∫ Steam Traps & Their Wily Ways

Highrise in need of steam trap fixingThere is a lot of talk in the energy efficiency world stating that repairing or replacing steam traps saves oodles of money and energy, and it’s true. Rare, however, is a clear, simple explanation of how exactly replacing steam traps saves money and energy. This post delves into the exciting world of steam traps and explains: what they are, what they do, why they’re so important, and how replacing them can save oodles of money, energy, and carbon.

Steam systems in buildings are used for heating. Remember those beautiful radiators in your grandparents’ house or your Brooklyn apartment? Those radiators provide heat by filling with steam (some systems operate with hot water instead of steam), and then letting the heat of the steam warm the pipes and radiate out into the room. Hence the term radiators.

As the steam releases its heat to the room, it looses its energy and condenses into hot water. Steam systems rely on the pressure of the steam to naturally force the steam to flow throughout all the pipes, but water always follows gravity and flows to the lowest point of the pipes. If the pipes fill with water the steam can no longer flow, so steam systems are equipped with clever mechanism to remove the condensed water from the pipes and allow the steam to continue flowing around the building and heating it. These clever drainage systems are called steam traps.

Steam Trap with simple Float MechanismThere are dozens upon dozens of types of steam traps, but they all accomplish one basic task: when there is too much water in the steam system, they drain it out. Otherwise, they stay closed and let steam flow through the system as normal. The way they accomplish this is usually fairly simple. The diagram to the right shows a simple steam trap. When the trap fills with water, the float (the grey circle) rises and opens the valve. The water then drains out, the float falls, and the valve closes again. (The valve is the small down arrow.)

Another type of steam trap, shown to the left (Click it to enlarge), uses temperature to open and close the valve and regulate the amount of water in the system. Steam is very hot, so when the trap is full of steam the fluid inside the valve expands and closes the valve. As the steam looses its heat to the building, the condensed water follows gravity to the bottom of the trap. The condensed water is colder, so the fluid inside the valve cools and opens the drain. The water flows out, is replaced by steam, and so the valve closes again.

Pretty neat systems, right? Right. But lots can go wrong. Valves can get stuck, fluids can leak, impurities in the steam can eat through the delicate parts of the steam traps, and a thousand and one other things can lead to the death of a steam trap. When steam traps die, one of two things happen: they seal shut, or they lock themselves open. If they seal shut the steam system will stop providing heat to an area of the building and the maintenance team will notice and fix the broken trap.

If, however, the steam trap seals open, there is no obvious way to notice. Steam will still flow through the system and heat the building. It will just also flow through the condensate return system and be wasted.

What’s a condensate return system, you ask? It’s a clever system that lets the condensed steam that has become warm water return back to the boiler to be made into steam again. This saves water because the steam can be recycled, but also saves energy because instead of the boiler needing to heat 55° water up to steam, it only needs to boil water that is already 150°. (Older systems just dump the condensate into the sewer. In cities like New York that have a temperature requirement for water entering the sewer, some buildings actually need to run their air conditioners just to cool the condensate water before it enters the sewer!)

The problem with putting steam into a condensate system is that boilers are designed to boil water, not reheat steam. If you put steam into a boiler you risk overheating and destroying your boiler, so boilers have a steam release valve to ensure no steam enters the boiler. Moral: any steam in your condensate system gets released into the air and wasted.

So imagine your steam trap has failed open: you are now constantly venting steam to the great outdoors. Bad? You betcha. Steam is not free, and neither is the oil or gas you made it from. So fix your steam traps! It will save oodles of money and carbon.

5 Responses to ∫ Steam Traps & Their Wily Ways

  1. I recently saw some interesting statistics on steam traps and the effects of maintenance efforts. According to the DOE (publication DOE/EE-0193, dated July 1999):

    - approximately 20% of the steam leaving a central boiler plant is lost via leaking traps in typical space heating systems without proactive assessment programs

    - a relatively “simple” steam trap maintenance program using portable test equipment once a year can easily cut those losses in half.

    - an “intermediate” program using more sophisticated portable test equipment twice a year can cut losses in half again.

    - the “best” program, using permanently installed test equipment (e.g., wireless steam trap monitors) to allow continuous monitoring and evaluation can reduce losses to less than 1%.

    Their bottom line — implementing almost any type of steam trap maintenance program will be beneficial; selecting the specific type of assessment equipment is of secondary importance.

    A few other relevant snippets from the report:

    - the trap-related portion of the energy audit costs were estimated to average $9.70 per trap.

    - the trap replacement cost was estimated at $94 for each trap replaced (for the referenced study, this corresponded to about $40 per trap when considering all traps in the facility)

    - the average trap lasts for about 5 years (i.e., you can expect a 20% failure rate)

    It is also interesting to note that these numbers reflect only changes in maintenance practices — no change in the steam trap technology. Depending on the number and size of traps in your facility, more sophistication might be warranted.

  2. Great article and very informative. Learned a great deal about steam traps. I agree that any sort of regular maintenance would reduce failures of the traps greatly. Another path to consider would be using materials with longer life cycles or perhaps just replacing the valve every certain number of hours, like often airplane parts are replaced even though the “seem to be working just fine”.

  3. Very interesting. Thanks for such a clear explanation of steam traps. I’m wondering if in the case that a steam trap seals open, do you think there would be a significant change on the building owners utility bills to signal that they have a maintenance issue?

    • Another great question. An individual steam trap is pretty small, and they typically break over time, so the leak will be very small at first and then gradually continue to grow as the trap gets ever more stuck. This would be tough to spot instantaneously on a single bill. But if steam bills have been creeping up over time, something you could find with a regression that is normalized for temperature, leaking steam traps are a good potential place to look for quick savings.



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