Air conditioner with a heat-pump hot-water booster on its hot gas
by HVAC Builder
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An air conditioner that makes hot water from the heat it would otherwise throw away, the way a hot-water booster does it: a second, R134a heat pump whose evaporator is a plate exchanger on the A/C's hot gas. The A/C is a 20 kW-class split drawn from a supplier's own selection — coil faces, rows, fins, circuits and airflows, 7.5 K superheat and 5 K subcooling — on a Mitsubishi Electric LNB53 inverter rotary at its 60 rps rating speed. Between its compressor and its air condenser sits a **cascade exchanger**: the booster takes what the saturation difference across the plate drives, the air condenser rejects the rest, and the A/C condenses cooler for it. The booster's compressor is a catalog R134a heat-pump water-heater scroll standing in for the Mitsubishi SBB172, whose map is not published; its condenser heats water from 55 to 62 °C. The plate and the water side are an example's, not a maker's.
Example18–22 kW coolingEUExample system. Published by HVAC Builder to show suppliers what their own page looks like. There is no company behind it and it is not a product offer — the specification is generic and the performance is solved from the model on this page.
Design-point performance
Solved from this example's own model as it is published — the same numbers a supplier's page shows for their machine.
Component schedule
| Component | Kind | Duty |
|---|---|---|
| Evaporator — 900×600, 6 rows, 7 circuits | DX evaporator | 21.7 kW |
| Supply fan | Fan | -0.6 kW |
| A/C compressor — Mitsubishi LNB53 inverter rotary | Compressor | 4.6 kW |
| Booster plate — the A/C's hot gas into the booster's evaporator | Cascade exchanger | — |
| Condenser — 1412×977, 2 rows, 8 circuits | Condenser | -17.3 kW |
| Condenser fans | Fan | -0.2 kW |
| Booster compressor — R134a heat-pump water-heater scroll | Compressor | 3.3 kW |
| Hot-water condenser — 55 → 62 °C | Pipe-in-pipe HX | — |
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