Air Conditioning Energy Research Articles

Novel activity classification and occupancy estimation methods for intelligent HVAC (heating, ventilation and air conditioning) systems

Reductions in HVAC (heating, ventilation and air conditioning) energy consumption can be achieved by limiting heating in the winter or cooling in the summer. However, the resulting low thermal comfort of building occupants may lead to an override of the HVAC control, which revokes its original purpose. This has led to an increased interest in modeling and real-time tracking of location, activity, and thermal comfort of building occupants for HVAC energy management. While thermal comfort is well understood, it is difficult to measure in real-time environments where user context changes dynamically. Encouragingly, plethora of sensors available on smartphone unleashes the opportunity to measure user contexts in real-time. An important contextual information for measuring thermal comfort is Metabolism rate, which changes based on current physical activities. To measure physical activity, we develop an activity classifier, which achieves 10% higher accuracy compared to Support Vector Machine and k-Nearest Neighbor. Office occupancy is another contextual information for energy-efficient HVAC control. Most of the phone based occupancy estimation techniques will fail to determine occupancy when phones are left at desk while sitting or attending meetings. We propose a novel sensor fusion method to detect if a user is near the phone, which achieves more than 90% accuracy. Determining activity and occupancy our proposed algorithms can help maintaining thermal comfort while reducing HVAC energy consumptions.

Beyond the end-consumer: how would improvements in residential energy efficiency affect the power sector in Saudi Arabia?

Abstract Energy efficiency in buildings has garnered significant attention in Saudi Arabia. This paper outlines the potential effects of higher residential efficiency on electricity load profiles in the Kingdom. It further presents the associated benefits that could have been realized by the local utilities in 2011. To perform the analysis, we designed an integrated methodology in which an engineering-based residential electricity demand model is used within an economic equilibrium framework. The modeling approach allows us to capture the physical interactions arising from higher efficiency and the structural changes that could occur in the economy beyond the end-consumers. Raising the average air-conditioner energy efficiency ratio (EER) to 11 British thermal unit (BTU)/(Wh) from its 2011 average would have saved 225,000 barrels/day of crude oil in electricity generation. Alternatively, increasing the share of insulated homes from 27 to 64 % would have allowed the power sector to lower its use of the fuel by 158,000 barrels/day. Combining both measures in a single simulation yields incremental yet not additive reductions. All alternative scenarios reduce costs to the utilities and improve the average thermal efficiency for the electricity generated. The studied efficiency options shift the load curve downward during the peak load segment when the least efficient turbines would be used. We additionally show how efficiency improvements in end-uses can affect the decisions of other sectors in the economy.

Monthly air-conditioning energy demand calculations for building energy performance rating

A new calculation method for monthly cooling energy demand is presented which extends the utilisation factor method of standard EN ISO 13790:2008 to take account of a number of important features of air-conditioning systems that are currently ignored. In all other respects it is compatible with this method, which is the most widely used means of producing building Energy Performance Certificates in Europe. In particular it enables the impact of free cooling, and of the tempering of supply air to be quantified; calculates tailored seasonal efficiency figures for chillers, and provides initial estimates of the potential savings of inter-room heat recovery and of the energy penalties associated with terminal reheat and dual duct systems. Practical application: This paper proposes an extension to the most widely used calculation method for Energy Performance Certificates in Europe, improving its ability to reflect important features of central air-conditioning systems. This is of particular importance for climates and buildings where cooling is required when the outdoor air temperature is relatively low. In particular it enables the impact of free cooling, and of the tempering of supply air to be quantified, calculates tailored seasonal efficiency figures for chillers, and provides initial estimates of the potential savings of inter-room heat recovery and of the energy penalties associated with some other systems.

Occupant-oriented mixed-mode EnergyPlus predictive control simulation

Model predictive control (MPC) has been studied in the building science realm for about three decades. However, the following two aspects of the building control have not been studied thoroughly in MPC research. One is the impact of the mixed-mode cooling system on the active heating ventilation and air conditioning (HVAC) energy consumption, and the other is the differences of individual thermal comfort preference and its impact on energy. This paper proposes an occupant-oriented mixed-mode EnergyPlus predictive control system to optimize HVAC energy consumption while meeting the individual thermal comfort preference. A web-based dashboard is implemented in the test-bed building for three months to collect individual thermal comfort preference data. The data analysis results suggest that occupants have various tolerances and preferences about thermal comfort. The simulation results show that, during one week of a typical swing season, the mixed-mode system further reduces the active HVAC energy consumption, and the diversified occupant thermal comfort preference has significant impact on HVAC energy consumption.

