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Liquid Phase Heating Systems
Liquid phase heating systems involve sensible heat transfer in a closed loop wherein a pumped fluid's temperature is raised in a heater, then lowered in a heat user and returned for reheating. No formation and condensation of vapor occurs. High Temperature Water (HTW) central district heating systems are far superior to steam systems in large, spread out installations such as airports, universities and office complexes. Water, pressurized to keep it in the liquid state, is distributed at 400oF and returned at 250oF. Fuel savings due to elimination of steam cycle losses are surprisingly large. HTW reduces distribution costs, eliminates corrosion and lowers maintenance. For temperatures much above 400oF, the pressure in a steam or water system becomes excessive. Here, the High Temperature/Low Pressure (HT/LP) organic thermal liquids are applicable. The higher the temperature, the greater the potential fuel savings over a conventional steam system. Less expensive low pressure heat users may be used. Water treatment, corrosion, freeze-up hazard, and blow down cooling and disposal problems are eliminated. Operating engineers are not required in many parts of the country for these safe, low pressure systems. HT/LP fluids have some drawbacks. They will degrade if overheated and will oxidize at elevated temperatures. They are flammable, difficult to contain and are somewhat costly. Most of them are toxic, and some of them have acute unpleasant odors. However, for most applications, their benefits far outweigh their shortcomings. Liquid phase heating systems have much to offer in initial, operating and maintenance cost reductions. Most important, they can significantly aid in our energy conservation efforts. Consider them for your next application.
SubjectLiquid Phase Heating Systems
High Temperature Water (HTW) Central Heating Systems
Mordt, E. H. (1979). Liquid Phase Heating Systems. Energy Systems Laboratory (http://esl.tamu.edu). Available electronically from