Vapor Compression Air Conditioning System Research Articles

Thermodynamic performance assessment of a solar-driven desiccant evaporative air cooling system (SDEAC) for outdoor environments- a dynamic study

In this work, a novel dynamic model of a solar-driven desiccant evaporative air cooling system for outdoor environments is proposed, namely the SDEAC system. The effects of operating and designing parameters on the performance of the SDEAC system are analyzed. The results indicate that the sensible cooling capacity, the latent cooling capacity, and the COP decrease monotonically as the rotational speed of the desiccant wheel increases. When the ratio of dehumidification area to total area (r1) is 0.5, the performance of the SDEAC system is optimal under the condition of sufficient solar radiation. The ratio of the dehumidified air flowrate to the regenerated air flowrate has a small effect on the cooling capacity but has a large effect on the COP. The SDEAC system has a higher sensible cooling capacity and total cooling capacity compared to the EAC system. Moreover, although the COP of the SDEAC is lower than that of the EAC system, it is still maintained at a relatively high level. The SDEAC system with a supply air flowrate of 670 m3/h to cool the outdoor air saves about 1283∼1617 kWh of electricity and 788 kg–1139 kg of carbon emission reduction compared to a conventional vapor compression air conditioning system in different cities during the period of June to August.

Impact of Ambient Temperature and Humidity on the Performance of Vapour Compression Air Conditioning System - Experimental and Numerical Investigation

Due to global warming, population growth, and urbanisation, demands for space cooling in buildings have significantly increased. Mechanical vapour compression cooling technology is relatively mature, well-understood and most commonly used globally. However, they suffer from high energy consumption and adverse environmental impact due to the refrigerants used. As ambient temperature and humidity have significant effects on the performance of vapour compression systems, this paper experimentally and numerically investigates their impact on the performance of vapour compression air conditioning system in terms of power consumption and cooling capacity. It was concluded that at ambient humidity of 55%, as the ambient temperature increases from 22 °C to 40 °C, the compressor temperature has increased from 46 °C to 59 °C which increased its power consumption from 751.2 to 935.52 Watts, giving an increase of 10.24 Watts for every one degree of ambient temperature increase. Also, as ambient humidity in-creased from 32% to 88%, the power consumption increased from 739.2 Watts to 853.2 Watts, an increase of 114 Watts. A validated CFD (Computational Fluid Dynamics) model was developed and predicted a loss in the enthalpy change from 11.7kJ/kg.d.a to 3.6kJ/kg.d.a. due to ambient temperature increasing from 22 °C to 40 °C and a loss of enthalpy change from 12.857kJ/kg.d.a to 5.524kJ/kg.d.a. due to increasing the ambient air humidity from 32% to 88%. This work high-lighted the impacts of ambient conditions on the performance of vapour compression cooling system in terms of increased power consumption and loss of cooling capacity.

Mass transfer research on the regeneration process of an air-conditioning battery system

Developing a sustainable and low-carbon society calls for energy conservation of buildings. On this purpose, green air-conditioning systems driven by renewable energy have been encouraged as alternative to the present vapor-compression air-conditioning system. Absorption system is one promising representative, but relatively lower performance impedes its application. To improve, we propose an air-conditioning battery system (ACBS) that evolves from the traditional absorption system. Its COP attains four by incorporating a refrigeration cycle with a battery cycle, realizing energy storage when producing cooling effect. Driven by renewable energy, ACBS is a green air-conditioning system for being environmental friendly with refrigerant water and avoiding the combustion of fossil fuels that emits a large amount of CO2 bringing in environmental issues. The critical part of ACBS is the capacitive deionization (CDI) regeneration process, which concentrates absorbent by electrical adsorption. The mass transfer mechanism of regeneration is important for system optimization. Simulation investigation has been made in this paper to reveal the mechanism. A two-dimensional model has been established and validated to depict the dynamic response at different electric adsorption stages. Analysis has been conducted based on the models to expose the influence of some critical parameters. The results show that the enhancement of COP could exceed 50% with optimum design parameters.

