Thermo-mechanical behaviour of ground-source thermo-active structures

Abstract High energy prices and new environmental policies have made geothermal energy increasingly popular. The EU, including Finland, aims to increase the use of renewable energy resources and reduce carbon emissions. Geothermal energy pile foundations, so-called energy piles, are considered a viable alternative technology for producing energy instead of traditional methods. Geothermal heat pump systems are economically efficient and renewable environmentally friendly energy production systems in which the ground acts as a heat source in winter and as a heat sink in summer. Energy piles are economical systems, as they act as dual-purpose structures in energy production and load transfer from buildings to the ground, avoiding extra expenses in ground boring solely for energy production. However, use of ground heat exchangers (GHE) for energy production in energy piles can result in temperature variations in the pile shaft and surrounding soil, in turn affecting the thermo-mechanical behaviour of pile shaft and soil in both structural and geotechnical terms. Despite large numbers of energy piles being installed, there is still a lack of reliable information and experience about the thermo-mechanical behaviour of these structures and their energy efficiency in cold climates. This thesis investigated the efficiency performance of energy pile foundations and their productivity in cold climates by considering different groundwater flow effects and short-term imbalanced seasonal thermal loadings. The structural and geotechnical bearing capacity of different types of energy piles fitted with GHEs were also evaluated, using numerical models, and the possibility of collapse due to use of thermal systems was examined. Use of the model to compare the performance of different GHEs in terms of their efficiency revealed that at a particular fluid flow rate, double U-tube systems had greater productivity than other systems tested. The results also indicated that using energy piles under medium groundwater flow can improve the productivity of systems by around 20% compared with saturated conditions with no groundwater flow. It was also concluded that in a design context, the structural bearing capacity of piles needs to be reduced due to the additional thermal stresses induced by heating/cooling pile operations.Tiivistelmä Kasvaneet energiakustannukset ja kiristyneet ympäristösäädökset ovat lisänneet geotermisten energiaratkaisujen suosiota. EU, mukaan lukien Suomi, on asettanut tavoitteekseen lisätä uusiutuvien energialähteiden käyttöä ja vähentää hiilidioksidipäästöjä. Geotermistä energiaa hyödyntävä paaluperustukset, niin kutsutut energiapaalut, tarjoavat uudenlaisen teknologian vähäpäästöisen energian tuottamiseen. Geotermiset lämpöpumppujärjestelmät, maalämpöpumput, ovat taloudellisia ja ympäristöystävällisiä energiantuotantomenetelmiä, jotka talviaikaan siirtävät maaperään varastoitunutta energiaa rakennuksen lämmittämiseen ja vastaavasti jäähdyttävät rakennusta kesällä siirtämällä lämpöä maaperään. Energiapaalujen taloudellisuus syntyy siitä, että ne pystyvät palvelemaan rakennusta kahdessa roolissa. Ne ovat osa rakennuksen energiajärjestelmää ja toimivat samalla myös kantavana rakenteena, joka siirtää rakennuksen kuormia perustuksilta maaperään. Lämpöpumppujärjestelmän kytkeminen paaluihin voi johtaa lämpötilan vaihteluun paaluissa sekä niitä ympäröivässä maaperässä, mikä puolestaan vaikuttaa paalujen ja maaperän lämpömekaanisiin, rakenteellisiin sekä geoteknisiin ominaisuuksiin. Vaikka energiapaaluja on asennettu jo paljon, ei paalujen lämpömekaanisesta käyttäytymisestä tai energiatehokkuudesta kylmien ilmastojen alueilla ole vielä paljoa tutkittua tietoa. Tässä väitöstutkimuksessa selvitettiin numeerisesti energiapaalujen rakennuspaikan pohjaolosuhteista riippuvaa tuottopotentiaalia Skandinaavisissa olosuhteissa ja ilmastossa. Tarkastelut kohdistuivat erityisesti pohjavesivirtauksen sekä vuodenaikojen ja ilman lämpötilan vaihtelun vaikutuksiin. Tutkimuksessa arvioitiin myös paalujen lämpötilan vaihtelujen vaikutuksia paalujen geoteknisiin ja rakenteellisiin ominaisuuksia sekä kestävyyteen. Numeeristen simulaatiotulosten perusteella betonipaaluun asennetun U-putkirakenteen avulla saavutetaan paras tuottopotentiaali. Tulokset osoittivat, että kohtalainen pohjaveden virtaus parantaa systeemin tuottoa noin 20 % verrattuna tilanteeseen, jossa vedellä kyllästetyssä maassa ei tapahdu pohjaveden virtausta. Analyysitulokset osoittavat myös, että paalujen lämpötilavaihteluista aiheutuvat lisäjännitykset vähentävät paalujen kantokykyä, mikä tulee ottaa huomioon paalujen mitoituksessa

