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New construction offers the greatest opportunity for incorporating
passive solar design features, as demonstrated by the design of
the Solar Energy Research Facility in Golden, Colorado. For retrofit
projects, consider daylighting strategies, heat control techniques,
and using passive solar heating strategies to allow modification
of HVAC systems.
Passive solar systems make use of natural energy flows as the
primary means of harvesting solar energy. Passive solar systems
can provide space heating, cooling load avoidance, natural ventilation,
water heating, and daylighting. This section focuses on passive
solar heating, but the other strategies also need to be integrated
and coordinated into a whole-building design. Passive solar design
is an approach that integrates building components—exterior
walls, windows, and building materials—to provide solar collection,
heat storage, and heat distribution. Passive solar heating systems
are typically categorized as sun-tempered, direct-gain, sunspaces,
and thermal storage walls (Trombe walls).
Topics in this section include:
New construction offers the greatest opportunity for incorporating
passive solar design, but any renovation or addition to a building
envelope also offers opportunities for integration of passive methods.
It is important to include passive solar as early as possible in
the site planning and design process, or when the addition or building
is first conceived. Ideally, an energy budget is included in the
building design specifications, and the RFPs require the design
team to demonstrate their commitment to whole-building performance
and their ability to respond to the energy targets. This commitment
is emphasized during programming and throughout the design and construction
process.
For retrofit projects, consider:
- Daylighting strategies, such as making atria out of courtyards
or adding clerestories, along with modification of the electric
lighting system to ensure energy savings
- Heat control techniques, such as adding exterior shades or overhangs
- Using passive solar heating strategies to allow modification
of HVAC systems-perhaps down-sizing if the passive strategies
reduce energy loads sufficiently.
When renovating older buildings, determine whether passive features
that have been disabled can be revitalized. See the renovation
section of this site for more renovation suggestions.
Sun tempering is simply using windows with a size and orientation
to admit a moderate amount of solar heat in winter without special
measures for heat storage. Direct gain has more south-facing glass
in occupied spaces and thermal mass to smooth out temperature fluctuations.
A Trombe wall puts the thermal mass (e.g., tile floors) directly
behind the glazing to reduce glare and overheating in the occupied
space.
A sunspace keeps the glass and mass separate from the occupied
space but allows for the transfer of useful heat into the building
by convection or a common mass wall; temperatures in a sunspace
are allowed to fluctuate around the comfort range.
Highlight passive solar as a project goal. A good general project
goal is "to produce a beautiful, sustainable, cost-effective building
that meets its needs, enhances productivity, and consumes as little
nonrenewable energy as possible, through the use of passive solar
design, energy efficiency, and the use of other renewable resources."
Establishing energy performance goals conveys the seriousness
of energy consumption and the use of passive solar as a design issue.
For small offices, warehouses, and other smaller projects—10,000
sq ft (930 m2) or less—facility managers or their contractors
can develop energy budgets easily using software such as Energy-10.
For larger multi-zone projects (for example, laboratories or high-rise
office buildings), national average energy consumption data by building
type can be cited as targets to be exceeded, or more complex analyses
can be run by consultants.
The building design should allow passive solar strategies to be
effective (for example, large multistory core zones are hard to
reach with passive solar). Building requirements, such as privacy
and security, may influence the type of passive solar heating system
that can be used.
Thirty to fifty percent energy cost reductions below national
averages are economically realistic in new office design if an optimum
mix of energy conservation and passive solar design strategies is
applied to the building design. Annual savings of $0.45 to $0.75
per sq. ft ($5 to $8/m2) is a reasonable estimate of achievable
cost savings.
Passive solar design considers the synergy of different building
components and systems.
For example:
- Can natural daylighting reduce the need for electric light?
- If less electric light generates less heat, will there be a
lower cooling load?
- If the cooling load is lower, can the fans be smaller?
- Will natural ventilation allow fans and other cooling equipment
to be turned off at times?
Passive solar design is often more challenging than designing
a mechanical system to accomplish the same functions. Using the
building components to regulate temperature takes a rigorous analytical
approach to optimize performance while avoiding such problems as
overheating and glare.
Generic design solutions or rules of thumb are of limited value.
Rules of thumb may be useful in anticipating system size and type,
but only early in the design process. Computer
simulation provides much more accurate guidance because of the
complexity of system combinations and interactions. Some of the
variables involved include:
- Climate (sun, wind, air temperature, and humidity)
- Building orientation (glazing and room layout)
- Building use type (occupancy schedules and use profiles)
- Lighting and daylighting (electric and natural light sources)
- Building envelope (geometry, insulation, fenestration, air leakage,
ventilation, shading, thermal mass, color)
- Internal heat gains (from lighting, office equipment, machinery,
and people)
- HVAC (plant, systems, and controls)
- Energy costs (fuel source, demand charges, conversion efficiency).
An hourly simulation analysis combines all of these parameters
to evaluate a single figure-of-merit, such as annual energy use
or annual operating cost. The integrated interaction of many energy-efficient
strategies is considered in passive solar design. These include:
passive solar heating, glazing, thermal mass, insulation, shading,
daylighting, energy-efficient lighting, lighting controls, air-leakage
control, natural ventilation, and mechanical system options such
as economizer cycle, exhaust air heat recovery, high-efficiency
HVAC, HVAC controls, and evaporative cooling.
Cost and technical analyses are conducted at the same time in
passive solar design to optimize investments for maximum energy
cost savings. It is rarely feasible to meet 100% of the building
load with passive solar, so an optimum design is based on minimizing
life-cycle cost: the sum of solar system first-cost and life-cycle
operating costs. It is difficult to separate the cost of many passive
solar systems and components from other building costs because passive
solar features serve other building functions-e.g., as windows and
wall systems.
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