Water conservation is increasingly critical at the same time power demand and emissions from air-conditioning are becoming unsustainable. Advanced evaporative cooling technology can address both needs while replacing upwards of 80% of the work done by compressors. These technologies are proven to meet modern expectations for comfort conditioning at a fraction of the energy cost, while easily doubling fresh air ventilation rates, and can even be suitable for Outdoor Cooling. The concept of “Industry Standard CFM” for direct evaporative coolers (DEC) facilitates comparison of premium products, that achieve high saturation effectiveness and colder supply temperatures, to traditional approaches that must treat higher volumes of air to address the same loads. This allows some of the cost of advanced media to be recouped in the fabrication of smaller equipment and balance of system, but importantly also leads to water efficiency gains by virtue of having to bring less outside air down to space neutral conditions, a significant source of water consumption inherent to fresh air displacement cooling. This is doubly so for indirect evaporative coolers (IEC) that have the added burden of cooling a secondary airflow which does not directly contribute to meeting the space load. More impactful still are the water savings possible when replacing outdated constant bleed practices with active water quality management that monitors water properties so that the system is drained only when required to protect systems from mineral fouling. Tailoring Cycles of Concentration (CoC) to that which is appropriately protective for current conditions is far superior to a constant bleed set to prevent mineral scaling during peak cooling season and produces excessive drain water during mild and moderate weather. Psychrometric analysis of water efficiency is presented on representative traditional and advanced DEC and IEC system solutions for applications in challenging climate and water conditions.

To mitigate global warming, demand for more efficient working fluids in refrigeration systems has increased over the past 30 years. One promising approach is the addition of nanoparticles to refrigerants at small concentrations. Nanoparticles possess favorable thermophysical properties that have been shown to enhance the COP of the refrigeration system by nearly 50%. In this study, seven different nanoparticles Cu, Al2O3, CuO, ZnO, TiO2, SiO2, and Fe3O4. were individually added to five different natural mixed refrigerants to investigate their effects on the thermophysical properties of the resulting nanofluids. The properties considered include thermal conductivity, viscosity, specific heat, and density under varying pressures (1–21 bars) and nanoparticle concentrations (0-1 wt.%). AspenPlus software was utilized to calculate these properties. The results indicate that the addition of nanoparticles to natural mixed refrigerants significantly enhances the thermophysical properties of the nanofluids. The specific heat wasdecreased by 30% and density increased by 80%, suggesting their potential for improving the COP of the refrigeration system. The compressor work was calculated to validate this finding. It was found that for MR7 with 1% Fe2O3, as an example, the compressor work decreased by almost 6%. However, higher reductions are expected for other MRs and nanoparticles. This enhancement could be particularly beneficial for applications such as cryogenic refrigeration systems.

The global building sector encompasses 242 billion square meters and emits around 10 Gt CO2eq in operational emissions annually, representing approximately 39% of the world's energy-related CO2eq emissions according to the UN Environment Programme and World Green Building Council. Thus, buildings present a significant opportunity for energy-use reduction, particularly through reduced loads on heating, ventilation, and air conditioning (HVAC) systems.

In the wake of the COVID-19 pandemic, indoor air quality (IAQ) has become critical in mitigating the spread of airborne pathogens. Facilities have started using several measures to mitigate long-range airborne transmission risk primarily by using higher MERV filters, and increased outdoor air intake, along with other pathogen inactivation technologies. However, all these options often increase energy consumption, and many require additional capital investment.

This study estimates the energy and CO2eq savings for a theoretical office and gym of 10,000 sf and default occupant density per standard 62.1, located in Doha, Qatar by comparing the use of silver-graphene oxide coated MERV-A 9-A filters (M9AZG) which exhibit higher viral filtration efficiency, instead of uncoated MERV-A 9-A filters (M9A). Minimum outdoor air rates were calculated to achieve the equivalent clean air flow rate (VECAi) per ASHRAE Standard 241 while keeping the recirculated air passing through M9AZG and M9A filters constant. Annually, energy savings of 3.68 kWh/sf for office spaces and 13.39 kWh/sf for gyms were observed by replacing M9A with M9AZG filters. During the peak energy month of August, about 24% of CO2eq savings, which equates to 2.7 t for office and 9.7 t for gym were achieved, with annual savings of 16.2 t and 58.8 t, respectively. Additionally, M9AZG have lower resistance to airflow, longer operating life and lower cost compared to higher MERV-rated filters and is compatible with existing HVAC systems.