CHPs are better than the grid in terms of overall NO emissions but not at a more neighbourhood level Bill Sinclair IN-DUCT EVAPORATIVE COOLING When used in an AHU, the Condair ME delivers up to 800kW of cooling from less than 1kW of electricity. Put Condair technology at the heart of your free air cooling strategy. Outside air Condair ME Evaporative cooler Evaporative cooler Supply air Return air Exhaust air Contact us for free expert advice Tel: +44 (0)1903 850 200 Email: uk.sales@condair.com Web: www.condair.co.uk Humidification and Evaporative Cooling achieve the level of carbon savings they have until now. If gas-engine CHP is proposed, applicants will be expected to supply sufficient information to justify its use and minimise the carbon and air quality impact. This new guidance has increased the attraction of using electric technologies, such as heat pumps, says Clark: Historically, electricity was a challenging fuel to use in new-build developments but is now a lot more carbon-light withinLondon boroughs, which means heat pumps are preferable options from a carbon point of view compared against CHP. By introducing CHP, you are reducing performance of the system, he says, adding that developers of energy centres will have to find offsets elsewhere for the carbon emitted by gasfired plant if they are determined to use it. Sinclair acknowledges that the new carbon factors have changed the equation for CHP plants. The less carbon-emitting technology was also the less expensive technology, so it made sense to use gas from a carbon and cost point of view. With the reduction of the carbon factor under SAP 10, they are now diametrically opposite: the more expensive technology is the less carbon-emitting technology. On a practical level, Woolley worries about the lack of detail to flesh out the London Plans policies. She says: The industry doesnt know what it is aiming for. The policy is there, but the supporting planning guidance isnt. They may have an idea, but they are not telling anyone yet. For example, while the plan says new boilers should have ultra low NOx emissions, it doesnt specify how this should bedefined. Abatement measures, such as catalytic convertors and timing controls, may enable most models of gas-CHP engine to meet the more stringent NOx emission requirements. The modulated systems will flex up and down, depending on the demand of the building, which reduces the size of the thermal store, which should be more energy efficient and have positive benefits on ultra-low NOx emissions, says Clark. And Sinclair argues that gas-fired CHP engines can continue to play a role as part of a hybrid heating solution. Heat pumps can pre-heat water in the systems cost effectively to about 45C. But increasing the temperatures to the levels required to ensure the water is sterilised and any bacteria, such as legionella, are killed can be most cost effectively achieved by using gas heating. He says: This gives you the best trade-off of running costs and savings. And increased reliance on electricity will revive concerns about Londons grid capacity, says Wealend: We are placing increased demand on the grid at peak times. Nevertheless the thrust of the London policy is clear: once again, the days of power plants in the capital are numbered. CJ 28 April 2019 www.cibsejournal.com CIBSE Apr19 pp26-28 Air Quality.indd 28 22/03/2019 16:53