Account for DOAS air when sizing zone units
I cannot believe this is not a feature request but I could not find it so here goes.
If you have a DOAS system in E+ (eg Fan Coils of any kind, radiators, etc) combined with a ventilation system, E+ does not currently take into account heating and/or cooling effects of the DOAS air when sizing the zone units (coils and fans)
This is a gross error. It is very common in DOAS systems for the air to be conditioned for dehumidification, meaning that air could be supplied from the DOAS system as low as say 13C / 55F and at 50-100% above the minimum ventilation rate (for dehumidification).
The zone units do not account for this load in sizing, meaning that cooling components are over-sized and heating components are undersized.
If a system is designed with separate DOAS ventilation and zone units then the zone units must be sized with the DOAS air included (at the very least fix the under-sized coils!!!)
The way it is currently implemented is very counter-intuitive because it adjusts the space loads rather than showing how it is one of the active ways the system manages the space load to maintain the design conditions.
Most practitioners would not consider the ventilation impact of the DOAS air to be incorporated into the space loads. They would expect this impact to be tracked as an HVAC load in the space that provides some kind of contribution in adding or removing both sensible and latent heat.
If this was implemented properly we would expect to see:
- Space loads that are consistent across all air-based HVAC options with the same setpoints
- Clear reporting on the sizing load contributions of both the zone equipment and the DOAS air
- If it's included as a setting it should be the default. Very few users would go looking for this as an option - everyone would expect it to be applied.
Mike - it's not a setting that gets applied with expand objects templates. Now we know about it we're investigating it a bit more and will add comments but I would still recommend at the very least that expand object templates using DOAS systems should do this by default.
Thanks Mike we will review and let you know.
New input fields were added to Sizing:Zone in v8.4 to account for this.
If that is not adequate, please describe what additional capabilities are required.