A method for gas-free filling of water circuit heating and cooling systems is developed in this work. Even large systems can quickly be filled without using venting screws. The system, evacuated to a low-end pressure, is filled with degassed water. For the evacuated system, the leakage constant (increase of pressure per time) is measured. It is constant during the filling process until the critical pressure ratio (0.53) is reached. The evacuated system is filled using a mobile vacuum-boiling device, which removes over 99% of the gases dissolved in warm tap water. The capacity of about 4 m³/h results in a short filling time. The main factor increasing the air concentration in the system is the leakage during filling. A model is derived which enables easy calculation of the air or nitrogen concentration in the system after filling, using the variables end pressure, the vapour pressure in the system, leakage constant and filling time. The oxygen in air disappears quickly in a radiator system due to corrosion. The calculated nitrogen concentration in the system is mostly below 0.5 mol/m³, which guarantees that the nitrogen remains dissolved in water even at a temperature of 70°C, provided the minimum pressure in the system is greater than 146 kPa. Another important result is that, even in open systems, the nitrogen gas absorption from the atmosphere into the system stops at a level of about 0.5 mol/m³; therefore, no degassing afterwards is needed. The theoretical study shows that the micro-bubble separators in radiator systems connected to district heating are ineffective because of too low surface temperatures on the secondary side. New formulae are derived for heating curves and radiator sensitivity using different heat transfer models. Radiator sensitivity is a concept introduced by Trüschel (2002) in his doctoral thesis. New and efficient methods for adjusting the balancing valves to accommodate cases with and without pipework drawings are presented. In certain buildings where pressure drops in the pipework are very small, only presettable radiator valves are required, making the balancing of valves unnecessary. The methods presented here have been tested successfully in hundreds of buildings.
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