Discussion on the Application of Variable-air-volume Air-conditioning System on Ships

A scheme of marine VAV A/C systems was presented in this paper. The system flow is as follows: the return air form air-conditioned cabin is mixed with fresh air before the cooling coil-direct expansion (DX) evaporator. The temperature and humidity of mixed-air through the evaporator are reduced. The processed air is supplied by fan and enters air-conditioned cabins through respective VAV terminals. The following differences between marine VAV A/C systems and land-use VAV A/C systems were introduced in detail (1) the VAV air-distribution system is connected with the refrigerating unit directly, no intermediate chilled water system exists. (2) The system capacity is relatively small and the number of VAV terminals in the system is few, hence the regulation and variation of damper opening in terminals are comparatively frequent. (3) The system load and total supply air flow rate have a large varying range. (4) Controls of system air-side and refrigerating-unit side interfere with each other directly. The controls of supply air humidity, cabin air temperature, supply air static pressure and supply air temperature, and the direct-digital-control DDC technology for the marine VAV A/C system were analyzed. The high-quality control for cabin air temperatures and the desirable independent zoning control were expected to be achieved. It was found that the application of such a system on ships should be feasible and promising.