Air Conditioning Load Research Articles

Residential precooling on a high-solar grid: impacts on CO2 emissions, peak period demand, and electricity costs across California

Abstract As regional grids increase penetrations of variable renewable electricity (VRE) sources, demand-side management (DSM) presents an opportunity to reduce electricity-related emissions by shifting consumption patterns in a way that leverages the large diurnal fluctuations in the emissions intensity of the electricity fleet. Here we explore residential precooling, a type of DSM designed to shift the timing of air-conditioning (AC) loads from high-demand periods to periods earlier in the day, as a strategy to reduce peak period demand, CO2 emissions, and residential electricity costs in the grid operated by the California Independent System Operator (CAISO). CAISO provides an interesting case study because it generally has high solar generation during the day that is replaced by fast-ramping natural gas generators when it drops off suddenly in the early evening. Hence, CAISO moves from a fleet of generators that are primarily clean and cheap to a generation fleet that is disproportionately emissions-intensive and expensive over a short period of time, creating an attractive opportunity for precooling. We use EnergyPlus to simulate 480 distinct precooling schedules for four single-family homes across California’s 16 building climate zones. We find that precooling a house during summer months in the climate zone characterizing Downtown Los Angeles can reduce peak period electricity consumption by 1–4 kWh d−1 and cooling-related CO2 emissions by as much as 0.3 kg CO2 d−1 depending on single-family home design. We report results across climate zone and single-family home design and show that precooling can be used to achieve simultaneous reductions in emissions, residential electricity costs, and peak period electricity consumption for a variety of single-family homes and locations across California.

Potential evaluation of energy flexibility and energy-saving of PCM-integrated office building walls

Building energy flexibility is important for reducing peak-to-valley differences in air-conditioner loads. Integrating phase change material into office building envelopes and precooling can effectively reduce peak load, but precooling may increase total energy consumption. Therefore, it is imperative to investigate its energy flexibility and energy consumption features. In present work, a heat transfer model of phase change material (PCM)-integrated office building walls was established firstly and verified by experiments. Then, the energy flexibility and energy-saving potential of the PCM-integrated wall under different precooling strategies were studied, and the effects of various PCM parameters on energy flexibility and energy-saving potential were evaluated. Finally, the influence of different peak-to-valley electricity tariff differences on electricity costs was analyzed. The results show that the optimized precooling strategy and peak-to-valley electricity tariff difference make the energy flexibility index of the PCM-integrated wall up to 69.7% at a total load reduction of 1.3% and save the electricity cost by 51%. The PCM location and melting point have the most significant effect on the energy flexibility and energy-saving potential of the PCM-integrated wall under precooling operating conditions. This study guides the selection of energy flexibility and energy-saving precooling strategy and PCM parameters for PCM-integrated office building walls and the formulation of time-of-use tariff policies.

Evaluation of renovation strategies for existing residential districts in Shanghai based on coupling calculation of microclimate and energy consumption

This study aims to analyze the impact of renovation strategies on the air-conditioning load in existing residential districts in Shanghai by using the Grasshopper platform coupled with ENVI-met and EnergyPlus. These strategies include increasing the greening rate (G), improving pavement reflectivity and permeability (P), increasing the reflectivity of external wall coatings (C), increasing roof material reflectivity or applying green roofs (R), and improving the thermal performance of windows (W). The results show that microclimate and weather station data cause a 13.9% maximum deviation in energy consumption simulations. W and R4 significantly reduce the air-conditioning load throughout the year. W contributes to a decrease of 34.8 kWh in the cooling load and 110.4 kWh in the heating load. When the application level of P is low, and that of other strategies is high, the cooling load of the target building reaches its minimum. The minimum cooling load scenario is 302 kWh (25.1%) lower than the maximum. When the application level of G and C is low, other strategies have a high application level, and green roofs are used, the heating load of the target building is minimal. The minimum heating scenario is 386 kWh (29.3%) lower than the maximum.

