Research on the influence of air humidity on the annual heating or cooling energy consumption

Just taking 960 m² model building with improved envelope for example, this paper studies the influence of outside air humidity on the annual heating and cooling energy consumption and their relative variation rates (RVRs) and the discrepancy between temperature–humidity control (THC) and temperature control (TC) with the same increase of ventilation rates. The research shows that the discrepancy of annual heating and cooling RVRs is significant under different climatic conditions for the same building with the same increase of ventilation rates by the mode of THC. In general, the heating RVRs decline with the increase of average outside air humidity and the cooling RVRs rise with the increase of average outside air humidity. However, annual heating and cooling RVRs are both approximate in different cities under the climatic conditions of approximate annual average air humidity. The annual heating or cooling need by mode of THC is higher than or equal to the corresponding energy consumption by mode of TC and there exists a close relationship between the absolute increment of energy consumption and outside air humidity; furthermore, as the annual average air humidity increases, the absolute increment of annual cooling need increases while that of annual heating need decreases and both have good linear relation.     

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.     

Five-year data of measured weather,energy consumption,and time-dependent temperature variations within different exterior wall structures

This paper presents coherent 5-year measured data that have been gathered for analyses of building energy consumption and thermal performance of exterior walls. The data is also very suitable for calculations and simulations of heating and cooling energy need of buildings. The data was collected from six identical test buildings, having exterior walls that are constructed of different building materials. The data include the following: indoor–outdoors temperatures; temperatures at various depths within the northern, southern, eastern, and western exterior wall facades; indoor–outdoors relative humidity, heating energy, wind speed and direction; air tightness, infiltration, and horizontal global solar radiation. A computer system (data logger) was used to monitor, check, calculate, integrate, and save the data acquired from approximately 520 sensors in each test building. Measurements were taken with a time interval of 20 s. The 20 s values were then integrated over a time interval of 30 min and the minimum, maximum, and mean values were subsequently stored to a computer database. Analyses of the results indicated that temperatures within the buildings’ exterior walls are constantly changing and, that occasionally the flow of conduction heat is reversed (i.e. outside–inside) due to solar radiation. For accurate results of temperature distribution and the actual heat losses through building envelopes, none steady-state calculations are essential. Depending on the intensity of solar radiation and the material characteristics of the walls, temperature gradient at the inner surfaces of exterior walls may become milder compared to that of the outer surfaces.     

The effect of reflective coatings on building surface temperatures,indoor environment and energy consumption—An experimental study

This paper presents an experimental study on the impact of reflective coatings on indoor environment and building energy consumption. Three types of coatings were applied on identical buildings and their performance was compared with three sets of experiments in both summer and winter. The first experiment considers the impact of coatings on exterior and interior surface temperatures, indoor air temperatures, globe temperature, thermal stratification and mean radiant temperatures for non-conditioned buildings (free-floating case); the second one focused on the impact of coatings on reduction of electricity consumption in conditioned spaces; in the third experiment, the impact of different envelope material properties equipped with different coatings was investigated. The results showed that, depending on location, season and orientation, exterior and interior surface temperatures can be reduced by up to 20 °C and 4.7 °C respectively using different coatings. The maximum reduction in globe temperature and mean radiant temperature was 2.3 °C and 3.7 °C in that order. For the conditioned case, the annual reduction in electricity consumption for electricity reached 116 kWh. Nevertheless, the penalty in increased heating demand can result in a negative all-year effect in Shanghai, which is characterized by hot summers and cold winters.     

Energy consumption and ventilation performance of a naturally ventilated ecological house in a cold climate

In this paper, the thermal and ventilation performance of an ecological house in Helsinki, Finland are presented. The single-family dwelling has a well-insulated, wooden frame construction with no plastic vapour retarder. The measured and simulated results show that the energy consumption of the house is low and that the outdoor ventilation rate is generally satisfactory based on the measured CO₂ concentrations. Extrapolating the measured ventilation data shows that, when the operable windows are closed, the ventilation rate is expected to be about 0.45 air-changes-per-hour (ach) in the winter and about 0.25 ach in the summer. The consumption of total primary energy and space heating energy were measured to be 30% less (162 kWh/(m² a)) and 36% less (76 kWh/(m² a)) than in typical Finnish houses, respectively. The paper also uses a numerical model to investigate the sensitivity of energy consumption to the insulation level, household electricity and domestic hot water consumption, window area, ventilation rate and heat recovery effectiveness.     

