This is the most common heat pump for hot water in India. It needs no well, no borehole and no waste stream. It needs only outdoor air and a place with good airflow.

The fan blows outdoor air across the evaporator (a finned coil where the refrigerant boils and absorbs heat). The compressor raises refrigerant pressure and temperature. The condenser (a plate or shell-and-tube heat exchanger) gives this heat to the water. The expansion valve drops the pressure so the cycle can repeat.

Most of India is warm, so air is a good source for most of the year. In Chennai or Mumbai, outdoor air is 25–35 °C almost all year. In Delhi winter nights it can drop to 5 °C, and in Leh to well below 0 °C. COP falls as air gets colder.

(All values typical; check the machine's datasheet.)

Worked example — Hotel hot water in Pune

A hotel needs 1,000 L of water heated from 25 °C to 55 °C each day. Compare an electric geyser and an air-to-water heat pump (typical COP 3.5). Example electricity rate ₹9/kWh.

• m = 1,000 kg, cp = 4.186 kJ/kg·K, ΔT = 30 K
• Q = 1,000 × 4.186 × 30 ÷ 3,600 = 34.9 kWh of heat per day
• Electric geyser (about 98 % efficient): 34.9 ÷ 0.98 = 35.6 kWh → 35.6 × ₹9 = ₹320 per day
• Heat pump: 34.9 ÷ 3.5 = 10.0 kWh → 10.0 × ₹9 = ₹90 per day
• Saving: about ₹230 per day, or roughly ₹84,000 per year.

Remember

• Source = outdoor air; sink = water.
• Needs free airflow; do not box the unit in.
• COP falls in cold weather; below about 5 °C, the coil may frost and need defrost.
• Best fit for most Indian hot-water jobs.