Our design project consists of Classrooms, offices, conference rooms, dining rooms, library, atrium, and support spaces. The supply air system is a mixing system with supply air (Group A outlets) and return air devices at the ceiling level in all regularly occupied areas of the building. In order to obtain this credit, we have chosen to follow the second path of compliance, through design verification, as described on page 234 of the LEED reference guide by following guidelines mentioned in Chapter 31 of ASHRAE Fundamentals Handbook. However, we have the following questions: 1. ASHRAE Handbook of Fundamentals, Chapter 31, recommends a minimum ADPI of 80. Can we assume that an ADPI of 80 or more in each of the major spaces would satisfy the intent of the credit? If not, what value of ADPI will be acceptable? 2. In addition to submitting narratives, plans, sections, air velocities, location of supply and return air devices, we propose to submit outputs of a commercially available program that calculates Room ADPI based upon an actual design layout. This would be submitted for each of the typical spaces such as Classrooms, offices, conference rooms, dining rooms, library, and atrium. Would these be sufficient to comply with the requirements of the credit? A sample output sheet for a conference room is listed below for your review. Titus GRD Selection Room Air Device Calculations Large conference room ADPI: 82.0 Room Data Length x Width: 39.0 x 19.0 Ft. Maximum Room NC Level: 35 Ceiling Height: 9.0 Ft. Sensible Room Load: 26 BTUh/sf dT: 20 Area: 741.0 Sq. Ft. Air Changes: 8.0 ACPH Perimeter: 0 Ft. Mounting Type: Lay-in Supply Diffuser Data CD-2 Room Design Supply: 880 CFM: Room Comfort Model No.: PCS CFM: 110 Actual Max. Min Neck: 8 RND Throw: 6.0 Border Style: 1 - Surface Mount Pd: 0.03 ADPI 82 91.9 0.0 Throw Pattern: 4-way NC Level: 30 Description: Perforated Ceiling Diffuser Vt: 50.00 Heating TR: 0.4 Supply Drafting Data Tag: CD-2 No. of Diffusers: 8 CFM: (each):110Module Size: 24x24 Neck Size: 8 Throw: 4-way Layout: 2x 4 Return Device Data Room Design Return: 440 CFM: Model No.: : 0 Neck: 22x22 Pd: Module: 24x24 NC Level: 35 Border Style: Return Drafting Data Tag: No. of Returns: 2 Neck Size: CFM: (each):0 Module Size:
The submittal requirements and v2.1 Letter Template are in need of clarification. A table intended for the EQc2 Letter Template was in fact erroneously omitted, thus causing this confusion. Note that the credit requirements specify "ventilation systems that result in an air change effectiveness greater than or equal to 0.9" The first compliance path for this credit is a performance path. The system is designed and then tested using ASHRAE Standard 129-1997 to demonstrate that the air change effectiveness (ACE) is greater than or equal to 0.9. The test may be a field test of the actual diffuser installation or may utilize laboratory tests of diffusers tested under similar operating conditions. The second compliance path for this credit, and the subject of this CIR, is a design solution. ASHRAE Handbook of Fundamentals Chapter 32 may be used to document proper positioning and design of diffusers as described in the LEED v2.0 and v2.1 Reference Guides to achieve good air distribution. Diffusers must be located and selected to achieve an estimated Air Diffusion Performance Index (ADPI) of 80% or greater as described in Chapter 32, Table 4, ADPI Selection Guide, under all expected occupied operating conditions. The v2.1 submittal requirements and Letter Template are, as you point out, in need of clarification. A table intended for the EQc2 Letter Template was in fact erroneously omitted, thus causing this confusion.
