The Average Temperature of Energy Piles

Abstract

ABSTRACT:The geotechnical design of energy piles requires confirmation that the foundations can continue to carry safely the required load from the overlying structure and that no detrimental effects from the additional imposed temperature changes will occur. These additional design checks require assumptions to be made about the temperature changes within the pile. However, there is no universal approach for determining these, and routine application of over-conservative pile temperatures can lead to unrealistically adverse geotechnical design scenarios. This paper considers how the average temperature of a pile can be determined based on the analysis steps already carried out for the thermal design. The aim is to be able use the calculated fluid temperatures, along with readily available pile and ground parameters, to provide better assessments of the actual pile temperature so that the outputs of the geotechnical design can be improved. Two dimensional numerical simulations are used to determine the average pile temperature for different pipe, pile and concrete properties. The results of the simulations are compared with analytical approaches, allowing these to be validated for use on a routine basis. It is shown that the temperature of the center of the pile, which can be determined easily by analytical methods, can be used as a proxy for the average pile temperature.

Calculation of the representative temperature change for the thermomechanical design of energy piles

“…The influence of heat exchange pipe installation form and pile diameter on the representative temperature is mainly reflected by the concrete thermal resistance in the analytical model 46,[53][54][55][56] . According to the Eq.…”

“…The proposed model's applicability in a greater range of geometries should be assessed in the future. Additionally, it can be seen that the steady-state assumption of heat transfer in a pile will overestimate the representative temperature change 46 . Thus, the analytical model can be further developed to better account for the transient condition, which is especially important for larger diameter energy piles.…”

Finite element analyses of energy piles using different constitutive models

“…Since the scope of the present work is the evaluation of the effect of the thermal cycles on the pile behaviour, the circulation of the heat-carrier fluid has not been modelled and the temperature variation has been uniformly applied on all the elements of the pile. Past works have shown that the choice of a uniform temperature applied to each pile cross section and along its length does not significantly affect the results [15,16].…”

A Model of a Diaphragm Wall Ground Heat Exchanger

“…Although various studies have been conducted to investigate the performance of thermally activated piles [8][9][10][11], diaphragm wall heat exchangers (DWHE) have received less interest [5]. One of the first studies that focused on heat transfer in diaphragm walls corresponds to the work of Brandl [7].…”