Cold rooms heat load calculation

Gents,

Accoding to ASHRAE 2006 Handbook - Refrigeration

the total load includes:
(1) transmission load, which is heat transferred into the refrigerated space through its surface;
(2) product load, which is heat removed from and produced byproducts brought into and kept in the refrigerated space;
(3) internal load, which is heat produced by internal sources (e.g., lights, electric motors, and people working in the space);
(4) infiltration air load, which is heat gain associated with air entering the refrigerated space;
(5) equipment-related load.

Where in these paragrafs a pull-down load is included?

Cheers,

The pull down load is decided based on the product stored /loaded and time require to cool the product to storage temperature.Suppose you consider less number of hours your load will be high.You may refer book Principles of refrigeration by Roy Dossat where it is clearly brought out with examples.

Thanks for your quick answer, Sridhar!

Is it correct if the pull down load is added to the product load calculation?
Will it be an over sizing of the equipment?

All the loads you need were given in the ASHRAE 2006-Refr.
What do you mean with pull down load? Give once a real-life example you think of.

rooibos as PETER says you don't need consider that.

Notice that on 24 hours basis you have a certain amount of energy to be taken out of the air so its own temperature can be maintained. This energy then must be removed on a certain period of time (14...16...18h).

One thing that it should be consider and ASHRAE doesnt' is the heat load for the latent heat of fusion of part of the water that is condensed on the coils. Part of this water is transformed on ice and to create ice you need remove more energy due to this.

Interesting subject. In the above post - there should be consideration for favorable ice formation as studies carried out at Massey University which I saw showed an increase in heat transfer due to increased surface area on the tube from the ice to a certain thickness and type of ice formed. Hence defrost will be an important factor.
When I was taught (many moons ago) the compressor should only run for 1/3 of the time - but technology has moved forward and the max load may only be there for a short time. The product may continue a heat load once down to temp such as heat of respiration. So the Evap design will also be an important part considering the above and coil bypass factors. Depending on the product - humidity and air flow velocity will be also taken into account. This is all for when the room is new and efficiency of components and the whole system needs to be considered as the min and max loads. I find Dossat is an excellent reference on this subject.

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Originally Posted by Tesla

Interesting subject. In the above post - there should be consideration for favorable ice formation as studies carried out at Massey University which I saw showed an increase in heat transfer due to increased surface area on the tube from the ice to a certain thickness and type of ice formed. Hence defrost will be an important factor.
When I was taught (many moons ago) the compressor should only run for 1/3 of the time - but technology has moved forward and the max load may only be there for a short time. The product may continue a heat load once down to temp such as heat of respiration. So the Evap design will also be an important part considering the above and coil bypass factors. Depending on the product - humidity and air flow velocity will be also taken into account. This is all for when the room is new and efficiency of components and the whole system needs to be considered as the min and max loads. I find Dossat is an excellent reference on this subject.

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Tesla,

Albeit of what you say we aren't talking about equipment design but rather calculate the several heat loads. If the ice formation is favorable until a certain degree of thickness the point is that formation of ice is a real heat load and ASHRAE doesn't mention it. Maybe they never think about that.

Hi Sandro
I think your right that we don't have good literature regarding favorable ice/ice formation nor efficient refrigerant fluid flow for that mater. In saying that, I am not familiar with ASHRAE. As far as heat load calcs I consider this part of the design process. You have pointed out that perhaps as an industry we have a lack of R and D in the refrigeration process and I would agree. The original post is referring to pull down load which is seldom considered as it is normally done in a seperate room on a commercial/industrial scale, then transported to the holding room, then the retailers cool room at close to the desired temp.This ice formation on the coil is a heat load and has an increase in most cases on the load from decreased heat transfer due to poor defrost control. Therefore the ice formation is a part of the pull down load.
As far as the pull down load - it is explained well in Dossat as a basic principle of the process.

"pull down load" was refered to as being the load imposed upon the plant in pulling the temperature down from a warm, ambient condition. For example, a new cold store when turned on for the first time may, or may not, have loads imposed upon it that are initially greater than the expected running load when the system has reached operating conditons.

A blast freezer when intially loaded up will have a greater pull down load for the first 30% ( or there abouts) of it's running period. As the product cools down there will be a drammatic drop in the cooling load.

This "pull down" load needs to be factored into the system for correct sizing of heat rejection equipment in the case of blast freezers, where as with coldstores the commissioning engineers would make allowances for the intial loading by montoring head pressures and off loading the compressors as needed. etc.

Quote:

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Originally Posted by nevgee

"pull down load" was refered to as being the load imposed upon the plant in pulling the temperature down from a warm, ambient condition. For example, a new cold store when turned on for the first time may, or may not, have loads imposed upon it that are initially greater than the expected running load when the system has reached operating conditons.

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Based on this point of view a pull down load in fact exist. However this is only a transient regimen.

Do you happen to know where I could find how much food is required per day per person?
I was thinking about meat, fish, vegetables and dairies.

What I found was in ASHRAE 2006 - Refr. - Ch.31 Marine Refrigeration is:
Mass of refrigerated perishables: 4.5kg for freighters and 6.1kg passenger vessels.

Thanks meantime,

I think it is a lot of food for a one person. I was thinking in about one half (2,5 kg as most)

Sandro,
What is your basis of 2.5kg/person/day?
Thanks,

I never look up documentation about it. It's only my sense.