Most of my posts on this site are HVAC related. But as a hobby, I sometimes tinker with Microcontrollers. Microcontroller ADC’s have a “resolution” formula that is often stated incorrectly.
Hopefully, this post can clarify some confusion for beginners.
This is where I discuss the concept of VAPOR PRESSURE in detail. Vapor Pressure is without any doubt the most important psychrometric property that needs to be understood for the HVAC engineer trying to learn psychrometrics. It is bizarre that many students are going through “Psychrometric Chart” training without even talking about Vapor Pressure. The fact that ASHRAE chose not to show this property on their standard chart may have something to do with this trend. You can “draw process lines” on the charts without any mention of Vapor Pressure but the penalty you pay is a loss of key underlying psychrometric concepts.
As usual conversion from PowerPoint to PDF and no narration leaves out a lot. But I think the following will still be very helpful to new engineers.
Please send in your comments and corrections to me. Thank you.
The original talk on this topic was a Power Point presentation. The PDF attached does not have the benefit of the verbal commentary along with the slides.But it still conveys some key concepts and should prove useful. (There is some “inside” humor sprinkled around, as the original was intended for my own Company Project Engineers – please ignore.)
I wrote this booklet in the middle 80’s when pneumatic controls ruled in the HVAC Industry and DDC was just beginning to appear. (We were all fascinated with what can be done with a microprocessor based control with 16k bytes of memory!) Although the content is a little dated, I still think it should serve very useful for people trying to figure out just what a PID controller does and how it is different from a straight Proportional only controller.
I will post this booklet in 3 parts: Part-1 Introduction and Proportional. Part-2 Integral. Part-3 Derivative.
I hope you find it useful. Please click on the PDF link below and then come back here for your comments.
Many HVAC engineers work their entire careers and retire without realizing that what they always thought of as Fan Static Pressure is not how ASHRAE, AMCA or the fan manufacturer’s define Fan Static Pressure (FSP). The concept of Fan Static Pressure is a purely “defined” one – there is no direct measurement in the field that corresponds to “Fan Static Pressure”. FSP is commonly confused by Engineers with the Fan Static Pressure Rise or Duct Static Pressure Rise.
Confusion in the use of the terms STATIC PRESSURE and TOTAL PRESSURE is widely prevalent among HVAC Engineers and Contractors. There are serious consequences of not distinguishing clearly between the two, and one example would be that you make troubleshooting more difficult and in some cases impossible.
This article clarifies the distinction between Static Pressure and Total Pressure.