Vapor compression air conditioning system with solar heat collector

THE RELEVANCE of the study lies in the fact that air conditioning systems in Iraq consume more than half of the electricity generation. During the summer, when temperatures rise, the demand for air conditioning increases, resulting in constant power outages. Consumers are starting to use local generation - diesel generators, which increase environmental pollution. THE PURPOSE. Consider the problems thermal energy from the sun is an ideal solution for reducing electricity consumption, increasing the performance of air conditioners, ensuring continuity of power supply and reducing pollution from diesel generators and power plants, as well as saving energy and reducing the consumption of fossil fuels. METHODS. When solving the problem, a comparison of options for standard and (hybrid using solar thermal energy) air conditioning systems was used. In a hybrid system, thermal energy enters the system from a solar collector built behind the compressor. Thermal parameters and level of electricity consumption were calculated. RESULTS. The article showed that a hybrid air conditioning system using solar thermal energy is more efficient than a traditional system, as it increases the cooling coefficient by (38.9 - 46.3%) and reduces electricity consumption by (56.89 - 66.66). %). CONCLUSION. The use of a hybrid air conditioning system in the climate of Baghdad city with a vapor compression air conditioning system reduced the electrical energy consumption of the compressor and increased the performance of the system, which will lead to increased reliability of power supply and eliminate the need to use local diesel generators.

Energy consumption and feasibility study of a hybrid desiccant dehumidification air conditioning system in Beirut

In this work, the transient performance of a hybrid desiccant vapor compression air conditioning system is numerically simulated for the ambient conditions of Beirut. The main feature of this hybrid system is that the regenerative heat needed by the desiccant wheel is partly supplied by the condenser dissipated heat while the rest is supplied by an auxiliary gas heater. The hybrid air conditioning system of the present study replaces a 23 kW vapor compression unit for a typical office in Beirut characterized by a high latent load. The vapor compression subsystem size in the hybrid air conditioning system is reduced to 15 kW at the peak load when the regeneration temperature was fixed at 75 °C. Also the sensible heat ratio of the combined hybrid system increased from 0.47 to 0.73. Based on hour by hour simulation studies for a wide range of recorded ambient conditions of Beirut city, this paper predicts the annual energy consumption of the hybrid system in comparison with the conventional vapor compression system for the entire cooling season. The annual running costs savings for the hybrid system is 418.39 USD for a gas cost price of 0.141 USD/kg. The pay back period of the hybrid system is less than 5 years when the initial cost of the hybrid air conditioning system priced an additional 1712.00 USD. Hence, for a 20-year life cycle, the life cycle savings of the hybrid air conditioning system are 4295.19 USD.

Simulation of vapour compression air conditioning system using Al2O3 based nanofluid refrigerant

The energy crisis, Greenhouse Gas (GHG) emissions, and Chlorofluorocarbon (CFC) emis-sions are major environmental issues at present. It is critical to achieve and reduce emissions and energy consumption through the use of environmentally friendly refrigerants. Utilizing an environmentally friendly refrigerant such as HFC-32 may offer a viable solution to the ozone depletion potential (ODP) and global warming issues. This study examines the effects of aluminium oxide (Al2O3) nanoparticles at volume concentrations of 0.06, 0.08, 0.1, 0.12, and 0.14% in pure refrigerants such as HFC-32 and R-410a used in air-conditioning systems based on the vapour compression refrigeration cycle. The thermophysical properties of pure and nanorefrigerants have been determined using REFPROP (NIST properties of fluid Refer-ence) and a theoretical formulation model using MATLAB software. The important outcomes of HFC-32 nanorefrigerant show the maximum performance with 0.14% alumina nano addi-tives which results in a 46.14% increase in the coefficient of performance (COP) and massive power savings upto 31.59%. Thermal conductivity exhibited an increase with an increment in nanoparticle concentration. Maximum thermal conductivity of 0.172 W/m-K is recorded in the case of HFC-32/Al2O3 nanorefrigerant with 0.14% volume concentration. The net re-frigeration effect of pure refrigerants (R410a and HFC-32) is 77% and 79% and on addition of nanorefrigerants to the pure the net refrigeration effect increases to 81.2% and 83.5% for R410a and HFC-32 respectively.

Study of Solar Photovoltaic Array for Air Conditioning System

The vapor compression refrigeration (VCR) and air conditioning systems are widely used for cooling, refrigeration, air conditioning, heating purposes and consumes more than 33% of the world energy. Solar energy is available abundantly as renewable energy source in summer when requirement of comfort is in peak demand. The electrical energy is replaced with solar energy by properly selecting solar panels, battery, inverter, charge controllers for storing fruits and vegetables in rural areas due to uncertain pattern of grid electricity. In the paper, solar power VCR system is designed and simulated with Simulink to estimate the performance in terms of irradiance and temperature. It is found that with rise in irradiance, current and power outcome increases. The solar system is CO2 free with substantial saving of 9700 whereas conventional VCR system produces 5292 kg of CO2 during life time of solar PV system.

