Air Conditioning Flashcards

Question

Excessive condenser pressure, what are possible reasons and how to remedy situation

Answer 1

In the event of abnormally high pressures in the refrigeration system, there is a risk of damage to the compressor. At very high pressures, the risk of the components in the refrigeration plant exploding can constitute a threat to life. Abnormally high pressures may occur in the case of: Extreme heating of plant parts (fire, solar radiation or other abnormal heating) Volumetric expansion of fluids in sealed-off premises. Causes 1. Overfilling with refrigerant 2.Insufficient condenser cooling, e.g. if cooling water fails, fan/cooling water pump clogs, soiling, scaling or fouling of heat-transmitting surfaces 3.Presence of non condensable gases (especially air) in condenser Remedy 1.Refrigerant fills condenser and reduces its effective area. Draw-off coolant. 2.Regulate water/air supply or reduce compressor capacity, if called for. Check condenser as per instructions for same. 3.Blow air out of condenser. Follow instructions for condenser.

Answer 2

Causes 1.Error in setting of liquid regulation valve 2.Leaky suction valves. 3.Open by-pass between suction side and high-pressure side of compressor. Safety valves leaky, or opens prematurely. 4.Compressor lacks capacity. Remedy 1.Liquid refrigerant in suction line. Adjust, repair or replace expansion valve. 2.Remove cylinder covers; check valve plates. Renew if needed. 3.Check system for any by-pass detectable as for instance a warm connection. Adjust or repair leaky valves. 4.Regulate compressor capacity. Check whether all cylinders are operating. Check function of capacity regulator.

Answer 3

Abnormal low pressure in the refrigeration plant will increase the compression ratio of the compressor with a subsequent risk of damage to the compressor. The danger of air being sucked into the refrigeration plant also increases at abnormal low pressure. Causes 1.Oil in evaporator 2.Refrigerant charge of plant insufficient. Bubbles in liquid line sight glass and possibly a warm liquid line. 3.Freezing-up of expansion valve (HFC/HCFC plant) 4.Thermostatic expansion valve has lost charge 5.Excessive superheating of suction gas 6.Filter in liquid line clogged 7.Solenoid valve in liquid line fails to open 8.Compressor has excessive capacity Remedy 1.Draw-off oil 2.Check refrigerant charge. Charge plant with refrigerant. Find and seal any leak. 3.Thaw out expansion valve with hot, wet cloths. Replace desiccant in drying filter. 4.Valve fails to open. Change valve. 5.Regulate expansion valves to higher capacity 6.Check and clean filter in liquid line 7.Coil may have blown. Control signal lacking. 8.Reduce compressor capacity. Check capacity regulating system.

Answer 4

The main purpose of a marine compressed air dryer is to eliminate moisture from the compressed air. In a marine environment, humidity is ever-present, and when compressed air is exposed to it, it tends to become saturated with water vapour. When moisture-laden air passes through pneumatic systems and equipment, it can lead to several detrimental consequences. Some of these include the following; Corrosion of air tools and equipment – moisture in the compressed air can cause rust and corrosion in pneumatic components, pipes, and machinery, leading to premature failure and potential safety hazards. Damage to electrical components – moisture can damage sensitive instruments and controls, causing malfunctions and compromising the overall safety and reliability of the vessel. Reduced efficiency of air tools and equipment – water in the compressed air can hamper the performance of pneumatic tools and systems, leading to decreased productivity and higher operational costs.

Answer 5

Operation of Marine Compressed Air Dryer The humid air flows into the air inlet connection and is pre-cooled in the heat exchanger before it enters the evaporator. As the air passes through the evaporator, which is cooled by the liquid refrigerant, the air temperature drops to 10°C, which is the dew point at which the moisture in the air is condensed. The condensed water is now separated from the air and is purged out of the system through the automatic drain trap. The high pressure liquid refrigerant now passes through the expansion valve and is evaporated in the evaporator, before returning to the compressor to continue the refrigeration cycle. To operate a marine compressed air dryer correctly, it is important to follow the manufacturer’s instructions. To ensure the marine compressed air dryer operates efficiently and effectively do the following Proper Installation – install the dryer in a clean, well-ventilated area away from potential sources of contamination, such as chemicals or exhaust fumes. Adequate ventilation prevents overheating and prolongs the lifespan of the dryer. Filtration – prioritize the installation of filtration systems upstream of the dryer to remove larger particles, oil, and other contaminants that could clog the dryer and reduce its performance. Adjust Air Pressure – normally dryer is connected to the compressed air supply line. Set the air pressure within the recommended range as per the manufacturer’s guidelines. High pressures can stress the dryer unnecessarily, while low pressures may result in insufficient drying. Drain Moisture Regularly – most marine compressed air dryers are equipped with automatic drains. Ensure these drains are functional and regularly inspect and clean them to prevent blockages and ensure proper moisture removal. Monitor Performance – regularly check the dryer’s output dew point and pressure levels to verify its efficiency. An increase in the dew point may indicate potential issues that need to be addressed promptly.

