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Evaluation of the possibilities of substituting potent greenhouse gases (HFCs, PFCs and SF₆)

Appendix B:
Commercial refrigeration systems

This appendix is written in co-operation with Kim Gardø Christensen, MSc in Engineering, of the Danish Technological Institute.

Commercial refrigeration systems are systems used for refrigeration in supermarkets, specialty shops, hotels and restaurants, i.e. in the area of trade and service, agriculture and market garden.

According to the statement of the Danish Environmental Protection Agency /1/, 319 tons of HFC refrigerant was used in 1999 in "Commercial stationary refrigeration and air-conditioning systems".

Consumption of HFC refrigerant in "Commercial stationary refrigeration and air-conditioning systems" in 1999. The figures are taken from the annual statement of the Danish Environmental Protection Agency carried out by COWI Consult.

The commercial area of refrigeration is the most diverse area within the refrigeration industry. A large number of companies sell and install refrigeration systems. The refrigeration systems are often constructed of purchased standard component. In some commercial refrigeration systems (i.e. supermarkets), long pipelines have been used and the leakage rate has previously been very high (of the order of 20-25% of the refrigerant charge per year). In recent years, the association AKB (Authorised Refrigeration Installers Association), Selskabet for Køleteknik and the Danish Association of Refrigeration have done much to reduce leakages and in this way reduce the emission. This implies that the emission of new supermarket refrigeration systems is reduced to approx. 10% per year.

The commercial refrigeration systems constitute a very high economic value, as there are many of them. At the same time, there is a vast number of different refrigeration systems and an analysis of the different types and status for alternative systems not using HFC refrigerants is therefore carried out in this part.

The section is divided into two subsections in which the first deals with types of systems as these are divided into four categories: Plug-in units, split units, chillers and machinery, while the second deals with applications divided into supermarkets, specialty shops, kiosks, hotels, restaurants and agriculture. Finally, a total evaluation of the commercial area of refrigeration is made.

B.1 Types of systems

Plug-in

Plug-in refrigeration systems are primarily used in the area of trade and service. It is small units such as bottle coolers and ice cream freezers, and larger units such as small refrigeration cabinets and various single-purpose machines.

The plug-in appliances can be divided into large and small systems. The small plug-in units can use hydrocarbons, while the large are problematic because the charges with hydrocarbons will exceed 200-300 grams. The large plug-in refrigeration systems (above approx. 2 kW in cooling capacity) are used in many different places in various respects. Many supermarkets still use many large plug-in appliances/cabinets in the form of refrigeration cabinets and display cabinets with own compressor and condenser. These cabinets are also used to a great extent in the rest of the retail trade, in kiosks and in service stations as well as in the hotel and restaurant industry. The large plug-in cabinets are often cheap, prefabricated units, which are easy to install and cheap to service. Moreover, these cabinets have the advantage compared with remote refrigeration cabinets that they can easily be moved to other locations in the shop. This flexibility is prioritised highly in some shops. In addition to the types of systems mentioned, there are a number of single-purpose machines, i.e. multicoolers for soft drinks and beer in bars and restaurants, ice machines e.g. in fish monger's shops and other types, in which capacities and charges are so large that it cannot be justified immediately to use hydrocarbons as refrigerant. It is assessed that it will be necessary to use indirect refrigeration in many of the applications where plug-in equipment has been used previously.

Split units

The split units cover a wide range of applications. The units consist of two units. The first unit: the evaporator is placed in the cold storage or in the room where the air-conditioning is desired. The second unit: the compressor and condenser part (in total called the condensation unit) is often placed outdoors or in basements. This part emits heat to the surroundings. The split units are often prefabricated (primarily for air-conditioning) where the refrigerant has already been charged at delivery. When the two units are connected, a capsule is broken and the refrigerant can flow from the condensation part to the evaporation part. This type of unit is supplied by e.g. Panasonic, Toshiba, Carrier and Daikin (primarily for air-conditioning). The split units can also be made by installing a condensation unit from e.g. Danfoss, to which an evaporation surface can be connected, if desired.

The split units are used widely within the retail trade and the hotel and restaurant industry. They are used for cold storages, air-conditioning and remote refrigeration cabinets. The use of the split units is advantageous compared with the plug-in systems as the condenser heat is not emitted to the room itself and noise problems are avoided.

