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Sensible Heat Gain Caculation

Sensible Heat Gain Caculation

Sensible Heat Gain Caculation

(OP)
A. I am trying to get the heat load of all the existing connected equipment and other heat generating apparatus as well as the proposed ones in a laboratory to determine the right a/c size, I calculate the sensible heat load by using the nameplate data in watts multiplied by 3.4 how about the latent heat load, it's ok if there is an equipment of the same rating or falls within the range from table of recommended rate of heat gain. Ashrae

B. Also can I conclude that for the fumehood  there will be no heat gain for heat gain is equal to heat loss due to its outdoor supply and exhaust unit that is electrically interlocked mounted on the roof.

I would greatly appreciate if anyone out there could provide me a solution. Thank you.

RE: Sensible Heat Gain Caculation

A. Latent heat gain in this application generally means people breathing. Size the unit based on sensible heat output given. Keep in mind that nameplate heat output is often a maximum rating. Usual heat output can often be 20-30% of rated output. If the A/C is sized to accommodate manufacturer-stated room loads and has VAV capability, you would have a margin of error to work with. Don't worry about the latent load.

B. A make-up system for a hood will usually make up 70% or less than the volume exhausted. If the make-up air is supplied via auxiliary make-up just above the hood and downwashing along the sash, consider heat gain negligible. Note that supplying greater than 70% of the exhaust volume in this application will reduce the fume hood's effectiveness. Hood heat gain in most applications is negligible as compared to other typical equipment in labs (freezers, refrigerators, centrifuges, lights, etc.).

If there's too much gray area, allow for 2 cfm/ft2 of lab space (total supply), make sure the net flow into the lab is just less than the net flow out, and equip the system with VAV and reheat to cover varying heat loads.

RE: Sensible Heat Gain Caculation

(OP)
I greatly appreciate the help you provided, it made me comfortable with the calculations I had, how about in some certain cases where latent heat is to be considered & none also from the tables.

I also had another issue, the same lab, the fume hood fresh make-up air is being supplied, what is the requirement for the air make-up, does it need to be an air conditioned unit ( exhaust fan is electrically interlocked fresh make-up ). The current status is that condensation is present at the fume hood area most of the time at the fumehood portion where fresh make-up air comes in contact with the cold area of the fumehood, it occurs when outside temp is high ( on tropical place like guam ). Thank you very much in advance.

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