Master's Thesis Martin Theodor Kremer
Investigation on run around coil systems concerning their energetic and economic potential of improvementCopyright: EBC
To reduce the high primary energy consumption of central air handling units (AHU) different heat recovery systems are used such as the run around coil system (RACO), which combines the heat exchangers in the exhaust and supply air with a hydraulic circle.
In this thesis, the different variants and control concepts will be examined concerning energetic aspects and their life cycle costs depending on case of operation. Moreover, the RACO will be optimized regarding control and circuitry by questioning classical dimensioning rules and operation strategies.
The examinations have shown that the classical admixing circuit using a three-way valve can be substituted by a two-way valve in the bypass to reduce the electrical consumption of the system by 23 % ensuring the frost protection of the exhaust air heat exchanger. The power control of the system can be realized efficiently by a speed-controlled pump, which reduces the electrical power of the pump in the off-peak periods up to 85 % without impairing the control accuracy.
Next to the heat recovery the RACO provides the possibility of heat integration and indirect cooling using an additional heat exchanger in the hydraulic circuit. The heat integration in the hydraulic circuit has proven energetically adverse for the examined system compared to a heating register in the air duct. Indirect cooling on the other hand has shown profitable, because the necessary energy for cooling the supply air can be reduced by 7% due to the low operating hours, where the supply air needs to be cooled down.
The simulation compares the different control strategies of the RACO regarding the saved energy calculated for a whole year. It has become clear, that the primary energy saved due to the operation of the heat recovery system can be increased by 21,2 % by replacing the three-way valve by a two-way valve combined with a power control of the pump.