The split units have one problem with regard to conversion to other refrigerants. The use of hydrocarbons for air-conditioning or in connection with appliances/cabinets placed in public places will hardly be allowed unless the charge is limited. CO₂ is an option, but the system will probably be considerably more expensive in the small units i.a. due to the high pressures and thus the increased requirements for components. Furthermore, it will be difficult with CO₂ to compete with regard to energy with optimised, conventional HFC units. However, hydrocarbons could often be used e.g. by using indirect refrigeration, but it has to be kept in mind that the equipment is small especially in connection with refrigeration in specialty shops, kiosks, service stations and restaurants. In this field, it is hard to find competitive alternatives. As to price, small indirect units will be considerable more expensive than the conventional split units and the energy consumption will undoubtedly also be higher.

Chillers

Chillers (or liquid coolers) are compact refrigeration systems, which cool a liquid, e.g. water for process refrigeration or air-conditioning in large buildings, etc. In this area, there are no problems as the equipment by definition is indirect and hydrocarbons therefore can be used with certain modifications of the equipment. The chiller systems are often large prefabricated systems with capacities above 20 kW. Moreover, some equipment using hydrocarbons as refrigerant is already available on the market today. Prefabricated chillers for capacities below 20 kW cooling capacity are not yet available with natural refrigerants.

Compressor systems (Machinery)

Compressor systems are used widely in medium-sized and large supermarkets. Moreover, compressor systems are used in large cold storages and in refrigeration systems within the agriculture. What characterises the systems is that a number of remote cabinets/evaporators are parallel coupled on the evaporator side, while the condenser also is remote coupled. The compressor system, which typically has cooling capacities above 15-20 kW, is placed in a machine room, while the condenser is placed outdoors e.g. on the roof of the building.

In Denmark and especially in Sweden, several compressor systems have been built in connection with supermarkets using hydrocarbons as primary refrigerant. In the shop, CO₂ is used as refrigerant on the freezing side, while conventional brines are used as secondary refrigerant on the cooling side.

Figure 1:
Outline of the plant

The figure shows a schematic outline of the semi-indirect refrigeration system with propane and CO₂ in the demonstration system in LokalBrugsen in Odense. /2/.

B.2. Applications

Approx. 15% of the total Danish energy consumption is used for refrigeration and freezing equipment. DEFU has calculated the energy consumption for refrigeration trades and households in 1993 /3/.

Energy consumption for refrigiration
Energy consumption for refrigeration in Denmark /3/.

As it appears, the energy consumption is primarily dominated by the private households which make up 48% (1900 GWh/year). For the rest of the trades, the individual consumption stems from few dominating consumption groups /4/:

Commercial refrigeration consists of the area of trade and service, agriculture and market gardening.

Energy consumption and refrigerant charge in trade and service

The total annual energy consumption for refrigeration and air-conditioning within trade and service is estimated to be approx. 870 GWh per year, of which approx. 240 GWh is used for air-conditioning per year. Of the 630 GWh per year used for refrigeration purposes, 450 GWh per year is used for supermarket refrigeration.

Energy consumption for cooling in Trade and Service [GWh/yr]. Total: 630 GWH/yr
The figure shows the energy consumption for four different categories within the area of trade and services.

In the following the area of trade and service is divided into four categories:

Supermarkets and grocer's shops: This area covers the area traditionally understood as daily retail shops from small to large systems.

Local shops: This area covers service stations and kiosks

Other grocer's shops: This area covers all specialty shops like retail butcher, cheesemonger's shops, etc.

Hotel and restaurant: This area covers hotels, motels, inns, restaurants, coffee shops, canteens and catering.

Supermarkets and grocer's shops

Supermarkets are the largest consumers of refrigeration equipment within trade and service. In Denmark there are approx. 2,200 supermarkets, where food is displayed in both refrigeration and freezing display cabinets. The major part of refrigeration and freezing equipment in supermarkets has been connected to remote systems (machinery), however plug-in units are very common. In addition, there are approx. 2000 small grocer's shops. The refrigeration systems are primarily designed as compressor systems/remote systems or in the small shops as a split system.

Supermarkets range from very small to very big shops. The figure below shows the division of load on refrigeration and freezing respectively for different supermarkets.

Cooling capacities and refrigerant charges for different sizes of supermarkets.

The total charge for groceries is approx. 350-400 tons.

The systems are typically large. It is demonstrated both in Denmark and in other European countries how systems with natural refrigerants can be used.

Alternative technology:

Compressor system: The systems can be used either indirect or semi-indirect with hydrocarbons and CO₂

Price: +10% for the large systems /+15% for the small systems.

Energy consumption: ± 5%

Split-system: The systems will typically be indirect using hydrocarbons and traditional brine (development is required).

