Fuel Cell efficiency and heat rejection 1

[frankn88]

Hi, my first post, hope you all can help, thanks!
I'm doing a preliminary study on a marine fuel cell installation and am looking at the ventilation requirements for the space. I asked the fuel cell manufacturer what the heat rejection to atmosphere on the fuel cell (250kW) is, and they told me, "Our 125 kW (net) Forza power module has 50% or more efficiency. Therefore, heat rejection to the atmosphere will be approximately 250 kW for 250 kW electric output. Rejected heat will be approximately at 60C."
Does this make sense? For one thing, is heat rejected at a certain temperature, i.e., 60C? If this is correct I need about 26,000 CFM to keep to a 15 degF heat rise (before I even get to solar and other heat loads). Is this the penalty of 50% efficiency?

 

[IRstuff]

I don't know whether you've given anywhere near enough information, but yes, a 50% efficiency means lots of waste heat.

Presumably, the 60ºC refers to the highest surface temperature under some condition, which they can't much exceed, since an accessible surface at that temperature can cause skin burns with a long enough exposure. I'll go out on a limb and suggest that the temperature given only applies to a system with 25ºC ambient temperature, so you're dumping the heat load through a 35ºC temperature difference.

TTFN

 

[ChrisConley]

Any potential to use that waste heat elsewhere in the building? CHP (Combination Heat and Power) systems are becoming more commonplace.

Water jacket cooling might be an option as well, and a nice way to capture waste heat.

 

[frankn88]

It's a test boat, and there's really no option for using the heat - just need to get rid of it. I guess I was just shocked at the amount of heat it's putting out and wanted confirmation that I wasn't seeing things.
I will talk to the manufacturer about water-cooling, which would certainly be a lot easier. Thanks!

 

[lilliput1]

Check your calculation. The 26,000 CFM at 15°F temperature rise is only for 125 kwh rejected heat, not 250 kwh. You may also need to consider the motor efficiency as additional heat gain. Overall efficiency of the system may only be 24 to 36%.

 

[frankn88]

Oh how sad that you are correct... so it's even worse than I thought. Man, this thing is just a HEAT MACHINE! Thanks.