Consulting-Specifying Engineer - December 2007 - (Page 39) BY ERIN MCCONAHEY, PE, Associate Principal, Arup, Los Angeles EP engineers are no longer an afterthought in building design. The push for green buildings has thrust MEP engineers into the limelight, and getting involved early in the design process is a must. These days, sustainable design and the drive for low-energy buildings has encouraged many owners and designers to examine the impact of all resource-consuming systems, with particular attention to those within the MEP engineer’s sphere of influence. Now placed into a position as early influencers of design and then placed into the ongoing role of technical interpreter, MEP engineers must share their knowledge of systems in an accessible manner to ensure that key decisions are made at the appropriate time. MEP engineers’ roles must shift to become more involved early in the design decisions, as these decisions have significant downstream effects in first cost, lifecycle cost, sustainability, and occupant safety, health, and comfort. Timing matters Timing is crucial in maintaining trust—the right information delivered six months too late results in a lost opportunity. With the escalating cost of materials and numerous cycles of value engineering, MEP engineers need to show all of their cards as a gesture of trust in the team, and then MEP engineers may advocate on the basis of logic and calculation for a preferred approach. Selection of MEP systems must complement the building configuration and usage, which are defined by others. Commissioning, in M Table 1 Hidden factors may falsely escalate cooling needs Typical approach Early-phase intervention: The mechanical engineer asks what workstation type the assumption was based on. Owner defines three typical workstation types: -Light use = 2 CPU/2 monitors -Moderate use = 3 CPU/4 monitors -Heavy use = 5 CPU/6 monitors Owner then identifies in plan where light, moderate, and heavy use is anticipated Mechanical engineer uses ASHRAE 2005 Fundamentals pages 30.8-30.12 to calculate W/sq. ft for each workstation type and apply it against the whole building Building-average heat load drops to 3 W/sq. ft 1,200 tons of refrigeration required 600,000 cfm of cooling air required $905,000 annual energy cost 1,050 tons of refrigeration required 520,000 cfm of cooling air required $795,000 annual energy cost E H L P The owner requests a 6.25 W/sq. ft small power load based on actual electrical measurements of the worst case rendering workstations commissioning plan that defines the roles and responsibilities and provides for documentation of communication channels (ASHRAE Guideline 0-2005 clauses 5.2.4.4 (b) & (c)). As in commissioning and its basis of design reports, the first step in communication on design teams is to make sure that everyone sees the building in a similar way and through the lens of common assumptions. Subconsultants under the typical AIA contract usually have minimal access to engaging with the owner-client unless the lead designer facilitates and encourages the contact. Furthermore, because the definition of an engineer’s best work means that it is never noticed, MEP engineers work in a cloud of “presumed proficiency.” decision later in the project cycle, with order of magnitude jumps in cost-to-fix for the owner to absorb. Once access to the key decision makers is granted, then the worth of presence is at stake. Mechanical engineers can make the greatest impact in internal heat load assumptions and building envelope. Fine-tuning assumptions Occupancy patterns/diversity and small power loads are key areas where early communication with the owner/operators/tenants of the building can pay off by reducing first costs and operating costs, by defining appropriate levels of performance, and by improving indoor air quality and comfort. Engineers are now taking a more active role in the overall building design, especially at the beginning of the process. particular, does a good job of focusing the team on understanding the owner’s project requirements and then ensuring that these priorities are kept at the forefront of subsequent decision making and also reflected in deliverables. The commissioning process, as defined by ASHRAE Guideline 0-2005, regiments and systematizes communication surrounding those issues by requiring a Because we do not have the seriousness of behavior for that standard structural engineering retort “because otherwise it will fall down,” the onus is on the MEP engineer to articulate his worth in early design discussions. In the attempt to get a seat at the table early enough to make a difference, our firm often uses two diagrams (Figures 2 and 3) to demonstrate how much harder it becomes to correct a bad Look at the typical hidden fudge factors that are built into the normal design process. Table 1 shows a recent example of an extreme case: a computer-intensive production studio shows how these hidden factors escalate into over-sizing methodology. This comparison shows how one question posed to the owner could have enormous consequences on the design result. Consulting-Specifying Engineer • DECEMBER 2007 39
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