Summary
This article is about a Humidity Calculator which I created at Czech Metrology Institute. You can download the program for FREE from official CMI web site here. Upload version is meant for public and is written in Czech language. For an English version please contact me. I will arrange an upload of an English version of program to the CMI website. All rights of this programme is reserved by CMI.
Importance of humidity calculation
If you are dealing with measurment of moisture in air, you will soon find out that you might need to recalculate the humidity variables between each other. For example you know the relative humidity and temperature, but you need to know the dew point. Or vice versa.
It could be for practical reason (because some humidity variables just have better properties – like dew point that is temperature independent unlike relative humidity). This applies especially to gauge calibrations in humidity metrology (if you are not sure what metrology is, you can found out more here). And how often do you need recalculation? In metrology almost all the time. Usually it’s because your instrument measure with better accuracy dew point than relative humidity, so you measure DP and then do recalculation to RH.
A limping competition? It depends
There is no point in disguising that there are commercial products for this purpose. Some are available freely, others need to pay extra. Paid versions usually cost several thousand crowns. In addition to the design and features offered, such calculators differ in the quality of the calculation. Some moisture calculators count better, others worse. This is mainly due to the fact that the formulas used can be quite complex and their implementation into the program is then much more demanding. In such cases, simpler expressions or simplifying assumptions (state behavior of ideal gas, etc.) are used. Therefore, if you need exact values to calculate the humidity values, you need to look for a really good calculator. This is especially true when working at other (higher) than atmospheric pressures where the presence of media is increasing. Relatively, the effect of pressure on calculated values typically ranges from units percent to tens of percent at pressures in MPa.
My personal experience with several such programs is that they either don’t use correction factors at all, or just with very strange results. It may even happen that the correction factors are implemented correctly in the program, but still cannot be reliably used. I think this is an exception, although the program may have different setup options, but it is very difficult to ensure a certain repeatability so that it always works with the specified settings. For example, if you turn on the use of correction factors, you expect that the program will actually use them and not “how ever.” The settings may not have responded correctly and the results could not be relied upon.
Affliction and Motivation
This brings me to the latest outreach of commercial programs, and the biggest one: the app can look good, use the best equations and offer different functions, but we don’t see it in such a nice commercial program. On the one hand, it’s understandable – the authors protect their know-how, their code. But, on the other hand, we as a user never know what the program actually uses the equations and procedures. In other words, we do not know what is under the cover – by which equations the calculation is solved or by what procedure. Given the typical complexity of calculating some variables, especially the correction factor, the risk of error is relatively high and the user cannot perform any check or just verify that the calculation takes place according to his needs (eg a particular standard or scientific article, etc.).
I said no, it wouldn’t work like that and decided to do my own program. In addition to the huge learning potential of such creation, I can intervene at any time and make any changes. I see the program and know exactly how and with what key equations the calculator counts.
Sample of Moisture Calculator
On the picture below is a preview of the graphical interface of created Humidity Calculator in version 1.03.
Humidity Calculator, Lukáš Kolík, 2018
Read me:
This calculator is not meant for sale. I created this at Czech Metrology Institute and all rights belongs to CMI. The full public version of the calculator you can still download for FREE on the CMI website (link here).
What you can do with the Humidity Calculator v1.03
The calculator offers several options. You can choose between the used equation, whether you want to use the enhancement factor or not, the type of carrier medium, and then specify the desired input quantity in the input and write its value along with some other data. As I wrote in the introduction, the following are available: dew point / frost point, relative humidity and water vapor partial pressure.
If you do not know what an enhancement factor is, it is basically a correction factor – such a crutch used in moisture practice – to correct the media’s influence. The medium in this case is air. Equations describing the effect of partial pressure on temperature are given for equilibrium over pure water without the presence of other gases (air). However, air molecules cause the vapor partial pressure to increase. Actually, the air acts as a solvent for water molecules, which helps to get from the liquid surface to the gaseous state.
