Based on irreversible four-temperature-level (FTL) cycle models, an ecological criterion function of absorption heat pump (AHP) plants is proposed. This function can attain a compromise in inter restricted relations between exergy output and exergy loss of AHP plants. Relations among ecological function, coefficient of performance (COP), heating load, exergy output and exergy loss, and various loss factors are derived. Simplified relations are derived when various irreversibility factors can be ignored. The exergy-based ecological characteristics are analyzed through numerical examples. The results can provide some new suggestions about parameter selection for practical AHP plants. (C) 2018 Elsevier Ltd. All rights reserved.