Space temperature difference,cooling coil and fan—energy and indoor air quality issues revisited

In designing an energy-efficient air-conditioning system that also simultaneously addresses the needs of adequate ventilation and acceptable indoor air quality, several factors begin to play an important role. Among several others, the cooling coil, the fan and the temperature difference between the space and the supply air (commonly known as the Space ΔT) can be considered to be crucial. For a given space cooling load, the choice of a particular Space ΔT has an implication on the amount of supply air required, which further has an impact on the performance of the cooling and dehumidifying coil as well as the fan. Inherent in these implications are issues related to energy, ventilation and indoor air quality. This paper investigates these implications and quantifies them by considering a hypothetical building in a tropical climate and subjecting the design to several parametric variations involving different Space ΔTs for a given space temperature and humidity condition. The total power requirements, comprising additional cooling, reheating and higher fan power, for a design involving a Space ΔT of 5 °C can be as high as a factor of 2.2 of the total power for a design with a Space ΔT of 8 °C. The implication of higher supply air flow rates on duct design is qualitatively discussed. For a given space cooling load and a given Space ΔT, the implication of increased design ventilation rates to address part-load ventilation requirements can lead to an additional installed cooling capacity of 17.5%. Finally, emerging technologies that are aimed at addressing both energy efficiency and IAQ are discussed.     

Effect of moisture and temperature on the mechanical properties of concrete

Concrete mechanical properties are determined under laboratory conditions of ideal air temperatures between 20 and 22 °C and relative humidity between 40% and 60%. This paper describes the development of concrete mechanical properties when cured under different environmental conditions. Tests to measure modulus of elasticity, compressive strength, and split tensile strength were conducted at varying temperatures and humidity conditions to examine their effects on normal concrete. An environmental chamber was constructed in the laboratory using available materials. The chamber works in conjunction with a freezer to provide chilled air and a heat gun to provide hot air. The heating and cooling functions were controlled via a microcontroller. The moisture content in the concrete specimens was controlled by massing the specimens. The results indicate that concrete strength and modulus of elasticity are inversely related to temperature as well as moisture content in the concrete. Concrete modulus of elasticity was directly related to concrete compressive strength in both temperature and moisture testing. Mathematical formulas were developed for modulus of elasticity, compressive strength, tensile strength, and Poisson’s ratio.     

Optimization of a liquid desiccant based dedicated outdoor air-chilled ceiling system serving multi-zone spaces

A liquid desiccant based dedicated outdoor air-chilled ceiling (DOAS-CC) system is proposed to serve a multi-zone space. The outdoor airflow rate and the supply air humidity ratio are two crucial variables in such a system, which significantly influence indoor thermal comfort, indoor air quality and energy consumption. Two strategies are presented to optimize these two variables in the study. They are the demand-controlled ventilation (DCV) strategy and the supply air humidity ratio set-point reset strategy. To evaluate the performances of these two strategies, a basic control strategy, i.e., the strategy adopting constant ventilation flow rate and constant supply air humidity ratio, is selected as the benchmark. Performances of the two strategies in terms of indoor air temperature, relative humidity and CO₂ concentration as well as energy consumption are analyzed using simulation tests. The results show that the supply air humidity ratio set-point reset strategy is effective for the indoor air humidity control. It can save about 19.4% of total energy consumption during the whole year. The DCV-based ventilation strategy can further reduce about 10.0% of energy consumption.     

