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Comment by alliao | Hacker News Reader

Japan do have such system though not for export as they're still iterating through at their own pace. Daikin do used to have an Altherma product for sale, but heatpump for heating isn't as nice as gas furnace if you consider the fact that body temp is usually higher than the temperature heatpump outputs at efficient levels.

For example, to heat a room to 70 degrees indoor meant if they can output heat at 75 degrees then it'd be sufficient, unfortunately no one would want to have 75 degrees wind blowing on them in winter. We want something like 150 degrees so it actually feels warm.

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That's actually one of the general issues with heatpumps - because they aren't literally lighting something on fire (or using resistive heating which just lights money on fire) they have smaller temperature deltas when designed properly as you mention. This leads to things like oversized air conditioners in hot places because people will cycle the AC creating a high peak demand and if it isn't 'blowing cold' they think it isn't working.

Heat pumps (assuming they can vary their output, which most new ones can) work much better to keep a constant temperature whether hot or cold and actually create a really nice indoor environment if a) designed or sized correctly and 2) have good thermostat placement. There's plenty of software, standards, and guides out there to hit both of those and then you just have to educate the users to set a temperature and then forget about it other than monthly filter cleaning. This is hard coming from 100% or 0% duty cycle systems like most fossil-fuel heat and old-style air conditioners so some think heat pumps are 'wimpy' and don't work. Placement is also part of that - you shouldn't be sitting in the output of the unit (which tend to be lower velocity than forced hot air etc) because the unit should be placed so it can cool the entire space.

>We want something like 150 degrees so it actually feels warm.

The reason why you want the air cooler in the summer and warmer in the winter is to achieve a similar (comfortable) rate of heat loss through your skin. The reason why that feels different even at the same air temperature is due to humidity and radiative heating differences. Your HVAC isn't just heating and cooling you, it's also heating and cooling all of your walls. If your wall temperature varies by 10 degrees between summer and winter, even with the same air temperature, it'll feel different because of the increase or decrease in infrared coming off of the walls. The better insulated and less leaky your house is, the lower that differential will be. If you could run radiative cooling through external walls and ceilings, you would only need a fraction of the typical air movement in a house for ventilation and you would still feel totally comfortable.

We don't need to heat rooms with body temperature ventilation, we just need to keep a comfortable rate of heat loss for human occupants. That's dependent on radiative heat, air temperature, humidity, and air velocity.

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