Multifunction Mechanical Systems

This RMI briefing evaluates three 'retrofit-ready' multifunction mechanical system approaches—fully packaged, partially packaged, and distributed—designed to reduce the cost and disruption of decarbonizing multifamily buildings in California by integrating heating, cooling, ventilation, and hot water systems.

• The 'fully packaged' approach utilizes an all-in-one-box system providing heating, cooling, DHW, and energy recovery ventilation (ERV). An example is the Systemair Genius, which uses R32 refrigerant and is housed in a 3’ x 3’ x 7’ enclosure consisting of a base module (40-gallon hot water tank, pump, electrical components), a middle module (heat pump, compressor, heat exchangers, refrigerant circuit), and a top module (heat recovery ventilator with enthalpy flywheel and fans). It requires a single 40A, 240V electrical connection.
• The 'partially packaged' approach, exemplified by the Villara AquaThermAire (AQTA) using R454b refrigerant, provides heating, cooling, and DHW via a single compressor. It consists of an off-the-shelf air handler, a proprietary hot water tank without a backup electric resistance heater, and an outdoor condenser/compressor unit. The system can perform heat recovery by rejecting heat from cooling into the DHW tank and uses stored hot water to defrost the coil, reducing defrost cycle times to two to three minutes and preventing cold air from blowing into heated spaces.
• The 'distributed' approach uses room-by-room through-wall equipment for space heating, cooling, and ventilation, paired with a separate heat pump water heating system. The Ephoca All-In-One Wall Mount (AIO WM) + ERV uses R32 refrigerant and provides ductless conditioning and energy recovery ventilation. This can be paired with a centralized system like the SanCO2, which uses R744 refrigerant and inverter-driven heat pumps with 119-gallon storage tanks to provide hot water to multiple apartments.
• Multifunction mechanical systems are proposed as a solution to the high cost and disruption of building decarbonization retrofits in existing homes, where extensive modifications are typically required to accommodate replacement technologies. By combining heating, cooling, ventilation, and hot water into 'retrofit-ready' packages, these systems aim to streamline installation and improve performance through coordinated controls and heat recovery.

APA

RMI (2025). Multifunction Mechanical Systems. https://rmi.org/resources/multifunction-mechanical-systems/

Chicago

RMI. Multifunction Mechanical Systems. 2025. https://rmi.org/resources/multifunction-mechanical-systems/.

Wikipedia

{{cite report |author=RMI |title=Multifunction Mechanical Systems |date=15 April 2025 |url=https://rmi.org/resources/multifunction-mechanical-systems/ |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{rmi2025multifunction, author = {{RMI}}, title = {{Multifunction Mechanical Systems}}, institution = {RMI}, year = {2025}, month = apr, url = {https://rmi.org/resources/multifunction-mechanical-systems/}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }