A ground–source heat pump system (GSHP) can be an alternative to air–source heat pumps (ASHP), as exchanging heat with the ground instead of with the air can result in higher coefficients of ...performance (COP). However, unbalanced loads can significantly shift the temperature profile in the ground, decreasing the GSHP’s overall performance. Hybrid systems can reduce the imbalanced loads and improve performance. This study proposed the use of personal comfort systems (PCS) and natural ventilation (NV) to decrease the thermal load imbalance in a cooling–dominated building.
Building energy simulations were used to assess the performance of eight renewable heating and cooling solutions in three Portuguese cities (Porto, Lisbon and Faro): (1) ASHP, (2) GSHP, (3) ASHP–PCS, (4) GSHP–PCS, (5) ASHP–NV, (6) GSHP–NV, (7) ASHP–PCS–NV, (8) GSHP–PCS–NV. The simulation results show that without hybridization, the use of the GSHP resulted in an increase in ground temperature of more than 20 °C, over 50 years, which decreased its COP and rendered it unable to supply the full cooling load, and may not be acceptable in environmental terms. The use of either PCS or NV for hybrid cooling decreased the thermal cooling load and increased the energy efficiency of the GSHP system relative to the equivalent ASHP–hybrid. However, full coverage of the cooling load was still not always possible, as ground heat build–up was still high. Hybridization with both NV and PCS allowed full coverage of the thermal load by the GSHP. Both the cooling load and final energy needs decreased by over 90%, and the increase in ground temperature was limited to about 6 °C.
Climate change will increase the magnitude and frequency of high temperatures, resulting in higher cooling demands in buildings and a possible diminished efficacy of the passive solutions that could ...be used to limit that increased demand. However, building energy simulations are often performed with past weather data files, ignoring the effect of the changing climate.
Portuguese building certification regulations use standard TMY (typical meteorological year) weather files that were updated with RCP4.5 predictions. These updated weather files were used to reassess the impact of climate change on a hybridized ground–source heat pump (GSHP) system with piles, natural ventilation (NV) and personal comfort systems (PCS). Cooling loads increased the most in Porto and the least in Faro, varying from 3 to 163%, with the exception of the GSHP–NV–PCS hybrid scenario in Lisbon, where the cooling load decreased 27%. This increased unbalance of the thermal loads resulted in a higher build–up of heat in the ground, decreasing the fraction of load that could be covered by the GSHP, especially in Porto. Despite the increase in final energy needs for heating and cooling, the GSHP–NV–PCS approach is a resilient solution to supply heating and cooling in a warming climate, as it can still reduce final energy consumption by more than 90%, relative to a non–hybrid approach.
•Heat exchange between piles and surrounding ground.•Contextualizes reported response thermally-activated piles in cohesive media.•Demonstrates influence of pile mobilisation under mechanical load on ...thermal response as function of: factor-of-safety on shaft resistance, pile spacing within groups.•Characterises impact of heat loss from building on: Thermo-mechanical response of pile foundation, Heat exchange between piles and surrounding ground
The thermal-activation of pile foundations for use within shallow geothermal energy systems has received much attention with a number of studies having reported full- and small-scale testing and/or numerical analysis. Various conditions in terms of pile type, ground profiles and thermal loading, have been considered in these studies, leading to a broad understanding of the thermo-mechanical behaviour of thermally-activated pile foundations. One area that requires further attention is the clarification of the foundation response under seasonal cyclic thermal loading. This study systematically assesses the impact of cyclic thermal loading in relation to the initial mechanical loading, for isolated floating piles and pile groups in a cohesive soil medium. For piles where the shaft resistance dominates the pile total resistance, it was found that irrecoverable movement will be small and thermal stress and pile head movements change in a cyclic and regular manner. It is shown that the effect of the coefficient of thermal expansion of the soil, is much reduced from that suggested in studies using constant thermal loads applied over long periods. The effect of the overlying building was explored and it is shown that thermal-activation of the pile foundation mitigates the effect of the imposition of a higher average temperature at the surface.
Micropiles are small-diameter foundation elements that are widely used in building refurbishment to reinforce existing foundations or provide new foundations where access for construction is ...difficult. Thermally-activated (TA) micropiles could be useful as an efficient means of providing cost-effective ground-coupling when shallow geothermal energy systems are considered in building rehabilitation. It is well-established that thermal activation of pile foundations results in thermo-mechanical interactions between the pile and the surrounding soil. These thermally-induced effects need to be examined to ensure that they do not adversely impact the load transfer function of the micropile. Numerical analysis is able to produce reliable predictions of thermo-mechanical behavior of TA piles, and this study applied this technique to examine the cyclic thermal behavior of micropiles, isolated and in groups. For the situations considered in this study, it is shown that during cyclic thermal activation, irrecoverable movements are unlikely to be significant in design terms, if the initial mobilization of the shaft resistance is low. Though stable, cyclic thermal movement amplitudes are large enough that they should be considered in design. The study highlights that large changes in thermal stress can develop and be locked-in to the response of long flexible piles, and that these should be verified in design. Further, as pile spacing reduces, thermal interference results in a loss of heat exchange capacity per pile, which has to be considered in the design of large groups of TA micropiles. Therefore, TA micropiles can offer an efficient and secure means of providing ground coupling in shallow geothermal energy systems.
