Rooftop Air Conditioners Research Articles

A Virtual Supply Airflow Rate Sensor Based on Original Equipment Manufacturer Data for Rooftop Air Conditioners

A Virtual Supply Airflow Rate Sensor Based on Original Equipment Manufacturer Data for Rooftop Air Conditioners

Hybridization of energy systems for air conditioning application in an educational building

This study reports the hybridization of energy systems for an air conditioning (AC) application in an educational building, using the Faculty of Engineering Lecture Theaters at Rivers State University, Port Harcourt, Nigeria as case study. It includes conceptual design of a hybrid energy system of thermoelectric and solar energy, analysis of cooling load to select suitable air conditioning system for the building using Carrier’s Hourly Analysis Program (HAP) software, analysis of the required energy to drive the air conditioning system, and techno-economic analysis of the system. The analysis carried out shows that a total of 4 packaged rooftop air conditioners each of 10.6kW (30,000 Btu/h) capacity would be required to handle the building’s cooling load of 38.28kW, and would require 344.5kWh of energy per day, out of which 249kWh/day would be generated from the thermoelectric generator (TEG) modules, and the remaining 95.5kWh/day would be generated from the photovoltaic (PV) modules. The 249kWh/day of energy required from the thermoelectric energy system would require a total of 1600 TEG modules of 26W each, and the 95.5kWh/day of energy required from the solar system would require a total of 65 PV modules of 330W each. The energy generated would be stored in a 679kWh capacity battery storage system which contains 72 batteries of 48V and 200Ah capacity each, which are wired into 3 parallel strings, which would supply the AC system. The techno-economic analysis carried out shows that the system designed can be implemented at a cost of ₦98,558,000, with a payback period of 9years, and would mitigate 72,050.5kg of CO2 emissions annually.

Performance of refrigerants employed in rooftop air-conditioners

Unlike earlier studies, this study examines six refrigerants with various properties using the same rooftop air conditioning system of a building to evaluate performance. Performance metrics such as cooling capacity, energy consumption, temperature, and pressure were calculated. Laboratory testing of a rooftop air conditioner with R410a was performed to validate the simulation program's predicted data. Six distinct refrigerants' carbon emissions in two different scenarios were calculated using the Life Cycle Climate Performance technique, which was evaluated for environmental studies. These experimental tests were carried out at temperatures of 20 °C, 25 °C, 30 °C, and 35 °C, respectively. Maximum discrepancies between simulated and experimental results for cooling capacity, energy consumption, and energy efficiency were calculated to be 2.8%. The study found the lowest value in the R1234yf carbon emission at 51.30 kg CO2e. The highest cooling capacity was 154760.34 W in R454b, and the lowest cooling capacity was 76949.94 W in R1234yf. The highest EER value was 3,018 in R454b, while the lowest released was 2.257 in R22. The SEER value was 4.101 for R32 and 2.298 for R1234yf. The simulations concluded that R410a, R454b, and R32 refrigerants have superior cooling capacities.

Model-based optimizations of packaged rooftop air conditioners using low global warming potential refrigerants

Based on laboratory investigations for R-22 and R-410A alternative low GWP refrigerants in two baseline rooftop air conditioners (RTU), the DOE/ORNL Heat Pump Design Model was used to model the two RTUs and the models were calibrated against the experimental data. We compared the compressor efficiencies and heat exchanger performances. An efficiency-based compressor mapping method was developed. Extensive model-based optimizations were conducted to provide a fair comparison between all the low GWP candidates by selecting optimal configurations. The results illustrate that all the R-22 low GWP refrigerants will lead to slightly lower COPs. ARM-20B appears to be the best R-22 replacement at normal conditions. At higher ambient temperatures, ARM-20A exhibits better performance. All R-410A low GWP candidates will result in similar or better efficiencies than R-410A. R-32 has the best COP while requiring the smallest compressor. R-452B uses the closest compressor displacement volume and achieves the same efficiency as R-410A.

