ASHRAE 90.1: Energy Modeling, Lighting and Insulation

ASHRAE 90.1 Energy Modeling

ASHRAE (American Society of Heating, Refrigerating, and Air Conditioning) Standard 90.1 deals with energy guidelines that a designer must comply with and surpass, in order to design energy efficient buildings.  Energy Modeling is described in Appendix G of the standard ASHRAE 90.1, where it has a guide with benchmarks to follow when designing the building envelope, lighting systems, HVAC systems, domestic hot water systems, and when selecting equipment and materials for these systems in the building.

The energy modeling process in  Appendix G consists of developing two different energy models: a baseline building model and a proposed building model.  The baseline model is developed by using ASHRAE’s minimum energy guidelines, making it the building that is going to be used for comparison to your actual building.  The proposed model is an energy model of the building that is being designed and constructed in real life.

Appendix G of the standard has a step by step list of the proper baseline building and proposed building modeling strategy using ASHRAE 90.1 parameters for the elements listed in the paragraph above.  Energy modeling for LEED requires surpassing ASHRAE 90.1’s requirements by at least 10% for new buildings and 5% for existing buildings.

ASHRAE 90.1 Lighting

The ASHRAE 90.1 standard presents lighting power density (LPD) requirements, listed in watts per square feet (W/ft2), depending on the type of space being illuminated.  These requirements are listed in the standard starting on tables 9.4.5, 9.5.1, and 9.6.1.  LPD requirements can be followed by using either the building area method; in which the LPD for the entire building is calculated and taken as a whole.  Or by using the space-by-space method, in which the LPD is individually accounted for in each space.

To give an example, if you would like to comply with the LPD requirements for an office building, the LPD using the building area method is 1 W/ft2.  If you were to use the space-by-space method, you would split it by each space type in the office building and then you would add of of them up.  Your minimum LPD requirements for the building would be: offices at 1.1 W/ft2, corridors at 0.5 W/ft2, restrooms at 0.9 W/ft2, stairs at 0.6 W/ft2, and so on for each space type inside the building.

ASHRAE 90.1 Insulation

This standard contains a list of insulation values required for building roofs and walls that depend on the climate zone where the building is located.  For example, if the building is located in a hot and humid climate zone (i.e. zone 1-A), insulation is not required on walls, but it is required on roofs, where the insulation resistance value has to be R-15 or better.  If you building is located in a cold and dry climate zone (i.e. Zone 6-B), R-13 or better insulation is required on walls and R-20 insulation or better is required on roofs.  You can find more insulation information for all climate types starting on table 5.5-1 of the standard.

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