Conventional Air Conditioning Research Articles

Experimental Findings and Analysis of a Split Unit Evaporative Cooler for Efficient and Eco-Friendly Cooling Applications

As the global energy demand surges, there is a pressing need to develop energy conservation methods to ensure future comfort requirements are met sustainably. Traditional air conditioners, employing vapor compression refrigeration systems, consume substantial power (around 1.5KW) and entail high costs. Alternatively, evaporative coolers offer a cost-effective and lower-power option for comfort maintenance. However, their drawback lies in the excessive humidity in the cooled air, leading to discomfort for individuals. To address this issue, our article focuses on designing and manufacturing a split cooling unit that efficiently cools the air without increasing its humidity. By recirculating the air through the split unit, we aim to maintain optimal room conditions for comfort. This becomes increasingly vital as inefficient building designs in India contribute to 20-25% of electricity wastage in government buildings, resulting in significant annual energy-related financial losses. Conventional heating, ventilation, and air conditioning (HVAC) systems further exacerbate the problem, consuming about 50% of building energy, mostly sourced from fossil fuels, rendering them environmentally unfriendly and unsustainable. Our split cooling unit seeks to provide an eco-friendly and sustainable solution to tackle this energy challenge.

Indoor Environmental Quality assessment of mixed-mode ventilation with ceiling fans in the tropics

Mixed-mode ventilation in buildings has a potential for significant energy savings. However, previous attempts in the tropics were unsuccessful due to the hot and humid weather. Indeed, there is little to no natural ventilation potential in tropical climates if conventional air conditioning systems are used. Additionally, existing studies typically do not consider the noise and air quality constraints while the performance of mixed-mode buildings is susceptible to outdoor conditions. Using elevated air movement has proven to be an effective strategy to offset the rise in the room temperature setpoint without sacrificing occupants’ thermal comfort as it helps dissipate body heat through the convective cooling effect. Hence, this study aims at investigating the total indoor environment quality (IEQ) performance of mixed-mode ventilation operations with various air speeds based on tropically acclimatized subjects. To this end, a testbed was designed and constructed in Singapore, consisting of a variable air volume (VAV) system, ceiling fans with continuous speed control, personal ventilation (PV) desks, and plenum acoustic windows. Five operating modes have been tested: fully air-conditioned (AC) mode using VAV alone, hybrid air conditioned (AC+PV) mode using VAV and PV desks, concurrent ventilation (CV) mode using PV desks with the windows partially opened, natural ventilation (NV) mode with the windows fully opened, and acoustic natural ventilation (Acoustic NV) mode with the windows partially opened. 57 subjects were invited to the experiment and asked to complete a comprehensive IEQ survey under 16 different indoor conditions, which are combinations of these operating modes and air speeds ranging from 0.10 to 1.15 m/s. Experiment results show that NV and CV in Singapore can achieve more than 90% thermal acceptability with adequate air movement. More importantly, the median standard effective temperature (SET*) for thermal neutrality is approximately 3°C higher when operating in NV as compared to AC+PV or CV modes, indicating adaptation even when the modes switches are within the same day.

Numerical Analysis of dew point Indirect Evaporative Cooler

An indirect evaporative cooler that uses a Maisotsenko (M) Cycle has the potential to be a green and sustainable solution for managing a building’s cooling demand since it can attain sub-wet bulb temperature without humidification. This study presents the design and simulation analysis of a crossflow indirect evaporative cooler using the COMSOL Multiphysics software for various ambient conditions. The cooler’s performance was evaluated by varying the inlet air temperatures. The analysis was conducted using numerical simulations, and the outcomes were compared with experimental data. The simulation results demonstrated that the cooler could achieve significant temperature reductions at a minor energy consumption as compared to traditional air conditioning systems. This study delivers that this system reduces the temperature of inlet air up to 22°C as well as cooling capacity and coefficient of performance values are 3.699 kW and 27.40. Overall, the results demonstrate the potential of crossflow indirect evaporative coolers as an energy-efficient alternative to conventional air conditioning systems.

