Large diameter earth-air heat exchanger (EAHX) built for standalone office room cooling

Monitoring results for hot and dry summer conditions

Abstract

Earth-air heat exchangers (EAHX) use the soil thermal capacity to dampen the amplitude of outdoor air temperature oscillations. This effect can be used in hot and dry climates for room cooling and, depending on the EAHX design, this cooling can be achieved with very little resources other than those used during the EAHX construction. This is an obvious advantage compared to the significant energy consumption and operational costs of refrigeration machines traditionally used in room cooling. Despite the large number of papers on EAHX available in the scientific literature, very few deal with large diameter EAHX (with pipe diameters larger than 0.30 m), and even fewer present monitoring data gathered from a built and functional large diameter EAHX. The present paper uses monitoring data and provides a detailed quantitative analysis of the performance of a large diameter EAHX built for standalone cooling of an existing office building. The field monitoring was carried out during a characteristic hot and dry summer period of the south of Portugal. Results show that outdoor air to EAHX exit air temperature gradients reach 9 K and cooling capacities exceed 27 kW. Moreover, the studied EAHX is capable of standalone cooling for outdoor air temperatures up to 33ºC and meets more than 50% of the room design cooling demand for outdoor air temperatures as high as 37ºC. This evidences that large diameter EAHX have the potential to achieve significant reductions in CO₂ emissions and in energy consumption associated with building cooling in hot and dry climates.