The final energy savings of distributed CHCP projects, like district cooling schemes, are highly dependent on the system design and equipment used. Generally speaking, there are no final energy savings for standard distributed CHCP; in fact they will tend to use more final energy. However, the potential benefits of distributed CHCP systems come when the energy system as a whole is examined and the avoided primary fuel input for electricity generation is considered. Primary energy savings for cooling are harder to achieve than for space and water heating, given the high seasonal energy efficiency ratings of conventional vapour-compression air conditioners. The following figure presents the potential primary energy savings from a distributed micro-CHCP compared to conventional air conditioners with a SEER of 2.7 and for a conventional boiler with an efficiency of 90%. CHP systems can achieve significant primary energy savings compared to the separate provision of heat and electricity. However, for CHCP systems, the primary energy savings for cooling are only achieved if electrical efficiencies of the CHCP plant are 30% or more.
The costs of small-scale CHCP system components are presented in the figure below. The CHP system will cost between €2,000 and €4,500/kWe, while the thermally driven chiller is likely to cost in the range of €800 to €1,500/kWth. Total system costs for a four family dwelling would be in the order of €30,000. This needs to be compared to a likely cost of€ 7,500 to €8,500 for conventional boilers and room air conditioners. Annual operating and maintenance costs at around €1,150 would be around twice that of the conventional solution.
Distributed CHCP systems financial benefits stem from the reduction in electricity purchased, plus the revenues from surplus electricity generated that is fed into the grid, but this is reduced by increased fuel purchases compared to a conventional boiler. The net financial position depends strongly on the price ratio for electricity and gas, as well as the residential electricity tariff paid for purchases by the household and the price paid by the electric utility for the electricity fed into the grid.
Assuming average values for Europe suggests that today’s CHCP systems aren’t typically economic. However, in countries with high electricity prices and more modest gas prices, savings can be anticipated, for instance in Germany. The following figure shows the gross margin for cooling given different gas and electricity prices. The gross margin for heating will typically always be positive in the European context, but for the combined heating and cooling system, this isn’t always the case.
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