Experimental assessment of a standing column well performance in cold climates

Abstract

Standing column wells can provide energy savings at lower first-costs than conventional vertical ground heat exchangers while having a higher potential in dense urban areas. Unfortunately, operating these open wells with groundwater near the freezing point has limited so far their use in northern climates and studies illustrating their successful operation in heating mode are limited. The objective of this study is to provide insights on the various operating conditions affecting the performance of heat pumps linked to standing column wells and demonstrate their potential in cold climates. This work relies on a major research infrastructure designed to operate water-to-air heat pumps connected to a standing column well and its companion injection well under realistic dynamic heating and cooling conditions. During its first operating year, the laboratory was operated continously in heating mode for 26 days. Results show that combined use of a plate heat exchanger and heat pumps allows heat extraction from the ground at significant rates (between 120 W/m and 160 W/m), while keeping the groundwater temperature above 0 °C during peak heating periods. This is approximately two times more than typical values reported for conventional closed loop borehole heat exchangers. Such efficiency was possible owing to the bleed control used, which allows transferring to the injection well part of the groundwater pumped and thus promotes advective heat transport towards the standing column well. Our measurements indicate that bleed was required only 30% of the time and represented 4.6 m3 of groundwater per day on average. These results should dimiss doubts raised in the literature and demonstrate the potential usability of SCWs for cold climates.