What is the definition of ‘critical charge’?
The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE), defines ‘critical charge’ as follows:
“Refrigerant quantity required by a system to maximize performance when a capillary or fixed restriction expansion device is used.”
The inverter mini split world has been using the term ‘critical charge’ in describing the critical nature of the charge in their systems but if we look at the literal definition of ‘critical charge’ it is an inaccurate use of the term…I have been guilty of this myself.
Most inverter mini splits utilize an Electronic Expansion Valve (EEV) as the refrigerant metering device. The EEV by its anatomy is NOT a ‘fixed restriction expansion device’ like a traditional capillary tube or Thermostatic Expansion Valve (TXV).
The following comes from an article written by John Tomczyk, a professor of HVACR at Ferris State University and published in the August 2, 2004 issue of The ACHR News:
“EEVs control the flow of refrigerant entering a direct expansion evaporator. They do this in response to signals sent to them by an electronic controller. A small motor is used to open and close the valve port. The motor is called a step or stepper motor. Step motors do not rotate continuously. They are controlled by an electronic controller and rotate a fraction of a revolution for each signal sent to them by the electronic controller. The step motor is driven by a gear train, which positions a pin in a port in which refrigerant flows.
Step motors can run at 200 steps per second and can return to their exact position very quickly. The controller remembers the number of step signals sent by the controller. This makes it possible for the controller to return the valve to any previous position at any time. This gives the valve very accurate control of refrigerant that flows through it. Most of these EEVs have 1,596 steps of control and each step is 0.0000783 inches”.
So, by the strict interpretation of the ASHRAE definition of ‘critical charge’ and the nature of the anatomy and function of an EEV, the term ‘critical charge’ does not apply to most inverter mini splits…so what do we call it?
Well, here is my proposal…‘Non-Fixed Orifice Critical Charge’ (NFOCC).
Are we splitting hairs here…maybe…but this misuse of the term ‘critical charge’ was brought to my attention in a recent mini split class I conducted in Canada and I had to admit to the faux pas.
Another area where the literal definition of ‘critical charge’ does not apply to most inverter mini splits is the fact that rarely is it required for an installer to remove refrigerant should the installer not use the maximum lineset length determined by the
pre-charge. Where a receiver is present in these systems, any unused refrigerant will be stored in the receiver…in smaller systems that do not have a receiver; unused refrigerant will be stored in the accumulator. If the charge was truly defined as ‘critical charge’, refrigerant would need to be removed in this scenario.
The charge in inverter mini splits is so…here I go again…critical, that it can’t be over stated…these systems are a hot mess, (pun intended), when the charge is less than exact! I have experienced this first hand…you can convince yourself that the problem is in a control board, (either indoor unit or outdoor or both), and in fact your problem is being under charged.
Here is my advice when you have a problem with an inverter mini split system…pull the charge, calculate the weight of the correct charge and weigh it in…trust me…more often than not this will lead you toward resolution of your problem!
14/4 wire – 14/3 with ground wire? Tomato – tomahto?
I had another interesting discussion come up in Canada about the wire / cable requirement between the Comfort-Aire inverter mini split outdoor and indoor units. I have been describing the cable as 14/4…14 gauge wire, 4 conductors. A gentleman attending a mini split class stated it is 14/3 with ground…
tomato – tomahto?
I never had this come up before…I always thought it was pretty straight forward but I do see in the MARS product catalog, (they got EVERYTHING), that it is stated and available as both…14/3 with ground and 14/4.
Hey look, I’m no electrician, but best I can tell the only difference between the two is that in 14/3 with ground, the ground wire is bare and solid and in 14/4 the ground is insulated, (green).
Seems to me both will work just fine for the Comfort-Aire VFH, VMH and DV equipment.
Class notes downloads
The past couple years I have been making the class notes for all my classes available as a download on my website. The past six months has seen the curriculum for all my classes change substantially and as a result I encourage all past students to once again download the notes for the class you attended…there’s a lot of new stuff in there!
If you have forgotten your password, just email me with the subject of the class you attended and where and when the class was held I will email you back with the password.
I suggest downloading the class notes at least once a year as the products change, technology changes and my class curriculums change accordingly. You can update yourself by simply downloading the class notes…no need to take the course again…unless you want to! I would be glad to see you again!
I strongly suggest anyone who attended a mini split class in the past to download the notes again…this subject has seen the most changes to the curriculum and I believe you will be pleasantly surprised how multi-zone mini split technology has continued to evolve.
Just click on ‘DOWNLOADS’ in the upper tool bar. Click on the class subject you attended and then enter your password…you can now download the class notes.
Some months back in a previous newsletter I wrote about my positive experiences with the business networking tool known as LinkedIn. I want to re-visit the LinkedIn subject with you once again.
After each class I conduct, I use the class sign-in sheet to capture attendee’s email addresses so I can add them to my newsletter distribution list and I also check to see if the attendee is registered on LinkedIn…if they are, I send them an invitation to ‘connect’.
Let me say again, as I have said many times…LinkedIn is NOT social media! I hate social media…right or wrong, I am NOT on Facebook or Twitter and have no desire to find old girlfriends, (there weren’t many anyway), or kindergarten classmates. I find the concept of social media to be a bit creepy…there is usually good reason why we move on from people in our past.
LinkedIn is business networking…I don’t care if you’re a one man / woman ‘Mom & Pop’, (or just Mom or Pop), in the HVACR contracting world or you’re a big HVACR manufacturer…you will find it beneficial to use LinkedIn. LinkedIn can help you find new clients, stay in touch with current clients and expose you to ideas, companies, products and people that you otherwise may not have encountered on your own.
You may find a new job…you may find your next employee through LinkedIn.
Look, we all need a little help growing our business and staying ahead of the curve…LinkedIn is a tool to help you do just that.
You can register for LinkedIn here.
Give it a try and when you do, send me an invitation to ‘connect’…I will look forward to it!
I haven’t written anything other than serious HVAC stuff in a long time so a little music discussion is long overdue.
I just came back from a week in Canada conducting mini split classes. I got turned on to a band from Kingston, ON. called ‘The Tragically Hip’.
One of the many reasons I love working in Canada is I always get turned on to music I haven’t heard down here in the States. Canadian radio stations are actually mandated by law to dedicate at least 35% of their air time to Canadian artists…I think this is a great concept!
As you would expect, you hear a lot of RUSH, The Guess Who, BTO and Gordon Lightfoot, but you also hear bands like Doug & The Slugs, Big Sugar, The Kings, Coney Hatch and The Tragically Hip, (the locals just call them ‘The Hip’).
The Hip have a tune you got to check out titled, ‘50 Mission Cap’. It is the story of the 1951 Toronto Maple Leafs and their Bill Barilko. Bill scored the winning goal clinching the 1951 Stanley Cup for the Leafs…and then four months later he went missing. The Barilko story is fascinating and the song does a masterful job of telling that story in a clever and rocking manner.
Check out The Tragically Hip performing ‘50 Mission Cap’ back in 1993 on YouTube.
A special thanks to my friend Mike Duffy of Delta Components for turning me on to The Hip!
See you soon!
The views and opinions expressed in this newsletter are those of the author and do not necessarily represent those of ESPCO’s sponsors and training partners.