SOLAR ENERGY FOR WATER HEATING BROOKS 175 



COMBINATION OF SOLAR HEATER AND FURNACE OR RANGE WATER COIL 



In the most economical water-heating system (fig. 7), the solar 

 heater is depended upon from early spring to late fall; then, dur- 

 ing the winter, the furnace coil or water-back in the range is used 

 for obtaining hot water. If the furnace or range is in daily use, 

 usually the solar heater is shut off and drained to avoid freezing. 



Location and connection of solar absorber. — The solar absorber is 

 most conveniently placed on a roof sloping south and in front of 

 attic windows so that the glass cover can be readily cleaned with 

 a hose (attached to the storage-tank drain) or with a mop. The 

 usual absorber construction is similar to that of a skylight, but 

 with a special provision for an insulated pipe outlet at the top 

 that permits a continuous rise in the pipe to the storage tank. 

 This requirement usually interferes with standard flashing prac- 

 tice. A simple method is shown in figure 7 ; the hot pipe is brought 

 through the end of the absorber above the roof surface and turned 

 to enter the attic through a separate hole higher in the roof, the 

 pipe being insulated and enclosed in a lead sheath under which 

 the rain water can pass from around the top of the absorber. The 

 flashing around the lead sheath where it pierces the roof is separate 

 from the flashing around the absorber box. In an alternative 

 method, the hot pipe leaves the top edge of the absorber through 

 a special box running from the roof slope out to the absorber frame, 

 with the roof flashing arranged to drain each way from this ob- 

 struction along the top edge of the absorber. 



Safe piping practice for furnace or range coil. — Valves between 

 the tank and the cold-water supply line and between the auxiliary 

 heaters and the tank are intentionally omitted to avoid danger of 

 bursting. If a valve were provided in the supply line to the hot- 

 water tank, the tank might be drained to avoid freezing; and later 

 the range or furnace might be thoughtlessly started with all valves 

 closed and result in an explosion. A single valve at the meter, 

 shutting off all the water, is not objectionable, for the cold-water 

 supply is always turned on before one thinks of starting a hot-water 

 heater. If hot-water shut-off valves are to be installed, recom- 

 mended dairy sterilizer connection practice should be followed, 

 which specifies a check valve in a bypass around each shut-off 

 valve so that in case of higher pressures in heaters the water can 

 back up in the supply line even though the manually-operated valves 

 are closed. This bypass and check-valve system permitting reverse 

 flow is alternative to the pressure relief valve, which might not 

 operate properly after long periods of nonuse. 



