A general method to evaluate the applicability of natural energy for building cooling and heating: Revised degree hours

Abstract

Utilizing natural energy directly for building cooling and heating can reduce the energy use of the HVAC systems significantly. There are various utilization forms of natural energies for building cooling and heating. The applicability of natural ventilation was evaluated in the previous studies by degree hours method which cannot be used for the evaluation of other natural energy utilizing forms. To provide guidance for selecting proper natural energy and the utilizing forms for building cooling and heating, a general method, i.e., the revised degree hours method, is proposed. Firstly, the conception and rationality of the revised degree hours method are indicated by comparing with the degree hours method. Then, the utilizations of revised degree hours method in evaluating the applicability of natural energy are discussed in terms of different climates, different natural energies and different utilizing forms. The results show that the revised degree hours can directly reflect the energy saving potential of natural energy and it is capable of fairly evaluating different utilization forms with different kinds of natural energies. According to these cases analyzed in this paper, the mechanical ventilation shows a quite promising potential in the temperate region; both the dew point evaporative cooling and the ground heat exchanger fresh air handling system are outstanding in the dry and cold region; the cooling tower combined with pipe-embedded window system works well in the hot summer and cold winter region as well as the hot summer and warm winter region. In conclusion, the revised degree hours method contributes to the low carbon development of HVAC systems by guiding the full use of natural energy for building energy efficiency.