E C Bi T B2

where

C = the constant energy use below the change point,

B-i = the coefficient or slope that describes the linear dependency on temperature, B2 = the cooling change point temperature, T = the ambient temperature for the period corresponding to the energy use, + = positive values only for the parenthetical expression.

E. Four-parameter Model

The four-parameter change-point linear heating model is typically applicable to heating usage in buildings with HVAC systems that have variable-air volume, or whose output varies with the ambient temperature. Four-parameter models have also been shown to be useful for modeling the whole-building electricity use of grocery stores that have large refrigeration loads, and significant cooling loads during the cooling season. Two types of four-parameter models are listed in Table 27.16, including a heating model and a cooling model. The four-parameter change-point linear heating model is given by

Bi = the coefficient or slope that describes the where linear dependency on degree-days, DDbj = the heating or cooling degree-days (or degree hours), which are based on the balance-point temperature.

The three-parameter change-point linear model for heating is described by154

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