Book - School of Science and Technology

Emergent technologies 699Figure 24.8 Typical system for heat recovery to airEmergent technologiesIn recent years a number of new technologies have been developed and are,at the time ofwriting,approaching commercial availability. These emergent technologies may offer anincreased range of opportunities for integrating CHP into buildings; offering a widerrange of sizes and heat to power ratios. The following paragraphs give a brief descriptionof three such technologies.Micro turbinesMicro turbines are similar to the conventional machines described previously but extendthe size range of this technology. Originally designed as generators for standby or localgeneration needs,the potential as prime movers for CHP installations has been quicklyrecognised. There are a number of collaborative groups working towards the commercialisationof this technology and as such micro turbines are likely to be the first of theemergent technologies widely available.To date,machines ranging in electrical output from 30 to 500 kW are under development.Heat to power ratios vary between 1.5:1 and 2.5:1 depending whether the unitconfigures for maximum electrical or thermal efficiency.Fuel cellsFuel cells electrochemically combine hydrogen and oxygen to produce electricity,heatand water. Originally developed for use on space missions,fuel cells have generatedconsiderable interest in recent years as a pollution free,reliable and quiet solution topower generation.Fuel cells are generally split into five different types,depending upon the type ofelectrolyte used.Proton exchange membrane (PEM)PEM fuel cells use a moist polymer membrane and are sometimes referred to as SolidPolymer fuel cells. The advantages of this type of cell include its high power density,low