Development of Sky-source Heat Pump System

In order to realize a decarbonized society, which is an urgent global issue, the introduction of renewable energy is being expanded. Currently, renewable energy is mainly used to create electricity, such as via photovoltaic cells and wind turbines, while the high introductory costs of other renewable energy sources, such as solar and geothermal, is an impediment to its popularization. We have developed a high-efficiency, low-cost “Sky-sourced Heat Pump SystemⓇ (SSHPⓇ)” that utilizes renewable heat, and is operating at a demonstration site in eastern Japan. Unlike conventional air conditioning systems, our SSHPⓇ system is a unique water heat-sourced heat pump system which connects various renewable energy heat sources, such as solar, air, and geothermal heat, with air conditioning units and hot water heat pumps via a heat source water loop. Based on measurements taken from March 19 to August 28, 2022, and system simulations, primary energy consumption and CO2 emissions were significantly reduced by about 22%, or 32% when compared to typical electric heat pumps. The results indicate that the introduction of SSHP is highly effective.

An Investigation to Reduce Electricity Bills using Inverter AC in Pakistan

The cost affiliated with energy consumption of a conventional air conditioner is so high, an average salaried person cannot afford it. 5.8 m x 4.5 m x 3.6 m room is used for the energy assessment, in which the Inverter/VRF and Conventional air conditioning systems are used separately to attain a set temperature of 25 OC for the weather in Hyderabad, Pakistan. Through the simulated results, May has the highest energy use, with 467 kWh for conventional air conditioning and 310 kWh for inverter air conditioning. When compared to conventional air conditioners, inverter or VRF air conditioners can save up to 50% on energy. In Pakistan, according to NEPRA pricing, inverter air conditioners can have a payback time of 5 to 11 months for various brands of air conditioners, and they can reduce an ordinary consumer's annual electricity cost by up to 48 percent.

Wireless, AI-enabled wearable thermal comfort sensor for energy-efficient, human-in-the-loop control of indoor temperature

The conventional heating, ventilation, and air conditioning (HVAC) systems are based on a set-point control approach that only considers the temperature of the environment without reflecting the thermophysiological status of the occupant. This approach not only fails to fully satisfy individual thermal preferences, but it also makes an HVAC operation energy-inefficient. One possible solution is to control the indoor thermal condition based on an accurate prediction of the occupant's thermal comfort to prevent any unnecessary energy consumption. Here, we present an artificial intelligence (AI) wearable sensor-based human-in-the-loop HVAC control system that is operated on a real-time basis reflecting the thermophysiological condition of the occupant to automatically improve their thermal comfort while reducing the energy consumption of the building. The wristband-type, AI-based, three-point wearable temperature sensor offers excellent thermal comfort prediction accuracy (93.9%), enabling a human-centric HVAC control operation. A proof-of-concept demonstration of closed human-in-the-loop HVAC control using the AI-enabled wearable sensor system confirms both the accuracy of the thermal comfort prediction and the energy-efficiency of this approach, demonstrating its potential as a new solution that improves the occupant's thermal comfort and provides building energy savings.

Workload and energy management of geo-distributed datacenters considering demand response programs

Datacenters usually consume huge energy and their workload can be adjusted dynamically, which makes them become good potential participants of demand response (DR) programs in the smart grid system. To overcome the drawbacks of centralization and enable fault-tolerance of a single datacenter, geographically distributed datacenters could be connected by a wide-area network to build up an integrated infrastructure, upon which multiple datacenter workloads could be balanced by taking advantage of space–time electricity price differences to reduce electricity costs. Particularly, when geo-distributed datacenters participate into DR programs, in order to obtain more economic benefits and to help achieve the load control objectives issued by the grid, it is necessary to consider a variety of external and internal conditions to optimize the workload and energy management strategy. Aiming at this problem, we propose an optimal power regulation scheduling method (OPRS) to simultaneously manage workload and energy consumption in geo-distributed datacenters, which comprehensively considers various factors including variation of electricity prices, operating costs, renewable energy constraints, and DR requirements. On the basis of the conventional computer room air conditioner system, additional devices are also incorporated into the architecture for datacenter cooling, including a solar-powered absorption cooling system and a chilled liquid storage system. Based on such framework, the OPRS method not only uses local renewable energy to reduce the energy consumption of the datacenter, but also can reduce the operating cost of the geo-distributed datacenters by leveraging the difference of electricity prices between time and space. Second, the method increases the frequency of uninterruptible power supply (UPS) usage and thus enhances the flexibility of datacenter power regulation. Furthermore, the OPRS method manages the workload by jointly considering task reassignment and delayed scheduling according to specific DR programs, thereby helping to maintain the stability of the regional power grid system. Experimental evaluation results show that, compared with other alternative strategies, the OPRS method can reduce the total operating cost by 19.52 %–66.96 %. Furthermore, the detailed analysis of the power regulation process illustrates that the OPRS method can also achieve better management of datacenter power consumption in the demand response stage.

