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

The project is a greenhouse-exhibit-office space complex located in urban Denver, CO that serves as a horticulture production facility for the regional botanic gardens. Since the project consists largely of greenhouse space, the project team would like confirmation of baseline assumptions in this process-load dominated space. In addition, modeling limitations exist within the EnergyPlus simulation software for simulating evaporative cooling. The project team would like to confirm acceptance of the analysis method proposed for overcoming the software limitations. Greenhouse Baseline Characteristics In the CIR dated 4/30/2008 concerning energy use in greenhouses, the ruling clearly states that any conditioned space that is used primarily to support plant growth should be modeled as a process space and all characterizations for the space, its space conditioning equipment, and controls should be the same in the baseline and the proposed-design energy model. Therefore, in order to demonstrate efficiency improvements for these end-uses, the project team must follow an exceptional calculation method (ECM) that compares standard design practice to design improvements. The design team desires to demonstrate design improvements in three areas as outlined below. 1) The greenhouse proposed design includes high performance glazing. The project team has found standard design practice for glazing selection for greenhouses to include single-pane clear glass. The team would like to confirm that this is an acceptable baseline for the analysis. 2) The greenhouse design includes an automated shading system to decrease solar heat gain and radiative heat loss in the space. The project team would like to confirm that a greenhouse design without a shading system is an appropriate baseline. 3) The greenhouse design includes an automated natural ventilation system controlled by space and ambient temperature sensors. The ventilation system releases heat from the upper-most portion of the greenhouse when the space temperature exceeds the set-point temperature during mild ambient conditions. The project team believes that automated natural ventilation controls are not part of standard design practice and should be excluded from the baseline greenhouse. The team would like to confirm this baseline condition. Evaporative Cooler Controls Implementation of evaporative cooling systems with EnergyPlus is problematic as active control of evaporative cooling can not occur in conjunction with system or zone heating controls. If there is a need for evaporative cooling, the system operates. Otherwise, the system is off and no heating can be provided at the system or zone level. The EnergyPlus development team has been made aware of these issues but the fix is not foreseen for the near future. This problem results in heating zone loads not being met in the greenhouses. The project team proposes the following solution to work around this evaporative cooling modeling limitation. The solution implemented by the energy analyst is to schedule the evaporative cooling on/off for each hour in the year (8760 schedule), based upon the cooling and heating set points and achieved zone temperatures. Establishing the schedule is an iterative process. However because the evaporative-cooler on-schedule is specified at an hourly time step (and not smaller), the zone temperature for some hours falls below the set point. To minimize these occurrences, the evaporative coolers were shut off when they overcooled the space. But in doing so, this increased the number of hours that loads were not met in the space to be beyond 300 hours. Since this is a process space, the baseline model and proposed design models were treated similarly. Is it acceptable to exceed the 300 hour loads-out-of-range limit due to this simulation software limitation?