This is not a direct answer to your question - I'm easily exceeding the max # characters for a comment.
I'm also curious about others' experiences with modelling natural (or hybrid/mixed-mode) ventilation when it comes to compliance and energy ratings. I suspect there would be a range of answers when it comes to ECB, given the significant role played here by the authority having jurisdiction (AHJ). A few points:
- I disagree that the budget building design (BBD) becomes naturally ventilated if the proposed design (PD) is naturally ventilated. BBD HVAC systems are determined by 11.5.2 of ECB. BBD HVAC systems would however inherit (from the PD) agreed-upon heating/cooling setpoint temperatures.
- Agreed-upon PD cooling setpoint temperatures become key IMHO. This would depend greatly on context (location, architecture, loads, client expectations). What could work in coastal Newfoundland, likely won't in Louisiana. I would first simulate the passive/hybrid strategy to get a time distribution of likely room temperatures and OA cfm. Uncertainty becomes significant when the strategy is strictly manual (e.g. operable windows). If the client is willing to accept 2 or 3 weeks of 30°C and 70% RH indoors (my neck of the woods; quite cool for a North American urban setting), then the next step is convincing the AHJ (as per ECB 11.4.5 and 11.5.1).
- From ECB 11.5.1 Design Model: "All conditioned spaces in the PD shall be simulated as being both heated and cooled, even if no cooling or heating system is being installed". If both client and AHJ gave the OK for the preceding points, I'd propose approximately the same agreed-upon cooling setpoint temperatures for the BBD HVAC. I'd stick to 62.1 for BBD minimum OA cfm, etc. So the BBD would have cooling, fans, etc., but the energy credit from natural ventilation/cooling would be modest (as both PD and BBD would +/- share the same cooling setpoint temperature schedules in their respective models).
- If there's an automated switch to mechanical ventilation and cooling in the PD, I'd lean towards App G rules, well discussed in Section 3.2.6 here.
In summary, my understanding of ECB is that some credit can be given to natural ventilation. But nothing like comparing a naturally-ventilated PD to a BBD mechanically-cooled at 24°C. I occasionally remind myself that ECB (or similar codes) is strictly to assess minimum code-compliant designs. An AHJ might wonder what deficiencies in minimum envelope, lighting or HVAC warrant energy credits from natural ventilation to ensure minimum compliance. Seeking additional credit for App G/LEED (beyond code minimum) seems easier to justify IMHO. Cheers.
