Impact of Standing Column Well Operation on Carbonate Scaling

Léo Cerclet,Benoît Courcelles,Philippe Pasquier

doi:10.3390/w12082222

Abstract

Standing column well constitutes a recent promising solution to provide heating or cooling and to reduce greenhouse gases emissions in urban areas. Nevertheless, scaling issues can emerge in presence of carbonates and impact their efficiency. Even though a thermo-hydro-geochemical model demonstrated the impact of the water temperature on carbonate concentration, this conclusion has not been yet demonstrated by field investigations. To do so, an experimental ground source heat pump system connected to a standing column well was operated under various conditions to collect 50 groundwater samples over a period of 267 days. These field samples were used for mineral analysis and laboratory batch experiments. The results were analyzed with multivariate regression and geochemical simulations and confirmed a clear relationship between the calcium concentrations measured in the well, the temperature and the calcite equilibrium constant. It was also found that operating a ground source heat pump system in conjunction with a small groundwater treatment system allows reduction of calcium concentration in the well, while shutting down the system leads to a quite rapid increase at a level consistent with the regional calcium concentration. Although no major clogging or biofouling problem was observed after two years of operation, mineral scales made of carbonates precipitated on a flowmeter and hindered its operation. The paper provides insight on the impact of standing column well on groundwater quality and suggests some mitigation measures.

Highlights

IntroductionGround source heat pumps (GSHPs) have the capacity to reduce greenhouse gas emissions for heating and cooling buildings [2], which represented 61% of the total energy consumption in the commercial and institutional sector in Canada in 2016 [3]
Nowadays, it is mostly accepted that greenhouse gases are responsible for global warming [1].Ground source heat pumps (GSHPs) have the capacity to reduce greenhouse gas emissions for heating and cooling buildings [2], which represented 61% of the total energy consumption in the commercial and institutional sector in Canada in 2016 [3]
To identify the factors impacting carbonate scaling in a standing column wells (SCWs), the geothermal laboratory and its groundwater treatment system were used between 16 January and 10 October 2018 under various heating and cooling conditions

Summary

Introduction

Ground source heat pumps (GSHPs) have the capacity to reduce greenhouse gas emissions for heating and cooling buildings [2], which represented 61% of the total energy consumption in the commercial and institutional sector in Canada in 2016 [3]. The GSHPs are sustainable technologies [4]. Due to their renewable aspect and mostly their high energy efficiency, the number of GSHPs has been rising worldwide over the past 15 years [5]. Among the different types of ground heat exchangers, standing column wells (SCWs) have proven to be a promising solution because of their high heat exchange rate and lower first costs [6,7]. Another significant advantage is that SCWs can be installed more in urban areas as they require a smaller footprint than closed-loop systems, and less groundwater than open-loop systems [8]

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