Passive Solar Design

Definition:

• Utilizes the sun's energy to heat and cool living spaces through exposure.
• Materials can reflect, transmit, or absorb solar radiation causing predictable air movement.
• Passive systems use design elements, material choices, and placements for heating and cooling, unlike active systems, which use mechanical devices.

Passive Solar Design Basics

Five Elements:

1. Aperture/Collector:
   • Large glass areas facing within 30 degrees of true south.
   • Should not be shaded during 9 a.m. to 3 p.m.
2. Absorber:
   • Darkened surface absorbing sunlight as heat.
   • Could be masonry walls, floors, or water containers.
3. Thermal Mass:
   • Retains/stores heat (located behind the absorber).
4. Distribution:
   • Solar heat circulation via conduction, convection, and radiation.
   • Fans, ducts, blowers can aid distribution.
5. Control:
   • Overhangs for shading apertures.
   • Devices like thermostats, vents, dampers, and blinds for control.

Passive Solar Heating

Objective:

• Capture sunlight heat and release it when absent, maintaining comfortable temperatures.

Primary Elements:

• South-facing glass and thermal mass.

Approaches:

1. Direct Gain:

   • Living space serves as collector, absorber, and distribution system.
   • Uses masonry materials to absorb/store heat, radiating it at night.
   • Water containers can store heat but require structural support.
   • Utilizes 60-75% of sun's energy.

2. Indirect Gain:

   • Thermal mass between sun and living space.
   • Most common system: Trombe Wall.
   • Utilizes 30-45% of sun's energy.

Trombe Wall:

• 6-18 inches thick masonry behind south-facing glass.
• Heat absorbed, stored, and radiated into living space.
• Operable vents aid convection and radiant heating.

Passive Solar Cooling

Objective:

• Reduce unwanted heat gain, facilitate non-mechanical ventilation, and store coolness.

Methods:

1. Shading:

   • Overhangs, awnings, shutters, and trellises on windows.
   • Vegetation helps in shading.

2. Thermal Mass:

   • Moderates temperature increases by absorbing heat.
   • Cooled at night for reuse.

3. Ventilation:

   • Cross ventilation with open windows and wing walls.
   • Focus on bringing in cool night air in climates like New England.

Convective Cooling:

• Use of natural air movement for cooling.
• Thermal chimneys or sunrooms can enhance convective cooling.

Thermal Chimney:

• Utilizes rising warm air and exhaust outlets.
• Can be assisted by design features like sunrooms.