Heat Load Calc.

[Zeroman]

I am working on the design of an HVAC system for a plant located in Africa. Total Heat Dissipation is based on Instrumentation(62kW) and lighting(11kW) totalling approx. 92kW. The Vendor is saying that this number is too high too cool. But the fact is is that these values are as such so the unit has to be sized appropriately o remove the 92kW. ie. 92 kW Cooling. Please tell me if my logic is correct.

Thanks, Dave

 

[briand2]

Dave,

With regard to the lighting, I agree with you that the "...values are as such...". This is because the lights are (probably) all on at the same time.

With regard to the "instrumentation", I have some reservations. If 62 kW is the total nameplate rating, then it is extremely unlikely that this is the load the air conditioning will see. You will need to allow an element of diversity, but I don't know how much in your particular circumstances. I can say, however, that the realistic allowance for computer-type equipment is more like half the name plate rating.

Hope this helps.

Brian

 

[Zeroman]

Thanks Brian for replying and helping out.

 

[Zeroman]

The situation is like this. I have calculated the heat gain for the interior of the building based on design day. I have also been told the values for the heat dissipation of equipment in the building. Should I not total these amounts and state that this is my COOLING LOAD? The rest should be the vendors issue, right? I have been working with a German company and a lot is lost in the translation. They said that cooling by air was unrealistic. BUT, I don't want them to cool by air, I want them to cool using R-22 cycle, and condenser/evaporator combo with some sort of heat exchanger to recycle the cool air prior to being exhausted. Total cooling load is about 80kW. Do you think that the design of my unit is crazy? Do you have any suggestions, remember this is Africa.
Thanks for your help (Am I griping)

 

[HeatTreater]

As a rule of thumb, I have always used 12,000 btu cooling per 1000 sq ft of space. 12,000Btu cooling = 1 Ton. For example, a 4000 sq ft space with 10 foot ceilings would require in the neighborhood of 48,000 Btu of cooling or 4 Ton. If your in between sq footages,,, always size the evaporator coil one half ton higher than the condenser, IE: 4800 sq ft space = 4 Ton condenser and 4.5 Ton Evaporator. The evaporator should always be sized higher by no more than one half ton if you can't quite exactly match heat load. Hope this helps

 

[quark]

Even with lighting, you should not consider the bulb rating as the cooling load requirement. The total tonnage is coming out to be 27 tons (TR) approximately. What is the size of the building? 1000 sq.ft/ton is a not a good value. Even for domestic applications 400 to 600 sq.ft /ton is considered.

Adding the heat gain from external heat to the equipment load is correct. But as far as electric load is concerned, 50 to 60% of tag kW rating is considered even incase of power panels.

Secondly, why do you want to throw away the air? Is recirculating the air against local codes? Maintain minimum fresh air required (16 cfm/perso) if possible and recirculate the air through filtration.

HeatTreater!

Can you please tell me why the evaporator heat capacity should be more than that of condenser? Generally evaporator has to remove the heat necessary to maintain a certain temperature in a controlled environment. (which is called Refrigeration Effect). But on the other hand, condenser has to take care of Refrigeration Effect + Heat equivalent to the work done by the compressor.