Actual Reduction of Power Consumption by the Compressor
The APR Control directly saves power by reducing the lift of the compressor. Because the APR Control is a modulating external unloader, it diverts refrigerant around the compressor. This action of diverting refrigerant around the compressor lowers the system’s high pressure and raises the system’s low pressure. This is known as reducing the lift. Reducing lift decreases horsepower requirements, thereby decreasing power consumption.
Utilizing the APR Control in a DX system’s refrigeration circuit reduces kw/hr while operating to match changing load conditions. Because compressor lift is reduced, the compressor has less work to do. The APR Control, when active, also improves evaporator efficiency by increasing the refrigerant quality in the evaporator. This dual effect of increased evaporator efficiency and decreased compressor lift is a proven method of power reduction (See Sporlan Pressure Enthalpy Chart for more detail). Multiple evaluations of APR Control power savings have demonstrated this. We have seen up to a 63% reduction in kw/hr in a unit tested at real world, low-load conditions versus full-load AHRI testing conditions. That same test revealed a 14% reduction in kw/hr at the compressor.
Compressor work can expressed as
W = h * q
W = compression work (Btu/hr)
h = heat of compression (Btu/lb)
q = refrigerant circulated (lb/hr – mass flow)
During high modulation the refrigeration effect is improved. Reducing mass flow (through the evaporator and the condenser coils) results in reduced velocity in the heat exchangers allowing for greater heat transfer.
The Adiabatic Process
The APR Control modulates the adiabatic process. This happens twice within the refrigeration system. Inside the compressor and also after the expansion valve but before the entrance to the evaporator. Another way of expressing this, the APR Control proportionally modulates the differential pressure or compression ratio (lift) in reaction to actual load.
The APR Control does this proportional modulation while maintaining an extremely efficient evaporator. Notice the black arrows (on the right edge of the diagram) showing the beginning and end of the compression line, which represents the work (hp) the compressor is engaged in, are closer together indicating that there is less work performed during “adiabatic modulation.” The work required by the compressor is represented by the line from point 1 to point 2, the APR Control will reduce work from point 1a to point 2a during modulation. The diagram exaggerates the differences for demonstration purposes.
This means that the compressor is now doing less work for increased evaporator efficiency. While the APR Control is active, kw/hr consumption is improved (The APR is NOT Hot Gas Bypass).
The APR Control delivers a cost effective solution when part of an energy optimization plan!