The demands of mixed-use facilities
Mixed-use facilities require engineers to handle several complex components. Here, engineers with experience on such facilities offer advice on bringing successful execution into the mix.
Timothy Chatterton, PE, Project Manager, RMF Engineering, Selbyville, Del.
Kari Engen, PE, CxA, LEED AP, Senior Mechanical Engineer, WD Partners, Dublin, Ohio
Taner Tekin, PE, LEED AP, Project Manager, exp, Maitland, Fla.
John Torre, PE, LEED AP, Principal in Charge of Electrical Engineering Services, OLA Consulting Engineers, Hawthorne, N.Y.
Scott Vollmoeller, PE, LEED AP BD+C, Associate DBIA, Managing Principal, Glumac, Seattle
CSE: What’s the No. 1 trend you see today in the design of mixed-use facilities (facilities that have a mixture of retail and residential units and may include offices, parking space, cultural space, or a variety of other needs)?
Timothy Chatterton: Recently, we have seen an increase in owners requesting variable refrigerant flow (VRF) systems. These types of systems are on the rise in the industry, in general. However, VRF systems do present their own unique challenge in a mixed-use project depending on how many stories a space has and how that space is being used. The biggest challenge when using VRF systems is that they require a separate system to provide outdoor air.
Kari Engen: Becoming more common is the use of a 1st-floor retail strip space, with residential on upper floors. This appears to create more of a community within a single building.
Taner Tekin: The most recent trend we have been seeing in mixed-use projects is the combination of hotel and condo with associated parking and retail spaces. Parking garages are commonly both underground and above ground to meet the number of parking spots required for the project. Office spaces are often thrown into the mix to increase the long-term profitability.
Scott Vollmoeller: What we’re seeing is a push toward maximizing the amount of glazing along the major view corridors, creating amazing amenity spaces (rooftop gardens, comfortable "living room"-type lobbies, etc.) and selecting systems for enhanced energy efficiency to meet current energy codes.
CSE: What other trends should engineers be aware of for such projects in the near future (1 to 3 years)?
Tekin: Engineers should expect to see more projects that include building types with different occupancies. Fire separation and smoke management are some of the challenges engineers have to address when designing these projects. In addition, LEED certification is almost becoming a standard in modern building design, not only in the U.S. but in other countries as well.
Engen: The retail experience appears to be moving toward a shorter time frame for the in-store customer experience, so occupancies are more intermittent.
Vollmoeller: Ensuring systems (mechanical, envelope, shading, etc.) are designed to maximize efficiency in an effort to maximize glazing percentages.
CSE: Please describe a recent mixed-use facility project you’ve worked on—share details about the project including location, building type, systems engineered, team involved, etc.
Engen: The facility was located in a major metropolitan high-density urban location, with a restaurant in a 1st-floor tenant space and residential units on upper floors; the building was circa 1930s with brick façade; MEP systems included variable refrigerant flow HVAC.
Tekin: One of the recent projects that I worked on was a fairly large mixed-use development in South Florida. The complex spans the entire three city blocks with an 18-story hotel, two 17-story residential buildings, one 12-story office building, underground and above-ground parking garages, and retail spaces on the first 2 floors of each building. Total floor space of the project is close to 3 million sq ft. The underground parking garage is beneath the ground floor of the whole site including the streets that divide the city blocks. This required a detailed coordination between the plumbing systems and the structural design, especially in a geographical location where constructing anything below-ground is a challenging task.
CSE: Describe your experience working with the contractor, architect, owner, or other team members in creating a BIM model for such a project.
Vollmoeller: Our BIM experience was limited on this project. However, on other similar projects, we work directly within the architect’s Revit model to develop a coordinated set of design documents for future use by the design-build subcontractors.
Engen: Generally in mixed-use buildings where tenant work is involved, the BIM model work is often segregated; the tenant BIM is a stand-alone kit-of-parts model and the remainder of the building is modeled as part of the shell. Architectural coordination is facilitated through the use of BIM. Opportunities are available for the owner to incorporate BIM into its building management structure; however, this is not yet common practice.
Tekin: Taking the size of the project site into account and the volume of the BIMs that the design team had to work with, it was very challenging to design our systems inside multiple models. Where architects and structural engineers could limit their work to one model at a time, we had systems serving multiple buildings and therefore had to reside in multiple models and travel between models.
CSE: Have you designed any such projects using the integrated project delivery (IPD) method?
