Watrous Associates Architects

Passive Solar

What is Passive Solar?

The term "passive solar", in its purest sense, means collecting the sun's heat without any machines or moving parts, like pumps or fans. Think of the way an automobile sitting unused for several hours can still be nice and warm on a sunny but cold winter day. The sun simply shines in through the windows and heats the interior of the car -- this is passive solar in action.

House Diagram
(click for more detail)
In contrast, "active solar" means collecting the sun's energy and using machines, pumps, fans, or moving parts to move the heat where it is needed. For a house, this form of solar requires specially-manufactured solar collectors on the ground or roof of a house. If a water mixture is run through the collector, a pump and piping are required to move the fluid to a heat-exchanger inside the house. If air is run through the collector, fans, ductwork and a heat exchanger are required.

How Do Sun-Earth Homes Work?

Watrous Associates Architects designs for year-round energy efficiency. Their designs for homes and other buildings, such as churches, offices, and daycare centers, are based on national standards developed by the National Renewable Energy Laboratory in Golden, Colorado.


Passive solar, rather than active solar, is best for energy efficiency in the Midwest region. This is because active solar requires clear days, while passive solar works well on partially cloudy days more typical of our region. And even on an overcast day, more solar energy is gained through south facing windows than is lost -- just as one can get a sunburn at the beach on an overcast day.

When the sun shines in through the south facing glass of a Sun-Earth Home, the concrete subfloor is heated, as well as the air in the room. The warm air is drawn off near the ceiling and driven by a regular furnace fan into the house heating ducts. The ductwork then delivers the passive solar heat into all rooms of the house through the hollow concrete subfloor. This cycle is repeated over and over, transmitting the solar heat to the floor for radiation back to the house at night. On cold, cloudy days the furnace functions normally, providing the fast heat-up of a regular gas-fired system as well as the benefits of radiant floor heating.

Even without the energy-saving benefits, some people would choose this type of home because even on a "gloomy" winter day, a Sun-Earth home is bright and cheerful. Our designs also provide our clients with a constant connection to nature and to the drama of the sky.


Super insulation techniques cut summer air-conditioning bills in half compared to conventional construction. In addition Watrous Associates uses methods such as radiant barriers, natural ventilation, sunshading by trees and vegetation, whole house fans, and building placement on the site to take advantage of summer breeze, sunshading from trees, etc. to further reduce cooling costs.


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