An insight into environmental footprints of emerging air-conditioning systems towards sustainable cities

In this study, the environmental impacts of six conventional and modern air conditioning systems, including vapor-compression air conditioning (VAC), hybrid membrane-based air conditioning (HMBAC), desiccant enhanced evaporative air conditioning (DEVap), solar HMBAC, solar DEVap, and inverter VAC, are analyzed using a cradle-to-gate life cycle assessment (LCA) approach. The assessment is based on climate change, ozone depletion, terrestrial acidification, freshwater eutrophication, human toxicity, photochemical oxidant formation, ecotoxicity, water depletion, and fossil fuel depletion impacts. The LCA findings reveal that membrane-based systems (HMBAC and DEVap) are highly environmentally-friendly in comparison to the regular VAC systems (household split coolers), showing the capability of membranes in developing efficient air conditioning systems. In addition, solar-assisted systems reduce seven out of eleven environmental impacts, while they cause severe eutrophication, marine and freshwater ecotoxicity, and human toxicity consequences. Furthermore, it is unveiled that the inverter can reduce up to 38% of the environmental impacts of VAC systems which are the most common air conditioning system in buildings. Therefore, the manipulation of the inverter system in VACs can be considered as one of the short-term solutions in reducing the environmental footprints of air conditioning. Finally, the sensitivity analysis is applied to show the reliability of the outcomes.

Real life test of a novel super performance dew point cooling system in operational live data centre

This paper presents the development and application of a super performance dew point cooling technology for data centres. The novel super performance dew point cooler showed considerably improved energy saving and carbon reduction for data centre cooling. The innovations of this technology are built upon a series of technological breakthroughs including, a novel hybrid flat/corrugated heat and mass exchanging sheets, an innovative highly water absorptive and diffusive wet-material for the sheets which enable an intermittent water supply with well-tuned water pressure and flow rate, and the optimised fan configurations. Following a list of fundamental research including theoretical, numerical and lab experimental testing of a small scale prototype system, a specialist 100 kW rated data centre dew point cooling system was dedicated designed, constructed, installed and real life tested in an operational live data centre environment, i.e., Maritime Data Centre at Hull (UK) to investigate its dynamic performance, suitability and stability for application in operational data centre environment conditions.During the testing period, the system showed its reliability and capability to remove a tremendous amount of heat dissipated from the IT equipment and maintain an adequate space temperature in the operational live data centre. The dynamic data collection and analysis during the continuous testing and monitoring period showed the average COP of 29.7 with the maximum COP of 48.3. Compared to the existing traditional vapor compression air conditioning system in the data centre, the energy saving using the super performance dew point cooling system is around 90 %. The work presented in this paper include detailed innovation aspects of the technology and the system operation, as well as the established bridging knowledges, methodology and technical procedure for bringing this new technology into real life operation which involve in data centre survey, optimum design and modularization of the specialist cooling system for data centre application, proven system installation, operating method and cooling air management for data centre as well as the assurance of the continuous sufficient cooling supply to the data centre.

Assessing Energy Performance and Environmental Impact of Low GWP Vapor Compression Chilled Water Systems

The global concern regarding the environmental repercussions of refrigerants has escalated due to their adverse effects. These substances deplete the ozone layer and intensify the greenhouse effect. International agreements such as the Montreal and Kyoto Protocols and COP21 have imposed restrictions on refrigerants with high global warming potential (GWP) to address these issues. This study aims to explore the feasibility, energy efficiency, and environmental impact of utilizing the HFO (hydrofluoric-olefin) refrigerant R1234ze as a substitute for HFCs (hydrofluoric-carbon) (R134a, R407C, and R410A) and HCFCs (R22) in air-cooled vapor compression refrigeration and air conditioning systems. To determine their effectiveness, we evaluate the energy performance of various refrigerant operating cycles across a wide range of ambient and evaporating temperatures. Additionally, we conduct environmental impact analyses based on the total equivalent warming impact (TEWI) parameter calculated for commercially available chillers that utilize the fluids mentioned above. Our findings indicate that vapor compression chilled water systems employing R1234ze exhibit the highest performance coefficient and the lowest annual TEWI.

