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. 2019 Oct 1;6:189. doi: 10.1038/s41597-019-0199-y

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© The Author(s) 2019

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Fig. 6 — Estimation of COP curves. Quadratic regressions are performed on manufacturer data⁹ distinguishing between air-source heat pumps (ASHP), ground-source heat pumps (GSHP), and groundwater-source heat pumps (WSHP).