Transport refrigeration

Transportation of deep-frozen or chilled products, mostly food, is increasing worldwide.

Products are transported by road, rail and water. The means of transport used are refrigerated vehicles, semi-trailers, intermodal containers (combined road/rail transport), containers for international shipment (e.g. by container ships) and refrigerated ships

This chapter deals with the refrigeration systems only; insulation issues can be found in Chapter 4.

Alongside vehicle air-conditioning, transport refrigeration is one of the relevant applications with regard to energy consumption and greenhouse gas emissions arising from artificially generated cold. There is a considerable potential for savings here, in terms of both energy and refrigerants.

In 2007 transport refrigeration systems (vehicles, refrigerated containers) in Germany were filled with around 950 tonnes of hydrofluorocarbons (HFCs). Total emissions from these systems in 2007 came to around 155 t HFC, thus accounting for 3.5% of the HFC emissions in the refrigeration/air-conditioning sector.

Road vehicles

Worldwide freight transport performance by road came to 16 trillion (10¹²) tonne-kilometres in 2005, and growth rates of 2.5% per year are expected until 2030. In Europe the annual freight performance is about 50 billion (10⁹) tonne-kilometres. A fleet of 650,000 refrigerated vehicles is available for this purpose [UNEP 2006]. In Germany there were some 55,500 refrigerated trucks registered in 2007 and 44,500 trailers with refrigeration units [KBA 2009].

Transport refrigeration systems have to ensure reliable refrigeration at ambient temperatures ranging from -40°C to +40°C; in some cases it is also necessary to cool down the transported goods. There are international requirements on the refrigeration capacity for the transport of perishable food (ATP Agreement, see Glossary); the internal and external dimensions of the vehicles are standardised [FRIGOBLOCK 2003].

The refrigeration units contain 2-15 kg of refrigerant. Refrigerated vehicles with 6-15 kg of refrigerant are used for long-distance transport; these are trucks, trailers and semi-trailers with

(distribution vehicles) with charges of around 2 kg of refrigerant take care of local distribution of chilled products and to some extent deep-frozen products. Many vehicles are used for both chilled products and deep-frozen products.

Traditionally CFC-12, CFC-502 and HCFC-22 have been used as refrigerants in refrigerated vehicles [UNEP 2003]. CFCs are now banned in Europe by Regulation (EC) No. 1005/2009 on the basis of the Montreal Protocol [Montreal Protocol 2000]. Under existing regulations HCFC-22, which is permitted as a substitute in some countries, is banned for use in new vehicles in Germany. Today hydrofluorocarbons (HFCs) are used as refrigerants in new vehicles. The blends R 404A and R 410A (especially in Germany) are used for long-distance vehicles carrying chilled and deep-frozen products, and HFC-134a is used for chilled products [FRIGOBLOCK 2003; Öko-Recherche 2003; Thermo King 2003a].

HFC emissions from refrigerated vehicles in 2007 came to about 86 t [Schwarz 2009a].

Emissions on disposal of many long-distance vehicles do not take place in Germany, since the vehicles are sold to purchasers in other countries before being scrapped. Distribution vehicles containing R 134a are mostly disposed of within Germany.Refrigerated containers

Refrigerated containers are used in international transport of goods by road, rail and ship.

They may have integrated or external transport refrigeration units [Peilnsteiner, Truszkiewitz 2002]. Today the usual containers, the Integrated Reefer Containers, are equipped with an integrated refrigeration unit. Containers without their own refrigeration unit, so-called porthole containers, are rare [Kauffeld, Christensen 1998]. Until the ban on CFCs the refrigerant of choice for refrigerated containers was CFC-12. It was replaced by HFC-134a, the blend HFC-404A and also HCFC-22. Annual worldwide production totals about 100,000 containers; today they use HFC-134a and the blend HFC-R404A for refrigeration [UNEP 2003; Wild 2008]. In the meantime the entire production of marine containers has been shifted to China [Wild 2008].

In 2007 the German share of HFC emissions from container refrigeration units came to about 51 t; some of these emissions took place outside Germany [Schwarz 2003b; Schwarz 2009].

Ships

Refrigerants are present in the refrigeration and/or air-conditioning systems of factory ships as used for fishing, refrigerated ships for transporting goods that require cooling, other cargo vessels, research vessels, navy vessels and passenger ships. This chapter on “Transport refrigeration” discusses ships’ refrigeration systems only; ships’ air-conditioning systems are discussed in Chapter 3.3.7.

There are no longer any refrigerated vessels operating under the German flag [Öko-Recherche 2003]. Older refrigerated vessels use direct-evaporation systems to generate their cold. These systems contain 3-5 t of refrigerant. As in other transport refrigeration sectors, they originally

used CFC-12; after the ban on CFCs⁴

Older deep-sea fishing vessels (factory ships) used ammonia or the refrigerant R 22. HFCs did not gain acceptance as substitute refrigerants for factory ships and are only used in a few isolated cases [Schwarz 2003b].

this was frequently replaced by HCFC-22. Owing to the restrictions on this refrigerant, HFC blends of the 400 series are used [UNEP 2003]. Today hardly any refrigerated vessel is built with direct-evaporation systems; instead, refrigerated containers with their own refrigeration units are used (see section on Refrigerated containers).

