Building Services Engineering Research and Technology recent issues

Formaldehyde exposure risk in air-conditioned offices of Hong Kong

Mui, K., Wong, L., Hui, P., Chan, W. — Mon, 16 Nov 2009 02:51:28 PST

Formaldehyde (HCHO) is a carcinogenic toxicant commonly present in an air-conditioned office environment. This study examines the lifetime exposure risk of HCHO in air-conditioned offices of Hong Kong under various indoor environmental conditions. Using the regional indoor air quality assessment results of 511 Hong Kong offices recorded from 1996 to 2005, together with the mathematical correlations among HCHO exposure concentration, ventilation and thermal environment verified at 43 other local air-conditioned offices, the exposure risk in terms of loss of life expectancy (USEPA standard) was predicted for an office environment preset at certain air temperature and atmospheric carbon dioxide (CO₂) level. It was reported that the average increment of HCHO exposure risk was 2% for every 1°C increment in the air temperature range of 22.5—25.5°C, or 2.5% for every 10 ppm increment in the CO₂ concentration range of 800—1000 ppm. This study presents useful information on HCHO exposure risk evaluation for air-conditioned offices associated with various policies on indoor air temperature and ventilation demands.

Practical applications: This study outlines an approach to lifetime exposure risk assessment for HCHO inhaled in air-conditioned offices of Hong Kong under various indoor environmental conditions. In a typical office environment, the findings demonstrated that the average increment of HCHO exposure risk was 2% for every 1°C increment in air temperature or 2.5% for every 10 ppm increment in CO₂ concentration.

Fuzzy multi-criteria evaluation model of HVAC schemes in optimal combination weighting method

Wang, J., Jing, Y., Zhang, C. — Mon, 16 Nov 2009 02:51:28 PST

Six heating, ventilation and air conditioning (HVAC) schemes, constant air volume, variable air volume, fan-coil, induction unit, variable refrigerant volume and distributed HVAC system are evaluated and compared in multi-criteria. Because of the uncertainty of qualitative criteria, this paper presents a fuzzy multi-criteria model to select the optimal HVAC system. The methods of fuzzy set theory, linguistic value, analytic hierarchy process, entropy weighting and optimal weighting are used to obtain the criteria weights. Fuzzy technique for order preference by similarity to ideal solution (TOPSIS) method is employed to get the ranking of HVAC schemes. Finally, the application of the fuzzy multi-criteria evaluation model demonstrates detailedly the computation and evaluation procedure in the selection of HVAC schemes.

Practical applications: The fuzzy multi-criteria evaluation model combined with the optimal weighting method in this paper is believed by the authors to contribute to the selection and comparison of HVAC systems or schemes in the building. It is proposed that both qualitative and quantitative criteria existing in reality are used to evaluate HVAC schemes and the decision-making method combines both subjectivity and objectivity. In addition, simple and practical computation and evaluation procedure is easily applied by HVAC designers or decision-makers. Such an approach could become a powerful tool to make an optimal selection for HVAC schemes.

Modelling sanitary demands for occupant loads in shopping centres of Hong Kong

Mui, K., Wong, L., Lam, H. — Mon, 16 Nov 2009 02:51:28 PST

This paper presents a quantitative mathematical model of sanitary demands from occupants in shopping complexes. In-situ measurements and interview surveys with occupants were conducted in typical local shopping malls in order to determine the model parameters for their visiting patterns, load patterns, demand patterns and their preferred or acceptable duration for waiting and using water closets (WCs). The model is used to assess the probable acceptance of sanitary facilities towards the acceptable amount of time for waiting at a typical female washroom designed for an occupant load of 600 occupants in a shopping mall. The results showed that the current sanitary provisions for female washrooms in local shopping malls could meet occupants’ minimum expectation, while with an additional 33% of WC, the sanitary would fully satisfy ‘all’ occupants in terms of amount of time for waiting.

Practical applications: This paper presents a quantitative mathematical model of sanitary demands from a group of building occupants. This model is applied to evaluate the performance of sanitary provisions at typical female washrooms in Hong Kong shopping malls and to quantify the provisions required to achieve the most acceptable amount of time for waiting to their users.

