Emerson Daniel 3415 - Energy Rate and Totals

4.5.9 Energy rate and totals
These calculations require that the flow-condition pressure and temperature are available
(either fixed or optional analog inputs, ), the gas property data (composition and heating
value) are available (either fixed or optionally read from a GC, ), and the AGA8 calculations
are performed (internally by the meter or externally with the results written to the
meter, ).
The energy rate is calculated as shown in Equation 4-17
Energy rate Equation 4-17:


= 

×  ×
1
1000
×
1000
3
1
3
Equation 4-17
where
Q
E
energy rate (MJ/h) (EnergyRate)
Q
E
energy rate (MJ/h) (EnergyRate)
Q
Base
base-condition volumetric flow rate (m
3
/h) (QBase)
HV
"in-use" heating value (kJ/dm
3
) (HeatingValueInUse)
The sign of the energy rate indicates the flow direction: a positive value indicates flow in
the forward direction, a negative value indicates flow in the reverse direction.
The energy rate validity is indicated by the EnergyRateValidity data point TRUE(1) indicates
valid). The energy rate is valid if the base-condition volumetric flow rate is valid (indicated
by QBaseValidity where TRUE(1) indicates valid) and if the in-use gas properties are valid
(indicated by AreGasPropertiesInvalidInUse where FALSE(0) indicates valid).
The energy rate is accumulated into the corresponding direction energy total regardless of
the energy rate validity.
The forward and reverse direction energy totals are each stored in non-volatile memory as
a data pair: a 64-bit unsigned integer portion and a 32-bit floating point fractional portion.
For example, an energy total of 12345.750 MJ is stored as 12345 MJ for the integer portion
and 0.750 MJ as the fractional portion. Note that while the energy rate can be positive
(indicating forward flow) or negative (indicating reverse flow), the energy totals are always
positive values.
The non-volatile energy total data points are as listed in the table below:
Forward direction
Reverse direction
Integer Fraction Integer Fraction
PosEnergy PosEnergyfrac NegEnergy NegEnergyFrac
Measurement
Operations manual 31