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Optimized mechanical room design balances building elements with the integration of mechanical, electrical and plumbing (MEP) systems. For the engineer, the project begins with systems diagrams, which then inform equipment types selected to meet program needs. Preliminary equipment selections then define the footprint of the equipment as well as its associated service and operational clearances.
System demand calculations lead to flow rates, allowing piping and ductwork, previously lines on a diagram, to be sized. Taken together, this establishes the building blocks for what will become the building’s mechanical rooms (see Figure 1).
Laying the Groundwork for Success
Planning for mechanical rooms ideally begins when the project is in its infancy. While we tend to focus on the size of the mechanical room, the location and proximity to other services are important factors. Can the mechanical room be adjacent to or share access with a loading dock? If multiple exits will be required by code, does the proposed room location accommodate that without the second exit into a restricted or limited access area?
Being integrated into the design team, either as an integrated firm or by establishing clear and consistent communications with the architect, goes a long way toward allocating physical space and optimizing the mechanical room location. With the design team on the same page relative to the space requirements, the mechanical room and its requirements become a defined program element instead of an afterthought.
With a rough room size defined, the engineer and architect work together to establish how to best optimize the mechanical room’s placement. If the site becomes constrained or other program elements have a higher importance factor, the engineer then prioritizes what systems must remain and which can be located elsewhere. Main electrical rooms, for example, require proximity to site transformers to limit distribution costs. Similarly, standby power systems desire adjacency not only to the main electrical room but also to the generator.
Establishing System Parameters and Relationships
When designing the mechanical room, it is important not to overlook any plumbing or fire protection elements. Similar to mechanical systems, it is crucial that all the plumbing systems are identified. While there is likely insufficient information to size the plumbing systems early on, a good understanding of the project scope and program elements will inform assumptions, allowing the creation of system diagrams to inform equipment needs.
Meetings with the client and the architect will reinforce the system diagrams and sizing. Are special or isolated systems needed for the program? Are there any requirements for redundant capacity, and will the building or systems grow in the future? It is important to get this feedback early to establish boundaries for system sizing and to help ensure that spaces allocated for these systems decrease with optimization rather than increase.
Plumbing systems are categorized both by their relationship to program elements and their relationship to other building systems. Often plumbing systems are located alongside mechanical systems.
For example, a new laboratory building includes a combined ground-level mechanical/plumbing room adjacent to a small fire riser room (see Figure 2). Fire flow data later determines that a fire pump will be required, but this was not initially planned for. The fire pump must be on the ground level, but what equipment in the plumbing room could be relocated to support it if no other options are available?
The building is planned for natural gas serving water heaters and boilers shown in the mechanical penthouse. Understanding that the natural gas distribution must go to both locations, the plumbing engineer then recommends moving the water heaters to the penthouse near the boilers, where there are more options to optimize the equipment layout (see Figure 3). This change generates additional space on the ground level to support the larger fire pump room without impacting any building program spaces.
Defining System Boundaries
With the systems in the mechanical rooms identified and their relationships established, organizing and laying out the mechanical room can begin. Larger equipment or equipment with significant service clearances are normally placed first, with smaller, more flexible systems designed around them.
Arranging as optimized blocks helps to visualize the relative sizes of systems to each other. This concept simplifies placement in the room and allows different systems to be grouped together based on room geometry, direct access to the outdoors or service elevator, and other criteria.
As is the case with most projects, available mechanical room size tends to decrease over the life of the project as other program elements grow and become more defined for an already limited floor area. Another common condition is that the room area does not change, but the room geometry does, forcing further reorganization of the systems within the mechanical room.
When this occurs, further optimization can come from studying the design concepts of packaged central plants. Packaged central plants are prefabricated in the shop and shipped to the site in pieces. While most packaged central plants become separate structures within an equipment yard, the concept also can be applied to the system equipment skids within a mechanical room.
The biggest limitation of a packaged central plant is that it is shipped on the back of a truck. Each module width is ideally less than 8 feet wide but could extend to a maximum width of 12 feet. That width includes all the equipment connections and service clearances within the enclosure.
However, unlike a packaged central plant, system equipment skids do not have walls. And if properly planned, access can be available on all sides within the mechanical room or prioritized with access to a single side for placement against a wall.
System Diagrams and Mechanical Room Layouts
An optimized system layout will closely follow the system diagram. For example, a project requires a large reverse osmosis (RO) water system to support a laboratory program. From the system diagram, incoming water is first softened, then passes through particulate and carbon filters before reaching the RO system.
