Designing HVAC Systems for Decarbonization: Lessons from the Field
Net zero is a common goal in building design today — but there’s a real gap between a building that’s net zero on paper and one that achieves it once it’s occupied and running. More often than not, that gap comes down to the HVAC system, since heating, cooling, and ventilation typically account for the largest share of a building’s energy use.
We’ve designed HVAC systems for net zero and near-net-zero buildings across Ontario. Here are five lessons that consistently separate a system that performs on paper from one that performs in the building.
1) Right-Size the Equipment
Oversizing “just to be safe” is a long-standing habit in HVAC design — and in a net zero context, . Oversized equipment short-cycles instead of running efficiently at partial load, which is exactly how heat pumps and modern systems are meant to operate. Right-sizing requires a detailed, building-specific load calculation, not a rule of thumb based on square footage.
2) Don’t Overlook the Distribution System
It’s easy to focus on the headline equipment — the heat pump, the boiler — because that’s the piece with the efficiency rating on the spec sheet. But the piping or ductwork moving heating and cooling through the building matters just as much. Heat pumps typically run best at lower supply temperatures than the boilers they replace; if existing radiators or piping were designed around a high-temperature system, the new equipment can end up working harder than intended. Equipment selection and distribution need to be evaluated together, not in sequence.
“The best HVAC system for a net zero building is often a smaller, simpler one — and that only happens when the envelope and the mechanical design are developed together.”
3) Design the Controls Strategy on Purpose
A well-selected, well-sized system can still underperform if the controls aren’t designed with the same care. Net zero buildings often need controls to do more than turn equipment on and off — sequencing multiple systems, adjusting setpoints based on occupancy, and ensuring the more efficient equipment runs first. This needs to be designed intentionally as part of the mechanical package, not added afterward.
4) Plan Electrical Capacity Early
Net zero buildings lean more heavily on electricity — heat pumps, heat pump water heaters, and often EV charging. You don’t want to have a project where mechanical systems were selected before anyone confirmed the building’s electrical service could support them, leading to costly late-stage surprises. Coordinating mechanical and electrical design from the outset avoids this, and creates room to plan for future electrification.
5) Commission — Then Commission Again
Even a carefully designed system can underperform if it isn’t properly commissioned. Small installation or configuration issues — an uncalibrated damper, an off control sequence, a factory-default setpoint — are common and fixable, but only if someone is looking for them. We recommend commissioning before occupancy, and again after a full heating and cooling season, since real operating conditions often reveal what initial testing doesn’t.
Designing Systems That Perform, Not Just Specify
None of these lessons are complicated on their own. Together, they’re the difference between a building that’s net zero on paper and one that’s net zero in practice. At Efficiency Engineering, our mechanical and electrical design work is grounded in this kind of integrated thinking — bringing field experience to every project so your system performs the way it’s supposed to, not just on the spec sheet.
Thinking about a decarbonization Project? Get in touch with our team early in the process — the earlier our engineering team is involved, the better your building will perform