Abstract
The scheduling of both absorption cycle and vapour compression cycle chillers in trigeneration plants is investigated in this work. Many trigeneration plants use absorption cycle chillers only but there are potential performance advantages to be gained by using a combination of absorption and compression chillers especially in situations where the building electrical demand to be met by the combined heat and power (CHP) plant is variable. Simulation models of both types of chillers are developed together with a simple model of a variable-capacity CHP engine developed by curve-fitting to supplier’s data. The models are linked to form an optimisation problem in which the contribution of both chiller types is determined at a maximum value of operating cost (or carbon emission) saving. Results show that an optimum operating condition arises at moderately high air conditioning demands and moderately low power demand when the air conditioning demand is shared between both chillers, all recovered heat is utilised, and the contribution arising from the compression chiller results in an increase in CHP power generation and, hence, engine efficiency.
Highlights
Trigeneration systems have received substantial attention recently mainly because they have the potential to utilise summer waste heat from combined heat and power plant that would otherwise be wasted
The first assumed that the absorption cycle chiller and vapour compression chiller were each sized at the cooling demand value leading to a 100% over-sizing margin
The best results arise at very low power-to-cooling ratios when the power demand is moderate (Figures 6b and 7b). In these conditions the absorption cycle chiller and compression chiller share the load, all combined heat and power (CHP) waste heat is utilised, and the increase in power generation prompted by the power required by the compression chiller results in the CHP module operating at higher efficiency
Summary
Trigeneration systems have received substantial attention recently mainly because they have the potential to utilise summer waste heat from combined heat and power plant that would otherwise be wasted. The singular disadvantage of using reciprocating engines in trigeneration plants with absorption cycle chillers is that part of the engine heat recovery (i.e., jacket wall and oil cooler) is realised at relatively low temperatures with maximum jacket cooling inlet temperatures of typically 97 °C (or lower in smaller CHP modules) [5]. At these temperature limits, application is restricted to the lower-performing single-effect absorption cycle chiller
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