A hybrid method for refrigerant flow balancing in multi-circuit evaporators: Upstream versus downstream flow control

A hybrid method for optimizing refrigerant distribution in evaporators is presented that involves the use of small balancing valves in each circuit along with a primary expansion device to control the overall superheat from the evaporator. The flow balancing valves could be located upstream or downstream of the evaporator. This paper presents the results of a study to investigate the benefits of this hybrid scheme for both upstream and downstream flow balancing for the case of air flow mal-distribution. In order to perform this investigation, a simulation model was developed to consider evaporator flow mal-distributions for a 10.55 kW residential R410A heat pump and then validated through comparisons of predicted results with measurements. Simulation results show that there are significant benefits in controlling the superheat of each circuit of evaporators through the hybrid–individual superheat control method. Furthermore, the upstream refrigerant flow control consistently outperforms the downstream refrigerant flow control, and recovers most of the loss in cooling capacity and COP due to non-uniform air flow distribution.