The 3Smart team from University of Belgrade Faculty of Mechanical Engineering published an article titled:" Approximate method for the estimation of energy performance of heat pumps connected to the system of energy management of facilities", at the Third International Symposium on Agricultural Engineering ISAE 2017. A relatively simple mathematical model of a heat pump, with wich it is possible to get valuesfor the Coefficient of performance (COP) at any given time and under given conditions is presented in the article.

You can take a look or download the article preprint here.