Using Exhaust to reduce heat load

[Maximusprime]

Im working on a space that has some equipment with high heat gain into the room. It is a lab with 100% exhaust and I am placing the exhaust grilles over some of the higher loads in an effort to remove them from the space and reduce the volume of supply air required to cool the space. Is there a way to estimate the load reduction without resorting to a full on CFD analysis?

 

[GMcD]

Umm, how does one reduce the amount of supply air while using 100% exhaust? Either you'll have a lot of negative pressure in the room, or you still have to have air in = air out, so what really is the issue? Are you asking if you can reduce the amount of cooling load in the space? You still need the same amount of air in = air out, so all that means is that you may be able to adjust the SAT higher based on the room cooling load. Yes, exhaust grilles over heat sources can take away some of the perceived "room load" but there is still the radiant heat to deal with from the warm stuff.

 

[EnergyProfessional]

your devices heat up the space in 2 ways: conduction to the air, which you would remove with the hood. but they also radiate heat to the space, which you still need to account for.

as GMcD said, all your exhaust will need to come in as makeup air. either through a device, or infiltration. But your idea is good, you basically "heat up" the exhaust to get more btu out of the room with each ft³ of air.

 

[IRstuff]

If you want to reduce the air flow, then you need to be more efficient, by ducting air directly into loads.

This is a classical conflict of requirements. To be efficient in air use, you'd like the air to increase in temperature as much as possible, but to be efficient in cooling the equipment, you'd like the air to be as cold as possible. One scenario is to make the equipment be the exhaust inlet, so that all the air that enters the room exits through the equipment being cooled. Your only two additional controls are the surface area of the heat sink and the velocity of the air going through the heat sink.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[SAK9]

It is very difficult to accurately estimate the percentage of heat transmitted from the equipment by convection and radiation.If the surface temperatures are low say below 40C it is likely that you have a high percentage of convective heat transfer.If you look up technical data of a good hydronic radiator,you would get a better idea as to how to apportion the heat transmission.If you can contain high heat emitting equipment in an enclosure(for eg autoclaves),you can use the lab exhaust air to cool them.Using chilled water wherever possible to cool the equipment is also a good strategy.