Industrial heat-pump feasibility

Start with heat, not a product

A credible first screen plots heat sources and demands by temperature, capacity and time. It also checks whether direct recovery can serve any demand before compression is considered. The result should expose the pairings with the smallest temperature lift and longest coincidence.

Evidence needed for a first screen

Hourly or sub-hourly data is preferable to monthly fuel totals. Useful records include utility meters, boiler logs, refrigeration suction and condensing conditions, water flows, production schedules, clean-in-place cycles and shutdown periods.

• Source inlet and outlet temperatures
• Required supply and return temperatures
• Flow rates and heat capacity
• Operating hours and load variation
• Electricity connection and tariff
• Fuel price, boiler efficiency and backup duty

Build a source-sink matrix

List every recoverable stream down the rows and every heat demand across the columns. For each pairing, record the available and required temperatures, coincident hours, distance, contamination risk and maximum transferable duty. Eliminate pairings that fail on timing or temperature before estimating equipment.

The matrix should keep a direct heat-exchanger option beside the heat-pump option. Compression is justified only for the part of the duty that cannot be served at the recovered temperature.

Move from screening to concept design

A positive screen is not an investment case. Concept design needs a process flow diagram, exchanger approach temperatures, performance maps, electrical single-line review, control philosophy, backup duty and an installation plan. Uncertainty should be attached to each assumption rather than hidden inside one contingency.

Reasons to stop early

A project may be weak when the sink is intermittent, the source and sink never overlap, the lift is too large, the grid connection cannot support the compressor or process hygiene makes integration disproportionate. Stopping a weak concept after screening is a useful engineering result.

A screening calculation

Suppose a cooling circuit can release 900 kW for 5,500 hours each year and a hot-water loop needs 1,200 kW over the same hours. At a provisional COP of 3.5, a heat pump delivering 1,200 kW would absorb about 857 kW from the source and use about 343 kW of electricity. The source is large enough for that operating point, subject to exchanger approaches and variation through the year.

This calculation does not prove the project. It shows which measurements deserve attention. If the source falls to 500 kW during part of production, either heat-pump output must fall, storage must bridge the gap or another source must be found. The model should use a duration curve rather than the best recorded hour.

Decision gates before concept design

A useful screen has explicit gates. The source and sink must overlap for enough hours. The required lift must sit inside a credible product envelope. The electrical connection must support compressor starting and sustained demand. Process integration must preserve hygiene, pressure, control and production availability.

Failing one gate is not always final. A lower process supply temperature, larger heat exchanger, different heat source or phased electrical upgrade can change the result. Each change should be tested as a separate option so that the final concept does not hide a dependency.

The evidence a decision paper should contain

The decision paper should show the source and sink data, calculation boundary, equipment operating points, annual energy balance, backup arrangement, electrical demand and capital-cost boundary. It should separate measured values from estimates and supplier selections.

Sensitivity cases should include fewer operating hours, a colder source, a hotter return, lower COP, higher electricity cost and delayed grid work. A project that only works at the central estimate is not ready for an investment decision.