help with refrigeration course work questins (new to the industry)

hi all
im after some help with some questions on refrigeartion
i am enployed as a trainee AC maintenace engineer but need help

Q. name four main heat loads that effect commercial refrigeration systems

Q.at what stage is a heat load taken into account for the evaporator fan motor

any help with these two questions would be great help thanks

been looking into the first question all day and got the answer needed for that so no need for anyone to reply to the first question
but still unsure on the second question ie
Q. At what stage is a heat load taken into account for the evaporator fan motor ??


please reply if you read
dean

.

The wording is poor and it would help if you gave the whole question
and in context of how it was written.

But as for fan motors you need to know their heat load before you size the
evap, the same as lights and defrost heaters.

All the best

Coolrunnings

.

Quote:

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Originally Posted by dean_thomas

Q. name four main heat loads that effect commercial refrigeration systems

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Out of interest what have you come up with for the above?

All the best

coolrunnings

.

hi coolrunnings
thanks for your reply to my questions
sorry about my wording but that is how the question is asked in my course work

for the first question ive got the answer of
product load , ambiant air temp , air exchange load (fresh air in ) and equipment load (fans lighting ,defrost etc)

and for the secod question ie.
At what stage is a heat load taken into account for the evaporator fan motor .

ive got an answer of.
At the design stage should the evaporator fan motor be taken into account for the heat load.
??

thanks
dean

Hi Dean,

I agree that the wording isn't the best. Its correct that it should definately be taken into account at the design stage.

Example:

If the fan your using generates 1kW of heat, you are adding that 1kW of heat into the air (aka fan heat gain).

If the AC unit is designed to do 15kW Total Sensible Duty, you would need to take off the fan heat gain to get the Net Sensible Duty. This figure is important because it is what clients/customers would be able to add into the space they are trying to cool.

In other words, they would only be able to add 14kW of there own load even though the AC unit is capable of cooling 15kW, the fan is 'stealing' some load off the unit capacity.
Hope this makes sense.

Jon

Hi Dean,

your first answer is OK
Product Load
Energy Infiltration through the structure (how much heat comes through the walls, floor etc)
Air Infiltration (how much air comes through the doors and the like)
Equipment load (this cover a number of things including people, light, forklift, electrical equipment, fans anything that produces energy or absorbs energy)

Your second question.
The heat load of the evap fan is calculated at the end of the above design process.
What this means is before you can determine your required airflow, you must first know the duty of the air to be cooled, (how much energy is to be removed), this determines roughly the equipment to be selected, which would indicate the fan size, you add this back into your calcs, re-select the equipment, check for any changes, calculate again if needed.
With a lot of AC equipment (not all) the evap fan is already calculated into the cooling performance of the equipment.