Heat Pump Waste Heat Recovery: Lifting Low-Grade Heat

The low-grade problem

Much recoverable heat is low-grade – 25-60C drain water, vent air, or process streams. Too cool to use directly, but too warm to waste. A heat pump lifts it to a useful temperature using a little electrical work.

How it pairs with air-to-air recovery

Start with passive air-to-air or air-to-water recovery to catch the easy grade, then a heat pump upgrades the remainder. In a pool or laundry, drain-water recovery feeds the heat pump’s evaporator.

Where it pays

• Domestic hot water from ventilation or drain heat.
• Process water pre-heat in food plants.
• Space heating backed by waste-heat basics.

COP and payback

A heat pump delivering 3-5x the input energy (COP 3-5) can make low-grade recovery economic where passive methods alone fall short. Validate with a payback calculation and read the industrial waste-heat case for a real example.

The temperature-lift principle

A heat pump value is that it moves more energy than the electricity it consumes, expressed as COP. For low-grade waste streams of 25 to 60C, a correctly sized heat pump can deliver three to five times the input energy as useful heat, lifting drain, vent, or process heat to the 45 to 60C needed for hot water or heating. The higher the source temperature and the smaller the required lift, the better the COP.

Layering passive and active recovery

The efficient pattern is passive first, active second: catch the easy grade with air-to-air or air-to-water recovery, then let the heat pump upgrade what remains. In a pool or laundry this means drain-water recovery feeding the heat pump evaporator, with the condenser supplying hot water. Stacking the two extracts more from the same waste stream than either alone.

Verification and control

Measure the heat pump actual COP under operating conditions, not just the nameplate, and confirm the source stream is reliably available, since recovery that idles because the drain or vent flow stops delivers nothing. Control should prioritize the heat pump when the source and demand coincide, and fall back gracefully otherwise. Validate the whole scheme with a payback calculation.

Questions fréquemment posées

What is heat pump waste heat recovery?
Using a heat pump to lift low-grade waste heat of 25 to 60C to useful temperatures with a small electrical input.

What COP can I expect?
Typically 3 to 5, delivering three to five times the input energy. The COP improves with a higher source temperature and a smaller lift.

How does it pair with passive recovery?
Passive air-to-air or air-to-water recovery catches the easy grade first, then a heat pump upgrades what remains, such as drain water feeding the evaporator.

Where does it pay?
Domestic hot water from vent or drain heat, process pre-heat in food plants, and space heating. Validate with a payback calculation.

Questions fréquemment posées

What is heat pump waste heat recovery?

Using a heat pump to lift low-grade waste heat of 25 to 60C to useful temperatures with a small electrical input.

What COP can I expect?

Typically 3 to 5, delivering three to five times the input energy. The COP improves with a higher source temperature and a smaller lift.

How does it pair with passive recovery?

Passive air-to-air or air-to-water recovery catches the easy grade first, then a heat pump upgrades what remains, such as drain water feeding the evaporator.

Where does it pay?

Domestic hot water from vent or drain heat, process pre-heat in food plants, and space heating. Validate with a payback calculation.