Thermal Comfort Requirements of Step Code
The BC Energy Step Code requires new buildings to meet or exceed the targets of TEUI (Total Energy Use Intensity) & TEDI (Thermal Energy Demand Intensity) and requires whole building airtightness tests to be completed before occupancy. However, the goal to reduce energy consumption and carbon emission cannot sacrifice thermal comfort. In general, thermal comfort can be maintained in mechanically cooled buildings but not easily in passively cooled buildings. However, the majority of residential buildings in BC are passively cooled.
Therefore, the BC Energy Step Code also references the City of Vancouver (COV) Energy Modelling Guidelines V2, which requires the analysis of overheating in passively cooled buildings.
What is passive cooling?
Passive cooling means thermal comfort can be maintained in a non-mechanically cooled building through optimized glass design, adequate shading, and natural cooling strategies. In simple terms, there is no air conditioning in buildings, but people inside should still feel comfortable.
Requirements of COV (ZEBP)
The COV Energy Modelling Guidelines V2 requires:
For buildings that do not incorporate mechanical cooling, it must be demonstrated that interior dry bulb temperatures of occupied spaces do not exceed the 80% acceptability limits for naturally conditioned spaces, as outlined in ASHRAE 55-2010 Section 5.3, for more than 200 hours per year for any zone (for Vancouver, refer to Table 4 below).
For buildings or spaces with vulnerable groups (for example, seniors housing, shelter and supportive housing, daycares, schools, healthcare facilities, etc.), it is recommended that project (teams) work with owners and user groups to determine if mechanical cooling may be required to achieve their thermal comfort needs. Where pursuing passive cooling, it is recommended that projects target a more stringent threshold of not exceeding the 80% acceptability limits for more than 20 hours per year.
Note: 80% acceptability means 80% of occupants are satisfied with the thermal comfort conditions in the occupied space.
Any penalties if compliance fails?
However, in the Zero Emissions Building Plan Energy Checklist, as required by the COV, the overheating analysis/passive cooling is not required to be reported. The province/municipalities have not provided clear guidance on reporting this issue or associated penalties. Energy modelling/building simulation is a great tool for design assistance, but it is not 100% accurate and occasionally far from reality.
Because thermal comfort is addressed in the Step Code, what will happen if an occupant files a complaint about overheating in the unit? What if the complaint is superseded by a lawsuit? Can adding a portable air conditioner for the occupant be a solution if there is a dispute? What about engineers only making sure the thermal comfort study on paper is correct while ignoring the actual thermal comfort?
Alternatively, should we just add mechanical cooling for all residential developments?