Price: +20%

Energy consumption: +10%

Kiosks and service stations

It is estimated that approx. 1700 service stations and 900 kiosk are available in Denmark /5/. Plug-in equipment and split equipment are mainly used in these shops. The entire refrigeration energy consumption is approx. 45 GWh per year. The number of systems changes with the size of the shop. It is estimated that 4-8 systems have been installed in the shop, where the main part is smaller plug-in systems, which can be delivered with hydrocarbons as refrigerant. The refrigerant charge is approx. 10 tons.

Alternative technology:

Compressor systems: The systems can be either indirect or semi-indirect using hydrocarbons and CO₂ (development is required).

Price: +20% for these systems (relatively small, which explains the high additional costs).

Energy consumption: ± 5%

Split system: The systems will typically be indirect systems with hydrocarbons and a traditional brine (development is required).

Price: +20%

Energy consumption: +10%

Plug-in systems: The small plug-in systems are already available on the market, but there is no immediate alternative to large systems (development is required). It will probably be necessary to replace the large plug-in systems with indirect refrigeration.

Price: ± 5% for the small plug-in systems/+30% for the large systems (indirect refrigeration).

Energy consumption: -5% for the small plug-in systems/+15% for the large ones (indirect refrigeration)

Other food shops/specialty shops

This area covers all specialty shops like butchers, fish- and cheesemonger's shops, bakeries and others. The shops are very differently equipped because special equipment adapted to the purpose of the shop has been installed.

The energy consumption for this area is approx. 65 GWh/year and the total refrigerant charge is estimated to approx. 20 tons.

The systems are primarily plug-in or split systems. Some of the equipment is purpose-made, i.e. flake ice machinery at fishmonger's shops.

Alternative technology:

Compressor system/parallel system: The systems can be either indirect or semi-indirect using hydrocarbons and CO₂ (development is required).

Price: +20% for these rather small systems

Energy consumption: ± 5%

Split system: The systems will typically be indirect using hydrocarbons and a conventional brine (development is required).

Price: +20%

Energy consumption: +10%

Plug-in: The small plug-in systems are already available on the market, but no alternatives are available yet as far as large systems are concerned (development is required). It will probably be necessary to replace the large plug-in systems by indirect refrigeration. Some of the special equipment will be very difficult to convert.

Price: ± 5% for the small plug-in/+30% for the large system (indirect).

Energy consumption: -5% for the small plug-in/+15% for the large systems (indirect)

Hotels and restaurants

Except from the small units, i.e. coffee shops, cafeterias and grill bars, some restaurants are equipped with cold storage for animal products, cooling storage for vegetables and a smaller freezing area. In addition, there is a varying number of refrigeration and freezing cabinets in the kitchen area, including cooling cabinets, ice cube machinery, draught beer coolers and bottle coolers.

Typically, these systems are separate plug-in or split units (4-6), and a central refrigeration system is rarely used.

Number of hotels, restaurants, canteens etc.

The energy consumption for this part is approx. 70 GWh, whereas the refrigerant charge is estimated to 40 tons.

Alternative technology:

Compressor system/parallel systems: The systems can be indirect or semi-indirect using hydrocarbons and CO₂ (development is required).

Price: +20% for these rather small systems.

Energy consumption: ± 5%

Split units: The systems will typically be indirect using hydrocarbons and a conventional brine (development is required).

Price: +20%

Energy consumption: +10%

Plug-in systems: The small plug-in systems are already on the market, but no alternative is immediately available for larger systems (development is required). It will probably be necessary to replace the large plug-in systems with indirect refrigeration. Conversion of some of the purpose-made equipment will be difficult.

Price: ± 5% for small plug-in systems/+30% for the large systems (indirect refrigeration)

Energy consumption: -5% for the small plug-in systems/+15% for the large systems (indirect refrigeration).

Agriculture

The primary energy consumption for refrigeration in the agriculture is based on refrigeration of milk tanks used for milking and cold storages for crops (root crop, fruit and vegetables). The total refrigeration energy consumption is approx. 66 GWh per year.

Typically, a split system including a condensing unit placed on the roof or behind the building is used.

Alternative technology:

Split systems (indirect): The systems are typically indirect systems using hydrocarbons and a conventional brine (development is required).

Price: +20%

Energy consumption: +10%

Split systems (direct): Hydrocarbons might in the future be accepted in small amounts may be accepted under category B according to EN-378, if sufficient safety consideration has been taken. Category B is an area where no public access is allowed, only the permanent staff /7/. The systems will thus be cheaper and more energy-efficient than an indirect system. Because handling of ammonia is known by agriculture already, use of hydrocarbons may not represent any obstacle. (Development is required).

