ID#2083 made on
EQc7.1 - Thermal comfort - compliance
LEED BD+C: New Construction, LEED ID+C: Commercial Interiors, LEED BD+C: Core and Shell, LEED O+M: Existing Buildings
Our project is a 571,400 square foot automated distribution center in central Ohio. The space breaks down into: - 160,800 square feet of racked material storage with limited transient access by users...
Our project is a 571,400 square foot automated distribution center in central Ohio. The space breaks down into: - 160,800 square feet of racked material storage with limited transient access by users - 375,800 square feet of automated order fulfillment space - 200,000 square feet of elevated equipment platforms in the order fulfillment space - 35,000 square feet of office (10,000 SF in a central core and the remainder on the outside edge of the building) Operator characteristics for these areas will result in clothing insulation values below 0.5 clo and timeweighted metabolic rates above 2.0 for the equipment operators and order fulfillment staff. In ASHRAE 55, Section 5.1 clarifies the use of the standard as: "The vast majority of the available thermal comfort data pertains to sedentary or near sedentary physical activity levels typical of office work. This standard is intended primarily for these conditions. However, it may also be used to determine appropriate environmental conditions for moderately elevated activity." This is further noted in the two options for determining thermal comfort: - The Graphical Method only applies to occupants with 0.5 to 1.0 clo of clothing and a metabolic rate between 1.0 and 1.3 met. - The PMV-PPD Method only applies to occupants with clothing values less than 1.5 clo and metabolic rates between 1.0 and 2.0 met. Normative Appendix A to the standard (a fully incorporated part of ASHRAE 55) also states: "As metabolic rates increase above 1.0 met, the evaporation of sweat becomes an increasingly important factor for thermal comfort. The PMV method does not fully account for this factor, and this standard should not be applied to situations where the time-averaged metabolic rate is above 2.0 met. Typically, rest breaks (scheduled or hidden) or other operational factors (get parts, move products, etc.) combine to limit timeweighted metabolic rates to about 2.0 met in most applications." We are proposing to exclude the warehouse and order fulfillment areas from the Thermal Comfort: Design Credit Calculations due to process requirements that do not permit the use of ASHRAE 55. In addition, the normal industrial practice of spot-cooling for operators cannot be measured in ASHRAE 55 as the PMV-PPD model does not allow for airspeeds over 0.2 m/s (40fpm) and the adjustment factors provided in section 5.2.3 of the standard do not apply to situations where either the clothing is outside of the 0.5 to 0.7 clo range or the metabolic rate is outside of the 1.0 to 1.3 met range. Will it be acceptable to exclude the warehouse and order fulfillment areas from this credit due to process considerations while still complying with the standard for all other building areas?
The project team is inquiring as to whether or not they can exclude the warehouse and order fulfillment areas from meeting ASHRAE Standard 55-2004. In summary: No, the project team must not exclude the warehouse and order fulfillment areas when considering compliance with thermal comfort requirements in accordance with EQc7.1. Although there are not any previous NCv2.2 CIRs that specifically address this, an NCv2.0-2.1 CIR Ruling dated 9/8/2004 and another dated 7/10/2006 do not allow exclusion of these type of spaces, but instead refer the inquiring parties to ASHRAE Standard 55-2004, Section 5.3. Optional Method for Determining Acceptable Thermal Conditions in Naturally Conditioned Spaces. Your request does not indicate if the spaces being considered for exception are naturally conditioned or not, but most warehouses and packing areas tend to be either partially conditioned (semi-heated space) or naturally conditioned. The project team should consider this approach. The arguments in this CIR that ASHRAE Standard 55 does not apply to these spaces is not strictly correct. Standard 55 has an alternative calculation method using a computer model that applies to your situation as described in section 220.127.116.11 of ASHRAE Standard 55-2004, " 18.104.22.168 Computer Model Method for General Indoor Application. The method in this section may be applied to spaces where the occupants have activity levels that result in average metabolic rates between 1.0 met and 2.0 met and where clothing is worn that provides 1.5 clo or less of thermal insulation." The computer Model method is incorporated into the ASHRAE thermal comfort software tool available for purchase from ASHRAE. The computer model applies to your situation with low CLO values, high metabolic rate, and also incorporates the cooling effects of elevated air speeds. Regarding your discussion of the applicability of increased air speed, section 5.2.3 ASHRAE Standard 55-2004 says the predicted cooling effect of elevated air speed in figure 5.2.3 is actually conservative above 1.3 MET and for CLO less than 0.5 so can be used in those circumstances (increased skin wettedness and low clothing both increase the cooling effect). Figure 5.2.3 can be used to estimate the cooling effect of increased air speed or you can use the built in air speed input in the ASHRAE comfort software tool. This CIR points out that Standard 55 is mostly applicable to sedentary office type environments and is less applicable to an industrial environment where occupants have high metabolic rates. Section 5.2.3 states that elevated air speed cannot be above 0.8 m/s which is based on comfort studies only in sedentary environments. In industrial environments where MET is greater than 1.3, such as the one you describe, it is reasonable, energy efficient, and considered standard practice to use higher air speeds for comfort cooling up to 1.6 m/s (figure 5.2.3 extends to this range). In fact, predictions of the cooling effect of air movement will be underestimated if you use the table in the standard, as stated in the paragraph above. If you want a more accurate prediction of the cooling effect you will have to use the SET* index. SET* calculation procedures are described in Chapter 8 of ASHRAE Fundamentals and are also incorporated into the ASHRAE Comfort Software. To meet the intent of Standard 55 you determine the SET* at the upper boundary of the PMV/PPD comfort zone (when PPD= 10%) and then compare this value to your actual design conditions (elevated air speed, actual humidity, etc.). Because evaporation is a key factor at higher air speeds be sure to use actual space humidity in the SET* calculation. Alternative compliance methods with a clearly documented engineered approach that use reasonable logic to meet the requirements are considered to be generally acceptable pathways within the LEED Rating System, but are considered on a case by case basis. In summation, warehouse spaces are typically not allowed exclusion from the calculations for this credit. However, the project team should consider applying for this credit using ASHRAE Standard 55-2004, Section 5.3. and/or utilize an alternative compliance method or extrapolation of existing data to show compliance with the credit. Keep in mind that this credit is meant to promote thermal comfort as measured by a defined standard. If the project cannot provide thermal comfort for a number of its occupants, it should not necessarily be allowed to exclude those occupants. Additionally, CIR Rulings do not constitute credit acceptance, as each submittal must be ruled on individually and demonstrate compliance with all credit requirements and provisions as outlined in the LEED NCv2.2 Reference Guide.
Related Addenda (Corrections & Interpretations)