How efficient are centralised steam systems?
Friday, July 3rd, 2009We have recently been working on a site with a centralised steam system. It has two natural gas fired boilers supplying steam to a number of plant rooms, with the steam used to generate domestic hot water and heating hot water amongst other things. So how efficient is this system? And are there alternatives to steam that use less energy?
The short answer is that the steam system is very inefficient. It could be replaced with a decentralised system using a combination of hot water boilers and, where process steam is needed, small steam boilers. This would halve energy use.
Centralised steam systems have losses designed into them that cannot be avoided. Firstly the boiler blow down results in energy wastage. Then, because of the high pipe temperatures, any heat losses from uninsulated pipe is higher than it would be if the temperature was lower. Failed steam traps waste energy by not using the steam before it turns to condensate. And leaks and steam vents waste valuable condensate. Finally because still steam will eventually condense and needs to be taken away by a steam trap then reheated the standby losses are high. All these losses add up to large inefficiencies.
Steam is a old technology, and its use should be limited to only where absolutely necessary. Using steam to generate hot water is very inefficient. Much more efficient would be to use a high efficiency condensing flue hot water boiler, a direct exchange boiler, which will use half the energy to generate the same benefit. Heat pumps could also be considered if a water temperature of no more than 60 degrees Celcius was required.
