This section will apply whenever the line or duct temperature is below ambient temperature.
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| Objective |
- The thickness of thermal insulation to be such that the outer surface temperature of the insulation is above the dew point for the design conditions stated also the thickness of insulation will significantly reduce heat gain.
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| Material requirements |
- Thermal conductivity (l) and outer surface coefficient of heat transfer (he) for calculation.
- High resistance to the transmission of water vapour through the material (µ factor).
- Flexible for ease of installation.
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| Design condition |
- Ambient temperature; Line temperature; requirements Relative humidity; Pipe diameter.
- For the UK the conditions are normally taken as ambient temperature 20 ¨¬C and relative humidity 70%. The "worst case" conditions should always be used in condensation control calculations.
- Increased relative humidity has a marked effect on the thickness of insulation required. For the following conditions,ambient temperature 20 °C, line temperature 6 °C and pipe diameter 54 mm;
at 70 % RH the insulation thickness will be 7 mm
at 80 % RH the insulation will be 12 mm and
at 90 % RH the insulation will be 25 mm
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| Thickness requirement |
- Calculate the thickness required in accordance with BS 5422 Appendix G.
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| The calculation of the thickness of Armaflex required for condensation control assumes: |
- Still air conditions, natural convection, and the absence of direct sunlight.
- Proper spacing between insulated surfaces, an air gap of at least 25 mm should be allowed between the insulated pipes.
- High emissivity surface, greater than 0.9, so that the outer surface coefficient of heat transfer may be calculated in accordance with table 32 of BS 5422:1990.
- For the calculation of insulation thickness for Armaflex in this manual a computer spread sheet has been utilised.
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| For more detailed information refer to |
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