Nutritional status modifies pregnane X receptor regulated transcriptome

Abstract Pregnane X receptor (PXR) regulates glucose and lipid metabolism, but little is known of the nutritional regulation of PXR function. We investigated the genome wide effects of the nutritional status on the PXR mediated gene regulation in the liver. Mice were treated with a PXR ligand pregnenolone 16α-carbonitrile (PCN) for 4 days and subsequently either fasted for 5 hours or after 4-hour fast treated with intragastric glucose 1 hour before sample collection. Gene expression microarray study indicated that PCN both induced and repressed much higher number of genes in the glucose fed mice and the induction of multiple well-established PXR target genes was potentiated by glucose. A subset of genes, including bile acid synthesis gene Cyp8b1, responded in an opposite direction during fasting and after glucose feeding. PXR knockout abolished these effects. In agreement with the Cyp8b1 regulation, PCN also modified the bile acid composition in the glucose fed mice. Contribution of glucose, insulin and glucagon on the observed nutritional effects was investigated in primary hepatocytes. However, only mild impact on PXR function was observed. These results show that nutritional status modifies the PXR regulated transcriptome both qualitatively and quantitatively and reveal a complex crosstalk between PXR and energy homeostasis

Pregnane X receptor activator rifampin increases blood pressure and stimulates plasma renin activity

Abstract We conducted a clinical trial with 22 healthy volunteers to investigate the effects of pregnane X receptor (PXR) agonist rifampin on blood pressure (BP). The study was randomized, crossover, single‐blind, and placebo‐controlled. Rifampin 600 mg or placebo once daily was administered for a week and the 24‐hour ambulatory BP was monitored at the end of each arm on the eighth day. Rifampin elevated the mean systolic and diastolic 24‐hour BP (4.7 mmHg, P < 0.0001, and 3.0 mmHg, P < 0.001, respectively) as well as the mean heart rate (3.5 bpm, P = 0.038). The serum renin concentration and the plasma renin activity were increased. Although rifampin increased circulating 4β‐hydroxycholesterol (4βHC) as expected, the plasma 4βHC concentration strongly negatively correlated with 24‐hour BP, especially systolic, in both rifampin and placebo arms (rifampin systolic BP, r = −0.69, P < 0.001; placebo systolic BP, r = −0.70, P < 0.001). The 4βHC, an agonist for liver X receptor (LXR), induced renin expression modestly in LXR‐α expressing Calu‐6 cells but only at unphysiologically high 4βHC concentrations. In conclusion, rifampin stimulates renin activity and has a hypertensive effect. This finding should be considered when designing interaction studies involving rifampin or other PXR agonists. Furthermore, PXR may represent a putative therapeutic target for the treatment of hypertension

Activation of nuclear receptor PXR impairs glucose tolerance and dysregulates GLUT2 expression and subcellular localization in liver

Abstract Pregnane X receptor (PXR) is a nuclear receptor that senses chemical environment and is activated by numerous clinically used drugs and environmental contaminants. Previous studies have indicated that several drugs known to activate PXR appear to induce glucose intolerance. We now aimed to reveal the role of PXR in drug-induced glucose intolerance and characterize the mechanisms involved. We used PXR knockout mice model to investigate the significance of this nuclear receptor in the regulation of glucose tolerance. PXR ligand pregnenolone-16ɑ-carbonitrile (PCN) impaired glucose tolerance in the wildtype mice but not in the PXR knockout mice. Furthermore, DNA microarray and bioinformatics analysis of differentially expressed genes and glucose metabolism relevant pathways in PCN treated primary hepatocytes indicated that PXR regulates genes involved in glucose uptake. PCN decreased the expression of glucose transporter 2 (GLUT2) in mouse liver and in the wildtype mouse hepatocytes but not in the PXR knockout cells. Data mining of published chromatin immunoprecipitation-sequencing results indicate that Glut2 gene is a direct PXR target. Furthermore, PCN induced internalization of GLUT2 protein from the plasma membrane to the cytosol in the liver in vivo and repressed glucose uptake in the primary hepatocytes. Our results indicate that the activation of PXR impairs glucose tolerance and thus PXR represents a novel diabetogenic pathway. PXR activation dysregulates GLUT2 function by two different mechanisms. These findings may partly explain the diabetogenic effects of medications and environmental contaminants