Building foundation piles can be used as heat exchangers in ground-source heat pump (GSHP) systems to provide highly efficient renewable heating and cooling (H&C). Unbalanced H&C loads lead to heat ...build-up in the ground, decreasing the system's overall performance. In this study, the introduction of natural ventilation (NV) has been examined to decrease cooling load imbalance in cooling-dominated buildings to improve system efficiency. Building energy simulations estimated the H&C loads for an office building in three Portuguese cities: Lisbon, Porto and Faro, yielding heating loads of 0.2–3.6 MWh/year and cooling loads of 260–450 MWh/year. Four renewable H&C technology scenarios were used to assess energy performance: (1) an air-source heat pump (ASHP) system; (2) a GSHP system utilizing energy piles; (3) hybrid ASHP-NV and (4) hybrid GSHP-NV. Over 50 years of operation, in Scenario (1) COP values of 2.45–2.55 (heating) and 3.62–4.15 (cooling) were obtained. In (2), COP values increased to 4.15–4.34 (heating) but fell to 3.36–3.79 (cooling), which increased annual final energy needs by 7–8%. Unbalanced cooling loads increased the ground temperature by 21–24 °C, which is unlikely to be acceptable. Compared to (1), introducing NV reduced cooling loads by 65–90% in Scenarios (3) and (4), with the final energy needs decreasing by 59–80% and 62–88%, respectively. A further benefit of the GSHP-NV hybrid is that the ground temperature increase was limited to 8‑12 °C. For cooling, the COP in (3) decreased compared to (1) (3.14–3.69), while in (4), COP improved to 3.45–6.10. This study concludes that hybrid GSHP-NV systems should be considered in some cooling-dominated scenarios.
Thermal integrity profiling (TIP) is a common non-destructive technique to evaluate the quality of construction of piles by analysing the temperature fields due to heat of hydration from freshly cast ...concrete piles. For this process to be accurate, a reliable concrete heat of hydration model is required. This paper proposes a practical and simple technique to calibrate a four-parameter model for the prediction of concrete heat of hydration. This model has been shown to be able to reproduce the evolution of heat of hydration measured in laboratory tests, as well as field measurements of temperature within curing concrete piles, as part of a TIP operation performed at a site in London. With the simplicity of the model and the small number of model parameters involved, this model can be easily and quickly calibrated, enabling quick predictions of expected temperatures for subsequent casts using the same concrete mix.
Combating climate change requires a significant reduction of energy use, in particular that used for heating and cooling of buildings. Innovative solutions, such as the hybridization of ground-source ...heat pump (GSHP)-based heating, ventilation and air conditioning (HVAC) systems with personal comfort systems (PCS) and natural ventilation (NV) can be employed to improve energy efficiency. However, although climate change will alter the need for HVAC and the efficacy of passive solutions, most building energy simulations use historical weather data, and thus, do not consider the effects of climate change. This study focused on the impact of warmer future weather on the performance of eight heating and cooling scenarios, which result from different combinations of heat pump, either air-source (ASHP) or ground-source (GSHP), and PCS and/or NV, in an office building in fourteen cities across the Iberian Peninsula.
Building energy simulations confirm that, while heating loads decrease in most cities, cooling thermal demand increases significantly as a consequence of warming due to climate change. The resulting increased energy imbalance increased heat build-up in the ground, reducing the thermal load satisfied by the GSHP. The warmer outdoor air and ground led to lower cooling coefficients of performance (COP) for the ASHP and GSHP, respectively, which, with the increased need for cooling, resulted in electricity needs for heating and cooling increasing significantly.
Revised simulations based on decreasing the internal heat load generated by equipment and lighting were carried out to explore measures that could be used to mitigate these climate change impacts. The reduction in internal loads resulted in a noticeable shift in the thermal loads towards the heating demand. This reduced imbalance resulted in a decrease in cooling demand, as well as a lower build-up of heat in the ground, which consequently improved the coverage of the load by the GSHP and increased the cooling COP, resulting in a decrease in electricity needs for heating and cooling of up to 71%, relative to standard internal loads.
