Question on air flow in HVAC unit

[JSV]

I have a problem figuring out air flow in a building we need to cool down.

We have an outside air temp of 40 deg. C and need an inside temp of 20 deg C.

The building has a total volume of 3500 m^3

The heat transfer from outside to inside is approximately 15 kW (poor insulated).

We know the cooling need is 37kW with an airshift of 0.5 x total volume / hour. But I don't know how much extra airflow or lower temp is needed to work against the 15 kW input through the walls.

Could anyone please help me.

Brgds. Jon

 

[Golestan]

It seems that your total heat load could be the heat from bringing-in outside air with 20-deg-C delta T, and the heat from the walls at 15 KW, you may also have heat load from the ceiling/roof and from the floor (concrete, etc...) And any other loads, such as lighting and people...

Then, you will need to select an air conditioner that has the capacity to overcome the sensible and latent heat loads that you have added.

Hope this helps. Others on this forum are much more experts in the field. Hope they will give you added advise.

regards,

 

[mechanicaldude]

I'm not quite sure I understand all your numbers, but if I assume your supply air temp. is 13 degrees C, your airflow requirement will need to be about 4200 l/s for the cooling need of 37kw and you will need an additional 1700 l/s for the 15kw heat transfer from walls. Sizing your equipment is a different story because you will have to factor in your latent loads from the outside air and people and other possible equipment. The airflow rates only take into account you sensible heat gains.

I don't know where you got the your numbers from but keep in mind other sources of heat to keep in mind are from people, lighting, equipment (ie computers) and solar thru windows.

I hope this helps answer your question.