Calculate Required Refrigeration Consumption Based On Food Physical Property

2017/10/31

The method is used for calculating the required refrigeration consumption in IQF freezing, the result can be a reference value for the compressor selection. The formula involves the parameters of food physical property: freezing point, specific heat and latent heat.

We hypothesize the food temperature before freezing is t1, final temperature is t2, freezing point is t0, specific heat up to freezing point is h1, below freezing point is h2, latent heat is h0. Food mass for freezing is m, wastage rate of energy in insulation and processing is p. Required refrigeration consumption is r

The formula is: r=((t1-t0)*h1+(t0-t2)*h2+h0)*m/(1-p)

For example, 1 ton corn for freezing, the initial temperature is 15℃, final temperature is -18℃, wastage rate is 20%, freezing point of corn is -0.8℃, specific heat up to freezing point is 0.79 kcal/kg℃, below freezing point is 0.42 kcal/kg℃, latent heat is 59 kcal/kg. So if we need to freeze one ton corn, the required refrigeration consumption is

R = ((15-(-0.8))*0.79+(-0.8-(-18))*0.42+59)*1000/(1-20%) = 89333.55kcal = 103kw/h

If the freezing capacity is 1 ton/h, the capacity of compressor should be bigger than 103kw, if the capacity is 500kg/h(IQF freezer) or 1ton/2hours(blast freezer), the compressor can supply 52 kw refrigeration output at least. Then select the right model of compressor according to the working condition. Use the formula can evaluate the refrigeration accurately and scientifically. Of course the value is also for reference, most of the experienced engineers will amend the result based on their experience.

Here are the physical property of some foods which is usual in freezing:

Carrot--freezing point:-1.7℃, specific heat up to freezing point: 0.87 kcal/kg℃, below freezing point: 0.45 kcal/kg℃, latent heat:66 kcal/kg

Fresh fish--freezing point:-2℃, specific heat up to freezing point: 0.82 kcal/kg℃, below freezing point: 0.43 kcal/kg℃, latent heat:58 kcal/kg

potato--freezing point:-1.8℃, specific heat up to freezing point: 0.82 kcal/kg℃, below freezing point: 0.43 kcal/kg℃, latent heat:62 kcal/kg

Poultry--freezing point:-1.7℃, specific heat up to freezing point: 0.80 kcal/kg℃, below freezing point: 0.43 kcal/kg℃, latent heat:59 kcal/kg

Cabbage--freezing point:-0.5℃, specific heat up to freezing point: 0.93 kcal/kg℃, below freezing point: 0.47 kcal/kg℃, latent heat:73 kcal/kg

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