特灵空调

Quantum Climate Changer Engineering Bulletin

CLCH-PRB004-E4

1) Thermal Bridging standard and AHU Casing Selection Procedure

They are five ahu-casing classifications spelt out in the Eurovent’s Thermal Bridging standard (prEN1886) namely: TB1, TB2, TB3, TB4 and TB5.

How can these TBs be used in predicting the AHU casing condensation?

It can only be useful as a condensation prediction tools once all the TB values were plotted on the psychometric chart. The TB for the several casing design are drawn on 6 separate psychometric charts with each having a supply air leaving DB of 6o C, 8o C 100C, 120C, 140C and 160C respectively. Illustrations are in chart 1, 2, 3, 4, 5, and 6.

Each chart has four ahu-casing classifications designated as follows:

•Potential Casing Condensation Limit with Thermal Bridging Factor of TB4 class The lowest line of the chart represents the highest limit of an ambient condition that is most unlikely to produce external surface condensation when the TB4 ahu casing is specified. This is the lowest class in Eurovent. Although there is TB 5 but no requirement being specified, thus it is being ignored in The TB4 class in the Eurovent as TB5

•Potential Casing Condensation Limit with Thermal Bridging Factor of TB3 class The second range of the chart represents the highest limit of ambient conditions that are unlikely to produce condensation on the air-handling unit when the TB3 ahu casing is specified. Trane’s CLCP25mm casing has been tested and certified to TB3 class.

•Potential Casing Condensation Limit with Thermal Bridging Factor of TB2 class The third range represents the highest limit of an ambient condition that is unlikely to produce external surface condensation on the air-handling unit when the TB3 ahu casing is specified. Trane’s CLCP 50mm casing has been tested and certified to TB2 class.

•Potential Casing Condensation Limit with Thermal Bridging Factor of TB1 class The last range represents the highest limit of an ambient condition that is unlikely to produce external surface condensation on the air-handling unit when the TB1 ahu casing is specified.

The following steps should be followed to determine what air handling casing type is suitable:

Step 1:

Choose the chart that represents the supply air leaving dry bulb closest to your application. For example if the cooling coil design leaving dry bulb is 120C, select chart 4 that entitled “Supply Air Leaving Dry Bulb is 120C”

Step 2:

Plot the job site AHU equipment room ambient conditions on the selected chart i.e the equipment room ambient (DB & WB). Designer shall provide this. It is important to predict the equipment room ambient conditions accurately. These are not necessarily the design conditions for the job site. Trane tests have shown that there are substantial differences in equipment room ambient that can effect surface condensation within a 24hour period. Items such as time of day, auxiliary equipment operations and ventilation, to name a few, all effect the ambient air in the equipment room. Hourly outdoor air conditions can be obtained from data sources such as airports and weather stations near the job site. If the AHU plant room design is exposed to the outdoors, use these outdoor conditions to estimate the equipment room ambient. It is recommended to plot the ambient conditions at the hours of the day when moisture level is the highest. Typically the moisture level is the highest at 5 am, 10 am and 10 p.m. for the region.

Step 3:

To determine type of AHU casing design from the psychometric chart:

-Once you have done the step two above, you should know now what TB class of ahu casing design that you required to prevent the likely hood of ahu casing condensation. Let’s look at the example set below.