Sensitivity of the total heat loss coefficient determined by the energy signature approach to different time periods and gained energy

In order to identify buildings that have energy saving potential there is a need for further development of robust methods for evaluation of energy performance as well as reliable key energy indicators. To be able to evaluate a large database of buildings, the evaluation has to be founded on available data, since an in-depth analysis of each building would require large measurement efforts in terms of both parameters and time. In practice, data are usually available for consumed energy, water, and so on, namely consumption that the tenants or property holder has to pay for. In order to evaluate the energy saving potential and energy management, interesting key energy indicators are the total heat loss coefficient K_tot (W/K), the indoor temperature (T_i), and the utilisation of the available heat (solar radiation and electricity primarily used for purposes other than heating). The total heat loss coefficient, K_tot, is a measure of the heat lost through the building's envelope, whereas T_i and the gained energy reflect the user's behaviour and efficiency of the control system.In this study, a linear regression approach (energy signature) has been used to analyse data for 2003-2006 for nine fairly new multifamily buildings located in the Stockholm area, Sweden. The buildings are heated by district heating and the electricity used is for household equipment and the buildings’ technical systems. The data consist of monthly energy used for heating and outdoor temperature together with annual water use, and for some buildings data for household electricity are also available. For domestic hot water and electricity, monthly distributions have been assumed based on data from previous studies and energy companies. The impact on K_tot and T_i of the time period and assumed values for the utilised energy are investigated.The results show that the obtained value of K_tot is rather insensitive to the time period and utilised energy if the analysis is limited to October-March, the period of the year when the solar radiation in Sweden yields a minor contribution to heating. The results for the total heat loss coefficient were also compared to the calculations performed in the design stage; it was found that K_tot was on average 20% larger and that the contribution to heating from solar radiation was substantially lower than predicted. For the indoor temperature, however, the utilised energy had a large impact.With access to an estimate of K_tot and T_i, an improved evaluation of the energy performance may be achieved in the Swedish real estate market. At present the measure commonly used, despite the fact that monthly data is available, is the annual use of energy for space heating per square metre of area to let.     

Evaluation of simplified models for predicting CO2 concentrations in small commercial buildings

Evaluation of a building for application of demand-controlled ventilation (DCV) typically involves the use of computer simulations to predict energy use/costs for both fixed ventilation and ventilation adjusted to maintain fixed CO₂ levels within the space. The simulation tools incorporate models for predicting CO₂ concentrations in response to internal sources (people), infiltration/exfiltration, and ventilation. This paper presents a detailed evaluation of different modeling approaches for predicting levels of CO₂ in occupied spaces for small, single-zone commercial buildings employing packaged air-conditioning equipment. Two-zone and three-zone transient models were compared with a quasi-static equilibrium model applied to three distinctly different building types. Baseline data were derived from computational fluid dynamic models that were developed for field sites. A complete building system simulation model was then used to compare the impact of the different modeling approaches on the predicted energy cost savings associated with application of DCV in each building type. The use of a transient CO₂ model did not have a significant impact on model prediction accuracy and energy cost savings predictions as compared with the quasi-static model. The difference in predicted annual energy costs between the various CO₂ modeling types were small and less than might result from errors introduced by factors such as CO₂ sensor uncertainty. Therefore, the use of an equilibrium model is sufficient for use in evaluating DCV for small commercial buildings.     

Predetermined overall thermal transfer value coefficients for Composite, Hot-Dry and Warm-Humid climates

This paper attempts to formulate Overall Thermal Transfer Value (OTTV) coefficients for Composite, Hot-Dry and Warm-Humid climates, the three main tropical climates in India. Four existing air-conditioned office buildings - two mid-rise and two high-rise were modeled as case studies using eQuest v.3.6, which is a DoE2.2, based building energy simulation tool. Based on the study of building envelope, loads, operation and HVAC system characteristics of these case study buildings, a hypothetical high-rise, 16 storey office building, octagonal in plan was created for parametric studies. 98 types of opaque exterior wall constructions and 93 types of glass constructions were varied sequentially in parametric runs to obtain results for hourly wall conduction, glass conduction and glass radiation heat flow in eight orientations for each of the climate type. These hourly results were processed to obtain annual heat gain intensities for each parametric case for all three modes of heat transfer. Regression analysis was used to obtain the OTTV coefficients - TD_eq, DT and SF for the three climates. A new OTTV equation is obtained and presented. The set of coefficients obtained were verified by calculating the OTTV for the four case study buildings, for various parametric runs. The computed OTTV for the four case study buildings exhibits good linear correlation with the annual space cooling plus heating energy use in three climates.     

