Professionals who care
By Michael Young , Pr . Eng .
MICHAEL YOUNG
Michael Young is a trainer , coach and mechanical engineer in the HVAC industry . He graduated from the University of the Witwatersrand in the field of Mechanical Engineering ( B . Sc Mech Eng ) in 2008 and qualified as a Professional Engineer ( Pr . Eng ) in 2013 . Michael is passionate about promoting knowledge and helping other young engineer grow within the industry through his training workshops and coaching sessions . Michael can be contacted on michael @ myhvaccoach . com or 073 171 2311 for any questions or HVAC training needs .
THE EASIEST WAY TO KILL
THE PERFORMANCE OF A DX COOLING SYSTEM
Part 1 : blindly trust the computer results .
The world that we live in has evolved over the past 20 years .
What used to take us years to complete is now done within a matter of hours and this is all thanks to the invention and implementation of computers .
Now , would it be possible to say that while computers have made life simple and more efficient , they have also opened the door for errors to be easily made ?
Think about it , to select a cooling unit , all we need to do is input some variables , click on the select button and bam ! a unit is selected for us without even thinking .
What about doing the design of an AHU unit ? We input some variable and bam !, the AHU is designed , selected , costed , and even drawn in 3-dimensions within a matter of seconds .
But what if I told you that while these systems have been fantastic in helping us design systems more efficiently , these computer systems / programs are not fool-proof and are prone to error . Think about it , have you ever questioned the results from a
computer program ?
How do you know the computer program results are even accurate ? Have you ever had to insert some crazy inputs into a program and get a crazy result as an output ?
I had this experience where I had to select a cooling unit with a return air condition of 37⁰C / 50 % RH , and I had to increase the unit size to get to the net sensible cooling load .
In reality , it ’ s highly unlikely that air will be returning to the cooling unit at this condition . So , I contacted the client and learnt that a typing error was made on the specification document and that an addendum was to be shortly issued with the correct return air conditions .
Now don ’ t get me wrong , computers are awesome , but they are just a tool . Quality and accuracy come with being able to use these tools correctly and by having a good understanding of the physics being applied .
Let ’ s talk about refrigerant pipe design as an example . There are tons of tools out there and some are even free and are available online . Now if you leave the selection on “ auto ”, the program will size the correct pipe size for you . However , when it comes to sizing the suction line of a DX system , the system has two options , namely a horizontal run and a vertical run selection .
Now why would we have two different options for the same line ? Is it insane to install two different refrigerant pipe sizes on the suction line ? What are the implications if we get this pipe sizing wrong ? Do we size the piping for maximum or the minimum load ?
Unfortunately , no computer program will tell you this answer but if you join us in next month ’ s publication , we will share with you the procedure on how to size refrigerant piping without blindly trusting the computer results .
Wishing you a successful month ahead and chat soon . RACA
" How do you know the computer program results are even accurate ?"
www . refrigerationandaircon . co . za RACA Journal I August 2022 47