Performance Analysis of a Solar Cascaded Absorption Cooling System Using a Performance-Enhanced Parabolic Trough Collector

Abstract This article proposes an innovative approach to improve the performance of solar cooling systems by utilizing a cascaded absorption cooling (CAC) system. This article also examines the viability of coupling an NH3–H2O absorption system with an H2O–LiBr absorption system to simultaneously satisfy both a refrigeration load and an air-conditioning load. Results of this analysis shows that the CAC system uses 7.1% less thermal energy than the sum of the energies used by the ammonia absorption system and the LiBr absorption system if they were to operate separately to meet the same cooling load. In addition, the article investigates the impact of a performance-enhanced parabolic trough collector (PEPTC) on the thermal and exergetic efficiencies of the solar cooling system. By employing a PEPTC, the area required for the solar field in a given solar cooling system will be reduced by 14% compared to the area required by a conventional parabolic trough collector (PTC). Combining the CAC system with the PEPTC results in a 22% increase in the overall efficiency of a cooling plant compared to a conventional PTC coupled with an ammonia system and a LiBr system in the same plant. In summary, it is suggested that the simultaneous utilization of the proposed CAC system and the PEPTC can considerably improve the efficiency of solar cooling systems. Doing so will lead to sustainable cooling alternatives.

Demonstration of a Solar-Driven Ejector Chiller Assisting the Air Conditioning System of a Building

Days with greater amounts of sunshine often have higher cooling demands. This makes solar energy one of the best solutions to mitigate the use of fossil fuels in cooling systems. On the other hand, scientific studies on ejector technology have demonstrated promising improvements in terms of enhancing the efficiencies of cooling and refrigeration systems. This work involved field testing of a solar thermal plant combined with an ejector-compression system for space cooling applications in buildings. The thermal plant uses parabolic solar collectors that focus a large area of sunlight toward tubes where circulating oil captures the energy. This energy activates the ejector system, which produces a nominal 15-kW cooling effect. A solar ejector cooling system is integrated into the CanmetENERGY Research Centre’s building, covering part of its air conditioning load, and consequently decreasing the electrical consumption of the main building’s chiller. The system has operated with a coefficient of performance (COP) of up to 0.27 at this location. Design characteristics of the system are presented and the mode of operation and analysis of collected data are elaborated.

Aggregated large-scale air-conditioning load: Modeling and response capability evaluation of virtual generator units

Aggregated large-scale air-conditioning load: Modeling and response capability evaluation of virtual generator units

Evaluation of Multi-Utility Models with Municipal Solid Waste Combustion as the Primary Source under Specific Geographical and Operating Conditions

Developments in waste incineration technology in terms of efficient fuel preparation, combustion, and emissions reduction, as well as the growing needs of the community in terms of electricity, water, and air conditioning loads, are the prime motive for this study. This study presents a novel approach, in which three models of the fluidized bed combustion of municipal waste for simultaneous power generation, freshwater production, and district cooling are analyzed for their energy and exergy performance. The three simultaneously evaluated utility models are different configurations of a fluidized bed combustion system with Rankine cycle power generation, cooling with a vapor absorption refrigeration system, and fresh water production using multiple effect desalination. The output from the turbine, cooling system, and desalination system is determined using the Engineering Equations Solver for different boiler operating pressures. Energy and exergy analysis data for different pressures are used to identify the best configuration. Two variants of the absorption cooling system, namely, single effect and double effect, are considered. The variants of the multiple-effect desalination are the three-stage and five-stage methods. Input parameters used in this study are municipal solid waste generation and composition data collected for an urban community in an arid climate zone with high demand for electric power, cooling, and fresh water. Model 2, which contains two turbines with the reheating and cooling systems connected to a high-pressure turbine and water desalination connected to a low-pressure turbine, gave the best overall performance. Significant savings in terms of the replacement of conventional energy were observed from these waste conversion plants with greater benefits in arid weather conditions. The results obtained by different models under different operating criteria constitute a guideline for municipal planners for the selection of appropriate waste utilization technology, as well as the appropriate operations.

New Evacuated Tube Solar Collector with Parabolic Trough Collector and Helical Coil Heat Exchanger for Usage in Domestic Water Heating

Buildings represent approximately two-thirds of the overall energy needs, mainly due to the growing energy consumption of air conditioning and water heating loads. Hence, it is necessary to minimize energy usage in buildings. Numerous research studies have been carried out on evacuated tube solar collectors, but to our knowledge, no previous study has mentioned the combination of an evacuated tube solar collector with a parabolic trough collector and a helical coil heat exchanger. The objective of this paper is to evaluate the thermal behavior of an innovative evacuated tube solar collector (ETSC) incorporated with a helical coil heat exchanger and equipped with a parabolic trough collector (PTC) used as a domestic water heater. To design the parabolic solar collector, the Parabola Calculator 2.0 software was used, and the Soltrace software was used to determine the optical behavior of a PTC. Moreover, an analytical model was created in order to enhance the performance of the new model of an ETSC by studying the impact of geometric design and functional parameters on the collector’s effectiveness. An assessment of the thermal behavior of the new ETSC was performed. Thus, the proposed analytical model gives the possibility of optimizing ETSCs used as domestic water heaters with lower computational costs. Furthermore, the optimum operational and geometrical parameters of the new ETSC base-helical tube heat exchanger include a higher thermal efficiency of 72%. This finding highlights the potential of the heat exchanger as an excellent component that can be incorporated into ETSCs.

