Interface Engineering provided mechanical, electrical, plumbing engineering, and Fire Life Safety as well as sustainable consulting services that included energy modeling. The project consists of a new 220,000 square foot, six story office building that includes office spaces, a 240,000 square foot underground garage, and retail space.
The developer, during the time of a terrible economy (2011) challenged the team with several constraints:
- The building could not have mechanical equipment on the roof due to height limitations imposed on the project which were inclusive of equipment on the roof.
- The systems had to be below market (i.e. cheaper than the typical central plant and VAV systems)
- The systems had to fit within constrained floor to floor head heights, minimizing duct sizes.
- The design had to maximize floor space.
- The design had to maximize the ability to pursue any tenant with needs for any capacity of loads (i.e. high tech with high computer loads or law firm with low loads).
- The design had to offset as much first cost as possible without delaying construction until a tenant was in place (i.e. putting central plants in the basement garage were not an option)
The design implemented, maximized floor heights and achieve all the goals set forth by the developer.
The project achieved the goals using a water-cooled variable refrigerant system. The system implemented full heat recovery to insure all interior cooling loads provided the heating needed at the perimeter of the building while providing all auxiliary heating needs at very high COP’s in comparison to a traditional gas boiler system. The system also never uses any reheat throughout the building.
The building design also incorporated LED lighting throughout to minimize lighting and glazing optimization to maximize both passive heating as well as daylighting for the future tenants.
Energy modeling was performed at each stage of the project to inform design decisions and help the team select a high efficiency VRF system with heat recovery and an optimized southern overhang shading system. The result was a predicted 32% energy savings, reducing the EUI from 66.8 to 45.5 over the ASHRAE baseline building. The project pursued Title 24 energy code compliance using the performance method, demonstrating 15.6% savings over a baseline building.
Indoor Air Quality
The project, without being able to use the roof for ventilation systems, used horizontal injections system on two sides of the building and natural relief air on two sides of the building, basically a reverse natural ventilation scheme. This resolved several issues:
- Equipment on the roof.
- Small ductwork with no shafts, maximizing leaseable square footage.
- High level of ventilation control and variable capacity depending on tenant.
- Demand based ventilation on each floor.
- Filtration at each floor.
- Low fan energy usage due to limited duct runs.
- Zero energy for pressure relief which was achieved through modulating louvers on two sides of each floor.
At the time of design conceptualization (2011), variable refrigerant fan coil systems were not used in large commercial developer buildings in the Bay Area. However, the use of the system proposed provided all the advantages noted but most importantly had two major attractions to a developer:
Took up almost no floor space (there are no shafts within the building footprint except for toilet exhaust) and there are no mechanical rooms other than one small pump room in the garage and one small closet for housing the condensers on each floor. The savings of floor space at an estimated rent (back then) of $40/sf (today closer to $60/sf) increased revenue for the client of $48,000 per year. The savings of a central plant space in the basement freed up over twenty parking spaces, again increasing revenue.
Since systems did not have to be installed during the core and shell, the Developer could market to any tenant with any load desired which was important during the economic downturn as the market for viable tenants were not known. It also offset cost at approximately $25/sf or $5,500,000 until a revenue source (lease) was identified.
Operation and maintenance
Prior to committing to a variable refrigerant system, Interface Engineering and the developer engaged a third party maintenance contractor to provide a maintenance and operations budget between the system proposed and a typical water cooled VAV system with gas heating and reheat piping distribution. At the time of comparison the M&O costs returned as negligible difference between the two systems.
The systems was not just cost neutral, it was lower than traditional costs at the time even though mechanical sub-contractors were not yet fully familiar on the system at that time. The reduction in first cost helped the project become more viable to start construction which allowed construction to complete as the boom happened in the Bay Area. As a result, the developer was able to secure a full building lease prior to the completion of the core and shell.
As a result of the integrated design process to optimize the building’s envelope, lighting, mechanical, and plumbing systems the building significantly reduced the consumption of fossil fuels and water. The building’s 32% energy savings equates to a greenhouse gas reduction of 2,343 Metric Tons annually.