Display omitted
•Climate change will alter heating and cooling needs and passive solutions' efficacy.•Building energy simulations were performed with late 21st Century weather in Iberia.•Climate change reduced overall heating and cooling efficiency.•Lower internal equipment and lighting heat load decreased load imbalance.•Hybrid solution and lower indoor loads decreased electricity needs by up to 71%.
•The finite element method can reliably capture heat exchange between embedded walls and the ground given sufficient attention is paid to mesh refinement and the assessment of key parameters.•For ...experimental case studies careful consideration should be given to the characterisation of such geostructures, their constituent materials and surrounding environment to ensure the heat transfer processes are understood.•The thermal properties of the wall elements are at least as important as, and in some cases more so than, those of the ground in determining the heat transfer potential.•Wall geometry in terms of the height of wall exposed to any internal space relative to the height of the wall panel height and the wall thickness have been revealed to have an important influence on heat exchange potential.
A number of operational cases exist where embedded retaining walls, used in the construction of underground spaces such as basements and shallow tunnels, have also been utilised as ground-heat exchangers in shallow geothermal energy systems. These are complex structures in terms of their geometry, the surrounding temperature field and boundary conditions, and there are currently no methods to assess their heat exchange capacity in a simple and expedient manner. This contribution uses the finite element method to validate the use of the method in predicting heat flow for this application and then, to assess the influence of wall and excavation geometry in the heat exchange process. The influence of the soil and wall thermal conductivity is shown to be quasi-linear with the latter showing the greatest influence on peak heat exchange. The work identifies a geometric parameter - the ratio of excavation depth to total wall panel depth, H/L which in combination with the wall thickness (D), provide a consistent and simple means by which the heat exchange potential can be estimated, for a given set of wall and soil thermal properties and boundary conditions.
IMPORTANCE: The Cornea Donor Study (CDS) showed that donor age is not a factor in survival of most penetrating keratoplasties for endothelial disease. Secondary analyses confirm the importance of ...surgical indication and presence of glaucoma in outcomes at 10 years. OBJECTIVE: To assess the relationship between donor and recipient factors and corneal graft survival in the CDS. DESIGN, SETTING, AND PARTICIPANTS: Multicenter prospective, double-masked, controlled clinical trial conducted at 80 clinical sites. One hundred five surgeons enrolled 1090 participants undergoing corneal transplant for a moderate-risk condition, principally Fuchs dystrophy or pseudophakic or aphakic corneal edema (PACE). Forty-three eye banks provided corneas. INTERVENTIONS: Corneas from donors younger than 66 years and donors 66 years or older were assigned, masked to donor age. Surgery and postoperative care were performed according to the surgeons’ usual routines. Participants were followed up for as long as 12 years. MAIN OUTCOMES AND MEASURES: Graft failure, defined as a regrafting procedure or a cloudy cornea for 3 consecutive months. RESULTS: The 10-year cumulative probability of graft failure was higher in participants with PACE than in those with Fuchs dystrophy (37% vs 20%; hazard ratio HR, 2.1 99% CI, 1.4-3.0; P < .001) and in participants with a history of glaucoma before penetrating keratoplasty, particularly with prior glaucoma surgery (58% with prior glaucoma surgery and use of medications to lower intraocular pressure at the time of surgery vs 22% with no history of glaucoma surgery or medication use; HR, 4.1 99% CI, 2.2-7.5; P < .001). We found trends toward increased graft failure in recipients who were 70 years or older compared with those younger than 60 years (29% vs 19%; HR, 1.2 99% CI, 0.7-2.1; P = .04) or were African American (HR, 1.5; P = .11) or who had a history of smoking (35% vs 24%; HR, 1.6 99% CI, 0.9-2.8; P = .02). Lower endothelial cell density (ECD) and higher corneal thickness (CT) at 6 months (6% vs 41% for ECD ≥2700 vs <1700 cells/mm2 P < .001; 14% vs 36% for CT <500 vs ≥600 μm P = .001), 1 year (4% vs 39% for ECD ≥2700 vs <1700 cells/mm2 P < .001; 18% vs 28% for CT <500 vs ≥600 μm P = .04), and 5 years (2% vs 29% for ECD ≥1500 vs <500 cells/mm2 P < .001; 7% vs 34% for CT <550 vs ≥650 μm P < .001) were associated with subsequent graft failure. CONCLUSIONS AND RELEVANCE: Most penetrating corneal grafts for Fuchs dystrophy or PACE remain clear at 10 years. The risk for failure is greater for graft recipients with PACE and those with a history of glaucoma. Measurements of ECD and CT during the course of postkeratoplasty follow-up are associated with a risk for failure. However, even with very low ECD and high CT at 5 years, most corneas remain clear at 10 years.
PDF
