Refrigeration Requirements for Food Storage

Generally the product load consists of three separate components. a) Sensible- This is the amount of heat to be removed to bring the product to storage temp. It depends upon the specific heat of the product.b) Latent- this is the amount of heat to be removed to freeze the product. It depends upon the latent heat of fusion c) respiration- fresh fruits and vegetables release heat of respiration. Your case this may not be applicable. When product load is calculated on per hour basis then a correction factor for taking into account pull-down time other than 24 hours to be applied as( 24 hrs/pull-down time). Add 10 % as safety factor to decide the total kW load.

Regards.

Dr.Ram

If it were simply water and external influences were ignored, energy would need to be removed at the rate of 568W. External influences, such as the environment that the butter is stored in, will increase this figure, and as these are not described yet, the increase cannot yet be quantified.

The heat load is equal to Q= m c deltaT, m=mass of the product in lbs, c= its specific heat in Btu/lb-deg F, delta T= temperature difference between initial and final temp in deg F. units will cancel out and you will have net Btu.

Specific heat of butter are 0.3 and .024 Btu/lbdegF above and below freezing respectively. Sum up the two Q (above and below freezing), you will have 74,844 Btu, and 12,000 btu= 1TR, or around 6.237 TR. specific heat value from www.engineeringtoolbox.com/specific-heat-capacity-food-d

Its not yet over , your full down time is too long, 72 hrs. divide Q with your full down time since this is computed in one hour load. very small.

you still have to consider air exchange, lighting, occupancy and heat migration load of panels. There still a math here, in my practise, I add another 30% of the total load. Still pretty small, for an industrial refrigeration.

Hope this lights your way.

dear sir

greetings and good day

thanx for your reply

i think considering the time factor and utilization of only 50% of cold store volume and packaging of butter carton,i assume the referegeration tonnage requirement for 1 mt of butter shall be 62.37TR

pls correct me and i once again thank you

i still invite comments of the people

sps sawhney

09915742601

6.237 TR (not 62.37 TR) if you full down it in one hour. This is around 22 KW of net evaporating capacity at -20 deg C. (also add 30% here)This around 15 HP compressor at 32 deg C condensing)

Your full down time is 72 hrs. 6.237 TR divide 72 hrs. So you have 0.086625 TR add 30% on others load. this will be 0.1126 TR, that why I said its pretty small because you have three days of full down period. A chest freezer will do the job, just compensate for the volume.

Hope this help.

dear sir

it means if i and 30% it works out to be 8.1tr per tonne of butter and if i assume the power cost at rs4.5/unit,it works out to be rs36.48/mt of butter freezing

is it ok

kindly advise

sps sawhney

TR is not a power consumption, it is express as evaporating capacity with the variables in it. your KW rating is 11.25 KW (15 Hp) + 30% in w/c around 15 KW.in case of one hour blast freezing.

These are theoretical, actual situation may vary on your given condition.

Ok.

And of course the latent heat during the freezing of the water on your evaporators!

This will slow the rate of pull down due to the inefficiency of the evaporators because of ice build up.

You may need 2 x evaps to maintain the pull-down,one in operation whilst one in defrost.Does depend very much on the amount of air within the room of course.

A neat trick is to dehumidify to the dew point using a dessicant system,with de-hum air curtain.That way you only need 1 x evaporator,oh sweet joy.

Regarding the pull down time factor, LMTD does come into play,and if using a d/x system the compressor efficiency will vary as the system approaches the desired temp.I recommend sizing the system at the Tr calculated,at the evaporating temp needed to maintain the end temp.

dear sir

thanx for your reply

Why was the latent heat of fusion (freezing) ignored?

At 23.04 Btu / pound it is about twice the sensible heat.