Thermostat strategies impact on energy consumption in residential buildings

This paper identifies the impact of thermostat strategies on heating and cooling energy consumptions in buildings, thus suggesting the importance of a database for understanding the effect of thermostat settings and for deciding energy-conscious strategies.Using computer simulation, diverse thermostat strategies – change of setback period, change of set-point temperature, and change of setback temperature – were tested parametrically in a typical USA single-family homes, located in two climate zones, namely cold (Detroit, Michigan) and hot-humid (Miami, Florida).Analysis revealed that heating and cooling systems were significant energy-consuming components in each climate zone. Accordingly, heating energy in cold climate zones and cooling energy in hot-humid climate zones have potential for matchingly significant saving. Diverse thermostat strategies (changes of setback period, of set-point, of setback temperature) demonstrated their obvious impacts on such saving. In the cold climate in particular, the heating system showed the most significant energy-saving effect via proper thermostat strategies. Proper setback period, set-point and setback temperature need to be established to achieve energy efficiency in residential buildings.     

Development of a radiant heating and cooling model for building energy simulation software

Efficient radiant heating and cooling systems are promising technologies in slashing energy bills and improving occupant thermal comfort in buildings with low-energy demands such as houses and residential buildings. However, the thermal performance of radiant systems in buildings has not been fully understood and accounted for in currently available building energy simulation software. The challenging tasks to improve the applicability of radiant systems are the development of an accurate prediction model and its integration in the energy simulation software. This paper addresses the development of a semi-analytical model for radiant heating and cooling systems for integration in energy simulation software that use the one-dimensional numerical modeling to calculate the heat transfer within the building construction assemblies. The model combines the one-dimensional numerical model of the energy simulation software with a two-dimensional analytical model. The advantage of this model over the one-dimensional one is that it accurately predict the contact surface temperature of the circuit-tubing and the adjacent medium, required to compute the boiler/chiller power, and the minimum and maximum ceiling/floor temperatures, required for moisture condensation (ceiling cooling systems), thermal comfort (heating floor systems) and controls. The model predictions for slab-on-grade heating systems compared very well with the results from a full two-dimensional numerical model.     

Estimation of heat rejection based on the air conditioner use time and its mitigation from buildings in Taipei City

The main work in the research focuses on the analysis and mitigation of the anthropogenic heat discharged from buildings, which is one of the main reasons leading to the heat island effect. The residential and commercial buildings, divided into 10 categories, with HVAC systems were analyzed by the building energy program, EnergyPlus. With the help of GIS, the heat rejection of all the residential and commercial buildings in DaAn Ward of Taipei City were evaluated, in which the spatial data and diurnal variation of the heat rejection were described by 3-h time periods. Furthermore, the effect of mitigation strategies was discussed. The first strategy was to change the wall/roof material of building envelope. The second and third strategies, from the viewpoint of energy saving, were to change the temperature setting of air conditioners and to turn off the lighting and equipment when not in use. The fourth strategy was to use a better efficiency of the cooling systems. Finally, the evaluation of installing the water-cooled cooling system, which discharges heat in the form of sensible and latent heat, was also included.     

New concepts and approach for developing energy efficient buildings: Ideal specific heat for building internal thermal mass

The shortcomings or limitations of the traditional approach to developing energy efficient buildings are that they can not determine: (1) the ideal thermophysical properties of building envelope material, where “ideal” means that such material can use ambient air temperature variation and/or solar radiation efficiently to keep the indoor air temperature in the thermal comfort range with no additional space heating or cooling; (2) the best natural ventilation strategy; (3) the minimal additional energy consumption for space heating in winter or air-conditioning in summer. To overcome these problems, some new concepts for developing energy efficient buildings are put forward in this paper. They are the ideal thermophysical properties of the building envelope material, the ideal natural ventilation rate, and a minimal additional space heating or cooling energy consumption. A new approach for determining these properties is also developed. In contrast to the traditional approach (the thermophysical properties of building envelope material are known and constant so that the relating equations describing the indoor air temperature tend to be linear differential equations), the new approach solves the inverse problem (thermophysical properties, etc. of a buildings are unknown), whose solution can be a function instead of a value. As a first step, the ideal specific heat of the building envelope material for internal thermal mass is analyzed for buildings located in various cities in different climatic regions of China, such as Beijing, Shanghai, Harbin, Urumchi, Lhasa, Kunming and Guangzhou. We found that the ideal specific heat is composed of a basic value and an excessive one which is of δ function for the cases studied. Some limitations that would need further study are introduced in the end of the paper.     

