HVAC Fun

A new semester has begun at PGE's Pacific Energy Center and I've been going to alot of classes (as usual). The past few months as I make my transition from Photovoltaics back to Energy Efficiency there's been a need for me to learn more about commercial HVACR. Heating, Ventilation, Air Conditioning (and) Refrigeration.

HVAC is  complex , it's made gain a real perspective about another transition that's going on in my Engineer life as I transition from Electrical to Electro-Mechanical.  Mechanics seems easier because  you can usually see mechanics so less abstract than electrics can be.  The same thing that took me from GA. Tech Computer Engineering to Georgia Southern Electrical Engineering Technology: if something catches fire than you know you did something wrong. No missing commas blowing up rocket ships here.

But HVAC has a lot of moving parts and any EE knows moving parts equal trouble, hence electronics. Okay I'm being a bit sarcastic here.  The fact is, WRT to HVAC electronics can cause more harm than good sometimes.  When I was doing residential energy efficiency and working at Laney College in the Environmental Controls Technology (ECT basically HVAC) department, HVAC seemed incredibly simple.  A couple types of of domestic hot water heaters (DHW) a few kinds of air conditioning and heating systems and two simple rules: Laws of Thermodynamics and the refrigeration cycle.

Simple right? source

What keeps me grounded (pun so intended) is that in the end the same thing that applies with residential also applies in commercial Laws of Thermodynamics and the refrigeration cycle.  The refrigeration cycle is one of those things that once you learn it, you see it everywhere! Okay once you have it encounter your daily life. I probably learnt about the refrigeration cycle in middle school but only noticed it recently.






So the refrigeration cycle works like this:

1. The compressor compresses the gas. The compressed gas heats up as it is pressurized.
2. The coils on the back of the refrigerator let the hot ammonia gas dissipate its heat. The ammonia gas condenses into ammonia liquid at high pressure.
3. The high-pressure ammonia liquid flows through the expansion valve (often a thermal expression valve). It reminds me of the spray part of a bottle of perfume. One side of the hole is high-pressure ammonia liquid, the other side of the hole is a low-pressure area
4. The liquid  immediately boils and vaporizes, it's temperature drops rapidly. This is how refrigators get cold
5. The cold  is sucked up by the compressor
6. Rinse and repeat

You're probably noticing a relationship between Pressure and Temperature, there's another part to this equation: volume.  The refrigeration cycle is a real life example of the Ideal Gas Law. Yea, I'm taking it back to Chemistry Class!  But we'll save that fun for another time.