What are some technical considerations a building owner/developer should think about when electrifying a central domestic hot water system in a multifamily building?

Electrifying a central domestic hot water system (DHW) in an existing multifamily building requires careful planning. The project will need to balance first cost, operating cost, and energy funding considerations when selecting the electric DHW retrofit technology. Electric resistance, heat pump, and dual fuel systems all have pros and cons that should be explored in the context of the site and local utility tariff rates. It is recommended that a design engineer with electric DHW multifamily retrofit experience produce drawings for the permitting and bidding process. Additionally, a third-party commissioning agent should be engaged to help ensure a quality installation. Finally, for larger buildings, it may be worth engaging with an energy consultant to evaluate utility cost impacts.   

Key technical considerations include: 

• Constructibility considerations should be fully explored during early design and technology selection:  
  • Added electrical service, and possible coordination with the electric utility, may be required and could pose cost obstacles. 
  • Heat pump DHW plants often require more space for hot water storage, which can be tricky in tight mechanical rooms. 
  • Consider impacts from heat pump DHW compressor sound levels. If heat pump components will be located in an indoor space, plan for cold exhaust air.  
  • Central heat pump DHW systems typically require substantially sized outdoor equipment. Determine if the property has space for ground or roof mounting. 
• DHW distribution loops may have undiagnosed heat loss issues that existing boilers plant compensate for via extra capacity and quicker recovery times. Heat loss issues can include hot water crossover, uninsulated distribution pipes, and other existing building conditions. Heat Pump DHW plants typically have slower recovery times, especially when heating water in heat pump mode. Diagnosing and fixing DHW loop heat loss issues is an important first step. 
• Appropriately size the electrified DHW plant and hot water storage for the true demand of the building based on existing water fixtures and usage patterns. 
• Evaluate if components of the existing system can be reused, or serve as a backup system. 
• Projects in cold climates should take special care with heat pump technology selection, equipment location. and back-up heat sources.  

For more information, the Building America Solutions Center offers general guidance for central heat pump water heaters in multifamily buildings.