This project is a new approximately 4000 square foot Emergency Medical Services (EMS) station in Austin, which will be occupied 24/7. This question pertains to EA Credit 1 (Optimize Energy Performance) and relates to the determination of the baseline HVAC system. The two systems proposed by the mechanical engineer are: Option 1: One ductless split system heat pump per zone. Outside air will be provided to the zones by one central outside air unit with DX cooling and gas heating. (Single zone AC, multi-zone ventilation) Option 2: Ducted DX split systems serving multiple zones with gas heating. Outside air same as in #1 above. (Multi-zone AC, multi-zone ventilation) In our current baseline modeling, we selected the baseline system in accordance with ASHRAE 90.1-1999 section 11.4.3. This section offers three possible system type categories. The applicable category for baseline modeling is based on the type of system proposed in the actual design. The possible system categories are \'Single Zone Residential\', \'Single Zone Non-Residential\', and \'All Other\'. Given that ventilation outside air for either of the two proposed systems above is multi-zone, we categorized the proposed system as \'All Other\'. According to ASHRAE 90.1-1999 Figure 11.4.3 the baseline system is a Packaged VAV with parallel fan-powered boxes and VAV fan control. Question #1: Is this baseline system correct? Question #2: Does this system qualify for the exception (b) of ASHRAE 90.1-1999 6.3.2.1? ASHRAE 90.1-1999 allows for the baseline modeling of a constant-volume packaged unit with parallel fan-powered boxes in place of the packaged VAV system with parallel fan-powered boxes if a VAV system would be considered impractical for the subject project. Question #3: Since system #1 is single-zone, we would like to know if we can base our modeling of the baseline system chosen by the \'Single Zone Non-Residential\' category. Using this category will require a baseline system that is significantly different than the baseline system currently required under the \'All Other\' system category. In short, in our use of ASHRAE 90.1-1999 11.4.3, do we have flexiblity to treat the HVAC system as single-zone, although ventilation air is provided with a multi-zone system?
This is a complicated question, and only some of the information needed to evaluate your project\'s ASHRAE baseline is provided. The basic answer to your question 1 is that you have not identified the correct baseline according to ASHRAE 90.1. See discussion below. Likewise, for question 2, you do not need to apply exception (b) of ASHRAE 90.1-6.3.2.1 because neither VAV nor fan-powered boxes accurately describe your system configuration. In question 3, you are on the right track, because for purposes of this discussion, your system(s) are each single zone, not multi-zone systems, as described more specifically below. For Option 1 Your system utilizes two separate system types and two separate heating fuel types. In this case, ASHRAE requires you to model the two systems separately (See section 11.4.3 (k)). The ductless heat pumps must use the efficiencies in Table 6.2.1A, B, or D (depending on configuration) as the baseline, using the values for small individual equipment. This equipment is not considered multi-zone, because each heat pump serves only one zone. (System type 9) The packaged rooftop equipment (ventilation) should be modeled as a System type 11, and meet the appropriate efficiency requirements for use of gas heat with AC. Both systems should be present in the baseline, based on their respective capacities. Option 2 As we understand your system, you are using split system heat pumps with zone dampers. This equipment probably does not include fan boxes, nor does it include the capacity to vary fan speed based on zone demands. Therefore, it is effectively acting as a single zone system, and should be modeled as such. There is no reason to model this system against a VAV baseline, nor can we see how this would be advantageous to your energy performance, since VAV systems account for adjustable fan power in the baseline energy use, and your system cannot. In this option, all equipment in the baseline should meet the efficiency requirements for each piece of equipment (zone HP\'s, ventilation HP) based on the capacity of the individual equipment. These questions have been answered based on limited information about your system configuration and control strategies. It will be important to confirm the assumptions here about system configuration with your mechanical designer.