The theory of Thermal Response Testing (TRT) is a well-known part of the sizing process of the geothermal exchange system. Multiple parameters influence the accuracy of effective ground thermal ...conductivity measurement; like testing time, variable power, climate interferences, groundwater effect, etc. To improve the accuracy of the TRT, we introduced a procedure to additionally analyze falloff temperature decline after the power test. The method is based on a premise of analogy between TRT and petroleum well testing, since the origin of both procedures lies in the diffusivity equation with solutions for heat conduction or pressure analysis during radial flow. Applying pressure build-up test interpretation techniques to borehole heat exchanger testing, greater accuracy could be achieved since ground conductivity could be obtained from this period. Analysis was conducted on a coaxial exchanger with five different power steps, and with both direct and reverse flow regimes. Each test was set with 96 h of classical TRT, followed by 96 h of temperature decline, making for almost 2000 h of cumulative borehole testing. Results showed that the ground conductivity value could vary by as much as 25%, depending on test time, seasonal period and power fluctuations, while the thermal conductivity obtained from the falloff period provided more stable values, with only a 10% value variation.
Classic and extended step thermal response test were conducted on three different locations in Zagreb. Measurements with the classical thermal response test were used to determine thermogeological ...properties of the ground and thermal resistance of the borehole for each location. Different values of thermal conductivity are the result of differences in the geological profile and depth of the sites. In addition, experimental research of the steady-state thermal response step test (SSTRST) was carried out to determine heat rejection rates for passive and active cooling in a steady state regime. Results showed that the heat rejection rate is only between 8-11 W/m, which indicates that the coaxial system is not suitable for passive cooling demands. Furthermore, the heat pump in passive cooling mode uses an additional plate heat exchanger which causes heat losses and additional temperature rise of the working fluid by approximately 1.5 °C. Therefore, the steady-state rejection rate for passive cooling is even lower for a real case project. The coaxial heat exchanger should always be designed for an active cooling regime with an operation of a heat pump compressor in a classical vapour compression refrigeration cycle.
The utilization of shallow geothermal energy is well known in several European countries. Even though large parts of the Republic of Croatia show significant potential for its use, the installation ...of ground source heat pump systems (heat pump and heat exchangers) is slowly progressing. Therefore, a short overview of research published thus far concerning the utilization and assessments of shallow geothermal potential for Croatia was done. In Croatia, there is no agency or government department in charge of collecting and publishing data concerning installations of heat exchangers. Therefore, a study was done to collect the available data on installed closed-loop heat exchangers either from scientific research or from personal contacts with drilling companies. Based on the collected data, a map was produced that shows general locations of installed heat exchangers. From the obtained data of installed heat exchanger length, a first assessment of utilizing shallow geothermal potential in Croatia was given.
One of the most common geoexchange system in practice today is a vertical two-loop heat exchanger. There is also a growing trend of inclined drilling of multiple 40–50 m boreholes with coaxial heat ...exchangers, which are efficient when installing in areas where there is a favourable groundwater flow. Special care should be taken in hydraulic design of coaxial system, since laminar flow often occur in annular channel, due to glycol mixture implementation. In this research, vertical and inclined coaxial borehole exchangers were compared in identical geological environment, to express differences in heat extraction and thermal resistances, as well as in flow regimes and pressure drop. Extended Steady-State Thermal Response Step Test was implemented, which incorporate series of power steps to determine borehole extraction rate at steady-state heat transfer conditions. Results show that 2U-heat exchanger has advantages over coaxial heat exchangers, in terms of greater steady state heat extraction rate and more favourable hydraulic. Defined extraction rate at 0/-3 °C borehole temperature, in dominantly clay ground, was 43,5 W/m for coaxial system, compared to 54,5 W/m for vertical 2U-loop. Borehole resistance analysis showed almost double value for coaxial system compared to 2U-loop, due to frequent problems in cementation of inclined boreholes.
