Modeling Evaporative cooling systems (ambiator)

The amount of fresh air for a zone must be equal in both baseline and design case models. Typically, for DOAS, it means zones get a little more air than is usually nessesary as per minimum fresh air requirements such as ASHRAE 62.1. This is okay. The baseline VAV system must bring the same amount of fresh air into the zone as the DOAS. It is a requirement of 90.1 App. G. Why are the proposed model's capacities not enough to meet the setpoint? Either your capacity is too small or your setpoints are not right. A narritive would have to be pretty convincing as to why your case should be handled different.

In a similar climate, Tucson, AZ, evaporative cooling also exceeds unmet load hours on an annual basis. Management and workers accomodate this with more breaks, earlier working hours, shorter days during the hottest season, as we have done for decades, but ASHRAE and LEED allow no exceptions. It is still the most efficient cooling system for a hot, dry climate. We just can't prove it with the existing criteria.

Joyce described schedule adjustments managers and workers make to avoid the hottest part of the day (I just moved to Phoenix, so I understand!). It would definitely require more effort, but close attention to your thermostat and occupancy schedules may help with unmet hours in the situation you describe. If you adjust your occupancy schedules (for proposed and baseline) to reflect the actual building occupancy, such as 6 am-3pm, or with shorter days in the hottest part of the summer, and then schedule the unoccupied hours at a higher setpoint temperature (this part is very important!), you may be able to mitigate the unmet hours in the situation you describe. Also, someone please correct me if I'm wrong, but I don't know of any requirement within the mandatory requirements of 90.1 or Appendix G that require specific thermostat setpoint temperatures. Ensuring your space setpoint in the model reflects the actual operational setpoint, which tends to be higher in our climate than in cooler areas, would also be a good thing to check. I haven't modeled evaporative cooling for a LEED project, so I can't speak specifically to that technology. Best of luck!

We are modeling a factory, there will be no HVAC system only heating and ventilation, the thing is that the ventilation will be supplied by a direct evaporative cooling. Can we assume the proposed system to be Heated only?

You must model the proposed as designed so it must include the evaporative cooling system.

Got this response from GBCI: "Thank you for contacting GBCI regarding a LEED v4 BD+C factory project in Hyerabad with evaporative cooling.1. The baseline ventilation rates shall be modeled in accordance with the minimum requirements of the applicable ventilation code (i.e. ASHRAE 62.1-2010, local code, or the applicable industry standard or guideline for the space type, as applicable), per ASHRAE 90.1-2010 G3.1.2.6 exception (c). The proposed case must be modeled as designed.2. No specific adjustments are required for evaporative cooling systems. For all systems, the calculations must reflect the worst-case operating conditions, meaning the lowest supply airflow rate that can reasonably be expected to occur when each space is fully occupied. 3. The space setpoints must be modeled identically, and unmet load hours must be maintained within limits of Appendix G. It is expected that the conditions maintained within the Proposed case will in a large part be dictated by the outdoor weather conditions. To ensure that similar conditions are maintained within the baseline building model, it is recommended that the temperature setpoint in the baseline case be adjusted to match the maximum temperature maintained during cooling mode within the proposed case model, modified on a monthly basis (or smaller intervals) to better reflect the seasonal impacts on the cooling conditions provided within the proposed case.Note that if the proposed case requires additional mechanical cooling to keep the unmet load hours within the required limits, a cooling system with identical efficiencies to that of the baseline case may be modeled as a supplemental cooling system. However, if the baseline cooling setpoint schedule is adjusted as described above this should not be necessary."


However, can anyone help me with the clarification on why in case of an evaporative cooler, the baseline  OSA shall be as per 62.1 only. My reasoning is that in the proposed case the OSA will act as dehumidifier cfm and this will create a very big difference in the OSA in basecase compared to proposed case. For example, the base case will have around 2 cfm/sqft and proposed will have around 3.5 cfm/sqft.