Modeling global residential sector energy demand for heating and air conditioning in the context of climate change

In this article, we assess the potential development of energy use for future residential heating and air conditioning in the context of climate change. In a reference scenario, global energy demand for heating is projected to increase until 2030 and then stabilize. In contrast, energy demand for air conditioning is projected to increase rapidly over the whole 2000–2100 period, mostly driven by income growth. The associated CO₂ emissions for both heating and cooling increase from 0.8 Gt C in 2000 to 2.2 Gt C in 2100, i.e. about 12% of total CO₂ emissions from energy use (the strongest increase occurs in Asia). The net effect of climate change on global energy use and emissions is relatively small as decreases in heating are compensated for by increases in cooling. However, impacts on heating and cooling individually are considerable in this scenario, with heating energy demand decreased by 34% worldwide by 2100 as a result of climate change, and air-conditioning energy demand increased by 72%. At the regional scale considerable impacts can be seen, particularly in South Asia, where energy demand for residential air conditioning could increase by around 50% due to climate change, compared with the situation without climate change.     

Thermally activated building systems (TABS): Energy efficiency as a function of control strategy,hydronic circuit topology and (cold) generation system

By integrating the building structure as thermal energy storage into the building services concept, thermally activated building systems (TABS) have proven to be economically viable for the heating and cooling of buildings. Having already developed an integrated design method and various control concepts in the past, in the present paper the impact of different aspects of TABS regarding the energetic performance of such systems is analyzed. Based on a simulation case study for a typical Central European office building, the following conclusions can be drawn. The energy efficiency of TABS is significantly influenced by the hydronic circuit topology used. With separate zone return pipes energy savings of approximately 15–25 kW h/m² a, or 20–30% of heating as well as cooling demand, can be achieved, compared to common zone return pipes, where energy losses occur due to mixing of return water. A strong impact on energy efficiency can also be observed for the control strategy. Thus, by intermittent operation of the system using pulse width modulation control (PWM), the electricity demand for the water circulation pumps can be reduced by more than 50% compared to continuous operation. Concerning cold generation for TABS, it is shown that free cooling with a wet cooling tower is most efficient, if the cold source is the outside air. Variants with mechanical chillers exhibit 30–50% higher electricity demands for cold generation and distribution, even though their runtimes are much shorter compared to the cooling tower runtimes. In conclusion, the results show that significant energy savings can be achieved using adapted system topologies and applying appropriate control solutions for TABS.     

大连某宾馆冷热电联供系统设计及运行分析

为大连市某宾馆设计三种冷热电联供方案,对每种方案在冬、夏、春秋季节的三种运行模式进行分析,通过系统经济性、环保性等方面的对比,选出最佳的运行方案和运行模式,并对联供系统进行了可行性分析。     

Dynamic modeling of the environment in a naturally ventilated, fog-cooled greenhouse

A dynamic simulation model for heat and water vapor transfer in a naturally ventilated, fog-cooled greenhouse was developed to predict the temperatures of air, plant, cover and floor surface and the relative humidity in the greenhouse. Transpiration and evaporation were also predicted. An experiment was conducted on a hot summer day (Aug. 9, 2004) in the Tokyo area to measure the environments inside and outside a glass-covered greenhouse with a floor area of 26 m². The greenhouse was cooled intermittently by spraying water fog at a constant rate of 0.01 kg s⁻¹ for different fogging and interval times (0.5 min on followed by 1.5 min off; 1 min on–3 min off and 1.5 min on–4.5 min off). The system of equations of the model was solved numerically by using the predictor–corrector technique for the differential equations and the iteration procedure for the algebraic equation. The input parameters to the model were the meteorological conditions and the thermo-physical properties of the greenhouse cover, plant, air and soil. The predicted results using the present model were compared with the measured values and showed a good agreement at different fogging and interval times.     

