Thermal Analysis of an Absorption and Adsorption Cooling Chillers Using a Modulating Tempering Valve

Read from local Zotero full-text PDF (group 5183627 / Joule Heist).

Key findings

• Typical operating windows compared: absorption system uses H2O-LiBr or NH3-H2O with generator temperature 85-180 C and COP 0.6-1.1; adsorption system uses H2O/silica gel with generator temperature 50-100 C and COP 0.4-0.6 (Table 1).
• TRNSYS model (book chapter, “Zero and Net Zero Energy”, IntechOpen) of a single-effect solar chiller for a building in Temixco City, Mexico: HTP evacuated-tube collector HP-30SC, net aperture 3.86 m2, efficiency eta = 0.418 - 1.17(T_in - T_env)/Q_rad; stratified storage tank (Type 4a) heat capacity 2.24 kJ/kg.K, initial 70 C, loss coeff 0.75 W/m2.K.
• Chiller catalog components: absorption (Type 107) rated 37,800 kJ/h at COP 0.70; adsorption (Type 909) rated 37,800 kJ/h at COP 0.53; both thermal fluid Cp 2.13 kJ/kg.C. Building (Type 56) kept at 25 C +/- 1 C.
• Operating conditions (Table 2): absorption (ABS) chilled-water setpoint 6.7 C, T_chilled 5.5-10.0 C, cooling water 26.6-32.2 C, hot water 108.9-116.1 C; adsorption (ADS) setpoint 6.7 C, T_chilled 5.0-12.0 C, cooling water 10.0-35.0 C, hot water 65.0-95.0 C.
• MTV consists of a diverter (Tee1) and mixer (Tee2) that blend high-temperature storage-tank water with lower-temperature chiller-return water to cap the generator inlet at 116 C (ABS) and 95 C (ADS); without MTV the controller turns off the collector pump once the tank reaches 130 C.
• Optimization results: without MTV, storage specific volumes of 35 and 27 L/m2 were best for absorption and adsorption respectively; with MTV, 23 and 22 L/m2 at a fixed collector tilt of 7 deg, with minimum generator-inlet temperatures of 111 C (ABS no MTV) / 109 C (ABS with MTV) and 75 C (ADS, both cases).
• The MTV produced a significant reduction in auxiliary heater energy for both chillers, the effect being larger for the absorption chiller.