Manufacturers’ advice for systems in office buildings

Two manufacturers of systems used in office buildings provide advice about electrical, cooling, and other engineered stems.

By Consulting-Specifying Engineer October 31, 2013


Kent Walker, Vice president, technical services, Mersen 

Michael Smith, Senior marketing manager, Mitsubishi Electric Heating & Cooling

CSE: What solutions do you provide to engineers for office building projects?

Mersen: Mersen provides a number of tools to help engineers with the protection and coordination of the different building electrical systems, such as programs for the proper selection of overcurrent protection for motor and transformer in the building systems. The same program will also help with the proper coordination of overcurrent devices, which will look at upstream and downstream devices to make sure they both don’t open under a fault condition in the building system. Mersen also provides help with the proper selection of surge protection or overvoltage devices throughout a building system. Our selection tool will take into account things like system voltage, location in the building, and the possible amount of surge currents available throughout a building during overvoltage conditions.

MEHVAC: Our variable refrigerant flow (VRF) zoning systems provide one of the most flexible, cost-effective, and environmentally friendly options in commercial construction today. There are a number of benefits that appeal to engineers, especially for office building projects. With electric INVERTER-driven compressors, our VRF zoning systems offer full-range variable capacity to deliver exactly the amount of conditioned air needed to match a zone’s cooling or heating demand. The systems manage different zones inside a building based on load diversity and usage. As people move around in a building or the sun moves across the building during the day, the system adjusts the capacity delivered to each zone. Our VRF zoning systems share heat energy across zones to provide simultaneous cooling and heating. Depending on the style of the building, VRF zoning systems tend to have fewer components than conventional HVAC systems. This reduces equipment costs, complexity, and installation time, which always appeals to engineers. With discreet indoor units that blend into their environments and compact outdoor units that are easy to install, VRF zoning systems minimize disruptions to a building’s aesthetics.

CSE: Please describe a recent office building project you’ve provided assistance on—share challenges you encountered, how you solved them, and aspects you’re especially proud of.

Mersen: Not our last project, but something we are certainly proud of, was securing the overcurrent protection part of the electrical system in the new Freedom Tower in New York City. The challenge was working with different electrical distributors and working with the consulting engineer—and bringing it all together through the bid process.

MEHVAC: Turner Construction Co., the largest general builder in the United States, decided to relocate its Columbus, Ohio, headquarters to a 30,000-sq-ft historic structure—a factory built in 1910 to manufacture mattress box springs. Turner envisioned a space that would showcase the old bones of the original building, with exposed ceilings that would highlight the circuitry of the HVAC linesets and indoor fan coils. Turner also wanted to achieve a minimum of U.S. Green Building Council LEED Silver certification. There were many challenges at play in this renovation, in terms of energy efficiency, aesthetics, and system control. Our VRF zoning systems were selected because they met each of these challenges. A perfect match for buildings (like Turner) constructed before air conditioning was invented, VRF zoning systems require minimal or no ductwork. And the systems also require less piping and space. Because the VRF zoning system uses smaller refrigerant piping, it gives back space in the form of higher ceilings, which appealed to Turner’s aesthetic goals. As for energy efficiency, VRF zoning technology was critical in enabling the office to achieve LEED Gold. The selected units can cool or heat up to 50 individual zones, maximizing the building design options. Networked control options allow for the management of the building’s HVAC system down to the indoor unit level schedules and setpoints. 

CSE: What factors do you need to take into account regarding building automation systems (BAS) or building management systems (BMS)?

MEHVAC: When considering automation and management systems, take into account what kinds of functions the systems will allow you to monitor. Our commercial controls network together as a seamless, comprehensive system to support functions like dual setpoint and setback, performance data storage, and energy management monitoring. The controls allow users to monitor and operate our VRF zoning systems plus third-party equipment, which means easier, more convenient system-wide HVAC control. Our systems integrate into a building’s BAS via our LonWorks and BACnet interface. 

CSE: What types of tools do you recommend for office building projects? What should be in every engineer’s “toolbox”?

MEHVAC: Building energy modeling software such as the Dept. of Energy’s EnergyPlus gives engineers a faster, streamlined process for energy modeling and is especially helpful in large projects. We find that government clients particularly appreciate the 3-D models that some programs produce. We worked with EnergySoft to develop the VRF zoning system software EnergyPro.

Mersen: I would recommend having Select-A-Fuse and Select-A-SPD in their toolbox. Both are Web-based programs and will help with selection and the proper coordination of overcurrent and overvoltage devices through any electrical system.

CSE: What’s the one factor most commonly overlooked when working on office-building electrical system projects?

Mersen: Proper electrical fuse or circuit breaker selectivity and coordination, meaning making sure only the overcurrent devices closest to any fault condition open without causing other upstream devices to open causing further power outage in the larger buildings.

