Over-design

Posted on June 16, 2009. Filed under: sustainability | Tags: , , |

Would you wash your hands with a fire hose?

Over the last few weeks I’ve been thinking about a significant source of energy waste, one that burdens utility budgets, frustrates maintenance personnel, and ultimately leads to building occupants who are either too hot or too cold, but never just right.  This pernicious source of energy waste is over-design.

Over-design of heating and cooling systems is hard for me to visualize.  I am admittedly at a disadvantage in this discussion as like most campus sustainability professionals I am not a mechanical engineer by training.  Or an HVAC technician.  Or a controls technician.  Or an architect.  Or a contractor.  In fact, if you are looking for an expert on the subject, you’ve come to the wrong place.

Yet, I’m increasingly on the look-out for over-designed mechanical systems.  In a recently completed project for Rice, the MEP (mechanical, electrical, and plumbing) engineering consultant originally recommended 2,000 tons of cooling.  An internal team from Rice whittled this down to 300 tons of cooling – an 85% reduction.  To date, the building’s actual consumption has not peaked above 40 tons, although it eventually will.  The difference between the original recommendation and the actual peak from operations to date is a factor of 50.  That’s over-design!  As a comparison, when we wash our hands under a sink, the stream of water is typically flowing at a rate of 2.5 gallons per minute.  If this were over-designed by a factor of 50, the flow rate would be 125 gallons per minute, which is typical for a fire hose.  So again I ask the question, would you wash your hands with a fire hose?  Certainly not, and no consultant would recommend that we do so.  But when it comes to energy, we’ll get the equivalent of a fire hose to wash our hands if we’re not careful.

Over-designed mechanical systems are bad for a number of reasons.  To name just a few, they cost more up-front, and then also to operate.  They operate inefficiently, far outside of their optimal ranges, which shortens the lifespan of the equipment.  They are difficult for maintenance people to control (imagine trying to adjust the flow on that fire hose to fill a cup of water without spilling!)  And when the systems are hard to control, space temperatures will either be too cold or too hot, and the building occupants will suffer as a result.

So what’s a campus sustainability professional to do?  As I’ve noted in other posts on this blog, we can’t be experts in everything, but we can bring the conversation to a fundamental level that enables us to partially overcome our lack of technical experience and play to our strengths.  Following are a few tips:

  • Enable the conversation. We operate horizontally in an organization of vertical silos.  Our job is all about making connections and facilitating communication between experts.  I recommend organizing one or several energy-focused conversations during the design of a new building.
  • Get the system in the room. Think carefully about the different voices and skill sets that need to be at the table.  From your institution, this may include one or several maintenance representatives, an energy manager, a project engineer, and a project architect.  From your consulting team, the MEP consultant, the LEED consultant, the design architect, and so forth.  The full range of stakeholders need to be present.
  • Gather benchmarking data. One of the best ways to ferret-out over-design is to gather operational data in either dollars per square foot or units of energy per square foot for comparable facilities.  If any of your campus buildings are individually metered (and hopefully most of them are!), then calculating annual energy consumption per square foot is easy and provides you with operational data for facilities that you can readily visualize.
  • Apply diversity factors. This is a big one, and often you’ll have to know to ask this question.  For certain facilities, designs are created assuming that everything is in a worst-case scenario, with additional factors of safety layered-in.  Suppose your consulting team is designing a laboratory with fume hoods.  For the sake of design, they are likely to assume that all labs are in full use at all times with all fume hoods opened to their 100% position. In reality, this simply does not happen.  It’s not that they’re designing the equivalent of a church parking lot for the Easter service.  It’s that they’re designing the church parking lot as if Christmas, Easter, and Palm Sunday all happen on the same morning, with additional spaces provided in the event that the church might double its size at some future date.  The diversity factor is a multiplier that enables for a more realistic sizing of mechanical systems in recognition that a “worst x worst x worst x safety factor” scenario just doesn’t happen.  Consultants will be hesitant to even suggest a diversity factor to apply; you’ll have to do this legwork on your own.
  • Set the parameters. The previous recommendations are often reactive.  In a sense, they’re a recipe for an intervention.  Ideally, you don’t want an intervention, you want right-sized systems as part of the original design.  One approach would be to gather benchmarking data prior to a project, establish a “do not exceed” figure for energy per square foot based on real operational data from your institution (or comparable), and then see if the consulting team has the discipline to stay at or below the target.

These steps will help the campus sustainability professional to orient a project team towards eliminating over-design.  As you step back to consider the system-wide impact of over-design, one on top of the other, from the upsizing of air handling units and pumps by a manufacturer’s salesperson to setting an excessive minimum number of air changes to assuming improper design temperatures to failing to apply diversity factors and on and on and on…. well, suddenly it’s not so hard to see why when it comes to energy, we do sometimes end up with the equivalent of washing our hands with a fire hose.  But as the era of cheap energy draws to a close, this will be one mistake that we simply cannot afford to keep making.

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7 Responses to “Over-design”

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Any idea why the Rice system was over-designed by such a large amount? Was there a valid rationale?

Joe –

I was not close enough to that particular project (with the x50 overdesign) to know, but fortunately my colleagues stopped it. However, many of the projects that I’ve been involved with have also initially suffered from significant overdesign. Some common themes include not applying diversity factors, assuming a wintertime 99% design temperature that is way below ASHRAE for this area (ASHRAE recommends 34 degrees for this part of Houston, and I’ve seen our consultants use 20 degrees), lack of available operating data to guide designers, etc. There are lessons here for both the owner and the consultant, and I think Stephen’s remarks offer a pathway for better performance from both.

It is refreshing to hear this from the campus sustainable design community and speaks to the over-whelming need for a unified integrated design team. Doing right sized energy reducing high performance buildings requires an unusual level of committed collaboration, shared feedback and common design goals. One of the most effective tools for this is developing early on a design intent or design brief document which encompasses the LEED or BREEM framework to clarify and agree upon what specific performance / design goals must be met to produce an expected quality level, be it certified, silver, gold, platinum or living building etc. This document starts at the pre-design level and travels through the design process, progressively getting updated with further specifics and richer levels of information.

Then study your building design with energy modeling and some level of BIM (Building Integrated Modeling)which works in your setting and capabilities.

Another area to apply is corporate social responsibility and bring in triple bottom line accounting standards to not under design that important more intangible area. Often this is a neglected area not on anybody’s radar screen.

Stephen –

Excellent comments. This is the general direction that my lessons have been leading me, and you captured what that new process would look like quite nicely.

Richard Johnson

Richard, Thanks! I’m glad they’re helpful. I forgot to mention the importance of conducting incremental cost estimates at each stage of design dovetailing with energy modeling and systems selection. This way true and complete feedback loops are in place to help shape truly informed design decisions.

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I would consider that many cases of over design are a simple case of contracters wanting to up-sell when undertaking a build. Like convincing a guy who wants an MPV to buy a Ferrari!


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    Insights and observations on the campus greening movement, from the perspective of a campus sustainability professional

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