Have any of you run into a review team telling you that you must model the baseline fan supply volume and baseline fan power the same in the proposed design? I have a project under review that is a distribution center primarily served by heating only make up air units. I have modeled cooling in both models and modeled the setpoint high enough that it would never turn on.
My interpretation of the requirement to model cooling the same in both models if cooling does not exist on the proposed design is just that, you only model the cooling the same. However, this is the response we received after our initial design comments review:
2. The response narrative to preliminary comment 5 states that the baseline case was modeled with a fan supply volume determined using Section G3.1.2.8 and a fan power determined using Section G3.1.2.9; however the proposed case must also be determined using these parameters. Per Table G3.1.10(d) in the proposed building column, where no cooling system exists, it must be modeled identically to the baseline case. Because the fan supply volume and fan power are cooling driven, it is unacceptable to auto-size the baseline case fan supply volume and fan power and not auto-size the proposed case fan supply volume and fan power. Currently, the baseline fan supply volume is sized to meet cooling needs and the proposed fan supply volume is sized to meet heating and ventilation needs. If appealing this credit, revise the Proposed case fan supply volume and fan power so that they are determined using Section G3.1.2.8 and Section G3.1.2.9. Note that it is appropriate for the proposed fans to be modeled as VAV since HVAC System 7 applies. Additionally, provide SV-A reports confirming the changes.
Another comment we received claimed that we must model the 0.4 CFM/SF requirement on the proposed model because the airflows are sized based on cooling and therefore, the airflow rules from System 7 apply (i.e. 20 delta T, min flow requirements, etc.)
3. The response narrative to preliminary comment 12 states that the full load equivalent hours are so high due to the 0.4 cfm/sq.ft flow rate; however the 0.4 cfm/sq.ft rate applies only when the building is occupied or when the interior fans are cycled on during unoccupied hours to meet heating or cooling loads. Based on the information provided in Section 1.2 of the Prerequisite form the occupied hours are only 40 per week. If appealing this credit, revise the schedules in both cases to reflect the actual anticipated schedules of the interior fans installed in the building. Additionally, revise the baseline case (and proposed case as necessary for equipment auto-sized per Table G3.1.10(d)) so that the 0.4 cfm/sq.ft minimum flow rate applies only when the building is occupied or when they are cycled on.
I already took care of the scheduling of the when the fans turned on. However, I honestly feel like the rest of both comments step over the line in terms of what we are suppose to model on the proposed design. The changes we would need to make (primarily forcing the airflows to be sized the same as the baseline and 0.4 cfm/sq ft) do not represent the design intent of the system shown on the drawings.
What do you guys think?
William Mak, LEED AP BD+C
