How efficient are centralised steam systems?
July 3rd, 2009 at 17:01We 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.
Tags: domestic hot water, heating hot water, steam efficiency
September 16th, 2009 at 1:36
Hi Messrs Carbonetix,
Interesting comments, indeed if a steam boiler’s only purpose is generating steam to produce hot water, then indeed there are more efficient ways of achieving the end result. I suggest you consider the Armstrong Flo-Direct Complete Thermal Exchange Gas Fired Water Heater. At 99.7% efficiency it appears hard to beat. But, it is horses for courses. If a site has other Steam requirements it is imperative the system is designed & installed correctly. Feel free to contact me for assistance.
Bye Bruce & Darren,
Rob
December 3rd, 2010 at 1:42
Interesting thoughts,
You left out one of the biggest losses, “the pressure let down”, which posses huge opportunities to “recover waste energy” through a “Micro Steam Turbine”.
Pressure let down:
The boiler generates steam at around 10bar while the end processes (heating water or majority of industrial processes) need a much lower pressure, between 2 and 4bar.
What happens is the pressure is let down via a Pressure Reducing Valve (PRV), that generates heat through frictional losses.
Recover Waste Energy:
The pressure energy from the steam is lost as frictional losses on the PRV, a Micro Steam Turbine can be used to reduce the pressure instead of the PRV and as a by-product of the pressure let down generate Free Clean Electricity.
Micro Steam Turbine:
Common steam turbines have been around for years, the lack of adoption of the mentioned solution is due to some drawbacks that today have been solved by new available models. The Micro Steam Turbines achieve efficiencies of 80% , are smaller than a fridge, easy to operate, plug and play, design for saturated low quality steam, 85db noise and offer paybacks between 2 and 4 years while generating up to 400kW.
https://docs.google.com/fileview?id=0B-Unp2XAV2PeYjYwNDI5ZjktNGNlNS00OTRjLTllZWYtZTUxZTMyNzliNzIw&hl=en
Regards
Daniel