Building energy-saving mechanism for indoor cooling temperature set-point with different envelope: A case study in Guangzhou

The temperature set-point of air conditioning system is a crucial parameter for behavior adjustment. Nevertheless, the thermal characteristics of building envelopes are different at varied construction ages. In this context, there are already several systematic studies demonstrating the differences in energy savings as a result of raising the same temperature set-point for air conditioning. In this study, an office building was used under four assumed envelopes representing different construction ages, and the characteristic temperature method was applied to simulate the hourly dynamic air-conditioning load before and after the set temperature rise of 1°C presenting monthly and annual cooling consumption. We then explored the energy-saving effect and difference in the mechanism of air conditioning with increasing indoor temperature set-point. The results showed that, provided that the temperature set-point is increased by 1°C under the same climatic conditions, the worse the thermal performance of the envelope, the higher the annual air-conditioning energy and the higher the annual energy-saving rate of air conditioning, which indicates that the behavioral energy-saving guidance for the groups with the poor performance of the older envelope has more immediate effects. The hourly load reduction of different envelopes at the outdoor temperature between 26°C and 27°C constitutes the behavioral energy-saving effect, which is the main contribution of air-conditioning energy saving (58 – 79%), while the energy-saving effect contribution of temperature difference reduction is secondary. The newer the construction age, the better the performance of the envelope, the smaller the hourly load reduction amount of the building, and the smaller the relative energy-saving rate, but its energy-saving behavior in the total energy saving ratio is greater, and the contribution of the energy-saving behavior is greater. The results of this study can provide a reference for guiding occupant energy-saving behavior and standard formulation.

Probability-based temperature-set-point control of aggregate air-conditioning loads

The Air-Conditioners (ACs) are important participants in the Demand Response (DR) programs due to their good heat/cold storage characteristics. However, traditional temperature-set-point control methods of ACs neglect the fact that Minimum Step-size of Temperature Adjustment (MSoTA) for most ACs is no smaller than 1 °C. In this paper, the load following control method is designed for ACs with MSoTA of 1 °C. To realize smooth control of the aggregate ACs, probability-based temperature-set-point broadcasting control method is designed. By adopting a prioritized mechanism, the room temperature deviation is lowered. The testing examples verify the effectiveness of the proposed method in bi-directional, smooth, and comfortable regulation of the aggregate ACs.

Economic Load-Reduction Strategy of Central Air Conditioning Based on Convolutional Neural Network and Pre-Cooling

Central air conditioning in large buildings is an important demand-response resource due to its large load power and strong controllability. Demand-response-oriented air conditioning load modeling needs to calculate the room temperature. The room temperature calculation models commonly used in the existing research cannot easily and accurately calculate the room temperature change of large buildings. Therefore, in order to obtain the temperature change of a large building and its corresponding power potential, this paper first proposes a building model based on CNN (convolutional neural network). Then, in order to fully apply the demand-response potential of the central air conditioning load, this paper puts forward an evaluation method of the load-reduction potential of the central air conditioning cluster based on pre-cooling and develops an economic load-reduction strategy according to the different energy consumption of different buildings in the pre-cooling stage. Finally, multiple building examples with different building parameters and temperature comfort ranges are set up, and the economic advantages of the proposed strategy are illustrated by Cplex solution examples.

Effect of window-glass type on solar heat gain and velocity and temperature distributions inside air-conditioned rooms – A conjugate numerical analysis

Conjugate mixed-convection numerical analysis is conducted in order to investigate effect of employing different types of window glass on solar heat gain in air-conditioned rooms using mixing air-distribution system. ANSYS Fluent and RNG k-ε turbulence model are utilized. Single- and double-pane clear and tinted window glass are considered with window-to-wall ratio of 0.33. The rate of air change per hour (ACH) is varied in range 5–20. Part of solar radiation absorbed by glass is conducted indoor while solar radiation transmitted through glass heats portion of floor and is released as a heat source to inner space. The numerical model is validated against measurements available under simpler conditions. Results of model application show that airflow pattern and temperature distribution are sensitive to the solar heat gain and, hence, to the type of glass used. It is found that air-conditioning load due to window glass heat gain is reduced by 55% by using double-pane tinted glass compared to using single-pane clear glass. A criterion to distinguish between forced and mixed convection situations in terms of ACH is also developed. In addition, further calculations are made using standard k-ω turbulence model and satisfactory agreement with RNG k-ε model results is obtained.

