Parkview Place, a Zero Net Energy six-condominium project, is a living fact on the ground at 4th and D streets in Davis.
Fully occupied, the project may be the first in Davis which produces more energy than it consumes and was built at a commercially-competitive price. Honda House, a Zero Net Energy single-family home on the UCDavis campus, has not made public the cost of the demonstration project, but it is not expected to be competitive in the current market.
The project was engineered by Dick Bourne, founder of the Western Cooling Efficiency Center at UCDavis, and designed by Mike Corbett, former Davis Mayor and developer of Village Homes. It was conceived by Dick and Carol Bourne and five other couples who wanted to age in place in bikeable downtown Davis and advance the idea of zero net energy construction.
The project incorporates several technologies that were developed by Bourne and his associates, including NightSky cooling, cost-effective coiled, plastic tube heat exchangers for a geothermal heat pump which supplies water to radiant floor heating and cooling. The heat pumps do triple duty, heating domestic water, space heating and auxiliary cooling. Primary domestic water heating provided by thermal solar collectors.
A 20-kw roof-mounted solar photovoltaic is expected to produce 30,000 kilowatt hours of electricity, 3000 kwH more than the building will use. A Night Sky cooled water tank on the roof sprays water on the roof to cool the upper floors and clean the solar collectors.
The building is oriented north/south according to passive solar energy principles.
Although the project was unanimously supported by the City Council, it was initially turned down by the Planning Commission. It seemed to be inconsistent with the city’s core-area plan. Fortunately, the Council disagreed.
Bourne has supplied the following technical details:
Our 20 kW roof-mounted SunPower photovoltaic system generates electricity and is sized for “net zero” performance. When the PV system generates more energy than we are using, surplus flows out into the electric grid. When used exceeds PV output, the building draws power from the grid. Projected annual PV output is about 30,000 kWh and project total energy use in the building is about 27,000 kWh. Washing the PV each night with the NightSky systems maintains full output.
Cooling arrives via water circulated in the radiant floor loops, pumped either from the water tank under our storage units (primary), or from the heat pumps in cooling mode (secondary). Tank water is cooled at night when pumped up and sprayed on the roof. When high night temperatures or winds prevent the NightSky system from supplying all cooling, the heat pumps are activated to pre-cool the radiant floors, but the heat pump operation is not allowed during summer on-peak hours.
Heat pumps are reversible air-conditioners; in heating mode, a heat pump moves heat from outdoors to indoor. The warmer the source, the more efficient the operation; in winter, it is better to extract heat from the ground than from outdoor air. Ground-coupled heat pumps are less expensive to operate than the best gas heating systems.
The two geothermal heat pumps extract heat from the ground loops and efficiently deliver warm water through the radiant floors upon command from the ten zone thermostats (two each in the upstairs apartments, one in the ground floor apartment, and one in the common space.)
NightSky sprays stored water on the roof and solar array at night, cooling water by radiating to the sky and cleaning solar panels. Cooled water collected in the gutter drains through a filter into the 11,000 gallon tank under the garage storage units. Stored cool water is pumped through radiant floors to cool the building.
Heating and cooling is from one-half inch diameter high density polyethylene tubing embedded in six inch center in two inch concrete over the wood-framed floor. Heating water is from the heat pumps, and cooling water is from either the NightSky tank (primary) or head pumps (secondary). Each upper floor apartment has separate control bedroom and living zones.
Two ground-coupled heat pumps provide comfort heating, auxiliary domestic water heating, and auxiliary comfort cooling.
The geothermal system transfers heat from the ground into the building. The heat pumps extract heat from an anti-freeze solution pumped through 16-20 foot deep helical ground loops along south and east sides. Heat pumps boost the temperature, then deliver warm water to the radiant floors and domestic water. Our 22 inch diameter helical ground heat exchangers offer a cost-effective option for the geothermal heat pump industry.
Pressurized water is heated as it flows through plastic tube heat exchangers in the non-pressurized, 600 gallon hot water tank under the stairs. Heated water is supplied to the showers, faucets and clothes washers. The tank is heated from plastic heat exchangers; one connects to the rooftop solar collectors (primary); the other to the heat pumps (secondary). The heat pump is only activated for water heating when the solar loop is inadequate.