System design and long-term field test for a novel multi-mode heating tower heat pump system in cold regions

Aiming at the shortcomings of the cooling and heating sources of conventional building air conditioning systems, a multi-mode regeneration HTHP system is proposed and the working principle and working mode in detail are described. The system is applied in the actual energy-saving retrofit project, and control strategies and evaluation calculation method are given. The cooling performance, heating performance, and moisture absorption characteristics of HTHP systems are calculated hourly, daily, and throughout the year. The results show that: the average comprehensive cooling efficiency is 4.34 when the average air temperature in summer is 30 °C and the average relative humidity is 67.1%, and the average comprehensive heating efficiency is 3.12 at the temperature of -1.52 °C and humidity of 77.3%. The annual comprehensive cooling and heating operation efficiency are 4.47 and 3.49. The average regeneration efficiency during the test is 4.34 kg/kWh, which is less affected by the external environment and operating conditions. During the operation in winter, the moisture between the solution and the air migrates in two directions: evaporation dominates at higher temperatures and lower humidity, and absorption is on the contrary. Comprehensive moisture absorption accounts for about 3.9% of the whole year.

Design & development of a prototype of the layman’s air-cooler

This paper deals with the design & development of a prototype of the layman’s air-cooler. In summer seasons, we require cold water and cooled air because of scorching temperature. Modern appliances fulfilling these requirements need high power and are costly. So, we propose modified simple air cooler, which is portable and is low maintenance machine. Air cooler is one of the major consumers of electrical energy in many parts of the world today. Air cooler causes energy shortage for example in China. The demand can be expected to increase because of changing working times increased comfort expectations and global warming. Air conditioners are pretty expensive themselves and adding to them their power bills makes it out of reach for most common man. So opting for an air cooler is probably one solution which not only is cheaper as an appliance, but also uses lower power than conventional air conditioners. The work presented here is the mini-project work of the second semester engineering students of electronics & communication engineering department of Dayananda Sagar College of Engg., Bangalore, Karnataka

Performance analysis of a novel dual-evaporation-temperature combined-effect absorption chiller for temperature and humidity independent control air-conditioning

Temperature and humidity independent control (THIC) air-conditioning (AC) systems are promising alternatives to conventional AC systems. A novel dual-evaporation-temperature combined-effect (DETCE) absorption chiller for THIC AC application is proposed. It can produce high-temperature (16–18 °C) and low-temperature (7 °C) chilled water with a thermal coefficient of performance (COP) above 1 by the deep utilization of heat source at around 100–120 °C. Theoretical models were established to investigate effects of generation temperature (Tgen), evaporation temperature and high-temperature cooling capacity ratio (HCR) on thermal performance of the novel chiller. The results show that the COP of the proposed chiller (COPch,prop) is largely affected by Tgen and HCR. The COPch,prop is 24.1 %-50.4 % larger than that of the conventional single-effect absorption chiller (SEABC) under typical HCRs (0.5–0.7). Performance comparison of the DETCE absorption chiller-based THIC AC system and the conventional SEABC-based AC system was also conducted under different room sensible heat ratios (RSHR), fresh air ratios (FR) and ambient conditions. It is found that the proposed system has a greater energy-saving potential when applied in an air-conditioned space with a large RSHR and FR. Under typical RSHRs (0.6–0.8), both the thermal energy saving rate (ESR) and the heating fluid saving rate of the novel system are over 20 %. Besides, the proposed system can achieve an average ESR of around 30 % under a wide range of ambient conditions. This study provides a novel solution for the deep utilization of solar energy or waste heat at around 100–120 °C to achieve efficient and environmentally friendly THIC AC.