Design and simulation of a new energy conscious system, (ventilation and thermal performance simulation)

This paper presents the results of simulating the ventilation and thermal performance of a new passive cooling and heating system. The new system was integrated into the roof of a typical contemporary North African house, which was modelled and mounted inside a wind tunnel, for natural ventilation simulation. Thermal performance of the new system was simulated using a new computer programme (BTS), developed by the author. Results are presented in terms of indoor temperature and CATD and HATD, which are newly introduced concepts in defining the building cooling and heating loads.     

Comparison of the modeling of a solar absorption system for simultaneous cooling and heating operating with an aqueous ternary hydroxide and with water/lithium bromide

This paper compares the theoretical performance of the modeling of a solar absorption system for simultaneous cooling and heating operating with water/lithium bromide and alternative aqueous ternary hydroxide mixtures. Aqueous ternary hydroxide working fluid consists of sodium, potassium and cesium hydroxides in the proportions 40 : 36 : 24 (NaOH : KOH : CsOH). Plots of Carnot coefficients of performance and enthalpy-based coefficients of performance are shown against the evaporator temperature. The results showed that, in general, the system with the hydroxide mixture may operate with higher coefficients of performance than the system with the lithium bromide mixture. Also it was shown that the system with the hydroxide may operate with a higher range of temperatures.     

Heating and cooling potential of an underground air-pipe system

The annual heating and cooling potential of an underground air-pipe system has been evaluated in terms of dimensionless parameters of the system. The effect of diurnal and annual variations of environmental parameters (solar radiation, ambient temperature and relative humidity) has been considered. The results are obtained for hot—dry, cold—dry and composite climatic conditions typified by the Jodhpur, Leh and Delhi climates respectively. The effect of suitable earth surface treatments on the thermal performances of the air-pipe system has also been analysed. For wet—shaded earth surface the cooling potential of a pipe of length 50 m and radius 10 cm at a depth 6 m in Jodhpur climate is found to be 4472 kW h, while for the Leh climate under glazed and blackened earth surface conditions the heating potential of such an air-pipe system is found to be 9097 kW h.     

Temperature distributions in boreholes of a vertical ground-coupled heat pump system

The objective of this study is to show the temperature distribution development in the borehole of the ground-coupled heat pump systems (GCHPs) with time. The time interval for the study is 48 h. The vertical GCHP system using R-22 as refrigerant has a three single U-tube ground heat exchanger (GHE) made of polyethylene pipe with a 40 mm outside diameter. The GHE was placed in a vertical borehole (VB) with 30 (VB1), 60 (VB2) and 90 (VB3) m depths and 150 mm diameters. The experimental results were obtained in cooling and heating seasons of 2006–2007. A two-dimensional finite element model (FEM) was developed to simulate temperature distribution development in the soil surrounding the GHEs of GCHPs operating in the cooling and the heating modes. The finite element modelling of the GCHP system was performed using the ANSYS code. The FEM incorporated pipes, the grout and the surrounding formation. From the cases studied, this approach appears to be the most promising for estimation the temperature distribution response of GHEs to thermal loading.     

Influence of a building’s integrated-photovoltaics on heating and cooling loads

Building integrated photovoltaics (BIPV) has the potential to become a major source of renewable energy in the urban environment. BIPV has significant influence on the heat transfer through the building envelope because of the change of the thermal resistance by adding or replacing the building elements. Four different roofs are used to assess the impacts of BIPV on the building’s heating-and-cooling loads; namely ventilated air-gap BIPV, non-ventilated (closed) air-gap BIPV, closeroof mounted BIPV, and the conventional roof with no PV and no air gap. One-dimensional transient models of four cases are derived to evaluate the PV performances and building cooling-and-heating loads across the different roofs in order to select the appropriate PV building integration method in Tianjin, China. The simulation results show that the PV roof with ventilated air-gap is suitable for the application in summer because this integration leads to the low cooling load and high PV conversion efficiency. The PV roof with ventilation air-gap has a high time lag and small decrement factor in comparison with other three roofs and has the same heat gain as the cool roof of absorptance 0.4. In winter, BIPV of non-ventilated air gap is more appropriate due to the combination of the low heating-load through the PV roof and high PV electrical output.     

