Numerical modelling of multiple standing column wells for heating and cooling buildings

A model for simulating clusters of standing column wells (SCWs) for use in geothermal heating and cooling systems is described in this paper. The model is three-dimensional, dynamic and solves the governing equations using a finite volume discretisation scheme with a fully implicit algorithm. The slower-acting field equations are solved using a wider time interval than that used for the faster-acting well equations and the two sets of equations are coupled through the field equation source terms. A groundwater bleed feature is incorporated. The model is applied to two evaluative test cases the first of which involves heating only and the second, heating and cooling. Results of the applications suggest that SCWs can deliver substantially higher rates of heat transfer than conventional closed loop borehole heat exchanger arrays especially when groundwater bleed is operational. An important practical consequence of this is that far less geotechnical drilling is needed when using SCWs than is the case with closed loop arrays

Scheduling of Multiple Chillers in Trigeneration Plants

The scheduling of both absorption cycle and vapour compression cycle chillers in trigeneration plants is investigated in this work. Many trigeneration plants use absorption cycle chillers only but there are potential performance advantages to be gained by using a combination of absorption and compression chillers especially in situations where the building electrical demand to be met by the combined heat and power (CHP) plant is variable. Simulation models of both types of chillers are developed together with a simple model of a variable-capacity CHP engine developed by curve-fitting to supplier’s data. The models are linked to form an optimisation problem in which the contribution of both chiller types is determined at a maximum value of operating cost (or carbon emission) saving. Results show that an optimum operating condition arises at moderately high air conditioning demands and moderately low power demand when the air conditioning demand is shared between both chillers, all recovered heat is utilised, and the contribution arising from the compression chiller results in an increase in CHP power generation and, hence, engine efficiency

Numerical modelling of multiple standing column wells applied to geothermal heating and cooling in UK buildings

Standing column wells (SCWs) have the potential to deliver much higher rates of heat transfer to geothermal heating and cooling systems in buildings via heat pumps than conventional vertical borehole heat exchange arrays. Its open-end column design with porous casing along the borehole (depending on the formation) encourages the flow of groundwater from the rock’s porous matrix into the well or the opposite way according to the hydraulic gradients. This approach induces a further heat transfer mechanism in addition to the conduction: it is advection. Advection induced by the groundwater movement due to the hydraulic gradient and the action of the well pump causes warmer water (in winter) and cooler (in summer) to be drawn into the well thus increasing heat transfer capacity. This is beneficial for SCWs to offer much higher heat transfer performance than other conventional approaches. The development of a numerical model for clusters of standing column wells is described in this thesis. The model is three-dimensional, dynamic and solves the governing equations using a finite volume discretisation scheme with a fully implicit algorithm. The slower acting field equations are solved using a wider time interval than that used for the faster acting well equations and the two sets of equations are coupled through the field equation source terms. A groundwater bleed feature is incorporated. The model has been validated thermally and hydraulically using existing field data. Two test cases have been applied to reveal the advantages of using SCWs in UK conditions, competing with the conventional closed-loop system of vertical borehole heat exchangers. The results of the applications suggest that SCWs can deliver substantially higher rates of heat transfer than conventional closed-loop borehole heat exchanger arrays, typically up to 250Wm-1, especially when groundwater bleed is operational. The results also confirm that a bleeding operation can offer up to 2.2K improvement (reduction) in the outlet well water temperature in summer and (increase) in the well water temperature in winter. Investigation results on borehole diameter confirm that a larger well borehole diameter would offer improved heat transfer performance in some cases, according to the relative change of the heat transfer coefficient. Analysis of borehole to borehole spacing seems to suggest that 5m is the most effective spacing of the three different spacing choices for this type of application. The results also show that SCW installation in London Clay performs less well than Magnesian Limestone and Old Red Sandstone; the latter two seem to be appropriate formation types to work with this type of application. The advantage of adopting multiple well arrangements (SCW clusters) over the use of single wells has also been confirmed. The important practical consequence of this is that far less geotechnical drilling is needed as the required borehole depth reduces substantially under multiple well arrangements. The results gathered from three different buildings also reveal that the balance between heating and cooling demands appears to have less impact on the mean formation temperature change than the large cooling application, which is beneficial to maintain a steady system performance over a long period of time. The results also suggest that the impact on the rock formation was very dominant in the first few years but it declined towards the end of the 5 year analysis period used in this work. The results from the CO2 emission analysis demonstrate that an annual carbon emission reduction of up to 46% can be achieved by using the geothermal system with SCWs instead of the conventional system consisting of a gas-fired condensing boiler and a conventional aircooled chiller. They also confirm that the balance between heating and cooling demands has a substantial impact on the carbon saving delivered by this technology

Sintered aluminium heat pipe (SAHP)