A methodology for estimating occupant CO2 source generation rates from measurements in small commercial buildings

It is necessary to know CO₂ source generation rates and system flow parameters, such as supply flow rate and overall room ventilation effectiveness, in order to evaluate cost savings for demand-controlled ventilation applied to commercial buildings. This paper presents a methodology for estimating schedules for generation rates and flow parameters using short-term testing. These parameters are used within a model that predicts return air CO₂ concentrations as part of an overall energy analysis model. As a first step in developing the methodology, two different parameter estimation techniques were evaluated using simulated data. Each method gave models that provide good predictions of return air CO₂ concentrations, but differed in terms of the identified parameters. The preferred parameter estimation method provides estimates of both average hourly source generation rates and day-to-day variations. This technique was applied to three different types of commercial buildings using field monitored data. The sites are small commercial buildings with packaged HVAC equipment and included modular schoolrooms, children's play areas in fast food restaurants and a pharmacy retail store. The impact of the length of model training data period on estimated CO₂ generation rates was investigated. Eight weeks of data is sufficient for training. Expressed in terms of the coefficient of variation, the errors in predicted CO₂ concentrations ranged from 4% to 15% depending on the sites. The predicted frequency of time that CO₂ concentrations were within a given range agreed well with the field measured data.     

Life cycle primary energy analysis of residential buildings

The space heating demand of residential buildings can be decreased by improved insulation, reduced air leakage and by heat recovery from ventilation air. However, these measures result in an increased use of materials. As the energy for building operation decreases, the relative importance of the energy used in the production phase increases and influences optimization aimed at minimizing the life cycle energy use. The life cycle primary energy use of buildings also depends on the energy supply systems. In this work we analyse primary energy use and CO₂ emission for the production and operation of conventional and low-energy residential buildings. Different types of energy supply systems are included in the analysis. We show that for a conventional and a low-energy building the primary energy use for production can be up to 45% and 60%, respectively, of the total, depending on the energy supply system, and with larger variations for conventional buildings. The primary energy used and the CO₂ emission resulting from production are lower for wood-framed constructions than for concrete-framed constructions. The primary energy use and the CO₂ emission depend strongly on the energy supply, for both conventional and low-energy buildings. For example, a single-family house from the 1970s heated with biomass-based district heating with cogeneration has 70% lower operational primary energy use than if heated with fuel-based electricity. The specific primary energy use with district heating was 40% lower than that of an electrically heated passive row house.     

The interactions of 54Mn with aminopolycarboxylic acids in aquatic systems

The interactions of ⁵⁴Mn radionuclide with ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) were studied in freshwater system (Butoniga impoundment), and in diluted seawater system (the Raša Bay) by high voltage paper electrophoresis. Depending on the EDTA or NTA concentrations it was possible to detect the distribution of cationic, anionic and immobile ⁵⁴Mn species, and to calculate their electrophoretic mobilities.The apparent concentration stability constants of ⁵⁴Mn-EDTA or ⁵⁴Mn-NTA complexes were calculated from the respective titration curves. Logarithmic values of the apparent concentration stability constants for ⁵⁴Mn-EDTA complex corrected for the influence of pH, K_c(αH), are in the range 6.20–7.38 in two different water types, while corrected for the effect of pH and Ca²⁺, K_c(αL), in 5% seawater amount from 11.29 to 11.89. Logarithmic values of the apparent concentration stability constants for ⁵⁴Mn-NTA complex corrected for the influence of pH, K_c(αH), are in the range 6.42-5.21 in two different water types, while corrected for the effect of pH and Ca²⁺, K_c(αL), in 5% seawater amount from 6.92 to 6.47.     

