“Sensible” heat refers to energy that can be released through a temperature change. Heating water from 32°F to 212°F (0°C to 100°C) is a change in “sensible” heat. “Latent” heat refers to energy stored or released in a phase change, such as the heating that is done when steam changes from vapor to water, without any temperature change. As it turns out, the energy released when a pound of steam turns into a pound of water, all happening at 212°F (100°C) (no temperature change, so this is latent heat) is some five times the energy released when that same pound of water is cooled from 212°F to 32°F (100°C to 0°C). All this to say there is a lot of energy released in the phase change from water vapor to liquid water.
Therefore, condensing heat recovery technology, which can capture latent heat, is much more efficient than the typical feedwater economizer, which can only capture sensible heat. When it comes to overall boiler plant efficiency, FLU-ACE is able to provide a 10% to 15% improvement, while a typical feedwater economizer provides an improvement of 2% to 4%.