Incongruous DES District Steam Policy
Regarding the new (Aug 13, 2010) guidance document for treatment of District Energy Systems:
Yes, I get that the use of an older and possibly inefficient DES to serve a new building perpetuates the use of a relatively inefficient system, and LEED seeks to encourage the use of better technology, perhaps with an eye to encouraging the owner to gradually phase out an older plant. In an intellectual vacuum, this seems reasonable. But in the real world, the requirements of this new document may have unintended and undesirable results.
Many of these plants absolutely will not be replaced any time soon. I’m on a project at a military base where they are actively upgrading the steam plant. It’s there for the duration, period. And it’s a cogen plant – up to 10 MW.
But, as is not unusual for these systems, the distribution grid is old (WW II era, with a few upgrades since then.) It’s really impossible to make any quantitative estimate of line losses. It’s a big system serving many buildings, some of which are ancient energy hogs. None of that really has any bearing on this project, which is a tiny 13,000 square foot building. It is what it is. And the plant operator has no hard data for steam that gets used on the grid vs. steam vented to atmosphere. In general, they make more steam than they can use while generating power, and this new building’s energy use won’t even be a blip on the radar.
We will use this steam source for our new building; the underground pipe is within 100 feet of our mech room. The steam is effectively free for the owner, and we’re using it for building heat, two large-capacity laundry dryers, a very significant (for the size of the building) domestic hot water demand (large number of showers per day), and a MUA unit for a small industrial area. We are also considering using the outgoing condensate to make the 85-degree water for our radiant slab, effectively creating a “two-pass” arrangement. And, we are considering the use of a 20-ton absorption chiller, which are now available from some Asian manufacturers. Finally, we will use a steam-to-steam heat exchanger to make clean steam for a therapeutic steam room, eliminating the rather significant electrical use which otherwise be incurred.
To summarize, we’re using free steam year-round that would otherwise be wasted to serve all these energy requirements, including innovative applications to capture additional energy from the steam and use of new chiller technology, all of which would otherwise be served by natural gas boilers and an electric chiller.
With no hard data to use for an “Option 2” simulation (and even if we had it, it might reveal that the big-picture efficiency of the steam plant is not that great), we’ll have to use “Option 1” to model a stand-alone building. The building envelope and lighting would probably give us 12-15 credits for energy efficiency, even ignoring the HVAC and domestic water systems. But under Option 1, we’ll be capped at 6 points.
Not surprisingly, this will probably make the difference between silver and gold. The owner is not set on gold, and we'll use the steam. It’s the right decision, and as a taxpayer and engineer, it’s my opinion that any other decision would be ridiculous.
It appears that we’ll still be well into the credit range for silver. Given that all the energy is effectively free, the owner could reasonably decide to delete energy-efficiency measures from the project back to providing only the minimum for silver, and spend that funding on aesthetic and functional items which will benefit the end-user. If I were the end-user, I’d probably demand it, frankly.
Do we see the issue here? We could get way more points, and a LEED gold building, using a boiler-chiller system. It would cost the owner $8-10,000 a year for gas, and use gas and electricity that will not be consumed using the excess steam. The electricity would be from the cogen, but it’s at the end of a 30% efficient generation process instead of using the waste steam for the chiller and steam room. And all this would happen for the life of the building, year after year.
So should we use the steam, which would otherwise be wasted, and then delete energy efficiency features from the design to maximize the building content for the end user, achieving a silver rating by the skin of our teeth? Or, should we make the insane decision to provide a boiler-chiller, at an added construction cost in the 6-digits by the way (there were other energy-efficiency measures integrated into the design up to the point that we decided to go with steam), providing a building that has reduced content and aesthetics, and will use gas and power for the life of the building, with the owner spending thousands of dollars a year to buy said gas, and then hang a LEED gold plaque in the lobby?
Not surprisingly, we’ll be going with the former, at the cost of LEED gold. Is it the intent of the USGBC to create an incentive to make what is clearly the wrong decision in cases such as this?