R-32 Retrofit in a Basement Plant Room
Your company is replacing a failed R-410A split system in a basement plant room of a city-centre hotel with a 4 kg R-32 (A2L) system. The room is 4.0 m × 3.0 m × 2.6 m, accessed by a single door at the top of three steps, with no permanent mechanical ventilation and no refrigerant detection. The adjacent boiler house shares a ceiling void, separated by a fire wall. The manufacturer's data sheet gives R-32 a practical limit of 0.061 kg/m³ and requires brazed joints to be made under nitrogen. The duty manager wants no interruption to the kitchen cold rooms, so the plan is to braze the new interconnecting pipework in situ during service hours, under a fire permit, with two technicians and the plant room door propped open.
1. Using the data given, evaluate whether the proposed 4 kg charge can be accommodated in this plant room as it stands, and state what you would require before installation proceeds.
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Volume check: 4.0 × 3.0 × 2.6 = 31.2 m³. At the manufacturer's practical limit of 0.061 kg/m³ the room can hold 31.2 × 0.061 = 1.9 kg. The proposed 4 kg is more than twice that, so the room as it stands cannot take the charge and the design must change.
Why the physical details matter:
- R-32 vapour is denser than air, so any release pools at low level. Extraction must be low-level; a high-level extract would achieve nothing.
- The single door at the top of steps gives no secondary escape and no cross-draught - "door propped open" is not ventilation.
- The shared ceiling void with the boiler house introduces ignition sources outside your control, which drives the DSEAR/ATEX assessment.
Options I would put to the designer, in order of preference:
- Reduce the charge below 1.9 kg (split into two smaller circuits, or move the condensing side out of the basement).
- Mechanical ventilation, low-level extract, plus refrigerant detection interlocked to alarm and forced ventilation.
- If neither is possible, relocate the equipment - do not proceed.
I would not accept a risk assessment that simply notes the exceedance; EN 378 charge limits are a design input, not a paperwork step.
2. Set out the hot-work controls and the brazing sequence you would insist on for the joints made in this room.
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First decision - avoid the hot work where possible. Prefabricate as much of the interconnecting pipework as the routes allow outside the basement, and carry in only the minimum number of field joints. Every joint made in an unventilated, unmonitored basement is a controllable hazard you can design out.
Controls for the joints that must be made in situ:
- A hot-work permit signed by both your company and the hotel, with the fire watch named and a 60-minute post-work check recorded.
- Gas-free verification before the torch is lit and continuous flammable-gas monitoring at low level with a calibrated meter set for R-32, not a generic "refrigerant" sniffer.
- Forced ventilation running before, during and after; the boiler house isolated from the shared void for the duration.
- All ignition sources removed or isolated, including non-ATEX-rated tools, chargers and the door-propping arrangement.
- Nitrogen purge through the pipework with a regulating valve and a vent, never a sealed system; no oxygen or air purging.
- Fire blanket, screens, appropriate extinguisher, and anyone without a role kept out.
Sequence: isolate and recover any existing charge, purge, brace and support the line, brace, pressure test with OFN, vacuum, then charge by weight. Record the purge, the test pressure and the hold time.
3. The duty manager presses you to keep the kitchen running and accept the propped-door arrangement. How do you handle that conversation and what do you commit to?
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I would take it out of the realm of opinion and put the numbers in front of them: 31.2 m³, a 1.9 kg ceiling, a 4 kg proposal. That is not a judgement call about being cautious; it is a design that does not comply, and I cannot install to it and then certify it.
What I would say:
- I will not braze in that room under a propped door, and I will not sign the commissioning record for a system that exceeds the room's charge limit.
- Here is what I can influence: a two-stage programme that keeps the kitchen on its existing plant while we build the replacement on a reduced charge or with ventilation and detection.
- Here is the cost of the alternative options and the lead time on the detection kit.
What I would commit to: a written summary of the constraint and the options within 24 hours, a firm date for the revised method statement, and a named contact for the hotel's own risk assessment.
I would also record the exchange in the project file. If the hotel then instructs a different contractor, that is their decision, but the site record should show that the charge limit was identified, quantified and raised before work started - not after.