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



Thank you!



--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Philip Haves <phaves@...>
wrote:
>
> To convert from SI to IP, use
> 
>     Hip = 0.0004296 * Hsi + 7.674
> 
> where Hip is the specific enthalpy in BTU/lb and Hsi is the specific 
> enthalpy in J/kg.
> 
> To convert from SI to IP, use
> 
>     Hsi = 2327.96 * Hip - 17864
> 
> These equations are derived from the ones in my previous email by 
> combining the constants.  I left the multiple constants in to indicate 
> how the conversion was derived.  Note that, while enthalpy depends on 
> temperature, humidity ratio and specific heat, the values of these 
> quantities are not needed to perform the conversion from SI to IP.
> 
> 
> On 5/28/2008 4:16 PM, JV Dirkes II wrote:
> >
> > 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 
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, 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)
> > >
> >
> >  
> 
> -- 
> __________________________________
> 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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