Since refrigerated containers only need a power connection, they can be transported on most freight vessels.

All other refrigeration systems on “vessels” – from ferries to research vessels – mostly use HFCs. Air-conditioning applications commonly use R 134a, refrigeration systems (food stores etc.) use R 404A or R 407C. In some cases the R 134a that is already used for air-conditioning is also used for refrigeration purposes. Although it is more efficient to use R 404A for low-temperature refrigeration, R 407C is also used as a sole refrigerant for chilling and low-temperature refrigeration. The refrigeration capacity needed is considerably lower than that required on factory ships.

Estimates indicate that HFC emissions (refrigeration and air-conditioning) from ships belonging to the EU-27 states amount to 241 t, of which 38 t come from refrigeration [BiPRO 2008].

Aircraft

A maximum of 20% of aircraft use small quantities of fluorinated refrigerants for cooling food; the refrigerant charge per compact unit is 0.5 kg, with leakage rates of <0.1% per annum; cooling in aircraft is normally by means of dry ice [Schwarz 2007].

Reduction options Road vehicles

Possible halogen-free refrigerants for road vehicles are hydrocarbons and carbon dioxide (CO₂; R 744).

In the 1990s, one manufacturer of transport refrigeration systems equipped a refrigerated vehicle with a demonstration system using hydrocarbons. This system was used for several years by a food retailer chain and proved to be suitable from an energy point of view.

However, economic operation of such systems has not been possible to date under the prevailing legal conditions (safety requirements and standards for hydrocarbons) [FRIGOBLOCK 2003, 2009]. A refrigeration system for “multi-temp operation” (i.e. vehicles

4 Annex VI to the International Convention on the Prevention of Pollution from Ships (MARPOL 73/78) also contains rules on the use of ozone-depleting substances on ships [MARPOL 1997]. These are of no significance for Germany and the EU because of the more stringent regulations in force here (see

for both chilling and deep freezing) using the natural refrigerant propene was shown at the IAA 2010. A safety concept was prepared by the technical inspection authority TÜV, and field tests with refrigerated vehicles are planned [FRIGOBLOCK 2010].

The use of CO₂ as refrigerant in refrigeration systems for food distribution (chilling and deep- freezing) has been demonstrated in a multi-year prototype test in a research project at a discounter (Aldi). The test results for the mobile refrigeration system developed by Konvekta AG show that using CO₂ as a refrigerant for this application in temperate climate zones (e.g.

in Germany) is an environmentally sound alternative to the use of HFCs [DBU 2003]. Its extension to a two-stage system could lead to further efficiency improvements for transport refrigeration, especially where temperatures in the refrigerated compartment are low and ambient temperatures are high [DBU 2009]. Another new development is a transport refrigeration system on the basis of CO₂ as refrigerant for chilled products. The system is of two-stage design. No measurements have been published yet, and two-stage systems for generating low temperatures are planned. First a field test of the system in chilled product distribution is planned. It will be installed in a newly developed semi-trailer based on carbon fibre material, which has yet to be tested in operation [IAA 2010].

Refrigeration systems in vehicles around the world are still filled with R 404A. Apart from reducing the greenhouse gas contribution of the refrigerant, one of the most important issues is the energy consumption of the transport refrigerant system.

In an overall assessment (TEWI), one manufacturer of transport refrigeration systems came to the conclusion that the environmental impact caused by the use of hydrocarbons at higher temperatures (evaporation temperatures from 0 to -10°C) is lower than when using the blend HFC-410A. The global warming potential of HFC-410A is even lower than that of the blend HFC-404A [FRIGOBLOCK 2003].

The introduction of CO₂ as a refrigerant in transport refrigeration for chilled and deep-frozen product distribution also depends on developments in the field of air-conditioning systems for cars. Suppliers of transport refrigeration systems would welcome broad use of CO₂ systems in the market. One reason is that CO₂ could, as sole refrigerant in the transport sector, cover the entire range of chilled and deep-frozen product distribution. This would eliminate the additional costs arising from the need to use more than one HFC refrigerant [Konvekta 2003].

Konvekta [2002] produced an initial cost comparison. In this, an R 134a series-production system was compared with a fictitious CO₂ system ready for series production. The study makes a first estimate of the costs. Depending on the calculations, the authors arrive at total costs which are 16 to 34% higher for the CO₂ system if it goes into series production. These must be set against non-quantifiable cost reductions in the fields of maintenance, refrigerant and disposal [Konvekta 2002]. Despite the extra capital cost, the use of CO₂ as refrigerant is justified because of the associated advantages (ready worldwide availability of refrigerant, lower adverse effects on the environment, simpler disposal, reduced operating costs etc.) [DBU 2003].