Normalised spectrum for flow-generated noise prediction using computational fluid dynamics

Mak, C., Au, K. — Mon, 16 Nov 2009 02:51:28 PST

Flow-generated noise from in-duct strip spoilers was radiated from an open exhaust termination unit into a 70 m³ reverberation chamber and have been measured in 1/3 octave bands using sound power spectra. Computational fluid dynamics (CFD) software package was adopted to model the strip spoilers in the air duct. Based on the results of CFD simulation of relevant configurations, the technique of Mak and Au and Mak and Oldham was adopted to normalise the experimental data. A normalised spectrum has been produced for predicting the sound power level of flow-noise produced by the strip spoilers in a rectangular air duct. The data collapse for the strip spoilers is generally good at higher Strouhal numbers, but is less efficient at lower Strouhal numbers where considerable scatter is observed. Together with the normalised spectrum, the predictive equations of Mak and his co-investigators can be used to predict the flow-generated noise produced by in-duct strip spoilers in a ventilation system at design stage using CFD.

Practical application: Together with the normalised spectrum, the predictive equations of Mak and his co-investigators can be used to predict the flow-generated noise produced by in-duct strip spoilers in a ventilation system at design stage using CFD.

Thermal behaviour model identification for an office space using BMS data

Mustafaraj, G., Chen, J., Lowry, G. — Mon, 16 Nov 2009 02:51:28 PST

In this study, linear Box—Jenkins, output-error and non-linear neural network autoregressive NARX models are investigated to predict the thermal behaviour of an office positioned in a modern commercial building. External and internal climate data recorded over a summer season were used to build and validate models. The paper exploits the potential of using linear and non-linear models to predict room temperature at different time scale ahead (5 min or 4 h ahead). The prediction performance is evaluated using the criteria of goodness of fit, errors and mean-squared error between predicted model output and real measurements. The results demonstrate that all models provide reasonably good predictions but non-linear models outperform linear models.

Practical application: Prediction of room temperature by black-box linear and non-linear models obtained can be utilised in the building temperature control strategy. When there is any change in the building thermal behaviour (e.g. more equipments added or office equipment re-arranged), the performance of traditional non-adaptive building temperature proportional—integral (PI) or proportional—integral—derivative (PID) controls will deteriorate. The models based on immediate past records and actual behaviour can be adapted to any changed. The PI and PID controller with such models integrated are adaptable to any changes and hence maintain performance. The modelling techniques studied in here are not restricted to office building temperature prediction and control problems; they can be extended to other types of buildings such as hospitals, supermarkets, airports and schools.

An urban drought-prevention model using raft foundation and urban reservoir

Cheng, C., Liu, Y., Ting, C. — Mon, 16 Nov 2009 02:51:28 PST

The main purpose of this research is to develop a practical operation model for water conservation, in responding to the challenges of climate change, to propose a solution for urban drought period. This paper presents an urban drought-prevention model with allocation to prevent-drought using abundant idle raft foundation of existing buildings and the information of urban reservoir implemented by linear programming. The proposed model is developed to provide substantial demand for residential water utilisation during a period of urban drought. This operation model is of adaptable system underpinned by sustainable water management principles. The simulation and validation assumed that the water used is the rainwater and just to flush the toilets. According to the results of this research, the proposed model has been proven to be practicable and feasible for urban drought-prevention solution.

Practical implications: This research illustrates the important contribution of abundant idle capacity in existing building raft foundations. This paper also shows the sustainable water management technologies and the solution for the designer, which has the opportunity to implement and adapt to the best benefit for water conservation and sustainability.

Improvements to the Meteorological Office equations in the computation of degree days

Layberry, R. — Mon, 16 Nov 2009 02:51:28 PST

Meteorological Office (MO) equations are used to calculate daily degree days from daily minimum and maximum air temperatures. The resultant degree days are widely used in building energy analysis for monitoring, targeting, prediction and exception reporting and their accuracy is consequently important. Regression analysis has been performed on minimum, maximum and average daily air temperatures and daily degree days from over 100 weather stations over a 20-year time period. The results show how the MO equations consistently overestimate the degree days. This overestimation becomes progressively severe as the air temperature increases relative to the base temperature used in the degree day calculation. The use of optimised equations containing the maximum, minimum and average temperatures in a day most accurately calculates degree days and where the daily average is not available, using the daily minimum and maximum with different coefficients to those used in the MO equations leads to a significant improvement in the calculated degree days. Practical applications: Degree day data is vital in building energy management. Often hourly temperatures are not available and degree days have to be calculated from the MO equations using daily minimum and maximum temperatures. These equations are approximations developed from limited datasets and this paper describes better equations using minimum and maximum data and further improved equations when average daily data is also available. The reductions in errors in either degree days or energy use is important for reducing errors in data extracted from the resultant performance charts.

Thanks to Reviewers

Mon, 16 Nov 2009 02:51:28 PST

Erratum

Mon, 16 Nov 2009 02:51:28 PST

The articles listed below were first published online ahead of print with incorrect DOIs. The articles have subsequently been published in journal issues with correct DOIs. The articles have now been removed from the Online First listing. SAGE apologises for any inconvenience the error may have caused.