A rapid calibration procedure and case study for simplified simulation models of commonly used HVAC systems

A rapid procedure for calibrating simplified building energy simulation models of commonly used HVAC systems has been developed. The procedure developed will allow building professionals to project annual cooling and heating energy consumption of buildings with multiple HVAC systems from short-term field measurement data. This paper describes the general calibration procedure developed, and demonstrates the use of the calibration procedure by applying it to an office building. The calibration methodology requires as little as two weeks of measured hourly heating and cooling consumption data. In the example presented, the simulation model was calibrated using only two weeks of measured heating and cooling data. After calibrating the simulation using this procedure, the RMSE is reduced significantly. The simulation calibrated to two weeks of measured data is then used to simulate the hourly consumption of the building for the year 2004. Comparison of the results of this simulation with the measured data gave monthly CV(RMSE) values of 10.3% and 3.7% for cooling and heating, respectively, which are both well below the 15% values considered acceptable in ASHRAE Guideline 14 [1]. It also shows monthly NMBE values of 2.2% and 1.4% for cooling and heating respectively.     

Application of latent heat thermal energy storage in buildings: State-of-the-art and outlook

Latent heat thermal energy storage (LHTES) is becoming more and more attractive for space heating and cooling of buildings. The application of LHTES in buildings has the following advantages: (1) the ability to narrow the gap between the peak and off-peak loads of electricity demand; (2) the ability to save operative fees by shifting the electrical consumption from peak periods to off-peak periods since the cost of electricity at night is 1/3–1/5 of that during the day; (3) the ability to utilize solar energy continuously, storing solar energy during the day, and releasing it at night, particularly for space heating in winter by reducing diurnal temperature fluctuation thus improving the degree of thermal comfort; (4) the ability to store the natural cooling by ventilation at night in summer and to release it to decrease the room temperature during the day, thus reducing the cooling load of air conditioning. This paper investigates previous work on thermal energy storage by incorporating phase change materials (PCMs) in the building envelope. The basic principle, candidate PCMs and their thermophysical properties, incorporation methods, thermal analyses of the use of PCMs in walls, floor, ceiling and window etc. and heat transfer enhancement are discussed. We show that with suitable PCMs and a suitable incorporation method with building material, LHTES can be economically efficient for heating and cooling buildings. However, several problems need to be tackled before LHTES can reliably and practically be applied. We conclude with some suggestions for future work.     

Energy saving in buildings by using the exhaust and ventilation air for cooling of photovoltaic panels

A building integrated photovoltaic-thermal (BIPVT) setup has been developed for using the cooling potential of ventilation and exhaust airs in buildings for cooling the photovoltaic (PV) panels and also heating the ventilation air by heat rejection of PV panels. The setup has been tested numerically for the Kerman city located in Kerman province in the south of Iran. Results showed that, the exhaust and ventilation airs in heating ventilating air conditioning systems can be used as the cooling fluid of the PV panels and increase their efficiency. On the other hand, the heat rejection of the PV panels could provide some part of the ventilation air heating load.     

Bin weather data for five climatic zones of Morocco

ABSTRACT

The Bin method is one of the well-known and accurate steady-state approach to predict heating and cooling energy consumption of buildings. The application of this method requires detailed ambient temperature bin data. In this paper, the dry-bulb temperature bin data for five climatic zones of Morocco was generated. It was calculated from ?12°C to 45°C with 3°C increments in six daily 4?h shifts (1–4, 5–8, 9–12, 13–16, 17–20 and 21–24?h) for Marrakech, Ifrane, Fez, Errachidia and Agadir. The bin data given in this paper may have the positive impact on building energy efficiency in Morocco.     

