Electric HVAC Systems
2019 Title 24, Part 6 provided an alternative pathway for all-electric HVAC system for low-rise residential buildings(three stories or less) in both the prescriptive and performance pathways. The Energy Commission changed low-rise residential HVAC baselines such that the baseline system fuel type is the same as the proposed system fuel type. For buildings with electric space heating, the baseline is a minimum efficiency heat pump system.
The 2019 Title 24, Part 6performance baseline is a central furnace with split direct expansion (splitDX) for mid-rise buildings (four to seven floors) and a four-pipe fan coil (FPFC) system for high-rise buildings (eight floors and more) regardless of the fuel used for the proposed building. As part of the 2019 Title 24, Part 6 post-adoption process, the Energy Commission is working with decarbonization advocates to minimize the impact of this baseline on all-electric buildings. A study coordinated by NRDC and supported by several designers, engineers and consultants including members of the Statewide CASE Team showed that the four-pipe fan coil system in particular is the primary challenge for all-electric multifamily buildings. As seen in Table 4, using any heat pump system–even those that are the most efficient in the market –result in significant TDV penalties since they are compared to a baseline of aFPFC system for high-rise buildings. For mid-rise multifamily buildings, using a heat pump also results in a compliance penalty when compared to a natural gas-fired furnace and split DX but this penalty is much smaller than that for high-rise multifamily.
The Energy Commission has proposed to change the high-rise baseline for eight floors and above to be the same as that for four to seven floors –split DX for cooling and gas-fired furnace for heating. This CASE Report builds on this proposed realignment of the baseline and the analysis presented in later sections of this document assumes this proposed change to the system baseline for high-rise multifamily buildings
Central Heat Pump Water Heater (HPWH) Systems
Central HPWH systems use electricity to produce hot water by transferring heat energy from one source, typically air,to potable water. This process can be two to three times more energy efficient than a fossil-gas or electric-resistance water heating system. HPWH is also a key technology to decarbonize domestic water heating as the system uses electricity instead of fossil fuel.
Central HPWH systems are DHW systems with recirculation loop designed to deliver hot water produced by HPWH equipment from a centralized location to multiple end users. Several successful central HPWH designs have been implemented and are operational in California and Washington.However, energy performance of the systems is highly dependent on design and not guaranteed. Example design considerations reported from several field studies include:
- Heat pump water heaters require low entering water temperature and warm incoming air temperature to operate at high efficiencies.
- Design variables critical to system performance include energy loss in the distribution system, hot water usage by occupants, and hot water draw schedules throughout a multifamily building.
- Stratification strategies such as tank sizing and piping configuration keep HPWHs operating at desirable conditions.
- Multiple modules of a water heater can operate in parallel to increase overall capacity, and each heat pump water heater model has different performance characteristics.
In the 2019 Title 24, Part 6, low-rise residential DHW baseline is an electric HPWH when the proposed system is a heat pump or electric resistance system serving individual dwelling unit or serving multiple dwelling unit with no recirculating loops. The prescriptive pathway allows either heat pump water heaters meeting federally regulated efficiency levels along with supporting measures such as compact hot water distribution, drain water heat recovery or a Northwest Energy Efficiency Alliance (NEEA) Tier-III rated heat pump water heater. NEEA Tier-III rated equipment represent the most efficient heat pump water heaters available in the market that are rated to perform at outdoor conditions found in cold climate locations. The performance approach uses the federal minimum efficiency heat pump water heater along with the associated measures.
Under 2019 Title 24, Part 6 code, the high-rise residential DHW baseline follows the same rules as low-rise residential buildings. The 2016 Title 24, Part 6 baseline DHW was gas water heater regardless of the proposed system fuel type.
2019 Title 24, Part 6 provides an alternative performance approach for HPWHs that serve more than one and up to eight units without the use of recirculation loops or pumps. This option is often called a ‘clustered’ design or approach. Under 2019 Title 24, Part 6, the clustered approach is considered analogous to the individual heat pump water heater approach and does not incur any compliance penalties.
Under the 2019 Title 24, Part 6 as well as previous code iterations,there is no prescriptive or performance pathway for central HPWH with recirculation. As of January 2020,central HPWH with recirculation cannot be modeled in the official compliance software. Current prescriptive and performance limitations effectively eliminate a designer’s ability to replace a conventional central gas-fired water heater including recirculation with a central heat pump water heater. As a consequence, proponents of central HPWH design shave to resort to reconfiguring their preferred design approaches for high-rise multifamily buildings (i.e., central HPWH with recirculation serving the entire building) to comply within the constraints of the energy code compliance tools.Some local jurisdictions have allowed modeling central heat pump water heaters as minimally efficient natural gas boilers,but this adjustment is not universally accepted,nor is it endorsed or supported by the Energy Commission.
On Dec 19,2019, the Energy Commission provided an Executive Director Determination Pursuant to Section 150.1 (c)8Cthat allows central HPHW systems that meet specified design and installation criteria,in addition to solar thermal or photovoltaic (PV) system requirements,to show compliancewith2019 Title 24, Part 6under the prescriptive path(California Energy Commission 2019).The specified design allowed under this exception is a single-pass system with a specific configuration of heat pump water heaters, storage tanks, valves and other controls. The Energy Commission is also developing modeling capabilities within the compliance software to model the performance of this specified system with an expected release date in the first quarter of 2020.
This measure is not required nor adequately modeled by other codes, such as the International Energy Conservation Code (IECC) and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 90.1, or voluntary rating systems, such as Leadership in Energy and Environmental Design (LEED) and ENERGY STAR®.
Electric Appliances and Miscellaneous Load
The Residential ACM Reference Manual applicable to low-rise multifamily (three stories or less) contains a methodology for calculating appliances and miscellaneous loads that accounts for the specific appliances included in the dwelling units as well as the size of the dwelling unit and number of bedrooms. This appliance and miscellaneous load is used both to calculate internal loads for space conditioning as well as total energy consumption for the whole building energy use using the Energy Design Rating (EDR) compliance approach. However, the Nonresidential ACM Reference Manual applicable to high-rise multifamily (four stories or more) contains a fixed plug load density of 0.50 W/ft2with no accounting for the specific appliances in the dwelling units or the size of the dwelling unit, or number of bedrooms. The Statewide CASE Team proposes that dwelling units in high-rise residential buildings to use values and calculation methods from the Residential ACM Reference Manual.
Measure proposals, supporting documents, and other outside references will be made public as they become available.
Round Two Utility-Sponsored Stakeholder Meeting Materials
- Presentation – March 17 – Multifamily Water Heating and All Electric Package (Updated 4/13)
- Multifamily All Electric Package Submeasure Summary (Updated 4/13)
- Multifamily Central Heat Pump Water Heating Submeasure Summary
- Notes – March 17 – Multifamily Water Heating and All Electric Package
Round One Utility-Sponsored Stakeholder Meeting Materials
- Multifamily All Electric Submeasure Summary – July 30, 2019
- Multifamily Central Heat Pump Water Heating Submeasure Summary – August 22, 2019
- Presentation – Sept 10 – Grid Integration Utility-Sponsored Stakeholder Meeting
- Notes – Sept 10 – Grid Integration Utility-Sponsored Stakeholder Meeting
- Notes – Sept 5 – Nonresidential and Multifamily Outdoor Sources and Daylighting Stakeholder Meeting
Give Us Your Feedback
The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.
Use the form above to provide feedback on this measure.