Thermal storage and nonlinear heat-transfer characteristics of PCM wallboard

For the materials with constant thermophysical properties, the thermal performance of wallboards (or floor, ceiling) can be described by decrement factor f and time lag φ. However, the phase change material (PCM) may charge large heat during the melting process and discharge large heat during the freezing process, which takes place at some certain temperature or a narrow temperature range. The behavior deviates a lot from the material with constant thermal physical properties. Therefore, it is not reasonable to analyze the thermal performance of PCM wallboard by using the decrement factor f and time lag φ. How to simply and effectively analyze the thermal performance of a PCM wallboard is an important problem. In order to analyze and evaluate the energy-efficient effects of the PCM wallboard and floor, two new parameters, i.e., modifying factor of the inner surface heat flux ‘α’ and ratio of the thermal storage ‘b’, are put forward. They can describe the thermal performance of PCM external and internal walls, respectively. The analysis and simulation methods are both applied to investigate the effects of different PCM thermophysical properties (heat of fusion H_m, melting temperature T_m and thermal conductivity k) on the thermal performance of PCM wallboard for the residential buildings. The results show that the PCM external wall can save more energy by increasing H_m, decreasing k and selecting proper T_m (α < 1); that the PCM internal wall can save more energy by increasing H_m and selecting appropriate T_m, k. The most energy-efficient approach of applying PCM in a solar house is to apply it in its internal wall.     

Applied research of reaction coefficient method for unsteady heat transfer in the wall

According to a building's characteristics, a wall may be divided into three categories (heavy, middle and light) from the aspect of heat transmission. Using theory on unsteady heat transmission of the wall and simulated calculation by computer, the influences on reaction coefficients (y_n) exerted by a series of roots (α_i) from the transcendental equation B(s)=0 and on heat transmission calculation exerted by the items (n) of reaction coefficients are analyzed. In this paper, when heat transfer reaction coefficients y₀ and y₁ are calculated, α_i⩽100 and when y_n are calculated, α_i⩽30. The definite values for the items of reaction coefficients for different wall types are introduced, that is, n=96 for heavy wall, n=72 for middle wall and n=48 for light wall. The work of calculation may be greatly simplified and the accuracy of reaction coefficients is guaranteed. The calculation method of heat transfer reaction coefficient was further perfected and the condition to use this method was improved.     

Climate classifications and building energy use implications in China

Cluster analysis of summer and winter discomfort in terms of heat and cold stresses based on 102-year (1901-2002) weather data in China was conducted. Five bioclimate zones were identified. These were compared with the corresponding thermal and solar zoning classifications. Bio-I and Bio-II tended to locate largely within severe cold and cold climates in the north with excellent solar availability (annual clearness index K_t generally exceeding 0.5). Bio-III and Bio-IV covered mostly the hot summer and cold winter and mild climate zones. Despite the relatively low K_t in winter, passive solar heating should be able to meet a significant proportion of the heating requirements. Bio-V covered the hot summer and warmer winter region, where heat stress and hence cooling requirement dominated. Decreasing trends in the zone-average annual cumulative cold stress during the 102-year period were observed for all five zones. There was, however, no distinct pattern for the heat stress and the changes tended to be more subtle. These indicate that climate change during the 20^th century affected winter discomfort (especially in colder climates in the north) more than the summer discomfort. This could have significant implications for energy use in buildings if such trends persist.     