In addition, it is possible to convert a given quantity from the measured pressure to another, which is also a very common operation.
Czech is perhaps the most sophisticated language in the world, but in practice – it’s just not good enough
Maybe you would be happy or at least OK with Calculator written in Czech, but I don’t expect that you are a majority :-). Thus, I also made an international English version of the Czech version. Preview of this Humidity Calculator the graphical interface you could see above. Original Czech version is for comparison down bellow.
Humidity Calculator, Lukáš Kolík, 2018 – originall Czech version 🙂
Read me:
This calculator is not meant for sale. I created this at Czech Metrology Institute and all rights belongs to CMI. The full public version of the calculator you can still download for FREE on the CMI website (link here).
Echo
What surprised me probably the most is the reactions of people who came into contact with the Moisture Calculator. I do not want to boast about this, certainly not, but for the time being, the reactions are very positive. A large percentage of the people who heard about the calculator – whether through a lecture or hearing – were interested in it. And I am really pleased, because even if it sounds like a cliché, I can do something that I enjoy and the other people find it useful. And it’s a really beautiful feeling. So I know that the job was and has a point.
Vision and crisis
Every program, application, or any software you can find have one thing in common – they are not perfect. In a few cases they might be close but not close enough. And the same is true here – Humid Calculator is not perfect.
Although I have made quite a lot of effort to create a good moisture calculator for calculating and recalculating moisture values – which I did in the end – I still see room for improvement. Actually great. There are plenty of plans for further enhancements and program extensions. The development of the program is certainly far from over. To begin with, here are the known issues and in the next section of the chapter I present a part of the vision for this program.
A) Known Issues
- the enhancement factor for air is up to about 2.03 MPa,
- for other gases (nitrogen, oxygen, argon, neon) are not at all,
- validation with enhancement factors only partial – it is difficult to find sufficient quality software to compare,
- coefficients for the Sonntag equation for the calculation of the saturated water vapor pressure: the first two lines are swapped against the search, which requires further investigation, however, there is absolutely no impact on the results (validation was in complete agreement with the Michell or Vaisala programs) – it is possible that the work of the program with the coefficients is correct or only the search has been swapped.
B) Vision for the future development
- add more moisture parameters,
- add equations to calculate error errors (exist on Sonntag’s formula),
- Add a choice between supercooled water and ice (the current version automatically recognizes by temperature whether it is a balance over liquid or solid phase),
- Tune the VK work with enhancement factors (eg using a reliable reference program, if any),
- Extend the scope of the enhancement factors for air for pressures above 2.03 MPa (not possible for the absence of relevant data that does not exist at the time of the search),
- add enhancement factors to other gases (same problem as in the previous point),
- rewrite to a separately executable program.
Conclusion, summary
About Humidity Calculator
The Moisture Calculator program allows calculation and recalculation of the most commonly used humidity variables in humidity metrology (dew point, frost point, relative humidity, partial pressure, absolute humidity).
Advantages of Moisture Calculator
- offers conversion of the most used humidity variables to another pressure,
- is easy to use – contains a well-arranged graphical interface, which is embedded in Microsoft Excel compatible with version 2007 (for older versions of Excel it is necessary to download a plugin on the web, which allows opening of .xlsx files)
- easily portable – because it is an Excel file, you can easily transfer the calculator to another PC,
- it is quite flexible – it allows user a basic configuration of the input: you can choose from two equation variants, there is the possibility of enhancement factor to further increase the accuracy, then whether input type setting quantities (dew point / frost point, relative humidity, partial vapor pressure) and carrier medium type (air, nitrogen, oxygen, argon) were successfully validated – with the same assignment, the outputs were successfully compared with several professional calculators.
Did you find this project interesting?
If you are interested in this kind of project, do not hesitate to contact me with your request. There is a contact form down at the end of this website.
Lukáš, author
27th May 2018