FEATURE COMBINED HEAT & POWER THE HYBRID SYSTEM: A MATCH MADE IN HEAVEN
For commercial buildings with high and continuous heating loads, pairing CHP with a condensing boiler ensures that the system can perform to its full potential and meet user requirements. Paul Wilson, national sales manager, at Remeha CHP, explains how these technologies can work together to deliver optimum efficiency
configured correctly so that return water to the condensing boiler is not preheated. This is because condensing boilers work most effectively at lower water temperatures to recover both sensible and latent heat from the flue gases. Condensing occurs at around 54°C when the flue gases are at or below their dew point, therefore the boiler return water must be at this temperature or lower to allow continuous condensing to take place. This approach ensures that the building gets maximum output from the CHP, reducing gas consumption and carbon emissions as well as extending their operating life. At the same time, the boiler only runs for the shortest possible time at higher efficiencies during periods of high heating and hot water demand.
C
ommercial interest in Combined Heat and Power (CHP) has been rising
steadily over the last decade. In particular, there has been an increase in the awareness of the significant energy savings and green credentials that this innovative technology can offer, especially on premises that 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, costing up to three or four times less.1 Secondly, further savings are provided by the heat created by on-site CHP, which 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. Because a high proportion of our
buildings still depend on gas for heating, CHP is often used alongside gas condensing boilers to further raise efficiency and cut carbon emissions. Whether it is retrofitted as a ‘bolt-on’, or installed with boilers as part of a fully- contained internal package or energy centre, good design, integration and installation are all vital to ensure that building owners and users can reap the benefits from both technologies.
28 SUMMER 2017 | ENERGY MANAGEMENT
SUCCESSFUL SYSTEM SIZING The key to a well-designed system is to consider it as a whole to maximise the efficiency of both the CHP unit and condensing boilers. The smallest sized CHP unit should be used to cover baseload heating requirements, with energy-efficient condensing boilers or water heaters used in conjunction to meet additional heat and/or hot water demand at peak times. It is important to size the CHP unit correctly. An oversized CHP increases the capital expenditure unnecessarily, and it will operate less efficiently. Oversizing CHP units will mean the CHP units will not be used as the heat demand will not be present. As a result the anticipated electricity will not be generated, or the heat produced being ‘dumped’ in order to continue generating electricity. Either way, building owners would be left with higher operating costs and ultimately disappointed with the performance of their equipment. A CHP unit running continuously will generate low cost, low carbon electricity as a by-product of producing base load heating.
BEST OF BOTH WORLDS In a properly designed and commissioned hybrid system, the heating and hot water system within the building will draw on the CHP first. Pipework should be
Figure 1: CHP systems from Remeha
COLLABORATION IS KEY By involving heating engineers at the early stages of the conversation, a project can be supported by all of the necessary information and expertise, which is key to identifying the right solution. Specifiers and building managers can also benefit in terms of compatibility and assistance with system design by sourcing both the boiler and the CHP unit from the same manufacturer.
Even after the commissioning process,
REFERENCE 1. 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/content /our-calculations)
it is important that the CHP supplier remains involved with the project to maintain and monitor the system. This ensures that the system is being used as intended and is performing to the highest levels of efficiency. In addition to design and commissioning, Remeha also provides remote monitoring and maintenance solutions to help make sure its CHP system is delivering the desired ROI for its owners. As the gap between electricity prices and gas prices - often referred to as the spark gap - continues to widen, the case for implementing a combined heat and power (CHP) system grows stronger. Combined with a condensing boiler, CHP can deliver lower energy bills and reduce carbon emissions whilst meeting users’ heating and hot water requirements.
Remeha CHP
www.remeha.co.uk T: 0118 974 3066
/ ENERGYMANAGEMENT
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