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View Code? Open in Web Editor NEWown psychrometric calculations for Moist Air required for Mollier Chart
License: GNU Lesser General Public License v3.0
own psychrometric calculations for Moist Air required for Mollier Chart
License: GNU Lesser General Public License v3.0
Describe the bug
Contact Factor method for cooling process returns wrong value
Steps to recreate the bug
Versions: Revit , Rhino
Screenshots
Test file
Describe the bug
adjust logic to:
Steps to recreate the bug
Versions: Revit , Rhino
Screenshots
Test file
explanation...
Where we have Cooling process - two points ie P1(35 degC, RH 55 %, x 19.59 g/kg, h 85.61 kJ/kg ) and P2(12 degC, 100%, x 8.73 g/kg, h 34.14 kJ/kg)
We have also mass flow m = 1 kg/s
we know that to calculate the total load for this Q total = Q sensible + Q latent
Q sensible = mass flow * cp * (T P2 - T P1)
Q sensible = 1 kg/s * 1.01 kJ/KgK * (12 degC - 35 degC)= -20.20 kW
Q latent = mass flow * r0 * (x P2 - x P1)
Q latent = 1 kg/s * 2.450 kJ/kgK * (8.73/1000 kg/kg - 19.59/1000 kg/kg)= -0.03 kW
we know that Q total = Q sensible + Q latent
Q total = -20.20 kW + (-0.03 kW) = -20.23 kW
However when I use the equation:
Q total = mass flow * (h P2 - h P1)
Q total = 1 kg/s * (34 kJ/kg - 85.61 kJ/kg) = -51.47 kW
so
The discrepancy you're observing in the total heat load (Q total) calculations for the air cooling process using the psychrometric properties arises due to a few key factors related to the nature of the calculations and the properties of air.
Specific Heat Capacity (cp) Variation: In your calculation of Q sensible, you've used a constant specific heat capacity (cp) value of 1.01 kJ/kgK. However, the specific heat of air is not constant and varies with temperature and moisture content. The value of cp used in your calculation might not accurately represent the specific heat of air at the conditions of P1 and P2.
Use of Approximate Formulas: The formula for Q latent assumes a linear relationship between the enthalpy and the humidity ratio, which might not be perfectly accurate over a wide range of conditions. This is because the enthalpy of moist air is a nonlinear function of both temperature and humidity ratio.
Accuracy of Psychrometric Data: The values for enthalpy (h) at points P1 and P2 are taken from a psychrometric chart or calculated using psychrometric equations. These values are subject to the accuracy of the chart or the equations used for their determination. Small errors in these values can lead to significant discrepancies in calculations, especially when dealing with large changes in temperature and humidity.
Difference in Calculation Methods: The method using sensible and latent heat separately (Q sensible + Q latent) and the method using enthalpy change (h P2 - h P1) are based on slightly different principles. The enthalpy method accounts for the total energy change, including both sensible and latent heat, in a more integrated manner. This method is often more accurate for processes involving both temperature and moisture content changes, which is typical in psychrometric applications.
To resolve this discrepancy, you may need to:
Use more accurate or variable-specific heat capacity values for air at different temperatures and humidity levels.
Employ more precise psychrometric equations or charts to determine the enthalpies at points P1 and P2.
Ensure that all psychrometric properties (temperature, relative humidity, specific humidity, enthalpy) are consistently and accurately determined.
In practice, the method using enthalpy differences is generally preferred for calculating the total heat load in psychrometric processes, especially when both temperature and humidity changes are involved.
Describe the solution you'd like
add sources to all default values used in MollierChart
Additional context
Describe the bug
Steps to recreate the bug
Versions: Revit , Rhino
Screenshots
Test file
Describe the solution you'd like
Add new node:
SAMMollier.ModifyProcessByBypassFactor
Input:
- _process
- _bypassfactor_ (Default 1)
Output:
- mollierProcess
- end
- color
- epsilon
Additional context
Sometimes we allow air to bypass coil.
The term "bypass factor" in the context of Air Handling Units (AHU) and cooling coils refers to the fraction of air that does not come into contact with the cooling surfaces (like the fins of the coil) and hence does not get cooled. This concept is crucial in understanding the efficiency and performance of cooling systems.
Here we would use 0.33 which represet 33% of air. This means 66% of air goes via coil and 33% bypass
Describe the solution you'd like
sometimes to adjust calculations according to specific conditions requirements to adjust constants are needed..
allow modification to :
https://github.com/HoareLea/SAM_Mollier/blob/master/SAM_Mollier/SAM.Core.Mollier/Variables/Zero.cs
when we query these values via Inspect.mollierPoint or:
- SAMMollier.Psychrometrics
- SAMMollier.LoadByProcess where we can connect optional input ( _cp_ use current default but allow modification)
- SAMMollier.CalculateLoads
Additional context
input could be node:
SAMMollier.SpecificHeat
Describe the solution you'd like
new Output
MoistureGainsMassFlow [kg/s]
Condensation [l/h]
Additional context
test file attached
Issue48.zip
Question
Latent Heat of Vapourization (Evaporation heat of water), enthalpy of vaporizarion (r0)
similar to: SAMMollier.SpecificHeat
Test file
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