Our physical environment is endowed with unlimited amount of natural and artificial sources of energy at various low exergetic levels which leaves them almost impossible to be thermally utilized at such source states. The thermal upgrading of these low exergetic energy sources could render them amenable to various practical thermal usages. This paper provides a comparative study through simulations, of the effectiveness, robustness and reliability of the often two most promising heat upgrading technologies (the chemical and mechanical heat pumps) systems for the sustainable heat upgrading of low-temperature heat sources for district heating. The simulation results reveal that for a low to medium energy demand, low-temperature heat source upgrading using the chemical heat pumps seems more promising than the mechanical heat pumps, while the mechanical heat pump is best suited for high energy demand space heating. In the simulation, use was made of an artificial low-temperature heat source (a nearby pharmaceutical industry waste heat) with source temperature state of between 25 and 35 degrees C as the feed to the upgrading units. The high energy demand (assumed to be able to serve the space heating energy requirements of a given locality) was estimated to be 923 TJ/annum at a consumer-side temperature level of about 95 degrees C. The selected most robust system (the mechanical heat pump-based process) for upgrading the low-temperature heat source at such given high energy demand has been conceptually designed. (C) 2007 Elsevier Ltd. All rights reserved.