M. Davies and Z. Ye. A ‘pad’ sensor for measuring the moisture content of building materials. Building Services Engineering Research and Technology, first published on July 16, 2009 as 10.1177/0143624409339964. This version is no longer available. The version of record is published in Vol 30 No 3 as 10.1177/0143624408339964

Erratum

Mon, 16 Nov 2009 02:51:28 PST

M. Ning and M. Zaheeruddin. Fuzzy set-based uncertainty analysis of HVAC&R systems: a simulation study. Building Services Engineering Research and Technology, first published on July 16, 2009 as 10.1177/0143624409338321. This version is no longer available. The version of record is published in Vol 30 No 3 as 10.1177/0143624408338321

Erratum

Mon, 16 Nov 2009 02:51:28 PST

A. Baranowski and J. Ferdyn-Grygierek. Heat demand and air exchange in a multifamily building simulation with elements of validation. Building Services Engineering Research and Technology, first published on July 16, 2009 as 10.1177/0143624409338139. This version is no longer available. The version of record is published in Vol 30 No 3 as 10.1177/0143624408338139

Heating and cooling degree day prediction within the London urban heat island area

Kolokotroni, M., Zhang, Y., Giridharan, R. — Wed, 29 Jul 2009 02:12:06 PDT

This paper describes the London Site Specific Air Temperature prediction model, which comprises of a suite of artificial neural network (ANN) models to predict site-specific hourly air temperature within the Greater London Area (GLA). The model was developed using a back-propagation ANN model based on hourly air temperature measurements at 77 fixed temperature stations (FTS) and hourly meteorological data (off-site variables) from Heathrow; it also includes six on-site variables calculated for each FTS. The temporal and spatial validity of the model was tested using data measured 7 years later from the original dataset, which include new FTS locations. It was found that site-specific hourly air temperature prediction is within accepted range and improves considerably for average daily and monthly values. Therefore, the model can be used with confidence to predict daily and seasonal variations of air temperature within the GLA and in particular for the calculation of monthly and annual heating degree days (HDD) and cooling degree hours (CDH). It was found that as expected HDD increase and CDH decrease with distance from the urban heat island centre point; however, all variations cannot be explained with distance and six key on-site variables namely aspect ratio, surface albedo, plan density ratio, green density ratio, fabric density ratio and thermal mass have been identified to explain the remaining variation.

Practical applications: Research studies have confirmed the extent of Urban Heat Island (UHI) within many cities in Europe. Studies have also confirmed the impact of the UHI on energy demand by buildings. There is therefore need to consider this in the design of building by using site-specific external temperatures in the energy calculations for urban buildings. This paper describes the development of a model, which can generate site-specific air temperature in a large number of locations in London. The model's predictions can be used for the calculation of HDD and CDH for any base temperature across London using any Heathrow weather file for a specific year, design years or future climate years; such values can be used for the calculation of site specific building heating and cooling loads.

Evaluation on screening strategies for indoor air quality assessments in air-conditioned offices

Wong, L., Mui, K., Hui, P. — Wed, 29 Jul 2009 02:12:06 PDT

Unsatisfactory indoor air quality (IAQ) in air-conditioned offices would make the occupants uncomfortable and lead to productivity loss. Strategic IAQ monitoring and assessment conducted with optimised resources for representative pollutants and air sampling are developed. This study proposes a simple screening process; with a readily developed IAQ express assessment protocol (EAP), to improve the accuracy in screening the office environment of unsatisfactory IAQ. This screening process is conducted with an `IAQ index', correlated with an event of unsatisfactory IAQ regarding its `failure' due to other six unmeasured air pollutant levels in the EAP; where the IAQ index is defined as the average fractional dose to certain exposure limits from the assessed top dominant contributors. The screening strategies were examined against the existing IAQ assessment results.

Practical applications: Testing on the screening strategies for EAP in 422 air-conditioned offices in Hong Kong showed that, with a defined screening level of probability of unsatisfactory IAQ, the proposed screening process would improve the overall performance of EAP. It would be a useful source of reference in setting up any practical public IAQ surveillance programmes for policymakers, building owners and professionals to quantify the IAQ problems in offices and make decisions on resources and manpower management for efficient mitigation actions.

