Retrotec DM32 User Manual download pdf (Page 19)

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©Retrotec Inc. 2014

“TrueFlow”

2.6.4. Estimate Results with [@ Pressure]

The [@] pressure key enables the gauge to calculate and display the estimated [Channel B] Result that

would be achieved, as if the target pressure was reached (also known as “extrapolation”). The [@

Pressure] key only appears on the Home screen if [Set Speed] or [Set Pressure] functions are used and the

gauge is measuring pressures on Channel A and B.

 This function is useful in situations when the fan has reached 100% speed and the enclosure

pressure still has not reached the target pressure.

 Additionally, this function is useful since the measured [Channel A] pressure will usually be slightly

over or under the desired/set pressure, making it difficult to report results that exactly at the

specified pressure.

Tapping [@ Pressure] will toggle the extrapolation function on or off. The label under [Channel B] display

will change to indicate whether [@ Pressure] “is On” (e.g., CFM@25.0Pa) or “is Off” (e.g., CFM).

Details of how the gauge calculates the flow at exactly the target pressure, when [Channel A] has not

reached exactly the set target pressure, can be found in Appendix D.

 If the [Set Speed] function is used, [@ Pressure] extrapolates the [Channel B] Result to the [Default

@ Pressure] set in the “Settings” screen, using the “n value” chosen in [Settings].

 If the [Set Pressure] function is used, [@ Pressure] extrapolates the [Channel B] Result to the

pressure entered for [Set Pressure], using the “n value” chosen in [Settings].

The @ Pressure function provides unique advantages over non-extrapolated results:

 There is no need to achieve an exact [Channel A] pressure (e.g. to a precision of 0.1 Pa)

 [Channel B] Results can be obtained even if the test pressure cannot be reached**

**Although the gauge can extrapolate results to any pressure, it is more accurate when the actual

enclosure pressure read on [Channel A] is close to the target pressure. As a rule of thumb, extrapolation

can be used if the actual enclosure pressure reaches at least 80% of the target pressure. If 80% cannot be

reached, more fans are needed to complete the test (See Retrotec’s Manual-Lge-Multi-Fan Testing).

Example #1 - Inaccuracy

A 50 Pa building pressure is desired, but only 20 Pa can be reached (due to severe leakiness). In this

instance, the extrapolated results for flow “@ 50 Pa” do not represent the reality of the testing conditions

and might be highly inaccurate.

In the same situation, a 45 Pa building pressure is achieved. The extrapolated “@ 50 Pa” pressure is now

much more accurate, and provides an acceptable result.

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Retrotec DM32 User Manual Page 19