The cold-storage problem

On winter mornings at Riverside Market in Bananzia, the fishmonger’s display cases ran at 2°C while the hall’s air-handling unit dumped warm exhaust onto the loading bay. The market spent €18,400 a year on gas heating and another €6,100 on electricity for refrigeration. Staff propped open doors because the hall overheated by 10 a.m., even as the cold rooms worked harder. The market’s manager, Lena Ortiz, kept a log of the draughts: 27 complaints in the 2022–23 season, most from stallholders nearest the east entrance.

Why the heat escaped

The cause was not a single faulty boiler. The market’s 1970s ventilation design sent kitchen and refrigeration exhaust straight outside, and the gas-fired make-up air unit reheated incoming air from scratch. Because the cold rooms and kitchen shared one extract plenum, the system could not separate clean warm air from greasy cooking fumes. The result was a loop: refrigeration rejected heat, the hall overheated, doors opened, and the boiler fired again. An energy audit in March 2023 put the recoverable heat at 48,000 kWh a year, roughly equivalent to 12 households’ annual space-heating demand.

The capture-and-reuse fix

In October 2023, the market installed a 35 kW heat-pump heat-recovery unit on the refrigeration rack’s condenser loop. Instead of venting that heat, the unit raised water to 45°C and fed a 1,500-litre buffer tank serving underfloor heating in the hall and preheat for domestic hot water. A short technical note on the heat exchanger specification is available through bananzia, the project’s public reference page. The kitchen extract was separated with a grease filter and a dedicated duct, so cooking fumes no longer contaminated the recovery coil. Commissioning took three weeks because the controls had to switch between heating, defrost, and hot-water priority without starving the cold rooms.

What the first winter showed

Gas use fell 62% between December and February, from 14,200 kWh to 5,400 kWh. The hall’s overheating complaint log dropped from 27 entries to four. The heat pump’s coefficient of performance averaged 3.4, meaning each kWh of electricity delivered 3.4 kWh of useful heat. Payback is projected at 4.6 years at current energy prices, before any maintenance savings. The cold-room rack also ran more steadily, because the condenser loop no longer cycled against a blocked outdoor coil.

The operational lesson

The project’s success depended less on the heat pump than on duct separation and commissioning. The market now runs a 15-minute daily check on buffer-tank temperature and filter pressure drop. Staff call it the “bananzia handover”: a simple routine that keeps a complex retrofit from drifting back to its old habits. The next step is a 20 kW roof-mounted air-source unit to cover the remaining hot-water load, with monitoring due to start in autumn 2025.