Buildings In Subtropical Climate Research Articles

Sensitivities of energy use reduction in subtropical high-rise office buildings: A Hong Kong case

Office buildings are a major contributor to energy consumption in high-density urban contexts where building high-rises is a norm. It is important to understand the parameters affecting high-rise office buildings’ energy consumption. However, previous research generally used isolated buildings as target buildings, regardless of the impact brought by the surrounding buildings. Also, there lacked a comprehensive calibration method to validate the energy baseline model. This paper aims to quantitatively analyse the energy use in high-rise office buildings by tackling these two issues and examining the impacts of various energy-saving measures (ESMs). A real-life 26-story office building in Hong Kong was selected as a base case. Multiple methods were used to calibrate the building energy model, including onsite microclimate measurement, metered data, architectural drawings and official documents, and onsite surveys. Parametric sensitivity analyses were then conducted to quantify the importance of ten selected parameters from five types of ESMs. Results indicate that fan efficiency and cooling setpoint temperature had the most significant energy-saving potential. The base case of the ESMs in use was considered as the base scenario. Two new scenarios were proposed to examine the range of total energy consumption by adopting the most and least energy-efficient ESMs, which were referred to as the “optimistic scenario” and the “pessimistic scenario”. The maximum reduction/increase in energy use is expected to be approximately 13.2%/39.3% for the optimistic/pessimistic scenario compared to the base scenario. The findings on the sensitivities and scenarios contribute to a more comprehensive understanding of the critical parameters that influence energy use in high-rise office buildings in subtropical climate. The findings also provide scenario-based design solutions for delivering low-energy office buildings.

Thermal design of energy piles for a hotel building in subtropical climate: a case study in São Paulo, Brazil

The use of shallow geothermal energy through energy piles for the air-conditioning of buildings is increasing worldwide. This type of renewable energy technology is still not utilized in Brazil, where the hot dominating weather regions and the air cooling demand predominate. In this case of unbalanced heat transfer to the ground, the efficiency of the system may decrease with time due to the excessive heat injection into the soil. In order to investigate the possibility of an efficient application of this technology in São Paulo city, a balanced use of the ground for a ground-source heat pump (GSHP) system utilizing energy piles is evaluated in the present paper. Energy foundations were designed to meet the balanced heating and cooling loads (air conditioning and water heating) of a hypothetical business hotel building located in a site at the campus of the University of São Paulo, where thermal response tests (TRTs) were conducted on different types of energy pile. The number of energy piles required to supply the building thermal loads were estimated using the pile heat exchanger modelling software PILESIM 2.1 and compared with an analytical model prediction. The evaluations were done for three different types of pile tested at the site chosen for this study: micropiles, steel pipe, and continuous flight auger (CFA) piles. The results indicate that the ground heat extraction should be considered for the use of GSHP systems with energy piles in air cooling-dominated scenarios similar to the case studied here.

Energy use of subtropical high-rise public residential buildings and impacts of energy saving measures

The rapid growth of energy consumption in buildings has become an alarming threat to the climate. Various building-level energy saving measures have been studied and adopted to achieve energy efficiency. However, high-rise public residential buildings in subtropical climate as an important contributor to building-level energy consumption have received insufficient attention of research. The aim of this paper is to analyse the energy use of high-rise residential buildings in subtropical climate and examine the impacts of different energy saving measures for developing strategies for achieving very low-energy high-rise buildings. A typical high-rise (40-storey) public residential building in Hong Kong was selected as the case building, which has the energy use intensity of 106.6 kWh/m2 for the total building area and of 153.8 kWh/m2 for the area inside the residential units. The energy model of the case building developed using EnergyPlus software was carefully calibrated using metered energy use data and expert consultations adopting a systematic approach. Sensitivity analyses were then conducted using the parametric analysis tool jEPlus to quantify the impacts of different energy saving measures on energy use intensity reduction. It was found the measures in relation to human behaviours have the largest impact, followed by building service system efficiency and renewable energy. Building form and building envelope have the modest impact. The findings enhance the knowledge of subtropical high-rise public residential buildings’ energy performance, and the developed and calibrated energy model could be used to explore more strategic energy saving measures in the long term. The quantified impacts of the measures should inform design decisions of low-energy housing production in high-rise sectors.

