Electric Air Conditioning Research Articles

An Optimization-Based Supervisory Control and Coordination Approach for Solar-Load Balancing in Building Energy Management

This work considers the problem of reducing the cost of electricity to a grid-connected commercial building that integrates on-site solar energy generation, while at the same time reducing the impact of the building loads on the grid. This is achieved through local management of the building’s energy generation-load balance in an effort to increase the feasibility of wide-scale deployment and integration of solar power generation into commercial buildings. To realize this goal, a simulated building model that accounts for on-site solar energy generation, battery storage, electrical vehicle (EV) charging, controllable lighting, and air conditioning is considered, and a supervisory model predictive control (MPC) system is developed to coordinate the building’s generation, loads and storage systems. The main aim of this optimization-based approach is to find a reasonable solution that minimizes the economic cost to the electricity user, while at the same time reducing the impact of the building loads on the grid. To assess this goal, three objective functions are selected, including the peak building load, the net building energy use, and a weighted sum of both the peak load and net energy use. Based on these objective functions, three MPC systems are implemented on the simulated building under scenarios with varying degrees of weather forecasting accuracy. The peak demand, energy cost, and electricity cost are compared for various forecast scenarios for each MPC system formulation, and evaluated in relation to a rules-based control scheme. The MPC systems tested the rules-based scheme based on simulations of a month-long electricity consumption. The performance differences between the individual MPC system formulations are discussed in the context of weather forecasting accuracy, operational costs, and how these impact the potential of on-site solar generation and potential wide-spread solar penetration.

A Customer-Centric Approach to Bid-Based Transactive Energy System Design

This study demonstrates how bid-based transactive energy system designs can be formulated from a customer-centric vantage point to encourage voluntary customer participation. Supportive evidence is provided for distribution systems populated by households with smart electric heating, ventilation and air conditioning systems. The optimal form of a household’s bid function is first derived from dynamic programming principles, based solely on the household’s general thermal dynamic and welfare attributes. The quantitative form of this optimal bid function is then explicitly derived, given quantitative forms for these attributes. A method is also developed for the systematic construction of household types based on these attributes. Bid comparison, peak load reduction, and target load matching test cases conducted for a 123-bus distribution system illustrate the usefulness of these methods for ensuring bid-based transactive energy system designs are able to align system goals and constraints with local customer goals and constraints.

Heating Performance Characteristics of an Electric Vehicle Heat Pump Air Conditioning System Based on Exergy Analysis

In this paper, a heat pump air conditioning system (HPACS) with refrigerant R134a based on the functional requirements of battery electric vehicle is designed and tested. Experiments were conducted to evaluate the effects of different ambient temperature, air flow rate of internal condenser, expansion valve (EXV) opening and compressor speed. The results demonstrate that air flow rate of internal condenser, EXV opening and compressor speed have important impact on heating capacity, compressor power consumption and coefficient of performance (COP) under several ambient temperatures. To verify the HPACS can also provide the heating capacity required by the battery electric vehicle cabin in cold climate, the system was also tested under a −5 °C ambient temperature, it was found that the heating capacity is 3.6 kW and the COP is 3.2, demonstrating that the system has high energy efficiency. In addition, heating process analysis of the HPACS under lower temperature is studied by exergy principle. The results indicate that compressor is the highest exergy destruction in all components, accounting for 55%. The percentage of exergy destruction in other components is about 28%, 12% and 5% for the expansive valve, condenser, and evaporator. Furthermore, air flow rate of internal condenser, ambient temperature and expansion valve opening have important impact on exergy destruction and exergy efficiency of the HPACS.