Thermal performance of a directional heat radiation device utilizing the Monte Carlo ray tracing method

Conventional air conditioning systems heat and cool an entire space for the total volume but are deficient in terms of energy efficiency. Partial and personalized devices rarely take into account moving occupants and are deficient in terms of flexibility. To address these problems, a directional heat radiation (DHR) device was introduced. The effectiveness of the DHR device under heating conditions was verified by experiments and the thermal performance of the DHR device under three different arrangements was analyzed. Based on energy balance, the radiation distribution factor calculation model and the heat transfer model of the DHR device were established by combining the Monte Carlo ray tracing method and the thermal network method. The results showed that the thermal performance of the DHR device arranged level downward was best and twice that of the level upward arrangement. The mathematical model of the heat transfer process was verified by experimental data, and the relative error was within 2 %. The simulation results showed that the radiation temperature at different positions θdprt in the center of the room increased with increasing tube diameter and reflecting cover opening width and decreased with increasing tube spacing. Under simulated heating conditions, the optimal structure of the DHR device has a tube diameter of 16 mm, reflecting cover opening width of 60 mm, and tube spacing of 80 mm. The heat flux per unit floor area of the DHR device was approximately 56 W/m2, which reduced the heating capacity by 20 % compared to that without the reflector cover, while improving the local thermal environment of the space and increasing energy efficiency.

Performance investigation of the solar direct-driven wood regenerator in liquid desiccant air-conditioning systems

Liquid desiccant air-conditioning (LDAC) systems are one of the most promising alternatives to conventional air conditioning systems due to the high energy efficiency. The most energy-consuming part of LDAS system is desiccant regeneration, while traditional regeneration methods often fail to balance the energy grade and energy efficiency. Inspired by solar heat localization for seawater desalination, the regeneration performance of this novel method has been investigated. Here, we fabricated a wood-based regenerator by drilling holes and spaying Chinese ink, which features high sunlight absorption and strong water transportation ability. Owing to the high hydraulic conductivity of drilled holes and low thermal conductivity of wood substrate, liquid desiccant can be regenerated efficiently with a low-temperature rise. Even for 40 wt% CaCl2 solution at 30 °C, the regeneration rate and efficiency can reach 0.64 kg·m−2·h−1 and 43.2 %. Comparisons between solar interfacial regeneration method and other traditional regeneration methods were also conducted. Results show that the solar interfacial method can significantly improve the regeneration rate at the same temperature. Given the low manufacturing cost and operating cost, high regeneration rate and efficiency, superior salt-rejecting property, and low-temperature rise, the wood regenerators based on solar interfacial regeneration show great potential in LDAC systems.

Experimental investigation of a hybrid configuration of solar thermal collectors and desiccant indirect evaporative cooling system

This paper presents the integrated performance of a solar-assisted desiccant dehumidifier along with Maisotsenko cycle (M-cycle) counter flow heat and mass exchanger. This system handles latent load and sensible load separately. The hybrid configuration of solar thermal collectors was analyzed for efficiency of solar collectors and solar fraction. High consumption of fossil fuels, which are already present in a limited amount, is also associated with environmental problems and climate change issues, as these increase the chances of global warming. These issues demand of us to shift towards renewable energy resources. Increase in world energy use results in a number of environmental problems, such as climate change, in addition to global warming and ozone depletion. In building services, HVAC systems are major concerns. To overcome the requirement, conventional air conditioning and vapor compression systems are mainly used for air conditioning, although these also have some environmental problems. Solar thermal applications in combination with other renewable-energy-dependent cooling practices have generated a huge interest towards sustainable solutions, keeping in view several techno-economical, environmental, and climatic advantages. The experimental investigation reveals that the maximum outlet temperature and efficiency of solar thermal collectors was 87°C and 56% respectively. The maximum cooling capacity of the system is evaluated at 4.6 kW.

