(a) Wherever steam is used for indirect heating, the resultant condensate, which is extremely hot (about 80-90°C) is recovered for re-use as boiler feed- water, thus saving a fair amount of fuel. This heat-recovery method is quite common and has been effectively used over the years.
(b) Refrigeration systems used for air-conditioning and cold storages and diesel engine operated generators use large quantities of water for cooling. The heat gained by the water (at 40-45°C) is normally rejected into the atmosphere in cooling towers.
These machines have now been modified to recover the rejected heat for heating, which in turn is used as boiler feed-water, thereby saving precious fuel for heating water to desired temperatures.