Modeling of hydrogen production with a stand-alone renewable hybrid power system

Hydrocarbon resources adequately meet today’s energy demands. Due to the environmental impacts, renewable energy sources are high in the agenda. As an energy carrier, hydrogen is considered one of the most promising fuels for its high energy density as compared to hydrocarbon fuels. Therefore, hydrogen has a significant and future use as a sustainable energy system. Conventional methods of hydrogen extraction require heat or electrical energy. The main source of hydrogen is water, but hydrogen extraction from water requires electrical energy. Electricity produced from renewable energy sources has a potential for hydrogen production systems. In this study, an electrolyzer using the electrical energy from the renewable energy system is used to describe a model, which is based on fundamental thermodynamics and empirical electrochemical relationships. In this study, hydrogen production capacity of a stand-alone renewable hybrid power system is evaluated. Results of the proposed model are calculated and compared with experimental data. The MATLAB/Simscape^® model is applied to a stand-alone photovoltaic-wind power system sited in Istanbul, Turkey.     

Thermal performance of a parallel earth air-pipes system

In the present analysis the thermal performance of a parallel earth air-pipe system has been evaluated in terms of annual heating and cooling potential. The influence of the pipes on each other's thermal performance has been considered. The effect of seasonal variation of environmental parameters (ambient temperature, solar radiation, relative humidity, earth temperature etc.) has been considered. The results are obtained for the hot-dry climate of Jodhpur and the composite climate of Delhi. From the various possible earth surface treatments to increase the effectiveness of earth storage systems for air conditioning purposes, the results are presented for wet-shaded earth surface conditions, the most effective earth surface treatment for the climate considered. Thermal performance of the parallel air-pipe system is evaluated for the two cases. In the first case, inlet air temperature to the pipes is taken to be the hourly mean of the ambient air temperature of the average day of each month, and, in the second case, the inlet air temperature is taken to be equal to that of a conditioned room whose set-point temperature varies from month to month.     

The performance of heat pumps in service-comparison of a computer model with a real installation

A comparison is made between a computer model which was developed in an earlier paper and experimental results in which a heat pump was used to heat a house during the heating season 1978–1979. The heat pump used was an air-to-water machine, and it is found that the radiator temperature in the experiment varies according to the heat demand of the house because of the effect of thermal inertia of the water and other thermal masses in the heat transfer system. The computer model simulates this effect, using hourly weather data to calculate the heat demand of the house and assuming that the radiators run at the temperature necessary to supply the heat demand during each hour. The model also calculates the coefficient of performance of the heat pump, and hence calculates the running cost in kilowatt-hours for each hour. The calculated running cost is compared with daily readings of kilowatt-hour meters. It is found that the comparison is very accurate during normal operation of the heat pump, with an accuracy of better than 1 per cent over a period of four months of the heating season, although the accuracy is not always quite so good. A comparison is also made between hourly calculated radiator temperatures and continuous recordings of flow and return temperatures. The comparison in this case is satisfactory, but there is a time lag due to the effect of thermal inertia of the building fabric which the computer model is not intended to simulate.     

Definition, test and simulation of a thermochemical storage process adapted to solar thermal systems

The increase in the use of solar energy closely depends on the development of efficient storage processes. Solid–gas sorption processes are a promising option as they offer a high storage capacity and their specific working mode. In this paper, the integration of a sorption process based on the use of bromide strontium as the reactant and water as the refrigerant fluid is investigated. Combined with flat plate solar collectors and direct floor heating and cooling, the system makes it possible to provide a heating and a cooling storage function. Experimental tests have been conducted in the temperature ranges used in the solar heating and cooling systems. A simple model is proposed which allows an estimation of the performances in line with the heat and mass transfer characteristics of the reactive solid.     

Recent works of A. N. Tombazis and Associates Architects

Eight recent projects of A. N. Tombazis and Associates are described. These buildings, five office buildings, a museum, a hospital and an exhibition centre, incorporate various bioclimatic design aspects which are incorporated for increased comfort, lower energy consumption and environmental impact and as a natural part of an integrated architectural design. A number of the projects have been part of low — energy research programmes funded by the European Commission.     

