Psychrometric question

[crusty demon]

Senerio ---- 100% outside air unit moving 2000 cfm with an outside air temperatureof 30 degrees F.
How many watts of electric heat will it take to raise the supply air temperature to 70 degrees F ?

Altitude = sea level
specific density = .075 lb/cubic foot

The answer i came up with just doesn't look right, need to see someone elses calculcations.

thanks

[frank]

30F = 1.1111C
70F = 21.1111C

therefore dt = 20C

1CFM = 0.028317m3/s therefore 2000CFM = 56.634m3/s

56.634m3/s x 20C = 1381.86kW

It's a little difficult when you mix SI units with Imperial units in your question.

[crusty demon]

86,400 btu
25,307.55 watts
25.3 kw
is this correct?

[Abby Normal]

2000/12.4x60x(19.81-10.16)/3413= 27.4 kW

30 degree air is a little denser, probably some water vapour in it as well

end up with more than 2000 CFM of supply

[nike123]

1CFM = 0.028317m3/s therefore 2000CFM = 56.634m3/s

1cfm = 0.0004719 m3/s

2000CFM = 0.9438948864 m3/s

Required heat is: 24,5 kW

[Abby Normal]

2000 / 60 x .3048^3 = 0.9438948...... cubic meters per second

30F is -1.11111C, its below freezing

24.49 x 22.1/20= 27.06 Kw

I allowed for about 80% RH to get 27.4

[Abby Normal]

the answer depends on whether you measure the cold air or the heated air flow

[nike123]

30F is -1.11111C, its below freezing

It seems that Frank has got hard Saturday.

30F = 1.1111C


1CFM = 0.028317m3/s therefore 2000CFM = 56.634m3/s

[Abby Normal]

NASA crashed 9 figures worth of probes into Mars because they had problems with IP and metric

[frank]

I know, I know. I saw it and then realised that you would all start pulling my leg before too long

Note to self. DON'T do calc's after BEER!

[vijay_study]

Sensible Heat (Btu/hr) = 1.08 x cfm x (Delta T)
=1.08 x 2000 x (70 - 30)
=86400 Btu/hr
=25Kw.