Planning of refrigeration engineering

1. Basics of planning a refrigerating plant

An important element in planning a canteen kitchen is the design of the refrigerating plants and appropriate cold-storage rooms.

The basics of all cyrogenic planning are mainly plant-specific design data and experience. In many building service installations they exist in engineering standards and guidelines as generally accepted codes of practice. Regrettably, so far no such rules have been drawn up for refrigerating plants in canteen kitchens.

For some time now, refrigeration has no longer been used solely for cooling storage rooms: in fact, in modern cooking processes product quality often depends on the systematic and controlled cooling of foodstuffs. At the same time, it is a fact that in comparison with unprocessed, raw products the amount of bought-in, pre-prepared products or foodstuffs is constantly increasing. In the meantime, because of changes in environmental legislation and the requirement to use new coolants, the demands made on the performance and capacity of refrigerating plants have become so diversified that a very extensive range of refrigerating components and systems is now available to deal with refrigerating issues.

When planning refrigeration all of the objectives and requirements of the kitchen user must be systematically recorded and analyzed. Investment costs and operating costs must also be recorded at an early stage to allow an economically-priced and sensible design concept to be made. Normally, planning decisions are primarily taken according to how “cost-efficient” they are whereby cost -efficient is generally understood to mean a minimum in investment costs and/or in operating costs and on this basis, the overall cost.


2. Analysis of refrigerating utilization

In order to set up a requirements profile, an analysis of the utilization of the refrigeration is carried out taking the type and size of the cold-storage room into consideration. There is currently no defined methodology for planning a refrigerating plant in a large-scale canteen kitchen. At first glance, it would appear difficult to determine the differing requirements regarding refrigeration engineering and its associated interfaces to other services such as electrical engineering, waste water systems and control equipment. And that is the reason why even experienced planners make mistakes because they have failed to consider one of the requirements. We must therefore try to analyze the requirements made of the refrigeration plant methodically..

A requirements list is drawn up, whereby the requirements are determined according to the size and type of kitchen. An exact requirements list is of elementary importance as it forms the basis for all other planning work. All of the cold consumers/refrigerating units and utilization must be noted. In ideal cases, there will be a layout plan of the kitchen and the relevant output areas available to form the basis of the requirements list. At least, the room datasheets and installation book should have been already prepared. If a numerical positioning of individual cold consumers has been carried out, these must also be taken into consideration by the planner.

Practice has shown that it is a good idea to divide the cold consumers into two groups – one group in which the cold-storage rooms - in this case, deep-freeze units and normal cold-storage rooms are registered- and another group with all of the other cold consumers such as refrigerating units in output areas, beverage coolers, shock-coolers or similar. Refrigerating units equipped with integrated aggregates (built-in cooling) are also to be included in this group. The planner can only determine the size of the plant on the basis of his own experience and not on the basis of specific operating figures, as these would certainly lead to inexact and faulty results.

To determine the level of refrigeration required, our planners calculate the refrigerating capacity in a cold-storage room or a deep-freeze room on the basis of the requirements list which has been compiled.


3. The function of a refrigerating plant

Large-scale canteen kitchens are almost all equipped with a compression refrigeration system. Exceptions are particularly low-noise absorption systems in noise-sensitive areas – especially in beverage coolers in conference zones. Absorber refrigerators play only a minor role in planning refrigerating systems for canteen kitchens.

A compression refrigeration system consists of four main parts – compressor, condenser, butterfly valve (expansion valve) and evaporator. The components are connected by tubing. The closed circuit is filled with a low-boiling substance, the coolant. When the compressor is placed into operation, it sucks in coolant vapour from the evaporator. The heat required to evaporate the coolant is extracted from the air around the evaporator and effects cooling. The heat led into the coolant in the evaporator is then discharged to the atmosphere at the condenser.


4. Choice of coolant

Problems concerning the ozone layer and the greenhouse effect have led to the refrigeration sector in implementing decisive changes which will most certainly be followed by further measures especially regarding the vast range of industrial refrigeration and air-conditioning systems. Up to a few years ago, refrigerating systems in canteen kitchens were mainly operated using coolants R12, R22 and R 502 (all from the HCFC and HHFC group).

