Energy savings potential of CO2 heat pumps in the South African industrial sector

Abstract

The South African industrial sector is the largest energy user, accounting for more than a third of the country’s energy usage and 80% of the heat demand. Heat pumps (HP) have the potential of reducing the industrial energy heat demand. However, a commercial HP typically have a low operating temperature of 65 °C. An alternative to commercial HPs is the introduction of CO2 as a natural refrigerant. CO2 holds several advantages for the industrial heat pumps market. Not only can multi-function CO2 HPs deliver water at discharge temperatures of 65 °C and 90 °C, but also chilled water as low as -9 °C. The wider operating temperatures can thus open a broader market of application for HPs in the industrial sector. This study firstly aimed to determine which divisions in the industrial sector are the most suited for the implementation of industrial heat pumps (IHPs). From the literature it became evident that the food, beverage, and tobacco division has the highest potential for energy savings. To determine the most suitable South African industrial division, the author estimated and analysed the heat demand for 12 divisions with a maximum temperature of 100 °C. The analysis showed that the food, beverage, and tobacco division was the most suitable division, with the poultry abattoirs being the most suited for the integration of CO2 HPs. To show the energy savings potential in the identified poultry sector, a techno-economic and environmental evaluation was done of the integration of CO2 HPs for a case study poultry abattoir. For the evaluation, a mathematical model was developed to compare CO2 HPs against four alternative heating sources, namely coal, paraffin, liquid petroleum gas, and electrical resistance. The model evaluated the CO2 HPs for various climatic zones of South Africa. The results showed that, on average, CO2 HPs use 4.5 times less energy than coal when combined with an ammonia chiller but cost 2.2 times more to operate than a coal boiler. A barrier to the implementation of CO2 HPs in the industrial sector is the uncertainties concerning inflation, capital layout cost, and energy cost. Consequently, a sensitivity analysis was done. The

investigation showed that the capital cost has the largest impact on economic indices investigated and influences the indices investigated positively. Finally, the impact of CO2 HPs on the greenhouse emissions of South Africa was investigated. This covered 17 high-throughput abattoirs, which represent approximately 75% of the country’s poultry throughput. The results showed that if all the abattoirs changed over to HPs, the greenhouse emissions could be reduced by at least 45%. Although CO2 HPs do not currently make sense financially when compared with coal boilers, they have a large environmental impact in the industry. CO2 HPs thus have the potential to reduce industrial sector greenhouse gases, a zero-ozone depletion value, very low greenhouse warming potential, and are non-toxic and non-flammable. CO2 HPs thus have the potential to make a significant environmental impact.