Answer 6

Cleaning – clean the dryer’s exterior regularly and ensure that the surrounding area is free from dust and debris that could obstruct air intake vents. Filter Replacement – Follow the manufacturer’s guidelines for filter replacement intervals. Clogged or dirty filters can restrict airflow, leading to decreased performance and increased energy consumption. Heat Exchanger Inspection – Regularly inspect and clean the heat exchanger to prevent a build-up of scale or debris, which can reduce the dryer’s efficiency. Check Drains – Routinely inspect and test automatic drains to ensure they are functioning correctly and effectively removing moisture from the system. Lubrication – If the dryer has any moving parts, ensure they are well-lubricated according to the manufacturer’s recommendations.

Answer 7

Insufficient Drying – if the dew point remains high despite correct settings, check for clogged filters, heat exchanger fouling, or malfunctioning drains. Clean or replace components as needed. Excessive Pressure Drop – a significant pressure drop across the dryer can indicate clogged filters or obstructions in the air passages. Inspect and clean the filters and air pathways to restore normal pressure. Unusual Noises or Vibrations – noises or vibrations may indicate loose components or worn-out bearings. Inspect the dryer and address any issues promptly to prevent further damage. Leakage – check for air leaks around fittings, valves, and connections. Repair or replace damaged components to maintain the dryer’s efficiency. If the dryer is not operating at all – it may have a problem with its electrical connections.

Answer 8

This is the most popular because of its simplicity. The accommodation is divided into zones, having different heating requirements. Separate air heaters for each zone are provided at the central unit as shown in the system below. see EOOW ORAL/ IAMI Sketch pack for system drawing 1.Filter 2.Cooler 3.One, Two, or Three zone heaters as required 4.Pre-insulated pipes delivering air to zones 5.Sound attenuating air terminal, with volume control 6.Automatic steam valves, one per zone heater 7.Steam trap, one per zone heater 8.Multi step cooling thermostat 9.Compressor 10.Automatic Capacity Control valves 11.Condenser 12.Thermostatic expansion valve 13.Sea water pump 14.Fan starter 15.Compressor starter 16.Sea water pump starter The regulation of air temperature by individual air quantity control in this system can give rise to difficulties unless special arrangements are made. For instance, a concerted move to reduce the air volume in a number of cabins would cause increased air pressure in the ducts, with a consequent increase in the air flow and possibly in noise level at the other outlets. This can be avoided but the economic factors usually put a limit on this. Some degree of control is possible through maintaining a constant pressure at the central unit, but since most of the variation in pressure drop takes place at the ducts, the effect is very limited. A pressure sensing device some way along each branch duct, controlling a valve at the entry to the branch, strikes a reasonable mean, and is fairly widely applied. The temperature of the air leaving the heater varies in accordance with the outside temperature prevailing. This can be effectively performed by a self actuating regulator controlled by two thermostat sensors, one in the air leaving the heater, the other outside. Air quantity control in each room served gives individual refinement. In summer, air temperature is controlled by a multi step thermostat in the re-circulating air stream, which governs the automatic capacity control of the refrigerating plant.

Answer 9

Air-conditioning systems are used to create and maintain certain temperature, relative humidity and air purity conditions in indoor spaces. This process is typically applied to maintain a level of comfort for passengers and crew. Air conditioning systems may be divided into two main classes, the central unit type in which the air is distributed to a group of spaces through ducting, and the self contained type, installed in the space it is to serve. Air-conditioning and ventilation-related conditions on ships have a considerable impact on the comfort of passengers, the well-being of the crew, and the efficient operation of equipment, systems, and installations, regardless of the type of ship. Both temperature and humidity must be controlled in order to provide a comfortable environment. Higher temperatures are more tolerable if the air is dryer. The cooling impact on the air as it travels over the evaporator coil removes moisture, but comfort requires a certain level of humidity, thus it is required to humidify the air again by sprinkling water into the circulating air flow. The central unit type is most widely used, in one or other of a number of alternative systems, characterized by the means provided to meet the varying requirements of each of the spaces being conditioned. The systems in general use are as follows: 1.Zone Control System 2.Double Duct System 3.Reheat System

Answer 10

In Double Duct system, two separate ducts are run from the central unit to each of the air terminals, as shown in figure below. In winter two warm air streams, of different temperatures, are carried to the air terminals, for individual mixing. The temperatures of both air streams are automatically controlled. In summer the air temperature leaving the cooler is controlled by a multi-step thermostat in the re-circulating air stream, which governs the automatic capacity control of refrigerating plant, as with the zone control. Steam is supplied to one of the heaters, so that two air streams are available at the air terminals for individual mixing. see EOOW ORAL/ IAMI Sketch pack for system drawing 1.Filter 2.Cooler 3.Low duty heater 4.High duty heater 5.Pre-insulated pipes delivering air 6.Sound attenuating air terminal, with volume and temperature control 7.Automatic steam valve for tempered air stream 8.Automatic steam valve for warm air stream 9.Steam traps 10.Multi-step cooling thermostat 11.Compressor 12.Automatic Capacity Control valves 13.Condenser 14.Thermostatic expansion valve 15.Sea water pump 16.Fan starter 17.Compressor starter 18.Sea water pump starter1.Filter 2.Cooler 3.Low duty heater 4.High duty heater 5.Pre-insulated pipes delivering air 6.Sound attenuating air terminal, with volume and temperature control 7.Automatic steam valve for tempered air stream 8.Automatic steam valve for warm air stream 9.Steam traps 10.Multi-step cooling thermostat 11.Compressor 12.Automatic Capacity Control valves 13.Condenser 14.Thermostatic expansion valve 15.Sea water pump 16.Fan starter 17.Compressor starter 18.Sea water pump starter

