CHARACTERISTICS AND PERFORMANCE OF A CO2 HEAT PUMP AT 50% OVERCHARGED CONDITIONS

A CO2 water to water heat pump system was used to investigate
the effects of throttle valve opening and water flow rates at higher
charge capacity (149% of the full charge). It was observed that the
throttle opening affects the gas cooler pressure (and inlet
temperature) where the less the opening the higher the pressure.
Although the increase in gas cooler pressure was improving the
gas cooler heat output and therefore the system efficiencies, there
is an optimum pressure which when exceeded, the system
performance deteriorates. This optimum pressure also is related to
a certain throttle opening which is approximately at 20% in this
study. Similarly, as the throttle valve is reduced, the overall system becomes more ideal as indicated by Lorentz efficiency.
On the other hand, the higher the flow rates the higher the performance although it’s better to keep the chilling water
(evaporator) flow rate low and cooling water (gas cooler) flow rates high than vice versa for the best heat pump
performance. However, if the main intention is to idealize the system, then it’s better to keep the chilling water flow rates
high and the cooling water flow rates low as stipulated by the Lorentz efficiency. Many systems tend to be overcharged
while the refrigerant is being refilled and therefore will behave as observed in this study, thus its importance.