Propane for heat pumps and chillers: What best practice looks like

– Introduction to best practice for R-290 and A3 refrigerants in building services

As tightening regulations drive the shift toward eco-friendly R-290 refrigerants, industry experts STIG RATH and HARALD ERÖS, authors of the book ‘Propane, naturally safe!’, explain why true best practice for propane heat pumps and chillers goes far beyond a CE mark—requiring a comprehensive, design-first safety concept from day one.

Propane (R-290) combines excellent thermodynamic performance with close-to-zero global warming impact. As restrictions on synthetic refrigerants tighten, it is becoming an increasingly important option for heat pumps and chillers in buildings. Its flammability classification means that fire and explosion safety must be addressed from the earliest design stage. Best practice is not simply a matter of selecting a CE-marked appliance: it requires a complete safety concept covering the product, its location, the installation, commissioning, operation and service.

Start with the operator’s risk assessment

The process should begin with a site-specific risk assessment once the building design and proposed plant location have been determined. The assessment should become incorporated into the project specification, defining what the manufacturer and installation contractor must demonstrate regarding fire and explosion protection.

Two different approaches to risk

Risk assessment can follow two fundamentally different lines of reasoning. One is to conclude that the overall risk is acceptably low, provided that the equipment is correctly installed, operated and maintained. The other is to design the equipment and installation so that a reasonably foreseeable fault does not result in the formation of an explosive atmosphere, propane reaching an ignition source, or any other dangerous situation.

Best practice is not to choose between good design and correct use. It is to use inherently safer design as the first line of defence, supported by competent installation, operation and maintenance.

Indoor and outdoor installations require different solutions

Applying this design-first approach leads to different solutions for indoor and outdoor installations. Outdoor installation normally provides better natural dispersion and reduces the consequences of a release. It does not, however, make the risk disappear. A unit placed beside an air intake or above a drain or other low point may allow propane to accumulate or enter the building. External ignition sources may also be present nearby, such as lighting and other technical installations.

Indoor installations demand greater control because a release is contained by the building. A common solution for liquid-to-liquid heat pumps and chillers is a ventilated enclosure. Potential release points are enclosed, air is continuously extracted to a safe outdoor location, and the enclosure is maintained at negative pressure. The enclosure, fan, ductwork, airflow monitoring, shutdown functions and power supply must be designed as one safety system.

The key question is therefore not whether the unit is installed indoors or outdoors, but whether any released propane can disperse and dilute safely without forming an explosive atmosphere or reaching an ignition source.

The refrigerant circuit is a fundamental design choice

A hermetically sealed refrigerant circuit is an important preventive measure because it removes release sources from the area-classification assessment. For such equipment, additional measures may include natural ventilation, continuous mechanical ventilation or ventilation initiated by gas detection, depending on the product design and installation conditions.

A non-hermetic circuit contains potential release points. Best practice must then prioritise prevention of accumulation through enclosure design, continuous ventilation or reliable natural dispersion. Where an explosive atmosphere can still form, ignition sources must be controlled, and equipment within the classified area must be suitable for that zone. Gas detection is a valuable reactive measure, but it should not be used as a substitute for prevention where ventilation is needed continuously.

Assess each release scenario separately

Three locations deserve particular attention:

the enclosure or compartment containing potential release points;
the outlet from any mechanical extraction system; and,
the discharge from pressure-relief valves. They can produce hazardous areas of very different sizes and shapes.

For outdoor installations, the arrangement of multiple units must also be considered, as discharge air from one unit may be drawn into the electrical switchboard air intake of another.

The manufacturer should provide a clear hazardous area drawing based on credible release assumptions. The operator remains responsible for verifying that the specified zones are compatible with the actual site, although the verification may be performed by a consultant.

Safety functions need a reliable power supply

Gas detection, extraction ventilation and automatic shutdown cannot be relied upon if they all lose power under the same fault condition that creates the risk. Where continued ventilation or detection is necessary for safe shutdown or dilution, an independent power supply shall be required.

EN 378 and CE marking are not the whole answer

EN 378 is an important refrigeration safety standard, but safe use of R-290 cannot be reduced to refrigerant-charge limits and CE marking. Where an explosive atmosphere may form, hazardous-area classification and ignition-source control must also be addressed using the relevant explosion-protection standards and workplace requirements.

Product documentation does not always contain everything needed for the site-specific assessment. Before specifying a unit, consultants and operators should ask:

Is the refrigerant circuit hermetically sealed?
Can an explosive atmosphere form?
Is the enclosure continuously ventilated?
What happens if ventilation or power fails?
Is equipment inside any classified area suitably protected?
Has the manufacturer documented the hazardous areas around the enclosure, ventilation outlet and pressure-relief discharge?

Technical and organisational measures must work together

The operator is not expected to be a refrigeration or explosion-protection specialist but remains responsible for appointing competent people and setting appropriate requirements. Independent review can be valuable where the manufacturer’s assessment is also being used to justify the product selection.

Safe operation also depends on competent commissioning and maintenance, clear service procedures, access control, warning signs and periodic testing of detectors, fans, alarms and shutdown functions. Even a well-designed installation can become unsafe through disabled alarms, obstructed ventilation, unauthorised modifications or poorly controlled service work.

In conclusion

Propane can be used safely and effectively in indoor and outdoor heat pumps and chillers when the installation is based on realistic release scenarios, prevention of accumulation, safe discharge locations, ignition-source control and reliable organisational measures. The safest and least costly solutions are achieved when these requirements are defined before the equipment is selected.

For further practical guidance, real-world examples, hazardous-area assessments, and checklists for manufacturers, consultants, installation contractors, and operators, see the guidebook ‘Propane, naturally safe!’ by Stig Rath and Harald Erös. Copies are available from RSL Group Wholesalers at https://www.rslgroupwholesalers.com/pages/propane-naturally-safe-book