4 ms·

Are there even heat pumps where efficiency goes down when the delta-T decreases?

• londons_explore 4y ago
  Yes. If the cold side gets too hot, the pressure on the compressor input gets too high, which means the compressor is doing far more work with every stroke - and input electrical power goes up massively. The motor overheats and the thermal cutout stops it. When the motor is cutting in and out efficiency goes way down. This is an issue with fridges. When you buy a new fridge and first turn it on, it's called a 'pulldown'. The compressor gets far hotter than it ever normally gets in normal operation. Most fridges are only rated for 3 pulldowns in their lifespan - and if you do more than that and the fridge fails, they'll claim it isn't in warranty anymore. And in modern fridges, the software keeps track of how often so they can deny the warranty claim too...
  • maxerickson 4y ago
    Seems like that fancy software should be able to manage the pull down and prevent the compressor getting so hot. I guess people would get mad if their refrigerator took longer to cool off.
    • jnsaff2 4y ago
      Most heat pumps where I live are inverter based and have a very gradual ramp-up, they also control the compressor according to the demand. Some heat pumps even have several inverters to control the compressor and the fans. One of my fridges has inverter based compressor too.