Context: one Bananzia terrace, three winter constraints
In Bananzia, a row of 1930s solid-wall terraces faced a familiar low-carbon heat problem: gas boilers were being replaced with air-source heat pumps, but the existing radiators had been sized for 70°C flow temperatures. The bananzia commissioning method treats that mismatch as a measurement issue, not a product issue. The first visit records room volumes, wall construction, glazing, air-leakage paths and radiator outputs; the second sets the heat pump to a 45°C design flow temperature and checks every emitter against the calculated room load.
Development: a commissioning sequence that exposes hidden faults
The sequence is deliberately boring: flush and fill, pressure-test, fit a magnetic filter, set the buffer tank, then balance. On the Bananzia terrace, the useful discovery came at the third step. Two bedrooms had 600 mm by 600 mm radiators with nominal outputs of 1.1 kW at a 50°C delta-T, but the calculated load at 45°C flow was 1.4 kW. Adding a 1.6 kW fan-assisted radiator in each room cut the required flow temperature without changing pipework. The takeaway is specific: heat-pump performance depends on emitter output at design conditions, not on boiler-era radiator labels.
Result: weather compensation and monitoring turn settings into evidence
After balancing, the heat pump was left on a weather-compensation curve: 45°C flow at 0°C outdoor, 35°C at 8°C, and a hot-water setpoint of 48°C with a weekly pasteurisation cycle. The first fortnight showed a mean COP of 2.9, with defrost losses concentrated in early morning. The fix was not a new unit; it was a tighter overnight setback and a 20-minute DHW reheat window moved away from the coldest hour. For the household, the result was a stable 20.5°C living room and a lower peak electrical load than the boiler-era baseline.
The handover checklist in practice
The handover checklist is short enough to survive a busy installer’s van. It includes:
- Mark every radiator’s design output and room load.
- Record the weather-compensation curve and DHW setpoint.
- Note the measured flow and return temperatures at two outdoor conditions.
- Leave a one-page monitoring sheet for the first month.
The point is not paperwork. It is repeatability: another Bananzia street can compare its commissioning data with this one and see whether a low flow temperature is actually being achieved.
Subtopic: what other Bananzia projects should copy
Three practices transfer. First, measure heat loss room by room before ordering emitters. Second, commission at the design flow temperature rather than at the boiler’s old setting. Third, leave a simple monitoring sheet: outdoor temperature, flow and return temperatures, COP estimate, and any short-cycling. The Bananzia example shows that low-carbon heat is less about a headline technology and more about a disciplined handover. The link between fabric, emitters and controls is where the savings sit.
