Efficient absorption cooling for low district heating return temperatures

In the past years scientists of Technische Universitat Berlin, developed a new generation of single stage H2O/LiBr absorption chillers in the range of 50 to 500 kW nominal cooling capacity. In 16 installations 25 absorption chillers have been monitored within a broad field test (Feldtest Absorptionskalte fur Kraft-Warme-Kalte-Kopplung-Systeme, FAkS, funded by BMWi as project FKZ 03ET1171a-d) in the years 2013 to 2018. Annual performance figures of thermal coefficient of performance (COPth) in the range of 0.7 kWh(0)/kWh(2) and electrical coefficient of performance (CO P-el) superior to 20 kWh(0)/kWh(el) have been proven, serving district heat (DH) return line temperatures in the range of 62 degrees C to 68 degrees C. While the FAkS project focused on installation and operation of absorption chillers themselves, the follow-up project called ReKs (Regelung energie-aufwandsoptimierter Kalteerzeugungssysteme, FKZ 03ET1583), concentrates on overall system control and efficiency. Controlling absorption chiller cooling supply at low district heat return line temperatures is extended to an energy efficient control of all participating components including hot water, chilled water, heat sink pump and cooling tower fans. Models and strategies have been developed on thermal science theory and implemented in industrial control software. Proof of concept has been evaluated by monitoring field test installations while in parallel particular field test related parameters have been varied. Without diminishing quality of chilled water temperature and/or cooling capacity, electrical energy efficiency can at least be doubled, compared to the figures of FAkS installations. Moreover, new strategies enable efficient absorption cooling with DH return line temperatures in the range of 50 degrees C during moderate weather conditions periods. Field test results from 2020 and 2021 are presented here. (C) 2021 The Authors. Published by Elsevier Ltd.

Automated summary

Scientists from Technische Universitat Berlin have developed a new generation of single stage H2O/LiBr absorption chillers in the past years, with proven performance figures in thermal and electrical coefficient of performance. The follow-up project focuses on overall system control and efficiency improvement, aiming to double the electrical energy efficiency compared to previous installations. Field test results from 2020 and 2021 are presented to demonstrate the advancements in absorption cooling technology.