4-22 The specifications of a flat-plate collector is as follows: T= 0.88, a=0.97, U=1.3 Btu/h-ft. °E The heat removal factor for the collector is 0.92, the solar insolation is 210

Btu/h-ft, and the ambient air temperature is 60°F. Determine (a) the collector efficiency if the water enters the collector at 115°F and (b) the temperature of water at which the collector efficiency is zero. Take the incident angle modifier to be 1.