AHU total load calculation?

[Bashir01219]

Room Size: 168 m3, Air change/Hr: 20, CFM: 1975, Outside Temp:104 F, Room Required temp: 71 F, Outside RH: 85%, Expected RH: 22%, system required 20 % fresh air and 80 % return air.

So, Sensible Heat: 1.085X1975X(104-71)/12000 = 5.87 Ton
& Latent Heat: 4.840X1975X (139 - 31.43)/12000 = 86 Ton,

if I overlook other heating load, then total load = 91.87 Ton, but I don't think so, its too much for 168 m3 room, what was my problem with the calculation? Please help?

[Magoo]

Try electrcal loading from lights, computers, fans, and people loadings. Heat gain from solar effect on windows. heat gain from structure loads, ceilings walls and floors.

[nike123]

Your problem is that you are probably calculating whole air as fresh air, not mixed!
You need to handle only 20% of total air flow as fresh air.
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http://i55.tinypic.com/331impc.jpg
http://i54.tinypic.com/b5jm2v.jpg

[Bashir01219]

Thanks to you, you always help me lot.

Can you please provide me the software or the source of the software or how can I calculate it my self?

Waiting for your kind replay.

[nike123]

Windows Psychrometrics Calculator £28.00

http://www.marcobrien.org.uk/

[Bashir01219]

Windows Psychrometrics Calculator £28.00

http://www.marcobrien.org.uk/

ok I will do it.................

[Bashir01219]

Some problem with the calculation......
1. Supply air dry and wet bulb temperature is not correct our expected temperature 22 Deg C and 22% RH

[nike123]

That is exactly what I entered as return air.
Return air is actual state of air in room.
Supply air is mixing with air alredy in room.

Check your home air-conditioner suply air and room air.

[Bashir01219]

But this is not a total summary. Where is my 20% fresh air load and at the starting time room temperature and humidity are same as outside so how can I summaries total scenario?Its a pharmaceuticals plant......
My point is (Room Size: 168 m3, Air change/Hr: 20, CFM: 1975, Outside Temp:104 F, Room Required temp: 71 F, Outside RH: 85%, Expected Room RH: 22%, system required 20 % fresh air and 80 % return air.) if I want to calculate from the beginning what will be the steps?
1. Sensible Heat: cfmX1.085X (Tout-Tin)/12000 = (0.00 Ton)
2. Latent Heat: cfmX0.69143X(G1-G2)/12000 = (0.00 Ton)
Then add lighting, man, machine, sunlight, .........etc load, but problem is at normal condition and initial condition load is not safe so how can I summarized total thing that can help me to predict system total load and buy a AHU.

[nike123]

Where is my 20% fresh air load and at the starting time room temperature and humidity are same as outside so how can I summaries total scenario?Its a pharmaceuticals plant......


20% fresh air is in the calculation.
What is not in calculation:
-Latent load from people
-Heat gain from the supply air fan
-Heat gain from the return air fan
-Heat gain from supply air ductwork portion in unconditioned space
- Heat gain from return air ductwork in unconditioned space
- Infiltration (sensible & latent) if any
- Heat gain from lights
- Heat gain from plant equipment
- Heat gain from walls, floors, ceilings and windows
etc...


Also, you need to establish what is required time frame to lower your temperature from starting conditions.
Than , you could calculate aditional cappacity needed for that task.

[Bashir01219]

In the chart Mixed Air Return, for Supply Air, you take DB:12.3, WB: 11.3, RH:95 why? Is it not what for the room design? RH: 22, Temp.: 22 Deg C.