Systems - HOWATHERM

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2 Systems information orientation messages insights Systems create helpful standards, saving us time to develop individual solutions. Heat recovery in air handling units HOWATHERM Klimatechnik has been specializing for nearly 30 years in the development and production of efficient systems for air handling applications to create and maintain comfortable indoor atmosphere for people. For pre-heating the outside air in the winter and cooling it in the summer, a variety of technical heat recovery systems are in use. A distinction is made between the following methods: Closed systems (heat pipe) Cycle compound countercurrent systems Plate-type heat exchangers Heat wheels Heat recuperators based on the heat pump principle HYGIENE SYSTEM ETA SYSTEM HP-WRG SYSTEM HYDROPLUS SYSTEM UV-UNIT With the exception of the cycle compound countercurrent system, all of the foregoing are associated with potential risks of moisture carryover or leakage air effects which disqualify them for use in hygiene applications. HP heat recovery system with feedback circuit
Heat recovery based on a recirculation system Conventional systems operate with fairly low efficiencies of around 40-50%. The requisite additional heat or chill had to be provided by supplementary heat exchangers in the supply airflow. However, our engineers have discovered a way of eliminating this very disadvantage. The HP* cycle compound heat recovery system This system comprises heat exchangers in the exhaust air and fresh air. Between the two heat exchangers, a heat transfer medium is recirculated to carry the thermal energy from one register to the other. Using this design, our HOWATHERM HP heat recovery system achieves efficiencies of up to 80%. *HP stands for high performance How do we achieve this high efficiency? Factor 1: Design optimization Our HP heat recovery system attains its high efficiency of up to 80% by combining multiple heat exchanger stages, each measuring not more than 300 mm in depth in conformance to VDI 3803 or VDI 6022. The length of the assembled array varies bet- Series arrangement of multiple heat exchanger stages in countercurrent mode ween 600 and 1200 mm, corresponding to about 16 to 32 rows in the airflow direction. To reduce the pressure loss, the in-flowing air velocity must not exceed 2.5 m/s. Factor 2: Accurate management of the intermediate medium Another important factor is the management of the heat transfer medium circulating between the heat exchangers. This medium must get maximum countercurrent exposure in the heat exchanger. We have the- 0,8 4 n = 5 stages refore minimized crossflow and eliminated all 0,7 3 co-current flow, since the latter in particular gives 0,6 2 much lower transfer effi- 0,5 ciencies. 0,4 1 Our solution consists in arranging the individual heat exchanger stages in series in a specific countercurrent configuration 0,3 0 0,5 1,0 1,5 2,0 Stages in series which must be strictly Heat exchange rate as a function of the heat adhered to. As a result of this design, our system attains a thermodynamic flow capacity ratio at k x A / WW = const. countercurrent rate of > 99%. Factor 3: Control Proper matching of the air mass flow and water mass flow is of critical importance. The maximum heat recovery rate is obtained if the heat flow capacity of the two media is the same. To this end, the flow of the intermediate medium (e.g., brine) is continuously controlled as a function of the air mass flow. This is the only way to ensure a maximum heat transfer even in part-load operation. WL = WW mL x cpL = mW x cpW At medium cp values (cpL and cpW ), we thus obtain: Construction mL / mW = cpW / cpL mit cpW = 4.19 kJ/kg K und cpL = 1.01 kJ/kg K it follows that: mL / mW = 4,19/1,01 = 4,15 3
Page 1: HP-WRG SYSTEM HYDROPLUS SYSTEM Ther
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Systems - HOWATHERM

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