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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; (4)

(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.

Q7. (a) State a block diagram of a fully automated air conditioning system for accommodation spaces, annotating the relevant temperatures and relative humidities throughout the system. (7)

(b) Describe how bacteria are prevented from multiplying to a harmful level in an air conditioning system. (3)

Q8. (a) State THREE modes of heat transfer. (1)

(b)Describe how the design requirements of EACH of the following are met, detailing the materials used to promote or retard heat transfer:

(i)plate cooler in central cooling system;(3)          (ii)meat room in domestic provisions space;(3)  (iii)auxiliary steam system pipelines. (3)

Q6. (a) Sketch a diagrammatic arrangement of a fully automatic direct expansion domestic refrigeration system which supplies a number of cold rooms. (5)

(b) State, with reasons, FIVE desirable thermodynamic properties of a refrigerant. (5)

Q7. With reference to the lubrication of refrigeration compressors:

(a) state the advantage of using fully synthetic oils; (2)

(b) explain why oil may be carried over from the compressor; (3)

(c) describe a device which returns oil from the compressor discharge to the compressor sump; (3)

(d) state TWO reasons why an accumulation of oil in the evaporator is undesirable. (2)

Q6. With reference to a vapour compression refrigeration plant:

(a) explain the purpose of EACH of the following:

(i) expansion valve; (2)                  (ii) room thermostat; (2)      (iii) high pressure cut out. (2)

(b) explain why EACH of the following conditions are desirable:

(i) superheating at the compressor suction; (2)

(ii) undercooling at the condenser outlet. (2)

Q6. With reference to a domestic refrigeration plant, state TWO causes of EACH of the following

conditions, stating how EACH cause may be rectified:

(a) excessive pressure; (2)    (b) low pressure at evaporator suction; (2)

(c) compressor cycling; (2)   (d) compressor running for long periods but not lowering the temperature in the cold rooms(2)              (e) compressor operating noisily. (2)

Q4.With reference to ships' air conditioning systems:(a) state the effects of EACH of the following faults:

(i) corroded return air trunkings; (2)          (ii) blocked evaporator drains; (2)

(iii) defective capacity control. (2)

(b) state the main health hazard that may arise in the air conditioning plant, stating the conditions that need to arise and the measures that should be taken to prevent this occurring. (4)

Q6. With reference to refrigeration systems:

(a) explain why undercooling of the refrigerant at the condenser outlet is desirable; (3)

(b) describe, with the aid of a sketch, how a heat exchanger could be incorporated in the circuit to enhance undercooling; (5)

(c) explain the possible consequences of the refrigerant having a dryness fraction at the compressor suction. (2)