These substances, with the exception of R22, are no longer permitted in industrial countries. Germany and some of the Scandinavian countries chose to abandon R22 and the remaining EU countries began in to gradually phase out its use in January 2001. Substitute coolants mainly used in industrial refrigeration today are R134, R404a and R407c (HHFC group). However, since March 2001, Denmark has introduced a draft law regarding the ban on HHFC. The remaining alternatives are halon-free natural coolants such as R717 (ammonia) and various hydrocarbons such as R290 (propane), R1270 (propylene) and R 744 (carbon dioxide). In the recent past, more professional system solutions have been increasingly deployed in the use of ammonia.


5. Choice of refrigerating system

First a differentation must be made between decentralized and centralized frigorific units. Most of the kitchen refrigeration systems made today are equipped with a centralized frigorific unit, whilst smaller refrigerating units or plants with fewer refrigerating units and/or cold-storage rooms are cooled by using single aggregates i.e. decentralized.

Regarding the groups “decentralized” and “centralized” a difference is made between air-cooled single aggregates and “Stopfer” aggregates in decentralized systems, and split units, networks and dual-circuit systems in centralized systems.


6. Control and instrumentation systems for refrigerating plants in canteen kitchens

The demands made on control and instrumentation engineering in the refrigerating sector are constantly rising. Mechanical room temperature control via thermostats has been replaced in most cases by electronic control systems. From a simple but extremely efficient compact controller for single refrigerating units and cold-storage rooms through to complex PLC systems in large-scale networks – numerous solutions are available. Modular systems allow any desired single function to be implemented.

Primarily, the issue here is controlling room temperature and refrigerating machines. Subordinate points are the maintenance of constant machine room temperature or the control of heat recovery processes. Apart from the few infinitely variable control processes, mainly two- and three-point controllers or simple time controls are used in refrigeration engineering. According to HACCP, room temperature in cold-storage rooms must be recorded and documented at regular intervals.

In line with VGB requirements, large deep-freeze rooms must be equipped with an emergency alarm. To ensure that no-one is locked inside a deep-freeze room the room must have an emergency push button. Pressing the button will trigger an alarm in a permanently manned control unit. The simplest way of controlling a refrigerating system is to use a switching cabinet. An individual switching cabinet (compact enclosure) is required to control an individual aggregate. If a plant consists of more than three cold-storage rooms, it is recommended to install a common switching cabinet for facility of inspections and cost reasons.


7. Assembly methods

A number of technical standards and guidelines apply to the assembly of refrigerating plants. The installation of pipelines and cable routes and the design of machine and engineering rooms are particularly important elements of planning.

In addition to the installation of pipelines, and the fixing and insulation of pipes, fire safety precautions must be taken. Wall and ceiling ducts can be sealed off using fire protection plugs over fire-resistant bricks, fire-retardant pillows or fire-resistant mortar and other fire-resistant coatings. The basis of use and processing is DIN 4102. Installation, fire-resistance time and operating medium must be taken into consideration when choosing appropriate fire protection measures. Fire resistance time and fire compartments are determined by the architects in agreement with the local fire-fighting forces. Compared with sealing off pipe ducts, time and costs for sealing cable ducts are higher. Appropriately fitting cuffs (on both sides of the duct) are adequate enough for pipes more than 32 mm in diameter but ducts for smaller pipes and cables must be packed with backfill material (e.g. mineral wool) and fire-resistant mastic or mortar. The location of fire compartments must be clarified prior to the commencement of assembly in order to avoid follow-up costs for fire protection measures.


8. Insulation/protection against cold

As possible uses for artificially generated refrigeration vary greatly, the field of activities for cold protection measures has become very extensive.

a) Reduction of loss of cold to maintain cold level and thus reduce energy costs
b) Maintenance of prescribed operating temperatures of heat carriers and refrigerating agents
c) Prevention of non-permissible high temperature fluctuation in building or construction components
d) Avoidance of formation of condensation, condensate; ingress of moisture into construction
    material layers, in particular layers of insulation
e) Compliance with operating prescriptions (surface temperatures, fire behavior, preventing freezing up of lines)
f)  Prevention of damage to buildings and goods in deep-freeze storage, avoidance of corrosion
    in refrigerating plants