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CHP is increasingly used as a cost eecve, economic tool to produce hot water in hotels. But accurate load profile data and CHP sizing are key for maximum returns, says Baxi Heang’s naonal sales manager CHP, Mark Gibbons


n recent months, COVID-19 has, understandably, been at the forefront of our attention. But as we adapt to living with coronavirus, maximising building efficiency will also be high on the agenda for business owners and building managers to meet environmental commitments and keep running costs down. Take hotels, for example. As the hospitality industry reopens across the UK, the energy demand in buildings like hotels will often be relentless due to the need to provide a seamless supply of hot water 24/7. One technology that offers the opportunity to significantly reduce associated energy costs and carbon emissions is Combined Heat and Power (CHP).


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CHP produces useful heat and electricity at the point of use in a single highly efficient process. Rather than rejecting ‘waste’ heat to atmosphere like traditional power stations, CHP captures and re-uses it for high grade heating or cold water pre- heat for domestic hot water production. In this way, it is able to meet a building’s heat demand more efficiently, reducing total primary energy consumption typically by around 30%. As a CHP unit delivers maximum returns when operating constantly, this makes it well suited for use in hotels to provide cold water pre-heat. Indeed, CHP is increasingly used as a cost- effective, economic tool to produce hot water in hotels while generating lower-cost electricity on- site. It’s a greener way of using gas to reduce energy consumption and costs in hotels across the UK.


But here’s the caveat – for maximum benefits, it’s essential to avoid oversizing. A big building doesn’t always need a big CHP.


COMBINED HEAT & POWER Big buildings don’t always need big CHP Avoid oversizing


Why the focus on accurate sizing? A CHP needs to run for as many hours as possible to optimise performance. If oversized, the CHP will struggle to operate efficiently, reducing financial returns and carbon savings, as well as leading to maintenance and warranty issues. Given that each building will have a different energy demand profile, there is clearly no straightforward way to size a CHP. However, in hotels there are similarities: as well as having an ongoing demand for hot water, the buildings will often experience surges at peak times.


Sizing a CHP unit to the baseload size and topping up using water heaters will accommodate these spikes without compromising performance. This approach meets the lowest heat demand that occurs, resulting in the longest running hours and shortest payback period.


In existing hotels, building a clear picture of how and where electricity and heat consumption is used will reveal the variations in demand and the baseload level at which a CHP unit should be operating at maximum output.


When sizing a CHP system for new properties, the demand profiles can be estimated using a range of sources including design data and occupancy patterns.


Hot water profile


With detailed data to draw on, why then do we still hear reports of CHP units not running? One explanation is that hotels are required to ensure a seamless shower experience for every guest – providing a continuous supply of hot water that reaches the optimal temperature within seconds. So when estimating the hot water profile, there can be a counterproductive tendency to increase – even double – the calculation to ensure that the demand is met.


On other occasions, oversizing can be due to interpretations of the CHP contribution for compliance with Part L.


The Non-Domestic Building Services Compliance Guide advises 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’.


16 BUILDING SERVICES & ENVIRONMENTAL ENGINEER OCTOBER 2020


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