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its function is if the pressure in the evaporator go less than cert in level it shut off the compressor
Linear parameter varying (LPV) model-based predictive control method is proposed to regulate the chilled water temperature of centralized heating, ventilating and air conditioning (HVAC) systems. First, a LPV model structure is proposed to identify the dynamics of the refrigerant loop under varying cooling load. By defining the scheduling variable to be the chilled water mass flow rate, the working conditions, under which the HVAC system is operating, can be quantified. Thereafter, a certain number of operating points across the whole operation range can be determined and the corresponding local linear models are built. Subsequently, a global LPV model is attained by interpolating all local models along with transition process data. With the aid of the model, a LPV-based model predictive control mechanism is implemented to control the compressor frequency in order to maintain the chilled water temperature in the presence of varying cooling load and external disturbance. Experimental tests on a pilot HVAC system demonstrate that the proposed control scheme can accurately capture the nonlinearity of the process and deliver satisfactory performance to maintain a desired chilled water temperature.
Compressor low-Side Pressure Control Valves
Starting a compressor places a head load on the
Motor. Let has to overcome inertia of the moving Parts..
(Objects at rest tend to stay at rest.) It must also over-come high crankcase pressure.(In fact ,crankcase pressure may be at its highest at staring.)It is important usually taxed to the limit at the moment of starting.
This is especially true when starting against normal or above normal head pressures.
A compressor low-side pressure control is used on some installations. This keeps cmnkcase low-side pressures at a
Reasonable level, even though the rest of the Iow-side pressure may be high. It never permits the crankcase pressure to exceed a certain safe value, and is known as a reverse metering, two-temperature valve.
Low pressure valve ( L P V )
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