On a trip to Mumbai, where he grew up, co-owner Anjan Mitra was thrilled to see how dynamic
and urban the Indian city had become. The new Dosa on Fillmore space offered the opportunity
to capture that urban experience in a fully organic, sustainable restaurant.
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160–170°F (71–77°C) water into the storage
tank on summer days, 140–150°F (60–66°C) in
shoulder seasons, and in inclement weather and
winter about 90–120°F ( 32–49°C). The well-
insulated tank keeps the water at the collection
temperature into the night.
The city itself presents challenges as well.
The microclimates of San Francisco are a part of
everyday commentary from residents and visitors
alike. Locals always qualify the question, “How’s
the weather?” with the addition of “… in your
neighborhood?” Sun, fog, wind and temperature
ranges are not only seasonal, but can vary daily
and even hourly between different parts of the
city. Providing a constant supply of hot water to
a restaurant, no matter the weather, is imperative
to keep business running smoothly.
Because of these system constraints, Dosa’s
solar water-heating system was designed as a
preheating unit for a standard boiler. Energy
conservation is achieved by bringing preheated
water to the gas-fired boiler instead of having to
heat water from the average tap temperature of
55°F ( 13°C).
Design consultants at Sun Light & Power
recommended that an active, closed-loop solar
thermal system for water heating would best
meet the needs at Dosa. The system allows
for the most efficient use of limited roof space
and the quickest return on investment. Ten
Heliodyne Gobi 410 flat-plate collectors were
mounted on the roof and tie into a 585-gallon
( 2.2-kiloliter) hot water-storage tank (Hanson
Tank GS-48-585-V), producing the equivalent of
28,130 kilowatt-hours per year for the restaurant.
The system is expected to consistently deliver
Plans were made to install the future DC-to-AC
photovoltaic inverters on the northwest corner
of the roof, mounted on the parapet wall. AC
wiring has already been run from the invert-
ers location directly down to the point of grid
interconnection at the main electrical service
panel in a 2-inch conduit. To provide for future
web-based monitoring of the photovoltaic sys-
tem, additional conduit was run to the service
panel and CAT5 cable was run from the office
internet router to the service panel. These steps
provide for a future hardwired monitoring sys-
tem that will ensure proper data reporting and
consistent connectivity between the inverters
and the on-site internet hub.
Space in a restaurant is always at a premium
— if it isn’t being used to seat customers, it
needs to be used for food preparation, distribution and storage. So the placement of the
4-foot-wide by 8.5-foot-tall (1.2-meter-wide
by 2.6-meter-tall) storage tank had to be taken
into consideration. Ideally, mechanical equipment of this size would be located on the roof
to minimize the loss of usable interior space.
When full, however, the tank weighs in excess
of 5,000 pounds, or 2,268 kilograms, and the
existing roof structure was not built to handle
that amount of point load. Floor space in the
kitchen area was already tight, so the mezzanine was the chosen alternative. Located over
the original concrete bank vault, the vault itself
provided the structural framework necessary to
support the full tank. This interior location also
reduces the heat loss that could have occurred
from ambient temperature swings on the roof,
while mitigating wear and tear on the equipment and fittings from the outside air.
Not all of the desired solar elements,
including the photovoltaic elements, could
be installed within the project’s construction
budget. The consultants at Sun Light & Power
provided input so that the infrastructure is in
place for a future rooftop photovoltaic plant.
The Team
Owner: Dosa on Fillmore, Anjan and
Emily Mitra, 1700 Fillmore Street, San
Francisco, Calif., dosasf.com
Architecture & Interiors: Architects II, Jim
Maxwell and Cindy Beckman, principals,
fullplateconsulting.com
Mechanical/Plumbing Engineers: John-
son Engineering, Art Johnson
Solar Design Consultants: Sun Light &
Power, James Hatfield and Martin More-
house, sunlightandpower.com
Solar Installation: Sun Light & Power, Jon
Christianson, sunlightandpower.com
Construction: R3 Builders, Rick Dade and
Barry Nash, owners, r3builders.com
Environmental Restaurant Consultant:
Thimmakka, Ritu Primlani, owner,
thimmakka.org
Modeling Sustainable Business
Dosa’s solar system installation has been
providing cost-effective clean energy and reducing overall operating costs since opening day,
and has already saved thousands of dollars on
the restaurant’s utility bills. Owners Anjan and
Emily Mitra are also happy to be able to tell their
customers that every year the solar thermal system removes the equivalent of four cars from the
road or avoids burning 47 barrels of oil.
“We’re proud to be part of the growing trend
toward sustainability,” said Anjan. “Every aspect
of our restaurant reflects our holistic commitment to using primarily organic, biodynamic
and sustainable ingredients and products, from
countertops to rooftop solar, from food choices
to our wine list.” But Emily may have said it best:
“We’re not just investing in our environment,
we’re investing in our daughters’ future.” ST