Engen: With the advent of LEED v4, this method is more likely to be used. However, our firm has not had exposure to this method.
CSE: What unusual requirements do such projects have from an engineering standpoint?
Engen: The IPD model allows for and encourages more owner participation throughout the design process. During early stages, schematic designs for engineered systems tend to be more openly vetted between all team members. Such a process tends to result in more owner buy-in on systems design decisions. Owners have more confidence in how systems work because of the ongoing collaboration between the engineering team and the owner’s representative.
Vollmoeller: Communication is paramount from all parties.
CSE: Describe the commissioning process for a mixed-use project. At what point was your team brought in, and what changes or suggestions were you able to implement via commissioning?
Vollmoeller: Our commissioning team is most commonly brought in during the design development phase, although a few clients choose to bring us on board during the schematic design phase. The first course of action for commissioning is to define the owner’s project requirements. By working with the owner, architect, and engineers, our commissioning team helps the owner build a full document of HVAC, lighting, water, and energy requirements and desires. This document is used throughout the design and the commissioning process. One of the most important benefits for commissioning is testing the systems after they are installed; but to complete testing, the commissioning team needs to verify that all requirements, settings, and parameters for the equipment are defined in the construction documents. By writing a functional test procedure and providing it for review, the commissioning agent is putting the design and construction team on the same page and verifying that both have buy-off on the operation before any systems are installed and programmed. Common issues that we have found in the commissioning of mixed-use projects are economizers not being setup in the controls, minimum outside-air settings and damper positions not being set, or not allowing outside air in certain situations. If drawing reviews are included in our scope of work, then some recommendations that we commonly make are either defining locations of thermostats and possibly requesting the relocation of thermostats to prevent equipment short cycling. Also, if multiple spaces are a part of the same system, we make sure that the thermostat is located to best serve all spaces and all connected zones are of similar use. For example, not connecting an office space and a fitness room in the same zone.
Tekin: The process is the same as any other building. You just need to understand the appropriate sampling rate for each usage type and also determine if certain usage types require additional system types to be commissioned. Our team is typically brought on board early in the design phase, and the biggest changes/suggestions we typically make are to help clarify the control sequences so that the high-performance systems will actually work.
CSE: Describe a large mixed-use development you recently worked on. This may include a campus-style development with residential, cultural, industrial, retail, and other building types.
Engen: A recent large development project included a multiple-building, mixed-use facility that included an office building with parking levels, a high-rise residential building with 1st-floor retail, and several retail buildings. It was a lifestyle-center-type application.
Tekin: A large mixed-use development I worked on was Mandarin Oriental hotel and residences in Boca Raton, Fla. This project is in the second and third phases of a three-phase project, with two 12-story buildings connected to a 2-story bridge totaling up to more than 1 million sq ft. Two underground and two above-ground levels provide parking for both hotel and residences as well as ground-level retail spaces, which include an upscale shop and restaurants. The hotel was designed as a five-star hotel with rooftop pool and amenities, 158 rooms and suites, spa, ballroom and meeting rooms, and a private club.
CSE: What types of metering and submetering are building owners requesting? This may include electrical or HVAC systems.
John Torre: We have seen that submetering for residential tenants has become more popular, with direct utility metering for retail tenants. Submetering equipment generally requires less space than utility metering equipment. Submetering also helps minimize and simplify the electrical distribution system for the residential portion of the building, which reduces construction costs.
Tekin: Submetering is typical for spaces such as retail, restaurant, storage, etc. One of the challenges of submetering is when a space is powered or cooled from a system in the building where it is located, but the space isn’t actually within the limits of the building entity where the space belongs. For example, if a condo’s storage room is located inside an underground parking garage and it has to be powered from the hotel electrical panel; this room has to be submetered to monitor the power usage. Also, if the project is phased, the design should allow for separation of the phases so that a future change in ownership can be achieved flawlessly.
Chatterton: Owners on our recent projects have been requesting submeters for electric, gas, and water. I do not see this changing until something in the codes requires HVAC systems to be metered.
Vollmoeller: Seattle’s code requires electrical and centralized hot water submetering for projects over a certain size. In addition to those, our clients are requesting submeters for cold water and, potentially, natural gas.
Engen: Submetering of water services is common, where the landlord bills the tenants for water usage. For large water-cooled HVAC system-driven buildings, there is at least one example of a building owner requesting water metering of the condenser water feeds into retail tenant space.