An ETTV-based approach to improving the energy performance of commercial buildings

This paper aims to study the various parameters that affect the energy performance of commercial buildings in Singapore. The parameters are diverse, ranging from characteristics of construction of the walls and windows, to the various system settings and types within the building. Building energy performance is measured via two key indexes, namely, the Envelope Thermal Transfer Value (ETTV) and the annual cooling energy requirement (E_c). Parameters related to these two indexes are identified. An additional parameter, the solar absorptance of the wall, is further incorporated to calibrate the ETTV equation. A relative ranking on the functional parameters of ETTV has been performed to evaluate their effectiveness in lowering the ETTV of buildings. In addition, the impact of using cladding on ETTV is also studied. A correlation for E_c, expressed in the form of a simple linear equation, has been developed. This correlation accounts for the internal building loads, envelope loads, operating schedules and efficiency of the cooling equipment. Finally, ETTV and E_c have been employed to study the effects of chiller over-sizing and ventilation rates on building cooling energy. In the pursuit for better energy-efficient buildings, the approach presented in this paper contributes to the construct of sustainable energy-efficient built-environment.     

Natural ventilation potential of high-rise residential buildings in northern China using coupling thermal and airflow simulations

Natural ventilation is regarded as one of the most energy-efficient ways of ventilating a building. Suitable methods for predicting ventilation performance are essential for regulating indoor air parameters in buildings. This study establishes a method to predict the natural ventilation potential for residential buildings. The average annual ventilation rate (N) and annual cooling load saving ratio (ACSR) for the top six types of residential buildings were measured and analyzed under different conditions. The N calculation formula was summarized to calculate the natural ventilation air change rate for each of the designated buildings. In addition, the logarithmic regression curves of the ACSR (with N) were also obtained and then used to predict the natural ventilation potential for specific climatic conditions. The simulation results could be used to guide engineers in deciding when and where natural ventilation can be incorporated as an energy-efficient feature without affecting indoor comfort. Moreover, accurate strategic analysis could also be used to assist architects evaluate the potential of natural ventilation at the architectural pre-design stage.     

Improvement of natural ventilation in a large factory building using a louver ventilator

When heat generated from facilities inside a large factory building is not discharged outside the building due to a stagnant ventilation flow, the working environment of workers becomes worse, and the cooling of high-temperature products is delayed. In this study, wind tunnel tests were conducted to investigate the natural ventilation of entrained air inside a large factory building. The scale-down factory-building models were embedded in a simulated atmospheric boundary layer (ABL), and the mean and fluctuating velocity fields were measured using a two-frame particle image velocimetry (PIV) technique. For the original factory model, some of the outdoor air came in the factory building through the one-third open windward wall, while the stagnant flow region existed in the rear part of the target area. In order to improve the indoor ventilation environment of the present factory building, three different types of the louver ventilator were attached at the upper one-third open windward wall of the factory model. Among the three louver ventilators tested in this study, the ventilator model ?3 with the outer louver (θ_o=90°) and the inner louver (θ_i=−70°) was found to improve the natural ventilation inside the target factory-building model. It increased the flow rate of the entrained air by aligning the outer louver blades with the oncoming wind and guiding the entrained air down to the ground surface with the elongated inner louver blades.     

Inter-related effects of cooling strategies and building features on energy performance of office buildings

The paper compares effects on thermal performance and energy use of various pre-cooling and ventilation strategies, which might be used for reducing peak power demands in typical office buildings located in moderately warm climatic regions. Simulations were performed for different features of the building envelope, and for two levels of internal heat load.Results indicate: significant reductions of required daytime peak power loads may be obtained by cooling strategies that contribute to lowering internal mass temperatures. For buildings with large internal heat loads, intensive night pre-cooling is the most effective strategy for smoothing required power loads. However, for non-loaded buildings, it largely increases total energy loads, and night-time peak power loads. Intensive night ventilation reduces required peak power loads as well as total cooling energy loads for both building types. For non-loaded buildings, it is an extremely efficient strategy, whereas the efficacy of other pre-cooling strategies is highly questionable. Further research should include secondary effects (on required peak power loads, total energy loads, and electricity consumption) as they may decrease the efficiency differences between the two strategies.     