Sound absorption characteristics of PTFE membrane Material and their application to a multi-purpose stadium

Jung Joong Kim, , Jeong Ho Jeong, , Sohn, J.-Y. — Wed, 29 Jul 2009 02:12:06 PDT

Due to an increase in sport events such as world-cup soccer and other large-scale outdoor performances, a large number of multipurpose stadiums and gymnasiums were constructed throughout the world. Some research have been conducted on plans to utilise all-whether stadiums with fine figures, where large-scale spaces are available for various utilisations. All over the world, dome-type stadiums have been built, and are utilised not only for sports events but also for a variety of other large-scale events. PTFE (Polytetrafluoroethylene) is a membrane material mainly used for the outer ceiling surface of membrane structures. However, sufficient research has not been performed on the acoustical properties of the PTFE membrane material, which is widely used in the multipurpose stadiums. In this study, the air permeability values and sound absorption coefficient of PTFE membrane materials were measured and evaluated in a gymnasium.

Practical application: This research will provide guidance to solving acoustical problems in dome type stadiums by explaining absorption properties of membrane materials. Solving the acoustical problems will greatly extend the functionality of dome type stadiums, such as hosting live concerts or recitals. The extended functionality will ultimately result in increased revenues for existing stadiums.

Heat demand and air exchange in a multifamily building -- simulation with elements of validation

Baranowski, A., Ferdyn-Grygierek, J. — Wed, 29 Jul 2009 02:12:06 PDT

The experiment providing data on the energy demand and air exchange in the flat located in the multifamily building is presented in the paper. The measurement was carried out during 3 weeks in winter. The total energy consumption necessary for flat heating was measured continuously. During the same time air change rate in the flat was measured by means of tracer gas concentration decay methods. After measurements were finished the energy demand and ventilating airflows were calculated assuming the same weather data variation as measured during the experiment, using the ESP-r software. Contam program was used for the air infiltration simulation, giving more detailed results about the ventilation airflows within the tested object. Comparison was made between numerical results and measured data over the given cycle and a good correlation of results has been achieved.

Practical applications: Simulation methods can be an alternative to the assessment of energy consumption or heat demand in buildings when the direct measurement is impossible or difficult. A good agreement of simulation and measurement results is reached when the average values of the results are compared for a longer period of time.

Fuzzy set-based uncertainty analysis of HVAC&R systems: a simulation study

Min Ning, , Zaheeruddin, M. — Wed, 29 Jul 2009 02:12:06 PDT

The accuracy of model predictions plays an important role in model-based applications. However, mathematical models exhibit more or less uncertainties. In this study, a full-scale dynamic model of a two-zone variable air volume heating, ventilation, air-conditioning and refrigeration (VAV-HVAC&R) system is considered. A fuzzy set-based uncertainty analysis method is employed to study the effects of uncertain parameters on HVAC&R system modelling and describe the associated inaccuracies in HVAC&R system model predictions. In this study, uncertain parameters, i.e. zone cooling loads, heat transfer coefficient, chilled water and condenser water mass flow rate and water temperature at condenser inlet are considered and treated as fuzzy parameters. The extended transformation approach is used to evaluate the uncertainties in the model outputs including time history of the zone temperature, discharge air temperature, temperature of chilled water and condenser water. The upper and lower bounds of these outputs are determined for each a-cut level, and the probability distributions of the outputs are presented.

Practical applications: Compared to monitoring of real systems, model-based simulation provides an easier, faster and cheaper substitute to gather operating information and evaluate operating performance of HVAC&R systems. However, simulation results obtained from traditional methods by which model equations are solved with predetermined values cannot accurately represent the possible responses of the system. Thus investigating the probability distributions of the simulation results under parameter uncertainties is very important to ensure the accuracy of the model predictions. The fuzzy set-based uncertainty analysis method presented here helps in identifying the upper and lower bounds of model outputs by quantifying the range within which the responses fall under parameter uncertainties. Also, the contributions of individual uncertain parameters to the uncertainties of model outputs help in identifying the impact parameters.

A `pad' sensor for measuring the moisture content of building materials

Davies, M., Ye, Z. — Wed, 29 Jul 2009 02:12:06 PDT

A range of techniques are available to measure the moisture content of building fabrics. Indeed a thermal dual-probe has been successfully developed by the authors for measuring the moisture content of building fabrics in situ. However, the dual-probe technique has limitations due to the fact that two, small diameter, parallel holes must be drilled for inserting the dual-probe into the material to be measured. It is difficult to drill such holes accurately in many building envelops and thus, such a dual-probe may be most useful for relatively `soft' materials, such as aerated concrete. This paper describes the `proof of concept' of an innovation that surmounts this problem via the development of a `pad' sensor. Instead of the `traditional' dual-probe approach, the heater and temperature sensor are fixed to the surface of a thermally insulated block. The most important benefit of the pad sensor approach is that no holes are required to be drilled in the material of interest. The moisture content of the building envelops can be measured simply by placing the pad sensor against the wall surface. Extensive finite element modelling was carried out to design the pad sensor and a prototype built. Initial experimental work was then carried out to test the pad sensor — the measured moisture content obtained from the pad sensor was compared with the results of a series of gravimetric analyses. Encouraging agreement between the two methods was obtained.

