Cooling

Overview

Refrigeration and air conditioning are responsible for a significant share of global greenhouse gas emissions. Especially in developing countries and emerging economies, the demand for cooling equipment is rising. Cooling mostly relies on the usage of refrigerants which depending on the used substance can cause major climate and environmental problems. CFCs, HCFCs are both ozone depleting and climate damaging substances. Low levels of efficiency and high leakage rates of refrigerant gases with high global warming potential will increase these emissions drastically.

Direct and indirect emissions

Direct emissions are due to the release of refrigerant. They can occur during normal operation because of leaks from pipes and components. Without appropriate recovery and recycling facilities, most direct emissions occur when the refrigerant is exchanged during regular servicing or when a unit is dismantled (end-of-life emissions). Direct emissions are given in CO₂ equivalents and weighted according to the global warming potential (GWP) of refrigerants. Even though the amount of refrigerant in small units is only in the range of grams to a few kilograms, the high GWP of HCFCs and HFCs means that direct emissions contribute approximately 1/3 to total GHG emissions from the RAC sector.

Indirect emissions are due to energy consumption. They contribute the other 2/3 of the total emissions. These depend heavily on the source of electricity and how much CO₂ is emitted during its generation and are therefore different for each country. Indirect emissions can be reduced by raising the energy efficiency of a product or by decarbonising electricity production. Calculations on this website focus only on potential CO₂ emission reductions achieved by energy efficiency measures; the introduction of less carbon intensive renewable energies is not accounted for in the calculations. Indirect emissions are also given in CO₂ equivalents.

Cooling Sectors

The following subsectors have a substantial environmental impact due to refrigerant leakage and energy consumption. At the same time these subsectors have a high potential for emission reductions and the application of natural refrigerants instead of fluorinated gases.

Mobile air conditioning

Leakage rates are especially high in mobile air conditioners. Even though the amount of refrigerant per car is relatively low, the sheer number of cars worldwide makes mobile air conditioning an important contributor to global CO₂-emissions. In terms of energy efficiency, additional fuel consumption when driving with the AC switched on can be up to 20%.

Unitary air conditioning

Air conditioning in buildings is the fastest growing of all the RAC subsectors, especially as more and more people in developing and transitioning countries in warm climates can afford air conditioning in their homes. In some cities, AC use is already responsible for up to 40% of all electricity consumption.

Air conditioning chillers

Similarly to unitary air conditioning, the demand for large air conditioning chillers is growing rapidly as more and more new buildings have some kind of central air conditioning installed. These often contain several hundreds of kilograms of refrigerant and consume a lot of electricity.

Domestic refrigeration

A refrigerator is often the first electric appliance bought in a household and there are over 1 billion refrigerators and freezers worldwide. This is one of the few subsectors with a commercially available and successful natural refrigerant solution. Further distribution and improvement of energy efficiency is relatively easy and could save high amounts of energy.

Transport Refrigeration

Transport refrigeration is a vital part of every cold chain: Perishable goods, mainly food but also medical supplies and other goods, have to be refrigerated on their way from harvest or production to the consumer. Refrigerated transport increases food safety and prevents economic losses due to spoilage. Trucks and trailers are in many parts of the world the main mode of transport for refrigerated goods.

Cooling for Agriculture

Refrigeration is required across the entire food supply chain, it makes exporting foods viable and provides people in developed countries the food choices that are expected. It is especially crucial in post-harvest cooling and cold storage. Refrigerated storage can account for up to 10% of the total carbon footprint for some products when electricity inputs, the manufacturing of cooling equipment, and GHG emissions from lost refrigerants are taken into account. Active cooling depends on electricity supply. Passive evaporative-cooling technologies and stand-alone solar chillers exist as alternatives in developing countries but are not yet economically viable for developed countries. According to Bundschuh and Chen improvements to technical elements and operation of modern refrigeration systems have the potential to reduce energy consumption by 15-40%.

Green Cooling

Green Cooling is environmentally friendly air-conditioning and refrigeration (RAC) with minimum negative impacts on the environment.

The negative environmental effects of cooling appliances are due to their direct and indirect emissions. To avoid emissions, green cooling RAC equipment involves two main factors: Climate-friendly refrigerant and high energy efficiency, an example from the field: Greening the Indian Dairy Value Chain.

Natural refrigerants

In contrast to the artificial refrigerants CFCs, HCFCs and HFCs, natural refrigerants are substances occurring in nature. The “natural 5” are CO₂, ammonia, hydrocarbons, air and water and they have no ozone depleting potential, no or negligible global warming potential.

Energy efficiency

Emissions due to energy consumption are even higher than emissions from refrigerants. As long as electricity generation (or vehicle powering) is linked to CO₂ emissions through the burning of fossil fuels, the only way of reducing indirect emissions is making air conditioners and refrigerators of all sizes more efficient.

Standards

Standards are not mandatory, but especially in developing countries without their own standardisation bodies, international standards are often adopted as national standards and sometimes made into laws.

Evaporative Cooling

Evaporative cooling is a low cost cooling process for storing vegetables that does not use electricity.

Evaporative cooling devices include clay-pot coolers and larger evaporative cooling chambers (ECCs) that do not require electricity. These storage systems rely on the evaporation of water from a surface, which removes heat and causes a cooling effect inside the cooler.

Operating Conditions

To operate effectively, specific conditions are ideal for evaporative cooling devices, relative humidity should be lower than 40%, daily maximum temperature should be above 25C, there must be access to water to create the evaporative process, and availability of shade and good ventilation for proper air flow.

Construction

For household capacities, clay pot coolers can be constructed from a clay pot within another clay pot, with a layer of wet sand in between to provide the water for evaporation, or a simpler arrangement of a clay pot placed in a dish of wet sand covered in a wet cloth. For more storage, larger evaporative cooling chambers can be constructed from a double walled brick structure with wet sand in between and a straw and wood cover.

Effectiveness

When operating in appropriate ambient conditions, evaporative cooling devices are low cost, zero energy systems that can provide a stable storage environment with low temperature and high humidity and reduce water loss and spoilage in most vegetables. Studies show evaporative cooling devices to provide conditions of increased humidity to >80% and reduced temperature by 10C.

See also

Green Cooling Initiative (GCI)

External Links

• http://www.green-cooling-initiative.org/
  
• www.giz.de/proklima
  
• Evaluation of Evaporative Cooling Technologies for Improved Vegetable Storage in Mali - Evaluation
• Evaporative-cooling-best-practices-guide (2018)
  
• Evaporative Cooling Decision Making Tool
• Evaporative cooling overview by Practical Action