Hi Jim
On (29 Jan 98) Jim Dunmyer wrote to Mike Ross...
 JD> The problem with solar heat is that it's 'low grade', IE, not very hot.
And there is the joy and mystery of design. Fuel fired Boiler designers, have
had such fun! with flue gas energy recovery.
The task of building a durable cost effective heat exchanger, which doesn't
substantially increase the back pressure in an exhaust stack has had more
skilled attention than we might guess.
A familiar example, is the modern wood stove with exposed chimney running up
and thru the ceiling. Those few feet of hot tubing, add a lot of warmth to
the room. In our house [1940s] the new wood stove chimney, was turned into 
he
brick cavity wall then up. The room timber panelling caught fire!!
Modern central stations have "economisers"- huge rotating rooms about 40 feet
diameter. The exhaust gases thus preheat the incoming combustion air. Don't
ask me to describe the design. The design object is, recover lotsa heat
without requiring more fan power. These furnaces usually have Forced draft
fans to blow the combustion air into the flame, and Induced draft fans to 
uck
the burned gases out again. Any gadgets along the way [such as precipitators,
flue gas washers] demand more fan HP thus more fuel consumed.
 JD> Most engines or absorption systems need a high temperature to operate.
So boring. Just burn more fuel, dang! it's cheap enuff.
Cheers....ALEC
... ........The hasty and the slow meet at the ferry
--- PPoint 1.92
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