Practical application: A thermal dual-probe has been successfully developed by the authors for measuring the moisture content of building fabrics in situ. However, the dual-probe technique has limitations due to the fact that two, small diameter, parallel holes must be drilled for inserting the dual-probe into the material to be measured. This paper describes an innovation that surmounts this problem via the development of a `pad' sensor. The moisture content of the building envelopes can be accurately measured simply by placing the pad sensor against the wall surface. The pad sensor offers a non-destructive method to measure the moisture content and thus is potentially attractive for applications where this issue is of importance e.g. monitoring the moisture content of historical buildings.

Cavitation, aeration and negative pressures in siphonic roof drainage systems

Lucke, T., Beecham, S. — Thu, 23 Apr 2009 03:43:03 PDT

The main purpose of this study was to examine negative pressures in siphonic downpipes and to see whether these can be controlled through breaking the siphonic action by injecting air at certain points in a vertical downpipe. The study also investigated cavitation and its propagation through a prototype scale siphonic system. The paper presents methods for limiting the minimum pressure in siphonic downpipes in tall buildings. A distinctive drop in pressure between approximately —70 kN/m² and —96 kN/m² occurred in a 80 mm diameter downpipe and it was not possible to sustain pressures between these limits. The pressure drop to -96 kN/m² caused the formation of a distinctive cavitation zone. Any increase in downpipe length, beyond the cavitation zone, produced a proportional increase in the cavitation zone length.

Practical application: Cavitation is perceived to be a serious problem for designers of siphonic drainage systems to be installed in tall buildings. Using full-scale testing this paper provides evidence that in practice cavitation in plastic downpipes is unlikely to cause damage. The paper also provides guidelines for maximum spacing of air inlets to limit the minimum pressure to ~70 kN/m² below atmospheric pressure without significantly decreasing the system capacity.

Drainage demands of domestic washrooms in Hong Kong

Wong, L., Mui, K. — Thu, 23 Apr 2009 03:43:03 PDT

Drainage demand estimation for an effective and healthy drainage stack design is examined in this study. Empirical expressions that incorporate building occupant load, simultaneous usage patterns and discharge flow attenuation along a horizontal pipe into the probable drainage load determination for a stack serving a number of domestic washrooms as installed in typical high-rise buildings in Hong Kong are proposed. Patterns of probable drainage demand and probable discharge flow in the stack are determined via Bayesian analysis and Monte Carlo simulations, respectively. The study outcome enables more effective sizing of a drainage stack for some residential buildings in a dense urban environment.

Practical application: Providing a mathematical model for drainage load calculations, this study is a useful tool to aid drainage stack sizing for some high-rise residential buildings.

An energy consumption benchmarking system for residential buildings in Hong Kong

Wong, L., Mui, K., Law, L. — Thu, 23 Apr 2009 03:43:03 PDT

Since the energy crisis in the 1970s, the government and policymakers have endeavoured to promote energy conservation policy on sustainable building designs and operations. Various benchmarks of building energy consumption were developed. Unfortunately, the complicated benchmarking models would impose difficulties in general adaptation. This study proposes a simple sustainability benchmark using a 5-star rating system for electricity and fuel gas consumption in residential buildings. With this system, the least sustainable households, i.e. the top 10% of the survey samples in consumption, would be awarded with the lowest sustainability rating of `1 star', while the most sustainable households (i.e. the bottom 10%) would be awarded with the highest rating of `5 stars'. This simple model would be useful for identifying the extreme cases of energy consumption and promoting the policy on sustainable building practices without inclusive measurements.

Practical application: A simple sustainability benchmark model using a 5-star rating system for electricity and fuel gas consumption in residential buildings is proposed. This model would be useful for promoting the policy on sustainable building practices without inclusive measurements by identifying the extreme cases of consumption.

A methodology for post-occupancy evaluation of ventilation rates in schools

Mumovic, D., Davies, M., Ridley, I., Altamirano-Medina, H., Oreszczyn, T. — Thu, 23 Apr 2009 03:43:03 PDT

The importance of maintaining adequate indoor air quality in schools is recognised as a contributing factor to pupils' learning performance. This paper describes a series of field measurements that investigating the ventilation rates in four recently built secondary schools in England. All schools were assessed for compliance with the recently adopted Building Bulletin 101, which defines the set of criteria in relation to the ventilation rates and indoor air quality in new school buildings. Using the obtained results a methodology has been suggested for post-occupancy evaluation of ventilation rates in schools. The suggested methodology draws particular attention to the dynamic nature of the interaction between the building and their occupants.

