Using heat pipes as heat transfer elements, and porous ceramic tubes as water saturated media material integrated into regenerative indirect evaporative cooler (R-IEC) can sufficiently decrease air temperature with considerable minimum water consumption rates for evaporative cooling applications in buildings. As the performance of evaporative coolers is dependent upon the type, structure and flow scheme of the heat and mass exchanger, this paper presents new heat-mass exchanger design of a sub-wet bulb temperature indirect evaporative cooler for air conditioning in buildings. This regenerative indirect evaporative cooler is based on heat pipe heat exchanger and porous ceramic tubes where the heat pipes and the ceramic tubes straddle vertically across two adjacent air ducts to form a wet and dry channel. The upper passage is the heat sink of the cooling system in which the condensers of the heat pipes are embedded inside water-filled porous ceramic tubes, so called the wet-air channel. While, the finned evaporators of the heat pipes are positioned in the lower passage where the intake air flows through to be cooled down without increasing its moisture content. 1-D numerical model was developed to investigate the thermal performance of the system, the simulation is based on the principles of heat and mass transfer and coded using MATLAP software. Theoretically, it was found that under climatic conditions of 30-45 °C air temperature and 20-35% relative humidity the cooler wet bulb effectiveness ranged from 0.71 to 1.11, while the COP spanned from 6 to 17.Equally, the water consumption rates of the system varied from 0.974 to 1.657 l/kWh of the cooler cooling capacity.