# #138 NCEE 2001 AM



## Yingli (Oct 17, 2009)

Hello

Need help again, Q=500 gpm x delt T, How to get 500, Where can get the Cp and density of R22 and R12, the density can get from Appe. 24k.

I did 2001 AM exam this moring, got 31/40. I wish I can get 32-34/40 correct in AM, and 20-24/40 in PM on the real exam.

Thanks,

Yingli


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## JoeysVee (Oct 17, 2009)

I'll look at this...give me about 10 minutes...


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## JoeysVee (Oct 17, 2009)

You don't need the cp and density of the refrigerant. It's the Cp and density of water. It says the condenser has water entering the condenser at 75 and leaving at 85 so Q=mdot*CPwater*deltaT. Get mdot then convert to gpm and the refrigerant load is the 50,000/12000.

Does that help?


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## Yingli (Oct 17, 2009)

thank you, you are right , that is water, not R22.

Yingli


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## Yingli (Oct 17, 2009)

I still cann't get 500 ,

q=dencity.*v dout*Cpwater x delt T=62,4 x 7.48^3 (for ft^3 to gallon) / 60(for hr to min) x1 (Cp water) =435gpm*delt T, so I got 435, not 500, where did I get wrong?

Thank you,

Yingli


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## Yingli (Oct 17, 2009)

Yingli said:


> I still cann't get 500 ,
> q=dencity.*v dout*Cpwater x delt T=62,4 x 7.48^3 (for ft^3 to gallon) / 60(for hr to min) x1 (Cp water) =435gpm*delt T, so I got 435, not 500, where did I get wrong?
> 
> Thank you,
> ...



the unit convert is the real problem to me, at above ft^3= 7.48 gallon, not 7.48^3, but I still don't know how to get 500?


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## POPAC (Oct 17, 2009)

Yingli said:


> the unit convert is the real problem to me, at above ft^3= 7.48 gallon, not 7.48^3, but I still don't know how to get 500?


Q=m*cp*deltaT

for water cp=1Btu/lb'F

There are 8.33lbH2O/gallon

60 minute/hour

Q=GPM *8.33*60 *1*deltaT= 500*GPM*deltaT

This is an important formula used all the time when the give you water and GPM


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## Yingli (Oct 17, 2009)

Thank you very much.


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