In the early twentieth century, the world population was about 1500 million people, however just over a century the number of habitants increased to approximately 7000 million [1]. So as the human population increase affects the food production and conservation such as food storage. Food’s life can last longer if we put it in a low temperature. Turns out, not only building and people that needs cooling, but cooling is also needed to preserve meat, fish, ice cream, and others with the use of cold storage.

The main problem of the cold storage is the temperature of the food must be maintained 24 hours every day which will consume so much energy unlike the Air conditioner. So the solution is to minimize the cold loss by using better insulation, PhotoVoltaic integrated cooling system and using PCM(Phase Change Materials).

In many cases, though environmental conditions such as air humidity, temperature even air filters are taken into consideration[2]. Air filtration is applied, for instance, to clean and removes the sprores from the air. But The pressure drop across the filter should be low, in order to minimize operational cost. FYI the most efficient air filter technology has been made is HEPA (High Efficiency Particle Arresting) about 99.99% efficient [3].

Cold Storage

 

 

Definition

Cold storage is a room designed with a certain temperature conditions and is used to keep a wide variety of of products in order to maintain freshness and content of the material. [4]

Cold storages for fruits & vegetables in following three main categories as listed below and

is hereby, submitting technical standards etc in respect of the second one of them.

Categories of Cold Storage taken up for determining technical standards

(i) Cold storages for storage of fresh horticulture products which do not require pre-cooling

(ii) Multi-commodity Cold storages for short term and long term storage of fresh horticulture

products which require pre-cooling and varying storage requirements

(iii) Control Atmosphere (CA) Storages

Cold Storage Type – these type of cold stores are meant for storing different types fresh fruits and vegetables and other horticulture products which require pre-cooling or rapid room cooling to “seven-eighth-cooling” in a short time period of 4 hours to 24 hours depending on requirements in order to preserve there freshness, quality and self life. The 7/8 cooling time is the time needed for the product temperature to drop by “seveneighths” of the difference between the initial product temperature at the time of loading and the temperature of the cooling air circulating in the cold rooms

Commodity Storage Conditions- For designing a cold storage, product storage conditions must be

defined in terms of critical storage conditions of temperature, relative humidity, presence of CO 2 , ethylene, air circulation, light etc. In absence of research data for Indian conditions, it is recommended to adopt commodity storage conditions as prescribed by Commodity Storage Manual of WFLO. [5]

1. Temperature range: The temperature in the multi commodity cold store chambers should be kept within + 1ºC of the recommend temperature of the produce being stored. For storing at temperatures close to freezing point of the commodity, for increasing storage life, even a narrow range may be needed.
2. Humidity range: The humidity (RH) is again dependent on the produce storage requirements and may vary from 95% to 98% RH in case of fresh fruits and vegetables like grapes, kiwi fruit, carrots, cabbage etc and lower in the range of 65% – 75% RH in case of onion and garlic.
3. CO 2 level – not more than 4000 PPM during loading and 2000 PPM during holding. (Source – Industry) However if the cold store chambers is being used for Modified Atmosphere Storage for selective commodities like apples etc, the levels of CO 2 & O 2 should be maintained and regulated as recommended in the Commodity Storage Manual of WFLO.
4. Loading Rate- Generally the refrigeration system capacity is based on 4% to 5% loading rates of the total cold store capacity. The loading pattern is also a design consideration for sizing the storage chamber capacity for optimal utilization and performance. In case separate pre-cooling chambers are provided in the multi commodity storage facility, the load per batch is to be considered along-with initial and final desired product temperature, pull down rate etc while sizing the pre-cooling chambers and the refrigeration requirements.
5. Pre-cooling Time- 4-6 hours for pre-cooling to 7/8 th cooling time as recommended for majority of fresh fruits and vegetables. However, in case of fresh produce like carrots, apples etc meant for long/medium term storage, which are directly cooled and stored in the cold rooms, the cooling period, can be up-to 20 hrs per day and should meet the requirements specified in the commodity storage manuals.
6. Air Circulation- Multi Commodity stores should be design to provide an air flow of 170 CMH per metric ton of product, based on maximum amount of product that can be stored in each chamber. This is essential for rapid cooling of the produce. However the system should be designed to reduce air flow to 34 to 68 CMH per metric ton of product after the produce has reached the storage temperature. This is achieved by variable frequency drive and control system to automatically maintain the temperature variation within each chamber at less than + 1ºC through out the storage period. In case the fresh produce is pre-cooled in a separate pre-cooling chamber before loading and storage in the main cold store chambers, the air flow requirements may range from 67 CMH to 100 CMH.
7. Stacking – During room cooling, cold air from the coils flows past the produce stored in crates/ pallet racks/bins thereby removing the product heat. For best result the pallets/crates/ boxes/ bins should be stacked so that the moving air can contact all the container surfaces for adequate
8. Ventilation requirements in the cold store chambers- it may range between 2 to 6 air changes per day to maintain CO 2 less than 4000 ppm .
9. Lighting Condition- Dark
10. Application of Smart Fresh

