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## Laten and Sensible load in an operation room/area

I am working on an operation theater and in the process of heatload calculations.It’s been given a 100% fresh air as per code requirement. Thus final design calculations show sensible load as 22 tons and total coil load as 40 tons.Obviously the balance is from laten load. Is it possible for latent load to be that high and is it because of 100% fresh air. Does fresh air intake imparts such a big load on the coil.Plesae suggest if something is wrong or its just normal.Also note that the total operating room area is 60 sq.meter

2. Originally Posted by hasni
I am working on an operation theater and in the process of heatload calculations.It’s been given a 100% fresh air as per code requirement. Thus final design calculations show sensible load as 22 tons and total coil load as 40 tons.Obviously the balance is from laten load. Is it possible for latent load to be that high and is it because of 100% fresh air. Does fresh air intake imparts such a big load on the coil.Plesae suggest if something is wrong or its just normal.Also note that the total operating room area is 60 sq.meter
really, you are questioning why 100% outside air put's such a load.

3. unless the temps are matched exactly and latant is matched exactly,.... yes.

4. I think the calc is off. 60 sq mters? 40 tons?

how much air are you bring in? In CFM or liters.

What area is this in?

6. Originally Posted by beenthere
i thought the title looked differant. i was a bit confused, but nothing new.

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Originally Posted by hasni
Does fresh air intake imparts such a big load on the coil.

Explanation - You have calculated that the sensible load (22T) is 55% of the total load (40T). This would be extremely unusual, but it is certainly possible. I ran a sample calculation cooling 1000cfm from 95db/78wb down to 45db/45wb:

enthalpy of entering air = 34.0
enthalpy of leaving air = 10.1
change in enthalpy = 23.9

total load = 4.45 x 1000 x 23.9 = 106355 Btu/hr
sensible load = 1.08 x 1000 x (95-45) = 54000 Btu/hr (51% of the total)

Now, the question becomes, what equipment will you use to attain that much latent cooling. It will probably require a DX coil to get a sufficiently low suction temp to produce 45F air, but I don't think you'll find a standard DX unit that provides a cooling coil with enough rows deep to do the job.

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OR designs are special animals. you need to be cognizant of pressurization of the space relative to the interstitial, exhaust, and actual space conditions. typically you want to have a slighlty positive pressure, and need to compensate for losses around doors and other openings. you need to seal any penetrations such as pipe and duct. you then need to look at design conditions, and how you plan on getting there. many OR's today utilize several coils to get ultimate control. for example, on a recent project, precooling was accomplished with ordinary chilled water at 42 degrees, then reheat with boiler water, and final cooling with a dedicated process chiller running 40% PG at 36 degrees for the recool coil. airside management is accompished via air flow stations reading supply and exhaust, and a differential pressure monitor referencing the hallway to the or suite, with final output to the vfd via the bas. total cooling load was upward of twenty tons total but not near forty.

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## latent too high !

@chatenever
>>This would be extremely unusual, but it is certainly possible.
Yeh that is what i am worried about. But i have checked my calculations and all the inputs, they seem ok.
Well its a central chilled water system with a dedicated AHU for the operation theatre.

@beenthere
It is a coastal area (dahran - saudi arabia) and 1737 liters / sec is the fresh air that would be sucked into.

10. Perhaps its just my conversions.

But isn't 60 sq meters. less then 200 sq ft?

Isn't 1737 liters a second, 1880CFM? Lot of people to need that much fresh air.

Using that fresh air volume, I come up with 18.21 tons to condition the fresh air, using weather data from wundeground.

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[QUOTE=beenthere;8744071]Perhaps its just my conversions.

But isn't 60 sq meters. less then 200 sq ft?

60 sqm x approx 10 sf/sqm = 600 sf

Isn't 1737 liters a second, 1880CFM?

1737 ltr/sec x 1 gal/approx 4 ltr x 1cu ft/7.48gal x 60sec/min = approx3483cfm

Lot of people to need that much fresh air.

I don't think the OA requirement is based on a CFM/person requirement. It's an operating room, so it probably needs to be 100% OA for infection control.

12. He said operation theater. Doesn't really mean its an operating room as in operating on people. Could be an operations control room. Equipment, and people.

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