Warming With Windows

Warming With Windows--Passive Solar Primer

How solar energy is used in houses

Type	Collector Efficiency	Collector Cost	Maintenance	Primary Purpose/ Applications	Energy Storage	Storage cost
Photocells (usually on rooftop)	low (less than 20% of incident solar energy)	high	medium to high	Generates DC electrical power which must be converted to AC power for most home applications.	Requires batteries. In some cases the excess energy can be fed back into the power grid.	high for batteries. medium for feed back to grid
Active Thermal Collectors (usually on rooftop)	high (depends on many conditions but can exceed 50%)	moderate to high	medium to high	Water and space heating. Uses pumps or blowers to circulate water or air from the storage system to the collector and back.	Water tanks or other thermal masses such as gravel filled containers or phase change materials.	medium
Thermo Siphon Thermal Collectors (usually on rooftop)	high (depends on many conditions but can exceed 50%)	moderate	low	Water heating. The tank is placed above the collector in an attic or on a roof. No pump is required.	Water tank	low to medium
Passive Solar Design (whole house is the collector)	high (depends on many conditions but can exceed 50%)	low	low	Space Heating	Heavy building materials such as concrete slabs, brick or stone walls.	low to medium

Passive Solar: In a passive solar house, the house itself acts as the collector and storage system for solar energy. Properly designed, passive solar features will warm a home in the winter and lower air-conditioning bills in the summer without significantly adding to the home's original cost or ongoing maintenance.

5 Key Features of Passive Solar:

Orientation: South Facing Windows

In walls not roofs--roof windows or skylights are hard to shade in the summer and tend to lose heat rapidly in the winter.

Only south facing windows are effective--By minimizing windows on the other walls it's possible to have more windows on the south wall without a significant increase in a home's cost. East and west facing windows provide little warmth in winter but significantly heat up a house in summer.

Overhangs: Properly designed these shade in summer but not in winter
Thermal Mass: Can be a concrete slab (usually covered with ceramic tile), a brick or stone wall, and/or water containers. Properly done, thermal mass adds very little expense to a house.

The Sun must shine on the thermal mass.

The thermal mass should have a dark color.

The thermal mass has to be in contact with the room's air.

At night time the thermal mass warms the room's air.

Aside from heating the air, thermal mass with a lot of surface area located in a room will increase the feeling of warmth due to radiant heat transfer.

Heat Distribution System: Generally, air or some other fluid has to be moved around the house to create a uniform temperature.
Insulation: Passive solar is a gentle form of warming. It's not available at the touch of a switch and even when available will usually not supply heat as fast as a typical central heating system. The percentage of a home's heat supplied by passive solar depends heavily on the quality of the insulation.

Windows are the major source of heat loss in winter. Movable insulation on large windows greatly reduces this problem.

Wall, ceiling, and floor temperature is as important as air temperature for comfort level. A degree change in the temperature of these surfaces has about the same impact on comfort as a degree change in air temperature. insulation keeps these surfaces warmer.

Plantings to act as wind breaks on the East, West, and north sides of the house. These can be deciduous or evergreen.

Deciduous trees and vines to shade the South side.

Assessment -- Investigation of a solar home design

Specifications: Use Google Sketchup to design a 3D solar home with the following features:

Drawing 1: Shows how the house will look. Surfaces must be textured and windows transparent. Furniture and landscaping is not required. Thermal mass must be apparent and positioned so that the sun shines on it. The orientation of longest wall and majority of windows should be to the South. Overhangs must be included and properly designed to block the sun in the summer and let it through in the winter. This drawing includes:

a living area
a kitchen--must have a sink, stove, and refrigerator
a bathroom--must have a tub, sink, and toilet
two bedrooms

Drawing 2: has no furniture or textures but shows the dimensions on the walls, roof, and floor plan required to build the house

all the needed dimensions must be shown

Deliverable: Two 3D Sketchup file stored in your student drive labeled Passive Solar House 1 <your name> and Passive Solar House Dimensions <your name>.

Work Group: individuals.