Price: +10%

Energy consumption: +0%

B.3 Estimation

As far as the small systems are concerned (the large plug-in refrigeration systems including split and condensing units), the main problems are concentrated on replacement of HFCs. In connection with small air-conditioning systems in buildings with public access, the use of hydrocarbons and ammonia is hardly possible. Use of CO₂ is possible, but due to high pressures and a bad thermodynamic circuit process (in the relevant temperature area), further development work for introduction of this refrigerant is required. Furthermore, it is a major question whether direct use of hydrocarbons will be common in connection with refrigeration/freezing areas. The staff will belong to Category B, however it is not quite clear what kind of further measurements are required. This matter should be handled in such a way that a number of rules for this application is made possible. Alternatively, direct or semi-direct systems can be used, which are reasonably competitive primarily on the larger systems with refrigeration performances above 20 kW.

Energy consumption, refrigerant leakage and greenhouse effect

A refrigeration system using HFC refrigerants contributes to the green house effect in two ways: the indirect contribution from the production of the electricity, which is used for operating the system. In Denmark, this amounts to approx. 0.78 kg CO₂ per kWh. In addition, the direct contribution from the emission of refrigerant could be mentioned.

The sum of the two contributions makes the total. In Denmark and abroad, calculations of the entire contribution from many different refrigeration systems have been made.

If systems using natural refrigerants which use less energy than similar HFC systems can be used, the matter is clear: Systems with natural refrigerants are the most environmentally friendly solution when it comes to the greenhouse effect.

Those places, where direct refrigeration with natural refrigerants or semi-direct refrigeration can be used, the energy consumption will in general not be higher than of similar HFC systems. These systems will therefore be advantageous seen from an environmental point of view.

Indirect refrigeration with a brine (e.g. a water/glycol mixture) will generate a loss because of the necessary heat exchange between the primary and the secondary refrigerant. In that way, the energy consumption will be a little higher because of the demand for lower evaporating temperatures. This results in slightly higher energy consumption for the compressor. In addition, pumping efforts for the secondary refrigeration system should be mentioned. On the other hand, there will be less pressure losses in the suction valve at the direct system. In total, direct refrigeration will cause a slightly higher energy consumption in the size of 10%.

Concerning large integrated systems (like those in supermarkets), the entire contribution (CO₂ from electricity production and emission of refrigerant) to the greenhouse effect will be less for these systems (cf. calculation in enclosure 2) and other similar calculations (cf. enclosure 1). The reason for this is the large leakage and the large charge in e.g. supermarket systems.

When speaking about small and more compact systems (below 20 kW cooling capacity and approx. 10 kg. charge), the situation is different, as the energy consumption of indirect refrigeration still is somewhat higher (approx. 10%). However, the leakage rate of these systems is smaller than that of larger and more complicated systems. Consequently, it is not clear whether the use of natural refrigerants used with indirect refrigeration will be more environmentally friendly as these small commercial refrigeration systems are concerned.

A comparison between direct refrigeration systems using R404A and indirect refrigeration with propane/brine can be seen from enclosures 2 and 3. The comparison is based on a small compact refrigeration system (10 kW for refrigeration and 5 kg of charge).

According to Enclosure 2, a leakage rate of 10 % is preconditioned; however, the propane system presents the smallest contribution to the greenhouse effect.

According to enclosure 3, the leakage rate has changed to 5% per year, and the result is in favour of the HFC system.

It appears that the use of small compact refrigeration systems enables a minimisation of the leakage rates by 5 % p.a. In Denmark, the total emission from small compact HFC systems with a cooling capacity below 20 kW and a charge below 10 kg with direct refrigeration is estimated to be below the emission from a similar refrigeration system with indirect refrigeration.

References to Appendix B:

Enclosure 1:
Comparison of indirect and direct refrigeration used in medium-sized refrigeration systems (50 kW). The simulation model shows a large integrated refrigeration system with relatively high charg and leakage rate (50 kg of R404A and 10% per year).

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Enclosure 2:
Comparison between a direct system using R404A and an indirect system using propane. The refrigeration capacity of the system is 10 kW and has a refrigerant charge of 5 kg and a leakage rate of 10 % per year.

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Enclosure 3:
Comparison between a direct system using R404A and an indirect system using propane. The system is small and compact with a capacity of 10 kW, a refrigerant charge of 5 kg and a leakage rate of 5%.

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