Heat Exchanger Selection for Industrial Heat Pumps: Temperature Approach, Pressure Drop and Part-Load Performance

Introduction
Short Answer
Why Temperature Approach Matters
Working Principle: Duty, Area and Temperature Difference
Pressure Drop: Compare the Whole Operating Cost
Select the Circulation Pump Against the System
Part-Load Operation and Fluid Distribution
Engineering Practice: Prepare a Consistent Enquiry
Frequently Asked Questions (FAQ)
Conclusion
Sources

Introduction

Industrial heat pumps need more than an efficient compressor. The heat exchangers connecting the refrigerant circuit to the heat source and the process can strongly influence overall performance.

This connection was highlighted in Alfa Laval’s published programme for Chillventa, held October 13–15, 2026, in Nuremberg. The programme listed new brazed heat exchanger models for natural refrigerants and developments in semi-welded plate heat exchangers. A presentation scheduled for October 15 focused on heat exchanger performance in refrigeration and heat pump applications.

The manufacturer’s event page confirms the programme and product themes; it does not provide independently verified savings for a particular installation. Its publication date is not stated. (alfalaval.com)

For process engineers, the practical question is clear: how should a heat exchanger be specified so that the complete heat pump system performs well?

Short Answer

Evaluate heat exchangers together with the compressor, circulation pumps and operating conditions.

The key checks are:

Required heat duty and all inlet and outlet temperatures.
Temperature approach at the relevant operating points.
Allowable pressure drop on each side.
Performance at minimum, normal and maximum load.
Fluid compatibility, fouling and maintenance requirements.

A design that meets the peak heat duty can still be unsuitable if its pressure losses, operating limits or part-load behavior do not match the system.

Why Temperature Approach Matters

Temperature approach describes the temperature difference between the two fluids at a specified location in a heat exchanger. Always identify which terminal temperatures are being compared.

For a conventional subcritical heat pump condenser, the refrigerant must condense above the temperature of the fluid being heated. In the evaporator, the refrigerant must evaporate below the temperature of the source fluid.

For otherwise comparable conditions, reducing these differences can reduce the temperature lift required from the compressor. However, the benefit depends on the complete cycle and operating envelope.

Alfa Laval’s heat pump application guidance connects exchanger sizing and configuration with system performance and explains how insufficient heat transfer surface can increase refrigeration-cycle lift. (alfalaval.com.au)

The engineering implication is to ask for both exchanger performance and the resulting compressor operating conditions. A small approach temperature is useful only when its benefits justify the associated equipment and operating costs.

Working Principle: Duty, Area and Temperature Difference

A basic heat exchanger relationship is:

Q = U × A × F × LMTD

Where:

Q is heat transfer rate.
U is the overall heat transfer coefficient.
A is heat transfer area.
F is the correction factor where required.
LMTD is the logarithmic mean temperature difference.

For two positive terminal temperature differences:

LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁ / ΔT₂)

As an illustrative calculation, terminal differences of 20 K and 10 K give an LMTD of approximately 14.4 K. Differences of 15 K and 5 K give approximately 9.1 K.

If duty, U and F remain unchanged, the second case requires approximately 58% more area.

This is a simplified comparison, not a product selection. Refrigerant phase change, temperature glide and changing fluid properties can require a more detailed calculation.

Spirax Sarco’s heat transfer guide explains mean temperature differences and the thermal resistances that affect U. (spiraxsarco.com)

Pressure Drop: Compare the Whole Operating Cost

Pressure drop should be specified separately for each side of the exchanger.

On a circulation-water circuit, exchanger resistance contributes to the pump’s required differential pressure. However, demanding an extremely low exchanger pressure drop can also change the selected plate arrangement, channel velocities and purchase cost.

Alfa Laval’s pressure-drop selection paper discusses this trade-off for gasketed plate heat exchangers in HVAC applications. Its examples also connect low channel velocities with fouling risk. Those examples should not be treated as universal limits for industrial process fluids. (alfalaval.com)

A useful procurement approach is to request two technically acceptable alternatives with different pressure-drop allowances. Compare their purchase prices, predicted pumping requirements and maintenance assumptions using the same operating profile.

Do not choose an alternative solely because one number—area, pressure drop or initial cost—is lower.

Select the Circulation Pump Against the System

The circulation pump must deliver the required flow against the resistance of the complete circuit, including the exchanger, piping and other components.

Grundfos’s pump-curve guidance explains that pump performance curves relate flow to head and should be evaluated together with system characteristics. Efficiency also varies across the operating range. (grundfos.com)

For a heat pump enquiry, request the exchanger pressure drop at each specified flow case. Then use those results when checking the pump operating points.

This creates a clearer division of responsibility: the exchanger supplier provides its hydraulic performance, while the system designer evaluates the combined circuit. If the exchanger selection changes, revisit the pump calculation rather than carrying forward the original duty point automatically.

Part-Load Operation and Fluid Distribution

Industrial heat demand often changes during operation. A maximum-load calculation therefore provides only part of the selection evidence.

Alfa Laval’s heating and cooling FAQ identifies refrigerant distribution, oil return and freezing conditions as relevant considerations for brazed and fusion-bonded exchangers. It also explains that debris on the water side can obstruct small channels and disturb fluid distribution. (alfalaval.com)

Translate these concerns into specific supplier questions:

What is the permitted minimum operating load?
Which refrigerant and fluid conditions were used in the selection?
What filtration and commissioning cleanliness are required?
Which temperature and flow limits must the controls maintain?

Avoid assuming that a unit selected for one refrigerant, water quality or operating profile will perform identically under another.

Engineering Practice: Prepare a Consistent Enquiry

The following table is an engineering synthesis of the selection issues discussed above.

Enquiry item

Information to provide or request

Thermal duty

Minimum, normal and maximum heating requirements

Temperatures

Inlet and outlet temperatures for both sides at each case

Fluids

Refrigerant, secondary-fluid composition and relevant properties

Hydraulics

Flow rates and allowable pressure drop on each side

Operating envelope

Startup, shutdown and minimum-load requirements

Maintenance

Cleaning method, access needs and contamination assumptions

Supplier evidence

Thermal and hydraulic calculations for the offered configuration

Use the same operating cases for the heat exchanger, compressor and pump enquiries. Otherwise, individually acceptable equipment selections may be based on inconsistent assumptions.

Frequently Asked Questions (FAQ)

Is the lowest possible temperature approach always best?

No single approach temperature is optimal for every installation. Compare the resulting system performance with equipment cost and operating constraints.

Should exchanger pressure drop always be minimized?

Evaluate its effect on pumping, exchanger configuration and lifecycle cost. Request alternatives where the trade-off is significant.

Does a new product announcement establish project suitability?

An announcement identifies a product or technology to investigate. Project suitability requires configuration-specific calculations and documentation.

Can one peak-load calculation demonstrate acceptable operation?

It cannot establish performance at operating points that were not evaluated. Include the load cases that matter to the actual process.

Conclusion

The heat exchanger developments featured in the Chillventa 2026 programme highlight an important design relationship: heat pump performance depends on how heat is transferred into and out of the refrigerant circuit.

For practical equipment selection, connect temperature approach, pressure drop, pump performance and part-load requirements in one consistent enquiry.

The most useful supplier proposal demonstrates how the offered configuration performs across the intended operating envelope.