Energy Code Changes: What the Design Team Needs to Know: Session 5 -- Energy Modeling and the Energy Code
On January 20, 2010 Adrian Tuluca, LEED AP, Principal, Viridian Energy and Environmental, LLC gave the fifth and final presentation in the Energy Code series that began on January 5th in NYC. His topic, which had been briefly referred to by earlier presenters dealt with the Energy Modeling Method to show code compliance.
The NYS Energy Code covers the building envelope, HVAC, Domestic Hot Water, Power, Lighting, and Motors.
In addition to reviewing the prescriptive and pre-packaged pathways for compliance, it was emphasized that lighting must be performed on a space-by-space basis only, and is only required in common areas in residential buildings, such as hallways, stairwell, and foyers.
For all other areas, the Space-by-Space or Whole Building method can be used. Regarding the use of modeling it is almost always the envelope that will be the deciding factor as to just which method a design team will use. It is here that the advantages or shortcomings of each method will be seen. In general, we do not see much modeling done at the residential level; the prescriptive, or now, more often than not, the pre-packaged methods, such as RES Check suffice well.
All models must show compliance with Envelope U and SHGC values; areas with higher Visible Transmittance are allowed greater glazing areas above the 50% standard. The SHGC MUST be less than .25 if glazing area is greater than 40.1%. Heat loss during winter must be a maximum of U 0.46 if glazing area is greater than 40.1%, and in nonresidential areas the maximum U value for heat loss is 0.124, while in residential, it is 0.064 for curtain walls. Many designs cannot easily meet these requirements, especially those that contain more than 50% glazing, have a SHGC of greater than .25, or have a maximum U value of 0.064 for residential curtain walls. This is where energy modeling usually enters the design process.
Modeling can take three forms: Energy Cost of Design (less energy cost than code allows), Code Model (meets mandatory and prescriptive requirements) and Design Model (Meets mandatory requirements BUT non-compliant parts such as glass facade and lighting may be offset by other components that are higher performing.
It is of interest, that if a team chooses to use modeling, under NYS Chapter 8, only 35% of area can be glazed if the Whole-Building Performance via modeling.
For Energy Cost Budget Method via ASHRAE 90.1 there are many forms of energy modeling software on the market, but the most common used for hourly simulations in the commercial area are DOE-2, e-Quest, TRACE, and HAP. The entire building is modeled. For Budget (baseline) model vs. design model, we MUST note that the rules are different for LEED, and one MUST be careful here NOT to use LEED rules (Appendix G of ASHRAE 90.1) for NYS Energy Code compliance.
In Whole Building Modeling, for the envelope, we need massing of the building to reduce west exposure is needed, as are: Self shading, and exterior shading devices, daylight harvesting, active skins (solar panels), double envelopes that include internal shading and ventilation, as well as natural ventilation.
Solar Gain and Glazing Tilt can be of value here, as by means of tilting the glazing, heat can be deflected away from entering the building.
Regarding insulation in opaque walls, we always note that the assembly value is ALWAYS less than that of the Insulation U-Value. This is due to Thermal Bridging. This results in thermal short-circuiting in walls, roof parapets, slabs, mullions and columns. To deal with thermal bridging, one may use 3-D models such as Algor or HEATING-7, 2-D models such as FRAME or THERM, or the 1-D calculations that use the ASHRAE Handbook of Fundamentals. Lastly, tabulations can be made via ASHRAE 90.1.
We will always see lower actual R-values in a wall that has shelf angles. (a wall below windows) To deal with this, cantilevered shelf angles can help to restore a great deal of the lost R-value.
With lighting, the Energy Cost Budget Method (ASHRAE 90.1-2004 Chapter 11) it is now evident that lower lighting density is now needed, as well as daylight harvesting and occupancy sensors. Light Shelves often do NOT increase the amount of light that will penetrate a space, but can create more comfort for the occupants.
The Energy Cost Budget Method for HVAC involves picking the correct values from Figure 11.3.2 to decide on the Budget System Type, and then using Table 11.3.2A to get the Budget System Description. In the HVAC area, strategies include: Efficient equipment, controls, Ice Storage (I wrote on this in an earlier entry last July) Combined Heat and Power (Fuel Cells, Micro turbines, Reciprocating Cogen (I wrote on this in early 2009) as well as back pressure turbines.
A VERY important note regarding energy modeling: One must NEVER use a model to predict real -life energy use; it is to be ONLY used for compliance verification. One MAY be able to predict real-life energy usage by adjusting the Energy Code Model.
For Energy Code Compliance:
The Codes do NOT account for three-dimensional effects building envelope components, such as wall to slab assemblies, roof parapets, brick ties, shelf angles, as well as junction between horizontal and vertical mullions. In addition a process known as Stack Effect (where heat is drawn upward at greater velocities with increasing heights) heat loss from piping, as well as other energy usage not covered in the compliance areas such as voltage drops in feeders. Thus, a proper energy model MUST take these items into account.
In summary, Energy Modeling is a powerful tool, and is often necessary to prove compliance with the code. It is the design of the building envelope that will determine whether or not to use energy modeling. It is also important to note that at this time, energy modeling must NOT be used to predict actual energy usage; there are still too many variable that are not accounted for. Whatever method is used, perhaps the single most important item is to get the correct information together for the actual submittal to the Department of Buildings. Once again, the process known as Integrated Building Design can be of great help here. In this process errors are greatly reduced, as ALL team members are aware of what each other is doing at ALL times; they are all "on the same page."
The NYS Energy Code covers the building envelope, HVAC, Domestic Hot Water, Power, Lighting, and Motors.
In addition to reviewing the prescriptive and pre-packaged pathways for compliance, it was emphasized that lighting must be performed on a space-by-space basis only, and is only required in common areas in residential buildings, such as hallways, stairwell, and foyers.
