Compressor building requirement 4

[hollandhvac]

I have got a new design for a compressor building to review and the basic design indicates a positive air pressure ventilation system. I do know from a previous project that ashrea says something about it, but I have not got these books here.

In my previous design there was only a temperature criteria that stated that the temp. diference inside and outside the building should be no more than 5 degrees C or 9 degrees F.
There should be a minimum ventilation requirement done with one fan and an aditional to switch on incase of high temperature ( over de 5 deg C). Air intake to be fitted with sand trap louvers and bird wire mesh.

With this new design there is a positive pressure required in the building which is conflict with my previous design because that would be negative. Question is now, what are the criteria's? ventilation with positive or negative pressure with sand trap louvers?

 

[stanlsimon]

I think I know what you are talking about. You have a room with compressors (probably for refrigeration systems)in it that needs to to be ventilated to remove the heat. Also there could be refrigerant leakage. Right?

It is necessary to keep this room separated from the rest of the building. You don't want to mingle this atmosphere with other occupancies.

As for the louvers, they work well as long as the air velocity does not exceed the manufacturer's recomendations. You would probably have a fan close to the louver ducted to push the air out. The intake could be fan powered or could use the power of the exhaust fans. If there is no intake fan then the exhaust fan would need a bigger motor.

 

[hollandhvac]

It is about correct. The compressors are instrument air compressors and they are in a sepperate building. Since it is north Africa we are talkig about, it has also got some solar gain as well and the ambient temperature can go up until 49 deg C. 120 deg F.

The system described in the first situation was with only an exhaust fan and therfor creating a negative pressure in the building. The second system description wanted a possive pressure which required an air suppply to the building to make it possitive pressure. But in the way you have described by using a bigger exhaust fan motor, so you are indicating a negative pressure system.

Thanks for the info

 

[KiwiMace]

120degF (+ the 10degF in the room) is going to push the envelope on those compressors. I would check the manufacturers requirements for intake air, as this will determine how much air you need to pull over the machines. You may need to duct the compressors intakes from outside.

Typically I have used extract fans with operable louvres located in the immediate vicinity of the compressors (negative design). But this was for convenience, as extract is a much cheaper and easier installation.

 

[marcoh]

I would assume that the supply air is filtered (just the sand louvre or louvre+filters?) to provide clean air and therefore a supply fan is required to overcome the pressure drops. If negative pressure is required an exhaust fan will be required.

Have applied similar solutions when designing ventilation systems for mining sites (very dirty and dusty) and typically use filtered supply to provide clean air and then either use an exhaust fan or relief louvre.

If negative pressure is required the exhaust needs to be in excess of the supply and the difference will be leakage into the building (with resultant negative pressure and potential infiltration of dust)

 

[hollandhvac]

Thanks again for the good info provided.

Haveing talked to the rotating equipment engineer the instrument air compressor has a filtration system on the air in take of the compressor. So for the building I think a sand trap louvre as air intake will be sufficient.

The high temperature has been taken into account with the design of he compressor.

As ventilation system a ridge vent will be installed under normal conditions and a powered fan will be provided under emergency conditions ( still to be decided when this is the case with HAZOP study or fire and safety )

 

[hvacinsider]

The first thing you need to figure out is the emitting load from these compressors. And then add that to the building load. After this you can now see how much heat needs to be dissipated in order to maintain the correct room temperature.
You mentioned about the ambient air temp. can be 120 deg. in the summer. I really dont understand how you are going to get a heat exchange by bringing in that air?
In past jobs we added a cooling unit to the compressor room for high ambient temp days & exhaused thru a louver. In the winter we simply brought in outside air thru the louvers.
I dont know if this is what your looking for? Just my 2 cents.

 

[stanlsimon]

You should check the motor which drives the compressor. It will need to be rated to operate in an environment like this, also the thermal overloads, starters, switches and conductors. It is a good idea to have a redundant compressor so that your process can keep going if one gets fried.

 

[KiwiMace]

If you are going to use the ridge vent, remember you also need the louvers at low level. The natural stack ventilation that you will achieve is proportional to the height separation between the inlet and outlet.

See ASHRAE Fundamentals 2005 Chap 27 to calculate.

 

[sterl]

This machine room freestanding or surrounded by a process building? Process involve chemical vapors or similar?

Breweries do exactly this so they don't end up filling CmA instrument lines with "byproduct" and crudding them in a few weeks; positive pressure simply keeps the stuff from infiltrating the compressor room. And filters won't stop at least some of it...

Hospitals and University Labs do something similar. Chem plants could be a whole different can of worms....

 

[hollandhvac]

The building is part of a gas processing area and is freestanding and outside of a classified zone.

There are buildings serounding it like a controle building and security building.