Predictions of the heating and cooling energy requirements in buildings using the degree hours method

Methods for the prediction of seasonal energy requirements for heating or cooling buildings are briefly discussed, and a new method, the degree hours method, is described. This method requires the simulation of the pattern of internal temperature variations in a passive building over a season in response to exposure to the weather conditions. The seasonal heating or cooling energy requirement can then be calculated in relation to any chosen base temperature. Different base temperatures can be chosen for summer cooling and for winter heating, to allow for comfort requirements and casual heat gains. Predictions using this method are compared with results from an alternative published method, for an example building.     

The feedback of heat rejection to air conditioning load during the nighttime in subtropical climate

Taipei City, located in the subtropical zone, has a basin landform. The summer is always hot and humid and the air temperature right after sunset is typically higher than 30 °C. Heat rejection from residential buildings in urban area, equipped with lots of the window type air conditioners, not only increases the air temperature outside, but also burdens the cooling load. Based on the time schedule of air conditioner use of Taipei citizens, the heat rejection/building energy use and the air temperature distribution were evaluated, and finally the additional electric consumption of air conditioners was predicted. Two software, EnergyPlus (building energy program) and Windperfect (CFD, computational fluid dynamics software) were employed in this study. In the CFD simulation, the geometry of buildings that covers 700 m in diameter was created with GIS (geographical information system) and the total mesh number was more than 3 millions. Three specified temperatures (T_am, T_bu and T_ac) were used to describe the temperature distribution within the urban canopy by hourly time variation and spatial distribution with height and horizontal profile. The results revealed that the temperature gradually increased with height and the temperature next to the buildings was always higher than the ambient air. The feedback (penalty) of heat rejection to cooling load was found 10.7% during 19:01 to 02:00 h on the following day.     

Climate change impacts on building heating and cooling energy demand in Switzerland

The potential impacts of climate change on heating and cooling energy demand were investigated by means of transient building energy simulations and hourly weather data scenarios for the Zurich–Kloten location, which is representative for the climatic situation in the Swiss Central Plateau. A multistory building with varying thermal insulation levels and internal heat gains, and a fixed window area fraction of 30% was considered. For the time horizon 2050–2100, a climatic warm reference year scenario was used that foresees a 4.4 °C rise in mean annual air temperature relative to the 1961–1990 climatological normals and is thereby roughly in line with the climate change predictions made by the Intergovernmental Panel on Climate Change (IPCC). The calculation results show a 33–44% decrease in the annual heating energy demand for Swiss residential buildings for the period 2050–2100. The annual cooling energy demand for office buildings with internal heat gains of 20–30 W/m² will increase by 223–1050% while the heating energy demand will fall by 36–58%. A shortening of the heating season by up to 53 days can be observed. The study shows that efficient solar protection and night ventilation strategies capable of keeping indoor air temperatures within an acceptable comfort range and obviating the need for cooling plant are set to become a crucial building design issue.     

Building signatures: A holistic approach to the evaluation of heating and cooling concepts

A sustainable and environmentally responsible building concept aims at a high workplace comfort, a significantly reduced heating and cooling demand, a high-efficient plant system, and the use of renewable energy sources to condition the built environment. This paper presents a comprehensive analysis of the heating and cooling concepts of 11 low-energy buildings in terms of energy use, efficiency and occupant thermal comfort. All buildings investigated employ environmental energy sources and sinks – such as the ground, ground water, rainwater and the ambient air – in combination with thermo-active building systems. A limited primary energy use of about 100 kWh_prim/(m²_neta) as a target for the complete building service technology (HVAC and lighting) was postulated for all buildings presented. With respect to this premise, a comprehensive long-term monitoring in high time resolution was carried out for two to five years, with an accompanying commissioning of the building performance. Measurements include the useful heating and cooling energy use, auxiliary energy use for the hydraulic system, as well as end and primary energy use, occupant thermal comfort and local meteorological conditions. A new methodology is proposed for a holistic approach to the evaluation of heating and cooling concepts, which not only considers the occupants thermal comfort, but also the useful energy consumption and the efficiency of the generation, distribution and delivery of heating and cooling energy.     