•Paper focuses on modelling difference between vertical 2U and inclined coaxial borehole heat exchangers.•Hydraulic modelling was carried out for three typical variants of 2U and coaxial exchangers related to pressure drop, rheology, different glycol solutions and equivalent borehole resistances.•Steady-State Thermal Response Step Test (SS-TRST) novel approach was introduced to analyse BHE capacity and thermal resistance during long term operation for 2U and coaxial heat exchanger.•Case study on two real project was performed performing extended thermal response testing.
Large scale development of tight oil resources in US started after 2010. with following five-year period of favorable steady increase in crude oil price. During this relatively short expansion cycle, ...operating and capital expenses changed drastically for main tight oil plays due to technological improvements in both well drilling and completion, expansion of service sector as well as loose government monetary policy which allowed favorable financing. This paper analyzed trends in costs during expansion period, as well as correlation of oil price to number of operating rigs and production quotas. After 2008/2009. world financial crisis economy recovery in US was somewhat sluggish and it caused extreme volatile environment in both equity and commodity markets. In such volatile environment intra-day crude oil prices, as well as other commodities and equities, show significant reaction to monthly published macroeconomic indicator reports, which give better overviews of trends in economic recovery. Prior to announcement, these reports always have forecasted value determined by consensus among market analysts. Therefore, any positive or negative surprise in real value tends to influence price of oil. This paper investigated influence of such macroeconomic reports to closing intraday oil price, as well as effect of other important daily market indices. Analysis showed that only Producer Price Index (PPI), among other indicators, has statistical significance of affecting intraday closing oil price.
•New short term underground thermal energy storage system.•Experimental analysis of underground water tank for geothermal exploitation.•Efficiency improvement in cow barns, by direct thermal exchange ...for multiple purposes.•Innovative solution for underground water storage at fixed target temperature.
This paper presents an innovative ground heat exchanger with double-circuit, GeoUWT (Geothermal Underground Water Tanks), and the required preconditions for installing this kind of configuration in the livestock sector. Dedicated Thermal Response Test was conducted on the test site to represent barn conditions and to estimate the heat exchange capacity of the GeoUWT in a realistic case study performance. This dynamic simulation of geothermal heat exchange between the process fluids on the barn – precooling of the produced milk and warming required amount of water – proved enhanced potential compared to existing systems of direct heat exchange. The additional value is an innovative solution for underground water storage at fixed target temperature.
Large scale development of tight oil resources in the USA started after 2010 with a following five-year period of favourable steady increase in crude oil price. During this relatively short expansion ...cycle, operating and capital expenses changed drastically for main tight oil plays due to technological improvements in both well drilling and completion, the expansion of the service sector as well as the loose government monetary policy which allowed favourable financing. This paper analysed trends in costs during the expansion period, as well as the correlation of oil price to a number of operating rigs and production quotas. After 2008/2009, the world financial crisis economy recovery in the USA was somewhat sluggish and it caused an extremely volatile environment in both equity and commodity markets. In such a volatile environment intraday crude oil prices, as well as other commodities and equities, show a significant reaction to monthly published macroeconomic indicator reports, which give better overviews of trends in economic recovery. Prior to the announcement, these reports have always forecasted value determined by a consensus among market analysts. Therefore, any positive or negative surprise in real value tends to influence the price of oil. This paper investigated the influence of such macroeconomic reports to closing intraday oil price, as well as the effect of other important daily market indices. Analysis showed that only the Producer Price Index (PPI), among other indicators, has a statistical significance of affecting intraday closing oil price.
U nekoliko europskih država u znatnoj mjeri iskorištava se plitka geotermalna energija. Iako veći dio Republike Hrvatske pokazuje potencijal, iskorištavanje i instalacija samih sustava geotermalnih ...dizalica topline (dizalice topline i toplinski izmjenjivači) pokazuju lagani porast. S obzirom na navedeno u radu je dan kratak pregled dosad objavljenih istraživanja koja se odnose na iskorištavanje i procjenu potencijala plitke geotermalne energije u Hrvatskoj. Na području države trenutačno ne postoji agencija ili državni ured čija bi zadaća bila prikupljati i objavljivati podatke o instaliranim sustavima toplinskih izmjenjivača. Zbog toga je provedeno prikupljanje podataka, od kojih su neki dostupni u objavljenim znanstvenim radovima ili su skupljeni osobnim kontaktom, a koji se odnose na instalirane sustave izmjenjivača sa zatvorenim krugom. Na kraju je, prema skupljenim podatcima, dana procjena trenutačnoga stanja iskorištavanja plitke geotermalne energije za područje Republike Hrvatske.
