Estimation of Cooling Energy Demand and Carbon Emissions from Urban Buildings using a Quasi-dynamic Model

Global warming and the urban heat island effect in large towns and cities demand new approaches to cooling buildings in an efficient and sustainable way. Modern refrigeration, air conditioning and heat pump (RACHP) systems can achieve a high coefficient of performance and low emissions, but refrigeration technology already accounts for around 15% of worldwide electricity use and up to 10% of all greenhouse gas emissions, so in the context of international agreements to reduce global greenhouse gas emissions by up to 80% RACHP systems alone cannot provide a sustainable cooling solution for cities. The purpose of the model described in this paper is to provide a simple and easy to use tool to estimate the impact of different heating and cooling technologies, alternative building design and operating parameters and future global warming, on the energy demands and carbon emissions of buildings. Existing software tools for analysis of buildings can provide high quality results for a given scenario, but the determination of an optimal solution demands multiple simulations, which can be time consuming and require post processing to interpret the results. The Excel based tool uses a quasi-dynamic energy balance model and reduced weather data set to generate rapid results, allowing the user to view the building’s temperature profile, energy demands and carbon emissions in near real time and to develop an optimum cooling strategy. Results are presented for a single building version of the tool. When fully developed, it will allow the user to model clusters of buildings in an urban environment

Simulation of the heat recovery use of R744 systems in a supermarket

This paper describes the outcomes a research project that investigate the improvement in the COP of an enhanced booster R744 refrigeration system that provided MT cooling for chilled food cabinets and LT cooling for cold room/frozen food cabinets by recovering the heat rejected and using it more for other building services applications in the supermarket. For instance, the heat reclaimed can be used for heating, HWS or to drive absorption chillers, either in whole or in part. To demonstrate the potential of the heat reclaimed within the supermarket and its impact on the store’s CO2e emissions, a feasibility study has been performed to examine the innovative system compared to of the existing conventional system which will cover the cooling demands of an existing supermarket. In order to achieve this, the data collected by a smart energy monitoring system will be used to examine the working of the novel system when covering the cooling demands of the store. The energy consumption of the novel system will be analyzed according to thermodynamic theory. Using an Excel model, the potential heat reclaimed will be mathematically investigated for best practice applications of heat recovery. The energy saved and CO2e emission reduction achieved in apply the novel system will be determined and analysed

Recent observed and simulated changes in precipitation over Africa

Multiple observational data sets and atmosphere-only simulations from the Coupled Model Intercomparison Project Phase 5 are analyzed to characterize recent rainfall variability and trends over Africa focusing on 1983–2010. Data sets exhibiting spurious variability, linked in part to a reduction in rain gauge density, were identified. The remaining observations display coherent increases in annual Sahel rainfall (29 to 43 mm yr−1 per decade), decreases in March–May East African rainfall (−14 to −65 mm yr−1 per decade), and increases in annual Southern Africa rainfall (32 to 41 mm yr−1 per decade). However, Central Africa annual rainfall trends vary in sign (−10 to +39 mm yr−1 per decade). For Southern Africa, observed and sea surface temperature (SST)-forced model simulated rainfall variability are significantly correlated (r~0.5) and linked to SST patterns associated with recent strengthening of the Pacific Walker circulation

Application of Phase Change Materials to Domestic Refrigerators

The paper investigates the performance improvement provided by a phase change material associated with the evaporator in a domestic refrigerator. The heat release and storage rate of encapsulated ice, used as the thermal energy storage material, has been investigated numerically. The mathematical model for phase change is based on the enthalpy method and the governing equations were discretized on a fixed grid using the finite difference method. The influence of PCM thickness (2, 3 and 4 × 10-3 m slabs), ambient temperature (20°C, 25°C, 30°C and 43°C) and evaporating temperature (-15°C and -10°C) have been investigated. The results showed that the melting and freezing time increased proportionally with PCM thickness. The refrigerator autonomy was reduced by 47% when the ambient temperature was increased from 20°C to 43°C and the freezing time increased by 27% when the evaporating temperature was reduced from -10°C to -15°C. Overall, the model provides a useful tool for evaluating the design and operation of a thermal storage refrigerator