CO₂ is also used as a “refrigerant for consumption”. Liquefied CO₂ passes from a

vacuum-refrigerated compartment. Direct spraying into the vacuum-refrigerated compartment was abandoned, especially for health and safety reasons. The system does not have a power unit or a compressor, but the technical equipment in the refrigerated compartment is the same as with a usual refrigeration system. All the gasified CO₂ is released into the atmosphere. This open CO₂ cooling system is more suitable for chilled product distribution. Stationary CO₂ tanks with liquefied CO₂ need to be kept for refilling the CO₂ containers on the vehicle. The manufacturer sees advantages for this technology, which has so far been used mainly in Sweden, in lower noise levels and lower maintenance costs due to the simple design of the system [Thermo King 2003b]. For longer distances, a combination with a refrigeration system using conventional diesel power is possible [Peilnsteiner, Truskiewitz 2002]. There is as yet no full life-cycle assessment which might confirm the advantages of systems with CO₂ as a consumable refrigerant compared with optimised compressor systems.

Refrigerated containers

Due to their flammability, the use of hydrocarbons or ammonia in refrigerated containers is not permitted under the international rules for shipping (IMO regulations). The use of CO₂ was tested some years ago in various projects promoted by the Danish environmental authority. Those taking part included component manufacturers, refrigeration system manufacturers and users [Kauffeld, Christensen 1998]. In addition to hitherto unsolved technical issues, there are also logistical problems to be solved when using CO₂. For example, before their widespread use, it must be ensured that a reserve unit is available in every port [Bock 2003; VDR 2003]. Since the containers are now only made in China, and containers are used internationally, there is a need for international measures for conversion to CO₂ as refrigerant.

Ships

Up to the present, the refrigeration systems of deep-sea fishing vessels (factory ships, trawlers) have used HCFC-22 and also ammonia for the large refrigeration capacities needed.

In new vessels, HCFC-22 is not replaced by HFC, but by ammonia or ammonia/CO₂ [Schwarz 2003b; Lindborg 2003; Lund 2003].

Ammonia refrigeration systems are also used on refrigerated vessels [Grasso 2003b]. Today, only a few vessels with an integrated refrigeration system are built.

Germanischer Lloyd (a German ship classification company) has issued special guidelines on ammonia. Compliance with these safety requirements makes ammonia-based refrigeration systems more expensive [Grasso 2003b]. In factory ships with large refrigeration capacities the higher capital costs can compensate for the lower operating costs.

Otherwise there are only a small number of vessels with ammonia refrigeration systems. One example is the Greenpeace ship Esperanza. One of the world’s largest vessels for shock-freezing of fish has a cascade refrigeration system using ammonia and CO₂. Another example of the use of natural refrigerants in ships is a special crude oil transport and processing vessel with a 5 MW refrigeration system using propane as refrigerant [eurammon 2007].

In the German label UZ 110 “Environment-conscious ship operation” [UZ 110] the eco-label jury laid down requirements for environmentally sound ship operation. One of the requirements relates to the refrigerants used: they must not possess any ozone depletion potential. This rules out the use of CFCs and HCFCs. Since HFCs cannot be replaced by environmentally sounder substances in all applications in ships, HFCs are permitted as refrigerants, but must not exceed a GWP₁₀₀ value of 1,650. The eco-label UZ 141 “Eco-friendly ship design” has adopted this requirement [UZ 141]. UZ 110 has been under revision since 2009 and will in future lay down the use of the refrigerants ammonia and/or CO₂ as an optional measure.

Conclusions Road vehicles

Prototypes of CO2 transport refrigeration systems have already been developed for deep-frozen and chilled product distribution and have passed practical tests. Optimisation with regard to energy efficiency is desirable. The use of CO2 systems in transport refrigeration (refrigerated vehicles, especially chilled product distribution) also depends on developments in the car air-conditioning sector (see Chapter 3.3.7.1). If a positive trend towards CO2 for cars emerges, the development of efficient, inexpensive CO2-based system will be possible for refrigerated vehicles as well in the medium to long-term.

Other systems on the basis of natural refrigerants have been tested. When using flammable natural refrigerants in particular there are safety issues to consider and limiting standards to check.

CO2 as a refrigerant for consumption in chilled product distribution is used primarily in Sweden. A comprehensive life-cycle assessment is not available.

In the introductory phase the new technologies involve additional costs. Supporting measures are therefore needed for their introduction to the market.

Refrigerated containers

CO2 has been tested as a refrigerant for refrigerated containers. There are still technical and logistical problems to be solved, and development work is still in progress. If CO2 as a refrigerant is introduced on a widespread basis in other sectors, it will be possible to simplify the logistical issues in this sector. This could give a boost to CO2 for container refrigeration. Since refrigerated containers are transported worldwide and are now only made in China, the use of CO2 as refrigerant will have to be promoted and agreed at international level.

Ships

In factory ships and refrigerated vessels, refrigeration using ammonia and/or ammonia/CO2 systems is no problem.

Other vessels which only require smaller refrigeration capacities, e.g. for cooling provisions, use HFCs as refrigerants. The possibility of refrigeration using halogen-free refrigerants needs to be investigated on a case-by-case basis. There are already examples in which the use of HFCs has been dispensed with completely. Basically the possibilities do not differ from those in other fields of application. The special regulations for ship refrigeration systems need to be taken into account.

In future, operators using HFCs will be required to take measures to reduce emissions and should choose a refrigerant with a low global warming potential.