A free air cooling system that combines phase change material (PCM) with a natural cold source (i.e., cold air) was developed to reduce the space cooling energy consumption in telecommunications base stations (TBSs). Outside cold air, instead of air conditioning system was used to remove heat in the TBSs. In addition, a PCM technology was adopted to improve the mismatch between energy demand and supply on the electric grid. The proposed system was intended to operate in conjunction with existing air conditioning units within each TBS. Consequently, the running time the air conditioning units was reduced, resulting in energy and demand savings. A full scale prototype, herein referred. to as latent heat storage unit (LHSU), was designed, built and tested in TBSs located in five different climatic regions in southwest and eastern China during different seasons. In addition, a mathematical model was developed to simulate the operation of the proposed LHSUs. Energy savings ratio (ESR) was used as the criterion to evaluate LHSU's energy savings. The estimated average annual ESR in five climatic regions was approximately 50%, with a maximum value of 67%. The average percent running time in which the LHSU replaced the operation of conventional air conditioners was 82.6%, with values surpassing 75% in four of the five cities, and one city achieving a value of almost 100%. (C) 2015 Elsevier Ltd. All rights reserved.