Page 48 - Designing for Zero Carbon-Volume 2_Case Studies of All-Electric Multifamily Residential Buildings

CASE STUDY NO. 2
ROSECRANS PLACE
PORCELAIN TILE
R-38
R-19
R-21
R-15
(Above) Typical wall section used at multifamily buildings.
Building Envelope – Insulation and Windows
The three-story buildings are conventional wood-frame construction, using 2 x 6 framing for the walls and truss-joist floor and roof assemblies. Insulation levels meet or exceed the Title-24 requirements for the building envelope, with R-19 walls and R-38 roofs as the standard. The concrete ground-floor construction is typical uninsulated slab-on-grade with no edge insulation. (See typical wall section diagram at left.)
Windows used in the exterior walls also satisfy the minimum requirements of California Title-24 code, with a standard double-glazed product.
Building Envelope – Airtightness
No special measures, such as a Blower Door test1, were taken with this new construction to ensure airtightness other than “good practices” to control air infiltration heating/cooling energy losses.
Heating, Ventilating and Cooling Systems
Each residential unit is provided with its own ducted-air heat pump system. The condenser unit is mounted on the flat roof of each unit and is connected to a fan coil unit just below the roof level. Refrigerant circulates between these two parts of the heat pump, providing either heated or chilled coils at the fan coil to heat or chill the air being circulated throughout the unit. The con- ditioned air is supplied to and returned from the various rooms and spaces in the house through a conventional duct system, as shown in the diagrams for a typical townhouse and live-work design on the opposite page.
Air exhausted is exhausted from from bathrooms and kitchens by conventional means. No ener- gy recovery ventilator (ERV) is used, which would recover some energy via a thermal exchange process between incoming fresh air and conditioned air being exhausted.
Domestic Hot Water Systems
The heat pump also provides heating for the domestic hot water supply in the unit, known as a “hybrid heat pump” application. The heated water is stored in a tank, usually located in a utility closet. Since the Californnia energy code does not allow “tankless” electric water heaters, this is an additional space requirement for all-electric residential units, albeit a small one.
PLASTER EYE-BROW
PORCELAIN TILE
STUCCO FINISH
STONE VENEER
1 For a discussion of this method of testing air-tightness in buildings, see p. 12, Zero Net Energy Case Study Homes - Volume 1, available as a free PDF at https://calbem.ibpsa.us/wp- content/uploads/2020/04/ZNE-Case-Study-Homes-Volume-1.pdf. See also https://www.energy. gov/energysaver/blower-door-tests.
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Designing for Zero Carbon: Volume 2