Thursday, January 21, 2010

Passive Solar Design from a cat's perspective

I love anything that is simple to apply and powered by nature. I’m intrigued at how water always goes downhill and heat always rises. I want to use these forces of nature to work for me, not against me. Passive solar design does just that.

The term “passive solar design” is the use of various design techniques in a building to capitalize on heat and light from the sun along with using rain, wind, and other natural forces to reduce the need for mechanical and electric systems. These concepts were discovered by ancient man, have been used for thousands of years as the primary method to maintain comfortable heat, cooling, and humidity levels within human dwellings - until the discovery and implementation of central air and heat in the 20th Century.

(Sometime in the 20th Century we started making a lot of mistakes, but that’s a post for another day.)

Let me explain passive solar concepts in simple terms using domesticated house cats as examples.

• On cold days, our three cats jockey for prime sunspot position. They follow spots of sunlight on the floors and walls from the windows. The cats position themselves to be warmed by the sun and they avoid areas that are cold on their feet. Throughout the day, the sunspots slowly move (as the earth turns and the sun’s direction from us changes).

• During the cold times of the year, the cats will spend more time upstairs because it is warmer there. Even though we set our thermostats to be warmer downstairs, heat rises and collects in the game room at the top of the stairs.

• On hot days, our house cats try to find a cool area (solid surfaces like tile or concrete), that has not been exposed to the sunlight from a window. They lay on their stomachs to cool their body temperatures. They prefer to spend time downstairs where the concrete foundation keeps the air close to the floor nice and cool.

• If a cat is sitting in the sun and starts to get warm, it will move to under a table or behind a bookcase in order to cool off. The cat looks for areas that are shaded from direct light.

• If we have windows open during really rainy or windy days, our cats avoid the open window. They may even meow or otherwise verbally communicate their bodily discomfort. I interpret those sounds as “close the windows!” or “where’s my food?”. For the sake of keeping this topical, let’s assume she is making a request to close the window.

• Now if the temperature outside is cooler than inside but not too cold, then we will open a top story window and a bottom story window. Hot air rises and escapes through the top window and cool air is pulled in through the bottom window. This causes a breeze within the house. Cats don’t like breezes, so they move out of the breeze stream. (For those of you not acquainted with the charms of a cat, here's a tidbit of info:  Cats do not put their heads out of car windows to get fresh air like dogs do – if you see a cat with its head of a car window, she is trying to escape.)

I would be so happy if we used these concepts as primary building designs and used electrical systems as the ancillary systems because we would use a lot less energy and be even more comfortable in our homes. 

If you are just starting to learn about passive solar design, check out these books.  I own both of these beautiful books and refer back to their full color photos and drawings.
The Green House: New Directions in Sustainable Architecture

Off The Grid Homes: Case Studies for Sunstainable Living

Here are the concepts defined:

Geothermal Mass is defined as solid material (wall, floor, or counter) that absorbs and releases energy. A wall that absorbs the heat from a window sunspot is geothermal mass. It will continue to release heat from the wall even after the sunspot has moved on.

Warm Air Envelope is defined as the heat that is collected around your body. It is created by your body and it influenced by your immediate environment. When there is no breeze, the temperature one nch from your body is warmer than the temperature two inches from your body. Unless there is a breeze, your envelope will keep you warm. If you stand in front of a fan, the warm air is actually pushed away from your body and creates a cooling effect.

Standing air that is a few degrees cooler that the air around it may not be noticeable, but if the air is moving, your body will experience a cooling effect.


Heat Rises and Cold Falls is defined as … well, its self-explanatory, right?

Sun Orientation is defined as the angle and direction of the sun. Here are some rules to remember for those of us that live in the Northern Hemisphere.

• During the winter, strong sunlight comes through the south facing windows from morning till evening. This is because the sun is low on the horizon. East facing windows will get some sun in the morning. West facing windows will get some sun in the evening.

• During the summer, strong sunlight comes through the East facing and West Facing windows. Because the sun is high on the horizon during the summer (almost directly above us during the summer), South facing windows will bring in only indirect light.

• Windows on the North side of a structure will always get indirect light.