Sustainability – College Heights

College Heights seeks to achieve sustainability on multiple fronts. These fronts include sustainably sourced eco- and human-friendly construction materials and methods; side-by-side row house construction for conservation of materials; energy-efficient appliances, fixtures, heating and air conditioning for maximum comfort while maintaining sustainability.

Construction

Green Building Materials

Sustainably sourced lumber (certified by the Forest Stewardship Council or similar reputable certifier)
Health- and Eco-friendly paints and finishes
Low waste, high efficiency building techniques and materials
Rain screen siding which discourages mold

Air: Local and Global

Reduced fossil fuel use, less greenhouse gas production
Lowered dependency on oil
Resistance to rising fossil fuel costs
Reduced use of cars
Less air pollution from lower neighborhood traffic and congestion

Water

Water efficiency: fixtures, reduced inside and outside water use
Rainwater barrels for roof run-off collection for landscape use
Rainwater retention using large trickle-out pipes under walkways; zero runoff
Absorption on-site of rainwater and grey water for irrigation
Landscaping using drought tolerant, native plants, reducing irrigation needs
Less water pollution from oil drippage and other auto related pollution
Grasscrete for permeability

Land

Efficient use of land saves farmland and wildlife habitat
Housing clusters reduce walls and overall footprint
Conservation of the Crevice Creek riparian zone

Energy

Passive and Active Energy

The combination of passive and active energy support no net electricity from the grid over the course of a year–“net zero”–with electrical use in winter balanced by electrical generation in summer. Solar energy provides all domestic hot water, air conditioning, air cleaning, air renewal, and all electric uses.

Passive Energy

Heat retention is built into the building envelope. Passive energy design reduces the cost of active energy. It keeps warm air inside in cold weather and hot air outside in hot weather.

Three-story cross section. Three story row townhouses have the best cross section of depth and height for energy conservation. The depth of a building is influenced by how far sunlight can penetrate into a room, which, in a row house, is from the windows in front to those in back. Rooms not needing light, like bathrooms, closets, laundry rooms, hallways, and stairways, can be in the center, while living, dining, and bedrooms which need light from the outside are designed to be in the front and back. Room depths in the project range from 12 to 16 feet, with overall building depths of about 32 feet.

All units are three stories and 32 feet high, creating a square cross-section of depth to height. A square building is more energy conserving than a tall rectangular building which loses heat off the sides, and shorter rectangular buildings which lose more heat through the roof.

Solar roof area and living space. The roof area used for solar energy can serve about three floors of living space below. One and two story units have surplus roof area and higher buildings do not have enough for net zero.

Insulation. Abutting side walls provide insulation from side-by-side construction, allowing for thicker walls and more insulation. Current California building code allows 2×6 inch studs on two-foot centers. Radiant barrier roof sheathing can reflect heat both ways, keeping heat inside in winter and reflecting heat outward in summer. The total result of these measures is high insulation, R-30 or higher.

Windows and doors. High-efficiency windows avoid major heat-loss or gain. College Heights’ design calls for high-quality, double-paned, sound-rated windows with Low-E coatings and fiberglass frames.

Tight construction seals leaks and stops air from escaping. Tight construction of the building envelope is assessed with a blower door based on the amount of resistance to air pressure.

Heat Recovery Ventilators. Tight construction results in stagnant air and excess humidity, requiring Heat Recovery Ventilators to circulate with outside air. Then, to recover heat, the ventilators have baffles for heat exchange. Recovering heat from the out-going air reduces the ventilation energy requirement by up to 80%. The ventilators also filter dust from indoor air.

South windows. Large windows face south so the sun shines on the floor inside. The flooring would be a thermal mass designed to absorb heat. Solar panels outside above the windows increase shade in summer while letting the lower winter sun come in.

Passive energy is built in during design and construction. Three story row housing optimizes building energy conservation, using 2”x6” studs, not 2”x4”, creates space for more insulation in walls. The project may also use Structurally Insulated Panels (SIPs), which provide greater energy efficiency than standard “stick building.” SIPs are from 30% to 60% more efficient. A 6″ SIPs wall has an R-Value of 21.6 while a 6″ stud wall has an R-Value of 13.7.

Doors and windows are energy conserving. R-26 insulation for walls and R-50 for ceiling exceeds California Title 24 energy regulations.

Air exchangers with air filters and whole house fans keep the air circulating to maintain indoor air quality, continuously refreshing the air when windows are closed.

Reflective exterior building materials and double-glazed, reflective windows make efficient use of the sun’s energy, shielding from heat in the summer and maximizing light in the winter. Skylights and clerestories with exterior sunshades, awnings provide natural light to interiors and avoid bright/dark interior lighting contrast caused by direct sun.

Active Energy

The solar active energy system is sold separately from housing, reducing housing cost. It is paid for at time of purchase by direct purchase or by a lease. The cost is generally below a typical PG&E bill. Separate solar energy financing makes the mortgage on the unit more affordable.

Active Energy: Thermal

Active energy: the Thermal System

A combination of shifting regulations, expanded manufacturing, and high-capacity commercial technology has made solar panels, batteries, and heat pump systems the undisputed affordability standard for multi-family developments.

Solar panels are also called modules, collectors, or arrays. They are mounted on metal frame racks on a roof and tilted optimally toward the sun. The active energy system divides between thermal and electrical. PV means photovoltaic electricity created by sunlight on photovoltaic cells on solar panels.

The thermal system components are:

Mini-Split Heat pumps
Domestic hot water
Heated towel racks.

1. Mini-split Heat pumps

Mini-split heat pumps are called split because they have an outside unit split from inside units.

The system uses a refrigerant, a special fluid which optimally goes back and forth between being a gas and a liquid. When the liquid evaporates into a gas, it absorbs energy and cools the copper pipe it is in, like water evaporating off the back of your hand. When the gas condenses to liquid, it releases energy and warms up the copper pipe.

An air-source heat pump on the roof does both heating and cooling. It takes the refrigerant and pumps it to mini-split units in the room for air conditioning.

Tre goes to an Electronic Expansion Valve (EEV) on the mini-split in the room, which allows the refrigerant to enter the coils and, not under pressure, evaporate, which cools the coils and thus the room.

2. Domestic hot water

Hot water uses Heat Pump Water Heaters (HPWHs) separate from air conditioning. HPWHs are highly efficient, small hot water tanks in each unit. They are about one fourth the size of a conventional 80 gallon hot water tank. They extract heat from the surrounding indoor air with a Coefficient of Performance (COP) up to 4.0. Rather than storing large amounts of hot water, they meet short-term spikes in use e.g., for showers, dishwashing, etc.

3. Heated towel racks

These towel bars use hot water to dry towels and heat bathrooms.