Performance assessment of integrated liquid desiccant dehumidification with vapor-compression system for energy-efficient air conditioning applications

The present study aims to integrate desiccant dehumidification systems and vapor-compression air conditioning (VC) systems for energy-efficient air conditioning applications. A numerical model is developed for a dehumidifier/regenerator module based on the governing mass, energy, and species balance equations. Subsequently, the desiccant system is integrated with the VC system to investigate the overall system performance. The novelty of the present work is in its exploration of the integration of desiccant systems. The share of dehumidifier load in overall system is studied, and performance of the integrated system is compared with that of a standalone VC system. Trade-off analysis is also performed in consideration of all performance parameters. The comparative results reveal that a significant amount of the total latent heat load is controlled by the dehumidifier. Specifically, it is observed that the integrated system can improve the COP by 40.8–74.8% relative to the standalone VC system under different operating conditions.

Experimental performance of a three-fluid desiccant contactor using a novel ionic liquid

• Novel Ionic Liquid that is not corrosive to aluminum is used as liquid desiccant. • New three-fluid fin-tube desiccant contactor fabricated using aluminum. • Experimental performance of the fin-tube contactor using IL solution is investigated. • The fin–tube contactor showed superior performance than the packed bed contactor. • Lower solution flow rates and pumping power is expected using the fin–tube contactor. The experimental performance of a new three-fluid fin–tube contactor using a novel ionic liquid desiccant solution is investigated and compared with those of an adiabatic packed bed contactor with LiCl solution for liquid desiccant air conditioning system applications. Owing to the compatibility of the ionic liquid solution with aluminum, a fin–tube contactor is manufactured to exploit internal cooling from a third fluid. The results indicate the superior dehumidification performance of the fin–tube contactor, which yielded an outlet air humidity ratio of 10.5 g w ·kg da -1 at a solution mass flux of 3.06 kg·m −2 ·s −1 , as compared to a similar humidity ratio at a solution mass flux of 4.98 kg·m −2 ·s −1 achieved by the packed bed contactor. In terms of cooling performance, the outlet air temperature of the fin–tube contactor is 21.9 °C, which is lower than that of the packed bed contactor even at its highest solution mass flux. This indicates that the cooling performance of the fin–tube contactor has minimal dependence on the solution mass flux in achieving cooling effect, owing to the cooling medium flowing inside the tubes. Relatively lower solution pumping power than that of the packed bed contactor can be expected from the fin–tube contactor, in addition to the ability to achieve comfortable and hygienic indoor air at a cooling medium temperature of 17 °C or higher, the ionic liquid desiccant and three-fluid fin–tube contactor pair for liquid desiccant air conditioning system is elevated a step higher as an alternative to vapor compression air conditioning system.

Comparative investigation of low-GWP binary and ternary blends as potential replacements of HFC refrigerants for air conditioning systems

After decades of using reliable synthetic refrigerants, it is now necessary to look for their low-GWP climate-friendly safe alternatives. This paper summarizes a search for the best substitutes to commonly used refrigerants and their blends to be used in vapor compression air conditioning systems and temperature conditions typical for a moderate climate. 24 pure refrigerants (including several modern HFOs) were combined (using REFPROP10’s mixing functions) in binary and ternary compositions (at 10% mass fraction adjustments) producing 44 915 potential combinations. This broad database was screened on the basis of theoretical COP, specific cooling capacity, and volumetric cooling capacity which were obtained through simulations of an ideal cycle with the temperature of evaporation 0 °C, condensation 38 °C and superheating 10 K. Resulting blends were then further sieved on the basis of Global Warming Potential (GWP), discharge temperature, temperature glide, and flammability. The refrigerants that produced the highest COP under the above screening criteria are: R13I1 and its blends. The COP was 4.94, but R13I1 is hard to acquire in necessary quantities. The other high-COP/low-GWP blends contain R1234ze(Z) and/or R1233zd(E), but the evaporator would work below atmospheric pressure. Further screening returned R152a/R1234ze(E) [0.7/0.3 mass ratio] as the best refrigerant blend for the air conditioning purposes. It is inexpensive, belongs to flammability group 2L, and the ideal refrigeration cycle yields a theoretical COP of 4.861.

