Garage ventilation - Baseline

Hi Vassil
If your design includes supply and exhaust both, than I would include supply and exhaust in baseline as well and calculate fan power as 0.75*AREA*0.3.

Please note that, any spaces provided with less than 15 btu/hr of heating is considered as unconditioned space, so in that case you can model your garage as unconditioned space. For baseline, if you choose system 9/10, than fan control should be constant and you won't be able to provide savings from DCV. I would suggest creating exceptional calculations without considering effect of heating. Please refer to 2015 ASHRAE Handbook - HVAC applications, Figure 16 for fan schedule in Garage spaces.

Vassil,

I am assuming your Proposed heating system operates independently from the exhaust ventilation system, and no outside air is supplied by the heating system as makeup air for the exhaust. If this is the case, the Baseline heating system would also function independently from the exhaust system. The heating systems in both cases would cycle to maintain the heating temperature setpoint and supply no outside air. Makeup air for the exhaust system would be supplied by infiltration.

The Baseline system type used would depend on 1) whether the garage meets the ASHRAE 90.1-2007 definition of an "enclosed space", and 2) if the garage is an "enclosed space" whether it meets the definition of a "heated space" based on whether the heating capacity of the Proposed system exceeds the climate zone's heated space criteria in ASHRAE 90.1-2007 Table 3-1. If the garage can be defined as both enclosed and heated, the Baseline should be modeled using System 9/10. If the garage cannot be defined as enclosed and/or heated the Baseline heating system would be modeled identically to the Proposed system.

Here is the comment I received from GBCI, when DCV modeled using system type 9/10 in one of my energy model.

"Credit has been taken for demand controlled ventilation for the parking garage. Per LEED Interpretation 10371, the project team must demonstrate that the Baseline Case has been modeled consistent with the referenced section, and this measure must be modeled as an Exceptional Calculation Measure (ECM). In order for approval, the following conditions must be met. Address each of the followings:

a. Baseline Case shall meet the requirements of ASHRAE 90.1-2010, Section 6.4.3.4.5 Enclosed Parking Garage Ventilation. It is noted that Baseline fan volume shall be based on the minimum required ASHRAE 62.1 parking ventilation rates of 0.75 cfm/square foot. However, Baseline system fan power shall be calculated at 0.3 watts per CFM.

b. Proposed Case shall reflect the actual design. Evidence shall be provided documenting that demand control ventilation strategies are sufficient to automatically detect contaminant levels of concern in parking garages (Carbon Monoxide, Particulates, VOCs, etc. and NO2) and modulate airflow such that contaminant levels are maintained below specified contaminant concentration as identified in ASHRAE 62.1-2010 Addendum d. Evidence shall also be provided that contaminant sensors are placed in space in an appropriate manner for detection of contaminant in question and that the sensors be calibrated yearly.

c. It is noted that the Proposed Case was modeled such that a minimum air flow of 0.05 cfm/square foot is maintained.

d. A narrative shall describe all Baseline and Proposed Case assumptions included for this measure, and the calculation methodology used to determine the projected savings. The narrative and energy savings should be reported separately from the other efficiency measures in the LEED Form.

e. It is noted that only 58% fan energy savings are obtained from garage DCV system in the Proposed model which is less than a 75% fan energy savings that claimed for this measure."

You are correct that since it is semiheated the Baseline should not be modeled with System 9. The Baseline system should be an identical system type to the Proposed system, but yes the loads will be different due to the DCV.