Modeling Hourly Geothermal Loads Across a 37-Storey High-Rise

Building Loads & HVAC Optimization

The building energy model, developed in IES-VE from architectural and mechanical design documents.

Case Study Summary

Service	Energy Modeling — geothermal loads & hourly energy analysis
Building Type	High-rise residential tower, 37 storeys + below-grade level
Location	Toronto, Ontario, Canada
Floor Area	≈28,300 m² above grade (≈304,700 ft²) + 3,026 m² below grade
Software	IES-VE — ASHRAE 140-compliant hourly simulation
HVAC / Geo System	Distributed water-to-air heat pumps on a geothermal loop; select service spaces and domestic hot water served separately by gas boilers
Deliverables	Hourly geothermal load profile, peak heating/cooling loads, monthly peak & summed loads, full energy model report
Client	Confidential (geothermal design consultant)

The Challenge

Geothermal system design lives or dies on getting the load profile right — not the building’s total annual energy use, but specifically how much heating and cooling load the geothermal loop itself has to carry, hour by hour, across a full year. For a 37-storey residential tower with over 300,000 ft² of conditioned space, that’s a meaningfully different question than a standard energy model answers: some of the building’s heating — locker rooms, storage, mechanical spaces, and domestic hot water — was deliberately served by gas boilers rather than the heat pump loop. A whole-building load number would overstate what the geothermal field actually needs to be sized for. Handing a geothermal designer the wrong number, even a conservative-looking one, risks a field that’s expensively oversized or riskily undersized.

Our Approach

We built a detailed hourly energy model in IES-VE covering building geometry, envelope, space types, occupancy, and ventilation, along with the full HVAC configuration: distributed water-to-air heat pumps serving the majority of suites and amenity spaces, dedicated ERVs for residential units, make-up air for corridors, and a subset of basement and service spaces served separately by gas-fired unit heaters — deliberately excluded from the geothermal loop.

Eleven distinct HVAC system configurations modeled in IES-VE, reflecting the building’s mixed occupancy — suites, amenity spaces, retail, corridors, and back-of-house areas each handled on their own terms.

The deliverable wasn’t a single load number — it was two different views of the same building, reported side by side: the load at the geothermal loop (excluding gas-boiler-served spaces) versus the load at the heat pump coil level (excluding domestic hot water specifically). A geothermal designer sizing a field from the wrong one of these numbers would effectively be sizing for the wrong building. Both were calculated hour by hour and reported by month, so the field design could be based on how the load actually behaves through a full Toronto winter and summer — not a single assumed peak day.

Results

1,783 kW

Peak heating load at the heat pump coil level

1,640 kW

Peak cooling load

8,760

Hours of load data delivered per year, not just two peak numbers

The completed analysis gave the geothermal design team an hour-by-hour picture of how the building’s load actually moves through the year — not just two peak figures, but the full seasonal shape of heat extraction and rejection the field would need to handle, with domestic-hot-water and boiler-served loads correctly excluded so the field isn’t sized for demand it will never actually see.

Monthly peak and summed loads reported two ways — at the geothermal loop and at the heat pump coil level — so the field design is based on the load it will actually see, not the whole building’s total demand.

Why It Matters for Your Project

For a geothermal designer, a load number is only as useful as the assumptions behind it. Modeling the whole building hour by hour — and then correctly separating what’s actually on the geothermal loop from what isn’t — gives a field-sizing basis that reflects how the building really operates, not a simplified estimate. That’s the same rigor we bring to every geothermal loads analysis: distinguishing what belongs on the loop from what doesn’t, before a single number gets reported.