Multi-Residential Zero Net Energy
This is Parkview Place in downtown Davis, California. It is a new-from-the-ground-up structure that replaced a near-derelict building in downtown Davis and is the collective effort of four couples led by Richard Bourne, P.E., a well-known and respected mechanical engineer of many years’ experience in this region. The building is all-electric, consuming no Carbon.
At left, the building’s flat roof deploys 64 solar PV panels, each producing 335 watts (21,440 watts DC total), which is enough to produce approximately 30,000 AC Kilowatt-hours a year. Two 10 KW inverters are inter-tied to the electric utility via a net energy metering connection. Parkview’s roof also deploys three solar thermal panels for hot water production at a 40° tilt at its center. Eight sets of awnings above south facing windows look remarkably like additional solar panels, but they are shading louvre structures (because more PV was unnecessary).
(14) helix bores to a 22-foot depth provide the equivalent of 5.6 tons of capacity to serve (2) 40 Kbtu water-to-water geo heat pumps.
This remarkable building was ZNE Positive in its first two operational years, exporting more energy from the site than it consumed. Its LEED Platinum Certification by the U.S. Green Building Council in 2015 was the first ever for the City of Davis.
Parkview Place contains 9,260 square feet of conditioned space that supports four owner-occupied dwelling units (just over 1,400 square feet each). The ground floor contains an 860 square foot rental apartment and four common rooms for exercise, gathering, crafts and reading, with a full bath. There is also a garage with four parking spaces, two electric charging stations, and four 8′ x 10′ personal storage spaces. Heating and cooling in Parkview’s conditioned spaces are delivered by radiant in-floor coils with separate zones and thermostats.
The cooling function’s first stage is provided by direct circulation passing through a large ground floor tank of captured rainwater. A heat exchanger in the tank acts as a heat sink for interior heat picked up from radiant circulation. If/when this cannot satisfy interior thermostats, the geo heat pump system chills this same circulating loop for stronger cooling performance.
The rainwater tank is also connected to a Night Sky system which pumps and sprays the roof surface to chill the roof’s skin by evaporation while cooling the water returning to the storage tank. This system minimizes the cooling work which must be done by the geo heat pump and the electrical power consumed. It also cleans dust off the solar panels on hot summer nights. By collecting and re-using rainwater, this building extends its Zero Net Energy status toward an extremely low per capita consumption of water.
As can be seen at right, performance thus far verifies that electric cars should be attached to the building’s two electric charging stations! Surplus production is better used for transportation than for export to the grid.
This project reaches well beyond just simple renewable electricity and the satisfaction of thermal loads. It addresses storm water capture and partial evaporation along with the buffering of cooling loads to minimize mechanical cooling via geo heat pump. This process cannot be compared to a commercial cooling tower for multiple reasons. It is smaller, consumes only water captured during natural rainfall, and serves to clean near-flat mounted solar panels during dry summer weather when natural rain cannot, to maintain maximum solar electric production.
Dick Bourne has worked with a variety of evaporative cooling designs to boost the efficiency of standard air conditioning equipment and Parkview Place’s Night Sky system is a natural extension of that experience.
(Right) This is the vertical helix-style loop that makes Parkview’s heating and cooling possible. Coils of 1/2″ HDPE pipe in a 22-foot deep by 24″ wide auger-drilled borehole circulate loop water to and from the geo heat pump. This heat exchanger was photographed when it was ready for backfilling and after that it was ready for connection to supply/return headers in common with 13 additional boreholes that completed this underground heat exchanger. The lateral headers were buried two feet underground after connections were complete. This wide-auger system of drilling is only possible in silt-sediment soils of the kind found in the central valleys of California or many similar places around the nation. Before backfilling was completed, the gravel-filled, vertical PVC leach pipe was connected to the building’s rainwater capture system. More information about heat exchangers of all kinds is contained on our Ground Loop Types page.
(Below) Five helix coils in collapsed storage/transport configuration wait for deployment until their respective boreholes are drilled on the yellow target markers.