4 ms·

Can you explain why this is a big issue?

zbrozek 3y ago
The simplest devices are on or off. If they are grossly oversized they cycle a lot and make homes less comfortable by pushing a huge volume of hot or cold air briefly. Variable speed compressors are better, but blowers may not also be variable speed. So you'll get better efficiency but may still suffer a feeling of draftiness. A properly sized variable speed unit will operate within some optimal band of efficiency and constantly output nearly the minimum necessary air volume to achieve the target temperature.
- jlawrence6809 3y ago
  When I was shopping for a mini split recently all the models I could find seemed to be variable speed compressor and blowers, unless I was reading something wrong. So maybe this isn't an issue anymore? I oversized mine but wish I went even bigger after a cold snap we just had in the pnw this last winter.
  - zbrozek 3y ago
    Mini splits are better in this regard than traditional ducted installations.
danans 3y ago
Higher up front equipment costs , discomfort, potential humidity issues, higher energy costs, shortened equipment life, increased noise.
supertrope 3y ago
Combustion furnaces deliver very hot air so they can cycle on once in a while and then turn off. Heat pumps deliver warm not hot air so they have to run longer cycles. The slower rise in room temperature can even mean that it makes more sense to set a constant temperature on your thermostat instead of letting the temperature fall when you're away during the day (the conventional logic to save energy).
- notyourwork 3y ago
  Why is this an issue? We have a ducted/ductless system. Air handler for ducts on first floor and basement. Upstairs has a mini split in each room. Having air handler constantly push air at a reasonable temp makes for a very comfortable living condition. Compared to a furnace that’s on/off with wider temperature range and more divergent temperatures throughout the area.
moribvndvs 3y ago
I’ve had one for three years. While I generally love it, it cools too fast, which means it sucks at removing humidity, actually increases it a little. The installer over-provisioned.
- Tarrosion 3y ago
  I've heard this before -- that oversized cooling units (whether standalone AC or part of a heat pump) mean muggy interiors in the humid seasons. But...why? I'd think that a fixed amount of air compressed in the compressor means a fixed amount of condensation runoff from the unit, and it wouldn't matter much whether it's a big unit running occasionally or a small unit running frequently. Why is that wrong?
  - lbotos 3y ago
    I don't think it's about duty cycle -- it's seriously about speed of temp change and I _think_ dew point. But yes, I have a heat pump and in NYC Summer I cannot run it on anything but low otherwise it increases the humidity. It took me a few weeks of looking at the temp humidity graphs to understand that point.
    - BenjiWiebe 3y ago
      As it was explained to me, it is about duty cycle. The condensation doesn't instantly accumulate enough to make droplets and run all the way down the drain, so if the compressor only runs briefly the condensation is still on the fins and evaporates again. You need to keep the compressor going long enough that you actually have water running down the drain, instead of condensing/evaporating cyclically.
      - lbotos 3y ago
        Yes, I believe you are right!
  - throwup238 3y ago
    It's not a fixed amount of condensation because the air around the AC only has so much humidity. It quickly condenses just a little bit of water and then shuts off before the humidity in the rest of the house can redistribute to replace the now dry air. By running for longer it allows the water in the rest of the house to actually make it to the compressor.

The simplest devices are on or off. If they are grossly oversized they cycle a lot and make homes less comfortable by pushing a huge volume of hot or cold air briefly. Variable speed compressors are better, but blowers may not also be variable speed. So you'll get better efficiency but may still suffer a feeling of draftiness. A properly sized variable speed unit will operate within some optimal band of efficiency and constantly output nearly the minimum necessary air volume to achieve the target temperature.

jlawrence6809 3y ago
When I was shopping for a mini split recently all the models I could find seemed to be variable speed compressor and blowers, unless I was reading something wrong. So maybe this isn't an issue anymore? I oversized mine but wish I went even bigger after a cold snap we just had in the pnw this last winter.
- zbrozek 3y ago
  Mini splits are better in this regard than traditional ducted installations.

danans 3y ago

Higher up front equipment costs , discomfort, potential humidity issues, higher energy costs, shortened equipment life, increased noise.

supertrope 3y ago

Combustion furnaces deliver very hot air so they can cycle on once in a while and then turn off. Heat pumps deliver warm not hot air so they have to run longer cycles. The slower rise in room temperature can even mean that it makes more sense to set a constant temperature on your thermostat instead of letting the temperature fall when you're away during the day (the conventional logic to save energy).

notyourwork 3y ago
Why is this an issue? We have a ducted/ductless system. Air handler for ducts on first floor and basement. Upstairs has a mini split in each room. Having air handler constantly push air at a reasonable temp makes for a very comfortable living condition. Compared to a furnace that’s on/off with wider temperature range and more divergent temperatures throughout the area.

moribvndvs 3y ago

I’ve had one for three years. While I generally love it, it cools too fast, which means it sucks at removing humidity, actually increases it a little. The installer over-provisioned.

Tarrosion 3y ago
I've heard this before -- that oversized cooling units (whether standalone AC or part of a heat pump) mean muggy interiors in the humid seasons. But...why? I'd think that a fixed amount of air compressed in the compressor means a fixed amount of condensation runoff from the unit, and it wouldn't matter much whether it's a big unit running occasionally or a small unit running frequently. Why is that wrong?
- lbotos 3y ago
  I don't think it's about duty cycle -- it's seriously about speed of temp change and I _think_ dew point. But yes, I have a heat pump and in NYC Summer I cannot run it on anything but low otherwise it increases the humidity. It took me a few weeks of looking at the temp humidity graphs to understand that point.
  - BenjiWiebe 3y ago
    As it was explained to me, it is about duty cycle. The condensation doesn't instantly accumulate enough to make droplets and run all the way down the drain, so if the compressor only runs briefly the condensation is still on the fins and evaporates again. You need to keep the compressor going long enough that you actually have water running down the drain, instead of condensing/evaporating cyclically.
    - lbotos 3y ago
      Yes, I believe you are right!
- throwup238 3y ago
  It's not a fixed amount of condensation because the air around the AC only has so much humidity. It quickly condenses just a little bit of water and then shuts off before the humidity in the rest of the house can redistribute to replace the now dry air. By running for longer it allows the water in the rest of the house to actually make it to the compressor.