A view at how an overfeeding metering device would affect the refrigeration cycle. Orifice missing or too large, TXX stuck open or too large, or sensing bulb is loose or incorrectly attached.
I put a Sporlan See-All and 032 Catch-All onto a R134a mini fridge. It has a passive air cooled condenser. When it turns on the sight glass fills up with liquid and then it slowly empties as the head pressure reaches 165psi. Sometimes the cap tube begins to vibrate. Charge weight 1.76oz, if increased the suction line frosts back. I was hoping to "Clear" the sight glass but I think I would have to put a longer or smaller ID capillary tube in.
That's interesting. The larger filter drier and the larger sight glass should require more refrigerant to compensate. It will act like a recover. Frost back is not always bad, it can be below the freezing and dew point temperature but still he superheated vapor.
You're absolutely right. I thought I had recovered back to charge weight but I just recovered, evacuated to 500microns, charged to 1.76oz. It was in -15inHG vacuum low side. I ended up charging to 2.2925oz. The increased high side volume caused me to adjust charge to achieve a balanced system.
I understand this is based on a standard residential/ light commercial set up. I do have chillers who purposefully have flooded evaps. We have a SMARDT chiller that has 3400 lbs of 134a.
Your videos are great. Can you explain (or maybe one of your videos) about how they are using the larger inside coils to improve seer efficiency (for example a single speed 3 ton compressor with a 4 ton inside coil). An orifice tube can be sized ok but a txv is going to be a problem right? (I also hate adding extra components like solenoid valves to a system). They seem to be using large coils a lot now and I wondered how it works. Maybe they just can't use a txv or move the bulb down on the coil? Then the next issue is the two speed compressor and reduced liquid flow. I'm pretty familiar with refrigeration, just wondering about these new systems. (ha, not the one trick pony anymore). Somehow, they are combining two complete half sized units (separate compressors, valves and coils) into one single unit with changing compressor speeds.
There are a lot of different questions in there, I will do my best to answer them in text. 1st Larger coils = more surface = means better heat transfer = better efficiency. Bryan Orr with HVAC school wrote a great article called the evaporator coil with no Fins. It has to be the balance with the right amount of airflow. In one scenario a larger coil also means a warmer coil and less dehumidification, but one the airflow is adjusted the coil temperature will drop and you can have better dehumidification. Dehumidification always takes away from operating efficiency when rated in SEER. So to get a higher seer, a larger coil with more airflow hits those numbers but it does not provide proper dehumidification. This is why manual J (correct size) manual (s correct system selection) manual D (correct duct design) and manual T (correct registers) are so important. They all have to work together. Manual S works with manual J and the equipment sensible and latent capacities to choose the right system. A 3 ton unit is not a 3 ton unit, application is key. Manual S is the most overlooked part of system design. Once you look at the system capacities sensible and latent in a specific application you will see how one 3 ton will work when another will not. Manual S will also determine airflow rates. #2 metering device. TXV always beats a fixed office in every way except cost. A fixed office just just a hole, it cannot adjust. A TXV while not perfect adjusts to a variety of conditions. In a hot summer day and with a customer that keeps a cool indoor temperature you will see the fixed flood the evaporator washing oil away from the bearings reducing life of the system. On a cooler outdoor day there is not enough pressure to force enough refrigerant into the evaporator leaving high superheat and damaging the compressor from overheat. A TXV will do it's best to open and close the hole size. It will do it's best to keep the superheat from dropping too low damaging a compressor from flood back or being too high damaging the compressor from high superheat and overheat. #3 2 speed compressor. A Copeland scroll drops to 67% capacity unloaded or "low speed" It's moving less refrigerant overall. Even though it's moving less refrigerant into the evaporator coil it's also not "pulling" (time sake) as much either. If the indoor fan does not also slow to accommodate this will mean a warmer coil and less dehumidification. If the fan speeds adjusts with the staging it's still possible to be a low enough dew point to dehumidify. Regress if the suction pressure is higher or lower, regardless of the volume, the TXV will try to maintain a constant superheat. It has its limits. Even in Refrigeration, a rack will have multiple compressors to increase it decrease capacity as needed without affecting each individual metering device or Evap coils. #4 embrace solinoid valves. In there simplest form they can be installed before the metering device to control off cycle liquid migration to prevent flooded starts and elgrestly extend compressor life just as in refrigeration. They can also be used in a slue of other application, especially in cold climate heat pumps. #5 fixed orifice, TXV, single speed compressors, 2 stage compressors are in there way out. Already here and more every day is variable compressors and Electronic expansion valves. (The electronic expansion valve works like a solinoid too) love them or hate them, this is what the new HVACR will be.
Hi Ty, If you have a 2.5 ton compressor and a 3 ton air handler. You must change the TxV to match the 2.5 ton compressor? Or is a half ton difference ok to keep the 3 ton txv? Thanks 👍
The last lecture that I watched from this channel was fixed orfice metering device at 2021/6/14 ( length 42:40) who can I find the next lectures to follow up
does the meter valve for the outside unit need to match the one for the inside unit or is this a recommendation? Meaning if the outside unit is a .49 then the inside device needs to be a .49 as well or can they be different ?
No they will usually be different because the coil they are feeding will be a different size. On a side note fixed office metering devices have no place in the modern world. They "don't break" but they also don't operate very well either.
How many cfm of air is going across the evaporator coil? What metering device is used? Causes for flooded compressor new system. #1 airflow ductwork undersized #2 airflow return too small #3 Airflow filter too small/restrictive #4 airflow blower setup incorrectly #5 over recharged #6 Fixed office (piston)entering device outside design conditions #7 TXV sensing bulb not properly mounted #8 brazing without nitrogen flow leaves oxidation causes TXV to Stick open. #9 over heating TXV or sensing bulb during installation causes Stick open. #10 metering device missing or o resized #11 evaporator coil is too small #12 low load/temperature inside too low.