While it is not required that the water softeners be located next to the RO system, the other filters want that proximity. As the water softener also has a brine tank, provision is needed for bags of salt.
A similar strategy is used for water-cooled chilled water systems with cooling towers. The cooling towers operate by gravity and, as such, want to have direct adjacency to the chillers. Water-cooled chillers often include tube bundles that need to be cleaned periodically, with significant access requirements in the front or back. Organizing the chillers on an exterior wall with cooling towers can support exterior access for chiller tube cleaning as well as the adjacencies to the cooling towers.
However, moving from a ground-level mechanical room into a penthouse introduces other mechanical systems that begin to take priority. The air-handling units and other HVAC equipment are larger compared to hydronic mechanical and plumbing systems and have specific code requirements for the location of outside air intakes, building exhaust and others.
Ductwork from these systems to shafts may limit the placement of other systems, and large intake louvers may begin to drive aesthetic considerations from architecture.
Optimized Mechanical Room Design
With all the system building blocks in place, the placement of mechanical and plumbing systems within the building established, and proximity to outdoor or other areas defined, the mechanical room design can begin. The following is a step-by-step approach to move through that process and arrive at an optimized solution.
• Step 1: Define program assumptions. Meet early and often with the design team and the client to define systems and recommend placement within the building. As the program evolves and space becomes limited, propose alternate concepts to the team that prioritize what systems must be in select areas and which systems include placement flexibility. Where possible, identify unknowns as risks and propose space allocations should those unknowns become requirements.
• Step 2: Optimize landmark systems. Landmark systems can either be the systems with the largest footprint, smaller systems with specific location requirements, or a combination of both. Defining the preferred location of these systems and their relative sizes begins setting the boundaries for other systems.
If the building dimensions in these landmark system locations are forcing an inefficient solution, what changes in the building design could optimize this? Small changes in the right areas can minimize the footprint of these landmark systems, making more area available to other systems or allowing for an overall area reduction.
• Step 3: Locate larger system blocks, then follow with smaller systems. With the water-cooled chilled water system in the ground-level mechanical room and air-handling units optimized in the penthouse, the next largest system in the penthouse may be the water heating system. As the system serves both the air-handling units and the building, the preferred location is near the air-handling units.
A runaround heat recovery system, common in laboratory buildings, desires proximity to air-handling and exhaust recovery units but is much smaller. As such, its location is more flexible.
• Step 4: Define remaining systems and supporting infrastructure. With the focus on the mechanical and plumbing systems, remember that electrical systems also require space for distribution panels, transformers and other gear with specific clearances for equipment, clear height above, etc. Building control is another trade supporting the efficient operation of these systems and requires space for its panels. Facilities likely also require storage for filters, spare parts, etc., which is often overlooked in the mechanical room design.
• Step 5: An iterative approach to mechanical room optimization. It is extremely rare to land on an optimized solution the first time around. Taking a step back to evaluate the design decisions and consider alternative approaches can lead to further opportunities. Often presenting the approach to others and soliciting feedback identifies other considerations.
These considerations may include additional requirements for exiting that were not accounted for or even further optimization. When designing a new space, don’t limit the design by fixing systems that have yet to be built. Until the building and systems are constructed, there is still room for optimization.
Just as the building evolves from a series of program elements and their relationships, so too does the design of the mechanical room or rooms evolve over the life of the project. Being at the table and participating from the beginning offers the best opportunity to succeed in getting the right-sized mechanical room in the ideal place(s).
Working with the client and the design team toward a common solution and being flexible as programs evolve ensures that even if not ideal, the systems remain optimized for the building.
The best system configurations logically follow their system diagrams, are straightforward, and are grouped together to ease maintenance and system understanding. Prefabricated systems offer insight into improved space optimization and can even offer other benefits such as electrically pre-wired and pre-tested solutions, greatly reducing on-site startup and commissioning.
The evolution of mechanical room design begins by taking a step back to see the big picture and defining the systems, then advocating for an optimized solution integrated into and in harmony with the building and its programs.
Robert Thompson, PE, is a mechanical engineer and principal at SmithGroup. His focus is on science, technology and forensics with an emphasis on sustainability and energy efficiency. Lowell Manalo is the plumbing discipline leader for the western region at SmithGroup. He is a member of the American Society of Plumbing Engineers with more than 20 years of experience designing plumbing systems for various building types.