We request a ruling regarding building ventilation and its impact on EAp2/EAc1. The question is two-fold: (1) Will USGBC/GBCI allow credit for a design that increases ventilation effectiveness other than Displacement Ventilation (a noted exception for PDV now exists in ASHRAE 62.1-2010), and, (2) will USGBC/GBCI allow credit for reduced ventilation by decoupling the outdoor air from the multi-zone VAV system, which requires increased ventilation rates to ensure the appropriate airflow is reaching all of the zones? Project Design Information:The project is a multi-story office space undergoing a major renovation. In accordance with ASHRAE Standard 90.1-2007 Appendix G, the baseline system is System 8. Ventilation is handled by VAV air handling units, thus requiring multi-zone calculations. Due to elevated terminal heating temperature, zone air distribution effectiveness (Ez) is 0.8.Similarly, the proposed system will employ a VAV system, but with decoupled constant-volume ventilation, thus foregoing multi-zone calculations and reducing outdoor air. Ventilation is room neutral resulting in an Ez of 1.0.Referenced Standards/Guidelines/Research:Ez factors and ventilation rates are determined from ASHRAE Standard 62.1-2007 Tables 6-2 and 6-1, respectively.ASHRAE Standard 90.1-2007 Appendix G Section G.3.1.2.8 Design Airflow Rates states:(D)esign supply airflow rates for the baseline building design shall be based on supply-air-to-room-air temperature difference of 20°F
This exceeds the 15°F limit from Table 6-2. ASHRAE 62.1-2007 User’s Manual (page 6-27) instructs to use the worst case factor, which is the heating Ez of 0.8.
ASHRAE Standard 90.1-2007 Appendix G Section G.3.1.2.5 Ventilation states:
(V)ventilation rates shall be the same for the proposed and baseline building designs.
Reviewing the User’s Manual for this section adds:
(V)ventilation can be a major contributor to building energy consumption, but it is not considered an opportunity for energy savings... (V)ventilation is energy neutral as far as tradeoffs are concerned.
Spare a recent exemption for using PDV to reduce outdoor air rates via an allowable manipulation of Ez, no other exemptions exist. Yet, ASHRAE research recognizes the advantages of decoupling ventilation in its ability to reduce ventilation volume and therefore energy costs. From Jeong, J.W., et. al, ASHRAE Transactions 2003, Volume 109, Part 2:
“All-air [VAV] systems are widely used in many types of buildings, [even though] these common systems have several significant deficiencies. …(T)he multiple spaces method must be used to increase the [OA fraction... This increase… may add significantly to energy consumption and operating cost…
“The challenge of conforming to [ASHRAE Standard 62] in an energy efficient manner can be met with a dedicated outdoor air system (DOAS)… The DOAS provides 100% of the required ventilation air at constant volume”
In addition, EPA’s Technical Report PNNL-18774 (Strategies for 50% Energy Savings in Medium Office Buildings) recognized DOAS as a primary energy savings strategy using the previous research by ASHRAE noted above as support and justification.
Conclusions:
It is clear that, as written, the ventilation volumes should be the same in both models. But we respectfully ask the LEED® Reviewer to provide us feedback on whether this makes sense for the current LEED® Rating Systems. It appears the rules are evolving (ex. Displacement Ventilation) as technologies and techniques evolve. And yet full credit for decoupled ventilation systems doesn’t currently exist and therefore may discourage designers and owner from investing in a system that often has higher first cost. We recommend and endorse this investment because of the excellent returns both in terms of dollars saved and carbon emissions reduced. We ask for your ruling to create an exception that allows credit for increased ventilation effectiveness and reduced ventilation rates (compared to multi-zone VAV systems) using a DOAS.