Achieving Net Zero Energy and More!
The Electrical Training Institute (ETI) located in Commerce, California, decided to achieve net zero plus (NZP) status for all of the right reasons. As the training center for the IBEW Local 11 electricians, they wanted to show that they are at the forefront of the dynamic world of power generation and consumption. They made a commitment to put into action, many of the leading edge technologies that will someday become common to those students that they train. Along the way, they wanted to make their focus on supporting local manufacturing and local contractors.
Western Allied was introduced to the project as the design / build mechanical contractor. It was our job to determine the best mechanical system to achieve NZP with consideration to the project budget. Our in-house engineers began working on several scenarios right away. It became evident right away, that much of the existing infrastructure would lend itself easily to e very efficient chilled water VAV system.
We began running load calculations to determine the cooling and heating loads in the building. Since part of the project included adding envelope insulation, providing permanent shading and installing electrochromatic glazing, the loads in the building were bound to change. With all variables accounted for, we determined that the block cooling load would be approximately 175 tons. This is in stark contrast to the 325 tons of capacity that the existing system had.
Existing System: ETI is made up of (3) buildings. The existing HVAC was comprised of (18) constant volume packaged units located at the roofs. Each packaged unit served approximately (3) to (4) classrooms with a Variable Volume Variable Temperature (VVT) zone box for each space. The school encountered many problems with this system since the classrooms served by each packaged unit could only be all heating or all cooling. In addition, the packaged units were slightly oversized, so if only a single classroom that was served by a packaged unit was occupied, there typically wasn’t enough load to keep the unit from cycling constantly.
Our Solution: We replaced each of the packaged units with appropriately sized chilled water, variable volume air handlers. This allowed us to reuse most of the existing duct infrastructure under the roof. In fact, the only duct modifications that were required below the roof were; eliminating the VVT bypass at each unit, replacing oversized VVT boxes with appropriate sized VAV boxes and replacing each of the supply air diffusers with ones sized properly for the airflow that was expected in each space. The advantage of having several smaller air handlers serving similar spaces with similar exposures rather than (1) or (2) centralized air handlers is that we were able to implement more aggressive supply air reset schedules.
We designed a water cooled, variable primary, chilled water plant. However, in order to increase the efficiency of the system, we incorporated heat exchangers that allow us to recover waste heat from the chillers to be used for building heating when needed. This wasn’t just for efficiency, but was also a necessity since the net zero certification that ETI had planned to achieve does not allow the use of gas fired appliances such as boilers. The chiller plant utilizes a 150 ton chiller with magnetic bearing “TurboCor” compressors as well as (2) 30 ton chillers with positive displacement compressors. The DDC control system will activate the TurboCor chiller whenever there is a cooling load but no heating load. If there is a heating load, the smaller chillers are enabled and staged as needed. The TurboCor chiller may be brought on to supplement the small chillers if the load requires it.
Our DDC controls at each zone are tied into the space occupancy sensors. This allows us to only bring on full cooling if we know that the space is actually occupied. If the space is scheduled for occupancy through the BMS scheduler, but the occupancy sensors do not detect anyone in the room, the zone will go to “Standby” until the sensor sees that the room is occupied.
When Western Allied was awarded the project, we were given an energy budget of 337,000 kW-hr per year for the HVAC system in order to achieve the net zero target. Once completed, the building energy model showed that we are expected to actually use only 224,000 kW-hr per year!
NZP ETI is the focus of a documentary directed by Jim Jackson called “Building Below Zero”.