MEHVAC: It’s easy for engineers to overlook the total lifecycle costs associated with the systems that they specify. It’s important to consider how the performance, maintenance, and flexibility of the systems will affect the building owner and tenants’ bottom lines. Depending on the installation, the total installed cost of a VRF zoning system is often less than or equal to the total installed cost of some conventional systems. But a major difference to consider is in the maintenance, which is greatly reduced. No special trades are required to perform the simple functions of cleaning or changing the filters and cleaning outdoor condensing units. As the needs of the building change over time, a VRF zoning system can easily be adapted to fit that need, especially with the rotation of commercial office tenants who have specific cooling and heating needs. You can move or add and subtract indoor units easily with minimal interruption to system operation. 

CSE: What unique requirements do the HVAC systems have, and what questions/issues have you helped resolve?

MEHVAC: There’s a misperception that VRF zoning systems don’t work well in northern winter temperatures or function in extreme climates. We’re working to curtail this misperception with Hyper-Heating INVERTER-driven compressor technology, which enhances our systems by providing full heating capacity to -4 F outdoor ambient. Also, the low ambient cooling kit accessories are designed to block wind that could impede operation and allow full airflow when required at higher ambient temperatures or in heating mode. Our systems can provide 100% cooling capacity even when it’s -10 F outside.

Mersen: HVAC systems have a unique condition in that many of them are on the roof of the building and are much more susceptible to overcurrent and overvoltage conditions. 

CSE: Fire/life safety systems in office buildings often are a mixture of systems. Describe a recent project in which you provided unique solutions.

Mersen: Fire suppression systems and elevator power systems are often interconnected and need to be looked at more closely. Our elevator switch product allows for that proper interconnection and power isolation before water can flow into the elevator shafts, but due to the multiple fire systems that could be installed, the design engineers need to understand the different options for fire and life safety systems.

CSE: Describe a unique challenge and solution for a recent high-rise or large-scale office building project.

MEHVAC: Union Mill, located in Baltimore, was a uniquely challenging project for our team that has seen remarkable results. A centuries-old mill was restored into a mixed-use complex of 56 apartments, 30,000 sq ft of office space, and a restaurant. Facing stringent green building requirements from the city, the developers set a U.S. Green Building Council LEED Silver goal and projected an overall savings of 450,000 kWh annually. The design team selected our VRF zoning equipment because costs were less than expected and Mitsubishi Electric’s outdoor units are among the quietest available, which met the city’s noise requirements. The team also liked that the outdoor units had a small footprint when compared to conventional systems and that the indoor units come in many configurations, which provided the designers with choices to minimize demolition to the existing structure. The R2-Series simultaneously cools and heats different zones within Union Mill. This energy-saving function happens when heat energy is collected from the zones in cooling mode and then transferred to the zones that require heating. The benefits of the VRF zoning systems helped the building attain the equivalent standards of LEED Silver—and a sizeable rebate check.

Mersen: I would have to restate that Freedom Tower project—its scale, and its longer timelines, multiple buildings, and having to work with multiple switchboard houses caused challenges with the project management part of the project.

CSE: What types of metering or submetering solutions have you provided?

MEHVAC: Through the TG-2000 software, our VRF zoning systems easily integrate tenant billing. Through submetering, office buildings can bill each tenant for its equivalent share of energy use. The tenant billing function of the TG-2000 allows the energy consumption for each zone to be monitored and billed. A single PC (from a remote office) can control and monitor all functions. 

CSE: Have more office buildings been working toward U.S. Green Building Council LEED certification, and if so, how have you helped achieve this certification?

MEHVAC: in our experience, seeking LEED certification is expected of almost all major office building projects today. Building owners report that green buildings generate higher occupancy rates, rental rates, and special prices per square foot. A major reason that VRF zoning systems are poised for such dramatic growth in all areas of commercial construction is that they provide the precise zoned control that leads to LEED certifications. Our systems can contribute a great number of points in the Energy & Atmosphere (EA) and Indoor Environmental Quality (IEQ) categories. LEED v4, which passed in July 2013, contains updates to these two categories, and our systems still meet or exceed these standards. 

Here are some of the specifics: For the EA category, the systems exceed the prerequisite of commissioning by including an integrated control system that provides testing, control, and reporting. Also, the systems exceed ASHRAE Standard 90.1-2010 (new for LEED v4), which calls for a 30% energy improvement over the previous standard. Specifically, the INVERTER-driven compressors, and heat recovery and zone control capabilities provide the best opportunities for energy savings. In terms of IEQ, VRF zoning systems meet the prerequisite minimum performance through indoor units with ventilation connections or integrated dedicated outside air systems. (This enhanced prerequisite incorporates criteria from the LEED 2009 credit for Outdoor Air Delivery Monitoring.) Integrated controls for CO2 monitoring can be incorporated into our systems, and the zoning capability allows occupant control with wall-mounted remote controllers. Lastly, when properly designed into a building, VRF zoning systems provide temperature and humidity control in accordance with ASHRAE guidelines.