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Energy and Buildings 60 (2013) 410–419

Contents lists available at SciVerse ScienceDirect

Energy and Buildings

j our na l ho me p age: www.elsev ier .com/ locate /enbui ld

eview

spects of indoor environmental quality assessment in buildings

oan Sarbu ∗, Calin Sebarchieviciepartment of Building Services, “Politehnica” University of Timisoara, Piata Bisericii 4A, 300233 Timisoara, Romania

r t i c l e i n f o

rticle history:eceived 19 December 2012eceived in revised form 22 January 2013ccepted 2 February 2013

eywords:uilding

ndoor environmental

a b s t r a c t

Energy consumption of buildings depends significantly on the criteria used for the indoor environmentand building design and operation. The environmental factors that define the indoor environmental qual-ity are: thermal comfort, indoor air quality, acoustic comfort and visual comfort. This paper approachesthe numerical prediction of thermal comfort in closed spaces on the basis of PMV–PPD model, and itstesting to asymmetric or nonuniform thermal radiation, as well as the indoor air quality simulation andcontrol. The following are developed: a computation and testing model of thermal comfort in buildings,a computational model for indoor air quality numerical simulation, as well as a methodology to deter-

hermal comfortlfactory comfort

ndoor air qualityutside airflow rateomputational models

mine the outside airflow rate and to verify the indoor air quality in rooms, according to the EuropeanStandard CEN 1752. Also, the thermal comfort criteria for design of heating systems, the relationshipbetween thermal environment and human performance, as well as the influence of carbon dioxide onhuman performance and productivity are presented. The performance of the developed computationalmodels, implemented in two computer programs, is illustrated by using some numerical comparative

umerical applications applications for two building construction types.© 2013 Elsevier B.V. All rights reserved.

ontents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4102. Prediction of thermal comfort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

2.1. Mathematical model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4112.2. Numerical application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412

3. Thermal comfort criteria for design of heating systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4133.1. Criteria for general thermal comfort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4133.2. Criteria for local thermal comfort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413

4. The relationship between thermal environment and human performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4145. Evaluation of olfactory comfort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4146. Indoor air quality simulation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416

6.1. General equation for the time evolution of a contaminant concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4166.2. Equilibrium concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4166.3. Metabolic CO2 computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416

7. Computation of outside airflow rate and indoor air quality control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4167.1. Mathematical model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4167.2. Numerical application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417

8. Influence of carbon dioxide on human performance and productivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4189. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419

. Introduction

The greatest majority of people carry on 80–90% of their livesnside buildings, which must satisfy the objective and subjective

∗ Corresponding author. Tel.: +40 256403991; fax: +40 256403987.E-mail address: ioan.sarbu@ct.upt.ro (I. Sarbu).

378-7788/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.enbuild.2013.02.005

requests linked to vital functions of the occupants. In existingand future buildings there will be an increasing focus on energyuses and indoor environmental quality. Energy consumption ofbuildings depends significantly on the criteria used for the indoor

environment (temperature, ventilation and lighting) and build-ing design and operation. Indoor environment also affects health,productivity and comfort of the occupants. Recent studies haveshown that costs of poor indoor environment for the employer, the

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I. Sarbu, C. Sebarchievici / Ener

uilding owner and for society, as a whole are often considerablyigher than the cost of the energy used in the same building [1].

The design of the rooms must take into consideration these con-itions and present tendencies to reduce the energy consumptionhat are decisively influencing the optimal or admissible values ofomfort parameters. Thus, the inside microclimate of a buildingust be the result of a computation of multicriterial optimization,

aking into account technical and psychological comfort and thenergy saving.

The environmental factors that define the indoor environmen-al quality are: thermal comfort, indoor air quality, acoustic comfortnd visual comfort. In accordance with the dissatisfied person per-ent of the ensured comfort: 10%, 20%, and 30%, rooms are classifiednto three categories: A, B, and C.

Subjective comfort of persons in a room depends on manyactors: temperature, humidity and air circulation; smell and res-iration; touch and touching; acoustic factors; sight and coloursffect; building vibrations; special factors (solar-gain, ionization);afety factors; economic factors; unpredictable risks. Because ofome technical conditions the common influence of these factorsannot be analyzed, and the adaptation of the human body to aertain environment is a complex process, this one reacting to theommon action of more parameters.

In general nationally specified criteria for design of heatingystems must be used, but in case of no national regulations inter-ational standards give values for thermal comfort in informativennexes. The recommended criteria are given for general thermalomfort based on PMV (predicted mean vote)–PPD (predicted per-ent dissatisfied) model or operative temperature and for localhermal comfort parameters like vertical temperature differences,adiant temperature asymmetry, draft and surface temperatures.uch requirements can be found in existing standard and guide-ines.