Modelling of a thermal storage refrigerator

The paper investigates the effect of adding a phase change material in thermal contact with the evaporator in a natural convection domestic refrigerator. The enthalpy method has been applied to investigate the heat release and storage rate of encapsulated ice. The effect of three parameters was investigated by the numerical method: PCM thickness, ambient temperature and evaporating temperature. The results showed that the melting and freezing time increased proportionally with PCM thickness. The refrigerator autonomy was reduced by 48% when the ambient temperature was increased from 20°C to 43°C and the freezing time increased by 27% when the evaporating temperature was reduced from -10°C to -15°C. A CFD simulation of the airflow and temperature distribution in the natural convection refrigerator was carried out to evaluate the most effective position to place the PCM (top or back wall). The predicted airflow patterns and temperature profiles were considerably different for the two PCM orientations. The predicted air temperature was above 5ºC, thus a eutectic PCM may be required to reduce the temperature in the refrigerator compartment

Reflective Glass Effect on Energy Consumption and Food Quality in Delicatessen Cabinets

Retail supermarkets are responsible for around 3% of total electrical energy consumed in the United Kingdom and the most energy is used in refrigeration systems, particularly for operation of open displays such as delicatessen cabinets which consume approximately 50%. Although the cabinets are energy intensive, they are commonly used in supermarkets for displaying unwrapped chilled food stuffs. These cabinets are associated with the weight loss and quality deterioration of food stuffs being reported frequently as the cause for their high operational costs. This paper presents an investigation on the cause and rectification of weight loss in delicatessen cabinets. Specifically, the paper describes the effective use of low emissivity glass in reducing the impact of the thermal infrared radiation on the food temperatures and energy consumption

Performance Enhancement of Urban Ground Source Heat Pumps through Interactions with Underground Railway Tunnels

Ground source heat pumps (GSHPs) can provide an efficient way of heating and cooling buildings due to their high operating efficiencies. The implementation of these systems in urban environments could have further benefits. In such locations the ground source heat is potentially more accessible via alternative sources such as through underground railways (URs). This paper investigates to what extent the heat in the soil surrounding an UR tunnel could enhance the operation of urban GSHPs installations. To address this, a numerical investigation was set out which included a parametric study considering a number of geometrical options of the systems. The results showed that heat extraction rates of GSHPs installed near UR tunnels can be significantly improved by up to ~ 43%

Mitigation of Extreme Heat and Sustainable Cooling

The last 5 years have seen the hottest weather on record with many countries experiencing exceptionally warm spells. Extreme heat impacts on health, productivity and economics and the impact is greatest in cities and it dis-proportionally affects the urban poor. This paper initially gives data on global temperature change, as well as the prevalence and impact of extreme heat in cities. To help cities mitigate the impacts of extreme heat the Adrienne Arsht-Rockefeller Foundation Resilience Center and the Extreme Heat Resilience Alliance in collaboration with the UN Environment Programme, the Cool Coalition, RMI, the Global Covenant of Mayors for Climate and Energy, Mission Innovation and the World Economic Forum’s Global Commission on BiodiverCities by 2030 are developing a toolkit for city officials. This paper describes the toolkit called the Heat Action Platform. The Heat Action Platform is a living, engagement-oriented tool for city officials, practitioners, and financial institutions to find guidance, both existing resources and tailor-made solutions, on reducing the human and economic impacts of extreme heat at the regional or municipal level. The platform offers opportunities to engage with world-leading experts across a diversity of disciplines to plan, fund, implement, and measure heat resilience actions. The paper describes the rationale behind the heat action platform, its development and how it is being used to mitigate the impacts of extreme heat. Future opportunities to collaborate are identified

Carbon dioxide refrigeration with heat recovery for supermarkets

This paper describes the outcomes of a research project that investigates sustainable heating and cooling solutions for retail applications using a carbon dioxide (CO2) natural refrigerant (R744) for food refrigeration. The paper presents the findings from an applied research study on a booster CO2 (R744) system with high and medium temperature heat recovery. The paper includes a description of the conceptual design and a computer model along with its validation based on some experimental results. The energy consumption and carbon emission reduction are investigated using this novel system based on an existing supermarket as a case study. This is the version of recor