As requirements regarding energy efficiency are getting tougher, buildings in the arctic, as well as the rest of the world, need to be more energy efficient without compromising a good indoor climate. This article presents measured moisture supply and occupancy level in a Swedish arctic multi-family apartment block. Measurements were done over 1 year every 30 minutes in a building consisting of 51 apartments located in Kiruna, at latitude 67.9°. Averages and typical variations on different timescales, year and day, are presented for the different parameters, as well as correlations between the parameters; for example, moisture supply as a function of occupancy level. The results can be used when input data for simulations of energy use, moisture conditions and indoor climate are chosen, as well as a reference to compare measurements to during verifications. In energy efficient buildings, occupant behavior generally has an extensive impact on building performance, which means that the characteristics of behavior related parameters are important to be able to describe.
Variable air volume systems with direct digital controllers have been widely adopted in the HVAC system of commercial, industrial, and large residential buildings because they provide better energy efficiency and occupant comfort. Normally, a variable air volume terminal unit defines a minimum airflow rate to satisfy the space ventilation requirement and/or the proper operation of a terminal heating coil, if so equipped. However, it has been found that variable air volume terminal units often fail to perform as expected at the minimum airflow range (below 500 fpm [2.5 m/s]). Under such a flow range, the embedded airflow sensor becomes inaccurate, and the designed minimum airflow rate is less than the minimum controllable airflow rate. This results in a series of problems, including lack of ventilation, uneven airflow control, reduced damper and operator life, and energy waste. Through designed laboratory and field tests, this study (ASRHAE Research Project RP-1353) aims to identify the major factors that cause inaccuracy and instability issues in variable air volume terminal units and the relationship between the major factors and performance of the airflow sensor, controller, and terminal unit system. Laboratory tests performed in this study included a variable air volume sensor test, controller test, and system test. Four variable air volume boxes from three manufacturers and four controllers from four manufacturers were tested systematically. Two identical test beds with high accuracy (±0.5%) reference airflow meters were designed and constructed in the test facility. The size of the reference airflow measuring stations was carefully selected to provide maximum airflow measuring accuracy and maximum available system pressure drop. This article describes the laboratory test setup and summarizes the variable air volume sensor test results. A companion article summarizes the controller test, system test, and field test results. From the variable air volume sensor test, three factors, namely, inlet conditions, low variable air volume damper positions, and low airflow rates, are identified as strongly impacting variable air volume terminal unit performance.
In conventional air-conditioning design, the comfortable range of temperatures is between 25 degrees C and 27 degrees C with relative humidity levels of 40% to 60%; these numbers vary only slightly based on a person's race and country. Several studies in tropical climates show that the observed thermal comfort requirement often does not agree with those obtained based on experiments, which have mainly used North American subjects. However, there is no consistent rationale that explains why comfort requirements are different in hot climates, suggesting that more surveys on thermal comfort may be needed in the tropics. In Asia, there has recently been a rapid and widespread diffusion of air conditioners; therefore, a survey was conducted to clarify what temperature and humidity level people in Asian countries prefer in order to feel comfortable. Following that research, this article presents the results of a questionnaire survey on the use of air conditioners in houses in hot, dry climates. Nizwa and Rustak, Oman, characterized by the hot, arid climate of the Arabian Peninsula, were chosen as survey areas. The questionnaire survey was distributed to students of Nizwa University. Questions were asked about the duration of air-conditioner use and preferred air-conditioner temperature settings. To determine how respondents felt about their indoor environment, questions were also asked about the thermal sensations that were experienced while using the air conditioner. In both cities, the mean operating time of the air conditioner was very long. The respondents reported selecting a low temperature setting while sleeping, despite the fact that many of them reported that they were cold while sleeping. Ninety percent of respondents reported a cold, cool, or neutral thermal sensation while using the air conditioner without feeling discomfort.