Practical application: The new Building Bulletin 101 is quoted in Approved Document F as a means of compliance with Building Regulations for school buildings in the UK. This paper, based on four case studies, highlights some of the problems facing architects, mechanical engineers and building control officers associated with post-occupancy evaluation of ventilation rates in new school buildings. The methodology suggested in this paper, which differs radically from the current practice, takes into account the changing nature of the indoor environment in schools including occupancy level and occupant behaviour.

Prediction of flow-generated noise produced by an in-duct spoiler in a ventilation system using CIBSE Guide B5 methods

Mak, C., Ye, C., Wu, J., Yang, J. — Thu, 23 Apr 2009 03:43:03 PDT

Measurements of flow-generated noise produced by two different types of strip spoilers in the air duct and radiated from an open exhaust termination unit into a reverberation chamber have been made in 1/3 octave bands using sound power spectra. The measured values are compared with the predicted values using CIBSE Guide B5 method based on selected values of the constant C. It is found that the measured values agree well with the predicted values. The measured values are also compared with the predicted sound power levels using the generic equations given in the Appendix 5.A2 of the CIBSE Guide. It is found that the predicted values using the generic formulae and the single normalised spectrum given in the Appendix 5.A2 of CIBSE Guide do not agree well with the measured values, particularly at low frequencies. For very different in-duct elements, a single normalised spectrum for flow-generated noise may not be sufficient for all configurations of the in-duct elements. It is suggested that several representative normalised spectra for different types of in-duct elements should be given.

Practical application: This study provides an evaluation of the accuracy of the CIBSE Guide B5 method and the CIBSE Appendix 5.A2 generic formulae for the prediction of flow-generated noise produced by in-duct spoilers in a ventilation system. It also gives comments on the method for improvements.

Residential indoor humidity control in tropics and sub-tropics

Chan, M., Deng, S., Xu, X. — Thu, 23 Apr 2009 03:43:03 PDT

The use of direct expansion (DX) air conditioning (A/C) systems is widely seen in residential buildings in tropics and sub-tropics. However, most DX A/C systems are equipped with single-speed compressor and supply fan, relying on On—Off cycling as a low-cost approach to maintain only indoor dry-bulb temperature, whereas the indoor air humidity is not controlled directly. This also leads to potential inefficient energy use due to space over-cooling. This paper suggests a novel control strategy (termed Hi—Lo strategy) of using two-speed compressors in DX A/C systems for better indoor thermal environment control and higher energy efficiency. Experimental work has been carried out to test the Hi—Lo control strategy. Experimental results suggested that the novel control strategy can help improve the indoor humidity control without sacrificing energy efficiency.

Practical application: The use of ON/OFF control at part load conditions in conventional DX A/C systems will lead to undesirable relative humidity levels. The problem is more prominent when the latent load is dominant. In order to have a better dehumidification effect, a lower indoor dry bulb temperature has been often set. On the other hand, the use of variable speed compressors in DX A/C systems can be a solution to the problem of humidity control, but its cost is comparatively high. The suggested novel control strategy is a low cost approach, which can save energy and provide a better indoor humidity control using DX A/C systems.

Evaluation of micro-wind turbine aerodynamics, wind speed sampling interval and its spatial variation

Makkawi, A., Celik, A., Muneer, T. — Wed, 21 Jan 2009 07:32:06 PST

Large wind turbines are usually installed in areas where wind speed distributions have been observed long enough to make sure of their high efficiency. However, micro-wind turbines are mostly used in areas where wind conditions are not necessarily favourable for efficient power production. Therefore, micro-wind turbines require specific designs to work effectively in low and turbulent wind resource areas. However, because this is not the case, more experimental results are being published in recent years that report under-achieving micro-wind turbines. In the present article, a similar under-achievement is reported. The experience gained from the wind energy project undertaken at Napier University is reported, as well as the analysis of the wind speed data collected at the facility and at Edinburgh Airport, some 16 km away from it.

Practical applications: A micro-wind energy system can be one of the most promising technological solutions for producing electricity in residential applications for remote consumers as well as in urban areas provided that the problems reported in the literature are successfully tackled. The currently reported research project identifies such problems associated with micro-wind turbines, stemming from their use in urban areas on roofs of buildings. Thus, this will contribute both to the understanding of micro-wind turbines and to their possible improvements in the coming years.

