A primary school that burns gas and pumps heat

Northfield is two classroom wings and a cafeteria on reversible DX splits and a gym on a packaged rooftop with a 100 kW gas furnace. It needed two fields the model did not have: a heater's fuel (a gas heater's duty over its efficiency is fuel, never electricity) and a compressor's reversible flag — every circuit used to be a heat pump on heating hours, so the gas rooftop heated with its compressor first and burnt 100 kWh a winter week as a top-up.

A single-zone rooftop could not heat the gym and cool the cafeteria's kitchen in the same hour — 17 unmet cooling hours a winter week — so the cafeteria has a split of its own. The gym's furnace is 100 kW because 60 left it 106 hours short.

On Toronto's year the school reads 56 MWh of cooling, 175 of heating, 57.5 MWh of electricity and 179 MWh of gas. The heat-pump splits leave each classroom wing 51–58 unmet heating hours on the coldest mornings — no backup heat by design, left in to say what a reversed circuit does at −20 °C.

What it reads on Toronto

What it taught

• Gas is fuel, not electricity; a report that folds it into kWh of power misprices every gas building.
• A cooling-only machine says so (`reversible: false`) or the model runs its compressor backwards in January.
• A heat pump at −20 °C is little of a heater; the case shows the shortfall instead of hiding it behind a backup it does not draw.

The machines

• Example DX split, 12 kW class — open in the builder
• Example packaged rooftop with gas furnace, 4 m³/s — open in the builder

Sources

• Reznor Model X gas duct furnace catalog (80 % certified output)
• EnergyPlus frost derate model for heat pumps
• PVGIS TMY, Toronto

Readings of the shipped model on the building's own PVGIS typical meteorological year; engineering estimates from catalog data and published correlations. The building runs on every plan, including Free, a few times a day.