A simplistic and efficient method of estimating air-conditioning load of commercial buildings in the sub-tropical climate

Energy efficiency of buildings is attracting significant attention from the research community, as the world is moving towards sustainable building designs. The average heat gain is the crucial measure for estimating the energy consumption of the buildings. The Envelope Thermal Transfer Value (ETTV) is a simplistic method of determining average heat gain in buildings through its envelopes considering all heat gain components. It also measures the energy efficiency of buildings without inhibiting the design options. The values of ETTV coefficients highly depend on the climatic conditions, geographical locations and the orientation of the buildings. However, no study has been done to investigate the suitability of applying ETTV approach and to develop ETTV formulations for extreme solar radiation with hot and windy climatic conditions like Australian environments. In addition to this, the relevant studies reported in the literature are not comprehensive enough as the coefficient were developed using limited data and the developed formulations were not applied to a variety of real buildings to validate them. Therefore, the main aim of this study is to develop the coefficients of envelope thermal transfer value for commercial buildings, formulate new ETTV equations for buildings with external shadings and estimate the ETTV based annual cooling energy in the sub-tropical climates of Australia. In this study, real life building data relevant to all heat gain parameters of five existing commercial building have been collected and hourly data of wall conduction, window conduction and solar radiation for 11 different types of wall construction and 54 types of window construction have been analysed to determine coefficients of ETTV. Based on these coefficients, the new formulation of ETTV has been proposed to determine total ETTV value of commercial buildings in sub-tropical climate. The developed formulations have been used to estimate the cooling energy loads of 10 real life buildings. A comparative study has been conducted between these estimated cooling energy consumption based on ETTV, actual building load and simulated cooling energy using commercial software. It was demonstrated that developed equations accurately estimate the building cooling load. The computed values of ETTV are within the range 24–42 W/m2, which can be applied in any air-conditioned commercial building in sub-tropical climate like Australia.

Investigation on effect of indoor air distribution strategy on solar air-conditioning systems

Abstract Stratum ventilation (SV), a new indoor air distribution strategy, has been promoted for applications in different building premises in recent years. Compared to the conventional mixing ventilation (MV), the prominent advantage of SV is that indoor thermal comfort can be satisfied with a relatively high supply air temperature, hence less energy consumption in refrigeration. In solar air-conditioning, the energy performance can also be facilitated by high-temperature cooling. As such, the potential of SV to be involved in solar air-conditioning was evaluated. In this study, the solar air-conditioning systems included solar absorption cooling system (SAbCS), solar adsorption cooling system (SAdCS), solar desiccant cooling system (SDCS), hybrid solar absorption-desiccant cooling system (HSAbDCS) and hybrid solar adsorption-desiccant cooling system (HSAdDCS). Their performances using SV and MV were determined through year-round dynamic simulation. Compared to the counterpart using MV, SAbCS, SAdCS, SDCS, HSAbDCS and HSAdDCS associated with SV could have 35%, 54%, 59%, 29% and 44% saving in the annual primary energy consumption for building in subtropical climate respectively. Benchmarked with the conventional air-conditioning system, they could have primary energy saving up to 30%. Consequently, solar air-conditioning and SV can have synergetic merit in building application in hot and humid city.

Performance Assessment of Desiccant air Conditioning System in an Institutional Building in Subtropical Climate

Abstract In hot and humid climate, the heating, ventilation and air conditioning (HVAC) system consumes more than 40% of the total energy consumption of the building. Therefore, it is necessary to find out the ways of reducing overall energy consumption of such power-hungry systems. The goal of this paper was to model and analyze the performance of desiccant air conditioning system in an institutional building in subtropical climate similar to that in Central Queensland and investigate whether the incorporation of a desiccant cooling system is able to reduce the energy consumption of the existing HVAC system. The analysis involved modelling the reference building using OpenStudio to determine its cooling/heating requirements. This is then followed by HVAC performance assessment of the existing VRF system, installed in the reference building, through developing a model in EnergyPlus (EP). The model is validated with on-site measured data recorded in building management system (BMS). Then, include desiccant air conditioning (DAC) system into the model to provide the dehumidification for the reference building to reach “thermal comfort” in terms of both relative humidity and temperature.