Optimisation of solar-optical and thermal properties of buildings incorporating solar panels, emulating traditional Chinese building style

A building-integrated solar energy system, based on the traditional Chinese building (e.g., pagoda) - buildings with roofing at intermediate levels (known as eaves) - was investigated, with regard to providing for heating and cooling demands. A number of building parameters, related to energy exchange - solar absorptivity of the exterior wall, level of glazing, etc. - were optimised to minimise demand, and the orientation and tilt of the panels were selected to provide maximum energy at the times of maximum demand. Each parameter was investigated for a range of locations, in order to identify trends, which could then be applied to other locations. In most cases, solar power was sufficient to meet the cooling demands. For a number of locations, solar power provided some, but not all, of the heating loads.     

Optimum insulation thicknesses for building walls with respect to cooling and heating degree-hours in the warmest zone of Turkey

Thermal insulation is one of the most effective energy conservation measures for cooling and heating in buildings. Therefore, determining and selecting the optimum thickness of insulation is the main subject of many engineering investigations. In this study, the determination of optimum insulation thickness on external walls of buildings is comparatively analyzed based on annual heating and cooling loads. The transmission loads, calculated by using measured long-term meteorological data for selected cities, are fed into an economic model (P₁−P₂ method) in order to determine the optimum insulation thickness. The degree-hours method that is the simplest and most intuitive way of estimating the annual energy consumption of a building is used in this study. The results show that the use of insulation in building walls with respect to cooling degree-hours is more significant for energy savings compared to heating degree-hours in Turkey's warmest zone. The optimum insulation thickness varies between 3.2 and 3.8 cm; the energy savings varies between 8.47 and 12.19 $/m²; and the payback period varies between 3.39 and 3.81 years depending on the cooling degree-hours. On the other hand, for heating load, insulation thickness varies between 1.6 and 2.7 cm, energy savings varies between 2.2 and 6.6 $/m², and payback periods vary between 4.15 and 5.47 years.     

Modeling of a solar-assisted HVAC system with thermal storage

A numerical model of the solar-thermal-assisted heating, ventilation and air conditioning system in a 7000 m² educational building, situated in a high-desert climate, is used to predict performance and optimize control parameters. Heating, cooling and shoulder seasons are considered in the study. It is found that the solar assist can account for over 90% of the total heating requirements if certain energy conservation strategies are adopted. The solar cooling assist can reduce the total external cooling energy requirement by between 33% and 43%, the latter result achieved, surprisingly, at lower solar array operating temperatures. In the shoulder season, it is possible to operate the building without any external contribution, by heating the building in the coldest hours of the day, and using any excess heat to produce chilled water, to be stored and used when required. Operation of the solar-assisted system within a much larger district energy system makes it possible to achieve maximum performance.     

Evaluation of energy efficient design strategies for different climatic zones: Comparison of thermal performance of buildings in temperate-humid and hot-dry climate

Since the Kyoto protocol signed in December 1997 the majority of governments around the world have committed themselves to reducing the emission of the greenhouse gases. Thus, efficient use of energy and sustainability has become a key issue for the most energy policies. Sustainability and energy saving terms take place in building construction industry too since buildings are one of the most significant energy consumers. It is known that heating energy demand of a building has a great rate in building total energy consumption. In addition to that, the most of the heating energy has been lost from building envelope. TS 825, Heating Energy Conservation Standard for Buildings in Turkey, aims the reducing of heat loss in buildings through the envelope. But within buildings, one of the fastest growing sources of new energy demand is cooling and especially in hot-humid and hot-dry climatic parts of Turkey cooling season is much longer than the heating season. Moreover in hot-dry climate heat storage capacity of the envelope becomes more important issue than heat insulation for energy efficiency of the building. Since the Turkish standard is considering only heating energy conservation by using degree-day concept, Istanbul and Mardin are considered in the same zone, however those are in temperate-humid and hot-dry climatic zones, respectively. In this study energy efficient design strategies for these climatic zones have been explained and thermal performance of two buildings, which are constructed according to the TS 825 in Mardin and Istanbul cities were evaluated to show the importance of thermal mass in hot-dry climates.     