The Effect of Building Construction and Human Factors in Cooling Energy Use

This study's purpose is to evaluate air-conditioning energy consumption by conducting interviews and recording data from 50 single-family houses. All study houses applying similar styles of tropical architecture and has similar methods of building construction, with the U-values for building materials having moderate levels of thermal resistance. The finding reveals that the majority of households spends more than 37% of their energy costs on cooling during the raining season and estimating to increase by the drought seasons. The greater use of air-conditioners has resulted in an increased purchasing power of the population.

Predicting Comfort Temperature in Indonesia, an Initial Step to Reduce Cooling Energy Consumption

Indonesia has no reliable thermal comfort standard that is based on research works. The current national standard (SNI 6390:2011) states only a single range of comfort temperature that is 25.5 °C Ta, with a range of +1.5 °C Ta. Previous thermal studies in a number of different buildings in Indonesia showed that the neutral (comfort) temperatures of subjects were about 27 to 28 °C, which is higher than the values stated in the standard. As a big country with various ambient temperatures, Indonesian needs a better and more reliable thermal comfort predictor which can be applied properly across the country. This study is an attempt to propose an initial Indonesian thermal predictor, in the form of a simple equation, which could predict comfort temperatures properly across the country. Reanalysing the previous comfort studies in Indonesia, a simple regression equation is constructed as to be used as the initial Indonesian comfort predictor. Using this predictor, the comfort temperatures in a lowland or coastal cities like Jakarta is found to be higher than the current comfort standard. It is expected that this predictor would help to provide a better indoor thermal environment and at the same reduce the cooling energy in air conditioning (AC) building, thus reducing a building’s carbon emissions.

Impact of cool roof on energy consumption for a railway station

The roof reflectance surface and skylight shade reflectance are two significant factors affecting air-conditioning energy consumption and indoor lighting in a single-storey large volume building, such as a railway station. Based on qualitative analysis on the effect of cool roof on building performance, a model of a large tall railway station built in the software EnergyPlus was verified by field data. The model was applied to analyse the effect of cool roof reflectance and skylight shade reflectance on the installed capacity of air-conditioning system, lighting energy consumption and indoor thermal comfort under different climates. The results show that the high reflectance surface of opaque cool roof is beneficial by reducing the energy consumption for indoor cooling and the installed capacity of air-conditioning system and improve the indoor thermal comfort in summertime. However, the opposite is true in wintertime, and this could consequently lead to more annual energy consumption. The high reflectance of skylights could reduce the energy consumption for cooling in summer and limit the energy consumption for heating and lighting in winter, thus reducing the annual energy consumption by a large amount. This study indicates that the local climates and the inherent characteristics of roof structure should be considered in the practical use of cool roof technology.

Development for cool roof calculator for India

In tropical countries such as India, increasing the roof albedo helps to reduce the heat ingress through the roof. This further reduces air-conditioning energy consumption in conditioned buildings and increases comfort in unconditioned buildings. In order to help users determine the benefits of high albedo roofs under varying conditions, a simple calculator has been developed. Parameters such as location, building type, roof area, and surface properties of the roof are taken as inputs. Annual EnergyPlus simulations are performed for the given parameters and the results are displayed in both graphical and tabular formats. It also calculates the simple payback by comparing a given base case roof albedo with the proposed roof albedo. The calculator can perform comfort simulations for unconditioned buildings and simulates measures including a radiant barrier system and under deck roof insulation. The calculator also runs a parametric simulation between insulation thickness and roof albedo to find an optimum roof insulation thickness based on incremental internal rate of return. This paper presents the features of the cool roof calculator and the type of analysis that can be performed using the cached results.

