Industrial heat pumps recover heat from a low-grade liquid stream and raise it to a useful process temperature. For a duty described only as 15 MMBTU, the correct starting point is a custom process heat-pump study, not a catalog-unit price request. The load basis, temperature lift, source stability, and measured coefficient of performance must be fixed before equipment cost or savings can be trusted.
System Approach Comparison
Two equipment paths fit the described service. The deciding criteria are outlet temperature, heat-source behavior, and whether a packaged machine can meet both conditions without leaving its operating envelope.
| Approach | Best fit | Primary constraint | Procurement path |
|---|---|---|---|
| Packaged water-to-water heat pump | Domestic water, boiler feedwater, and process-water duties that do not require very high temperatures | Catalog leaving-water temperature, source temperature, flow limits, and compressor operating envelope | Request certified performance at the actual entering and leaving temperatures; McQuay is one identified water-to-water equipment source |
| Custom high-temperature heat-pump system | Large process duties, unusual fluids, or elevated supply temperatures such as 140°F and 170°F water |
Refrigerant temperature-pressure limits, compressor discharge conditions, heat-exchanger design, and controls | Issue a process-duty specification to qualified refrigeration-system suppliers and integrators |
Use the custom-system path for the proposed application until a packaged supplier produces a performance selection at the specified duty. A nominal water-to-water rating is insufficient because catalog ratings often use source and load temperatures unlike the process design point. Do not move on until the supplier’s selection states delivered heat, electrical input, flows, pressure drops, and operating limits at the required conditions.
Process Boundary Conditions
Before anything else, confirm whether 15 MMBTU means energy per batch, energy per day, or a heat-transfer rate such as MMBtu/h. Energy and power are not interchangeable. Equipment capacity requires a rate; an energy quantity also needs the transfer duration and operating schedule.
- Record the heat-source fluid, entering temperature, allowable leaving temperature, minimum and maximum flow, fouling tendency, and any contamination or corrosion constraints. Confirm the values under the worst production condition, not only at normal operation.
- Record the heated stream’s entering temperature, required outlet temperature, flow range, pressure, allowable pressure drop, and control tolerance. Confirm whether the existing steam exchanger remains available for startup, trim heating, or backup.
- Develop simultaneous source and load profiles. A large annual heat quantity does not justify a large heat pump if the source and demand occur at different times.
- Define utilities and site limits: electrical supply, cooling or rejection provisions during off-design operation, equipment-room constraints, maintenance access, and permitted refrigerant arrangements.
- Create a heat balance from measured flows and temperatures. Do not request vendor pricing until both sides of the proposed system close to an acceptable engineering tolerance.
Temperature-Lift Mechanism
The system is a refrigeration cycle arranged to absorb heat from the effluent stream and reject that heat, plus compressor work, into the process stream. The evaporator cools the source fluid, the compressor raises refrigerant pressure and temperature, and the condenser heats the destination fluid. An expansion device then returns the refrigerant to the low-pressure side.
Temperature lift drives the selection. The compressor does not operate merely between the two water temperatures: heat-exchanger approach temperatures place the refrigerant evaporating temperature below the source outlet and its condensing temperature above the required heated-stream outlet. A higher lift generally raises compressor power and discharge temperature while reducing heating COP.
High-temperature service therefore requires a refrigerant and compressor combination rated for the resulting pressures and temperatures. The supplier must plot the complete operating range, including startup, minimum source temperature, maximum requested outlet temperature, and reduced-flow conditions. Reaching 140°F or 170°F at one favorable test point does not prove that the machine can operate across the production envelope.
Capacity and Economic Calculations
Calculate heat duty independently on the source and load sides. For a single-phase liquid with negligible phase change, use:
Q̇ = ṁ × cp × (Tout − Tin)
Use consistent units and temperature-dependent fluid properties where they materially affect the result. If either stream changes phase or has a complex composition, calculate enthalpy change instead of applying a simple constant-specific-heat equation.