Evaluation of energy-related and economic aspects of heating a family house with dendromass in the north-east of Poland

This paper presents an evaluation of energy-related and economic aspects of production of thermal energy to heat a family house with wood briquette. The object of the study was a detached house with an area of 247 m², situated in Olsztyn, in the north-east of Poland. The study lasted three years, from October 2006 to September 2009. The highest monthly consumption of wood briquette for thermal energy production: heating water for the central heating system and hot utility water production were recorded in January (1052–1333 kg/month). The average annual briquette consumption ranged from 6.36 to 6.72 t/year. With the mean lower heating value of briquette of 17.99 GJ/t, the mean consumption of energy in the fuel ranged from 114 to 121 GJ/year. The annual cost of heat production for a family house with briquette as fuel ranged from €572 to €651, during the 2006/2007 and 2008/2009 seasons, respectively. It would have been cheaper by €187–228 year^?1 to heat the house with seasoned willow chips, whereas using alternative fuels, such as hard coal (fraction 0.5–2.5 cm) oak pellets, natural gas and heating oil would have increased the cost of heat production. If the last of those fuels had been used, it would have increased the cost 3.5-fold as compared with wood briquette.     

Effect of initial conditions,boundary conditions and thickness on the moisture buffering capacity of spruce plywood

In this paper, the moisture buffering capacity of spruce plywood is measured by recording the change in mass of a test specimen when the air relative humidity is changed between 33% RH and 75% RH. The aim is to represent diurnal cycles in indoor humidity with 33% RH maintained for 16 h and 75% RH maintained for 8 h. Measurements are taken using two different apparatuses, which provide different convective transfer coefficients between the air and the plywood, and the results are compared to a numerical model for validation. The validated numerical model is then used to investigate the effect of initial conditions, boundary conditions and thickness on the moisture buffering capacity of plywood. The results show that the buffering capacity of plywood depends on the initial conditions and thickness of the plywood as well as the surface film coefficient and humidity cycle.     

Preparation and performances of a novel intelligent humidity control composite material

A novel intelligent humidity control composite material with excellent humidity control performances has been prepared, comprising a natural polymer derivative (carboxymethyl cellulose (CMC)), a porous natural mineral (sepiolite), and an acrylic acid (AA)/acrylamide (AM) copolymer. It features high moisture adsorption capacity, fast response to humidity changes, small equilibrium humidity control range and good acid gas absorbability. It is suitable for maintaining a proper micro-environment for places such as museums or galleries. The appearance and structural properties of the resultant material have been investigated by scanning electronic microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The humidity control performances of the material at certain relative humidity (RH) and changed absolute humidity (AH) have been measured. The adsorption capabilities of the material for sulphur dioxide and nitrogen dioxide have also been investigated in this study. The results reveal that the material maintains a relative humidity in the 57–60.5% range at 25 °C, and reaches the equilibrium levels within 3.5 h. It is worth noting that the composite material shows an excellent humidity buffering effect at changed AH and temperatures. The equilibrium moisture adsorption amount is 78.6% of its own weight. The adsorption capacities for nitrogen dioxide and sulphur dioxide are 227 mg g^?1 and 288 mg g^?1, respectively.     

Development of regression equations for predicting energy and hygrothermal performance of buildings

Regression equations can be used for predicting indoor air temperature, relative humidity and energy consumption in an easier and more rapid way than building energy simulation tools. The independent variables, that is, the input data, are heating, ventilation and air conditioning (HVAC) power, outdoor temperature, relative humidity and total solar radiation. The present methodology for obtaining the regression equations is based on defining a couple of linear Multiple-Input/Single-Output (MISO) models, since two main outputs are involved, that is, indoor temperature and relative humidity. The methodology has been tested for the low- and high-thermal mass cases of the BESTest model (cases 600 and 900) and the output data is generated by using a building hygrothermal simulation tool. Validation procedures have shown very good agreement between the regression equations and the simulation tool for both winter and summer periods.     