INFLUENCE OF HEAT ACCUMULATION OF THE OBJECT ON THE OPERATION OF THE COOLED CEILINGS COOLING SYSTEM

The application of cooling systems is a relatively efficient way to ensure the required thermal comfort conditions. One option is the application of cooled ceilings, where the heat load is removed using a ceiling structure with integrated cooling panels. These systems allow for a suitable way remove the heat load, but at the same time, compared to conventional air conditioning systems, they are characterized by a certain time dependence. The presented article describes experimental measurements carried out on days with high exterior heat exposure. Measurements evaluating the effect of the phase shift of temperature oscillations on the operation of the system were carried out using two cooling operating modes. According to results, it can be concluded that cooling systems based on cooling ceilings can be used effectively even with high external heat gains.

Performance evaluation of a heat pump-driven liquid desiccant dehumidification system integrated with fresh air supply

With the higher demand for indoor thermal comfort and the accurate control of air temperature and humidity, energy consumption in air conditioning systems is increasing over these years, especially for buildings with high moisture load such as natatoriums. However, freezing dehumidification is still widely adopted in eliminating moisture load, which requires lower evaporating temperature and causes excessive energy consumption. To improve energy utilization and efficiency, a heat pump-driven liquid desiccant dehumidification system is proposed in this research, the surface condenser and liquid desiccant dehumidifier are adopted to realize two-stage air dehumidification. In the summer condition, the solution in regenerator is heated by the condenser of heat pump and the residual heat is to heat the regenerated air, and the cooling capacity of heat pump is applied to the surface condenser and terminal heat exchanger, simultaneously the solution in dehumidifier is cooled by cooling tower. Under the meteorological conditions in Nanjing, the coefficient of performance could reach 6.148 in this proposed system, and compared to conventional air source heat pump dehumidification air conditioning system, the rising ratio of energy efficiency is between 11.4% and 80.7%. Eight cities in China are selected to analyze the energy-saving effects, and energy consumption could be reduced by 31.9%-63.2%, the result demonstrates the superior energy-saving potential and application prospect of the heat pump-driven liquid desiccant dehumidification system.

Simulation of an energy-efficient cool roof with cellulose-based daytime radiative cooling material

Conventional air conditioners are considered the most energy-intensive components in residential and tertiary buildings. Besides high energy consumption, they are also harmful to the environment due to the emissions of hydrofluorocarbons into the atmosphere. Night sky cooling or radiative cooling is a naturally occurring phenomenon that takes advantage of the atmospheric transparency window in the wavelength range of 8–13 µm to effectively dissipate heat from a surface into outer space. However, this can only occur at night, which is incompatible with the cooling demand that peaks during the day. This paper aims to develop a cool roof that relies on a daytime radiative cooling (DRC) material with low solar absorptivity in the wavelength range of 0.3–2.5 µm and high emissivity in the atmospheric window. The used DRC material is derived from cellulose acetate-based films, which are recyclable, sustainable, and bioclimatic. This material is used to improve the energy efficiency of an existing building by reducing the temperature of the roof to improve the thermal comfort of the building in the framework of Moroccan climatic zones. Software simulations are used to assess the needs and the demand of the building and simulate the impact of the smart device on the building's thermal performance and evaluate the thermophysical and optical properties of the DRC material. This latter material will be compared with another DRC material based on titanium dioxide and silicon dioxide mixture coating in terms of cooling performances. Results have shown a drastic sub ambient cooling of more than 3 °C and a great reduction in the indoor temperature of the building and a reduction in the total electricity consumption of up to 60.38 %.

