Fault detection model for a variable speed heat pump

The impact of the COVID pandemic has resulted in many people cultivating a remote working culture and increasing building energy use. A reduction in the energy use of heating, ventilation, and air-conditioning (HVAC) systems is necessary for decreasing the energy use in buildings. The refrigerant charge of a heat pump greatly affects its energy use. However, refrigerant leakage causes a significant increase in the energy use of HVAC systems. The development of refrigerant charge fault detection models is, therefore, important to prevent unwarranted energy consumption and CO2 emissions in heat pumps. This paper examines refrigerant charge faults and their effect on a variable speed heat pump and the most accurate method between a multiple linear regression and multilayer perceptron model to use in detecting the refrigerant charge fault using the discharge temperature of the compressor, outdoor entering water temperature and compressor speed as inputs, and refrigerant charge as the output. The COP of the heat pump decreased when it was not operating at the optimum refrigerant charge, while an increase in compressor speed compensated for the degradation in the capacity during refrigerant leakage. Furthermore, the multilayer perception was found to have a higher prediction accuracy of the refrigerant charge fault with a mean square error of ± 3.7%, while the multiple linear regression model had a mean square error of ± 4.5%. The study also found that the multilayer perception model requires 7 neurons in the hidden layer to make viable predictions on any subsequent test sets fed into it under similar experimental conditions and parameters of the heat pump used in this study.

Tracking the Flu Virus in a Room Mechanical Ventilation Using CFD Tools and Effective Disinfection of an HVAC System

Recent concerns raised by the World Health Organization over the Coronavirus raised a worldwide reaction. Governments are racing to contain and stop the Coronavirus from reaching an epidemic/pandemic status. This research presents a way in tracking such a virus or any contagious germ capable of transferring through air specifically where such a transfer can be assisted by a mechanical room ventilation system. Tracking the spread of such a virus is a complicated process, as they can exist in a variety of forms, shapes, sizes, and can change with time. However, a beginning has to be made at some point. Assumptions had to be made based on published scientific data, and standards. The tracking of airborne viruses was carried out on the following assumption (for illustrative purposes);one person with one sneeze in a period of 600 s. The presence of viruses was tracked with curves plotted indicating how long it could take to remove the sneezed viruses from the mechanically ventilated room space. Results gave an indication of what time span is required to remove airborne viruses. Thus, we propose the following: (a) utilizing CFD software as a possible tool in optimizing a mechanical ventilation system in removing contagious viruses. This will track the dispersion of viruses and their removal. The numerical solution revealed that with one typical adult human sneeze, it can take approximately 640 s to reduce an average sneeze of 20,000 droplets to a fifth;(b) upscaling the status of human comfort to a “must have” with regards to the 50% relative humidity, and the use of Ultraviolet germicidal irradiation (UVGI) air disinfection in an epidemic/pandemic condition. A recommendation can be presented to the local authorities of jurisdiction in enforcing the above proposals partially/fully as seen fit as “prevention is better than cure”. This will preclude the spread of highly infectious viruses in mechanically ventilated buildings.

Airborne Disease Transmission Risk and Energy Impact of HVAC Mitigation Strategies

Significant emphasis has been placed on enhancing building HVAC systems to be more energy-efficient in recent decades. Often, these measures include reducing ventilation rates and overall airflows to achieve corresponding energy reduction. However, the COVID-19 pandemic caused an examination of how HVAC systems may help reduce the risk of airborne transmission of respiratory diseases via infectious aerosols. This new goal of infection risk mitigation often leads to the opposite recommendation-that outdoor air ventilation be increased,1 to the detriment of energy efficiency.2,3

COVID-19 Cross Contamination through Energy Recovery Ventilation Devices

Airborne diseases are a current concern. Infections can spread through the air even when a disease may not be characterized as "airborne" in medical terms. Some installed HVAC systems can spread infectious agents to those who are not currently infected. Cross contamination through leakage in energy recovery ventilation (ERV) devices can provide a pathway for infection. Energy recovery devices are currently required in many new buildings codes and standards. They are often installed in retrofit projects in older buildings in order to save energy. The risk from cross-contamination can be estimated using the Wells-Riley infection model. Energy recovery ventilation device applications can be designed, specified, and installed to effectively eliminate the risk of cross contamination in new systems using current technology so this is an avoidable risk.. A framework for evaluating currently installed ERV systems is providedfor facilities managers and HVAC systems operators to identify and minimize cross contamination infection risk.

