MEP engineers step up

MEP 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.


MEP 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 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 acommissioning plan that defines the roles and responsibilities and provides for documentation of communication channels (ASHRAE Guideline 0-2005 clauses (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.”

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 to demonstrate how much harder it becomes to correct a bad 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.

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.

For this project, what would it have cost the team if the mechanical engineer hadn't been allowed to ask just this one challenging question? The opportunity cost would have been the annual energy savings of $110,000/year and the first cost savings on the order of $710,000 (based on a typical installed cost of $1000/ton and $7/cfm for air handlers).

Just by challenging one key assumption, we learn about a 15% overage in refrigeration load. Moreover, in the typical design approach, the first thing the mechanical engineer does is to add 10% to his tonnage and his supply air fans just in case, because there is nothing so embarrassing as not having enough cooling. This bumps up the horsepower on almost every motor.

Then the electrical engineer goes to the electrical code, which requires sizing for the installed loads as opposed to the running loads. Last but not least, just to allow for future expansion, the electrical engineer specifies an infrastructure with 10% more spare capacity. Not only would equipment be oversized and possibly run in an inefficient manner, but the owner also is paying for an excessive amount of equipment capacity that may never actually be needed.

The only way to find such inherent assumptions is to have direct communication with the owner and the other engineers on the team. An early-phase decision to verify real densities and to hold them without safety factor through all disciplines could be a way to address this systemic bias in calculation procedures toward over-sizing. Based on his access to ASHRAE, American Society of Plumbing Engineers, and IEEE research data, the MEP engineer should be the first and most knowledgeable person to advise the owner about what assumptions should be used in relevant occupancies.

The envelope, please

The second critical area in which early communication can be invaluable is in the discussion surrounding building envelope and facades. The design of facades, their configuration, orientation, construction, and transparency are all contractually within the scope of the architectural team.

While these elements present the building's image portrayed to the world, a great deal of analysis by the MEP team is necessary to ensure that the building envelope is consistent with higher-performance buildings as defined by local energy codes. This is particularly true with the recent architectural emphasis on large quantities of glazing. There is a systematic tension in the design process between sunlight and thermal comfort in heavily glazed buildings. We all know this, and yet we spend many cycles performing involved calculations in order to prove it. A more proactive communication approach helps reduce the number of overly involved iterations for everyone. It's a question of yet another early-phase challenge to the architectural team.

Our firm has gathered data to help make the case, based on a 10 ft deep by 10 ft wide perimeter zone for three typical occupancy types and 12 different glazing configurations, assuming a 10 ft high wall exposure. If there is any hope to design a high-performance building with low-energy air conditioning, solar heat gain must be controlled right at the fa%%CBOTTMDT%%ade through either reduction of glazed area or a reduction of solar heat gain coefficient.

With targeted sensitivity analyses on single rooms rotated through multiple facade orientations, it is fairly straightforward to test with the architect a number of shading/glazing configurations, and the MEP engineer becomes an analysis and design partner. Then the team can move into the use of energy modeling as a design tool for a low-energy building.

Design convergence

With each discipline's decisions affecting the next moves of all other disciplines, the MEP engineer must not only state the current need, but also spin tales of alternate realities of how this might affect future decision-making.

Communication skills are not necessarily the forte of those who excel in engineering, and most engineering curricula do not spend a great deal of time teaching students how to get the most out of a design interaction. But MEP engineers no longer have the luxury of staying in the background of building design. With 36% of all energy in the United States used by commercial and residential buildings, and with HVAC and lighting systems in a typical office using some 68% of the building energy, it is obvious that MEP engineers can have influence over a substantial portion of the nation's energy use.

Typical approach Early-phase intervention: The mechanical engineer asks what workstation type the assumption was based on.
The owner requests a 6.25 W/sq. ft small power load based on actual electrical measurements of the worst case rendering workstationsOwner 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 required1,050 tons of refrigeration required
600,000 cfm of cooling air required520,000 cfm of cooling air required
$905,000 annual energy cost $795,000 annual energy cost


Experts: Integration is key

The key movers in the industry stress an integrated design approach as the appropriate philosophy for producing high performance buildings. For instance, the National Institute of Building Sciences Whole Building Design Guide has a compilation of suggestions, case studies, and checklists that are useful in coordinating and integrating with many other disciplines.

Similarly, the USGBC's LEED NC 2.2 rating program reveals how these influential benchmark measurements assume that a multi-point evaluation mechanism will best reflect the complexity of a holistic design approach.

Building design by its very nature is collaborative design. This is not design by committee, where everyone gets a vote, but rather it is design by advocacy. The reason that specialized consultants are hired into an architect's team is to ensure that the detailed necessities of discipline-specific design get the attention they need. Thus, the mechanical engineer tries to claim mechanical room space, as does the electrical engineer.

But as the industry moves toward a sustainable design philosophy, we see that the MEP engineer must understand himself as not only a service provider delivering the obligatory completion of his design work, but also as the most knowledgeable advocate for reducing energy and water consumption within the entire project. MEP engineers have the education and the detailed practical insight into what specifically can be done to minimize the use of natural resources in these areas.


2005 ASHRAE Handbook - Fundamentals

Lawrence Berkely National Laboratory Energy End-Use Forecasting

National Institute of Building Sciences Whole Building Design Guide

USGBC LEED NC 2.2 rating program

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