ed and/or Indexed in: American Chemical Society, Chemical Abstracts Service (CAS) and STN (Scientific and Technical Information Network); ASHRAE Abstract Center; BSRIA (Building Services Research & Information Association), Information Centre Quarterly and IBSA (International Building Services Abstracts); CNKI (Chinese National Knowledge Infrastructure); Ei (Engineering Information, Inc.), Ei Compendex and Engineering Index; Gale/Cengage Learning, Academic OneFile and InfoTrac; IIR (International Institute of Refrigeration) and Fridoc; ProQuest Technology Research Database, CSA Materials Research Database with METADEX, CSA Engineering Research Database and CSA High Technology Research Database with Aerospace; SciVerse Scopus and Compendex; Thomson Reuters (formerly Institute for Scientific Information [ISI]) Web of Knowledge, Current
This article investigates the aerodynamic effects of human movement by experiment and numerical simulations. In the experiment, a life-size thermal manikin, a double-track orbit, and a trolley were used to realize human movement, and the velocity distribution of the induced airflow was measured. In the numerical simulations, dynamic meshing was used to simulate the human movement. The aerodynamic effects and flow fields under moving speeds of 0.5, 0.75, 1.0, 1.25, and 1.5m/s were studied. The same timing relationship and tendency of the instantaneous velocity can be found between the measured and computed results, although the computed peak values are smaller than the measured ones. Apparent recirculation zones and vortices can be seen in the wake behind the human body in numerical simulations. The streamwise velocity profile and the structure of the wake depend on the profile of the human body and the moving speed. At each location, the nondimensional relative velocities of different moving speeds are substantially the same. The aerodynamic effects of human movements depend on the moving speed, moving distance, and spatial location. These results can be a good help for the studies on pollutant dispersion, control of air quality, and infectious diseases in indoor environment.
Blade passing frequency (BPF) noise is the dominating component of the flow induced noise of centrifugal fans. The numerical methods for BPF noise prediction, based on the computational aeroacoustics (CAA), have been published for decades. However, there are a couple of challenges for accurately predicting noise for industrial centrifugal fans. The first arises from the fact that the free field hypothesis, adopted in the numerical model, has not yet been carefully studied. The second challenge stems from the current criteria for which the prediction results are compared to the measurement data. Because the test conditions do not always satisfy the requirements of the numerical model, inaccurate predictions occasionally resulted. Therefore, since the prediction results may deviate largely from the test data, the applicability of these methods is severely limited.
The performance of different ASHRAE models besides their general development since 1997 forms the basis of this article. The experimental results of a few recent near-field pollutant dispersion studies are compared to those produced by ASHRAE models. These cases include isolated buildings and adjacent building configurations. In fact, ASHRAE can only be used to estimate rooftop dilutions on an emitting building and does not provide formulations to estimate dilutions on adjacent building surfaces. The results from this study show that ASHRAE models provide reasonable dilution estimates for low exhaust momentum ratios (M), while previous ASHRAE models predict lower dilutions than wind tunnel data for all cases. Furthermore, ASHRAE 2011 predicts reasonable dilutions on the leeward wall of the emitting building, which is an important contribution of the current ASHRAE model. It is suggested that future ASHRAE model versions should be capable of estimating reasonable dilutions on adjacent building surfaces for realistic urban scenarios, by taking into account the spacing between buildings.
To realize the long-term storage of liquid hydrogen for space application, different cooling enhancement components to control the pressure of the cryogenic tanks to a safety condition have been developed in the past decades. In this article, a microgravity, three-dimensional model of a liquid hydrogen storage system with heat pipe and pump-nozzle unit was built. Focusing on significant factors to the cooling performance, such as the heat transfer efficiency of the cool tip (evaporation section), the spraying direction of the nozzle, and the number of the pump-nozzle units, numerical simulations of six tanks with different components were carried out. Typical distributions of velocity and temperature of the fluid inside the tanks are illustrated and studied in detail. The maximum temperature and standard temperature deviation in the storage tank were chosen to evaluate cooling effect and mixing effect, respectively. By comparing the synthesized chilling performances of the six different configurations, an optimal structure has been obtained. This research is helpful to improve the performance of cryogenic liquid storage system for space application.
The distribution of airflow approaching a finned-tube heat exchanger is one of the predominant factors influencing the heat exchanger's performance. This article describes a method for measuring and predicting the inlet air flow distribution using particle image velocimetry (PIV) and a computational fluid dynamics (CFD) model, highlighting the source and magnitude of air side maldistribution. The studied case was a single-slab, four-depth-row, louvered-fin heat exchanger installed vertically in a horizontal duct. The measured data showed that the air approaching this very simple test case generally maintained velocities of 1.25 ms(-1) (4.1 fis(-1)) to 1.35 ms(-1) (4.4 fis(-1)), but certain portions of the coil were completely obstructed, resulting in no airflow, and other portions realized velocities of over 1.7 ms(-1) (5.6 fts(-1)). A CFD model of the air flow through this heat exchanger was developed based on a momentum resistance modeling approach. The CFD results agreed well with the Ply measurements, predicting the local velocities within 3% over most of the domain and within 10% in areas with the largest velocity gradients.