Tipski i prošireni test toplinskoga odaziva tla (TRT) izveden je na koaksijalnim izmjenjivačima topline na trima različitim lokacijama u Zagrebu. Tipskim testom toplinskoga odaziva određena su ...termogeološka svojstva tla i bušotinski otpor. Zbog različitosti geoloških profila toplinska vodljivost tla varira. Provedena su i eksperimentalna mjerenja „step” testom toplinskoga odaziva tla (SSTRST) u svrhu određivanja potencijala pohrane toplinske energije kod pasivnoga i aktivnoga hlađenja prilikom ustaljenoga stanja prijenosa topline. Rezultati su pokazali potencijal pohrane toplinske energije u tlo između 8 i 11 vata po metru bušotine, upućujući na nemogućnost pasivnoga hlađenja koaksijalnim izmjenjivačem topline. Nadalje, dizalice topline u režimu pasivnoga hlađenja koriste se pločastim izmjenjivačem, na kojemu dolazi do dodatnoga temperaturnog pada za otprilike 1,5 °C. Stoga je mogućnost pohrane toplinske energije još i manja kod realnih projekata s pasivnim hlađenjem. Koaksijalni izmjenjivači topline uvijek bi morali biti projektirani za rad u aktivnome režimu hlađenja gdje kompresor dizalice topline radi u klasičnome parnom kompresijskom ciklusu.
Ubrzani razvoj nekonvencionalnih ležišta nafte u SAD-u započeo je 2010. godine, uz naredno petogodišnje razdoblje sa stabilnim i relativno visokim cijenama nafte na tržištu. Tijekom toga relativno ...kratkoga perioda ekspanzije došlo je do znatnijih promjena u kapitalnim i operativnim troškovima zbog neprestanoga tehnološkog napretka u bušenju i opremanju, rastu pratećega naftno-servisnog sektora te povoljnijega financiranja projekata uz državnu politiku monetarnoga popuštanja. U radu su analizirani trendovi u troškovima razvoja nekonvencionalnih ležišta te ovisnost kretanja cijene nafte (WTI – West Texas Intermediate) o intenzitetu broja aktivnih bušotina i ukupnim proizvodnim kvotama s najvećih ležišta nekonvencionalne nafte. Nakon svjetske financijske krize iz 2008./2009. ekonomski oporavak u SAD-u bio je donekle usporen, što je uzrokovalo ekstremnu volatilnost na dioničkim i robnim tržištima. U takvim nesigurnim uvjetima dnevna kretanja cijena nafte te vrijednosti dionica i roba pokazuju znatno reagiranje na periodične izvještaje o promjenama glavnih makroekonomskih indikatora kao glavnih pokazatelja trenda ekonomskoga oporavka. Prije nego što državne institucije objave takve izvještaje, postoje i predviđanja vrijednosti indikatora temeljem anketa među ekonomskim analitičarima i očekivanim trendovima. Stoga, bilo kakvo pozitivno ili negativno iznenađenje prilikom objave stvarnih podataka u odnosu na predviđeno utječe na dnevno kretanje cijene nafte. U ovome radu statistički su analizi rani utjecaji takvih promjena u makroekonomskim indikatorima na dnevnu završnu cijenu nafte te utjecaj ostalih važnijih burzovnih indeksa u SAD-u. Analiza je pokazala da od makroekonomskih indikatora najveći utjecaj na dnevne pomake u cijeni nafte ima indeks industrijskih proizvođačkih cijena (PPI – Producer Price Index) kao temeljni indeks pokazatelja inflacije.
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