Making method and application of standards for energy consumption quota of civil buildings

Based on the energy consumption survey in Wuhan, the paper provides the civil building energy consumption quotas according to the three energy efficiency indicators, which include the limit value, the admission value and the advanced value. The paper also presents the uses of different energy consumption quotas and analyses the difference between them. Adopting a statistical analysis method, the paper analyses the limit values of 39 kinds of building using SPSS software. Adopting a simulation method and a device isolation method, the paper provides 15 kinds of admission values and advanced values using DeST simulation software based on energy efficiency design standards. The paper also analyses that judging and excluding outliers are the basis for accurately formulating energy quotas. According to the building energy efficiency and fair principle, the paper gives unit building area energy consumption indicators for buildings with 39 kinds of different functions, air conditioning and heating energy consumption accounts for the proportion of building energy consumption, the limit values of energy consumption indicators of annual per capita energy consumption, per household, per bed, per student which are concerned with building function and standard deviations of the limit values.

Influence of selected solar positions for shading device calculations in building energy performance simulations

Control strategies of building shading devices can achieve important savings in the air conditioning and lighting energy consumption of a building. Calculation procedures of the different solar control devices (overhangs, side fins, etc.) are of special interest in annual energy performance simulation programs, which have to obtain solar gains in hourly time-steps and, more recently, in five minute time-steps. A common approach used to overcome this problem in the past was to select a representative day of a certain period of time and maintain the same results of shading calculations for the rest of the period. Nowadays, the new generation computers have drastically reduced computational costs, but some programs still use the former approach. The present paper assesses the error made by the use of it. Different overhang and side fin typologies and orientations, location latitudes and simulation time-steps have been analysed. 25% of the studied cases have shown annual average relative errors of 5% or greater in the incident solar radiation over the glazing surface. Common configurations, such as south oriented overhangs, show daily deviations of incident solar energy up to 0.48kWh/m2, with a relative error of 17%, having hourly errors as high as 26%.

기존 Wi-Fi 인프라 기반의 재실 인원 예측

This study is to propose a method of predicting the number of present occupants using Wi-Fi, a sensor within the building. The accuracy and correlation of the estimated number of occupant by proposing method and schedule for generally used in a building energy simulation were compared with real occupant schedule. The validation of the proposed method has been made. MAC(Media Access Control) address and Wi-Fi was used to predict the number of present occupants, and data were collected and analyzed for 20 days. The energy consumption for air conditioning and the indoor concentration were analyzed to examine the influence of the number of present occupant using EnergyPlus. The results showed that the method considering the regression coefficient on the number of occupant accessing Wi-Fi is the most close to the real values and occupants, air-conditioning system energy use and concentration.

Reduction of carbon dioxide emissions by solar water heating systems and passive technologies in social housing

Growing global concern regarding climate change motivates technological studies to minimize environmental impacts. In this context, solar water heating (SWH) systems are notably prominent in Brazil, primarily because of the abundance of solar energy in the country. However, SWH designs have not always been perfectly developed. In most projects, the installation option of the solar system only considers the electric power economy aspects and not the particular characteristics of each climatic zone. Thus, the primary objective of this paper is to assess the potential of carbon dioxide reduction with the use of SWH in comparison with electric showers in social housing in several Brazilian climatic zones. The Brazilian government authorities have created public policies to encourage the use of these technologies primarily among the low-income population. The results of this paper indicate that hot climactic regions demonstrate a low reduction of CO2 emissions with SWH installations. Thus, solar radiation is not useful for water heating in those regions, but it does lead to a large fraction of household cooling loads, implying a demand for electrical energy for air conditioning or requiring the adoption of passive techniques to maintain indoor temperatures below threshold values.

Long-term changes of meteorological conditions of urban heat island development in the region of Debrecen, Hungary

Meteorological conditions have a remarkable impact on urban climate similarly to other local and microscale climates. Clear skies and calm weather are advantageous for the development of the urban heat island (UHI). There are numerous studies on the spatial and temporal features of the phenomenon. Much less attention is paid, however, to the meteorological conditions of UHI development. The aim of the present paper is to reveal the characteristics of the changes in the frequencies of advantageous and disadvantageous meteorological conditions for UHI development on the basis of a 50-year-long time series. Meteorological condition categories of UHI development have been established on the basis of wind speed values, cloudiness, and precipitation ranging from advantageous to disadvantageous conditions. Frequencies of occurrence of condition categories of UHI development were determined first. Advantageous and moderately advantageous conditions were found to be dominant in the time series. Linear trend analysis revealed a significant increasing trend in the time series of advantageous conditions. Increase of the frequencies of advantageous conditions was analyzed for the years, seasons, and months of the study period as well. Spring and summer (April and June) produced significant increasing trends of frequencies of advantageous conditions, while winter (with the exception of February) and autumn did not show significant increase of those frequencies. Change-point analyses detected a significant increase in the frequency of advantageous conditions in the time series at the turn of 1981/1982 especially in the summer and spring months. Detected tendencies have negative effects on urban energy consumption: they contribute to the increase of air conditioning energy demand in the summer and do not decrease the energy demand of heating in the winter significantly.

