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I live in a cool place. This winter we had extended periods of -20C. Heat pump efficiency drops, but still stays above 2. SCOP (for year round average for heati

I live in a cool place. This winter we had extended periods of -20C. Heat pump efficiency drops, but still stays above 2. SCOP (for year round average for heating coefficient of performance) units sold now are better than 5. Also, if you are worried about the refrigerant leaking, you can sacrifice a little bit of efficiency and buy a unit using CO2 as a refrigerant with a GWP of you know: 1. I think the biggest problem here for leakage are random construction dudes cutting the pipes when they demolish or remodel homes. If only they could gather the gas in the outdoor unit before, all of it would be saved.

coryrc 5y ago
If the hot water heat pump is a single unit (which is the vast majority of residential installations) and indoors, it is just stealing heat from your regular heating system. You're paying for that heat, so you aren't getting COP > 1.
- benhurmarcel 5y ago
  You're only paying for that heat in the winter though.
  - coryrc 5y ago
    Hence the preface of "cold area", but my heating season is over 6 months. The ROI is already long in HWHP even assuming the best numbers, and often negative once you account for reality in areas which get cold.
- larsalmen 5y ago
  Who has that, a "indoor heat pump"? That's just stupid. Sure, exhaust air heatpumps "use" the (excess) heat from indoors, but that would just get expelled anyways.
  - coryrc 5y ago
    https://www.hotwater.com/water-heaters/residential/hybrid-electric-heat-pump/ https://www.hotwater.com/water-heaters/residential/hybrid-el... this is what people are talking about when they reference hot water heat pumps without qualification, because they are the vast majority of the market. There is no excess indoor heat in winter in 99.9%+ non-passivhaus homes.
    - larsalmen 5y ago
      Right, I stand corrected. I had never seen such a heatpump (based in the nordics, that concept would never fly), and I'll agree with you that in homes heated by "regular means" (resistive/electrical, fossil fuels) they add little to no value, simply adding complexity. In heating season they would just siphon heat energy from the rest of the house... (They would however de-humudify the space they are in, but that's another thing...) I'd argue that every house that has any sort of ventilation, even naturally aspirated ones, have excess heat in that any amount of air leaving the house "unreclaimed" while there is any heating need contains wasted energy. Heatpumps using that energy are very prevalent in the Nordics and Scandinavia, even with a majority of the time being heating season here.

coryrc 5y ago

If the hot water heat pump is a single unit (which is the vast majority of residential installations) and indoors, it is just stealing heat from your regular heating system. You're paying for that heat, so you aren't getting COP > 1.

benhurmarcel 5y ago
You're only paying for that heat in the winter though.
- coryrc 5y ago
  Hence the preface of "cold area", but my heating season is over 6 months. The ROI is already long in HWHP even assuming the best numbers, and often negative once you account for reality in areas which get cold.
larsalmen 5y ago
Who has that, a "indoor heat pump"? That's just stupid. Sure, exhaust air heatpumps "use" the (excess) heat from indoors, but that would just get expelled anyways.
- coryrc 5y ago
  https://www.hotwater.com/water-heaters/residential/hybrid-electric-heat-pump/ https://www.hotwater.com/water-heaters/residential/hybrid-el... this is what people are talking about when they reference hot water heat pumps without qualification, because they are the vast majority of the market. There is no excess indoor heat in winter in 99.9%+ non-passivhaus homes.
  - larsalmen 5y ago
    Right, I stand corrected. I had never seen such a heatpump (based in the nordics, that concept would never fly), and I'll agree with you that in homes heated by "regular means" (resistive/electrical, fossil fuels) they add little to no value, simply adding complexity. In heating season they would just siphon heat energy from the rest of the house... (They would however de-humudify the space they are in, but that's another thing...) I'd argue that every house that has any sort of ventilation, even naturally aspirated ones, have excess heat in that any amount of air leaving the house "unreclaimed" while there is any heating need contains wasted energy. Heatpumps using that energy are very prevalent in the Nordics and Scandinavia, even with a majority of the time being heating season here.