME


Left: At Deewater Grange, the CHP is running non-stop, supplying all the heat


A


t Deewater Grange, a BREEAM-accredited 58-bed new build residential care home in Chester, a micro-CHP is “ticking over nicely,


operating non-stop, 24 hours a day,” according to maintenance manager Jordan Carrington. Early in the design process, M&E contractors Gas Tech, supported by the Baxi Heating CHP team, carried out a thorough assessment of the energy demand at the care home. Using the accurate load profile, they recommended installing a Remeha micro-CHP unit which provides a thermal output of 14.7kW and an electrical output of 5.5kWe. The CHP has been carefully sized to meet the


lowest heat demand in the building to ensure that the CHP will run constantly. In this way, it meets


the high hot water demand that boilers alone would be unable to satisfy, boosting the temperature of the hot water system and simultaneously avoiding any risk of legionella bacteria forming. Working alongside the CHP to meet peak heat demands are three Remeha Quinta Ace 115 boilers. “We’re really impressed,” said Mr Carrington.


“The CHP is supplying all the heat and doing all the work which will reduce our carbon footprint and energy costs.”


Right: At Deewater Grange, three Remeha Quinta Ace 115 wall hung condensing boilers were selected to work alongside the CHP to meet peak heat demand


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