3 ms·

Windchill is irrelevant here, it only indicates what the temperature feels like to warm blooded mammals.

by throitallaway 4y ago

doctoboggan 4y ago
windchill as a concept can be applied to all evaporative cooling systems.
- 16bytes 4y ago
  Heat pumps are not an evaporative system. You can't lower the temperature across a gradient lower than the fluid temperature, no matter how fast that fluid is moving. You can cool things down faster, but you can't go lower. So if it's 10F, a 5F heat pump will work equally well at 0mph wind and 30mph.
  - cmui 4y ago
    You got it. A brief technical aside, heat pump performance is hurt by frosting, which happens at intermediate outdoor temps (~35-50F). Basically the outdoor coil is both below freezing, and below the dewpoint of the air. The frost forms a thermal insulating layer around the coil, and intermittently you have to run a defrost cycle to melt off the ice. This is a small hit to system efficiency.
  - doctoboggan 4y ago
    Yes, I never claimed they were. I was responding to the idea that only warm-blooded mammals have the concept of wind-chill. Any system that takes advantage of evaporative cooling will have the concept of wind chill. A "swamp cooler" is one example.
nkurz 4y ago
I was tempted to give a similar answer, but I'm not so sure it's irrelevant. Yes, the windchill won't affect the energy efficiency of the heatpump. But it will affect the rate at which the house loses heat, and thus the BTU's the system needs to provide to maintain a temperature. If the heatpump has been exactly sized to maintain a house temperature of (say) 70F at the expected winter low, adding a strong wind on the exterior of the house seems like it might make for a chilly morning. The effect isn't as strong as it is for bare skin at body temp, and hence the exact numbers will be off, but it's still there, right?

3 ms·

Windchill is irrelevant here, it only indicates what the temperature feels like to warm blooded mammals.

by throitallaway 4y ago

Windchill is irrelevant here, it only indicates what the temperature feels like to warm blooded mammals.

doctoboggan 4y ago
windchill as a concept can be applied to all evaporative cooling systems.
- 16bytes 4y ago
  Heat pumps are not an evaporative system. You can't lower the temperature across a gradient lower than the fluid temperature, no matter how fast that fluid is moving. You can cool things down faster, but you can't go lower. So if it's 10F, a 5F heat pump will work equally well at 0mph wind and 30mph.
  - cmui 4y ago
    You got it. A brief technical aside, heat pump performance is hurt by frosting, which happens at intermediate outdoor temps (~35-50F). Basically the outdoor coil is both below freezing, and below the dewpoint of the air. The frost forms a thermal insulating layer around the coil, and intermittently you have to run a defrost cycle to melt off the ice. This is a small hit to system efficiency.
  - doctoboggan 4y ago
    Yes, I never claimed they were. I was responding to the idea that only warm-blooded mammals have the concept of wind-chill. Any system that takes advantage of evaporative cooling will have the concept of wind chill. A "swamp cooler" is one example.
nkurz 4y ago
I was tempted to give a similar answer, but I'm not so sure it's irrelevant. Yes, the windchill won't affect the energy efficiency of the heatpump. But it will affect the rate at which the house loses heat, and thus the BTU's the system needs to provide to maintain a temperature. If the heatpump has been exactly sized to maintain a house temperature of (say) 70F at the expected winter low, adding a strong wind on the exterior of the house seems like it might make for a chilly morning. The effect isn't as strong as it is for bare skin at body temp, and hence the exact numbers will be off, but it's still there, right?