5 ms·

Maybe I’m dumb, but aren’t compressors pressure-agnostic? They just add pressure, right? Other than needing to be a bit stronger to keep from bursting against

Maybe I’m dumb, but aren’t compressors pressure-agnostic? They just add pressure, right? Other than needing to be a bit stronger to keep from bursting against the higher delta with the ambient atmospheric pressure like the rest of the components.

Cerium 4y ago
In this case there is a higher delta between the system and the atmosphere as well as a higher delta between the hot and the cold side, which is what requires a stronger compressor.
- Gibbon1 4y ago
  I had a HVAC guy mention that seals are problematic always with non hermetic compressors. Everything larger than a fractional HP system has a shaft seal between the compressor and the motor. Small systems being a pain because there is less refrigerant and no way to monitor the amount.
  - warmwaffles 4y ago
    There is a way to monitor it, but you'd need to put in T-Junctions and add a pressure sensor on the high and low pressure sides. You'd then need to rig up some system to read those pressures. But _you_ would be unfortunately the one that has to do it because I don't think there are any off the shelf solutions.
mindslight 4y ago
The ideal model of everything is everything-agnostic. Refrigeration stuff is generally soft copper, and modern refrigerants are already working up in the hundreds of PSI. So I can see that getting expensive or requiring a sea change in materials.
- eloff 4y ago
  If they’re using copper, changing materials would probably save money. Copper is comparatively expensive. I suspect your premise that they are using mostly copper is incorrect, but then I write software for a living, what do I know.
  - loeg 4y ago
    Copper is (very) effective for conducting heat. Aluminum is also pretty effective but obviously has different material properties than copper. It might be a good fit here; I don't work in the space.
    - kazen44 4y ago
      aluminium also has the problem that it is a dissimaler enough metal from most other plumbing hardware (being either made of brass, copper or steel) that it will result in the buildup of a lot of gunk because the aluminium disolves.
      - eloff 4y ago
        That’s galvanic corrosion, but it’s usually an issue in water. I don’t know that it would be a problem with refrigerants, likely not.
    - bluGill 4y ago
      Aluminum generally has fatigue limits that mean it will fail eventually, releasing refrigerant (which is normally an environmental disaster)
      - dylan604 4y ago
        what qualifies as a disaster? the amount of refrigerant in a consumer unit just doesn't seem like a lot even if 100% of it was released. if it was a continuous supply, then maybe it could get disaster level, but these are closed systems with a finite amount. at these levels, it seems to me that just driving one's car would qualify as an environmental disaster.
SnowHill9902 4y ago
Power for compressible fluids is approximately proportional to the relation of pressures not difference.
zip1234 4y ago
Even if you do need to make thicker pipes, strength in a metal generally increases with the square of the thickness, so it doesn't cost twice as much in materials to double the strength.
- londons_explore 4y ago
  This isn't true. For pipes, double the pressure requires double the wall thickness, which requires double the material. However, I don't think raw material cost is a big part of the cost of refrigeration systems anyway.
  - samtho 4y ago
    The “soft” copper tubing they use in refrigerant lines is not only very cheap (it’s not 100% copper) but is very much over built for pressure it is likely going to be subject to. It’s way cheaper, in this instance, to simply sell a line set that works with 99% of systems instead of having dedicated factory lines and consumer confusion from having different grades of registrant tubing.
  - dragonwriter 4y ago
    > For pipes, double the pressure requires double the wall thickness, which requires double the material. Double the wall thickness requires more than double the material.
lazide 4y ago
Gearing on the motor driving the compressor, compression ratio, etc. all have a huge impact on wear and tear, power requirements, etc. These all change based on the pressure delta.

Cerium 4y ago

In this case there is a higher delta between the system and the atmosphere as well as a higher delta between the hot and the cold side, which is what requires a stronger compressor.

Gibbon1 4y ago
I had a HVAC guy mention that seals are problematic always with non hermetic compressors. Everything larger than a fractional HP system has a shaft seal between the compressor and the motor. Small systems being a pain because there is less refrigerant and no way to monitor the amount.
- warmwaffles 4y ago
  There is a way to monitor it, but you'd need to put in T-Junctions and add a pressure sensor on the high and low pressure sides. You'd then need to rig up some system to read those pressures. But _you_ would be unfortunately the one that has to do it because I don't think there are any off the shelf solutions.

mindslight 4y ago

The ideal model of everything is everything-agnostic. Refrigeration stuff is generally soft copper, and modern refrigerants are already working up in the hundreds of PSI. So I can see that getting expensive or requiring a sea change in materials.

eloff 4y ago
If they’re using copper, changing materials would probably save money. Copper is comparatively expensive. I suspect your premise that they are using mostly copper is incorrect, but then I write software for a living, what do I know.
- loeg 4y ago
  Copper is (very) effective for conducting heat. Aluminum is also pretty effective but obviously has different material properties than copper. It might be a good fit here; I don't work in the space.
  - kazen44 4y ago
    aluminium also has the problem that it is a dissimaler enough metal from most other plumbing hardware (being either made of brass, copper or steel) that it will result in the buildup of a lot of gunk because the aluminium disolves.
    - eloff 4y ago
      That’s galvanic corrosion, but it’s usually an issue in water. I don’t know that it would be a problem with refrigerants, likely not.
  - bluGill 4y ago
    Aluminum generally has fatigue limits that mean it will fail eventually, releasing refrigerant (which is normally an environmental disaster)
    - dylan604 4y ago
      what qualifies as a disaster? the amount of refrigerant in a consumer unit just doesn't seem like a lot even if 100% of it was released. if it was a continuous supply, then maybe it could get disaster level, but these are closed systems with a finite amount. at these levels, it seems to me that just driving one's car would qualify as an environmental disaster.

SnowHill9902 4y ago

Power for compressible fluids is approximately proportional to the relation of pressures not difference.

zip1234 4y ago

Even if you do need to make thicker pipes, strength in a metal generally increases with the square of the thickness, so it doesn't cost twice as much in materials to double the strength.

londons_explore 4y ago
This isn't true. For pipes, double the pressure requires double the wall thickness, which requires double the material. However, I don't think raw material cost is a big part of the cost of refrigeration systems anyway.
- samtho 4y ago
  The “soft” copper tubing they use in refrigerant lines is not only very cheap (it’s not 100% copper) but is very much over built for pressure it is likely going to be subject to. It’s way cheaper, in this instance, to simply sell a line set that works with 99% of systems instead of having dedicated factory lines and consumer confusion from having different grades of registrant tubing.
- dragonwriter 4y ago
  > For pipes, double the pressure requires double the wall thickness, which requires double the material. Double the wall thickness requires more than double the material.

lazide 4y ago

Gearing on the motor driving the compressor, compression ratio, etc. all have a huge impact on wear and tear, power requirements, etc. These all change based on the pressure delta.