![]() These winds are, however, usually dry and do not impose as high a load on the cooling plant. ![]() The figure commonly taken for outside dry bulb temperature by some designers is 32.2☌, but much higher temperatures may be experienced in tropical zones with offshore winds. Surveys have been carried out to determine the conditions over the main trade routes of the world. It can be seen that a large proportion of the total cooling load is required to reduce the moisture content of incoming fresh air and the relative humidity as well as temperature of outside air can be regarded as of the greatest significance in the specification of outside conditions for design. An adequate drain is required to remove what can be a considerable flow of water from dehumidification of the air. The air is warmed in the trunking or by contact with warmer air in the space, A zone heater could be used. Thus the air could be overcooled to about 1O☌ dry bulb temperature so that warming to about 21☌, would bring humidity to about 50%. The remedy of dehumidifying the air is achieved by overcooling to precipitate excess moisture, (removed via the drain -Figure 12.2) so that when air is brought to the correct temperature, its humidity will be at an acceptable level. People in an atmosphere at 21 ☌ with 100% relative humidity would be uncomfortable. Humidity of 100% would not be able to take up further moisture and perspiration would not be evaporated. Further cooling will cause moisture to be precipitated.Īir cooled to a comfortable temperature level of 21 deg C but having a relative The temperature drop reduces the capacity of the air to carry moisture in suspension. ![]() With the aid of a psychrometric chart (Figure 12.3) it can be shown that air, with an initial dry bulb temperature of 36 deg C and relative humidity of about 60%, will, when cooled to 27 deg C dry bulb temperature, have a relative humidity of 100%. Filters (Figure 12.2), unless regularly cleaned can provide a breeding ground for the legionella bacteria.įigure : Carrier-type psychrometric chartĪs the temperature of air is reduced, so too is its capacity for carrying water vapour. Of greater influence are the impurities such as lint carried in the circulating air, which must be filtered out to prevent eventual choking of the heating and cooling elements in the conditioning plant. It is desirable that outside air should be cleaned before being introduced to the space, but this is less essential than on land, except when the vessel is in port. ![]() On this basis the minimum Department of Transport requirement of 7 litre/s is usually exceeded. The actual quantity of fresh air supplied is partially governed by the provision that it must not be less than the total capacity of the accommodation exhaust fans (excluding galley). They are governed by factors such as body odours and smoking, which may require a fresh air supply of 12 litre/s per person or more. Space conditions can vary greatly in a short time. Outside air must be introduced to all living spaces, although the amount of fresh air necessary to sustain life is very small indeed. Heating and cooling loads and air quantities- Marine air conditioning systems guidelineĪir purification, Heating and cooling loads and air quantities- Marine air conditioning systems ![]()
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