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4.6 Validation of aircraft ventilation algorithms
As previously indicated in Section 4.3.1, the approach adopted in predicting environmental conditions in an aircraft hold in this version of LATSA was to treat the hold as being analogous to
any other form of enclosed animal housing, and utilise the methodologies and algorithms commonly adopted in modelling those environments. This approach is not inconsistent with
recommendations for transient, computer-based modelling provided in Section 4 of
SAE AIR1600. Nonetheless, to validate the resultant predictions it was considered desirable to obtain
comparative values using a different methodology. SAE AIR1600 provides an equation for estimating CO
2
concentrations in the holds of aircraft carrying livestock. The units applicable to CO
2
concentrations in that equation are percentage volume vv. Accounting for the influent concentration of CO
2
and converting the concentration into units of parts per million volume ppmv, in lieu of vv used in the original
equation, the modified equation can be expressed as:
6 cargo
2
10 exp
1 CO
h v
v
V F
F C
C
Equation 41
Where: C
= CO
2
concentration ppmv at time ;
C = CO
2
concentration mgm³ in influent air; CO
2 cargo
= CO
2
emitted by cargo mghr; and F
v
= ventilation rate kghr;
= time hr; and V
h
= hold volume m³. By applying the same principles, it is possible to modify Equation 41 to calculate effects on
temperature and humidity of sensible heat and water vapour loadings. The resultant equations are as follows:
p h
v v
c V
F F
T T
exp 1
3600
sen
Equation 42
Where: T
= outflow temperature °K or °C at time .
And:
h v
v
V F
F r
r
exp 1
total
Equation 43
Where: r
= outflow mixing ratio water:air as gkg at time .
By applying the above equations to a diverse range of scenarios, it was possible to validate the algorithms in version 2 of LATSA. In all cases the validation calculations gave very similar
results to the algorithms in this new version of LATSA, and which have been previously detailed in Section 4.3 of this report.
In respect to the secondary psychrometric calculations provided in Section 4.4, these equations were validated by comparing predicted values to those derived from the relevant psychrometric
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charts in ASHRAE 872-RP: Psychrometrics – Theory and Practice ASHRAE, 1996, and sample
calculations provided in Stull 2000.
4.6.1 Aircraft operational constraints
In utilising version 2.0 of LATSA, the Participant Exporter assumes that the nominated aircraft can operate at its full design ECS capacity. Where the Participant becomes aware that the
aircraft has temporary ESC limitations and checks that box in the document section of the program, progress is halted until that issue has been discussed and managed with the carrier.
Version 2.0 of LASTA also assumes that each aircraft is operating to its respective maximum or minimum design specification. As an example, the inlet air temperature for a Boeing 747-400 is
specified as 2
C and that inlet temperature is used by the program as the inlet temperature constant for that aircraft.
Selection of the correct aircraft is therefore an important factor when utilising version 2.0 of LATSA.
4.7 Software Development
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