Analysis of Energy Performance of Institutional Buildings in Subtropical Climate

Abstract Energy analysis and assessment are required to identify how much, where and how energy is used within a facility. The purpose is to analyse and assess the energy consumption pattern through the analysis of the historical energy consumption data by the buildings in an academic institution located in the subtropical region of Australia. This study reports some of the findings from the survey of the institutional buildings and the measurements of the energy consumption data related to the internal thermal load. The monthly monitored energy usages of the buildings are used to analyse the effects of climatic variation on energy utilization. The distinctiveness of this study is that the developed correlations between the energy utilization and weather pattern can be used to plan the sustainable operation of the institutional buildings in the subtropical region. Most importantly, the increased energy consumption pattern in the buildings will provide a good indication of the design feature and energy efficiency requirements in the building located in this climate.

Dynamic performances of trigeneration systems using different prime movers for high-rise building application: A comparative study

Trigeneration is a strategic deployment to achieve the energy saving target in response to climate change mitigation. Appropriate choice of prime movers is paramount to make trigeneration feasible. It is common for trigeneration to be considered in district-wide application; however, there is little study on the effectiveness of various available prime movers in building-scale use. As such, diesel engine (DE), gas engine (GE), gas turbine with recuperator, and combined gas turbine cycle (CGTC) were involved as prime mover options for trigeneration in this study. Through year-round dynamic simulation, the energy and environmental performances of different trigeneration systems were thoroughly evaluated for a high-rise hotel building in subtropical climate. It was found that the DE-primed trigeneration would have the highest primary energy saving, while the CGTC-primed trigeneration would be the largest in carbon emissions cut. However, the GE-primed trigeneration system was deemed to be the best choice with both energy merit and system simplicity. It was also found that the part-load performance of prime mover and the required fuel type were closely associated to the annual energy and environmental performances.

Effective design and operation strategy of renewable cooling and heating system for building application in hot-humid climate

The utilization of renewable energy sources is commonly constrained by the building form and the site environment particularly in a densely-populated city which limits the space available to install the respective facilities. The hybrid use of solar and geothermal energy helps improve the situation as the roof and the ground can be fully utilized. A renewable cooling and heating system (RCHS) was therefore investigated based on this approach when applied to a three-storey office building in sub-tropical climate. Solar energy was used in absorption cooling and water heating while ground source was utilized by a high-temperature chiller for radiant cooling. Appropriate control and operation schemes were adopted for the ground-coupled radiant cooling system according to the ambient conditions in order to minimize the system energy demand. By performing dynamic system simulations using TRNSYS, the year-round performances of RCHS were thoroughly evaluated under different design factors including radiant panel type, ground thermal conductivity, borehole length and water heating demand. It was found that the RCHS was effective to tackle the high cooling demand for building in the hot-humid climate, with 44.4% annual primary energy saving against the conventional system.

Comprehensive Evaluation of Energy and Environmental Performances of an Extensive Green Roof of a Building in Subtropical Climate

Green roof has been investigated to be one of the effective means for improving the building energy performance and relieving the urban heat island (UHI) effect. This study presents a case study in South China with a subtropical climate to evaluate the benefits of extensive green roof to the building energy, indoor and outdoor thermal environment through field tests and simulations. During the field tests in summer, a room on the top floor of a residential building was covered with green roof as the studied room, and another similar room with conventional roof was regarded as the reference room. The field tests showed that the green roof has better thermal behaviors in terms of heat insulation and thermal resistance capacities. The field measurements and thermal voting tests revealed that better comfort indoor thermal comfort and lower outdoor air temperature above the roof (reduction by 0.9-3°C) can be achieved using the green roof. Based on the results of field measurements and simulation study, 32.7% of the mean daily energy was saved by using the green roof for the room studied, and 0.75% of the total electricity consumption of the city was estimated to be saved if 15% of the buildings in the city are covered with green roofs.

A simplified model for evaluating the energy saving potential of adopting demand controlled ventilation in office buildings in Hong Kong

Demand controlled ventilation (DCV) to conserve energy while maintaining an acceptable indoor environment has been used for over 30 years. However, little work has been done on evaluating its energy saving potential in cooling dominant office buildings in subtropical climate. In this study, the energy saving potential of DCV system for use in six representative office buildings in Hong Kong was investigated by simulations. Simulation validation was done based on in situ measurements and site surveys. The findings show that, based on their original design conditions, the use of DCV could lead to 12.5–26.1% energy saving. To facilitate quick estimation of the energy saving potential of DCV system, further simulations were performed for the development of a simplified model. The simplified model relates the energy saving potential to key air-conditioning system and design parameters. Based on the simplified model, sensitivity analysis was conducted to quantify the influences of different parameters on the energy saving potential of DCV system. The developed model method can be used for prediction on the energy saving potential in a wider application of DCV in Hong Kong.