 

Functions Of Cold Storage

• Protect Perishable Food: At room temperature perishable food items like fish, meat, and milk made products have a tendency to get decayed. Nowadays industries are using blast freezers for the storage of meat and fish. Before making a delivery to final consumers, logistics companies store perishable food items in refrigerators with high storage.
• Protect Perishable Nutrient Products: There are various nutrient items like cold blooded aquatic vertebrates and flesh of animals which turn into radioactive product when they are kept in building temperature. At present there are several cold storage warehouse logistics which provide blare freezers to the flesh of animals and cold blooded aquatic vertebrates products.
• Storage Of Dairy Products: Along with food items, dairy products also need proper care or cold storage. Storage equipment for dairy products needs control of temperature.
• Storage Of Food And Vegetables: Fruits and vegetables also need certain kind of cold storage but they do need to be frozen. They just need to be kept at a cool temperature.

 

 Types Of Cold Storage Facilities

Along with refrigerators, there are three kinds of storage facilities. These are – Combi refrigerator rooms, industrial cool rooms and modular refrigerator rooms. The combi refrigeration rooms carry a mix of various temperatures. This one suits the need for food requiring different temperatures. It has various units for proper control on temperature. The industrial cold storage rooms are made especially to store a large quantity of food. It is primarily made for industries and generally a vehicle is required to transport goods from a place to refrigerators. As a large quantity of food is stored in the storage room, so rooms are made with pallet racks and large doors. The modular refrigeration rooms are used at our homes and they are used for commercial purposes. The feature of customized refrigeration setting gives it an extra edge and that is one of the main reasons why companies prefer modular refrigerators.

 

Type of Cold Storage based on chills room temperature

• Chilled Room is the cooling chamber low temperature between 1 ~ 7 deg C. This room is used for storing food fresh food, such as vegetables, fruits, and store other materials with durability up to two months. Can be enabled to thawing room for the food industry by changing the temperature setting to 10 deg C. thawing Room used to raise the temperature of meat, poultry and fish that has been frozen to a temperature of 7 to 10 deg C, before the cooking process.
• Freezer Room temperature of the room is generally between -15 ° C ~ – 20 ° C, for warehouse storage of fish, meat, chicken, sausage, milk, cheese, potatoes and for all kinds of foodstuffs and other materials that require freezing temperatures.
• Blast Chiller is used for rapid cooling after the cooking process is completed with a target temperature of 1 ° C to 4 ° C.
• Blast Freezer is used for cooling rapidly frozen for processed food as well as for meat, fish or shrimp. Target temperature – 20 ° C ~ – 35 ° C.

The purpose used Blast Chiller and blast freezer is to avoid bacterial contamination. Maintaining the flavor of food is maintained. Avoid the reduction of water content. Maintaining levels of nutrients is maintained [6].

 

System

Chilled water is used in cooling processes for industrial and HVAC applications and is commonly produced by compression and/or absorption cycle machines, which respectively require electrical and thermal energy. The mainly used temperatures for chilled water required by the user are:

– Inlet 12°C

– Outlet 7°C

The right amount of chilled water at the desired temperature can also be obtained by means of cold storage systems. Cold storage systems operate in cyclical phases. They accumulate cold produced by chillers when users are low or off; stored cold is released when users demand exceeds production, or when chillers are turned off. Two storage technologies are commercially available: [7]

1. Cold storage through eutectic salts.
2. Cold storage through heat exchangers with ice formation

 

How to increase efficiency of cold storage system [8]