Energy saving potential of latent heat exchanger-integrated dual core energy recovery ventilator

High-efficiency energy recovery ventilators (ERVs) have a significant impact on the conservation of building energy. In particular, the importance of the latent cooling performance of ERV which used in hot, humid climates has been growing. To enhance the latent heat recovery performance of the existing ERVs and attain satisfactory sensible heat recovery performance as well, a dual-core energy recovery ventilation unit combining a hollow fiber membrane-based latent heat exchanger (M-LHX) and a sensible heat exchanger (SHX) was proposed in a previous work. This study evaluated the energy saving potential of the proposed ventilation unit integrated air-conditioning system via a series of building energy simulation. As the reference system, a conventional ERV with a flat-plate membrane enthalpy exchanger was chosen. The M-LHX and SHX in the proposed ventilation unit enable decoupled sensible and latent heat recovery of outdoor air. Energy simulations were conducted for a single-story office building located in South Korea, which is one of the humid regions during the summer. The simulation results showed that the proposed ventilation unit could reduce 15.9, 14.4, and 14.1% of building air-conditioning loads in summer, intermediate season, and winter, respectively, compared with the reference ERV. This is because the proposed ventilation unit provided energy benefits by recovering more latent heat from the M-LHX and comparable amount of sensible heat from the SHX than the reference system. Accordingly, the proposed system presented the annual primary energy savings of 10.6% over the reference system, although the proposed system consumed more fan energy.

Temperature Regulation Strategy of Heterogeneous Air Conditioning Loads for Renewable Energy Consumption

In a power system with a high proportion of renewable energy, sudden increases in wind power or photovoltaic output can lead to huge challenges, such as difficulties in accommodating excess renewable energy and imbalances between supply and demand on the grid. As an important adjustable resource on the demand side, air conditioning load is a flexible load for realizing output consumption. In this paper, a heterogeneous air conditioning load regulation strategy for renewable energy consumption is proposed. Each air conditioning load regulation quantity is obtained based on the day-ahead dispatching mode. Then, the temperature setting value, rated power, and duty cycle are selected as the indexes. The load regulation sequence is obtained by the entropy weight method. Finally, the load regulation time of each air conditioning load is obtained based on the constraint of the quantity of loads during the possible adjustment time. The simulation analysis shows that the temperature regulation strategy presented in this paper can effectively reduce the power fluctuations of air conditioning loads, while ensuring that users with lower temperature settings are selected in the adjustment process.

Optimization of Atrium Thermal Environment in Summer Based on DeST Platform

The indoor environment simulation and optimization of atrium buildings are a research hotspot in the field of architectural technology. This article presents linear atrium buildings as the research object, introduces DeST simulation technology into thermal environment analysis, and studies the dynamic conditions and typical day time, the atrium itself structure, the structure of the rooms around the atrium and the thermal environment of the atrium space and its adjacent rooms. In the research process, two modes of natural ventilation and air conditioning were considered, and the optimal atrium building structure parameters under different outdoor weather conditions were obtained. The research results show that in natural ventilation mode, the thermal comfort temperature is the best when the atrium’s aspect ratio is 1.71; when using the air-conditioning mode, the air conditioning load is the smallest when the atrium’s aspect ratio is 1.55. In summer, the thermal environment of the linear A-shaped atrium is better than the H-shaped atrium. When the atrium window hole position is about 0.9 ∼ 1.5 m, the thermal environment is comfortable and energy saving.

Impact of heating and cooling loads on battery energy storage system sizing in extreme cold climates

Efficient operation of battery energy storage systems requires that battery temperature remains within a specific range. Current techno-economic models neglect the parasitic loads heating and cooling operations have on these devices, assuming they operate at constant temperature. In this work, these effects are investigated considering the optimal sizing of battery energy storage systems when deployed in cold environments. A peak shaving application is presented as a linear programming problem which is then formulated in the PYOMO optimization programming language. The building energy simulation software EnergyPlus is used to model the heating, ventilation, and air conditioning load of the battery energy storage system enclosure. Case studies are conducted for eight locations in the United States considering a nickel manganese cobalt oxide lithium ion battery type and whether the power conversion system is inside or outside the enclosure. The results show an increase of 42% to 300% in energy capacity size, 43% to 217% in power rating, and 43% to 296% increase in capital cost dependent on location. This analysis shows that the heating, ventilation, and air conditioning load can have a large impact on the optimal sizes and cost of a battery energy storage system and merit consideration in techno-economic studies.

