Optimizing Water Heating Performance for Multifamily Zero Net Energy
Research Team:
Franklin Energy (prime), AEA, Stone Energy Associates, Redwood Energy
Optimizing Water Heating Performance for Multifamily Zero Net Energy
Research Team:
Franklin Energy (prime), AEA, Stone Energy Associates, Redwood Energy
Challenge
As California approached its 2020 ZNE goal, there was a critical need for more research and evaluation of ZNE multifamily design and construction practices, which were not explicitly addressed in the ZNE Residential Action Plan. In addition, as the carbon reduction opportunity of buildings is better understood, under-researched topics in multifamily buildings are receiving new attention. Although currently there are twice as many single-family residences as apartments in the U.S, multifamily is becoming a larger percentage of new construction. Therefore, it is important to keep a focus on improving the efficiency and grid impacts of multifamily buildings if we are to achieve the State’s climate goals. Multifamily construction is more complex than single-family and presents additional barriers to achieving ZNE, and relatively little empirical data has been gathered on the performance of water heating systems in multifamily buildings, and even less on the energy use patterns for cooking, lighting, appliances, and other plug loads. A host of key design and engineering, modeling, performance, and operational issues remain poorly understood, particularly for emerging all-electric space heating and domestic hot water technologies. These include the performance and economic trade-offs of technology solutions, a lack of agreement between design and actual performance for key emerging technologies, appropriate modeling algorithms for emerging technologies, and a lack of understanding of how these technologies will impact tenants and property managers.
Project Objective
Four multifamily affordable housing demonstration projects offered timely opportunities to investigate ZNE issues in-depth, with the first project completing construction in 2016 and the last one completed in 2019. These projects shared a goal of all-electric ZNE construction with 100% renewable offset, and utilized breakthrough heat pump technologies to serve the buildings’ HVAC and water heating needs. The projects present the opportunity to study different domestic hot water (DHW) systems, which represent the largest load in multifamily projects. The Team monitored second-by-second energy and one-minute interval water usage and apartment electrical end uses in the developments totaling 208 residences with (a) individual heat pump water heaters, (b) central heat pump water heaters, and (c) central combined heat pump system.
The “Optimizing Water Heating Performance for Multifamily ZNE” Research Project addressed the challenge of incorporating these advanced technologies as a pathway to ZNE. The four demonstration projects provided a rich dataset to evaluate how energy was used in multifamily buildings, from domestic hot water systems to electrical end uses, and how the complex, interdependent systems (envelope, mechanical systems, etc.) can work together to achieve ZNE cost-effectively. The project established the feasibility of ZNE for large, low-income multifamily projects. The project will result in refining core best practices for ZNE design, specifications, engineering, installation, codes, and operations to help the multifamily community accelerate its adoption of ZNE technologies and practices.
Impact
Estimated savings are: 865,877 kWh, 14,599 therms, 429 MTCO2