Heating – Hot water vs steam

Steam is a highly efficient heat transfer fluid:

  • high efficiency (BTU/lb)
  • low mass density
  • great control possibilities
  • no temperature limitation
  • fast

However, there is a current trend to convert steam systems into hot water systems. But is such a radical and costly conversion necessary? What principles are used to justify it?

 

Installations strictly limited to heating

Beecause of their lower combustion temperature, hot water boilers are somewhat more energy efficient than steam boilers. In a new installation exclusively devoted to heating purposes, this difference in energy efficiency justifies the use of hot water.

 

Installations with a process requiring steam

As soon as a steam is required for one process (sterilization, humidification, etc.), even if this process only consumes a portion of the total generated heat, steam becomes the most insteresting heat transfer fluid.

In hospitals, for example, the greatest portion of generated heat is used for heating, while a smaller portion is used for sterilization. The needs for sterilization, which hot water cannot fulfill, justify nevertheless by themselves the use of steam as heat transfer fluid in hospitals, because a two-boilers solution (hot water + steam) is an option to avoid at all costs. Maintaining two boilers has inconveniences that cancel the sought-after savings:

  • additional pumps (thus, higher electricity consumption)
  • higher maintenance and inventory
  • less efficient steam system once it has been amputated of some of its original piping
  • more piping overall
  • additional water treatment station
  • etc.

Many industries and institutions share a similar situation.

 

Converting to hot water vs steam system optimization

There is currently a tendency to convert steam systems into hot water systems. This type of conversion is often proposed because the lack of expertise in steam system maintenance results in the fact that a large number of steam systems are under-performing.

The Lalonde Systhermique team is convinced that the difference in global efficiency between hot water system and steam system is extremely thin when the comparison is made with a well-designed steam system. In fact, it is so thin that it very rarely justifies the high cost associated with a conversion to hot water, unless one is prepared to face a very distant return on investment perspective.

Let’s not forget that most existing steam systems are open systems. In our experience, converting a conventional steam system into a SCCS>® (combined with installing an economizer, optimizing boiler combustion, insulating pipes, etc.) can eliminate all steam and condensate losses and achieve a global efficiency that is only sligthly (0% to 5%) lower than that of a hot water system.

In most cases, it is possible to reduce by 25% the energy consumption of an open steam system, while raising the efficiency and the level of control on temperatures and pressures. Conversion to a SCCS® generates major savings for a fraction of the cost of converting to hot water. This notwithstanding the benefits associated with a smaller scale project.

Finally, converting a steam system to hot water always implies a boiler replacement. Since the existing boiler is usually old, part of any savings observed after the conversion can be explained by the boiler upgrade. It’s important to keep in mind that this is an investment that can benefit the steam system also. The positive impact of the boiler upgrade should not be attributed to the hot water conversion.