This work is the product of an ongoing PhD project in the School of the Built and Natural Environment of Northumbria University in collaboration with the University of Liverpool and Thermacore Europe Ltd. The achievements at the end of the first year are summarized. The main objective of the project is to develop an aluminum ammonia heat pipe with a sintered wick structure. Currently available ammonia heat pipes mainly use extruded axially grooved aluminum tubes as a capillary wick. There have been a few attempts of employing porous steel or nickel wicks in steel tubes with ammonia as the working fluid (Bai, Lin et al. 2009)although it is a common practice in loop heat pipes but there is no report of aluminum-ammonia heat pipes porous aluminium wick structures. The main barrier is the difficulty of sintering aluminum powders to manufacture porous wicks. So far during this project promising sintered aluminum heat pipe samples have been manufactured using the Selective Laser Melting (SLM) technique with various wick characteristics. This SLM method has proven to be capable of manufacturing very complicated wick structures with different thickness, porosity, permeability and pore sizes in different regions of a heat pipe. In addition the entire heat pipe including the end cap, outer tube wall, wick and the fill tube can be generated in a single process

Understanding the reliability of localized near future weather data for building performance prediction in the UK

Access to reliable site-specific near future weather data is crucial for forecasting temporally-dynamic building energy demand and consumption, and determining the state of on-site renewable energy generation. Often there is a missing link between weather forecast providers and building energy management systems. This short paper discusses the potential to conduct building performance modelling using localized high resolution weather forecast freely available from the United Kingdom Met Office DataPoint service. It creates a great opportunity for building performance simulation professionals and building energy managers to re-use site-specific high resolution weather forecast data to predict near future building performance at both individual building and city scale. In this paper, authors have developed a framework of forecasting near future building performance and a Matlab script to automatically gather observed weather data from 140 weather stations and weather forecasts for nearly 6,000 locations in the UK. To understand the reliability of weather forecast, three-hourly forecasts of temperature, relative humidity, wind speed and wind direction are compared with observations from weather stations. This provides evidences to use the next 24-hour forecast to predict dynamic building energy demand and consumption, and determine the on-site renewable energy generation output. Because of the high accuracy of forecast, the rolling forecast can be recorded on daily basis to construct weather files for locations that do not have weather stations. This will increase current 14 locations of the CIBSE weather data to nearly 6,000 locations covering population centers, sporting venues and tourist attractions

Occupant adaptive behaviour: an effective method towards energy efficient buildings

Energy efficient buildings play an important role in achieving a sustainable society. Conventional methods achieving energy efficient buildings mainly focus on upgrading the physical properties of the building, such as increasing their thermal insulations, neglecting the occupants who are using the building. This study justifies the potential contribution of a new method, i.e. selecting offices for occupants with a consideration of their behavioural preferences and the building’s physical properties, to the building’s energy efficiency. Dynamic building performance simulation has been adopted for the justification, based on a case study building with a simple rectangular shape. The occupant window behavioural model was developed from field measured data in an office building and the up-to-date stochastic approach was used to predict the state of windows for the simulation. Simulation results clearly reflect that 1) building’s physical properties, such as window orientation, have impact on the thermal performance of the building; 2) occupant behaviour can also affect the thermal performance of the building; and 3) considering both occupant behavioural preference and building’s physical properties can promote building’s thermal performance, without requirement of changing occupant behaviour

Lipidomics Reveals Multiple Pathway Effects of a Multi-Components Preparation on Lipid Biochemistry in ApoE*3Leiden.CETP Mice

Background: Causes and consequences of the complex changes in lipids occurring in the metabolic syndrome are only partly understood. Several interconnected processes are deteriorating, which implies that multi-target approaches might be more successful than strategies based on a limited number of surrogate markers. Preparations from Chinese Medicine (CM) systems have been handed down with documented clinical features similar as metabolic syndrome, which might help developing new intervention for metabolic syndrome. The progress in systems biology and specific animal models created possibilities to assess the effects of such preparations. Here we report the plasma and liver lipidomics results of the intervention effects of a preparation SUB885C in apolipoprotein E3 Leiden cholesteryl ester transfer protein (ApoE*3Leiden.CETP) mice. SUB885C was developed according to the principles of CM for treatment of metabolic syndrome. The cannabinoid receptor type 1 blocker rimonabant was included as a general control for the evaluation of weight and metabolic responses. Methodology/Principal Findings: ApoE*3Leiden.CETP mice with mild hypercholesterolemia were divided into SUB885C-, rimonabant- and non-treated control groups. SUB885C caused no weight loss, but significantly reduced plasma cholesterol (-49%, p <0.001), CETP levels (-31%,

Finite Time Analysis of a Tri-Generation Cycle

A review of the literature indicates that current tri-generation cycles show low thermal performance, even when optimised for maximum useful output. This paper presents a Finite Time analysis of a tri-generation cycle that is based upon coupled power and refrigeration Carnot cycles. The analysis applies equally well to Stirling cycles or any cycle that exhibits isothermal heat transfer with the environment and is internally reversible. It is shown that it is possible to obtain a significantly higher energy utilisation factor with this type of cycle by considering the energy transferred during the isothermal compression and expansion processes as useful products thus making the energy utilisation larger than the enthalpy drop of the working fluid of the power cycle. The cycle is shown to have the highest energy utilisation factor when energy is supplied from a low temperature heat source and in this case the output is biased towards heating and cooling