Heuristic approach for transactive energy management in active distribution systems

The advent of distributed energy resources (DERs), which include small conventional and renewable generation units, energy storage, and flexible loads in distribution network needs distributed coordination for effective management. In this paper, a stochastic transactive management framework is proposed to minimize overall cost and avoid network constraints violation at the distribution network level. This framework includes day-ahead scheduling of electric vehicles and air conditioning loads under demand response aggregators (DRAs), and DERs under distributed generation owners (DGOs) into day-ahead wholesale market in a network managed by a distribution network operator (DNO). An agent called distribution independent system operator (DISO) is responsible for coordination among DRAs, DGOs, and DNO. A heuristic step-size update approach is proposed to calculate the Lagrange multiplier iteratively and improve the convergence speed. This framework is modeled as a quadratic constraint programming (QCP) problem and solved using the GAMS solver. Simulation results on a modified 33-bus system with considerable penetration of loads and DERs, shows that the suggested framework can efficiently reduce the iterations to converge and returns an optimal schedule. And demonstrate the effect of network congestion, demand, and generation uncertainties on the resulting objective values of the agents and magnitude of the Lagrange multiplier values.

PRINCIPLE OF DEVELOPMENT OF THE TRIGENERATION SYSTEM WITH SOLAR POWER UNIT

The development of small trigeneration systems with renewable energy sources solves the problem of life support for the population of many regions of the world which are remote from central electricity suppliers. The autonomous system provides year-round stable production of electric energy, hot water, air conditioning and heating in residential premises. The solar power plant is represented by two units: a photovoltaic converter for electric power generation and solar collectors for heating. A method for creating trigeneration systems based on the theory of thermal transformers is proposed. A thermodynamic analysis of the characteristics of compressor and absorption step-down and step-up thermal transformer for the conditions of the Middle East is carried out. The method of determining the characteristics of the elements of the system based on models of processes occurring in them is presented. An example of calculating the thermal characteristics of all elements of the trigeneration system taking into account energy conservation is given. Recommendations are developed for the selection of temperature operating conditions and equipment completing the system.

Natural gas engine driven heat pump system – a case study of an office building

ABSTRACT An eQUEST model was developed to conduct a simulation study of a natural gas engine-driven heat pump (GEHP) for an office building in Woodstock, Ontario, Canada. Prior to the installation of the GEHP, the heating and cooling demands of the office building were provided by rooftop units (RTUs), comprising of natural gas heater and electric air conditioner. Energy consumption for both GEHP and RTUs were monitored for operation in alternating months. These recorded energy consumptions along with weather data were used in the regression analysis. The developed eQUEST models were validated and calibrated with the regression analysis results with respect to the ASHRAE Guideline 14–2014. The eventual models were then applied to investigate the potential annual energy consumption, greenhouse gas (GHG) emission and energy cost savings achieved by using the GEHP in Woodstock, and other cities in Canada, particularly in Ontario.

District-Level Summertime Air-Conditioning Electricity Consumption and the Sensitivity of Peak Cooling Loads to Urban Weather Conditions in Beijing

AbstractUnderstanding how energy use responds to meteorological conditions is essential for anticipation of energy demands, which is of significance to maintain sufficient power supply and to prevent brownouts or blackouts during peak hours. Using the quarter-hourly and district-level electricity data for Beijing, this study calculates the district-varying cooling electric loads due to air-conditioning (AC) systems in five consecutive summers. Results show the occurrence of two major features that are common for summertime cooling loads in most districts, namely, double-peaked diurnal profiles and weekday–weekend fluctuations. With the increasing distance from the city core, the evening peak cooling load around 21:00 local time (LT) becomes more pronounced and comparable with its afternoon counterpart around 15:00 LT. Conversely, the weekday–weekend fluctuation is greatly weakened in suburban and rural districts due to the stable cooling demands on weekdays and weekends. The district-level sensitivity of peak cooling loads to surface meteorological factors is further investigated by linear regression analysis, and results show significant decreases from urban to rural districts. The correlation coefficients between peak cooling loads and heat index that combines air temperature and relative humidity reach up to 0.8–0.9 in most districts. If using air temperature or specific humidity solely, the coefficients of determination with peak cooling loads are roughly 0.1–0.3 smaller, possibly indicating the greater potential of heat index for effectively predicting peak cooling demands in Beijing.

