Maximum air changes per hour 1

[71713]

I have a large diesel generator located in a building and need to improve the ventilation. My calculation shows 49,000 cfm are needed for ventilation to maintain a 20 delta t in the room.

This flow rate equals about 1 air change per minute. That seems like a large number to me. Is this realistic?

What is a maximum number for ach without feeling like you are in a wind tunnel?

 

[walkes]

That number is not unreasonable. Generator rooms may feel like wind tunnels no matter what you do. Some designers like to install remote radiators to cut down on airflow, but in the end you will still put large quantities of air through the room to take the heat out.

The other solution would be to have the generator within its own enclosure outside on a skid.

 

[RossABQ]

Remote radiators have a trade-off tho; reduced reliability due to fan motors vs. belt-drive off engine. If it is a truly critical generator (life safety) this may be a factor.

The sections of exhaust pipes that are in the room are a often over-looked heat load. The low-emission diesels' exhaust gets REALLY hot!

 

[71713]

This unit is 2500 kW and cooled thru use of a cooling tower. The engine and generator still dissipate a lot of heat into the room; therefore the need for significant airflow to minimize the temperature increase in the room.

From a practical standpoint, at what number of air changes per hour is too much and direct ducting to the outside should be considered?

 

[AbbyNormal]

they should have combustion air data for you, heat radiating off of the block, off of the alternator, heat off of insualted exhaust

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

I did some for Ontario Hydro, diesl plants up towards James Bay, they had a 75 fpm cap, maybe to do with dust and eyeballs

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[RossABQ]

Is this an emergency generator or one used routinely?

 

[atlas06]

Typically, the motors are rated for around 124F, so you could go to 30F delta T if your air flow capabilities are limited.
why is it that most people omit to indicate their project location in these forums? It is so important. The reason I say this is that if you are in the rust belt (US of course), you may want to worry about that much cold air freezing your oil or your sprinkler system.
Check out the Tier 3 EPA regulations that just went into effect 3 weeks ago (January 1, 2007) about emissions, will you comply with EPA tier 3 emissions using a cooling tower?

 

[lilliput1]

Consider using variable speed supply and exhaust fans with speed on space temperature sensor control. Supply & exhaust CFM should be balanced or slightly positive. Provide the required combustion air makeup high & low openings.

 

[atlas06]

Got to KISS it liliput, the system is already on a cooling tower with an external fan, pump and may be even a cooling tower valve and Fan VFD. Adding two fans and VFD's makes the entire system not as reliable.
The less components, the better off you will be.
By the way, how do you handle your flue exhaust? Make sure that you go up to the highest roof. I've seen a 1500 KW gen set on grade about 50 feet away from the buuling that triggered the AHU duct smoke detector on the roof (150 feet away) by entrainment of gen set flues to the OA intakes.

 

[lilliput1]

The only other way to stage fan volume would be to use multispeed fan but nowadays VFDs are less expensive than multi-speed motors. Also multiple speed fans are not readily available and the rpm you need may not be available. Use of VFD will save on fan energy and heating energy. VFDs have proven to be reliable. Just make sure it has the option where you can lock out critical frequencies that causes resonance and a manul bypass.

 

[atlas06]

This is stand-by generator application, which means it is hardly energized. No run, no savings.

 

[marcoh]

I have completed a ventilation system design for for 2x2MW water cooled standby generators with 25,000L/s (53,000cfm) ventilation, ie similar to your numbers.

2 fans are installed and will be staged to provide 0%/50%/100% airflow. As the genertors are also standby machines we decided there were no real advantages to using VFD's.

Most difficult issue was providing sufficient acoustic attenuation in the makeup to achieve the required noise levels in the adjacent carpark.

 

[AbbyNormal]

http://www.cumminspower.com/na/technical/application/t030/chapter6.jsp

Take the "V" out of HVAC and you are left with a HAC(k) job.