• Fine tune the floating suction pressure set point to optimize compressor efficiency.
• Clean the evaporator coil regularly to improve heat-transfer efficiency. Typical simple payback of several weeks.
• Install controls to change constant- speed evaporator fans to an on/off cycle to reduce evaporator fan run time.
• Install VFDs on evaporator fans in refrigerated spaces that have a variable refrigeration load. When combined with proper control systems, evaporator fan speed can be continually optimized for dynamic refrigeration loads. Typical simple payback of one to four years.
• Optimize the minimum-speed setting for evaporator fans using VFD control.
• Reduce the frequency and duration of timed defrost to the minimum required to ensure that the evaporator coil remains free of ice. Defrost cycles can be adjusted and controlled by season to reduce cycling during periods with lower ambient temperature.
• Add sensor control for evaporators as a replacement for timed-defrost systems. This improvement decreases the amount of heat added to the cold storage space to the minimum required to insure a properly defrosted evaporator coil. Typical simple payback of two to four years.
• Retrofit with high-efficiency evaporators. Using evaporators that extract heat from the refrigerated space using a minimum of fan energy improves energy efficiency in the whole refrigeration system.
• Use evaporators that defrost with water or hot gas instead of electric resistance defrost.
• Install evaporators with electronically commutated, EC, motors when evaporator fans have a fractional horsepower rating.
• Replace existing shaded-pole evaporator fan motors with EC motors to reduce energy use by up to 65 percent. Typical simple payback of one to three years.
• Implement temperature setback for unoccupied hours.
• Install programmable thermostats to reduce unnecessary energy use during unoccupied hours and maintain comfort when employees are present.
• Optimize set points to ensure that existing HVAC systems are operating as efficiently as possible.
• Retrofit existing HVAC systems with economizers to take advantage of free cooling from outdoor air.
• Tune up demand controlled ventilation to optimize outside air based on occupancy.
• Update HVAC system controls to optimize systems such as demand controlled ventilation and economizers. Several retrofit options are available to improve the efficiency and efficacy of existing systems.

 

Thermal Energy Storage

Thermal energy storage (TES) is a technology with a high potential for different thermal applications. It is well known that TES could be the most appropriate way and method to correct the gap between the demand and supply of energy and therefore it has become a very attractive technology. Thermal energy storage (TES) systems for both heat and cold are necessary for good performance of many industrial processes. Over 88 materials that can be used as PCM, and about 40 commercially available PCM have been listed. The Problems are in long term stability of the materials, such as corrosion, phase segregation, stability under extended cycling or subcooling [9].

PCM have been applied to increase thermal energy storage capacity of different systems. PCM works by release or store heat at its latent(phase change) temperature. It can release heat when change from liquid to solid phase. Also can store heat when change from solid to liquid phase.

In the cold application, we use the heat releasing PCM so the refrigerator can pull the heat from PCM and the foods. As the result  the PCM become cold (from liquid to solid phase). When the refrigerator shutted down, the cooled PCM will subtitute the refrigerator work by pulling the heat from the foods. For a certain time, the PCM temperature raises until become liquid again. This will reduces the refrigerator work and decreases the energy consumption.

 

Now that the refrigerators series is over, we will take a 2 week break. We will come back with 5 issues of Global Warming Special. 

 

REFERENCE

[1] B. Lu,  Short-term scheduling of battery in a grid-connected PV/battery system,  IEEE Trans. Power Syst., 20 (2) (2005), pp. 1053–1061

[2] Nunes, José et.al.Predictive tool of energy performance of cold storage in agrifood industries: The Portuguese case study, Energy Conversion and Management, Volume 88, (12) 2014, pp. 758–767

[3] Brincat, Jean-Pierre et.al. A review of the state-of-the-art in air filtration technologies as may be applied to cold storage warehouses, Trends in Food Science & Technology, Volume 50, (4) 2016, pp. 175–185

[4] http://www.faithteknika.com/2013/04/cold-storage.html

[5] Cold Chain Development Centre National Horticulture Board, Cold Storage For Fresh Horticulture Produce Requiring Pre-Cooling Before Storage)

[6] http://www.faithteknika.com/2013/04/cold-storage.html

[7] MGM Engineering & Contracting, COLD STORAGE SYSTEMS

[8] Energy Trust of Oregon, Cold Storage Facilities Energy Savings Guide

[9] Oró, E. et.al. Review on phase change materials (PCMs) for cold thermal energy storage applications, Applied Energy, Volume 99, (11) 2012, pp. 513–533