Figure 7. Pump can also handle more general duties in larger systems.
Cutting refrigerant-pump energy consumption by better capacity control. Only a few systems operate with a constant refrigeration load -- therefore, effective capacity control of the refrigerant pump is important for performance and energy optimization. Not all capacity-control options decrease pump energy consumption. The use of a frequency converter and closed loop control of the pressure difference generated by the pump is one of the most attractive methods because it significantly reduces the pump's energy consumption.
Lessening refrigerant-pump energy consumption by better pump protection. The design of refrigerant pumps and the risk of vapor entering or forming inside the pump usually restrict the accepted operating envelope. By tradition, loss-generating protective devices such as permanent bypasses or Qmax orifices (to prevent too-high flows that could cause cavitation) have protected refrigerant pumps from operation outside the accepted envelope -- but at the cost of significant energy losses. A pump designed for CO2 coupled with intelligent electronic controls can obviate these protective devices and the losses they incur. Such electronic controls also enable improved monitoring of operations and regulating pump capacity and bypass in an intelligent way.
Field trials that employed all these measures achieved cuts in pump energy use on the order of 60–70%. Pump energy demand fell from a level of 6–7% of system energy consumption to just 2–3% .
BJARNE DINDLER RASMUSSEN is global product manager – refrigerant pumps for Grundfos Pumps, Olathe, Kan. Email him at email@example.com.
1. "Engineering Equation Solver," version 8.684, F-Chart Software, Madison, Wisc. (Oct. 2010).
2. Rasmussen, B. D. and Pachai, A. C., "Energy Saving Potential of Controlled Refrigerant Pumps in CO2/R404A-cascade systems," p. 987, Proceedings, 8th IIR Gustav Lorentzen Conf. on Natural Working Fluids, Copenhagen, Denmark (2008).