4. The type of boundary and current form depends beavily upon whether it is a 'pushing' current or being 'pulled' from a distance. 1IicJhe... - 5. All air currents are both locally and distantly determined. For example, the average temperature difference between two rooms may determine the amount of air flow, Dut which of the available currents will be exchanged is determined by other interactions. ~ I I /10 /~'ifiI~ ~' ~IE~ f:...- 6. The observable uniformity of many currents, both large and small, is often of a uniform velocity and direction rather than temperature. Currents act like tracks for parcels of air of different temp.-density. Parcels of cooler air, moving in a current across a warm wall, for example, f xchange momentum with still parcels of warmer air adjacen't to the wall This exchange takes place in a very wide range of times from very quick to a second. This still air layer I caUa voluntary air layer. The small parcels of warm air introduced to the stream path mix with each other as the cooler parcels are deposited into the voluntary layer for warming. This completes a direct current to current grafting in a continuous stream. The voluntary layer ranges in thickness from very thin to feet thick and from single layered to many or continuously layered. , ~t' , ILO.' ~~ I , .. -" , ~~ 7:'Every major air current IS a member of a five-part life cycle: the rising current, the top reservoir, the falling current, the bottom reservoir and the quiet air within which the others adjust themselves. One of the tools of climate design is to arrange materials in such a way as to eliminate certain reservoirs by creating direct curr,.ent-to-current linkages as described in number 6. ~ Convection Observation Technique The use of incense smoke to visualize climate dynamics is a very powerful tool if benefited by a little expertise and an informed intuition. I can't convey any amount of informed intuition; that is always something you make for yourself. The following suggestions might help a bit with the experrise. May] 979 RAIN Page 17 1. Carefully watch the difference between smoke rising from its own heat and smoke which has cooled and is passively following an air current. Learn how to shake off a bit of smoke to leave it hanging. Smokc often lies between currents, not necessarily in them. Smoke has a sketchy visual appearance, whereas the currents are always volumes. Look for what the smoke can tell you about what you can't see. 2. Wait five seconds after your own movements and five minutes after changing openings so that the natural motions may establish themselves. Stand at the side of where.you expect to find a current. Notice that floor currents will often part and rejoin in passing around your legs without apparent disturbance. Note the air between currents which doesn't move. 3. Scan across openings. Draw a horizontal line of smoke across an open doorway and watch how the line bends. Scan vertically across an open doorway by starting at the bottom and raising the smoke source at the same rate which the smoke is rising from 'its own heat. 4. Look especially for currents near floors, walls and ceilings. Note the difference between deep slow currents and thin fast ones. 5. Scan across a current in several places from its origin to its destination, Notice if the edge is sharply defined or not. 6. Expect current patterns to change on second, minute, hour, day and season time scales. 7. Check out a room with a fireplace and check out a stairwell. 8. Measure the temperature, speed and area of opposing sides of currents (top and bottom of doors). Heat content of air is in the neighborhood of .02 BTU per cu. ft. per degree F. 9. Look for gurgling type action of ah as it 'bubbles' through warmer or cooler bodies, which results from crossed flows or inversions. All pockets tend to be visited by intermittent puffs or currents. Note what geometries constitute a pocket. 10. Try to find the difference between 'push' and 'pull' currents, how a push current tends to billow out at a point and how a pull current can leave 'cracks' in the main air mass for very discrete air currents to slip into. Then there arc some suggestions for your mental process for making the observations really meaningful. 1. Develop your understanding of the basics of physics: density, momentum, balance, bounce, etc. 2. Try to develop an awareness and a habit of viewing whole cycles: ones of the moment, the day, the year, seed organism-seed, idea-thought-idea, etc. 3. Look for what never changes as a basis for understanding and responding to what does. I 4. Ask questions, develop and then refine uncertain ty, draw few if any conclusions. Value uncertainty. 5. Don't expect any of the above 14 comments to be very meaningful until after you're a good observer. Design with Air Currents The above discussion has stemmed from my delight with the intricate order and beauty of things. This is not sufficient to make things work, though it may be one of the essential fac· tors in letting things work. One of the basic problems in design is that it is hard enough to relate pencil lines to building materials which are visible and expected to stay put. Relating pencil lines to invisible things which change continuously is another matter entirely. While difficult to recognize, I think there is an inherent difference between arbitrary wiggling and genuinely thoughtful guesses. One of the differences is that natural air flow tends to be a sequence of straight lines and non-circular curves. All curves should contain a sense of elasticity. Drawings of air currents will often have crossing path and use the same path for intermittent currents in different directions. In the last annlysis, however, a well informed imagination is the only good key.
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