Conference Agenda

This paper presents a case study on the total replacement of an aging ammonia pumped circulation system supplying a cold and chill storage warehouse facility using multiple low charge modular packaged ammonia refrigeration systems in Scotland. Installation and commissioning took place across 2020-2021 with the package units replacing the plant room style system which had been operational since 1979.

This paper gives a design overview of the new plant and summarises the benefits of the external package unit type system over the original pumped circulation system with insight into the challenges faced implementing change on an aging site. This study will also analyse store temperature performance and energy usage across a 12-month period with comparison to historical site data.

At the same time climate-driven national policies are requiring increased uptake of heat pumps. Current refrigerants include HFCs that exhibit significant warming impact when emitted, thus accentuating the climate impact. Use of negligible-GWP hydrocarbon (HC) refrigerants can help mitigate this impact. The present work is a detailed assessment considering technical, economic, environmental and safety implications, all of which are interrelated to some extent. Differences in materials and other inputs are used to determine implications of cost, equipment size and lifetime carbon dioxide equivalent (CO₂e) emissions. Overall, significant benefits for emissions reduction are seen when switching from R410A (or from R32) to HCs. Thus, domestic heating and air conditioning, considering higher temperatures and decarbonisation targets, can be applied without adverse contributions to climate change or equipment cost.

The performance of the refrigeration plant is directly affected by the surrounding temperature and humidity. The heatwave in 2022 saw temperatures in some parts of the UK exceed 40°C for the first time. Climate models predict peak temperatures exceeding 40°C regularly in the near future. The integrity of the cold chain rests upon proper functioning of refrigeration equipment. Although forward thinking designers are considering higher ambient temperatures, there is no standard or operating guidelines to steer industry in the right direction.

This study carried out surveys and audits to investigate the preparedness of the cold chain to warmer ambient temperatures. Cold stores tend to have older plant (mean of 10.9 years) compared to retail (4.6 years). Condensing temperatures were often higher than optimum, with an example of 40°C recorded when the ambient was only 15°C.

This study recommends a standard method for choosing design ambient temperature, considering location in the UK and life of equipment.

The integration of microchannel heat exchangers (MCHEs) with phase change materials (PCMs) presents a promising approach for improving energy efficiency and thermal management in space heating systems. These are attributed to their high surface area-to-volume ratio, compact design, faster PCM charging, and higher energy density. Correspondingly, a purpose-designed MCHE was fabricated, utilizing airflow as the heat transfer fluid (HTF), and incorporating organic PCM A27 within microchannels. A series of experiments were carried out to study the thermal performance of the MCHE throughout PCM charging and discharging processes at different operating conditions. Furthermore, a validated computational fluid dynamics (CFD) model was developed to optimize the thermal storage performance at various operating and design conditions. The integration of advanced heat exchangers with energy-efficient thermal storage materials holds significant potential to enhance building heating technologies, offering improved energy efficiency, faster thermal response, and greater sustainability.