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Procccdings of Indoor Air '93. Vol. 3 471 RATIONAL IZUILI)ING Pf;RFORMANCE AND PRESCRIPTIVE CRITERIA FOR IMPROVED INDOOR ENVIRONMEN'I'AL QUALI`CY James E.Woods, Sanjay Arora, Nisha P. Sensharma and Bjame W. Olesen Indoor Environment'Program, College of Architecture and Urban Studies, Virginia Tech, U.S.A. ABSI'RAC'C Current building codes and standards may be inadequate to meet building objectives aimed at providing occupant comfort and well-being in addition to preventing deleterious conditions. Performance criteria for building elements, derived from human response, economic, and exposure criteria, are more appropriate for addressing these objectives. This paper proposes a rational process for developing performance criteria, and transfonning them to prescriptive criteria for use in design, specification, construction and operation. The proposed process can be used at each stage of the building's life. 1NTRODU(:I'H)N Current building codes and standards are promulgated to define minimum requirements for occupant safety and health. These documents are usually written in terms of prescriptive criteria for specific building elements (i.e. structure, envelope, enclosed spaces, and building services). '1'hey are intended to be used for project design and specification, construction, and project inspection. As a result, their usefulness during occupancy is limited. Conversely, performance criteria are usually based on evaluations of environmental and economic acceptability, and are established during the conceptual design phase to define the intended performance of the building. They include interactions amongg the building elements, environmental and economic factors, and are also intended to be used during occupancy. Only a few standards, such as ASHRAE 62-1989, provide both prescriptive and perforrnance criteria which have been rationalized (1,2). 1'he purpose of this paper is to demonstrate that a rational method can be used to transform human response criteria to exposure criteria to system performance criteria, and to further transform system performance criteria to system prescriptive criteria. RATIt)NALE FOR "1'tlt? !'ROt'OSEI) PROCESS The fundamental objectives of indoor environmental control are to provide for the comfort and well-being of the occupants and to prevent the existence of deleterious conditions. A 'healthy' building has been defined as "...not just free from building related illness and discomfort but indeed promotes well-being and health. Besides being non-hazardous, the salient features of the healthy building include thermal comfort, pleasant air quality, illumination and acoustical characteristics, support of social needs and productivity, and distinguished aesthetic qualities. These features should be maintainable over the building's life-time. The occupant should feel confidence in the building and its operation, be able to comprehend the systems and design, and be given a fair chance to control the systems (3)."

472 1'rw-ct'tlingc of Indoor Air '9 t. Vol. 3 According to the constitution of the World f lealth Organization "llealth is a state of complete physical. mental and social well-being and not merely the absence of disease or infinnity" (4). For consistency with this definition, acceptable building perforrnance criteria must specify (a) environmental conditions below which clinical signs of disease or illness are not known to occur; and (b) conditions that provide for occupant comfort and well-being. To address the criteria for comfort and well-being, affective response criteria are preferred over perceptual response criteria, as the latter do not ensure occupant comfort (5). It is proposed here that affective response criteria are best expressed in terms of acceptability of the physrcal erlvironment rather than ocurnmrt t: nrr jort because many factors affecting personal comfort are beyond physical control of the environment. From a pragmatic perspective, the relationship between human responses, exposure, systems and sources rests on a platform of economics (see Figure 1). Characterizations of human response and economics form the bases for the transformation of performance and prescriptive criteria for building systems. Numan responses to indoor environmental exposures are expressed in terms of four human response domains. These responses result from exposures of the primary physiological receptors that sense environmental conditions to four primary stressors: thermal, air quality, lighting and acoustic. The role of building systems is to provide acceptable exposures by responding to loads (e.g. contaminant, thermal, illumination, acoustic) that accrue from outdoor and indoor sources. Economic implications of these interactions are critical to the acceptable design and operation of these systems. Based on these conceptual relationships, a four step procedure for establishirlg performance and prescriptive criteria is proposed. Sources (Indoor and Outdoor Thermal Loads Contaminant Loads Illuminatlon Loads Acoustic Loads Systsms Structure Envelope S.rvlces Enclosed Spaces Exposure Thermal Air Ouallty Illumination Acoustic ~IH Human Response Envlronmental - Perceptual Personal-Perceptual Envlronmental - Aflectlve Personal - Affective Economics First Coats OparMing Costs Energy Use Productivity Figure 1. Conceptual model relating human response to indoor environmental factors. I'RUI'OSEl) PRO(:El)URF, FOR C;RI'TF,RIA T'RANSFURMA'TIUN Two sets of values for performance criteria should be determined. The first set should correspond to the best quality of environment (i.e. exposure) that can be attained, given Ihe state-of-the-art technology. For this set, the frequency of occupant acceptability Otoukl be maximized. The second set of values may relax the quality of the environment obtained,

