Rating System

LEED BD+C: New Construction, LEED BD+C: New Construction, LEED BD+C: Schools, LEED BD+C: Schools, LEED BD+C: Core and Shell

Rating System Version

v2 - LEED 2.2, v3 - LEED 2009, v2 - Schools 2007, v3 - LEED 2009, v3 - LEED 2009

Inquiry

This credit interpretation request is regarding the baseline system selection. The project is a campus classroom/laboratory building in Grand Junction, CO. The proposed building HVAC system is composed of distributed water source heat pumps served by a district geothermal condenser water loop. The district geothermal system has enough ground wells such that nearly all condenser heating and cooling loads will be met. However, there are gas fired boilers and cooling towers in place that will help to maintain loop temperatures during peak heating and cooling conditions. Our confusion is that the campus district cooling and heating system falls under the document, "Required Treatment of District Thermal Energy in LEED-NC version 2.2 and LEED for Schools." However, this document does not address the case of a district condenser water loop. If we were to follow Appendix G ignoring the fact that the building is served by a district condenser water loop, the system falls under the category of a hybrid system and ASHRAE 90.1-2004 Appendix-G dictates that the baseline system should be System 5 - Packaged VAV w/ Reheat. When we compare the baseline and proposed systems, this appears to be a clear case of fuel-switching. The proposed system is 90% or more electric heating, while the baseline system is 100% natural gas heating via hot water boilers. We are proposing to use the "Energy Cost Budget" method for determining the baseline system as detailed in ASHRAE 90.1-2004 section 11. Based upon figure 11.3.2 in ASHRAE 90.1-2004, the baseline system would be System 6 -Heat pumps on a condenser loop with boilers and fluid coolers. Note 7 of Table 11.3.2.A describes System 6 and the water-source heat pumps assumptions. We would use the electricity and gas rates paid by the campus in both models rather than following Steps 1 and 2 in the document, "Required Treatment of District Thermal Energy in LEED-NC version 2.2 and LEED for Schools." The air distribution system in both models would be through distributed heat pumps served by the condenser water loop.