Meteorological station for Wufi simulation

[Gunes Inan]

Dear All,

I recently joined the forum and first of all I would like to say Hi to everyone in this forum.

We are planning to install a meteorological station to our building to collect meteorological data for Wufi simulation, but before doing so, I would like to ask some questions to those of you who is doing the similar.

Q.1 There are a lot of meteorological dataloggers in the market, but I think most of them cannot store the data in a Wufi-recognized format, like *.try. I am wondering if any of you use a datalogger with such compatibility. Otherwise, am I going to manually convert to a recognized file format or use the spreadsheet file inside the tools folder ?

Q.2 To my understanding, using two sensors for radiation measurement, one for global radiation, the other for diffuse radiation, is a must. Am I right? What about atmospheric counter radiation? The convention is to calculate it or to measure it?

Thus my meteorological station will include following:

•Wind direction sensor
•Wind velocity sensor
•Rain gauge
•Temperature & RH sensors
•Global radiation sensor
•Diffuse radiation sensor

Am I missing anything?

Thank You,

Günes Inan

[Thomas]

Q.1 There are a lot of meteorological dataloggers in the market, but I think most of them cannot store the data in a Wufi-recognized format, like *.try. I am wondering if any of you use a datalogger with such compatibility. Otherwise, am I going to manually convert to a recognized file format or use the spreadsheet file inside the tools folder ?

Hi Günes, welcome to the forum!

I don't think that there is any data logger which can produce one of the required formats. Our own weather data once were collected in daily ASCII files, more recently they are written to a large central database (using our IMEDAS system). When we need weather data for a WUFI calculation, I extract the necessary data from the database and convert them to one of the formats recognized by WUFI, using data conversion tools I have written for that purpose.

You will have to do something similar. You can use the EXCEL sheet provided with WUFI. If you know how to write a program, you can also make a small software tool for the data conversion. For this purpose, the weather file formats that can be used with WUFI are extensively documented in the online help.

If you have problems creating the correct file formats from your data, we can do it for you as a free service, as long as you do not wish to have files converted on an industrial scale.

Q.2 To my understanding, using two sensors for radiation measurement, one for global radiation, the other for diffuse radiation, is a must. Am I right?

Yes. For other purposes, global radiation might be sufficient, but if the data are to be used for WUFI, then you need both. Otherwise WUFI cannot compute the solar radiation on differently oriented and inclined surfaces. (An exception might be if you only intend to do WUFI calculations for flat roofs; the solar radiation incident on this surface is simply the global radiation).

What about atmospheric counter radiation? The convention is to calculate it or to measure it?

Maybe you do not need the counterradiation at all. The earlier versions of WUFI ignored it, and the latest version only offers the option to use it. You need it if you wish to investigate the effect of night-time radiative cooling below ambient air temperature and the resulting dew deposition and possible mold growth. In almost all other cases you do not need it at all, and we then recommend to ignore it. Calculations allowing for counterradiation tend to be numerically more problematic, and the user should make the extra effort only if the nature of the investigation justifies it.

If you need the counterradiation for your investigations, it should be measured. There are empirical models to calculate it from other weather elements, but these models need data on the cloud cover, and you usually don't have data on that (the more elaborate models even need data on clouds at different heights).

If you intend to investigate the behaviour of vertical walls (subject to radiative cooling), then the wall is not only exposed to atmospheric counterradiation, but also to terrestrial counterradiation. In that case it might be advisable to measure not (or not only) the atmospheric countrradiation but also to directly measure the mix of atmospheric and terrestrial counterradiation incident on such a wall. We have demonstrated that WUFI can compute the resulting surface temperatures well if radiation data measured directly at the location are used. We do not yet have much experience with more indirectly acquired counterradiation data, and it may be that the quality of the data is then not good enough. The surface temperatures are influenced by the radiation balance at the surface, and the radiation balance (usually a few tens of W/m²) is the difference between two much larger numbers: the incident counterradiation and the thermal emission (both a few hundreds of W/m2). Even a relatively small error in the determination of the counterradiation might thus create a large error in the radiation balance and degrade the calculation results. We will have to investigate how accurately the counterradiation data must be in order to give useful calculation results.

Thus my meteorological station will include following:

•Wind direction sensor
•Wind velocity sensor
•Rain gauge
•Temperature & RH sensors
•Global radiation sensor
•Diffuse radiation sensor

Am I missing anything?

That's basically all you need. The barometric pressure has only a small effect on hygrothermal calculations; you can use an estimated average value.

Additional measurements may be useful if you are interested in specific situations. For example, if you are mainly interested in the behavior of west-oriented walls with exterior insulation and you have precisely such a wall at your location, you may directly measure the solar radiation incident on such a wall by installing a solarimeter vertically on the wall. Furthermore, you could directly measure the surface temperature of the wall and use this temperature as boundary condition for your calculations, avoiding the need to estimate solar absorptivities, heat transfer coefficients etc.

Regards,
Thomas

[Gunes Inan]

Dear Thomas,

Thank you very much for the extremely helpful information.

If you intend to investigate the behaviour of vertical walls (subject to radiative cooling), then the wall is not only exposed to atmospheric counterradiation, but also to terrestrial counterradiation. In that case it might be advisable to measure not (or not only) the atmospheric countrradiation but also to directly measure the mix of atmospheric and terrestrial counterradiation incident on such a wall.

Night time cooling is of high interest to us, as manufacturers of low heat capacity external thermal insulation systems. Thus, it wouldn’t be a mistake if we measure it. The only thing that I need to do, as I understand, is to locate the radiation sensor vertically at nights, so as to obtain the radiation data corresponding to the sum of atmospheric counterradiation and terrestrial counterradiation.

The reason I am asking this is that meteorological systems manufacturer, at least the ones I am in contact with, are not quite familiar with term like atmospheric counterradiation, and I need to figure out exactly what I need before I built my system.

Thank you,

Günes Inan

[Thomas]

The only thing that I need to do, as I understand, is to locate the radiation sensor vertically at nights, so as to obtain the radiation data corresponding to the sum of atmospheric counterradiation and terrestrial counterradiation.

The reason I am asking this is that meteorological systems manufacturer, at least the ones I am in contact with, are not quite familiar with term like atmospheric counterradiation, and I need to figure out exactly what I need before I built my system.

Hi Günes,

we are measuring the long-wave counterradiation with pyrgeometers. The attached picture shows one of them oriented horizontally for measuring the atmospheric counterradiation and two others oriented vertically for measuring the counterradiation (atmospheric and terrestrial) incident on the respective building components under investigation. In the third case, there is also a pyrheliometer (or solarimeter) for directly measuring the solar radiation incident on the facade. And of course they stay in these positions by day and by night because if you wish to explicitly take counterradiation into account for the energy balance at the facade, you must do so by day as well as by night.



I hope this helps. If you wish to use your measurements for WUFI calculations, please contact us about how to create climate files from the measurements. This can be a somewhat complex issue and it might be difficult to figure it out for yourself.

Regards,
Thomas