High-efficiency air filtration is an important means of preventing harmful aerosol overflow in biosafety laboratories. For convenience in the in situ scanning leak test of a high-efficiency particulate air (HEPA) filter to ensure the filter's intactness, a cylindrical blunt sampling probe is developed. The sampling inlet is of the slot type and the inlet's length equal the width of the HEPA filter. Thus, the entire downstream face of the HEPA filter may be scanned. To evaluate the blunt sampling probe's ability to detect leaks, the scanning leak test performed on a HEPA filter unit was compared with a test using the thin-walled rectangular sampling probe that is recommended by relevant standards. Based on the comparison, the leak penetration determined using the blunt sampling probe was slightly lower than that determined using the reference sampling probe. Additionally, differences were observed according to the location that was tested. However, the blunt sampling probe could detect leaks through the comprehensive analysis of the local penetration of most-penetrating particle size (MPPS) and non-MPPS particles.
To identify the germicidal effects of microwave radiation for evaporative humidifiers, we measured the germicidal effects of fungal spores of Fusarium solani and vegetative cells and spores of the bacterium Bacillus subtilis using a mock-up system. The germicidal effect was compared to the output powers, irradiation times, and water contents of the element to establish effective disinfection conditions of humidifier element surfaces. The results demonstrated that the fungal and bacterial strains were inhibited at 1200W for 20min, except for the B. subtilis spores under the nonoperation condition involving water spray and the blower. In general, the germicidal effects appear to be stronger on the upper portion of the elements than on the lower portion. The germicidal effect was stronger at higher output power and longer exposure time under wet conditions. To achieve a uniform disinfection on the element faces, it is necessary to consider variations of these methods to produce a uniform heating pattern.
An experiment of the development of two pure methanol droplets in array with different distances and sizes was investigated by the camera of DSA100 (Droplet Shape Analyzer). The contact angle and the baseline were recorded. Compared with the development of one droplet, the development is dependent on the distance between the two droplets and the cap ratio of the two droplets. It was observed that there were three distinct stages as the development of one droplet: the constant contact-angle stage (CA), the constant contact baseline stage (CD) or pinned triple-line stage, and the transition stage (TS) between CA and CD. The evaporation of the droplets in array will increase with the increasing of the distance between the two droplets and the decreasing of the cap ratio of the two droplets. The development of the two droplets in array also shows a characteristic of a lower evaporation rate and a shorter time of CA stage than that of single droplet. During the cross area, there is a negative effect on the evaporation of the droplets.
A performance comparison of experimental results for CO2 trans-critical cycle is presented for an overview of the current level of technology. The published performance data were collected as research objects through comprehensive literature review on experimental research. The methods for data processing, error analysis, and performance evaluation are introduced in the research methodology section. Through the proposed research method, 28 groups of performance results from developed prototypes or test rigs are compared and analyzed using the coefficient of performance and the second law efficiency of thermodynamics. A discussion of the performance comparison between developed CO2 devices and commercial products of synthetic working fluid is also presented based on China's national standards (General Administration of Quality Supervision, Insection and Quarantine of the People's Republic of China 2001, 2003). Based on the comparison results, the state-of-art and possible research directions for CO2 trans-critical cycle technology are summarized and presented.
Attending the 2014 Gustav Lorentzen Conference in Hangzhou, China, August 31 through September 2, reinforced my view that there is no consensus yet about which emerging refrigerants will be a long-...