降低建筑空调能耗研究

在分析贵阳市气候特点及实例建筑空调负荷特性的基础上,采用建筑环境模拟软件DeST对实例建筑室内基础室温以及全年建筑冷热负荷进行模拟,在分析模拟结果的基础上,结合贵阳市气候特点,提出如下三条贵阳市降低建筑空调能耗建议：1)舒适性空调设计应首先满足冬季采暖,然后考虑夏季制冷;2)自然通风是夏季降温的优先考虑方式,过渡季节调节是降低建筑制冷能耗的重要手段;3)增加围护结构保温和控制窗墙比是降低建筑采暖能耗的首要手段。研究结果不但能对贵阳市的建筑节能提供参考,而且还对广大温和地区建筑节能有参考意义。     

The impact of indoor thermal conditions,system controls and building types on the building energy demand

It is possible to evaluate the energy demand as well as the parameters related to indoor thermal comfort through building energy simulation tools. Since energy demand for heating and cooling is directly affected by the required level of thermal comfort, the investigation of the mutual relationship between thermal comfort and energy demand (and therefore operating costs) is of the foremost importance both to define the benchmarks for energy service contracts and to calibrate the energy labelling according to European Directive 2002/92/CE. The connection between indoor thermal comfort conditions and energy demand for both heating and cooling has been analyzed in this work with reference to a set of validation tests (office buildings) derived from a European draft standard. Once a range of required acceptable indoor operative temperatures had been fixed in accordance with Fanger's theory (e.g. −0.5 < PMV < −0.5), the effective hourly comfort conditions and the energy consumptions were estimated through dynamic simulations. The same approach was then used to quantify the energy demand when the range of acceptable indoor operative temperatures was fixed in accordance with de Dear's adaptive comfort theory.     

Using passive cooling strategies to improve thermal performance and reduce energy consumption of residential buildings in U.A.E. buildings

Passive design responds to local climate and site conditions in order to maximise the comfort and health of building users while minimising energy use. The key to designing a passive building is to take best advantage of the local climate. Passive cooling refers to any technologies or design features adopted to reduce the temperature of buildings without the need for power consumption. Consequently, the aim of this study is to test the usefulness of applying selected passive cooling strategies to improve thermal performance and to reduce energy consumption of residential buildings in hot arid climate settings, namely Dubai, United Arab Emirates. One case building was selected and eight passive cooling strategies were applied. Energy simulation software – namely IES – was used to assess the performance of the building. Solar shading performance was also assessed using Sun Cast Analysis, as a part of the IES software. Energy reduction was achieved due to both the harnessing of natural ventilation and the minimising of heat gain in line with applying good shading devices alongside the use of double glazing. Additionally, green roofing proved its potential by acting as an effective roof insulation. The study revealed several significant findings including that the total annual energy consumption of a residential building in Dubai may be reduced by up to 23.6% when a building uses passive cooling strategies.     

Energy saving in the conventional design of a Spanish house using thermal simulation

During the last decade, regulations designed to change the way of designing, building, maintaining, renovating and demolishing buildings and their surroundings have been developed at European level. However, sustainability targets shift throughout the life of a building and design solutions should go beyond strict compliance with each country's regulations. This study prioritises a building's energy behaviour during its use. It demonstrates the value of combining simple passive strategies with thermal simulation tools in standard architectural design practice. To achieve this, we started from the conventional design of a house in the North of Spain, applying passive techniques to achieve energy savings and environmental improvements that exceed regulatory requirements. Simple heating and cooling practices are incorporated into the design. The final house combines all favourable actions that manage to reduce consumption, especially during the most intense winter period. The final design is fully south facing, with an additional 20% glazing in the north and south façades, a 35-cm lintel in the window frames and an additional 2 cm insulation on the façade. Simulation reduced overall thermal consumption by almost 13%. The embodied energy used for the improvements is barely significant. Although the additional investment is arguably not profitable in economic terms, the increased investment is minimal in comparison with total investment in the building.