Excel formula for Calculating Humidity Using Dry/wet
Hi Guys i Need some help with my excel chart
i am a agronomist at a hydroponic farm and have to keep a track on humidity on hourly bases,
so what i am trying to do is create a excel sheet and when added the dry blub and wet blub temperature in a cell another cell should add humidity by itself so in that case i dont have to calculate the humidity every time
i hope i was able to explain what i want
please help
Welcome to the forum
I love the "blub" part, but have no idea whatsoever what you are talking about...
Please attach a sample workbook (not a picture or pasted copy). Make sure there is just enough data to demonstrate your need. Include a BEFORE sheet and an AFTER sheet in the workbook if needed to show the process you're trying to complete or automate. Make sure your desired results are shown, mock them up manually if necessary.
Remember to desensitize the data.
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Hi, welcome to the forum.
I don't know what the formula is to calculate humidity, but if you look that up you can add the formula to the cell next to it and have the calculation.
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Here is a Sheet for example where i have added the dry blub temperature and wet blub temperature and the difference between dry and wet was auto substracted in the following cell,
just like that i want a excel formula which will calculate the humidity by using dry and wet blub temperature readings and display it in the humidity cell
And what would you expect the result to be in the humidity column for your two examples?
It seems that humidity calculations require a dew point value, and that's not available in your data, so it's a no go: https://www.wikihow.com/Calculate-Humidity
Last edited by AliGW; 05-04-2021 at 12:56 AM.
Ali
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How much of your question is specific to Excel, and how much is a more general psychrometry (did I get that right?) question? We are usually good at programming stuff in the spreadsheet if the user can explain the necessary math, engineering, scientific, or other background information needed to do the programming, but we are not always knowledgeable in those areas to come up with the necessary algorithms.
Assuming "humidity" means relative humidity, most descriptions of how to calculate relative humidity from wet/dry bulb temperatures involve a psychrometric chart. Your sample file does not include any of that necessary information. I found this page (https://www.engineeringtoolbox.com/h...ent-d_561.html ) that includes a chart and table. Other sites I read suggested that psychrometric charts/tables would be pressure specific (your file does not include a barometric pressure anywhere), so this particular chart/table may not be useful. From what I can see, the basic programming procedure would be:
1) Enter dry and wet bulb and barometric pressure (if you decide it is necessary).
2) From dry and wet bulb, search your psychrometric chart/table using that information to get relative humidity. Excel's lookup functions could easily be used on a table like that shown in the engineering toolbox site, if you can get a table like that specific to your location/altitude/whatever. If you need help putting together a 2D lookup formula, let us know, because we have several examples across this site and can readily help with the lookup step if you can come up with the lookup table that you want to use for this.
I apologize that I cannot be more specific, but it seems that the big roadblock at this point is getting the necessary table or chart that will allow you to enter wet/dry bulb temperatures and back out relative humidity. Once you find a source that you like for that information, the Excel programming side of the problem should be straightforward.
Originally Posted by shg
@mrSorty, you used the correct words, we help without the knowledge the OP may probably have to carry things out.
So I don't know excel formulas very well (which is a reason I joined this site) and I'm not super with math. But I am a resourceful calibration tech that has to calculate relative humidity from dry and wet bulbs occasionally. Here's a site I found helpful. It asks for your dry and web bulb temps and calculates your RH from those only. Barometric pressure is not used nor is the dew point. I'm assuming since you're not using a decimal your calculation does not need high accuracy. This website also has all it's calculations at the bottom. I'm hoping somebody smart here can use those to create the formula.
(apparently, I haven't posted enough to post links, so here's the math)
Relative Humidity is measured using a device called a sling psychrometer. This consists of 2 side by side conventional thermometers, one of which (the wet bulb thermometer) has a wetted wick placed at the bottom, the other (the dry bulb thermometer) has no wetted wick.
When the psychrometer is swung around by its attached chain or handle, the air causes the water on the wick to evaporate which produces a lower temperature in the wet bulb thermometer. We now have a dry bulb and a wet bulb temperature which we can use to calculate relative humidity. The easiest way to do this is entering the dry and wet bulb temperatures into the calculator above and then click calculate. For example, if we have a dry bulb temperature of 20℃ and a wet bulb temperature of 15℃ what is the relative humidity? Using the calculator, we see that this is 58.4 %.
Now, let's try using the above equation. (The equation is so complex, for ease of use, it has been split into 3 parts.)
We have
dry bulb temp (Td) = 20℃ and wet bulb temp (Tw) = 15℃
What is the relative humidity?
Solving for ed
ed= 6.112 ✱ 2.71828(17.502 ✱ 20 ➗ 240.97 ✚ 20)
ed= 6.112 ✱ 2.71828(350.04 ➗ 260.97)
ed= 6.112 ✱ 2.71828(1.3413)
ed= 6.112 ✱ 3.8240
ed= 23.372
Solving for ew
ew= 6.112 ✱ 2.71828(17.502 ✱ 15 ➗ 240.97 ✚ 15)
ew= 6.112 ✱ 2.71828(262.53 ➗ 255.97)
ew= 6.112 ✱ 2.71828(1.0256)
ew= 6.112 ✱ 2.7888
ew= 17.045
Solving for relative humidity
rh = ([ew ➖ .66875 ✱ (1 ✚ .00115 ✱ Tw) ✱ (Td ➖ Tw)]➗ ed) ✱100
rh = ([17.045 ➖ .66875 ✱ (1 ✚ .00115 ✱ 15) ✱ (20 ➖ 15)] ➗ 23.372) ✱100
rh = [17.045 ➖ .66875 ✱ 1.01725 ✱ 5] ➗ .23372
rh = [17.045 ➖3.4014] ➗ .23372
rh = 58.376
rh = 58.4%
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