Hitachi launches CO2 heat pump water heaters with solar-friendly tariff controls
Hitachi’s new CO₂-based heat pump water heaters, tuned to run when solar-powered electricity is cheapest, highlight a broader shift toward high-efficiency, low‑GWP refrigerants in residential heating and hot water. Commenters compare CO₂, propane, and other refrigerants in terms of global warming potential, safety, and required operating pressures, and note that real-world coefficients of performance around 3–5 can cut electricity use by more than half versus resistive heaters. The thread also touches on time‑of‑use and dynamic electricity tariffs, regional product availability (notably in Japan and Australia), and how falling equipment prices—driven in part by Chinese manufacturing—are key to large‑scale heat pump adoption.
Refrigerants: CO2, Propane, Ammonia, Others
- CO2 (R-744) as a refrigerant is well-known in commercial/industrial systems; in residential, it’s more niche and often used for water heaters.
- Pros of CO2: GWP = 1, non‑flammable, non‑toxic, cheap, regulation‑light compared to F‑gases.
- Cons: very high pressures, expensive hardware, less common in residential HVAC, particularly outside Japan.
- Propane (R-290) and isobutane (R-600a) are praised for very low GWP and strong performance; concern is flammability, though several commenters feel the fire risk is overstated for typical charge sizes.
- Ammonia seen as efficient and good for outdoor-only systems, but widely regarded as too dangerous indoors (toxic, highly irritating).
Environmental Impact & GWP
- Multiple comments stress that legacy refrigerants (e.g. R-12, R-410A) have very high GWP and are being phased out.
- Hydrocarbons’ climate impact is argued to be limited because they oxidize quickly to CO2.
- Recent IPCC values cited: propane GWP revised down to ~0.02; R32 revised up.
- Some note that CO2 leakage from a heat pump is negligible compared to a person’s annual CO2 footprint.
Efficiency and COP
- JIS efficiency values (~4.1–4.2) interpreted as COP: ~4 kWh of heat per 1 kWh of electricity.
- Discussion of how heat pump water heaters behave in cold climates: COP drops in sub‑zero conditions but remains advantageous over resistive heating.
- CO2 systems said to excel at large temperature lifts (e.g. hot water tanks), less so for low‑delta applications like radiators.
Tariffs and Solar-Oriented Operation
- “Tariff” debated linguistically; in utility context it means pricing schedule, not import duty.
- Japan and parts of Europe use dynamic or time‑of‑use tariffs; devices like these heaters can be optimized to run when solar power is abundant or prices are low.
Japanese EcoCute Experiences
- Several users describe Japanese CO2 “EcoCute” water heaters with:
- External units sourcing heat from outdoor air.
- Integration with time‑of‑use tariffs and, optionally, rooftop solar and weather forecasts.
- Bath‑specific features (automatic fill, temperature maintenance via recirculation, app control), with bathrooms designed to tolerate overflows.
System Design & Alternatives
- Interest in hydronic systems (air‑to‑water heat pumps, monoblocks, R‑744 or R‑290) for future houses; seen as easier to route and quieter than forced air.
- Some curiosity about Stirling-engine heat pumps; cited research suggests they are 30–50% less efficient than vapor‑compression systems.
- For old radiator-based homes, options like high‑temperature air‑to‑water heat pumps are discussed but not deeply resolved.
Manufacturing, Costs, and China vs Japan
- Japan praised for quiet, robust, efficient heat pumps, but cost is high.
- Debate over future dominance of cheaper Chinese units: some fear quality loss; others argue Chinese manufacturers already deliver good performance, strong value engineering, and significant R&D.
- View expressed that lower-cost, “good enough” heat pumps may maximize global efficiency gains via higher adoption, even if top-end Japanese units are slightly better technically.