Understand Hydrocarbon RAC system design, installation, commissioning and servicing and maintenance techniques
This topic covers hydrocarbon RAC system design, installation, commissioning, servicing, and maintenance. It includes health and safety, legislative requirements, and specific techniques for hydrocarbon systems.
Assessment criteria
Topic Overview
The City & Guilds Level 3 Award in Hydrocarbon Refrigeration, Air Conditioning and Heat Pump Systems is a specialised qualification for experienced refrigeration engineers who wish to work with hydrocarbon refrigerants such as propane (R290) and isobutane (R600a). These natural refrigerants have a very low global warming potential (GWP) and are increasingly used in commercial and domestic applications due to environmental regulations. This award covers the safe design, installation, commissioning, servicing, and maintenance of systems using A3 flammable refrigerants, with a strong emphasis on risk assessment, leak detection, and compliance with BS EN 378 and the F-Gas Regulation.
Why does this matter? As the UK phases down high-GWP hydrofluorocarbons (HFCs), hydrocarbons offer a sustainable alternative, but they are highly flammable. Engineers must understand the unique properties of hydrocarbons, including their higher flammability limits and lower density compared to HFCs. This qualification ensures you can work safely with these refrigerants, reducing the risk of fire or explosion. It fits into the wider subject of building services engineering by preparing you for the growing demand for low-carbon cooling and heating solutions, aligning with the UK's net-zero targets.
You will learn to select appropriate components (e.g., hermetically sealed compressors, pressure relief devices), design systems with minimal refrigerant charge, and perform leak testing using methods suitable for flammable gases. The course also covers emergency procedures, storage, and transport of hydrocarbon cylinders. By the end, you will be competent to handle hydrocarbon systems independently, which is a valuable skill in the refrigeration and air conditioning industry.
Key Concepts
Core ideas you must understand for this topic
- →Flammability classifications: Understand ASHRAE Standard 34 classifications, particularly A3 (higher flammability) for hydrocarbons. Know the lower flammability limit (LFL) and upper flammability limit (UFL) for propane (2.1%–9.5% by volume) and isobutane (1.8%–8.4%).
- →Safe system design: Systems must be designed to minimise refrigerant charge (e.g., using microchannel heat exchangers, smaller diameter pipes) and include safety features such as pressure relief valves, gas detectors, and ventilation. The charge limit for indoor systems is typically 150g for propane unless additional safety measures are in place.
- →Leak detection and repair: Use electronic leak detectors calibrated for hydrocarbons. Never use a halide torch or soap solution with high water content (can cause corrosion). After repair, pressure test with inert gas (e.g., nitrogen) and evacuate to below 100 microns to remove moisture and non-condensables.
- →Commissioning and servicing: During commissioning, verify electrical safety (earthing, spark-proof components) and ensure no ignition sources are present. Servicing requires purging the system with nitrogen before breaking into the circuit, and recovering refrigerant using a dedicated hydrocarbon recovery unit.
- →Regulatory compliance: Adhere to BS EN 378 (refrigeration systems safety), the F-Gas Regulation (EU 517/2014, retained in UK law), and the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR). Keep detailed records of refrigerant usage and leak checks.
Learning Objectives
What you need to know and understand
- Understand the specific Health and Safety requirements which apply to the design, installation, commissioning, servicing, maintaining and de-commissioning of Hydrocarbon RAC systems, Understand the legislative and organisational procedures for the design, installation, commissioning, servicing, maintaining and de-commissioning of Hydrocarbon RAC systems, Understand the main principles for the design of Hydrocarbon RAC systems, Understand the specific requirements for installing Hydrocarbon RAC systems, Understand the specific requirements for commissioning Hydrocarbon RAC systems, Understand service and maintenance procedures for Hydrocarbon RAC systems, Understand the procedures for re-commissioning Hydrocarbon RAC systems, Understand the decommissioning procedures for Hydrocarbon RAC systems
Assessment Criteria
Key criteria assessors look for in your portfolio
- Identify health and safety requirements for hydrocarbon systems.
- Explain design principles for hydrocarbon RAC systems.
- Describe installation and commissioning procedures.
- Outline service and maintenance techniques.