Investigation on the density of Al2O3/R1234yf, TiO2/R1234yf and CuO/R1234yf nano-refrigerants

Nano-enhanced refrigerant is one of the promising heat transfer fluids in refrigeration systems. It has the capability to boost the efficiency of vapour compression refrigeration and air conditioning systems. In heat transfer application, the density of the fluid plays a crucial role in identifying various heat transfer characteristics such as the Reynolds number, Nusselt number, the friction factor and the pressure loss. Compared to thermal conductivity and viscosity, determining the density of nanofluids has received very less attention in research. The liquid and vapour densities of alumina (Al2O3), titanium dioxide (TiO2) and cupric oxide (CuO) nanoparticles suspended in 2,3,3,3-tetrafluoropropene (R1234yf) are investigated in this study. The Pak and Cho model was adopted to examine the densities of nano-refrigerants as the volume concentration of particles in the base refrigerant and temperature varies from 1% to 5% and 273 to 323 K respectively. The models are validated using the experimental studies conducted by various researchers on different nano-refrigerants. The analysis results indicated that the liquid and vapour densities of CuO/R1234yf nano-refrigerant are 10.3% and 62.93% greater than that of Al2O3/R1234yf at 5% particle concentration. From the liquid and vapour density point of view, the CuO/R1234yf nano-refrigerant is superior over Al2O3/R1234yf and TiO2/R1234yf. Results also indicated that at 308 K the liquid phase density of CuO added with R1234yf nano-refrigerant is higher by 12.99% and 8.65% than R134a and R141b respectively. Hence CuO/R1234yf significantly enhances the performance of refrigeration systems.

Performance evaluation of a metal organic frameworks based combined dehumidification and indirect evaporative cooling system in different climates

Evaporative coolers, although more energy efficient than vapor-compression air conditioning systems, are not suitable candidates for humid climates due to their evaporation-based operating principle. Integration of indirect-evaporative coolers with a desiccant can solve this problem but desiccant systems still require a high-temperature energy source for regeneration of the sorbent. In this work we investigate the integration of selected Metal Organic Frameworks (MOFs) including CAU-23, CAU-10 and Co2Cl2(BTDD) as the sorbent in a combined desiccant wheel and indirect evaporative cooling system and compare the system's optimal regeneration temperature and coefficient of performance (COP) with a traditional silica gel-based system under a wide range of outdoor conditions. We validate a first principles model with experimental data and then use this model to investigate different MOF-based systems. Our results show that depending on the inlet conditions, MOF-based systems can have a COP of 2.7 to 6 times greater than a silica gel-based system, with an optimal regeneration temperature of 40 to 75 °C. This allows for the feasibility of using low-temperature heat sources as the primary energy source for the system.

Dehumidification Analysis of Rotary Solid Desiccant Wheel System for different Surface Materials

In recent decades, desiccant dehumidification has been given much interest in the air conditioning industry area. Compared to the conventional vapour compression air conditioning system, desiccant dehumidification has various advantages, including separate humidity and temperature control. In this paper, the analysis of the Rotary Solid Desiccant Wheel System has been performed. Here, we have studied three diffusion coefficients: Ordinary, Knudsen and Surface diffusion coefficients for Rotary Solid Desiccant Wheel System. Also, the analysis has been performed for three different solid desiccant materials: Silica Gel, Molecular Sieve and Activated Alumina to incorporate and to study the effect of pore size on moisture transport and to examine the impact of Tortuosity factor on moisture transport phenomenon. This analysis can correctly select the best desiccant material suitable for the desiccant dehumidification industry.

A solar-assisted hybrid air-cooled adiabatic absorption and vapor compression air conditioning system

Absorption-compression hybrid systems which consist of absorption and vapor compression cycle have advantages on both energy efficiency and cost-effectiveness. In the open literature, a great amount of research on such hybrid systems focuses on the water-cooled system which requests a larger area for the whole cooling unit due to the size of the cooling tower. In this paper, an air-cooled solar-assisted hybrid system consists of an adiabatic absorption (ABS) and a vapor compression refrigeration system (VCR) with subcooling mode and cascade mode is proposed for miniaturization. Steady-state experiments of the proposed system in the cascade mode were carried out and subsequently a numerical model is developed to evaluate performance difference and possible application for the two kinds of coupled modes. Simulation results show an increment of 63.9%∼166.7% in the electric COP of the system (COPele,sys) in the cascade mode, which is similar to from the experimental findings. Although the simulated COPele,sys increases by only 15.9% ∼ 29.8% in the subcooling mode, electricity saving rate brought by unit thermal energy input (defined as ‘r’) and the exergetic efficiency (COPex,sys) are significantly greater than those of the cascaded mode. So is the primary energy efficiency (PEE). It is concluded that the subcooling mode driven by the compound parabolic collector (CPC) is applicable to residential buildings due to its distinct advantages —— lower levelized cost of cooling (LCOC) of 0.06 US $/kWh, shorter payback time (PBT) of 8.54 years and smaller collector area of 11.41 m2, in comparison with other configurations. The study of this paper can function as guidance for design of the air-cooled absorption-compression integrated air conditioning system.