Advanced Particle Removal Technology as an Efficient Tool for Addressing Emerging Global Air Quality and Safety Challenges

Indoor air quality is increasingly recognized as a serious health hazard in many international environments. During the recent pandemic, this concern was amplified as Covid-19-related mortality closely correlated with poor air quality. Even a comparatively small decline in the Air Quality Index (AQI) can be linked to a sharp mortality increase. Worsening air quality levels are compounded by distinct air-quality issues in different geographical areas. In the face of this serious and wide-ranging threat, the common solution-introducing a high MERV-rated filter-comes up short, as these filters create back pressure that often exceeds the capacity of the HVAC systems in which they are installed. High-backpressure filters also use more energy and require frequent filter changes, making them more expensive to maintain and bad for the environment. This paper describes a new form of electrostatic filtration that is ideal for international markets since it has a uniform performance, low back pressure, is energy efficient, and can be tuned to perform at a range of filtration levels depending on demand. Developed at the University of Washington, the technology features porous electrodes that collect and hold, a large capacity of particles regardless of their size and physical properties. This paper will describe the technology, prototype testing, including a 6-month pilot installation, and will detail how the technology can be used to achieve on-demand MERV 15 filtration levels in systems that require continuous low back pressure and reduced energy consumption.

Hygienic Design of HVAC Systems for Hospitals

Hygienic design of the Air Handling Unit (AHU), the custom-designed industrial HVAC system used in hospitals, laboratories, and similar sterile areas to supply clean, filtered, and conditioned air, has become more prevalent during the covid-19 pandemic. Improper maintenance of the air handling system can carry germs or viruses at any stage. This study concentrates explicitly on Air Handling Units used in hospitals, which should maintain higher quality standards than conventional air handling systems to reduce all kinds of dirt, debris, mold, and bacteria from the system. Throughout the paper, the critical parameters and control points of the air handling units for hospitals are analyzed from a hygienic viewpoint, and the existing hygienic design standards are explained through an implemented case study.

Editorial Special Section on COVID-19 Impact on Electrical Grid Operation: Analysis and Mitigation

COVID-19-related shutdowns have significantly impacted the electrical grid operation worldwide, as governments put strict measures in place to manage the global pandemic. The global electrical demand plummeted around the planet in March, April, and May 2020, with countries such as Spain and Italy experiencing more than 20% decrease in their usual electric consumption. On the other hand, countries like Canada experienced unusually high summer peaks due to the increase in demand for the residential HVAC systems. Electricity network operators are facing unprecedented challenges in scheduling energy resources;for example, energy forecasting systems struggle to provide an accurate demand prediction given massive changes in patterns of electricity consumption induced by COVID-19 restrictions.

Evaluation of Comfort Models Considering the Peculiarities of Hospitalization: Bedding, Clothing and Reduced Activity of Patients

The study of thermo-hygrometric comfort in hospitals involves several factors: the presence of different subjects: patients, operators, visitors;different conditions of hospitalization: patients bedridden or out of bed;psychological aspects and therapeutic treatments. In this paper, the analysis focuses on patients in ordinary hospitalization rooms of a hospital located in southern Italy. Different room orientations, several characteristics, and specific factors concerning hospitalized patients’ conditions that significantly influence the comfort indices have been considered. In total, 41 scenarios have been defined and analyzed by means of two comfort models: static and adaptive. The study aims to investigate the application of these models to the complex environment of hospitals, finding strengths and weaknesses, which also results in a re-definition of the HVAC system operation. Results show that patient position (in bed or out), clothing type, and level of coverage in the bed can make the same microclimatic condition more suitable for one scenario over another. Furthermore, room exposure has an effect on the comfort of the indoor temperature. The seasonal analyses highlight that during summer, for all scenarios considering bedridden patients, more than 50% of the PMV calculated values are out of the comfort zone. In winter, the indoor conditions are good for bedridden patients with a cover level of 67% during the nighttime (almost 100% PMV values in comfort zone), while during the daytime, they are more suitable for a 48% coverage level if the patient is in bed or if they are walking (lower than 10% dissatisfied).

Mobile Off-Grid Energy Generation Unit for Temporary Energy Supply

Temporary structures are being extensively used by emergency services (rescue, disaster relief, military response units), and other end-users requiring temporary mobile off-grid energy solutions for different purposes (event organization, vacation homes, summer camps, etc.). Yet energy systems for these purposes largely remain fossil-based (such as diesel generators). Although such energy systems are inexpensive, they are carbon intensive and inefficient. This study presents a methodology of simulating temporary shelter with access to an energy supply system through a mobile energy unit with renewable (PV) power supply systems to ensure on-site electricity production, as well as heating/cooling and ventilation. Digital modeling simulations have been performed for a simulated temporary shelter in different climate conditions incorporating different combinations of electricity generation systems with a fossil fuel-based solution and a PV system, using TRNSYS software. Study results show that the operation of a mobile energy generation unit can operate HVAC systems and generate electricity for temporary shelter occupants in off-grid solutions. The modeling results show that the use of a mobile energy generation unit can significantly reduce diesel consumption in temporary shelters from 54% annually (in Riga, Latvia) to 96 % annually (in Jerusalem, Israel). Furthermore, the output of PV-generated electricity is higher (in most cases) than the consumed electricity amount.