Assessment Guidance
Guidance for achieving higher grades
- 💡Know the properties and risks of hydrocarbon refrigerants.
- 💡Always use leak detection equipment during commissioning.
- 💡Follow safe handling procedures for flammable refrigerants.
- 💡Tip 1: Memorise the key safety distances and charge limits. For example, for a system with propane (R290) in an occupied space, the maximum charge without additional ventilation is 150g. If the charge exceeds this, you must install mechanical ventilation that activates at 20% of the LFL (0.42% by volume for propane). Examiners often ask you to calculate ventilation rates based on charge and room volume.
- 💡Tip 2: When answering questions on commissioning procedures, always mention the sequence: pressure test with nitrogen (1.1 x design pressure), then evacuate to below 100 microns, then charge with refrigerant using a scale to measure the exact amount. Never skip the standing vacuum test (hold vacuum for 30 minutes) to check for leaks. This shows you understand the critical steps.
- 💡Tip 3: For servicing questions, emphasise the need to isolate the system electrically and mechanically before work. Use a lockout/tagout procedure. When recovering refrigerant, use a dedicated recovery cylinder rated for hydrocarbons (yellow top, with left-hand thread) and never mix refrigerants. Examiners look for awareness of specific hydrocarbon handling protocols.
Common Mistakes
Common errors to avoid in your coursework
- Confusing hydrocarbon refrigerants with other types.
- Ignoring flammability risks during installation.
- Failing to follow manufacturer guidelines for servicing.
- Misconception: Hydrocarbon refrigerants are too dangerous to use in occupied spaces. Correction: With proper design (e.g., limited charge, ventilation, gas detection) and adherence to safety standards, hydrocarbon systems are safe. Many domestic fridges and small commercial units use R600a or R290 without incident.
- Misconception: You can use standard refrigeration tools and components for hydrocarbon systems. Correction: All electrical components must be spark-proof (e.g., sealed relays, hermetically sealed compressors). Standard pressure switches may create sparks; use intrinsically safe versions. Also, never use a vacuum pump without an oil separator to prevent hydrocarbon contamination of pump oil.
- Misconception: Leak testing with nitrogen is sufficient for hydrocarbon systems. Correction: While nitrogen pressure testing is essential, you must also perform a leak test with a suitable electronic detector after charging. Hydrocarbon molecules are smaller than HFCs, so leaks can occur at microscopic levels. Always check joints, valves, and service ports.
Frequently Asked Questions
Common questions students ask about this topic
Pass / Merit / Distinction Evidence Checklist
How your portfolio evidence is graded for CITY & GUILDS LIMITED Understand Hydrocarbon RAC system design, installation, commissioning and servicing and maintenance techniques
Every vocational unit is marked against named criteria rather than an exam percentage. Your tutor's brief lists the exact codes for this unit — here is what each band is asking you to do.
Demonstrate baseline knowledge, accurate terminology, and core practical application.
Provide detailed analysis, structured explanations, and clear workplace reasoning.
Deliver thorough evaluation, original problem solving, and fully justified recommendations.
Before You Start
Prior knowledge that will help with this topic
- •City & Guilds Level 2 Diploma in Refrigeration and Air Conditioning (or equivalent) covering basic refrigeration cycle, thermodynamics, and safe handling of HFC refrigerants.
- •Understanding of electrical principles (AC/DC, motors, controls) and safe isolation procedures.
- •Knowledge of pressure-enthalpy diagrams and how to read them for different refrigerants.
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Key Terminology
Essential terms to know
- Understand the specific Health and Safety requirements which apply to the design, installation, commissioning, servicing, maintaining and de-commissioning of Hydrocarbon RAC systems, Understand the legislative and organisational procedures for the design, installation, commissioning, servicing, maintaining and de-commissioning of Hydrocarbon RAC systems, Understand the main principles for the design of Hydrocarbon RAC systems, Understand the specific requirements for installing Hydrocarbon RAC systems, Understand the specific requirements for commissioning Hydrocarbon RAC systems, Understand service and maintenance procedures for Hydrocarbon RAC systems, Understand the procedures for re-commissioning Hydrocarbon RAC systems, Understand the decommissioning procedures for Hydrocarbon RAC systems
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