Comparative Study on Applicability of Plate Heat Exchanger and Mixed Water Pump in Constant-Temperature Water Chiller Controlled at Ultra-High Precision

A large-scale scientific facility uses constant-temperature air conditioning (CTAC) to control the air temperature fluctuation at an ultrahigh precision, i.e., ≤±0.1 ℃, which implies that the temperature of the chiller water must also be maintained at an ultrahigh precision level. Traditional CTACs depend on electric heating to maintain the chilled water temperature. However, such methods usually fail to address the issue of high-frequency oscillations and typically are not applied to ultrahigh-precision control. In this study, by conducting a reduced-scale experiment, we first validated the feasibility of two water chillers, one using a plate heat exchanger and another using a mixed water pump, to provide chilled water at an ultrahigh precision. Simulations using Modelica models based on these two approaches were established and experimentally verified. Finally, the steady-state and dynamic performances of these two systems were compared. Both approaches can achieve ±0.1 ℃ temperature fluctuation control when the hardware meets specific criteria, with the plate heat exchanger approach exhibiting superior steady-state performance. Under both schemes the root mean square error (RMSE) for the entire time period is below 0.1 ℃. The settling times for the plate heat exchanger and mixed water pump approaches are 5000 s and 600 s, respectively. The mixed water pump approach exhibits better dynamic performance. Both plate heat exchanger and mixed water pump approaches are capable of actively dampening high-frequency oscillations in the water supply temperature, with damping coefficients of 0.07 and 0.4, respectively.