Modeling of a pressure modulated desalination system using bond graph methodology

A desalination system is a complex multi energy domain system comprising power/energy flow across several domains such as electrical, thermal, and hydraulic. The dynamic modeling of a desalination system that comprehensively addresses all these multi energy domains is not adequately addressed in the literature. This paper proposes to address the issue of modeling the various energy domains for the case of a single stage flash evaporation desalination system. This paper presents a detailed bond graph modeling of a desalination unit with seamless integration of the power flow across electrical, thermal, and hydraulic domains. The paper further proposes a performance index function that leads to the tracking of the optimal chamber pressure giving the optimal flow rate for a given unit of energy expended. The model has been validated in steady state conditions by simulation and experimentation.     

Analytical model as a tool for the sizing of a hydrogen production system based on renewable energy: The Mexican Caribbean as a case of study

The main advantage of the hybrid system compared with separate array solar photovoltaic and stand-alone wind turbine is the possibility of the surplus energy storage by transforming it to hydrogen that can be use in fuel cells. However the design and sizing of this kind of technologies need to meet the local microclimate in order to reach higher efficacies. A tool based on an analytical model to sizing, analyze and assess the feasibility of the hybrid wind/photovoltaic/H₂ energy conversion systems using real weather data is presented in this work. The model considers an energy balance analysis and electrical variables of the system components; the tool calculates the subsystems efficacy and proposes the improvements to increase the efficiency of the use in surplus energy produced by the hybrid system. To validate the analytical model, simulation based on wind speed and solar radiation measurements from meteorological monitoring station in a Mexican Caribbean City is discussed.     

Application of a heat pump system using untreated urban sewage as a heat source

Untreated urban sewage contains large amounts of thermal energy; and its temperature is suitable as a heat source in heat pumps for the heating and cooling of buildings. However, it is not widely used in heat pump systems due to the problem of filth. This paper presents an untreated sewage source heat pump (USSHP) system in which auto-avoiding-clogging equipment is used to continuously capture suspended solids in the sewage. Thus, the block problems caused by filtration and fouling in the heat exchanger tubes can be efficiently resolved in this system. In an actual engineering application, the characteristic parameters of USSHP system are tested under typical operating conditions for heating status. Based on the test results, the performances of the USSHP system are examined. The results indicate that the thermal resistance of the convective heat transfer and fouling on the sewage side in the sewage exchanger is 80% of its total thermal resistance. The COP of the heat pump unit and the COP of the USSHP system are 4.3 and 3.6, respectively.     

Analysis of variable-base heating and cooling degree-days for Turkey

The degree-day method is one of the well-known and the simplest methods used in the Heating, Ventilating and Air-Conditioning industry to estimate heating and cooling energy requirements. In this study, the heating and cooling degree-days for Turkey are determined by using long-term recent measured data. Five different base temperatures ranging from 14 to 22°C are chosen in the calculation of heating degree-days. In the case of cooling degree-days, 6 different base temperatures in the range 18 to 28°C are used. Yearly heating and cooling degree-days are given both in tabular form and as counter maps for all the provinces of Turkey (78 weather stations).     

Dynamic modelling and simulation of a new air conditioning prototype by solar energy

This work presents a new design of an air conditioning prototype by solar energy developed at the Laboratory of Electromechanical Systems of the National Engineering School of Sfax, Tunisia. The new conception permits to produce heat or cold by using solar energy without polluting the environment. The installation, composed of four compartments, consists of three functioning modes according to the season of the year and according to the climatic conditions.A numerical model is developed to study the behaviour of the unit. This model uses real meteorological data to predict the performance of a thermal solar driven system. The dynamic modelling and simulation of only two modes of functioning (winter mode and summer mode without pre-cooling of air) are presented in this paper. This theoretical model is expected to help in predicting the behaviour of the installation in various climatic conditions. Besides, it would enhance the performance of such installation.