Proceedings of Indoor Air '93. Vol. 3 473 by allowing lower frequencies of occupant acceptability (e.g. 80%). These two sets of values define the bounds within which performance criteria for specific applications should be selected. Step 1: Develop Ihiman Response Criteria. For virtual (i.e. not yet constructed) buildings, results of previous studies of existing buildings and promulgated consensus standards should be used to determine appropriate human response criteria. As discussed above, the criteria at the upper bound of the range should correspond to maximum levels of acceptability that can be feasibly achieved. The lower bound should represent conditions that a predetermined percentage. (e.g. 80%) will find acceptable. For existing buildings, a six point scale developed by Rohles, Woods and Morey (6) may he used to assess human response to the indoor environment. If 80% of the respondents rate the environment as 5 (i.e., acceptable) or better on the scale, exposures, measured concurrently with human response, are deemed to meet the criteria defined at the lower bound of the range. Step 2: Develop Exposure Criteria. The selection of exposure parameters should be based on three considerations: (a) To assure the best practical association with the selected human response criteria, exposure parameters should be expressed in terms directly related to the relevant human sensory receptors; (b) to enable the transformation of exposure parameters to system perfonnance parameters, the former must also be amenable to control by appropriate design and operation of building systems; and (c) existing methods to assess exposure must be capable of measuring (detecting) the concentrations specified. Exposure criteria should be derived from existing standards and guidelines as well as from empirical data consisting of human response and exposures assessed simultaneously. An example, which has been developed to design and evaluate the performance of a research and demonstration facility at Virginia Tech is shown in Table 1. Two levels of values corresponding to human response criteria are presented. Table 1. llurnan response and exposure criteria for the two performance levels (See References 1, 7 - 14). Caitinuous Exposure Criteria ttuman 71scrmal Air Quality Restxxise Criteria Op. Temp. Relative Air Particulates CO2 TVOC NicotineZ Decipol ("C) IlumI velocity (tig/mY (ppm) (mg/m' eq. (jighn') (%) (m/s) toluene) Maximum 23.0±.5 45±5 < 0.15 < 30 < 400 < 0.5 <1 < 0.3 Accepta- bility . 80% 23.0±2 45±15 < 0.25 < 75 < 1000 < 3.0 <10 < 1.5 Acccpta- bility I For paticlc sizc less than 10 micrais: Z Derived from references 13 and 14

474 t'rocccdings of Indoor Air '93. Vol. 3 Step 3a: Develop System Performance Criteria. The performance of each system should be evaluated for its capability to effectively respond to the loads in the occupied space during peak and moderating conditions. System performance criteria may be expressed as: • The system should have sufficient capacity to match the design loads and maintain exposure criteria to within a specified precision. • The system should have adequate control to maintain exposure values within the same precision at partial loads (i.e. from design loads to minimwn occupancy) as specified for design loads. Step 3b: Derive System Prescriptive Criterio. Prescriptive criteria can be derived from the above by using rational model(s). For air quality, a simple, steady-state expression for a one compartment model can be used to develop prescriptive criteria for design of the system and its controls. The model may be expressed as (2,12): DC=(N-E)/V (1) where AC = C, - Ca the difference between ti>c unifonniy mixed indoc~r air concentration, C,, and Ihe outdoor air concentration. C,;, N = tiie net gcneraticm rate of the contaminant; E = removal rate of t1ie contaminant from the air: and V = voiumetric fiow rate of outdoor air for dilution control. Similarly, for a thermal energy balance: U.A.(t. - 4) + m„(ho - h,) + Qjm = mK (h, - h,) (2) where U,, = average thermal transfer coefficient of tlie building envelope: A„ = area of the building envelope: t„ = outdoor air temperature: t, = temperature in occupie«i tpace; m, = mass flow rate of air (ventilation and infiltration); h,,, h, ancl h, are enthalry of ciuWoor, rmttn :urd supply air, Q;,,, = Internal heat generation rate; and iiiK = mass flow rate of conditioned (i.e. supply) air. The outdoor air ranges from winter to summer design conditions, including moderate conditions when the indoor-outdoor temperature differential is negligible. These conditions define a prescriptive range. The internal loads are also variable and a range should be prescribed. These prescriptive criteria form the basis for evaluation of system operation. Enthalpy of air is a dependent variable while the mass flow of conditioned air can be controlled and therefore specified. if Cp is the specific heat of air then, the "sensible"' heat balance can be expressed as: N U„A•(t~ - t,) + m„Cp(to - 4) + Qim = rir., Co(4 - t.) (3) ~ or At = t, - to rnKC,,(t, - t,))1(U,A• + m,C1) (4) ~ N t11 where At is ,naiogot,s to AC; Q,M is analogous to N; ~iiKCr(4 - t,) is anatcIgows and 1~ (UaAa + m'C,) is analogous to V In Equation (1). ~ Simultaneous solutions to Equations I and 4 therefore allow quantification of the ~ prescriptive criteria E, U,, A., m,, and mK corresponding to the specified performance criteria C,, t,, t,, the loads N and Qi,,,, and the range of outdoor conditions ta and C,,.