The lack of standard procedures for filling climatic data has the potential to undermine design, monitoring, and control efforts aimed at climate-responsive building design, performance monitoring, and energy efficiency. This article addresses the challenge of long-term missing gaps in dry-bulb temperature data by examining three spatial methods, namely the inverse distance weighting (IDW) method, the spatial regression test (SRT) method, and the substitution with best match data (SSBM) method, as well as two temporal methods, namely the temporal regression test (TRT) method and the temporal substitution with best match data (TSBM) method. Using these methods, missing dry-bulb temperature data with long-term gaps, ranging from 1 to 60 days, are restored for use in building performance monitoring and analysis. Three one-year, hourly datasets were used to evaluate the performance of these approaches. Each method was applied to deal with artificial gaps which were generated randomly and represented different seasons of a year. In terms of the difference between estimated values and measured values, three evaluation indices, namely mean absolute error (MAE), root mean square error (RMSE), and standard error of bias (BIASSTD), were utilized. The comparison results show that spatial methods are better than temporal methods. The confidence level of the SRT method was further investigated by applying this method to existing data and missing data, and examining its performance. The results indicate that the uncertainty of the SRT method can be predicted and at least two neighboring stations are recommended when using it. This is the second part of the research results obtained through the ASHRAE 1413 research project (in press) with a focus on introducing gap-filling methods for long-term gaps in dry-bulb temperature.
Dynamic modeling of HVAC equipment is a subject of particular importance for control system design and fault detection and diagnosis, while the transient behaviors of the associated processes are, in principle, very complicated and feature strong interactions among multiple physical domains. Part I of this article reviews the research advancement in dynamic modeling of HVAC equipment, focusing on advancement of the past several years, including vapor compression cycles, air-handling units, major types of chillers, cooling tower, heating systems, and renewable-energy driven systems. In Part II, we will present a detailed review of advances in dynamic modeling of HVAC equipment using Modelica, an equation-based multi-physical dynamic simulation platform.
Condensate that appears on mechanical pipe insulation systems might deteriorate the insulation thermal performance and lead to failure of the pipelines. An optimized solution that accounts for cost and system energy efficiency must consider the rate of moisture absorption at various operating conditions, and how the pipe insulation thermal conductivity varies with moisture content. This article reviews the most up-to-date work available in the public domain and observes that a controversy may exist about the similarities and differences of thermal conductivity of pipe insulation systems and flat slab configurations. Since the dissimilar behavior can be associated with the testing methodology from which the thermal conductivity values are originally derived, this article first discusses the methodologies for measuring thermal conductivity of pipe insulation systems with the intention of providing some clarification about such controversy. Steady-state and transient methods are discussed, and the measurements from these two methods are critically compared. The thermal conductivities of several pipe insulation systems are also summarized under dry operating conditions. For wet insulation, four main methods for preparing the wet samples during laboratory measurements have been identified, and it was observed that they yielded very different results. The advantages and shortcomings of each moisturizing strategy discussed at length, and the thermal conductivities of a few available pipe insulation systems in wet conditions are compared. To date, challenges still exist with the measurement of actual thermal conductivity of pipe insulation systems with moisture ingress, and future research needs in this area are discussed.
We spend a large proportion of our lives indoors and yet, many people do not realize the adverse effects that poor indoor air quality (IAQ) can have on our day-to-day well-being and productivity. W...
This article assesses the most common architectural and environmental strategies in Ghadames housing in Libya. Preliminary data were collected through field surveys undertaken in July 2013, the hottest and driest season in Ghadames. The surveys investigated the indoor thermal environment and efficiency of energy use in Ghadames housing. The actual mean vote scale was used to investigate occupants' thermal feeling coupled with recording physical environment and also actual measurements of a number of existing houses. Additionally, objective surveys were conducted to (a) verify the subjective data, (b) provide an overall view of the residents' life style in the old town, and (c) understand the most significant techniques employed in old dwellings. The subjective survey "questionnaire" distributed among nine new and eight old houses shows that the majority of respondents is satisfied with the number of architectural issues in modern housing design. This general satisfaction excludes the inherited identity of the traditional architecture embedded within the society. On the other hand, occupants are more satisfied with old buildings in regard to indoor environmental conditions, energy consumption, and construction materials. The occupants of old houses expressed their thermal satisfaction with the indoor comfort conditions, but the predicted mean vote, based on measurements and ISO 7730, implied discomfort (hot).The survey also carried out interviews with a number of locals, underlining their personal impressions and preference toward the change of the existing built environment. Findings indicate that, occupants' satisfaction and perception toward the built environment have not been achieved in new housing developments of Ghadames owing to the lack of understanding of the sociocultural needs of the local community. In addition, a 3D digital model was created for the old town and imparted a full understanding of the building dynamics and physics, explicating the complexity of the compactness of its urban morphologies. The results also showed subjects were feeling neutral to slightly warm in old buildings even when indoor air temperatures reached 32 degrees C.
