Four prevalent themes in the discussion
- Refrigerant choice and environmental impact – Participants weighed CO₂’s low GWP (≈1) against its high operating pressures, and compared it with hydrocarbons like propane (R‑290) which have very low GWP but are flammable.
- “CO₂ as a refrigerant isn’t new… more in the commercial/industrial space (probably because of the higher pressures needed to get into a liquid state).” – throw0101d
- “Propane as a refrigerant is that it’s a really powerful one… if it got out, it’s got a Global Warming Potential of 3, making it three times as bad as carbon dioxide and about 475 times better than the same amount of R‑134a.” – ErroneousBosh
- “CO₂ has a GWP of 1… while other refrigerants are worse – for example, R32 has a GWP of 675.” – moepstar
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“The global warming potential of hydrocarbons as such is generally overblown, since they oxidize into CO₂ in the atmosphere…” – himinlomax
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Practical performance and installation considerations – Talk centered on COP values, outdoor‑unit requirements, and unique features of heat‑pump water heaters (e.g., bath‑recirculation, low‑temperature operation).
- “If I’m not mistaken, it means 1 kWh of electricity moves 4.1 kWh of heat into your hot water tank. Heat pumps are amazing.” – alex_duf
- “Our Mitsubishi has other nice features like it can recirculate the water in the bath through a heat exchanger… so it will keep the water from cooling down to lukewarm.” – kalleboo
- “These tend to work fine down to –25 °C or so ambient temperature…” – stephen_g
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Detailed COP calculation showing electricity use cut in half versus resistive heating. – dhx
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Regional/regulatory context (Japanese market, tariffs, adoption) – Many commenters noted that CO₂ heat‑pump water heaters are common in Japan, helped by time‑of‑use tariffs and safety preferences, contrasting with Western markets.
- “This is for the Japanese market so perhaps the cons of the CO₂ systems are outweighed by the safety aspects.” – throw0101d
- Tariff schedule example: “8 AM‑10 AM: 35 yen/kWh … 10 AM‑4 PM: 13 yen/kWh … 4 PM‑6 PM: 35 yen/kWh … 6 PM‑8 AM: 19 yen/kWh.” – kalleboo
- “One of the main reasons I went heat pump electric… I’m just not that comfortable with gas, especially living in an earthquake‑prone country.” – kalleboo
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“I can’t remember which is condenser… This heats 300 or 400 liters – about the size of a US tank water heater.” – bluGill
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Cost, manufacturing, and global supply chain (Chinese vs. Japanese) – Debate over whether Chinese heat pumps offer comparable performance at lower cost, versus Japanese leadership in quality and innovation.
- “Japan is so far ahead the rest of the world for quality and innovative heat pumps… I worry in 15 years we will all have crapily made Chinese heat pumps for a fraction of the cost.” – boringg
- “PRC’s been white labelling / JV components for tier1 HVAC brands for 15 years now… Flagship PRC heatpump already caught up to JP in HSPF2 @ ~11 (GREE).” – maxglute
- “Chinese brands have all but caught up, they’re within a few percentage points in performance, but 3‑4× cheaper.” – turtlebits
- Discussion of PV export fluctuations and market dynamics. – pbhjpbhj, ZeroGravitas