Heating COP is not an efficiency percentage:
COPh = useful heat delivered / electrical energy input
At a stated operating point, compressor-system electrical input follows from Ẇelectric = Q̇delivered / COPh. Multiplying COP by 0.5 is a derating assumption, not a second efficiency term. Apply such a factor only when it represents identified auxiliaries, degradation, part-load behavior, or an engineering contingency. Otherwise, calculate pump, fan, compressor, heater, and control-panel consumption explicitly.
Compare annual operating cost over coincident operating hours:
Heat-pump cost = total measured electrical input × electricity tariff
Steam cost = required useful heat / delivered steam-system efficiency × steam-energy tariff
Include demand charges, water treatment, source and load pumping, maintenance, backup heat, and downtime assumptions where they apply. Use the same annual heat delivered in both cases.
The quoted capital range of $50,000-$200,000 MMBTU is not dimensionally usable as written. MMBtu is energy, while installed-equipment comparisons normally require a defined capacity and scope basis. Obtain the original cost units, price year, included balance of plant, installation allowance, and capacity denominator before applying that range to the project.
Procurement and Commissioning Procedure
- Issue a duty specification containing the source and sink data, operating profiles, required availability, control interface, utility conditions, and fouling information. Require suppliers to identify every excluded item.
- Request a performance map rather than a single nominal rating. The map must cover the minimum and maximum source temperatures, required supply-temperature range, and expected flows. Confirm power input and heating capacity at each critical point.
- Compare proposals on installed scope: compressor package, heat exchangers, pumps, strainers, controls, electrical equipment, refrigerant management, insulation, piping modifications, commissioning, and performance testing. A low package price can omit most of the project cost.
- Select the design only after reviewing the refrigerant and compressor operating envelope. Confirm pressure and temperature margins at startup and at every specified corner condition.
- Define the control sequence. Establish permissives for proven source flow and load flow, then start circulation before enabling the compressor. Coordinate heat-pump output with the existing steam valve if the steam exchanger supplies trim or backup heat.
- Install temperature, flow, pressure, and electrical-power measurements needed for acceptance testing. Place sensors so they measure the heat-pump boundary rather than unrelated plant loads.
- Commission first at a stable, moderate condition. Verify flow, rotation, valve position, sensor plausibility, refrigerant-side operation, heat balance, and safety trips before moving toward maximum lift.
Performance Verification and Recurring Pitfalls
| Observed result | Likely issue | Check before adjustment |
|---|---|---|
| Outlet temperature is low | Insufficient capacity, excessive lift, low flow, or incorrect staging | Source temperature, both flow rates, actual duty, compressor loading, and operating envelope |
| COP is below the proposal | Different test conditions, auxiliary loads, fouled exchangers, or bad instrumentation | Use simultaneous boundary measurements and compare at the same source and sink conditions |
| Frequent shutdowns | Unstable flow, temperature-limit operation, pressure-limit operation, or control hunting | Trend permissives, temperatures, pressures, valve commands, and trip indication through each event |
| Good instantaneous savings but weak annual return | Low coincidence between heat availability and demand | Compare time-aligned production profiles and include standby or backup energy |
Calculate delivered heat and COP from synchronized measurements after temperatures stabilize. Reconcile condenser heat, evaporator heat, and electrical input within the project’s agreed measurement tolerance. Do not accept a test based only on reaching the outlet-temperature setpoint.
FAQ
Can I use a geothermal heat pump for industrial process heat?
A water-to-water or geothermal product can work when its certified operating envelope covers the actual source temperature, required outlet temperature, flow, and duty. Treat the search term as a sourcing route, not proof that a catalog unit fits the process.
Can I estimate power by multiplying COP by 0.5?
No. Calculate electrical input as delivered heat divided by heating COP, then add measured or specified auxiliary loads. Use 0.5 × COP only when the 0.5 factor has a documented engineering basis.
Does reaching the required water temperature prove performance?
No. Record stable source and sink flows, entering and leaving temperatures, total electrical input, delivered heat, and calculated COP at the design point; accept the system only after those values satisfy the approved performance test.