Decarbonising a remote school with an old two-phase electrical supply

The site

The school has a 1960s main building and a smaller separate teaching block. The gas boilers in both were between 10 and 15 years old. We put the peak heat loss at around 95 kW for the main building and 57 kW for the smaller block, before any fabric work.

The site was fed by an old two-phase supply at the end of a rural network, without the capacity for heat pumps.

Electrical upgrade

We raised the network enquiry early, with the letters of authority in place in February 2025, so the quotation was known before the design was fixed. The network operator's solution was a new 20 kV/415 V substation and a three-phase supply to the school.

We designed the site side: a new GRP enclosure housing the incoming supply, the meter and the main switchboard, and the rebalancing of the existing loads across three phases. The specification required the contractor to check every existing submain for the second phase, so the work was priced at tender.

Heating systems

The main school is served by propane (R290) air source heat pumps with a 2,000 litre buffer, sized so it can be charged on cheaper overnight electricity. Hot water has its own heat pumps, with immersion heaters as standby.

The smaller block is served by a VRF heat pump system rather than an extension of the wet system. The heat pumps sit in a timber acoustic enclosure next to the building.