Assessing climate-adaptation effect of extensive tropical green roofs in cities

Many cities have inadequate green infrastructures and cannot benefit from ecosystem services brought by greenspaces. Global warming and urban heat island (UHI) effect impose a dual warming impact on cities, especially compact ones. Green roofs offer a plausible solution for climate adaptation. In compact humid-tropical Hong Kong, two green-roof and a control bare-roof plots were installed on a high-rise building. Precision sensors were installed along a holistic vertical temperature profile extending from outdoor air to roof surface, green-roof material layers, and indoor ceiling and air. Three apartments under the plots were kept vacant to monitor air-conditioning energy consumption. The comprehensive-systematic data allowed in-depth analysis of thermal performance of vegetation (Sedum and Perennial Peanut) and weather (sunny, cloudy and rainy) in summer. Intense solar radiation at Control plot triggered significant material heating, which in turn warmed near-ground air to intensify UHI effect and indoor space to lift energy consumption. Sedum plot with incomplete plant cover, sluggish transpiration and limited substrate moisture storage had feeble evapotranspiration cooling. The warmed roof passed heat to near-ground air and subsurface layers to impose a small indoor cooling load. Peanut plot with high transpiration rate can significantly cool foliage surface and near-ground air to ameliorate UHI. Its high moisture-holding capacity, however, can generate an appreciable heat-sink to push heat downwards and increase indoor cooling load. Practical hints on green roof design and management were distilled from the findings for application in Hong Kong and beyond and to contribute to climate-resilient cities.

A case study on the effects of the wind catcher and Taiko-shoji in Japanese environment-friendly house

ABSTRACTRecently, people around the world have actively made efforts to conserve energy in residential homes as a countermeasure against global warming. The awareness of the importance of energy saving has continued to grow in Japan since the Great East Japan Earthquake in March 2011. The interest in cross-ventilation for air conditioning energy saving in summer is especially increasing. Japan's climate features high temperatures and humidity, and it is a country in which people used cross-ventilation in their homes during summer and the middle season earlier. However, due to changes in modern society, including the progress in air-conditioning facilities, the focus on an environmentally conscious house design was lost. Therefore, studies about cross-ventilation have not been conducted in recent years. This study reconsidered the value of Japanese traditional houses and evaluated the effect of the planar-shaped house in cross-ventilation. It also surveyed the heat-insulating effect of a Taiko-shoji that was developed from an ordinary shoji screen used in Japanese traditional houses. The results show that a skylight opening increased the cross-ventilation air volume and that the shape worked effectively as a wind catcher without any special equipment. Moreover, the study found that the installment of a Taiko-shoji had a significant effect on heat insulation in summer and winter.

Influence of Urban Microclimate on Air-Conditioning Energy Needs and Indoor Thermal Comfort in Houses

A long-term climate measurement was implemented in the third largest city of Taiwan, for the check of accuracy of morphing approach on generating the hourly data of urban local climate. Based on observed and morphed meteorological data, building energy simulation software EnergyPlus was used to simulate the cooling energy consumption of an air-conditioned typical flat and the thermal comfort level of a naturally ventilated typical flat. The simulated results were used to quantitatively discuss the effect of urban microclimate on the energy consumption as well as thermal comfort of residential buildings. The findings of this study can serve as a reference for city planning and energy management divisions to study urban sustainability strategies in the future.

