HVAC Evaporator Cooling cycle

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HVAC Evaporator Cooling cycle

During the normal cooling cycle controlled by a thermostat, as room temperature rises above the high setting on the thermostat there is a need for refrigeration. Liquid solenoid (valve A) and the built-in pilot (valve D) open, allowing refrigerant to flow. The opening of the built in pilot allows the pressure to bypass the sensing […]

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Valves used in direct-expansion systems

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Valves used in direct-expansion systems

The pilot solenoid (valve B) is a 1/8 in. ported solenoid valve that is direct operated and suitable as a liquid, suction, hot gas, or pilot valve at pressures to 300 lb. Solenoid valve A is a one-piston, pilot-operated valve suitable for suction, liquid, or gas lines at pressures of 300 lb. It is available […]

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HVAC Direct-expansion systems

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HVAC Direct-expansion systems

Figure 10-7 shows a high temperature system [above 32°F (0°C)] with no drip-pan defrost. During the normal cooling cycle, controlled by a thermostat, the room temperature may rise above the high setting of the thermostat. This indicates a need for refrigeration. The liquid solenoid (valve A), pilot solenoid (valve B), and the dual-pressure regulator (valve […]

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HVAC Coiled Evaporator

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HVAC Coiled Evaporator

Evaporator coils on air-conditioning units fall into two categories: Finned-tube coil is placed in the air stream of the unit. Refrigerant vaporizes in it. The refrigerant in the tubes and the air flowing around the fins attached to the tubes draw heat from the air. This is commonly referred to as a direct expansion cooling […]

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HVAC Scroll compression process

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HVAC Scroll compression process

Figure 9-81 shows how the spiral-shaped members fit together. Abetter view is shown in Fig. 9-82. The two members fit together forming crescent-shaped gas pockets. One member remains stationary, while the second member is allowed to orbit relative to the stationary member. This movement draws gas into the outer pocket created by the two members, […]

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HVAC Scroll Compressors

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HVAC Scroll Compressors

The scroll compressor (Fig. 9-80) is being used by the industry in response to the need to increase the efficiency of air-conditioning equipment. This is done in order to meet the U.S. Department of Energy Standards of 1992. The standards apply to all air conditioners. All equipment must have a Seasonal Energy Efficiency Ratio (SEER) […]

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HVAC Twin screw compressors

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The twin screw is the most common type of screw compressor used today. It uses a double set of rotors (male and female) to compress the refrigerant gas. The male rotor usually has four lobes. The female rotor consists of six lobes. Normally, this is referred to as a 4 + 6 arrangement. However, some […]

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HVAC Single screw compressors

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HVAC Single screw compressors

A single screw compressor is shown in Fig. 9-77. The compression process starts with the rotors meshed at the inlet port of the compressor. The rotors turn. The lobes separate at the inlet port, increasing the volume between the lobes. This increased volume causes a reduction in pressure. Thus, drawing in the refrigerant gas. The […]

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HVAC Screw Compressors

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Screw compressors operate more or less like pumps, and have continuous flow refrigerant compared to reciprocals. Reciprocal have pulsations. This results in smooth compression with little vibration. Reciprocals, on the other hand, make pulsating sounds and vibrate. They can be very noisy. Screw compressors have almost linear capacity-control mechanisms. That results in excellent part-load performance. […]

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