Investigation on variable flow control in existing water-cooled chiller plant of high-rise commercial building in subtropical climate

An all-variable-speed chiller plant has been advocated so that the chillers and their associated pumps can work at reduced speed during part-load conditions for energy saving purposes. In this new building project, the savings merit is certainly attractive. However, an existing chiller plant or retrofit project, which is constrained by the performance of installed equipment and the configuration of a hydronic circuit, may not benefit from the an ideal extent of savings. As such, an existing chiller plant serving a typical commercial building was used to evaluate this. Through year-round dynamic simulation, it is found that there were about 5%, 6%, and 8% energy savings of the whole chiller plant when applying variable flow control on secondary chilled water pumps only, both primary and secondary chilled water pumps, and all chilled and condenser water pumps, respectively. If constant-speed centrifugal chillers were substituted by the variable-speed ones, an additional 4% savings could be achieved, which was, however, less than that incurred from the associated pumps. The payback periods of different variable flow control strategies were well below 1 year, indicating the techno-economical feasibility for wider application in existing chiller plants in subtropical climates.

Recent Developments of Advanced Fuzzy Logic Controllers Used in Smart Buildings in Subtropical Climate

Building management system (BMS) has the ability to monitor and control buildings’ mechanical and electrical equipment including namely heating, ventilating and air conditioning (HVAC), lighting, power, fire and security systems. BMS can also provide indoor thermal comfort within commercial buildings including industrial and institutional buildings and able to reduce energy consumption. However most of HVAC systems are controlled by using conventional controller whose functions are based on ON/OFF controller and Proportional-Integral-Derivative (PID) controllers. These controllers are not the ultimate solution to save energy because the operations of HVAC systems are nonlinear. Thus, the implementation of fuzzy logic controllers within smart buildings will be more efficient which consequently will save more energy and money. This paper reviews, investigates and evaluates the use of fuzzy logic controller in HVAC systems and light controllers for smart buildings in subtropical Australia. Additionally, it highlights the recent developments in BMS controllers including its conceptual basis, capabilities and limitations.

An analysis on the energy efficiency of air-cooled chillers with water mist system

This paper presents the effect of operating water mist system to enhance the energy efficiency of air-cooled chillers under various operating conditions. A thermodynamic model for an air-cooled chiller with twin refrigeration circuits coupled with a water mist system was developed and validated by measured operating data. The validated model was used to investigate how the thermal properties of the entering condenser air and the performance of the air-cooled chiller varied under different operating schemes with water mist pre-cooling. Under the conventional head pressure control (HPC) with a designed water mist generation rate, the coefficient of performance (COP) increased by up to 21.3%. The chiller performance could be improved further under variable condensing temperature control (CTC). Under CTC, chiller COP was increased up to 51.5% with optimal water mist generation rate. The potential energy savings of these chillers serving a representative office building in subtropical climate was evaluated, and CTC coupling with optimal water mist generation rate would reduce the annual total electricity consumption for cooling by 14.1%. The water consumption of the water mist system was comparatively small, comparing with the total water losses for an open-loop cooling tower system with equivalent heat rejection capacity.

Energy conservation measures in an institutional building in sub-tropical climate in Australia

In this study, various energy conservation measures (ECMs) on heating, ventilating and air conditioning (HVAC) and lighting systems for a four-storied institutional building in sub-tropical (hot and humid climate) Queensland, Australia are evaluated using the simulation software called DesignBuilder (DB). Base case scenario of energy consumption profiles of existing systems are analysed and simulated first then, the simulated results are verified by on-site measured data. Three categories of ECMs, namely major investment ECMs (variable air volume (VAV) systems against constant air volume (CAV); and low coefficient of performance (COP) chillers against high COP chillers); minor investment ECMs (photo electric dimming control system against general lighting, and double glazed low emittance windows against single-glazed windows) and zero investment ECMs (reset heating and cooling set point temperatures) are evaluated. It is found that the building considered in this study can save up to 41.87% energy without compromising occupancies thermal comfort by implementing the above mentioned ECMs into the existing system.

Energy Efficient Cooling Technologies for Achieving Sustainability in Buildings in Subtropical Climate

Energy Efficient Cooling Technologies for Achieving Sustainability in Buildings in Subtropical Climate