IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask A Report, November 2009
• Very high ratio of surface to volume leads to relatively high heat losses.
• A pump is necessary to transfer energy from the one tank to the other.
• If an immersed heat exchanger only in the top of the hot water tank is used, to
transfer heat from the main heat store to the domestic hot water store, the main heat
store cannot be cooled to very low temperatures (mains temperature) leading to
lower collector efficiencies. A concept with a flat plate heat exchanger between space
heating tank and hot water tank performs better, but is much more expensive.
• A circulation loop connected to the hot water tank leads to very bad thermal
stratification in the space heating tank due to the high circulation return temperature.
• Parasitic energy (electricity for the pump) is required for hot water preparation.
• Relatively large volume on a temperature level that favors legionella growth.
• If the boiler is only heating the auxiliary volume of the space heating tank, the boiler
set point temperature must be relatively high.
Tank in Tank
The tank-in-tank concept was developed in order to reduce space requirements. The DHW
tank (100-200 ltr) is integrated in the heat store as shown in Fig. 3.
Fig. 3: Tank-in-tank system (Jenni, CH)
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