A heating, ventilation and air-conditioning (HVAC) system with integrated aquifer thermal energy storage (ATES) was designed for a supermarket building in Mersin, a city near the Mediterranean coast in Turkey (36degrees 49' N and 34degrees 36' E). This is the first ATES application carried out in Turkey. The peak cooling and heating loads of the building are 195 and 74 kW, respectively. The general objective of the system is to use the groundwater from the aquifer to cool down the condenser of the HVAC system and at the same time storing this waste heat in the aquifer. Cooling with groundwater at around 18 degreesC instead of utilizing outside summer air at 30-35 degreesC decreases consumption of electrical energy significantly. In addition, stored heat can be recovered when it is needed in winter. The HVAC system with ATES started operation in August 2001 in cooling mode with an average coefficient of performance (COP) of 4.18, which is almost 60% higher than a conventional system. (C) 2004 Elsevier Ltd. All rights reserved.