Proceedings of Indoor Air '93, Vol. 3 1 475 Step 4: Develop Energy and Economic Performance Criteria. Each system should also be evaluated for its efficiency in energy transformation and for the cost it incurs to deliver the required performance. System energy efficiency may be defined as the ratio of the energy required to maintain the environmental criteria to the energy consumed to provide the required environmental conditions (15). As a criterion we propose that: • A system energy efficiency of at least 80 percent should be achieved. Life-cycle-cost analysis evaluates all significant time-equivalent costs attributable to a given building design, system or component, and its impact on the productivity in the space, thus enabling a choice among alternative systems. The costs included are the investment (first cost), non-fuel operation and maintenance costs, energy costs, and a monetary value for enhanced productivity resulting from improved environments. Criteria for economic performance may be expressed as: • The selected system should incur minimum life-cycle cost, wherein the comparison of alternatives includes weighting for productivity improvements in the environment. CONCLUSIONS The process described above is applicable for use in virtual and existing buildings, and for different stages in a building's life cycle. For virtual buildings, performance criteria are essential at the design conception stage. When transformed to prescriptive terms, the criteria become useful for design and contractual documents. Prescriptive criteria also form the basis for testing, balancing and commissioning of systems. Once the systems are operational, i.e. in existing buildings, the performance criteria (system, exposure and human response) again become effective, for, human response and the corresponding exposures will ultimately determine the acceptability of the indoor environment. Performance criteria should be reestablished when adaptive reuse of buildings is contemplated. These should then be translated into prescriptive criteria to aid in the redesign of building systems. For the lower bound, while the human response, exposure, and system criteria serve as constraints, energy and economic criteria provide the desirnGle values which should preferably be achieved. By establishing the rational basis for the transformation of criteria, it is possible to assess the efficacy of building systems in meeting the primary goals of building performance. REFERENCES 1. ASIiRAE. ANSI/ASIIRAE 62-1989. Ventilation for acceptable indoor air quality. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, GA, 1989. 2. Woods JE, Janssen JE, Krafthefer BC. Rationalization of equivalence between the ventilation rate and air quality procedures in ASIIRAE Standard 62. In: IAQ '86. Managing Indoor Air for Ilealth and Energy Conservation. 1986; 181-191. 3. Berglund B, T Lindvall, I Samuelsson, and J Sundell. Prescriptions for healthy buildings. In: Berglund B and' Lindvall T, ed., Proc of CIB Conference Healthy Buildings '88. Conclusions and recommendations for healthier buildings. Swedish Council for Building Research, Stockholm, 1991. 4. World Ilealth Organization. Constitution of the World Ilealth Organization. Official Record of the World Ilealth Organization. 1946; 2, 100.

4 76 T'rocccclinp c+f Indoor Air 'o:1. VoI. 3 5. Sensharma NP, Edwards PK, Woods JE, Seelen J. A characteri7.aticm of methodologies for assessing human response to indoor environments. Submitted for publication: Indoor Air '93. 6. Rohles F'lI, JE Woods and PR Morey. Indoor environment accehlability: Irtie development of a rating scale. ASIIRAE 'iinnsactions. American Society (if lleating, Refrigeration and Air-Conditioning Engineers, Inc., Atlanta. GA, 1989;, 95(1): 23-27. 7. ASHRAE. ASIIRAE Revised Standard 55-1981 R(revised draft)."ihennal environmental conditions for human occupancy. American Society of ] leating, Refrigerating and Air-ConditioningrEngineers, Inc. Atlanta, GA, 1991. 8. CEN. CEN[tC156/WG6 N7 (Draft Document). Ventilation for buildings: Design criteria for the indoor environment. 1991. 9. 1S0. ISO 7730 (modified version). Document CEN//T'C156/WC6 N8. Moderate thermal environments - determination of the PMV and PPD indices and specification of the conditions for thennal comfort. 10. Swedish Indoor Climate Institute. Classified indoor climate systems: Gnidelines and specifications SCANVAC, Sweden. 11. Molhave L Volatile organic comPounds, indoor air quality and health. Proc of Indoor Air '90. 1990: 5:15-33. 12. Fanger PO. Introduction of the off and decipol units to quantify air Pollution perceived by humans indoors and outdoors. Energy and E3uildings. 1988: 12:1-6. 13. Leaderer 13, Cain, WS. Air quality in buildings during smoking and nonsmoking occupancy. ASIIRAE Transactions. American Society of lTeating„ Refrigeration and Air-Conditioning Engineers„ Atlanta, GA. 1983; 89(213):601-613. 14. Personal communication with Dr. Brian Leaderer, John 13. Pierce f oundation and Associate Professor, Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, CT.