Building heat recovery

Recovering heat in homes, hotels and offices.

Recovery and reuse · Shared heat and everyday recovery · No. 138

• Recovery and reuse
• Heat grade: Low

A Mumbai hotel heated its tap water from 30 C to 65 C using waste heat from its air conditioning chiller.

Chart: Illustration: Building heat recovery

Where it comes from

Chart: Map of where it comes from

Buildings throw heat away in stale air, shower water, cooking fumes and air-conditioner condensers. Each stream is lukewarm, so recovery uses simple exchangers or heat pumps.

Three things to know

1. A heat-pump water heater uses about 73-78% less electricity than an electric tank heater.
2. Drain-water heat units cost USD 300-500 and are just a copper coil wrapped round a vertical drain, with no moving parts.
3. In a US Army kitchen, demand-controlled exhaust cut airflow 23-32% and almost halved fan electricity.

The journey

1. 1 Wasted streamsStale air, shower water, condenser heat
2. 2 ExchangerPassive cores or copper coils catch heat
3. 3 Heat pumpUpgrades lukewarm heat where needed
4. 4 Hot water, airPreheated supply for taps and rooms
5. 5 Lower billsLess electricity, gas or diesel bought

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