Zero Energy Home
This
award winning zero energy efficient house with a low carbon footprint
received the prestgeous 2005 SANDEE award (from the California
Center for Sustainable Energy) for the most energy efficient home built in
2005. The original design of the house used 25% less energy than required by
California code contained in Title 24 (37 versus the standard of 50 kBtu/sf-yr
for this type of home). In
building the house, several modifications were madesuch as: The
wall construction was changed from 2x4 to 2x6 allowing the use of R-19 insulation
instead of R-13; the ceiling and roof used R-30 instead of R-19; a
radiant barrier was added to the underside of the roof plywood. These
changes and the four major solar systems that are used reduce the house energy
performance to about 50tor 60% less than required by Title 24. A zero energy
house uses 50% less energy than required by title 24.
In the cathedral ceiling zones of the home, a one inch air gap was placed between
the top of the R30 insulation and the radiant barrier on the underside of the
roof plywood. This allows venting of the cathedral ceiling sun load through
a ridge vent. This effectively doubles the insulation value of the roof to about
R-60. In the attic sections, exhaust fans are used to vent hot air and
are set to turn on at 90 degrees.
Top-line
Marvin double glazed windows and glass doors have a wood frame and Argon gas
between the dual panes to increase their insulation quality. The windows and
doors are Vinyl Clad outside to eliminate maintanance. The southerly glazing
used for the direct gain passive solar heating has a special glass called “clear
and low e”.
It is Cardinal LOE-178 (equivalent to PPG-500) which is relatively clear to
incoming sun (SHGC = 0.6) but has a low emissivity coating to block the infrared
heat leak to or from the house. This southerly facing glass area is about
10% of the floor area of the home, and it provides about half the winter heating
in a four season climate. The Marvin windows on the three other sides of
the house are “double low e” to block the solar and heat gain in
the summer and heat loss in the winter. Roof overhangs block
the summer sun from the windows. The small windows used on the west
and north sides of the house reduce sun load as well as winter heat loss. Shade
trees are planted on the East and West sides of the house to block low angle
sun at the beginning and end of the day.
Natural lighting is achieved via the extra southerly glazing of the passive
solar design. Solar tubes are used for natural lighting in two
interior bathrooms. Ceiling fans in each room increase comfort
in summer (blowing down), and in the winter are used to move hotter air
from the ceiling to the lower part of the room in by blowing up and down
the walls.
Energy star appliances are used throughout and 64 (95%) of the lights are fluorescents.
An air conditioner with a SEER greater than 12 was installed and is used in
a limited fashion to cool the house in the morning if the overnight temperature
was too high. The house then stays below 78 degrees on the hottest day
when the window are kept shut until early evening. In addition, a roof vent
is a second return to the central air system with two electrically controlled
dampers so that air can be sucked from the house interior or from the
outside. This allows whole house air flushing on cool
nights so that the house starts out cool in the morning.
The south facing
roof (150 degrees orientation) is tilted at the latitude angle (32 degree)
for maximum solar energy collection. This extra green home provides all its
own electricity using eighteen BP165 photovoltaic (PV) panels combined with
a high efficiency 2500 Sunny Boy inverter. The system is
rated at 2500 watts and provides about 5000 kWh/y which is about 100 % of the
homes electricity needs. The electric bill for the last two years was
about $40 per year.
Heating
in this four season climate is 100% renewable and is made up of a direct gain
passive solar heating using the large southerly glass area and clear low e
glass coupled with masonry floors (slate stone on concrete slab) for thermal
storage and heat buffering. The solar heating system provides about half the
winter heating and an efficient pellet wood stove provides the other half.
The wood pellets are made from waste wood products such as saw dust or agricultural
wastes and is renewable. In addition, there is a back-up propane heating system
via ducting to each room, and a full house efficient air conditioning system.
The home potable water is solar heated based the Butler Sun Solutions design
using non-toxic ethanol to prevent freezing. A solar water heater system uses
40 ft2 of active panels connected to a 50 gallon solar heat storage tank. An
ethanol loop is used to carry the solar heater fluid to the storage tank and
a double walled heat exchanger is used to pass the heat to the potable house
water in the tank. The solar heated water then passes through a high efficiency
30 gallon propane hot water tank for back-up heating in the winter. An anti-scalding
valve is used as the hot water leaves the solar heating system and cold water
is mixed to keep to water to the home at 120 degrees. This not only avoids
the possibility of burns since solar water could be heated to near boiling
temperatures, but stretches the solar hot water beyond the actual storage capacity
of 80 gallons. The solar water heater system provides about 80%
of the annual water heating energy.
Another
Butler Sun Solution solar water system heats the hot tub, located just outside
the master bedroom. The tub heating
is backed-up with heat from the 1.5 HP circulation pump and is needed only
in the winter months. This solar system provides about 75%
on the annual hot tub energy.
An automated gray water system collects about half the household water and
uses it for garden irrigation. In addition, a roof rain water collection
system with a 3000 gallon storage tank is used in conjunction with the
gray water system to irrigate the garden. The seven zone garden is designed
so that each zone has plants of similar water usage to avoid overwatering.
A solar heated greenhouse allows citrus trees to winter over with little energy
use. The guest quarters are heated with renewable fire wood in an efficient
stove.