Progressive Development and Challenges Faced by Solar Rotary Desiccant-Based Air-Conditioning Systems: A Review

A rotary desiccant-based air-conditioning system is a heat-driven hybrid system which combines different technologies such as desiccant dehumidification, evaporative cooling, refrigeration, and regeneration. This system has an opportunity to utilize low-grade thermal energy obtained from the sun or other sources. In this paper, the basic principles and recent research developments related to rotary desiccant-based cooling systems are recalled and their applications and importance are summarized. It is shown that with novel system configurations and new desiccant materials, there is great potential for improving the performance and consistency of rotary desiccant systems; at the same time, the use of solar energy for regeneration purposes can minimize the operating cost to a great extent. Some examples are presented to demonstrate how rotary desiccant air conditioning can be a promising solution for replacing traditional vapor-compression air-conditioning systems. Recent advances and ongoing research related to solar-powered hybrid rotary desiccant cooling systems are also summarized. The hybrid systems make use of a vapor-compression system in order to have better operational flexibility. These systems, although they consume electrical energy, use solar energy as the principal source of energy, and hence, significant savings of premium energy can be obtained compared to conventional vapor-compression systems. However, further research and development are required in order to realize the sustainable operation of solar rotary desiccant air-conditioning systems, as solar energy is not steady. Reductions in capital cost and size, along with improvements in efficiency and reliability of the system is still needed for it to become a player in the market of air conditioning.

Evaporative Cooling Integrated with Solid Desiccant Systems: A Review

Evaporative cooling technology (ECT) has been deemed as an alternative to the conventional vapor-compression air conditioning system for dry climates in recent years due to its simple structure and low operating cost. Generally speaking, the ECT includes two types of different technologies, direct evaporative cooling (DEC) and indirect evaporative cooling (IEC). Both technologies can theoretically reduce the air temperature to the wet-bulb temperature of outdoor air. The major difference between these two technologies is that DEC will introduce extra moisture to the supply air while IEC will not. The enhanced IEC, Maisotsenko-cycle (M-cyle) IEC, can even bring down the air temperature to the dew point temperature. The ECT integrated with solid desiccant systems, i.e., solid desiccant-assisted evaporative cooling technologies (SDECT), could make the technology applicable to a wider range of weather conditions, e.g., weather with high humidity. In this paper, the recent development of various evaporative cooling technologies (ECT), solid desiccant material and the integration of these two technologies, the SDECT, were thoroughly reviewed with respect to their configuration, optimization and desiccant unit improvement. Furthermore, modeling techniques for simulating SDECT with their pros and cons were also reviewed. Potential opportunities and research recommendations were indicated, which include improving the structure and material of M-cycle IEC, developing novel desiccant material and optimizing configuration, water consumption rate and operation strategy of SDECT system. This review paper indicated that the SDECT system could be a potential replacement for the conventional vapor-compressed cooling system and could be applied in hot and humid environments with proper arrangements.

Effects of multiple simultaneous faults on characteristic fault detection features of a heat pump in cooling mode

Faults in air-cooled vapor compression air-conditioning systems are known to reduce performance, including efficiency, capacity, and lifespan. Their effects have been studied, and fault detection and diagnostic (FDD) methods have been developed as tools for field technicians to install or repair systems, or for monitoring to alert operators to the fault’s presence. Most of this work has focused on faults that occur singly. It is likely that in some systems, multiple faults occur simultaneously, but it is uncertain what effects this may have on diagnostics. This paper describes a laboratory study of a split system air source heat pump in which combinations of two, three, and four simultaneous faults occur. The study includes all combinations of: improper evaporator airflow; overcharge or undercharge of refrigerant; liquid line restrictions; and non-condensable gas in the refrigerant, each at multiple fault intensities. Fault features – those characteristics that can be determined from measurements, for use in diagnostics – are analyzed, and the key fault features are presented. A robust existing method for determining refrigerant charge, the virtual refrigerant charge sensor (VRC) is tested using the multiple fault data, in order to understand how its performance is impacted by the combined faults. The VRC performs well, typically able to correctly determine whether a system is undercharged or overcharged, but the magnitude estimates are impacted. The results suggest that simple subcooling-based methods of charging a system are likely to provide unsatisfactory results when other faults are present.