Experimental Investigation on the Performance of a Dehumidifier Constructed from a Water-to-Air Heat Exchanger Coated with Composite Desiccant of Mesoporous Silica Gel and LiCl

Thermal environment in buildings in hot climate is conditioned for comfort by air-conditioning that is energy intensive. Presently, most air-conditioning systems in Thailand and other countries in Southeast Asia use electricity-driven vapor compression systems to cool down the air to the set-point temperature. However, latent load due to condensation of air humidity forms a large part of the air-conditioning load. This paper presents the results of experiments on a dehumidifier constructed from a water-to-air heat exchanger coated with a composite desiccant of large-pore mesoporous silica gel and LiCl, regenerated by low-temperature hot water. Moisture removal capacity (MRC), dehumidification capacity (DC), thermal coefficient of performance (COPth), and an equivalent air conditioning load of dehumidification (EALD) are comparative quantitative parameters derived from experimental results and are studied in this research. The composite desiccant requires low-temperature water for regeneration and offers a higher rate of vapor adsorption and desorption that leads to a shorter required desiccant dehumidification cycle time. The results demonstrate that the dehumidifier is able to effectively reduce moisture in ventilation air and substantially reduces the cooling load of air-conditioning.

Imbalanced data-oriented model learning method for ultra-short-term air conditioning load prediction

Imbalanced data-oriented model learning method for ultra-short-term air conditioning load prediction

Research on Air-Conditioning Cooling Load Correction and Its Application Based on Clustering and LSTM Algorithm

Climate change and urban heat island effects affect the energy consumption of buildings in urban heat islands. In order to meet the requirements of engineering applications for detailed daily design parameters for air conditioning, the 15-year summer meteorological data for Beijing and Shanghai and the corresponding average heat island intensity data were analyzed. Using the CRITIC objective weighting method and K-means clustering analysis, the hourly change coefficient, β, of dry bulb temperature was calculated, and the LSTM algorithm was used to predict the changing trends in β. Finally, the air conditioning load model for a hospital was established using DeST (version DeST3.0 1.0.2107.14 20220712) software, and the air conditioning cooling load in summer was calculated and predicted. The results show that, compared with the original design days, regional differences in the new design days are more obvious, the maximum temperature and time have changed, and the design days parameters are more consistent with the local meteorological conditions. Design day temperatures in Shanghai are expected to continue rising for some time to come, while those in Beijing are expected to gradually return to previous levels. Among hospital buildings, the cooling load of outpatient buildings in Beijing and Shanghai will decrease by 0.69% and increase by 12.61% and by 12.12% and 15.51%, respectively, under the influence of the heat island effect. It is predicted to decrease by 1.35% and increase by 29.75%, respectively, in future. The cooling load of inpatient buildings in Beijing and Shanghai increased by 0.27% and 6.71%, respectively, and increased by 7.13% and 8.09%, respectively, under the influence of the heat island effect, and is predicted to decrease by 0.93% and increase by 16.07%, respectively, in future.

Numerical and experimental investigations on melting heat transfer performance of PCM in finned cold thermal energy storage

Cold thermal energy storage (CTES) is of great importance for the enduring decrease in fossil fuel energy consumption. Moreover, CTES with phase change materials (PCMs) can be an effective measure to accumulate the heat or cooling energy for overcoming the mismatch between the supply and demand of air conditioning loads, augmenting system dependability and flexibility in operations of power grids. This paper numerically and experimentally examines the melting characteristics of PCM inside a CTES tank with the installation of interior fins. The computational fluid dynamics (CFD) software ANSYS/Fluent® is applied to predict the time sequences of liquid fraction contours and temperatures in comparison with the photographed images of ice-liquid water interface and measurement data in the CTES tank to verify the accuracy of CFD predictions. The simulations by the validated CFD model are extended to evaluate the influences of fin height and total number of longitudinal fins on the heat transfer outcomes in the storage tank. The present study further proposes a novel design adopting stratified fins to enhance the melting performance of the CTES device. The estimated mean power with the new stratified fin design is notably greater than that without fins by 156.3%, achieving the effectively liquefaction enhancement of ice for guiding the development of finned cold thermal energy storage.