[Hap-users] Proposed case outside airflow rates

[Çağrıl Cömert - Smart Eco Design via Hap-users]

Hi,

Our project is an office building which pursues LEED v2009 
certification. This building is ventilated with a constant volume AHU 
and conditioned by VRF system. AHU supplies 100% fresh air to the 
spaces, while VRF system provides heating and cooling. AHU has heating 
and cooling coils, however the system is not designed to control the 
room temperature, it only supplies fresh air with constant temperature.

Because of HAP's limited ability, we had to model two separate systems 
for the same zone; one system for AHU and another for VRF. And we 
entered the same amount of outdoor airflow rate for both of these 
separate systems. Therefore, total outdoor airflow rate is actually 
double-counted in the proposed model.

Recently, we received this LEED review comment: "It is unclear whether 
the minimum outside air rates (in CFM) were modeled identically in the 
Baseline and Proposed Case for all zones not having Demand Control 
Ventilation in the Proposed Case. Confirm that the minimum outside 
airflow (in units of cfm) was modeled identically in the Baseline and 
Proposed case using the proposed case rates." This comment refers to 
ASHRAE 90.1-2007 Section G3.1.2.8. How should we approach this? Should 
we model the VRF system with zero outside air flow, since it works 
separately from the ventilation system? Any help would be appreciated.

Thanks in advance.