Environmental assessment of residential buildings with an emphasis on water conservation

Ilha, M., Oliveira, L., Goncalves, O. — Wed, 21 Jan 2009 07:32:06 PST

The construction, operation and demolition of buildings represent one of the most damaging human activities in the global environment nowadays and water use and conservation is one of the most representative environmental loads to be considered. Brazil, unlike some other countries, has not yet implemented its own body building environmental assessment. The development of an environmental assessment system requires the identification of the most important topics to be considered in each theme for each country or region, due to local environmental agenda. This article presents a summary of the main topics concerning water conservation considered in some international environmental building assessment systems and presents a proposal of topics to take into account in a Brazilian assessment system.

Practical application: The civil construction industry is not only one of the biggest sectors in the economy but is also one of the greatest polluters. Along with standardisation, it is also necessary to establish measures to attract significantly higher levels in different topics related to sustainable construction. New mechanisms that allow users to recognise the difference between buildings with different sustainable performance levels need to be developed. This article will be used as a base for the development of a Brazilian system of assessment and rating for building environmental performance and sustainability in terms of water use and conservation.

Performance evaluation of dual-flush WC cistern in a multifamily building in Brazil

Oliveira, L., Goncalves, O., Uchida, C. — Wed, 21 Jan 2009 07:32:06 PST

The performance assessment as to water consumption in WC cisterns has contributed to the development of flushing system technologies, which allow smaller flushing volumes. The purpose of this work is to assess the performance of the the low water consumption requirement of WC cisterns with dual flushing system (6/3 L), when compared to 6 L flushing volume WC cisterns in multifamily buildings. The research methodology consisted of a case study in a multifamily residential building with submetering system, by monitoring the total water consumption and the two flushing systems using water meters installed in WC cisterns. By means of a mathematical model, a comparison of the design flowrate in the main branch was carried out considering the two types of WC cisterns. The results indicated that the water consumption in the 6 L WC cistern was 20% in relation to the total domestic consumption, whereas the water consumption observed in the dual-flush WC cistern (6/3 L) was 16%. The dual flushing system (6/3 L) presented about 18% consumption reduction impact as compared to the 6 L system. The design flowrate values in the main branch, obtained by the mathematical model, were 0.35 L/s for systems with 6 L WC cistern and 0.34 L/s with dual-flush WC cistern (6/3 L), that is, a reduction of ~3%.

Practical application: The knowledge of the performance in field of dual-flush WC cistern contributes to industry to improve this system and to users to aid their choice of technologies aimed at water conservation, and so assisting to the development of sustainable buildings.

Temperature gradient effects on moisture transport in porous building materials

Baker, P. H, Galbraith, G. H, McLean, R. C. — Wed, 21 Jan 2009 07:32:06 PST

Whilst considerable research has been carried out on the process of moisture transmission through porous building materials under a concentration gradient with isothermal conditions, limited experimental data are available on the influence of temperature gradients on moisture transfer rates. Such thermodiffusion can be predicted from irreversible thermodynamics, however, its significance to concentration-driven transfer in materials has not been definitively established. Models for the prediction of moisture movement in building structures generally neglect such effects, and rely on moisture transport properties based on isothermal measurements. This paper describes an investigation to determine the significance of non-isothermal effects on the total moisture transfer through building materials. The investigation concluded that the vapour pressure gradient is the critical driving potential for moisture transfer, whilst thermodiffusion is not significant.

Practical application: Building professionals can be confident that the use of vapour permeabilities of building materials measured under isothermal conditions are satisfactory for the prediction of moisture transport through building envelopes under temperature gradients: no correction for thermodiffusion effects is necessary.

Thermal comfort of an air-conditioned office through different windows-door opening arrangements

Daghigh, R., Adam, N., Sopian, K., Sahari, B. — Wed, 21 Jan 2009 07:32:06 PST

This paper investigates the thermal comfort level of an office room through various windows-door opening arrangements in hot and humid climate. To determine the windows-door opening performance, 14 opening configurations have been considered and the combination of opening arrangements was carried out in an air-conditioned office at UPM, Malaysia. After conducting objective measurement for each condition, Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) were calculated. The concentrations of carbon dioxide (CO₂) were also monitored. Subjective survey involved questions on the thermal environmental perception and indoor air quality for office occupants for this study. Objective data analysis showed that in most of conditions office had thermal conditions falling within the comfort zone of ASHRAE standard 55, and in all of conditions neutral temperatures are higher than ASHRAE standard requirements. Subjective results revealed that staff has higher thermal comfort level as compared to what PMV has predicted.

Practical application: It is believed that the results in this paper will contribute to knowledge that international standards are not applicable in hot and humid climate. Fanger equations would give the results for European conditions, people in hot- humid climate have some cultural preferences that are different from the Europeans hence modifying these equations and standards for this climate are necessary. In terms of the use of climatic control to modify the indoor environment it is found that when the occupants have the freedom to modify the environment, and make necessary adjustment, they always use windows-door opening arrangements to compensate for the less comfortable thermal condition and increase air movement.

