Technology
Expansion technology that recovers the work a throttle destroys
In every vapour-compression cycle the refrigerant is throttled from condensing to evaporating pressure. That step is isenthalpic: no work leaves the system, and the available energy in the pressure difference is dissipated. An expander takes the same pressure drop and turns it into work.
The throttling loss
Refrigerant leaves the condenser as a high-pressure liquid and has to reach evaporator pressure. An expansion valve does that by forcing it through a restriction. The pressure falls, but the enthalpy does not: the process is isenthalpic. Part of the liquid flashes to vapour on the way down, and that flash gas does no cooling in the evaporator — it has already absorbed its latent heat from the rest of the liquid.
In a P–h diagram this is the vertical line from point 3 to point 4. Everything to the left of it is refrigeration effect you paid the compressor for and did not get. The larger the pressure lift, the longer that line and the larger the loss — which is why deep-freeze and high-temperature duties suffer most.
What an expander changes
An isentropic expansion from the same starting point follows a sloping line to a lower enthalpy, point 4′. Two things happen at once: work leaves the system, and the evaporator gains the enthalpy difference between 4 and 4′ as extra cooling capacity. The recovered work can offset compressor input; the extra refrigeration effect raises the useful output. Both push the COP up.
One component changed, nothing else
The expander sits exactly where the expansion valve sits today, between condenser outlet and evaporator inlet. The compressor, both heat exchangers, the refrigerant and the charge stay as they are. That is what makes it a retrofit rather than a redesign.
Expansion becomes a controlled process instead of a fixed restriction: our electronics set the expansion to the operating point, so the device follows part-load and seasonal variation rather than being tuned once at commissioning.
How our expander works
Expantec's device is a Multiphase Pressure Exchanger (MPE). It is not a turbine: there is no high-speed rotating machinery in the refrigerant stream, which is what has historically made expanders fragile in two-phase flow. The MPE exchanges pressure between the high- and low-pressure sides of the cycle and hands the recovered work back to the system.
It is designed to run safely and unattended inside an existing refrigeration installation, under the same safety devices and refrigerant containment the plant already has. How it does that is covered by our patent application; what matters to an operator is that the cycle behaves exactly as before, with less electricity going in.
Operating range
The device is designed for industrial heat pumps and refrigeration systems from roughly 100 kW thermal capacity, new or existing. It suits subcritical cycles with multiphase refrigerant flow — the everyday case in cold storage, process cooling and heat pumps operating below the critical point — and has no rotating components in the refrigerant stream. A detailed specification sheet per capacity class follows the current pilot programme; ask us for the envelope that matches your installation.
Read about the first retrofit pilot on an office heat pump at The Green Village →
Savings calculator
How much COP could you gain?
Pick your refrigerant, switch between cooling and heating, and set your temperature lift and plant. The expander raises the COP dramatically — how much depends on your system, so read it off here.
Example results
The interactive calculator needs JavaScript. These example operating points show the order of magnitude the model gives; contact us for a figure for your own installation.
| Refrigerant | Duty | Lift | Baseline COP | With expander | Cost saving |
|---|---|---|---|---|---|
| Ammonia (R717) | 500 kW × 8,000 h/yr | 40 K | 3.06 | 3.15 (+3%) | €6,940 €/yr |
| CO₂ (R744, subcritical) | 300 kW × 8,000 h/yr | 45 K | 2.28 | 2.55 (+12%) | €20,360 €/yr |
| Butane (R600) | 1,000 kW × 7,000 h/yr | 50 K | 3.04 | 3.41 (+12%) | €44,524 €/yr |
Results
That combination is outside the modelled range for this refrigerant. Adjust the temperature lift.
- – Cost saving €/yr
- – Electricity saved MWh/yr
Sends us this scenario. We reply with an honest first estimate.
How is this calculated?
For each refrigerant we simulate a full subcritical vapour-compression cycle with CoolProp, once with an expansion valve and once with the Expantec expander, and read off the cooling COP. The heating COP is exactly the cooling COP plus one, from the cycle's energy balance. The evaporating temperature is fixed at a representative value for that refrigerant's usual duty; the slider varies the temperature lift to the condenser. The compressor runs at 61% and the expander at 80% isentropic efficiency. Electricity for a given duty is capacity × hours ÷ COP, so the cost saving follows from the COP gain.
Indicative only, based on modelled assumptions and a fixed evaporating temperature per refrigerant. Actual results depend on the installation. No guarantee is given or implied.
Retrofit and integration
Mechanically the expander replaces the expansion valve and its immediate pipework. Electrically it needs a supply for the control cabinet and, where available, a signal from the plant controller so expansion can follow load. The compressor, heat exchangers, refrigerant and charge stay as they are.
In the pilot at The Green Village the retrofit was carried out by the installation's own installer, Warmtebouw, with system engineering support from IBK — the way we expect every retrofit to be done: by the party that already knows the plant.
Frequently asked questions
What is expansion work recovery?
In a heat pump or refrigeration cycle, high-pressure liquid refrigerant has to be brought down to evaporator pressure. A throttling valve does that without producing anything; the energy in the pressure difference is dissipated. Expansion work recovery means letting the refrigerant expand through a device that extracts work from that pressure drop, so the compressor has to supply less.
Does a higher COP mean the same percentage less electricity?
No — a little less. Electricity consumption is capacity divided by COP, so if the COP rises by a fraction, consumption falls to 1/(1 + that fraction) of what it was. A 20% higher COP, for example, is about 17% less electricity, not 20%. The calculator shows both for your operating point.
Does the expander replace the expansion valve, or work alongside it?
It takes the expansion valve's position in the cycle. The compressor, condenser, evaporator and refrigerant charge are untouched, which is why the device is suitable for retrofitting existing installations.
Which installations benefit most?
The recoverable work grows with the pressure lift between evaporator and condenser. Deep-freeze cold storage, high-temperature process heat and steam-generating heat pumps therefore have the most to gain. Use the calculator above to see the modelled effect for your own operating point.
Is the Multiphase Pressure Exchanger a turbine?
No. Turbine expanders struggle with two-phase refrigerant flow. The MPE is a pressure exchanger, so there is no high-speed rotating wheel in the refrigerant stream, and it is designed to operate safely inside an existing installation.