Environmental impact assessment to support the development of new Photonic Meta-Concrete

The cooling demand in buildings has increased over the past decades due to global warming, the heat-island-effect in cities and the increased airtightness and thermal resistance of the building envelope. This led to an increased use of conventional air-conditioners, which now account for 7% of global greenhouse gas emissions and 10% of the total energy consumption. In this context, the MIRACLE project aims at developing a new Photonic Meta-Concrete (PMC) with remarkable photonic properties to reduce the CO2 footprint of buildings, mitigate the heat-island-effect and global warming. Besides the positive effect that this innovative material can have on the environment during the use phase of buildings, also the environmental impact of the production needs to be minimized. Environmental impact assessment (EIA) is used along the development process of this innovative material to guarantee a low material environmental impact. This paper discusses how EIA is used along the development process and presents the preliminary results in the early stages of the development of the PMC. To investigate the impact of this new material, a cradle-to-gate analysis of the resources, energy and machinery needed to create the concrete mixture is performed. The broad set of environmental indicators of the EC PEF (Product Environmental Footprint) method, such as climate change, acidification, eutrophication, particulate matter, ecotoxicity, water depletion and human toxicity are being considered. Considering such a large set of indications ensures that burden shifting is avoided. The environmental impact of the PMC is moreover compared to the impact of conventional concrete to understand how both perform.

Development and potential environmental impact of Photonic Meta-Concrete

In the overall aim to reduce the heat-island-effect in cities and the related use of conventional air-conditioners, which now account for 7% of global greenhouse gas emissions and 10% of the total energy consumption, a Photonic Meta-Concrete (PMC) is currently being developed. This “MIRACLE” concrete is designed to contain remarkable photonic properties to make daytime radiative cooling possible. With these characteristics, the PMC can be used to fight global warming, reduce the CO2 footprint and mitigate the heat-island-effect. This paper describes the principal working of the new PMC and presents the first results of the development. In the first stage, the most appropriate composition of the concrete mixture is searched for. This is done by trying to develop a mixture with the desired photonic properties, a high emissivity in the Atmospheric Window (AW) and a high reflectivity to minimize solar gains. A range of composites are tested and compared within this step. Secondly, an environmental impact assessment (EIA) study is performed along the development of the PMC in order to support decision taking. The resources and energy needed to create the concrete mixture are analysed from cradle-to-gate and a comparison with conventional concrete is made to investigate the impact of this new material. This EIA study is performed according to the EC PEF (Product Environmental Footprint) method, a broad set of indicators are assessed, including climate change. Considering such a large set of indicators ensures that burden shifting is avoided.

Optimal energy management system for residential buildings considering the time of use price with swarm intelligence algorithms

Revolutions in human activities and lifestyles result in a transition from conventional to intelligent residential building infrastructure. Conventional heating, ventilation, and air conditioning (HVAC), refrigerator and lighting system challenges are addressed without taking into account building heat gains, outdoor illuminance, and temperature. Based on these parameters, a mathematical model for cost estimation of residential building energy consumption, considering indoor heat gains, outdoor temperature, outdoor illuminance, and TOU price has been developed. A total of 46 swarm intelligence based optimization algorithms are used to optimize different building parameters. These swarm intelligence algorithms (SIA) are compared using the convergence curves, statistical and box-plot analysis and the Bald Eagle search (BES) algorithm is found to be the best algorithm among all 46 SIAs. The mean energy consumption costs of the best algorithm, BES, and the worst algorithm, fireworks algorithm (FA) are found to be Rs. 8.85 and Rs. 12.98, respectively. In addition, economic analysis has been conducted for the proposed study and it is compared with the existing models with building energy management systems (BEMS) and conventional model (without BEMS). It is observed that, based on this analysis, the cost savings achieved by the proposed study are nearer to 34% and 57% as compared to existing and conventional models.

Validated open-source Modelica model of direct evaporative cooler with minimal inputs

Direct evaporative coolers (DECs) are a low-energy cooling alternative to conventional air conditioning in hot-dry climates. The key component of DEC is the cooling pad, which evaporatively cools the air passing through it. While detailed numerical models of heat and mass transfer have been proposed for the cooling pad, these require many input parameters that are not readily accessible. Alternatively, simplified models lack accuracy and are confined to common types of cooling pad. To address these limitations, we developed and validated a physics-based model, that only needs the nominal data to compute the heat and mass transfer with considerable accuracy. The proposed model is implemented in Modelica, an equation-based object-oriented modeling language. For comparison, a basic lumped model from EnergyPlus based on the efficiency curve of the cooling pad is also implemented. The physics-based model exhibits <2% error from the experimental data and the lumped model exhibits a 12.3% error.