[EnergyPlus_Support] Re: Enthalpy conversion from US --> SI

["JV Dirkes II" <jvd2pe@xxxxxxx>]

Dear Phillip,

This is exactly the type of feedback I was hoping for!  I'm hoping
that you can take me one step further as well.

I searched the E+ documentation for info on the PsyHFnTdbW function,
and found that it is actually a function of both dry bulb temp and
humidity ratio, which is consistent with my calculations in US
measure, shown below.

Function Enth(DB, W)
'     Calculate Enthalpy given dry bulb temp, humidity ratio
Enth = Cp(DB) * DB + W * (1061 + 0.444 * DB)

I did not find the actual function equation, however. If I understand
you correctly, I could perform a straight US --> SI conversion for DB
and W, and then correct for the different zero values.  Can you tell
me the expected SI / E+ units for W?  Cp?

Thanks!



--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Philip Haves <phaves@...>
wrote:
>
> The conversion is not a straight multiplication because the zero of the 
> IP enthalpy scale is dry air at 0 degrees Fahrenheit whereas the
zero of 
> the SI enthalpy scale is dry air at 0 degrees Celsius.
> 
> Using the values of the coefficients in Function PsyHFnTdbW in 
> Energyplus and the corresponding IP values obtained using the
conversion 
> factors in Chapter 37 of the ASHRAE Handbook of Fundamentals:
> 
> Hip =  0.2398*((1.8*Hsi/1.00484E3)+32)    Btu/lb
> 
> Hsi =1.00484E3*(((Hip/0.2398) -32)/1.8)    J/kg
> 
> 
> 
> On 5/28/2008 1:31 PM, JV Dirkes II wrote:
> >
> > Dear E+ Forum,
> >
> > Will someone please confirm the following? (I'm not familiar with
> > enthalpy values in SI measure and want to be sure I am converting
> > values properly) Thanks!
> >
> > Enthalpy (US) = BTU/lb
> > Enthalpy (SI / E+) = J/kg
> >
> > "X" BTU/lb * 1055 J/BTU * 2.2 lb/kg = "X" * 2321 J/kg
> >
> > e.g., 28 BTU/lb = 64,988 J/kg
> >
> >  
> 
> -- 
> __________________________________
> Philip Haves
> Leader, Commercial Building Systems Group
> Lawrence Berkeley National Laboratory
> One Cyclotron Road, MS 90R3111
> Berkeley, CA 94720-8134
> (510) 486 6512 (office)
> (510) 486 4089 (fax)
>



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