Abstract:
The influence of variables such as; refrigerant amount, chilling
and cooling water temperature, throttle valve opening, cooling
and chilling water flow rates, on the efficiency (coefficient of
performance – COP) of a water to water carbon dioxide heat
pump was investigated. Design of experiments was done using
design-expert® 6 software for regression analysis. A response
surface method known as central cubic design was used to
provide optimum results with minimum experiments. Through
multiple regression analysis, an empirical equation relating the
COP to the variables was derived. Analysis of variance revealed
that these regressions are statistically significant at 95%
confidence level compounded with a very low standard
deviation and a high adequate precision. The close relationship
between the predicted COP values and the actual values further
proves the worthiness of the empirical equation. It was observed
that cooling water temperature had the highest influence
followed by the chilling water temperature. Surprisingly, the
amount of the refrigerant was third followed by the throttle
valve opening. Understandably, chilling water flow rate had the
least effect on the COP. Through response surface diagrams, the
interactive influence of the variables were also observed. The
COP values arrived at varied from 1.545 to 6.914 although if
the variables were optimized fully within the scope of this
study, a value of up to 11.8 could be achieved. Still, if the
variables range is increased further, higher COP could be
achieved. Finally, a discussion was done in a bid to explain
these results.
