Experimental performance analysis of a novel ultra-low charge ammonia air condensed chiller

Highlights: • A novel design of an Ultra-Low-Charge ammonia chiller is proposed and experimentally tested. • The chiller includes semi-hermetic compressor, micro-channel condenser and dry-expansion plates heat exchanger. • The miscible lubricant allows the use of a single-stage oil-separator while ensuring a proper oil return. • The optimized system achieved a charge 40% lower than the current systems in the market with up to 20% extra COP. • The package technology assessed simplifies the installations thanks to the use of secondary fluids. Environmental restrictions on the use of fluorinated refrigerants are turning the attention to natural solutions. Ammonia is historically proven as a refrigerant that requires low purchasing costs, has superior thermodynamic properties, and exhibits great values of coefficient of performance. Therefore, considering ammonia safety issues, solutions able to prevent leakages and minimize the charge of refrigerant are kind of welcomed. This paper conducts an investigation focused on the experimental analysis of the refrigerant charge and performance of a novel ultra-low charge air-cooled packaged chiller for medium temperature industrial applications. The unit is developed using emerging technology to reduce the amount of ammonia charge, such as the microchannel condenser, semi-hermetic screw compressor, miscible lubricant, single-stage oil separator, and dry-expansion plates heat exchanger. In doing so, the empirical adjustment of the ammonia charge revealed that there is an optimum that maximizes the coefficient of performance and the cooling capacity of the system. A charge capacity ratio of 75 g/kW was achieved for a unit with a rated cooling capacity of 230 kW and a gross coefficient of performance of 2.3, i.e, a reduction of 50% in the specific charge and an improvement of 20% in the performance, with regard to the systems in the market. Moreover, the system performance, such as operating temperatures, evaporator effectiveness, and oil return, are assessed for a wide range of conditions and compressor rotational speeds.