The impact of auxiliary energy on the efficiency of the heating and cooling system: Monitoring of low-energy buildings

This paper presents a detailed meta-analysis of end and primary energy use for heating, cooling and ventilation of 11 low-energy non-residential buildings and one residential building in Germany that belong to the EnOB research program launched by the German Federal Ministry for Economy. In particular, the analysis emphasizes the substantial impact of auxiliary energy use on the efficiency of heating and cooling performance. The investigated buildings employ environmental energy sources and sinks - such as the ground, ground water, rainwater and the ambient air - in combination with thermo-active building systems. These concepts are promising approaches for slashing the primary energy use of buildings without violating occupant thermal comfort. 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 over the course of two to five years, with an accompanying commissioning of the building performance. Measurements include the energy use for heating, cooling, and ventilation, as well as the auxiliary equipment, the performance of the environmental heat source and sink, and local climatic site conditions.     

Comparison of sand liquefaction in cyclic triaxial and simple shear tests

The liquefaction resistance and correction factors K_σ and K_α of Nakdong River sand obtained from cyclic triaxial (CTX) tests were compared with those determined by cyclic simple shear (CSS) tests to ascertain the importance of the reduction factor C_r and correction factors K_σ and K_α in liquefaction evaluations, especially in view of the lack of comparative liquefaction assessments based on different laboratory test apparatuses. All samples used for the comparisons were obtained from the same type of sand by using similar preparation methods and they were subjected to similar stress states to minimize the number of factors influencing the comparison results; moreover, the apparatuses used in the two tests were manufactured by the same company and all tests were conducted by a single operator. It was found that the liquefaction resistance in CTX tests was always greater than that in CSS tests. Furthermore, C_r varied from 0.63 to 0.36, and it depended on the relative density D_r and initial static shear ratio α. K_σ, which increased with the normal effective stress σ′_nc in CTX tests, was identical to K_σ observed in CSS tests when α was increased up to 0.1. By contrast, K_α in the CSS tests was 58%–97% of K_α measured in the CTX tests, and it depended on the combined effect of D_r, σ′_nc, and α. The relationship between K_α and α in both CTX and CSS tests was well represented by a parabolic function. Moreover, the differences in K_α values between the CTX and CSS tests were also found to be a parabolic function of α. This information can be used for converting CTX (or CSS) values into equivalent CSS (or CTX) values.     

Sorption of VOCs on material surfaces as the deciding factor when choosing a ventilation strategy

The interaction between different ventilation strategies, and the adsorption and desorption of volatile organic compounds on material surfaces in small test chambers, is investigated. In test chamber experiments, nylon carpet was exposed to a mixture of toluene and α-pinene at two different dosing rates. The ventilation strategies were chosen to mimic the conditions in real buildings, i.e. with an air exchange rate of 2 h⁻¹ during the working day (8–17) and a rate of 0.67 h⁻¹ during the remainder of the 24 h. The results show that the sorption behavior has to be included when estimating the concentration variations in a room based on source characteristics and ventilation rates. The software application “EnviSim” was used to model the concentrations in a model room based on the experimental conditions. As the ventilation strategy influences the resulting concentrations, it is recommended that the ventilation system be “turned on” a couple of hours before the start of the working day and “turned down” again soon after the occupants have left the building.     

Applying a multi-objective optimization approach for Design of low-emission cost-effective dwellings

Modern buildings and their HVAC systems are required to be not only energy-efficient but also produce fewer economical and environmental impacts while adhering to an ever-increasing demand for better environment. Research shows that building regulations which depend mainly on building envelope requirements do not guarantee the best environmental and economical solutions. In the current study, a modified multi-objective optimization approach based on Genetic Algorithm is proposed and combined with IDA ICE (building performance simulation program). The combination is used to minimize the carbon dioxide equivalent (CO₂-eq) emissions and the investment cost for a two-storey house and its HVAC system. Heating/cooling energy source, heat recovery type, and six building envelope parameters are considered as design variables. The modified optimization approach performed efficiently with the three studied cases, which address different summer overheating levels, and a set of optimal combinations (Pareto front) was achieved for each case. It is concluded that: (1) compared with initial design, 32% less CO₂-eq emissions and 26% lower investment cost solution could be achieved, (2) the type of heating energy source has a marked influence on the optimal solutions, (3) the influence of the external wall, roof, and floor insulation thickness as well as the window U-value on the energy consumption and thermal comfort level can be reduced into an overall building U-value, (4) to avoid much of summer overheating, dwellings which have insufficient natural ventilation measures could require less insulation than the standard (inconsistent with energy saving requirements) and/or additional cost for shading option.     

