.TT pocketengineer building services engineering

Condensation prediction software

Hello! Condensation (Android): a module in aDuctulator

quick design calculations for surface condensation occurrence, U-value, R-value, heat gain . . .

To take a glance at all pocketEngineer software and OS requirements, click Software List.

>>> go to aDuctulator (Android) - HVAC duct sizing

Hello! Condensation . . . every now and then, everywhere!

Principle 1: Heat flows from hot to cold.

Principle 2: Surface condensation will occur on the outer surface (hot side) when the outer surface temperature (Ts) falls below or equals the dewpoint temperature (Tdp) of the ambient air.

Principle 3: Add insulation materials (R1+R2+ ... ) to prevent condensation occurrence.

The Hello! Condensation app provides you with the greatest flexibility in predicting surface condensation occurrence. You build (add or delete) the material layers as required, and there is no limitation for the number of layers that can be created.

Predicting surface condensation occurrence involves dewpoint temperature and surface temperature calculations. This is best handled by the computer with just a few clicks.

The following design calculations are done with Hello! Condensation.

Worked Example 1 - Façade Glazing for viewing gallery (in SI units)

Results:

[Units: t(mm), K(W/m.K), R(m2.K/W) ]

Concluding Remarks:

Humid / rainy day raises outdoor dewpoint temperature, resulting in a risk of condensation potentially. Anti-condensation system may be necessary for condensation control if occasional condensation occurrence is unacceptable.

Worked Example 2 - Air Conditioning Duct (in IP units)

Is 0.5 inch of insulation thickness adequate?

Design and analysis parameters as follows:

[1] Outside duct environment: 80 °F DB, 95 % RH

[3] Inside duct temperature: 55 °F DB

[4] Duct insulation material: Fibreglass (K=0.236 Btu.in/hr.ft2.F)

[4] Insulation thickness: 0.5 inch

[2] Outside surface airfilm (bright, reflective surface): 0.994 hr.ft².F/Btu

[2] Inside surface airfilm (moving air, 3.4 m/s): 0.250 hr.ft².F/Btu

The following presents the results print-out.

=== Condensation Calculations ===

Outside air drybulb temp., To (°F) = 80

Outside air RH (%) = 95

Outside air film resistance, Ro (hr.ft².F/Btu) = 0.994

----------------

[Units: t(in), K(Btu.in/hr.ft2.F), R(hr.ft2.F/Btu) ]

Layer 1= Fibreglass, 32 kg/m3

... t= 0.5, K= 0.236, R= 2.119

----------------

Inside air film resistance, Ri (hr.ft².F/Btu) = 0.250

Inside air drybulb temp., Ti (°F) = 55

---results-------------

Hello! Condensation = YES

Outer surface temp., Ts (°F) = 72.61

Outside air dewpoint temp., Tdp (°F) = 78.43

Temp. difference, Ts-Tdp (°F) = -5.8191

Overall R-value (hr.ft².F/Btu) = 3.3630

Overall U-value (Btu/hr.ft².F) = 0.2974

Heat gain (Btu/hr.ft²) = 7.43

------------------------------

Concluding Remarks:

If the outside duct conditions is 80 °F DB, 55 % RH (say, normal conditions), 0.5 inch of insulation thickness would be sufficient for condensation control purpose. However, when the outside duct environment hits 80% RH (say, humid rainy conditions), condensation starts to occur. see results printed in pdf format at this condition.

It is important not to calculate the insulation thickness based on the normal condition, but the highest possible or anticipated relative humidity of the ambient air where the duct is installed.

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For Duct and Pipe insulation thickness calculation, refer to pockeINSUL (Windows program).

For U-value + Condensation prediction, see U-value calculator (Windows program).