Watertowater

Watertowater refers to a class of heat transfer systems in which heat is exchanged directly between two water streams or between water and a water-based fluid, without a gaseous medium such as air. In direct watertowater arrangements, two liquid streams come into contact or share a common medium, allowing heat to pass from the hotter to the cooler stream. Indirect watertowater systems use an intermediate heat exchanger or a closed loop, but still rely on water as the primary heat-transfer medium.

Common applications include hydronic heating and cooling networks, district energy systems, geothermal and groundwater heat pumps, and process heat recovery in industrial facilities. In a typical setup, a hot water stream transfers heat to a cold water stream, either by direct contact or via a liquid-to-liquid heat exchanger. The choice between direct and indirect designs depends on factors such as contamination risk, control precision, and water quality.

Advantages include high heat transfer efficiency due to the favorable thermophysical properties of water, potential energy savings, and simpler piping compared to air-based systems. Disadvantages involve water quality management to prevent fouling and corrosion, the risk of contamination when potable water is used, and issues related to freezing, scaling, and microbial growth in some configurations such as cooling towers.

Design considerations include temperature and flow ranges, materials compatibility, pressure drop, pump energy, and treatment requirements to control hardness, alkalinity, and microbial growth. Related concepts include water-to-air heat transfer, liquid-to-liquid heat exchangers, and direct-contact heat exchangers.