To assist manufacturers in their early stage of appliance design (i.e. component selection) an easy to implement charge equation, for hydrocarbon refrigerants R-290 and R-600a, has been developed. The equation estimates the appliance total refrigerant charge based on the type of refrigerant, the operating conditions and the internal volume of the components of the cooling system. This paper presents the charge equation developed and discusses the derivation, assumptions and underlying calculations in detail. It is shown that the influence of refrigerant mass flux cannot be neglected. However, a simple approximation of the effect of mass flux is shown to provide good results. The equation is validated based on the total refrigerant charge of 10 charge optimized glass door bottle coolers, varying in refrigerated volume from 50 to 1200 dm~3, having a cooling capacity between 50 and 1500 W and using hydrocarbon as the refrigerant. Validation showed an agreement within 15% between the calculated and the actual refrigerant charge of the appliances.
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