We propose that energy dissipation is an essential quantity in studying nonequilibrium first order phase transition driven by an external field, and the fieid scanning rate is a characteristic variable. The technique of differential scanning calorimetry (SC) is applied to investigate the temperature scanning-rate dependence of energy dissipation AQ in first order structural phase transitions of RbNOs powder, VO, ceramics and Fe-16.5 wt% Mn alloy. We tit the experimental results to a general power law "AQ=AQO+AT" where AQO and A are two constants, and n is an exponent parameter.