Starting With An Energy Budget

Mitigating the onerous demands of a high tech building through an ambitious energy performance solution

December 21, 2017

Written by: Kevin Stelzer, Principal

The Joyce Centre for Partnership & Innovation at Mohawk College is among the sixteen projects selected to participate in the Canada Green Building Council’s (CaGBC) two-year Zero Carbon Building Standard pilot project, which assesses the carbon performance of commercial, institutional, and multi-family buildings and warehouses, and will help determine the requirements and standards for the Zero Carbon Buildings Framework.

To navigate the pursuit of this ambitious energy performance goal, especially against the onerous energy demands of the engineering laboratory, B+H + mcCallumSather upended the typical design process, rooting their design in the development of an innovative energy budgeting strategy to help prioritize energy demands. This budget – as would any other significant project mandate such as schedule or capital budget – is honoured as a strict guideline to ensure the significant challenges associated with net zero energy performance are appropriately articulated, categorized, and overcome.

To inform this exercise, the design team studied published energy use intensity (EUI) values for known high-performance buildings in Canada. The team concluded that an EUI target of 75 kWh/m²-year[1] was not only desirable, but also achievable for the programming—which consists of primarily classrooms, teaching laboratories, and collaborative learning spaces.

Creating the High-Level Vision

From the outset, the team recognized two important strategies: first, the performance of the building enclosure must be exceptional, and second, the active building systems must be ultra-energy efficient.  The HVAC system design is based on a dedicated outdoor air ventilation system (DOAS) with local heating and cooling. The high-performance enclosure will maximize passive design strategies and significantly reduce the amount of heating and cooling required for the building mechanical systems. The DOAS is crucial to the design as this type of HVAC system eliminates simultaneously having to heat and cool spaces, thereby providing superior air quality as return air is not recirculated throughout the building, while maximizing the exhaust air heat recovery performance.

[1] In the US this equates to 24 kBtu/ft²-year, and 0.27 GJ/m²-year for Canadian government types.

Concept Design Energy Use Breakdown

A high-level energy model was created to investigate where energy would be used in the building and the potential impact of different HVAC approaches on the amount of on-site renewable energy that would be required to achieve the net zero energy target. Three lessons were learned from this exercise:

  • The building process and receptacle loads would be the single largest energy end-use in the building at an estimated 20 ekWh/m²-yr. This emphasized that understanding how the building will be operated and what equipment will be plugged into the building’s receptacles are critical to understanding required energy generation from the on-site renewable energy system.
  • The next two largest energy end-uses include space heating and lighting, immediately followed by pumps, fans, space cooling, and domestic hot water. From a building design perspective, enclosure heat loss performance and the efficiency of heating systems are of critical importance, as is the lighting design. However, the remaining energy end-uses were all significant to the low magnitude target of 75 ekWh/m²-yr — all design analysis required careful attention to detail in the design.
  • To achieve a high-performance building: all systems must be synergistic. The enclosure design, the DOAS ventilation system, as well as best-in-class low-energy lighting design, combine to allow for low intensity, low-energy heating and cooling plants with all investigated options achieving below 25 ekWh/m²-year. It was clear that heat pump-based solutions used significantly less energy than fossil fuel solutions. The design team’s early analysis included understanding the difference between modern air-source variable flow heat pump solutions and variable flow ground-source heat pump solutions. The differences were minor but warranted detailed evaluation – suitable for this level of building energy performance.

Energy Modeling Sensitivity Studies

To further clarify the energy performance design goals, a detailed hourly energy model of the building was created. This model was used to perform sensitivity studies on occupancy and demand responsive systems, as well as receptacle loads and infiltration. It demonstrated that the occupant load significantly impacted the building’s total energy consumption of the building with respect to their impact on ventilation and receptacle loads. Sensitivity studies on receptacle load and infiltration also demonstrated significant impact on the building energy consumption and focused the design team’s attention on these aspects of the building design and operation.

With the energy budget in place, a clear roadmap was established to inform each component of design, from the building’s orientation and material palette, to the mechanical needs and photo-voltaic targets—the latter of which informs the most iconic part of the Joyce Centre’s design: an on-site 545 kW photovoltaic array.