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