Determinants of winter indoor temperatures in low income households in England

The objective of this study is to quantify the extent to which variation in heating season indoor temperatures is explained by dwelling and household characteristics and increased by energy efficiency improvements in low income households. A survey of dwellings in the Warm Front home energy efficiency scheme was carried out in five urban areas of England. Half-hourly living room and main bedroom temperatures were recorded for 2–4 weeks over two winters. For each dwelling, regression of indoor on outdoor temperature was used to obtain estimates of daytime living room and night time bedroom temperatures under standardized conditions (outdoor temperature of 5 °C). The results indicate that the median standardized daytime living room temperature was 19.1 °C and the median standardized night time bedroom temperature 17.1 °C. Temperatures were influenced by property characteristics, including its age, construction and thermal efficiency and also by the household number of people and the age of the head of household. Dwellings that received both heating and insulation measures through the Warm Front scheme had daytime living room temperatures 1.6 °C higher than pre-intervention dwellings, night time bedroom temperatures were 2.8 °C higher. Warm Front energy efficiency improvements lead to substantial improvements of both living room and bedroom temperatures which are likely to have benefits in terms of thermal comfort and well-being.     

Setpoint control for air heating in a church to minimize moisture related mechanical stress in wooden interior parts

The paper presents the setpoint control for air heating in a church to minimize moisture related mechanical stress in wooden interior parts, with the focus on the preservation of a monumental organ. The setpoint operation of the heating, ventilation, and air conditioning (HVAC) system is evaluated by simulation using MatLab, COMSOL and Simulink models. The main model components are presented and combined in a single integrated Simulink model: (1) a HAMBase Simulink building model for simulating the indoor temperature and relative humidity, (2) a COMSOL partial differential equation model for simulating detailed dynamic moisture transport and related mechanical stresses in the monumental wood (organ) and (3) a Simulink controller model. The main advantage of the integrated model is that it directly simulates the impact of HVAC control setpoint strategies on the indoor climate and the related mechanical stresses in wooden objects, like a monumental organ. As control strategy the limited indoor air temperature changing rate is discussed. Recommendations from international literature suggest that a limitation of the relative humidity changing rate of 2 to 5RH%/h will preserve the interior of churches. This study shows that a limitation of indoor air relative humidity changing rate of 2RH%/h can reduce mechanical stresses by a factor of 2.5, compared to maximum capacity heating.     

Preparation,thermal performance and application of shape-stabilized PCM in energy efficient buildings

Shape-stabilized phase change material (PCM) is a kind of novel PCM. It has the following salient features: large apparent specific heat for phase change temperature region, suitable thermal conductivity, keeping shape stabilized in the phase change process and no need for containers. The preparation for such kind material was investigated and its thermophysical properties were measured. Some applications of such material in energy efficient buildings (e.g., in electric under floor space heating system, in wallboard or floor to absorb solar energy to narrow the temperature swing of a day in winter) were studied. Some models of analyzing the thermal performance of the systems were developed, which were validated with the experiments. The following conclusions are obtained: (1) the applications of the novel PCM we put forward are of promising perspectives in some climate regions; (2) by using different paraffin, the melting temperature of shape-stabilized PCM can be adjusted; (3) the heat of fusion of it is in the range of 62–138 kJ kg⁻¹; (4) for PCM floor or wallboard to absorb solar energy to narrow the temperature swing in a day in winter, the suitable melting temperature of PCM should be a little higher than average indoor air temperature of the room without PCM for the period of sunshine; (5) for the electric under-floor space heating system, the optimal melting temperature can be determined by simulation; (6) PCM layer used in the aforementioned application should not be thicker than 2 cm; (7) the models developed by us are helpful for applications of shape-stabilized PCM in buildings.     