SOLAR RADIATION PROTECTION SYSTEM WITH SIMULTANEOUS HOT WATER SUPPLY


 
 
 Problems. Windows in the summer let through a large amount of solar energy into the room, which causes an additional cost of cooling the air by conditioning. It is known that the limit of comfort is the temperature of 26 oC. To reduce the temperature, use air conditioners, which are required 0,3...0,5 kW of electrical power for 10 m2
 
 
 
 of housing. The study deals with the capture of solar energy by water and its use for domestic water purposes (DHW).
 The goal of the research. Experimental verification of patented developments and calculations of hot water quantity obtained per day, energy savings and economic indicators.
 Methods of implementation. Experiments were conducted on the south window of the room, with water pumping by a pump and periodic measurement of air and water temperatures at the outlet of the system by mercury thermometer. The calculations were performed using the methods developed by the authors. The studies were conducted within three days of November. The temperature inside ranged a room from 19 to 23 °C. The system was operated in circulating mode on a water battery tank located below the absorber. Isolation of the absorber from the side of the room was made of a transparent food film.
 Research results. Water temperature reached 45 °C per 1,5-2 hours. Water consumption is enhanced by the thermosiphon effect when water moves from the bottom up. On a clear day of spring and autumn, you can heat for 50-70 % more water than the average for the average day of months of the warm season. For preparing DHW with 1 m2 of absorber, it is possible to get 45-50 kW∙h of heat for each month from March to September, taking into account cloudiness. The savings from the use of hot water and from reducing the consumption of electricity in the air conditioner are calculated.
 Conclusions. The payback period of the system, taking into account the cost of the heat for DHW and electricity savings for an electric air conditioner, is approximately 4-5 years. The cost of the system is close to the cost of a home air conditioner, for a premise with a single window oriented south. To the energy-saving factor, an additional advantage is the environmental friendliness of the system compared to the air conditioner.
 
 
 
 
 

Environmental impact assessment of office building heating and cooling sources: A life cycle approach

Heating and cooling sources occupy a large proportion of the total energy consumption of office buildings and hence the related environmental impacts cannot be underestimated. In this paper, a localized life cycle impact assessment (LCIA) method was established based on local environmental policies and energy regulations according to the framework of life cycle assessment (LCA). It is used to analyze the heating and cooling sources for office buildings in northern China. The environmental impact inventory was classified, characterized, standardized and weighted based on local energy resources. The exergy exhaustion (EE) factor was adopted to analyze the importance of local primary energy. Cost analysis was conducted to increase the practical value and significance of the research results. Questionnaires were used to determine the weight of environmental impact, EE, and cost analysis (CA) for combination scheme selection. Different heating and cooling sources and 7 combination schemes for office buildings in the cold regions of northern China were comprehensively evaluated. Results showed that gas-fired cogeneration + conventional electric refrigeration air conditioners and ground source heat pump (GSHP) for both heating and cooling were two recommended schemes which had the least comprehensive environmental impact index. These investigations can guide decision-makers and designers to choose environment-friendly and economical heating and cooling sources, and help government departments to formulate appropriate incentive policies to encourage the use of suitable, sustainable, and economical energy sources.

Application of RBF Sliding Mode Control in Pump System for Electric Vehicle Heat Air Conditioning

Aiming at the characteristics of time-varying, time-delay and non-linearity of electric vehicle heat pump air-conditioning system, this paper presents a sliding mode control method based on RBF neural network. The RBF neural network can approximate the nonlinear function with arbitrary precision under certain conditions, and has strong self-learning and self-adaptive ability. Combining the RBF neural network with the sliding mode variable structure control not only has the anti-interference of the sliding mode control and the robustness to the parameter changes, but also effectively reduces the flutter caused by the sliding mode control. The simulation results show that the RBF neural network sliding mode control method can improve the system control accuracy, effectively weaken the chattering, and has good adaptability to the interference conditions.

