Q7. With reference to ships air conditioning plants:
(a) State the temperatures and relative humidities at EACH of the points that are regarded as the boundaries of the comfort zone. (2)
(b) Explain how the temperatures and relative humidities could be maintained within the comfort zone when the ship is in EACH of the following locations:
(i) North West Europe in winter. (2)
(ii) Arabian Gulf in summer. (2)
(c) State with reasons FOUR locations within the accommodation that conditioned air must not be recirculated. (4)
>> In special cases where unusually large surges are expected (e.g. from heavy-duty cargo cranes) the generator/AVR performance limits may be extended.
>> The AVR senses the generator output voltage and acts to alter the field current to maintain the voltage at its set value. A manual trimmer regulator may be fitted on the generator control panel to set the voltage level e.g. 440 V. More usually, the voltage trimmer potentiometer is on the control card of the AVR so is not accessible to an operator.
2021/OCT --> This question was generally well answered but a lot of candidates stated that the air would have to be humidified after cooling in answer to part (b) (ii).
2019/MAR --> The comfort zone can be interpreted in different ways and can be a matter of opinion. In Refrigeration and Air Conditioning by AR Trott and T Welch the points are approximately 18oC 72% RH, 22oC 32% RH, 24oC 72% RH and 27oC 32% RH. Other temperatures and humidity’s such 20oC 70% RH, 22oC 40% RH, 27oC 70% RH and 29oC 40% RH were also accepted.
Not many candidates mentioned recirculated air for part (b) or that the air in the Gulf would be humid at that time of year.
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