Maintenance cost of chiller plants in Hong Kong

Lai, J. H., Yik, F. W., Chan, A. K. — Wed, 21 Jan 2009 07:32:06 PST

Research findings about maintenance costs of chiller plants — a ubiquitous installation in large buildings, are rare. The study reported in this paper was conducted through inspection of 40 maintenance contracts, their associated monthly service reports and payment records, and interviews with the contract administrators. Routine maintenance cost was found to dominate among the maintenance resources. Repair maintenance work accounts for a less, but significant portion. The cost incurred for emergency maintenance work is minimal and condition analysis is seldom applied. Large chiller plants, by virtue of their scale, can economise on their maintenance cost. Total maintenance cost varies with plant age following a `bell-shape' pattern, with relatively less expenditure for new and old plants whereas that incurred for middle-aged plants spreads over a wide range. Factors that potentially affect the cost relation between preventive maintenance and corrective maintenance have been identified. Apart from investigating their effects clearer, future work is needed to explore how to improve the practice of recording plant faults, which are crucial performance data to reflect whether the costs spent on maintenance are value-for-money.

Practical application: The study has revealed the significance of various maintenance cost elements and the empirical cost relation between preventive maintenance and corrective maintenance. The effects of plant capacity, age of plant, operation period and heat rejection method on maintenance cost have also been analysed. Understanding the influence of these factors can help practitioners prepare maintenance budgets and perform benchmarking exercises. Besides, the lack of proper record of plant faults, as identified, is a barrier, which needs to be overcome before evaluating the value of maintenance service.

Analysis of errors in degree days for building energy analysis using Meteorological Office weather station data

Layberry, R. — Wed, 21 Jan 2009 07:32:06 PST

Heating degree days are widely used in building energy management for weather normalization of energy use. Degree days are normally calculated at Meteorological Office weather stations sited some distance from the building of interest and this can introduce errors between the degree days used in the calculations and the actual degree days at the building. This paper analyses the major sources of errors in the degree days derived from a newly available data set of Met. Office stations supplied by the British Atmospheric Data Survey (BADC) and compares these errors against those from other available data sets. The BADC data set consists of hourly temperatures for 242 weather stations in the UK from January 2001 until November 2007 and has been converted to monthly degree days for the analysis. The errors have been analysed in terms of measurement and recording errors, errors due to altitude and errors due to spatial separation between weather station and building. The largest error is due to spatial separation between building and weather station. It is therefore important to use data sets with high numbers of weather stations. The data set used in this analysis has been made available on the internet at http:// www.eci.ox.ac.uk/research/energy/degreedays.php and consists of daily, weekly and monthly degree days for over 200 UK weather stations at a range of building base temperatures for the years 1987—2006. Also included is the 20-year mean for the 55 stations with unbroken records for benchmarking purposes.

Practical application: The paper discusses how errors arise in degree day data when using Met. Office weather stations sited some distance from the building of interest. The paper discusses both the method and the extent of reductions in errors that are possible by using spatially rich weather station degree day data sets. The paper makes the data set used — the best for UK degree day monitoring of buildings — available through a website, daily, weekly and monthly, over a range of building base temperatures, back to 1986.

Acceptable noise levels for construction site offices

Mui, K., Wong, L., Wong, Y. — Wed, 21 Jan 2009 07:32:06 PST

This study examined acceptable noise level of a construction site office in Hong Kong by analysing responses obtained from interviews of 77 occupants. The equivalent continuous noise level L_eq measured in the office was chosen as an indicator and correlated with the occupant acceptance recorded on a visual analogue assessment scale and a dichotomous assessment scale. With the use of a logistic regression model, this acceptance was found to be significantly influenced by the working experience and age of occupants, which were in turn highly correlated. Satisfactory noise levels within the office have been evaluated by comparing acceptance responses given by the occupants at different L_eq. The proposed criterion of aural comfort was further identified by the survey samples and a conclusion was drawn: an indoor environment with an equivalent continuous noise level L_eq of 65 dBA would be deemed acceptable for a construction site office.

Practical applications: This study reported the occupant acceptable noise level in construction site offices was more adaptable to a noisy environment than a general office because the occupant acceptance would be significantly influenced by the outdoor noise level, working experience and occupant age. The construction site office with an equivalent continuous noise level of 65 dBA would be recommended as a design criterion for construction site offices as it can balance the cost of acoustical treatment and the satisfaction of occupants.