System design and feasibility of trigeneration systems with hybrid photovoltaic-thermal (PVT) collectors for zero energy office buildings in different climates

Zero or plus energy office buildings must have very high building standards and require highly efficient energy supply systems due to space limitations for renewable installations. Conventional solar cooling systems use photovoltaic electricity or thermal energy to run either a compression-cooling machine or an absorption-cooling machine in order to produce cooling energy during daytime, while they use electricity from the grid for the nightly cooling energy demand. With a hybrid photovoltaic-thermal collector, electricity as well as thermal energy can be produced at the same time. These collectors can produce also cooling energy at nighttime by long-wave radiation exchange with the night sky and convection losses to the ambient air. Such a renewable trigeneration system offers new fields of applications. However, the technical, ecological and economical aspects of such systems are still largely unexplored.In this work, the potential of a PVT system to heat and cool office buildings in three different climate zones is investigated. In the investigated system, PVT collectors act as a heat source and heat sink for a reversible heat pump. Due to the reduced electricity consumption (from the grid) for heat rejection, the overall efficiency and economics improve compared to a conventional solar cooling system using a reversible air-to-water heat pump as heat and cold source.A parametric simulation study was carried out to evaluate the system design with different PVT surface areas and storage tank volumes to optimize the system for three different climate zones and for two different building standards. It is shown such a systems are technically feasible today. With a maximum utilization of PV electricity for heating, ventilation, air conditioning and other electricity demand such as lighting and plug loads, high solar fractions and primary energy savings can be achieved.Annual costs for such a system are comparable to conventional solar thermal and solar electrical cooling systems. Nevertheless, the economic feasibility strongly depends on country specific energy prices and energy policy. However, even in countries without compensation schemes for energy produced by renewables, this system can still be economically viable today. It could be shown, that a specific system dimensioning can be found at each of the investigated locations worldwide for a valuable economic and ecological operation of an office building with PVT technologies in different system designs.

DER adopter analysis using spatial autocorrelation and information gain ratio under different census‐data aggregation levels

Residential consumers have been adopting distributed energy resources (DER) like photovoltaics (PV), electric vehicles (EV) as well as electric heating, ventilation and air conditioning devices (HVAC) in recent years – thus substantially reshaping power systems. This study is dedicated to the analysis of such adopters in continental Portugal, using both spatial analysis tools and census data with information theoretic criteria. Results suggest that the current uptake of EV, PV, and HVAC is characterised by spatially auto-correlated adoption patterns. The analysis of census variables, on the other hand, reveals that Portuguese EV, PV, and HVAC adopters exhibit a few surprising, unrecorded characteristics compared with previous studies. Comparing different dataset resolutions, EV and HVAC adopters are found to be most similar across all three aggregation levels considered. Results further show that fewer adopter groups tend to own both EV-HVAC and PV-HVAC, reducing per se synergy potentials that may arise behind the metre. One of the main outcomes from this work is that studies describing energy technology adopters using census variables might receive very unstable results across different data aggregation levels. This may lead to adverse effects on studies' conclusiveness and energy policy design choices.

An investigation of the cooling performance of air-conditioning systems in seven Chinese hub airport terminals

Airport terminals are key infrastructures with rapid development currently, where the air-conditioning (AC) systems aim to guarantee the normal operation. This research investigated the AC systems in seven Chinese hub airport terminals by a large-scale on-site measurement. The average annual electricity consumption was 177 kWh/(m2 · year), in which 30–60% was consumed by AC systems. The terminal device of AC systems is one of the key components restricting the cooling performance. The commonly used terminal devices (i.e. air handling units) accounted for 40–74% of the AC electricity consumption. As an alternative, the AC system combining radiant floor and displacement ventilation could save 34% of the AC electricity consumption in one investigated airport terminal. Furthermore, the designed cooling capacities were 132–176 W/m2, while the measured values were only 43–90 W/m2. Thus, the AC systems, especially the terminal devices, should have the ability to adjust cooling capacity over a wide range to cope with this prevailing situation of low load rates. This study is beneficial for the design and operation of AC systems in airport terminals.