Virtual sensors for rooftop unit air-side diagnostics

In this article, virtual sensors for air-side diagnostics are developed and validated for rooftop air conditioners. The virtual air-side sensors require indoor fan differential pressure and speed measurements. Experimental data from laboratory measurements are used to evaluate the accuracy of the virtual sensors. Methodologies for improving the accuracy of air-side temperature sensors often used for outdoor-air economizer diagnostics have also been developed and evaluated. Outdoor-air temperature correction correlations improve single-point temperature inaccuracy caused by exhaust-air recirculation. A model correcting a single-point mixed-air temperature measurement for inaccuracy caused by thermal stratification and non-uniform velocity distributions at the evaporator inlet has also been described and validated. Finally, methods for estimating outdoor ventilation air fraction are presented and compared to measurements.

Effect of urban neighborhoods on the performance of building cooling systems

This paper quantified the influence of the urban neighborhood on the degradation of Coefficient of Performance (COP) for the building cooling systems. Urban microclimate usually creates higher air temperatures in dense urban areas compared to surrounding rural and suburban regions. Computational Fluid Dynamics (CFD) combined with building energy simulations can predict local hourly temperatures in urban environments. This study uses open source software packages, including OpenFOAM and EnergyPlus, to calculate local air temperatures and heat fluxes on the building surfaces as well as resultant operational COP values. First, the simulated temperature calculations of local airflow temperatures are indirectly validated using on-site field measurements in an actual urban neighborhood. Further, the validated CFD simulations predicted local air temperatures in uniform neighborhoods of varying density. This study identified four types of COP equations to quantify performance of cooling systems as a function of outdoor air temperatures. The study findings indicate that for the present study's climate and flow conditions, rooftop air conditioners in urban areas can have a reduction in COP up to 17%, compared to COP in a corresponding rural area. Window air conditioners can have reductions in COP of over 16%, if located on the windward walls. However, this average COP degradation for the cooling systems installed on the leeward walls is not significant. Overall, the effect of neighborhoods on the performance of cooling systems is significant and quantifiable, and this quantification requires consideration of the common local design practices for the installation of building cooling systems.

High-Efficiency Rooftop Air Conditioners: Small Commercial ACs Could Add Up to Big Energy Savings

ABSTRACT This article describes a technology procurement conducted by the U.S. Department of Energy, the Pacific Northwest National Laboratory (PNNL), and the Defense Logistics Agency to increase the availability of energy-efficient, packaged unitary “rooftop” air conditioners. The procurement encourages air conditioner manufacturers to produce equipment that exceeds federal energy efficiency standards by at least 25 percent at a lower life-cycle cost. Program developers have also sought to aggregate market demand by organizing groups of large-volume buyers of air-conditioning equipment. A cost estimator tool developed by PNNL to help consumers determine the cost-effectiveness, based on local climate conditions, of purchasing energy-efficient air conditioners for their own facilities also is described.

Common Faults and Their Impacts for Rooftop Air Conditioners

This paper identifies important faults and their performance impacts for rooftop air conditioners. The frequencies of occurrence and the relative costs of service for different faults were estimated through analysis of service records. Several of the important and difficult to diagnose refrigeration cycle faults were simulated in the laboratory. Also, the impacts on several performance indices were quantified through transient testing for a range of conditions and fault levels. The transient test results indicated that fault detection and diagnostics could be performed using methods that incorporate steady-state assumptions and models. Furthermore, the fault testing led to a set of generic rules for the impacts of faults on measurements that could be used for fault diagnoses. The average impacts of the faults on cooling capacity and coefficient of performance (COP) were also evaluated. Based upon the results, all of the faults are significant at the levels introduced, and should be detected and diagnosed by an FDD system. The data set obtained during this work was very comprehensive, and was used to design and evaluate the performance of an FDD method (Breuker 1997a) that will be reported in a future paper.