For all other areas, the Space-by-Space or Whole Building method can be used. Regarding the use of modeling it is almost always the envelope that will be the deciding factor as to just which method a design team will use. It is here that the advantages or shortcomings of each method will be seen. In general, we do not see much modeling done at the residential level; the prescriptive, or now, more often than not, the pre-packaged methods, such as RES Check suffice well.
All models must show compliance with Envelope U and SHGC values; areas with higher Visible Transmittance are allowed greater glazing areas above the 50% standard. The SHGC MUST be less than .25 if glazing area is greater than 40.1%. Heat loss during winter must be a maximum of U 0.46 if glazing area is greater than 40.1%, and in nonresidential areas the maximum U value for heat loss is 0.124, while in residential, it is 0.064 for curtain walls. Many designs cannot easily meet these requirements, especially those that contain more than 50% glazing, have a SHGC of greater than .25, or have a maximum U value of 0.064 for residential curtain walls. This is where energy modeling usually enters the design process.
Modeling can take three forms: Energy Cost of Design (less energy cost than code allows), Code Model (meets mandatory and prescriptive requirements) and Design Model (Meets mandatory requirements BUT non-compliant parts such as glass facade and lighting may be offset by other components that are higher performing.
It is of interest, that if a team chooses to use modeling, under NYS Chapter 8, only 35% of area can be glazed if the Whole-Building Performance via modeling.
For Energy Cost Budget Method via ASHRAE 90.1 there are many forms of energy modeling software on the market, but the most common used for hourly simulations in the commercial area are DOE-2, e-Quest, TRACE, and HAP. The entire building is modeled. For Budget (baseline) model vs. design model, we MUST note that the rules are different for LEED, and one MUST be careful here NOT to use LEED rules (Appendix G of ASHRAE 90.1) for NYS Energy Code compliance.
In Whole Building Modeling, for the envelope, we need massing of the building to reduce west exposure is needed, as are: Self shading, and exterior shading devices, daylight harvesting, active skins (solar panels), double envelopes that include internal shading and ventilation, as well as natural ventilation.
Solar Gain and Glazing Tilt can be of value here, as by means of tilting the glazing, heat can be deflected away from entering the building.
Regarding insulation in opaque walls, we always note that the assembly value is ALWAYS less than that of the Insulation U-Value. This is due to Thermal Bridging. This results in thermal short-circuiting in walls, roof parapets, slabs, mullions and columns. To deal with thermal bridging, one may use 3-D models such as Algor or HEATING-7, 2-D models such as FRAME or THERM, or the 1-D calculations that use the ASHRAE Handbook of Fundamentals. Lastly, tabulations can be made via ASHRAE 90.1.
We will always see lower actual R-values in a wall that has shelf angles. (a wall below windows) To deal with this, cantilevered shelf angles can help to restore a great deal of the lost R-value.
With lighting, the Energy Cost Budget Method (ASHRAE 90.1-2004 Chapter 11) it is now evident that lower lighting density is now needed, as well as daylight harvesting and occupancy sensors. Light Shelves often do NOT increase the amount of light that will penetrate a space, but can create more comfort for the occupants.
The Energy Cost Budget Method for HVAC involves picking the correct values from Figure 11.3.2 to decide on the Budget System Type, and then using Table 11.3.2A to get the Budget System Description. In the HVAC area, strategies include: Efficient equipment, controls, Ice Storage (I wrote on this in an earlier entry last July) Combined Heat and Power (Fuel Cells, Micro turbines, Reciprocating Cogen (I wrote on this in early 2009) as well as back pressure turbines.
A VERY important note regarding energy modeling: One must NEVER use a model to predict real -life energy use; it is to be ONLY used for compliance verification. One MAY be able to predict real-life energy usage by adjusting the Energy Code Model.
For Energy Code Compliance:
- Sizing and energy cost -- use DOE-2, ENERGY-PLUS
- Daylighting and Lighting -- use RADIANCE
- Air Temperature and Movement -- use CFD 2000, FLUENT
- Thermal Bridges -- use ALGOR, THERM, FRAME
- Moisture Mitigation -- use MOIST, WUFI
The Codes do NOT account for three-dimensional effects building envelope components, such as wall to slab assemblies, roof parapets, brick ties, shelf angles, as well as junction between horizontal and vertical mullions. In addition a process known as Stack Effect (where heat is drawn upward at greater velocities with increasing heights) heat loss from piping, as well as other energy usage not covered in the compliance areas such as voltage drops in feeders. Thus, a proper energy model MUST take these items into account.
In summary, Energy Modeling is a powerful tool, and is often necessary to prove compliance with the code. It is the design of the building envelope that will determine whether or not to use energy modeling. It is also important to note that at this time, energy modeling must NOT be used to predict actual energy usage; there are still too many variable that are not accounted for. Whatever method is used, perhaps the single most important item is to get the correct information together for the actual submittal to the Department of Buildings. Once again, the process known as Integrated Building Design can be of great help here. In this process errors are greatly reduced, as ALL team members are aware of what each other is doing at ALL times; they are all "on the same page."
Posted by Alan L. Englander at 1/24/2010 7:07 PM 
Categories: Energy Cost Method, Solar Gain and Glazing Tilt, Thermal Bridging, Space by Space Method, U and UA Values, Envelope Trade-offs, ASHRAE 90.1, IECC, SHGC, Compliance Paths, Whole Building Method
Categories: Energy Cost Method, Solar Gain and Glazing Tilt, Thermal Bridging, Space by Space Method, U and UA Values, Envelope Trade-offs, ASHRAE 90.1, IECC, SHGC, Compliance Paths, Whole Building Method
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