Passive Solar Design

Design Techniques http://www.montanagreenpower.com/faq/passive_solar_design.php#q2

Direct Gain – Solar radiation directly penetrates and is stored in the living space

Indirect Gain – Solar radiation is collected and stored and distributed using thermal storage material. Trombe Wall

Isolated Gain – Solar radiation is collected in a space that can be isolated like a sunroom.

Direct Gain

Emissivity or Emittance

Material Surface Emittance

Asphalt 0.90 - 0.98

Aluminum foil 0.03 – 0.05

Brick 0.93

Fiberglass 0.80 – 0.90+

Glass 0.95

Steel 0.12

Wood 0.90

Indirect Gain

Cost

Additional Cost Glazing Added thermal mass Larger roof overhangs

Cost Savings Less mechanical heating Less mechanical cooling Less maintenance

Passive Solar Design Techniques Orient the house with the long axis

running east and west

Passive Solar Design Techniques Select, orient and size glass to optimize

winter heat gain and minimize summer heat gain.

Size south-facing overhangs to shade windows in summer and allow solar gain in winter

Add thermal mass in walls for heat storage Use natural ventilation to reduce or

eliminate cooling needs Use daylight to provide natural light

U-FactorU-FACTORThe rate of heat loss is indicated in terms of the U-Factor of a window assembly. The insulating value is indicated by the R-Value which is the inverse of the U-Value.

The lower the U-Value the greater a windows resistance to heat flow and the better the insulating value.

Solar Heat Gain CoefficientThe SHGC is the fraction of incident solar radiation admitted through a window.

SHGC is expressed as a number between 0 and 1. The lower a windows solar heat gain coefficient, the less solar heat it transmits.

Visible Transmittance

The visible transmittance is an optical property that indicates the amount of visible light transmitted.

Theoretical values vary between 0 and 1, but most values are between 0.3 and 0.8

Heat loss and gain occur by infiltration through cracks in the window assembly.

Air leakage is expressed in cubic feet of air passing through a square foot of window area.

.3 is recommended for Oregon

High number for cold climate. Low number for warm climates

The lower the number the better the insulating value

The best windows have air leakage rating between 0.1 and 0.6 cfm/ft.

Varies from 0 to 1.0 The higher the # the more light is transmitted.

Window Selection

Heating Climates Reduce window area on north, east and

west facing walls. South facing windows should have a high

Solar Heat Gain Coefficient (SHGC) 0.60 or greater

Low U-Factor 0.35 or less to reduce conductive heat transfer

Window Selection

Cooling Climates Use north facing windows along with

shaded south facing windows Shading can come from landscaping,

overhangs, shutters, and solar window screens

Use windows with U-Factors below 0.4 and a SHGC below 0.55, which will help cut cooling costs

Suntempering

A strategy used in cold climates where most of the glazing is oriented on the south side, is to provide glazing up to 7% of the total square footage.