Retrofit : Retrofit Volume 1 2012
28 • RETROFIT AUSTRALIA • VOLUME 1 NUMBER 1 2012 | Energy Efficiency What is cogeneration? Cogeneration (and trigeneration) has had a good deal of publicity in the last few years, whether it’s been implemented for a single building or multiple buildings – like the City of Sydney’s ‘green transformers’, which aims to connect multiple buildings with hot water and electricity, like many plants in Europe and the United States. ‘Cogeneration’ means generating together/jointly, and usually refers to using electricity and waste heat that is generated in the process of burning fuel (typically natural gas) to heat or cool spaces, or provide hot water for domestic use. Trigeneration (a subset of cogeneration) is three types of joint generation: usually electricity generation, waste heat and cooling (by passing the waste heat through an absorption chiller and, in simple terms, sucking heat out of water to create colder or chilled water). Typically, a cogeneration plant is a gas engine (initial varieties were similar to a diesel truck engine, but they tend to be much more sophisticated now) with micro- turbine options for small buildings, and gas turbines for larger or industrial sites. Natural gas-fuelled fuel cell technology is still expensive due to low production numbers, but is an option for individual dwellings (BlueGen). Larger units are typically three times the price of a comparable natural gas engine cogeneration unit. A key advantage of fuel cells is that there are no exhaust nitrogen oxide (NOx) and sulphur oxide (SOx) emissions that can potentially cause city smog. Engines are now much cleaner than in the past, and if required can have emissions scrubbing (like your car) to remove pollutants. This usually requires a constant supply of lime, which can reduce the financial viability of projects. It is best to seek out specialist advice in this area. Gas engines now typically lower pollutant emission levels for a small efficiency drop, in line with European emission requirements. What are the benefits? Cogeneration is about making electricity generation as efficient as possible. ‘Waste heat’ from a coal power station is not typically harnessed, but with a gas engine on site, this waste heat can be captured and used. Overall, this provides reduced fuel requirements and, combined with a switch to a cleaner fuel (gas instead of coal), can Retrofitting cogeneration BY TOBY ROXBURGH, SECTOR LEADER DISTRICT ENERGY AT AECOM, ON BEHALF OF THE ENERGY EFFICIENCY COUNCIL. Retrofitting is a key part of making buildings energy efficient. This article concentrates on the considerations for retrofitting cogeneration (sometimes called combined heating and power, or CHP) into an existing building. Cogeneration requires a number of factors to be optimised, and it is important to make sure that it is planned in a sustainable way. I will by start by introducing cogeneration, then look at the wider picture of sustainable energy, before getting to the key things to consider and some basic dos and don’ts when you are looking to retrofit cogeneration in your building.
Retrofit Volume 1 Issue 2 2012