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Condensation Resistance Factor Calculator

Heat Transfer Engineering
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HVAC System and Components Design and Engineering Data

Glass or Frame Condensation Resistance Factor (CRF) or Temperature Index (I)

Current measures of condensation resistance of a fenestration system are the condensation resistance (CR) as defined by NFRC500 (2014j) and its user guide (2014h), the condensation resistance factor (CRF) as defined by AAMA (1988), or the temperature index (I), as defined in CSA Standards A440 and A440.1.

Note that the temperature index method in CSA Standard A440 stipulates that the test is performed on the fenestration with all the cracks not sealed. This represents a major difference between the CSA Standard A440 method and the AAMA and NFRC methods.

Condensation resistance is a measure of condensation potential, based on both area and temperature weighting and expressed as a minimum of center-of-glazing, edge-of-glazing, and frame CRs. The novelty of this index is that it is determined using computer simulation tools unless the overall thermal performance cannot be validated with testing. If thermal performance cannot be validated, a testing option for determining CR is used.

Figure 1 can be used to determine the acceptable range of CRF/I for a specific climatic zone. Note that the two different standards differ in the methods used to determine temperature and as such should be consulted.

The condensation resistance factor (CRF) or temperature index (I) for fenestration glass or frame is calculated from

Eq. 1
CRF or I = ( t - t_c) / ( t_h - t_c )

Where

t_h = warm side temperature
t_c = cold side temperature
t = glass or frame temperature

Figure 1 Recommended Minimum Condensation Resistance Requirements (t_h = 68°F)

References

ASHRAE Handbook - Refrigeration, ASHRAE: 2014.

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