3.3.1.3 Stand-by heat loss coefficient (U) and surface area of tank (SA)
The amount of thermal loss from the EWH tank to the ambient temperature given in Eq. (3.1) is a function of the stand-by heat loss (U), surface area of the tank (SA), and the difference between TH (t) and Ta. The heat loss will be transferred through the insulation of the EWH tank, which has a thermal resistance (R). U is equal to the inverse of R. The surface area of the tank (SA) is assumed to be equal to the cylinder surface area, 2πrh + 2πr2. where r = the tank radius (ft), h is the tank height (ft). In some references, U and SA are represented by G, G=U*SA.
Due to the lack of information about the specifications of the tank, such as the height, radius and thermal resistance, the value of G is taken directly from reference [42]. The EWH tank volume (V) and G in this study are equal to 50 gallon (189.27L) and 3.6 Btu/°F. h, respectively.