Answer 11

In reheat system, the air is pre heated at he central unit; its temperature is being automatically controlled. The air terminals are equipped with electric or hot water heating elements. These raise the temperature of the air to meet the demands of the room thermostats which are individually set. In summer, the air temperature is controlled by a multi step thermostat in the re-circulating air stream, which governs the automatic capacity control of the refrigerating plant. In the case of electric reheat, fire protection is provided by overheat thermostats which shut down he heaters in the event of air starvation, while a fan failure automatically cuts off the power supply. The diagram shows a reheat system for air conditioning 1.Filter 2.Cooler 3.Pre heater 4.Pre insulated air pipe 5.Sound attenuating air terminal containing electric re-heater and overheat thermostat 6.Automatic steam valve 7.Steam trap 8.Multi step cooling thermostat 9.Compressor 10.Automatic Capacity Control valves 11.Condenser 12.Thermostatic expansion valve 13.Sea water pump 14.Fan starter 15.Compressor starter 16.Sea water pump starter 17.Heater Contractor 18.Room type thermostat

Answer 12

The air conditioning plant is designed in principle to be self-contained within the fire zones or water tight compartments and to perform the following functions: Supply cool air to the accommodation and wheelhouse. Provide heating to the accommodation and wheelhouse air when necessary. Remove excess moisture from the air or humidify it to a comfortable level if necessary. Filter the air before it passes to the accommodation and wheelhouse. The air is supplied to the accommodation by an air handling unit (AHU), which is usually located inside accommodation block, in the air conditioning unit room. The unit consists of an electrically driven fan drawing air through the following sections starting from inlet to the outlet: One air filter One steam preheating unit One enthalpy exchanger of the rotating composite type (Econovent) One steam reheating unit Two air cooler evaporator coils The exhaust section of the air handling unit comprises, from inlet to the outlet: One return air filter One exhaust ventilator

Answer 13

Air handling unit working principle. Automatic control for the humidification of the air is installed in the outlet portion of the AHU and the humidistat controller is positioned in the room housing the air handling unit. The humidifier nozzles are supplied with steam from the ship’s steam system. The air is driven through the distribution trunking that supplies the living quarters and wheelhouse. Air may be drawn into the system either from outside or from the accommodation via the recirculation trunking. With heating or cooling coils in use, the unit are generally designed to operate on 70% fresh air supply. The ratio of circulation air may be varied manually using the damper in the inlet trunking. The inlet filters are of the washable mat type and preheating of the air is provided by coils supplied with steam from the ship’s steam system.

Answer 14

The starting procedure of air conditioning compressor All stop valves, except the compressor suction, in the refrigerant line should be opened and fully back seated to prevent the pressure in the valve reaching the valve gland. The crankcase heater on the compressor to be used should be switched on a least 3 hours prior to starting the compressor. Check that the crankcase oil level is correct. Check the quantity of refrigerant charge. Start the cooling water supply for the condenser cooling. The cooling water comes from the engine room low temperature central cooling FW system and will probably already be running. Start the compressor. Slowly open the suction stop valve until it is fully open. If the compressor starts making a knocking noise, close the valve immediately as this indicates that liquid refrigerant has been drawn into the machine. When the noise has stopped open the suction valve again very slowly. Repeat this operation if necessary, until the compressor runs smoothly with the suction valve fully open.

Answer 15

AHUs are kept clean as follows: AHUs should be regularly cleaned internally. Air filter material should be replaced at suitable intervals depending on dust concentration in the air. Damper control mechanism must be lubricated at regular intervals. Steam heating coil steam traps are to be regularly checked for correct operation. In the cooling section, ensure that drip pans are kept clean and that drains are clear. It is also important to note that the moisture removed from the air is collected into a drain pan inside AHU and therefore it is essential that no water should be lying in the air conditioning system as this can become a breeding ground for legionella bacteria, which can have serious, or even fatal, consequences. Drains should be kept clear and areas where water can lie should be sterilized at frequent intervals.

Answer 16

When starting the ventilation system, the following procedure generally applies Check that the air filters are clean. Set the air dampers to the outside position. Start the AHU supply fan, exhaust fan and enthalpy exchanger. Check that air is flowing to all parts of the accommodation.

Air Conditioning Flashcards

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