Water-to-water heat exchanger using surface water

Easy system for sustainable heating and cooling
Water-to-water heat exchanger using surface water

Suitable for all types of homes and business premises located near surface water.


Withdrawing thermal energy from surface water

The average annual temperature of surface water in the Netherlands, such as the water of the River Rhine, is 14°C (see the figure below). This water contains an enormous amount of energy which can be used to heat or cool residential areas and/or business premises. Although the water temperature is not sufficient to heat a building to a comfortable temperature, a heat pump can be used for this purpose.


Source: DOI: 10.5268/IW-4.1.705‚Äč 
Mean annual water temperature (WT) of the River Danube near Vienna (Wien) for 1900–2006. Average water temperature for 1991–2006 and water temperature anomaly (WTA) for that period from the IPCC base period 1961–1990 are indicated. Linear and quadratic regressions for the period 1900–2006 and extrapolated to 2050 are inserted. In addition, the linear trend and extrapolation beginning in 1970 is shown. For each extrapolation the expected temperature in 2050 is inserted.



Water from the river is fed through the heat pump, extracting heat and cooling the water, e.g. by 5°C. The cooled water is returned to the river.
Feeding the water from the river directly to the heat pump would not be a wise thing to do for two reasons: 

  1. Heat pumps are not resistant to the contaminants in river water. 
  2. In cold periods, the temperature of river water can drop to, for example, 5 °C. When this water is fed to the heat pump and cools down in the pump, it may freeze, thus preventing the heat pump from working properly. 

These two problems can be avoided by creating a closed circuit in which the water from the heat pump circulates through the Exegy heat exchangers. Clean water with a certain percentage of glycol circulates through this circuit. This will prevent the pollution in the river water from causing any damage to the heat pump. In addition, the freezing point is lowered by adding glycol.



Energy calculation

One heat exchanger package enables 5.2kWh of energy to be extracted from river water.

In this case, a heat pump with a COP of 4 matches a heat pump capacity of 7 kW. 5.2 kW of this capacity is extracted from the water and 1.8 kW is consumed by the pump itself in the form of electrical energy. The cost of electricity at a kWh price of €0.22 per hour will then be €0.40. Using gas to generate this capacity would cost €0.58 (assuming an efficiency of 95%, 10.3kWh per m3 of gas and €0.814 per m3 of gas; source This means that every heat exchanger in the river brings daily cost savings of: €6.72.