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Heat pumps have always had a built-in resistive heating element as a backup option for when it gets too cold out. This is terribly energy inefficient, but if y

Heat pumps have always had a built-in resistive heating element as a backup option for when it gets too cold out. This is terribly energy inefficient, but if you're talking about a few days a year at most it is fine, no need to install a second heat source. Besides, 0C is far too conservative an estimate for heat pumps. -10C was no problem even for 30 year old units.

michaelt 4y ago
> Heat pumps have always had a built-in resistive heating element as a backup option for when it gets too cold out. This is terribly energy inefficient, but if you're talking about a few days a year at most it is fine, Won't it be a problem if heating becomes much less efficient across an entire city, just as demand for heat is at its highest?
- js2 4y ago
  Indeed! In NC this past January, Duke Energy asked everyone to turn their thermostats down. NC has the one of the highest percentages of heat pumps in the country: https://news.duke-energy.com/releases/duke-energy-thanks-customers-for-help-during-cold-snap;-sets-all-time-records-for-winter-energy-use https://news.duke-energy.com/releases/duke-energy-thanks-cus... https://www.canarymedia.com/articles/heat-pumps/chart-which-states-have-the-most-heat-pumps https://www.canarymedia.com/articles/heat-pumps/chart-which-...
0cf8612b2e1e 4y ago
Large parts of the country can be consistently below 0C for weeks at a time. Resistive heating cannot beat gas in that scenario.
- SOLAR_FIELDS 4y ago
  True, but conversely a decent swath of the US population lives in Texas, where being under 0C for weeks at a time is a near impossibility. For those use cases heat pumps work great (assuming you don’t have a failed state on its own grid that will fall over at the slightest whiff of abnormality, of course).
- PaulDavisThe1st 4y ago
  Modern air source heat pumps will not be using resistive heating in most winter weather across the USA. A Mitsubishi Hyper unit still has a COP of 1.0 at 5F.
  - maxerickson 4y ago
    Resistive heat has a COP of 1.0. So that heat pump loses its advantage at 5 ⁰F.
    - PaulDavisThe1st 4y ago
      I didn't say that they still had an advantage, I said that switching to resistive heat was unlikely for most winter weather across most of the US.
      - maxerickson 4y ago
        "Still has a COP of 1.0" implies it is still doing something is all. It would be clearer to just say that it works down to 5. I'm not in the coldest regions and would be using resistive heat many nights of 3 months with that performance.
        PaulDavisThe1st 4y ago
        Mitsubishi's approach is to avoid resistive heating, and instead drop COP to 0.85 at -13F If the unit is sized correctly, this will provide adequate heat, albeit less efficiently than resistive heating would. If you live in an area where most of the heating hours are at 5F or below, yes, resistive would make more sense. But where is that?

michaelt 4y ago

> Heat pumps have always had a built-in resistive heating element as a backup option for when it gets too cold out. This is terribly energy inefficient, but if you're talking about a few days a year at most it is fine, Won't it be a problem if heating becomes much less efficient across an entire city, just as demand for heat is at its highest?

js2 4y ago
Indeed! In NC this past January, Duke Energy asked everyone to turn their thermostats down. NC has the one of the highest percentages of heat pumps in the country: https://news.duke-energy.com/releases/duke-energy-thanks-customers-for-help-during-cold-snap;-sets-all-time-records-for-winter-energy-use https://news.duke-energy.com/releases/duke-energy-thanks-cus... https://www.canarymedia.com/articles/heat-pumps/chart-which-states-have-the-most-heat-pumps https://www.canarymedia.com/articles/heat-pumps/chart-which-...

0cf8612b2e1e 4y ago

Large parts of the country can be consistently below 0C for weeks at a time. Resistive heating cannot beat gas in that scenario.

SOLAR_FIELDS 4y ago
True, but conversely a decent swath of the US population lives in Texas, where being under 0C for weeks at a time is a near impossibility. For those use cases heat pumps work great (assuming you don’t have a failed state on its own grid that will fall over at the slightest whiff of abnormality, of course).
PaulDavisThe1st 4y ago
Modern air source heat pumps will not be using resistive heating in most winter weather across the USA. A Mitsubishi Hyper unit still has a COP of 1.0 at 5F.
- maxerickson 4y ago
  Resistive heat has a COP of 1.0. So that heat pump loses its advantage at 5 ⁰F.
  - PaulDavisThe1st 4y ago
    I didn't say that they still had an advantage, I said that switching to resistive heat was unlikely for most winter weather across most of the US.
    - maxerickson 4y ago
      "Still has a COP of 1.0" implies it is still doing something is all. It would be clearer to just say that it works down to 5. I'm not in the coldest regions and would be using resistive heat many nights of 3 months with that performance.
      - PaulDavisThe1st 4y ago
        Mitsubishi's approach is to avoid resistive heating, and instead drop COP to 0.85 at -13F If the unit is sized correctly, this will provide adequate heat, albeit less efficiently than resistive heating would. If you live in an area where most of the heating hours are at 5F or below, yes, resistive would make more sense. But where is that?