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In this article, after the design of a CCHP system for office buildings in Tehran, a mathematical analysis of the CCHP system following thermal demand management in comparison to separate system is presented. In order to have a comprehensive evaluation of the performance of the CCHP system, four criteria including primary energy saving, CO2 emission reduction, operational cost reduction and rate of return are employed for a typical office building in Iran. Also a sensitivity analysis of rate of return based on increasing natural gas and electric price is performed. Results show that the CCHP system with selling electricity to grid has much better performance than separate system when all of the criteria are involved. Also without selling electricity to grid the CCHP system achieves more benefits than separate system but these benefits are less than the benefits of the situation with selling electricity to grid. The sensitivity analysis shows that in the situation with selling electricity to grid, with increasing natural gas and electric price the ROR will be increased but in the situation without selling electricity to gird, with 40% increase in natural gas price the ROR will become less than Interest Rate.

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In this article, a mathematical analysis of a CCHP system following electrical demand management and thermal demand management in comparison to separate heat and power system for an office building in Tehran is presented. In the thermal demand management, two modes including with selling electricity to grid and without selling electricity to grid are investigated. In order to have a comprehensive evaluation of the performance of the CCHP system, four criteria including primary energy saving, CO2 emission reduction, operational cost reduction and rate of return are employed for a typical office building in Iran. Also the AHP method is used to specify the best operation mode of the CCHP system when all of the criteria are involved. Results show that from the energy and environmental viewpoints, the CCHP system following thermal demand management with selling electricity to the grid is the best operation mode. But the CCHP system following electrical demand management has the maximum rate of return. For the all of the operation modes, the CCHP system has lower operational cost than SHP system throughout the year. From an integrated view point, the CCHP system following thermal demand management with selling electricity to the grid is the most attractive option.