The estimated ADPI from Chapter 32, or ADPI measured according to ASHRAE Standard 113, can not be used in lieu of Air Change Effectiveness (ACE) for determining compliance with this credit. However, provided the HVAC design has been developed according to Chapter 32, Table 4, ADPI Selection Guide, for an estimated ADPI of at least 80%, one may use the Zone Air Distribution Effectiveness, Ez, in ASHRAE Standard 62-2001, Addendum n, Table 6.2, to identify the ACE for each zone. This table prescribes the Zone Air Distribution Effectiveness values for various HVAC air distribution designs. To apply the values in the table correctly, requires consideration of both heating and cooling occupied modes for each zone. Separately analyze each unique space design. Projects must document designed performance in a table showing, for each zone, estimated ADPI of 80% or greater as well as an average ACE of 0.9 or greater for the occupied hours under worst case ACE conditions (e.g. the design day where the greatest number of occupied hours are projected for the ventilation mode with the lowest ACE, e.g. typically the design day with the greatest number of occupied hours with heating). For example, the documentation table will show: Zone___ADPI*___ACE, Heating**___ACE, Cooling**___ACE, Average *** 1 2 n * Based on ASHRAE Handbook of Fundamentals Chapter 32, Table 4, ôADPI Selection Guideö ** Based on ASHRAE 62-2001, Addendum n, Table 6.2. ôZone Air Distribution Effectivenessö. *** Time averaged ACE based on above ACE heating and cooling values, and ASHRAE 62-2001, Addendum n, Equation 6-9, for calculating the average ACE during the occupied hours. Calculation to be made using the worst case conditions representing the design day where the greatest number of occupied hours are projected for the ventilation mode with the lowest ACE.
Software created by diffuser manufacturers or other credible sources may be used to calculate estimated ADPI as long as the LEED application narrative for this credit identifies the program by name and company. Any space with heating capability, such as a heating coil, serving a space with exterior walls or roof will typically operate in a heating mode at some point when the space is occupied. These spaces must document ACE under heating mode. Spaces without this type of heating condition can document ACE under cooling mode only. For designs with heating capability, where heating is designed to only occur during unoccupied hours (e.g. morning warm up), ACE may be documented under cooling mode only, provided submittal documentation demonstrates that heating does not occur during occupied hours,. For designs with heating capability, where both heating and cooling are expected to occur during occupied hours, one may use ASHRAE 62-2001, Appendix n Section 184.108.40.206, Short Term Conditions, Equation 6-9, to determine the average conditions over a defined time period, T, where T equals 3 times the room volume (ft3) divided by the breathing zone outdoor air flowrate (cfm) calculated in Equation 6-1. FOR EXAMPLE: In a 1000 ft2 office space with 5 occupants and 13 ft ceilings, including return air space above the suspended ceiling, Equation 6-1 requires 85 cfm per 1000 ft2. From Equation 6-9, T equals 3 times 13,000 ft3 divided by 85 cfm, or 459 minutes or 7.64 hours. This is the maximum time allowed for averaging. If the morning warm up continues for the first two hours of a 10 hour occupied period (e.g. 8AM to 6PM), followed by 8 hours of cooling, then the average ACE is calculated as follows for ceiling diffusers with a Zone Air Distribution Effectiveness of 1.0 in cooling mode and 0.8 in heating mode (i.e. supply air greater than 15 oF warmer than space and ceiling return air temperature) : For the first 7.64 hours (i.e. the maximum averaging period, T, as determined by Equation 6-9 above) the average ACE is calculated as (2 hours times 0.8 + 5.64 hours times 1.0) divided by 7.64 hours, for an average ACE of 0.95. This average is then averaged with the remaining 2.36 hours of cooling only, which has an ACE of 1.0 as follows: (7.64 hours times 0.95 + 2.36 hours times 1.0) divide by 10 hours, for an average ACE for the 10 hour occupied period of 0.96. The submitted table would provide this information, for example: Zone: 1 ADPI: 0.80 ACE, Heating: 0.80 ** ACE, Cooling: 1.0 ** ACE, Average: 0.96 ***
Regarding how to proceed with a design using perforated and louvered ceiling diffusers in a laboratory with room loads in excess of 50 BTU/hr-ft2, we acknowledge that there are no data for these higher room loads in Chapter 32 Table 4, or to our knowledge in any diffuser manufacturer calculation programs. There are other diffuser types that provide estimated ADPI values for room loads as high as 80 BTU/hr-ft2. Also, since as room cooling loads increase, the mixing of the indoor air increases (e.g. results in ACE values closer to unity). For applications with room cooling loads greater than those listed in ASHRAE Chapter 32, Table 4, we recommend use of the estimated ADPI and the T50/L range for the highest room load listed for that diffuser type. For designs utilizing different types of diffusers, air distribution configurations, or T50/LÆs not described in ASHRAE Chapter 32 or Standard 62 tables, the only options for this credit are to conduct measurements of ACE (ASHRAE 129) or ADPI (ASHRAE Standard 113) either in the field or in a laboratory simulation. Also, for application of ASHRAE 129 in the field for this credit, we note that the requirements in Section 4, "Criteria for Acceptable Test Space", are not required, provided the space is operated under normal design conditions.
Related Addenda (Corrections & Interpretations)