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psychrometric properties
04-14-2018, 12:45 PM
Post: #1
psychrometric properties
For those interested in a compact & concise formulation for the Numerical Calculation of psychrometric properties on a calculator, I suggest a perusal of Numerical Calculation of psychrometric properties on a calculator by A.K. Singha, Harpal Singha, S.P. Singh & R.L. Sawhney from PERGAMON at Elsevier Science Ltd (Building and Environment 37 (2002) 415 – 419).
Abstract
Simple and precise equations for calculation of saturation vapour pressure in three different temperature ranges are presented in the
paper. Input parameters required for calculation of psychrometric properties are wet- and dry-bulb temperatures, dew point and dry-bulb
temperatures and relative humidity and dry-bulb temperature. In this paper, the equations used for computing saturation vapour pressure
may also be used for determining dew point temperature for the entire pressure range. © 2002 Published by Elsevier Science Ltd.

Keywords: Dry-bulb temperature; Wet-bulb temperature; Dew point temperature; Humidity ratio; Specifc volume and relative humidity


explanatory excerpt:
… equations from (1) to (13) are used for the
determination of psychrometric properties, if any two
psychrometric properties of an air–water mixture are
known.
(see Table 1) [attachment=5833]
(1) Dry- and wet-bulb temperature, or
(2) dry-bulb and dew point temperature, or
(3) dry-bulb temperature and relative humidity.
Thus,
Case(1): When Ta and Tw are known:
Case(2): When Ta and γ are known:
Case(3): When Ta and Tdp are known:

The paper presents three equations for the calculation
of saturation vapour pressure in three different temperature
ranges 0°C to −40°C, 0°C to 63°C and 63°C to 110°C. The
same equations also calculate dew point temperature. The
relationships proposed here are valid from −40°C to 110°C.
Outside the stated limits, the equations need to be reformulated.
The paper also defines various physical and thermodynamic
properties of air–water mixture and determines their
values by direct calculations.

If you are interested & can neither find &/nor download the document, feel free to PM & I'll do my best to facilitate.

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SlideRule
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04-15-2018, 06:05 AM
Post: #2
RE: psychrometric properties
(04-14-2018 03:44 PM)Mike (Stgt) Wrote:  My approach was a simple, fast but sufficiently accurate approximation [...]
Hi Mike. You're utilizing the Magnus-formula, right?
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04-15-2018, 11:49 AM (This post was last modified: 04-16-2018 11:35 AM by SlideRule.)
Post: #3
RE: psychrometric properties
I hope my post on ©Numerical Calculation of psychrometric properties on a calculator is taken as value added to the member(s) on the topic. The material, in my assessment, only offers a different perspective on the material without claim to being simpler, more accurate, more complete etc. I proffer NO such critique of the comprehensive posting(s) by other members on the attendant subject but rather another historical reference on the same, hence the title of the web site, the Museum … Calculators. I would post the ©article in its' entirety except the ©article is still available from ®Elsevier. Perhaps a more seasoned and senior member will PM an alternative from individual downloads to an open post in this forum.

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ps: I do reply to PM's (+2)
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04-16-2018, 04:56 AM (This post was last modified: 04-16-2018 04:57 AM by Ángel Martin.)
Post: #4
RE: psychrometric properties
(04-15-2018 11:49 AM)SlideRule Wrote:  I hope my post on ©Numerical Calculation of psychrometric properties on a calculator is taken as value added to the member(s) on the topic. The material, in my assessment, only offers a different perspective on the material without claim to being simpler, more accurate, more complete etc. I proffer NO such critique of the comprehensive posting(s) by other members on the attendant subject but rather another historical reference on the same, hence the title of the web site, the Museum … Calculators. I would post the ©article in its' entirety except the ©article is still available from ®Elsevier. Perhaps a more seasoned and senior member will PM an alternative from individual downloads to an open post in this forum.

Yes I agree it's a value added and provides perspective to the same subject. Comparing approaches is always an excellent way to learn!

Thanks for posting the references.

"To live or die by your own sword one must first learn to wield it aptly."
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04-16-2018, 10:27 PM
Post: #5
RE: psychrometric properties
I've worked in water damage mitigation for over a decade and have used all kinds of psychrometric calculators over the years. I believe specialized nomographs and slide rules were also made but I haven't laid hands or eyes on these myself.

This link explains the use of a pyschrometric chart, which I was taught how to use, but I've only ever used electronic calculators for the task.

The one I used most often was sold by the Dri-Eaz company and they called it the "Digital Pyschrometric Calculator." It was made in Taiwan. Notably, it takes about one full second to run grain/specific humidity calculations. I don't remember the exact price but they were surprisingly expensive, over $40 apiece.

Below are some pictures:

[Image: gS8oQpO.jpg]

[Image: qBtxRg2.jpg]

There are a couple of free apps floating around which also perform pyschrometric calculations.
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