Improving the energy efficiency of room air conditioners in China: Costs and benefits

China is the world’s largest consumer of room air conditioners, and it contributes about a quarter of global space cooling CO2 emissions. We model the costs and benefits of recently proposed new room air conditioner minimum energy performance standards (MEPS) in China. Our results suggest that newly proposed MEPS brings accumulative CO2 emissions reductions of 12.8% between 2019 and 2050, and accumulative bill saving of 2620 billion RMB to China's consumers. The benefits of the proposed MEPS decrease with longer MEPS revision intervals and increase with shorter intervals—indicating that the intervals should be balanced to maximize benefits while accommodating constraints due to air conditioner manufacturer design cycles. We also model potential nationwide benefits from higher MEPS. Across two increasingly aggressive MEPS scenarios, China’s room air conditioner electricity consumption and CO2 emissions in 2050 are both reduced by 15–53% compared to the proposed MEPS. The highest-efficiency scenario (reaching MEPS of annual performance factor 5.4 in 2025) provides the largest long-term national benefits. These results could inform development of a Chinese regulatory regime that effectively updates room air conditioner MEPS. Because China is the world’s largest manufacturer of room air conditioners, the economic, energy, and emissions benefits resulting from higher Chinese MEPS could also have a global reach.

Novel Low-E filter for architectural glass pane

A good Low-Emissivity (Low-E) filter coated on glass reduces the amount of heat coming from solar light into the building, thus the expenses in electricity for air conditioning are reduced. Standard Low-E filters contain a Silver layer between two dielectric thin films due to its high reflectance of infrared wavelengths; however, one of the major silver drawbacks are its chemical and mechanical weakness which reduces the filter mean lifetime. In this paper, we investigate alternative materials to be a substitution of Ag, and they were compared with commercial filters. It was found that an aluminum-based filter has a good cost-benefit performance with peak transmittance better than 80% in the visible, while having less than 20% transmittance for wavelengths longer than 1500 nm. A simulation of the filters construction was made providing a tolerance of each layer thickness, so the filter keeps its optical performance

New Concentration Correlations of NaOH Aqueous Solutions for a Thermodynamic Process

Some processes such as air conditioning absorption systems have been developed as a feasible and economical alternative to help reduce the consumption of fossil fuels and prevent the impact of gas emission produced by electrical air conditioning. However, a main disadvantage of these systems is the absorbent’s crystallization phenomenon in the working mixture, which occurs when the absorbent concentration is higher than the saturation point. Among the aqueous working mixtures, NaOH solution shows several advantages for absorption system applications. The aim of this paper is to propose new mathematical correlations to predict or estimate the NaOH concentrations and refractive index in aqueous solutions (H2O–NaOH) for an air conditioning absorption system application. The experimental measurements of NaOH concentration and refractive index were made in situ from aqueous solutions with concentrations from 20 to 50% (weight/weight %, with increases of 5%) and temperatures between 10 and 60 °C (with increments of 1 °C). Two correlations for predicting the concentration of NaOH and refractive index based on cubic regression models with R2 of 0.99704 and 0.99918, respectively, are presented for the first time. The normalized error for NaOH estimation using experimental data lies between −0.026 and 0.040, and for refractive index, the estimation lies between −0.002 and 0.001. Both correlations present a good fit to predict the NaOH concentration between 25 and 45% of concentration ratio.