Performance of solar systems employing collectors with colored absorber

Flat plate solar collectors are of black appearance because of the color of the absorber, which is employed to maximize the absorption of solar spectrum. Generally, to avoid the monotony of the black color we can use collectors with absorbers of blue, red–brown, green or other color. These collectors are of lower thermal efficiency than that of the usual black type collectors, because of the lower collector absorptance, but they are of more interest to architects for applications on traditional or modern buildings. In this paper, applications of solar collectors with colored absorbers in a large hot water system suitable for multi-flat residential or office buildings, a house heating system, and an industrial process heat system are presented. The collectors are analyzed with respect to their performance and practical applications, aiming to give guidelines for their wider use on buildings. These systems are simulated on an annual basis at three different locations at different latitudes, Nicosia, Cyprus (35°), Athens, Greece (38°) and Madison, Wisconsin (43°). All simulations are carried out with TRNSYS. The results show that although the colored collectors present lower efficiency than the typical black type collectors, the difference in energy output depends on the absorber darkness. For a medium value of the coefficient of absorptance (α = 0.85), the colored collectors give satisfactory results regarding the drop of the amount of collected energy for the three locations (about 7–18%), compared to collectors with black absorbers (α = 0.95). This implies the use of proportionate larger collector aperture area to have the same energy output as that of typical black colored collectors. Additionally, the economic figures obtained for the systems investigated are very promising.     

The effect of street dimensions and traffic density on the noise level and natural ventilation potential in urban canyons

High external noise levels are often used to justify the use of air conditioning in commercial and residential buildings. Methods of estimating noise levels in urban canyons are necessary if the potential for naturally ventilating buildings is to be assessed. A series of noise measurements were made in ‘canyon’ streets in Athens with aspect ratio (height/width) varying from 1.0 to 5.0. The main purpose of the measurements was to examine the vertical variation in noise in the canyons in order to give advice on natural ventilation potential. A simple model of the noise level has been developed using a linear regression analysis of the measured data. The model can be used to predict the fall-off (attenuation) of the noise level with height above street level. The attenuation is found to be a function of street width and height above the street, but the maximum level of attenuation (at the top of the canyon) is almost entirely a function of the aspect ratio except in narrow streets. Background noise (L₉₀) suffers less attenuation with height than foreground noise (L₁₀). Measurements of acoustic comfort in a survey throughout Europe are used to estimate the potential for natural ventilation in canyon streets.     

A novel methodology for estimating space air change rates and occupant CO2 generation rates from measurements in mechanically-ventilated buildings

It is useful to know ventilation rates and carbon dioxide (CO₂) generation rates for evaluating indoor air quality and ventilation efficiency in mechanically-ventilated buildings. A strong limitation of the current models is either they focus solely on a whole building or they are too complicated for practical use in studies of individual spaces. This paper develops a new method for accurately quantifying ventilation rates (i.e. space air change rate) and CO₂ generation rates from measured CO₂ concentrations for individual spaces. The proposed method firstly determined space air change rate using Maximum Likelihood Estimation (MLE). Additionally, a novel coupled-method was initiated for further estimating CO₂ generation rates. Both simulated and experimental data were used to validate the model. Experiments were conducted in a school office by measuring indoor CO₂ concentrations and pressure differences between the return air vent and space. Excellent agreement was obtained. At least 0.998 R² values were obtained for fitting measured CO₂ concentrations when conducting MLE for estimating space air change rate, and the corresponding residual plots showed no pattern and trend. The estimated numbers of occupants were same as the actual ones. Furthermore, the predicted space air change rates showed great consistencies with those from CO₂ equilibrium analysis. The model is simple, handy and effective for practical use. Moreover, the model is also capable for dealing with time-varying space air change rates.