A gas-turbine-cycle modification has been proposed, optimized primarily for (district) heating purposes, with a side-effect of obtaining gas-turbine exhaust gas at very low temperatures and potentially GHG-emission-free. Since its primary purpose is district heating without power generation, the associated gas-turbine-cycle equipment (compressors, turbines, heat exchangers) is typically arranged so that a maximum possible ratio of heat output and heat input is achieved. Whenever the heat ratio is greater than unity, that is, greater than 100% of the heat input, the exhaust gas temperature at the last gas-turbine exit is lower than atmospheric temperature. In other words, this means that it is possible to achieve greater heat output (or GT-cycle “waste heat”) than the heat input, at the “expense” of the cold GT exhaust gas (its internal energy). It is possible to arrange proposed GT-cycle modification in various configurations, such as: simple GT cycle, recuperated, intercooled, intercooled-recuperated, reheat-recuperated and intercooled-reheat-recuperated GT cycle. Maximum achievable ratio of heat output and heat input is estimated to about 1.15 (115%) and corresponding minimum GT exhaust gas temperature can be lower than the CO2 solidification temperature at atmospheric pressure (−78°C or 195 K or −108.4°F). This also means that the GT exhaust-gas stream could be entirely GHG-emission-free, without GHG-s like H2O and/or CO2, which could therefore be captured and sequestered in solid state, and in addition at very low refrigerating temperature. Such low-temperature GT exhaust gas could then be used for refrigeration purposes, or ultimately to refrigerate the Earth’s atmosphere and thus mitigate global-warming effects. The proposed GT-cycle heating system can operate also in the combined heating/cooling and power (CCHP) mode or in the stand-alone power generation mode using a combined-cycle configuration. In such operating modes/regimes, the heating part of the CHP system could still maintain its inherent advantages (achievement of the ratio of heat output and heat input greater than unity, potentially GHG-emission-free GT exhaust gas at refrigerating temperature levels), with CC thermal efficiencies only slightly lower than today’s typical values and with the CHP performance similar or better than modern GTCC or steam-turbine based CHP cycles.