Fixed orifice metering device

Technical information Refrigeration Fixed metering devices and load

Fixed metering and load

A system using a capillary tube or fixed diaphragm dosing operates at maximum efficiency only in the design of the operating conditions for which the device has been selected. These devices do not have a mechanical means to change adaptation load in the system. Under all conditions, other than design conditions, the efficiency of the system, so not the best possible. Realistically, however, these devices work just fine for normal range of operation conditions. He quickly changed when the load changes, or well, or at extremely low loads occur, there is a problem.

One of the best ways to avoid low system load, in order to avoid overestimation of the system. Oversized system is forced to spend most of its time operating at low load.

While the fixed metering device has no mechanical means to change adaptation load in the system, they can automatically adjust the load or "float with loading, as compressors and evaporators to do.

For the average comfort air conditioning system about 3 tons of cooling capacity or less, the whole system swims with a load of good enough to work stably, without the need for complex devices control capacity of the compressor, a condenser, a metering device, or evaporator. The system automatically adjusts its power to, as the load increases, and down when the load is reduced to exactly match the cooling load capacity. Please consult the Compressor and evaporator modules in this series to see how this principle works. When the load drops below the ability of a system of automatic compensation system cycles off.

In the evaporator, less refrigerant vapor is less, because the refrigerant evaporates, because a smaller amount of heat is absorbed by the refrigerant in the coil. This condition occurs because less heat is available to be absorbed through reduced requirements in the cold.

But in the compressor the same volume of gas is removed from the evaporator in the unit of time (cfm). Therefore, the evaporator, the pressure becomes less. Therefore, in the compressor suction pressure falls and the discharge pressure, which decreases pressure and saturation temperature at the condenser. Click on the dispenser, less than the inlet pressure (pressure condensing) produces less refrigerant to flow through the dispenser. This means less refrigerant system throughput.

In addition to these changes, which was started in the evaporator, the condensing pressure is usually reduced in the future due to lower temperatures of the outside air that accompany cooling reduce the load on most small comfort jobs. This fact adds to the automatic down compensation in capacity. On the contrary, the reverse of the above steps is true, as the cooling load increases...

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