Delta T Calculation

[nrgeng]

Why is Tout of the Cooler Unit 313.15 C (273.15 + 40) below the expected 384.555 C {424.555 - 313.15 = 111.405}? Since ∆K = ∆C, why is 273.15 involved in the calculation? The fsd file has been emailed.

[jasper]

Indeed delta-K matches delta-C, but your variable has the dimension K, not delta-K. COFE does not know that this is a temperature difference, unless you indicate that. In the information calculator that calculates delta T, please change the unit of measure of output Delta T: mark the "Relative (e.g. pressure or temperature difference)" box.

[jasper]

Perhaps some future version of the information calculator will be smart enough to check the specified unit of measure; it will then have to perform unit of measure algebra, in which case it would have marked the result of the subtraction of two variables with dimension temperature as a delta-temperature.

However, such algebra would want to know the unit of measure of constants in the information calculator equation.

[nrgeng]

No difference in Tout whether IC Relative is checked or not. Set point changed to 0 C then Tout is 153.271 C. Something else is going on here. Please check, what is your Tout?

[jasper]

After changing the unit of temperature to delta-temperature, please delete and re-insert stream 33. It got populated with a variable with dimension of temperature rather than delta-temperature.

[nrgeng]

The IC Unit shows the Relative box checked. See attached image. Stream 33 was deleted and a new Steam, 36, was created and connected in place of Stream 33. No change in Tout (153.271 C). The problem is resolved by adding 273.15 to the IC output function (DeltaT). Any explanation for this phenomenon?

IC Unit Output Panel

Delta T Calculation-IC Unit.jpg (337.74 KiB) Viewed 24682 times

The thought that if set point = 0, then Tout = Tin. Not 153.271 C. Do you agree. Using IC version 2.7.0.0.

[jasper]

The controller itself had also inherited the unit of measure of the measured variable and applied it to the set point, can you re-insert it?

[nrgeng]

Stream 33 was deleted and a new Stream 36 was created so that should be equivalent to re-inserting the MV--right? Still Tout = 153.271. What do you have for Tout with SP = 0 C? Does the unit for DeltaT remain "K" after denoting the Relative status?

[jasper]

I am unable to check right now, but the quickest way to check if a number is a temperature or a delta-temperature is to change the unit of measure from C to K or vice versa. The number is a delta-temperature in case the value remains the same.

[nrgeng]

Previously I misunderstood what Unit to replace so I replaced the Stream. After re-reading your posting, I replaced the controller. The Tout result is now what I expected. Thanks for your help.

Do you know of any way the Controller Unit could "alert" that it was corrupted and needs to be replaced. We both have spent time on this minor aberration. As standard procedure, do I now replace every Controller Unit on a large flow sheet during the debug just in case it too is corrupted? Lots of work! What do you say?