夏热冬暖地区某开敞式大空间建筑的节能改造技术分析

为了探讨夏热冬暖地区开敞式大空间建筑的节能改造措施,以广州市某实际工程为例,应用Fluent软件,对自然通风、置换通风、遮阳、屋顶淋水降温的节能效果进行了定性分析,并应用DeST软件模拟了全年能耗。分析了自然通风与空调系统联合工作时的室内温度和速度场,并给出了室内温湿度的实测数据。结果表明:在该工程中,自然通风、置换通风、遮阳挡板和屋面淋水技术可明显改善室内热环境,同时降低建筑能耗;下沉式地面有利于增强室内置换通风效果;通过采用被动节能技术合理设计后,建筑节能率达61.9%。     

Influence of environmental temperature and moisture content of aggregates on the workability of cement mortar

In this experimental work, which is aimed at a subsequent industrial application, the results of a study of the effects of environmental temperatures on aggregate’s properties and on the resulting mortar workability are presented. For this work, several physical properties of fine aggregates (sand of 5 and 2 mm) were defined, in order to establish the influence of temperature on their performance and on the resulting mortar’s workability. In this study, three climatic conditions were used: reference, hot weather and cold weather conditions, both in terms of temperature and relative humidity. The results show that mortar workability is a function of the temperature of the aggregates and of their physical properties, such as absorption and friction; in general, the best results are attained under the reference conditions (20 °C). These results may be useful for the optimization tools development in ready-mix concrete production.     

Real-time determination of optimal indoor-air condition for thermal comfort,air quality and efficient energy usage

For building, “surroundings” that effect on indoor-air condition change with respect to the time. Without proper determination of the desired indoor-air condition to heating, ventilating and air-conditioning (HVAC) system, it may not be feasible to provide simultaneously occupants with thermal comfort and acceptable air quality with efficient energy consumption all the time. This paper presents an alternative methodology of real-time determination of optimal indoor-air condition for HVAC system in order to achieve such total requirements. Predicted mean vote (PMV), CO₂ concentration and cooling/heating load are used as parameter indices for thermal comfort, indoor-air quality and energy consumption respectively. The performance index of the HVAC system is then defined by summation in terms of square errors between those actual parameter indices and their desired values. This performance index is to be systematically minimized by a gradient-based technique in order to yield optimal indoor-air condition for HVAC system. A case study was chosen in 24 h operating HVAC system of a single-storey building by determining indoor-air temperature, indoor-air humidity, indoor-air velocity, and air-ventilation rate. The experiment results show that the proposed methodology can be efficiently implemented in the real-time determination of indoor-air condition to HVAC system that maintains PMV and CO₂ concentration close to the desired levels with less energy consumption when compared to those from the conventional approach.     

Energy-efficient terrace houses in Sweden: Simulations and measurements

Reducing energy use in buildings is essential to decrease the environmental impact. Outside Gothenburg in Sweden, 20 terrace houses were built according to the passive house standard and completed in 2001. The goal was to show that it is possible to build passive houses in a Scandinavian climate with very low energy use and to normal costs. The houses are the result of a project including research, design, construction, monitoring and evaluation. The passive house standard means that the space heating peak load should not exceed 10 W/m² living area in order to use supply air heating. This requires low transmission and ventilation losses and the building envelope is therefore highly insulated and very airtight. A mechanical ventilation system with approximately 80% heat recovery is used. The electric resistance heating in the supply air is 900 W per living unit. Solar collectors on the roof provide 40% of the energy needed for the domestic hot water. The monitored delivered energy demand is 68 kWh/m² a. Energy simulations show that main differences between predicted and monitored energy performance concern the household electricity and the space heating demand. Total delivered energy is approximately 40% compared with normal standard in Sweden.     

Are the relative variation rates (RVRs) of energy consumption approximate in different cities for the same increase of ventilation rate?

This paper makes simulations on the annual heating and cooling energy consumption of four kinds of buildings under the climatic conditions of 19 background cities in China, USA and Europe when ventilation rates increase from 0 to 1.5 vol/h, respectively by, CTM, DOE-2 and DeST-h. The simulation results by CTM show that the increments of annual heating and cooling may differ up to 10s of times or even more than 100 times in different cities for the same building with the same increase of ventilation rates, while the annual heating and cooling RVRs are both approximate in different cities. For the same building with the same increase of ventilation rate in the same city, its annual heating RVRs are far higher than its annual cooling RVRs. The above conclusion can be reached for any building whether with various envelopes or with different shape coefficients.