Multi‐objective optimisation operation of thermostatically controllable appliances for voltage management in low‐voltage distribution networks

The development of residential demand response (RDR) programs opens up another perspective for mitigating the problems of voltage magnitude and unbalance limit violation (VMULV) in the low-voltage distribution network (LVDN). Under this background, this study introduces thermostatically controllable appliances (TCAs) including electric water heater (EWH) and air conditioner (AC) to tackle the VMULV problems in LVDN based on the incentive RDR. Firstly, the response characteristics of TCA in LVDN voltage management are analysed. Then, a voltage management model incorporating EWHs and ACs in residents is established as a multi-objective optimisation model that jointly minimises the RDR cost, network loss, and customer dissatisfaction. In this model, the discomfort index associated with hot water and indoor temperature is employed to reflect users' discomfort. The proposed modelling method is examined on a 6-resident network and a 28-resident network in Sweden with considerable unbalanced and distributed generations. Moreover, the impacts on the optimisation result from different objective functions, photovoltaic (PV) penetration levels, and the tolerable temperature ranges set by users are also investigated. The results indicate that the proposed method effectively alleviates voltage amplitude and imbalance limit violation, and improves the capability of LVDN to integrate PV.

Joint optimal dispatch of electric vehicles and air conditioning loads in office buildings based on demand response

Centralized use of air conditioning loads and the disordered charging and discharging of large-scale electric vehicles in cities have become the important reason for peak-valley difference increase of grid load in summer, deepening the contradiction between supply and demand during the peak period. Therefore, it is of great significance to improve power grid load characteristic and realize stable and economic operation of power grid by excavating peak shaving potential of large-scale air conditioning loads and electric vehicles. Taking into account the dispatching cost of power grid companies and the benefits of power users, a joint optimal dispatching model of electric vehicle and air-conditioning load is proposed. The power grid provided a low price compensation for loads and a high price compensation for EVs due to its battery loses. The objective function is optimized with the minimum load difference rate of office buildings and the maximum total revenue of users. Analysis of calculation example shows that air conditioning load and electric vehicle have complementary characteristics in energy use, and the joint optimal dispatching has certain effect on office building "peak load reduction", eliminating "secondary peak load" and improving electricity user income.

Residential loads flexibility potential for demand response using energy consumption patterns and user segments

Demand response (DR) is considered an effective approach in mitigating the ever-growing concerns for supplying the electricity peak demand. Recent attempts have shown that the contribution from the aggregate impact of flexible individual residential loads can add flexibility to the power grid as ancillary services. However, current DR schemes do not systematically distinguish the varying potential of user contribution due to the highly-varied usage behaviors. Thus, this paper proposes a data-driven approach for quantifying the potential of individual flexible load users for participation in DR. We introduced a metric to capture the predictability of usage in a future DR event using the historical consumption data for different load types. The metric helps to sort the users with flexible loads in a community according to their potential for load shifting scenarios. We then evaluated the applicability of the metric in the DR context to assess the extent of energy reduction for different segments of users. In our analysis, we included electric vehicle, wet appliances (dryer, washing machine, dishwasher), and air conditioning. The analysis of real-world data shows that the approach is effective in identifying suitable user segments with higher predictive potential for demand reduction. We also presented a cross-appliance comparison for assessing the flexibility potential of different user segments. As a case study based on Pecan Street Project, the findings suggest that potentially ~160 MWh reduction might be achieved in Austin, TX through only 20% participation of the selected flexible loads for the residential sector during a 2-h event.

Research of University Building’s Electrical Energy Consumption Management Based on IoT & AI

Energy is an important factor in socio-economic development. The level of energy reserves is closely related to the national development, and has a great impact on the national economic development. However, many buildings in university/college, the management of electrical equipment, e.g., lighting and air conditioning is still under the control of students in manual way. According to the published data combined with the often seen phenomenon, the wastage of electrical energy in university/college is serious; and it has become a hot issue. This paper provides a solution to the above challenges in an automatic way through a combined application of technologies like Internet of things, AI, sensors, intelligent control devices and wireless communication technologies. It organized in four sections; the second is a comprehensive literature review after a brief introduction; the third section provides a case of Building Electrical Energy Consumption (BEEC) management and then presents a recommended solution; the future development trend and future work is given in the final part