Surface water (River, lake or reservoir) have a greater thermal instability with respect to groundwater but due to the thermal inertia of the water and their large masses, are still excellent sources for heat pump type water-water.
Il sea constitutes the heat source more widespread. In the seas around Italy the temperature varies from a minimum of 10 ° C in winter to a maximum of 25 ° C in summer: the exploitation of salty waters amplifies but the phenomena of corrosion.
Rivers and Lakes have an instability with higher temperatures, however favorable, which pass from a minimum of-4 6 ° C in winter to a maximum of 25 ° C in summer. With these waters decrease the corrosion problem but increase those of filtering because of the content of suspended material that must be intercepted before the fluid comes into contact with the heat pump.
The amount of water required for the system depends on the heat demand to be covered by the heat pump and the conditions of the source: approximately per KW of heat demand can occur from 250 l / h up to 400 l / h of water.
The exploitation of surface waters may occur in a direct way by passing through a intermediate heat exchanger the water source, or in an indirect way by exploiting a closed circuit intermediate in which circulates a heat transfer fluid.
In most cases the use is indirect with the closed circuit in which fluid flows glycolate that allows the plant to work even at temperatures below 0 ° C.
The heat exchanger in turn can have different locations. A possible application includes the exchanger placed directly in surface water as in the case of a river: it is a heat exchanger tube with pipes distant from each other at least 4 cm and protected by a grate and a protection system in order to avoid blockages.
The water that flows through it ensures excellent heat exchange and simultaneously prevents the formation of ice; application of this type, however, presents many difficulties of realization.
The solution is the most common heat exchanger installed directly in the boiler or better yet directly in the heat pump: The heat exchanger in this case is Plate-type fed directly from the source in case of open circuit with loosing water source, or from the fluid of the closed circuit intermediate.
The solution with plate heat exchanger installed directly in the heat pump is typical of water-water heat pumps, Posing carrying two plate heat exchangers of which one is dedicated to the plant side and the other dedicated to the source side.
The use of surface water requires an analysis of water quality and consequently a careful design of the entire system as well as the respect of a bureaucratic process for obtaining the necessary permissions.
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