Experimental Study of Factors Affecting the Performance of a Semi-enclosed Outdoor Air-conditioning Unit

To achieve a beautiful appearance, the outdoor machine of a residential air conditioning system is often placed in a groove and shield with a louver. This paper presents split air conditioner outdoor machine in the semi closed space within the optimal locations and louver form. This study is based on the enthalpy difference laboratory platform, to evaluate an outdoor unit installation and lover form effect on air-conditioning energy and EER. The results show that the condenser should be more than 80mm away from the walls; The EER increased with increasing distance and the optimal distance away from the fan louver was approximately 300mm. The heat dissipation effects of the air conditioner were better with a greater louver spacing. The optimal louver angle was approximately 30° when the outdoor wind come from the lateral direction. The air-conditioning efficiency was much higher than when the wind came from the front. Therefore, the outdoor unit and the local dominant wind direction should be presented to the lateral wind.

Perception of indoor environment quality in differently ventilated workplaces in tropical monsoon climates

Quarter of the global greenhouse gas emissions are related to generation of electricity by combustion of fossil fuel. Office buildings are one of the highest energy consumers of the built environment, employing over half of its end use energy for heating, ventilation, air conditioning and lighting. The intense solar radiation received in the equatorial regions requires that cooling and dehumidification provided inside buildings at all times to achieve comfort. Comfort is a strong indicator of workplace satisfaction which further influences productivity. The research investigates the perception of indoor environment quality (IEQ) in differently ventilated workspaces and the applicability of each ventilation type in the tropical monsoon climate. The surveyed utilized a seven point unipolar and bipolar scale to measure occupant's subjective evaluation of the indoor environment condition. Valid responses were collected from 523 participants of nine office buildings in Colombo, Sri Lanka. The buildings were categorized into three ventilation types for analysis: central air Conditioning (AC), ductless mini split system air conditioning (MM), naturally ventilated with operable windows and fans (NV). The perceived performance of AC and MM buildings were found to be similar in IEQ aspects; overall comfort, temperature comfort, temperature sensation, satisfaction with amount of natural light. AC and MM buildings were rated more satisfactory for overall comfort of indoor environment condition. The investigation reinforce the need for holistic, bottom up approach to design of environmentally sustainable office buildings.

Energy Efficiency in Buildings in Hot Humid Climatic Regions Using Phase Change Materials as Thermal Mass in Building Envelope

Air conditioning energy consumption in summer represents a challenge in many areas with hot and humid climates. Passive cooling with thermal storage in phase change materials (PCMs) is a very effective way to improve thermal stability of the rooms with light-weight envelope. The main objective of this research is to demonstrate experimentally that it is possible to improve the thermal comfort and reduce the energy consumption of a building without substantial increase in the weight of the construction materials with the inclusion of PCM. This work aims at presenting an overview of the key researches in the field of use of PCMs in buildings and presenting a green approach for their uses in building envelopes with specific implementation on the case of hot humid regions. Thermal behaviour of wall integrated with two different types of PCMS Polyethylene glycol (PEG) E600 and Capric Acid (C10 H20 O 2) was compared by measurements and calculations. Three test cells were built for comparative investigation of the efficiency of passive cooling with the use of the PCMs. This paper deals with the results of experiments carried out in the test cells and possibilities of activation of PCMs for effective passive cooling.

Numerical analysis of a shell-and-tube latent heat storage unit with fins for air-conditioning application

Free cooling is an effective way to make good use of night cold energy and helps to reduce air-conditioning energy consumption in the daytime. This research proposed integrating a new-type of shell-and-tube based phase change material (PCM) thermal storage system with conventional air-conditioner to increase cooling coefficient of performance (COP). The proposed PCM thermal storage unit uses two different kinds of media (water and air) for the heat transfer fluids (HTF). Water is used for charging loop while air is used for discharging loop. The two HTFs better fit the heat transfer needs of nighttime’s free cooling harvest and daytime’s condensing water use by the air-conditioning system. A numerical model for the PCM thermal storage unit has been developed, particularly with consideration of staged natural convection effects in PCM melting process. The numerical model equipped with a new PCM staged effective thermal conductivity has been validated by experimental data. Numerical study has evaluated the effects of HTF inlet temperature, mass flow rate and conductive fin height on the PCM thermal storage system’s performance. Modeling results show that HTF mass flow rate and fin height need to be designed through an optimization process according to the cooling load profile and achieve best performance of the PCM thermal storage system. Effectiveness of this proposed PCM thermal storage system is generally higher than 0.5. Case study of replacing conventional cooling tower by the proposed PCM thermal storage system for a water-cooled air-conditioner shows a COP value increase of about 25.6%.