How to Calculate Refrigeration Load? And What Are the Issues?

2025-02-20

For the calculation of any refrigeration system, it is essential to understand the user's requirements first. Otherwise, everything is based on assumptions, and the possibility of the proposed solution being recognized by the user is very low. Even if the user doesn't understand and the preliminary plan can be used to cope with the situation at the moment, it will be difficult for the user to accept the system during the acceptance process in the future, or the user may find it very inconvenient to use.

User Opinion Form:
In addition to the above questions, further detailed questions include:

Usage season: Is it used throughout the year or only in a certain season?
Working hours: For example, does it start and stop automatically throughout the day, or does it stop during the day and start during the off - peak electricity price period at night?
What is the temperature accuracy requirement inside the cold storage?
What is the quantity and frequency of each stock - in?
Is there a specific requirement for the cooling time after stock - in?
Is the cold storage frequently loaded and unloaded?
Are there people working in the cold storage for a long time?
Are there any other electrical or heat - generating devices?
What is the ambient temperature on each side of the cold storage, especially outside the cold - storage door?
What are the form, structure, and specific material thickness of the insulation layer?

Of course, the more specific the questions are, the more professional you seem, and the less likely there will be variables in the future. If the customer doesn't understand, you can give your opinions to the user. It is best to get the user's approval on the main issues before making a plan.

The above refrigeration calculation manual is based on my personal experience. Everyone's may not be exactly the same, but the general content should be similar.

First, determine the thickness of the insulation layer. Usually, my experience is as follows:
Spaces with a temperature above 20°C may not need an insulation layer. For spaces with a temperature of 10 - 20°C, the insulation layer is 50mm; for - 5 - 10°C spaces, it is 100mm; for spaces around - 18°C, it is 150mm; for spaces around - 35°C, it is 200mm; for spaces around - 60°C, it is 300 - 400mm. The above ambient temperatures outside the cold storage are based on normal temperatures. If it is a cold storage within a cold storage or an underground cold storage, the thickness of the insulation layer can be a bit smaller.
Secondly, the energy consumption of goods: Under the condition that the stock - in quantity and cooling time are known, the main difficulty lies in the enthalpy difference of the goods. If the enthalpy difference of some goods cannot be obtained, goods with similar water content can be used as substitutes.
Heat infiltration through the insulation layer:
After the calculation, usually, a margin of one - fold should be considered in the result. This is mainly to take into account the internal structure of the cold - storage panels. If there are fewer cold bridges, the margin can be smaller; if there are more severe cold bridges, the margin should be larger. (Cold bridges are mainly generated by structural components inside the insulation layer, joints of cold - storage panels, hangers, brackets, and all heat - conducting bodies connecting the inside and outside of the cold storage.)
Operational heat: including heat generated by ventilation, electrical equipment, and the human body:
The heat generated by ventilation is related to the size of the cold - storage volume. The larger the cold - storage volume, the fewer the ventilation times; the smaller the cold - storage volume, the more the ventilation times.
Note:
The ventilation times refer to completely replacing the air inside the cold storage with fresh air each time, not just opening the door once.

The heat from lighting refers to the average working time of all electrical equipment in the cold storage throughout the day.

Description of refrigeration operating conditions:
For most cold storages, the cooling of an empty cold storage only occurs once when the new cold storage is first put into use, and it hardly occurs again later. Therefore, it may not be a key consideration in the design, but it has some reference value during commissioning.
The cooling after loading usually has the largest load for all cold storages. In most cases, this is used as the basis for selecting the compressor.
The maintenance condition means that the temperature inside the cold storage reaches the required level, and there is no in - and - out of goods. For many cold storages, this is also a normal state. Although it has little impact on the selection of the compressor type, when choosing the number of compressors, the frequency of compressor start - stop needs to be considered. If the number of units is small during selection, and the compressor power is large, when the refrigeration system operates at a low load for a long time, it is easy to cause the compressor to start and stop frequently. If the number of units is too large during selection, the control and production difficulties will increase, and the cost will be relatively high.