This paper describes a computation and testing model ofhermal comfort in buildings based on PMV–PPD indices, a com-utational model for indoor air quality numerical simulation, asell as a methodology to determine the outside airflow rate and

o verify the indoor air quality in rooms, according to the Europeantandard CEN 1752 [2]. Based on these computational models twoomputer programs for PC compatible microsystems were elabo-ated. Also, it is presented the thermal comfort criteria for designf heating systems, the relationship between thermal environmentnd human performance, as well as the influence of carbon dioxiden human performance and productivity.

. Prediction of thermal comfort

The subjective sensation of thermal comfort is decisively deter-ined by the following parameters: indoor air temperature (ti);ean radiant temperature (tmr) of bordering surfaces; relative

umidity of air (�i); partial water vapours pressure (pa); air velocityvi); thermal resistance of clothing (Rcl or Rh), and their influencen the vaporization; heat production of human body and humanhermoregulation. The first four are physical parameters, and thether two express the capacity of the human body to adapt itself inrder to maintain the thermal equilibrium. The main factors thatnfluence the thermal equilibrium of the human body are:

Heat production of human body, which depends on the activitylevel, age, sex.

Body heat loss, which depends on clothing and on the other

parameters mentioned previously.

In general, comfort is gained when body temperatures are heldithin narrow ranges, skin moisture is low, and the physiological

Buildings 60 (2013) 410–419 411

effort of regulation is minimized. Surprisingly, although climates,living conditions, and cultures differ widely throughout the world,the temperature that people choose for comfort under similar con-ditions of clothing, activity, humidity, and air movement has beenfound to be very similar [3–5].

In order to evaluate the sensation of thermal comfort we use thethermal sensation scale with seven levels [6]: +3 (hot); +2 (warm);+1 (slightly warm); 0 (neutral); −1 (slightly cool); −2 (cool); −3(cold).

Numerical prediction of thermal comfort in a room is per-formed by using the PMV–PPD model, and testing is achieved atasymmetric thermal radiation, caused by building elements with atemperature tel lot different from the mean radiant temperature tmr.Radiant asymmetry is the difference in radiant temperatures seenby a small flat element looking in opposite directions. Four calcu-lation methods of radiant temperature asymmetry are available intechnical literature [7].

2.1. Mathematical model

Taking into account the thermal interaction of the human bodywith its environment it is possible to write the well known energybalance equation:

M − W = Qi = (C + R + Esk) + (Cres + Eres) (1)

where M is the rate of metabolic heat production; W is the rateof mechanical work accomplished (zero for most of activities); Qiis the internal heat production; C, R are the convective and radiantheat losses outer surface of a closed body; Esk is the rate of evapora-tive heat loss from skin; Cres is the rate of evaporative heat loss fromrespiration; Eres is the rate of convective heat loss from respiration.

All the terms in the basic heat balance equation are expressedper unit body nude surface area.

• Convective heat loss C is given by Eq. (2) and radiant heat loss Ris expressed in terms of the Stefan–Boltzmann law (3):

C = fcl˛c(th − ti) (2)

R = 3.96 · 10−8fcl[(th + 273)4 − (tmr + 273)4] (3)

where

fcl = Ah

AD(4)

AD = 0.202m0.425h0.725 (5)

in which ti is the indoor air temperature; th is the mean temperatureof the outer surface of the closed body; tmr is the mean radianttemperature; �c is the convective heat transfer coefficient; fcl isthe clothing area factor dimensionless; Ah is the actual surface areaof the clothed body; AD is the nude body surface area [8]; m is themass of human body; h is the height of human body.

The sensible heat (C + R) is transferred through conduction fromthe skin surface to the outer clothing surface:

C + R = Qs = tp − th

Rh(6)

where

Rh = 0.155Rcl (7)

in which Qs is the sensible heat loss from skin to outer clothingsurface; Rh is the thermal resistance of clothing, in (m2 K)/W; Rcl is

the thermal resistance of clothing, in clo; tp is the skin temperatureexpressed by:

tp = 35.7 − 0.032(M − W) (8)

4 gy and Buildings 60 (2013) 410–419

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transfer coefficient of building components: walls [0.7 W/(m K)],ceiling [0.4 W/(m2 K)], windows and doors [2.9 W/(m2 K)]; glasswalls surface: 7.5 m2; indoor air temperature: 24 ◦C; thermal powerof heater: 1900 W.

12 I. Sarbu, C. Sebarchievici / Ener

Evaporative heat loss from skin Esk may be computed with theequation:

sk = Ed + Ersw (9)

here

d = 0.35(1.92tp − 25.3 − pa) (10)

rsw = 0.42(M − W − 58) (11)

n which Ed is the evaporative heat loss by diffusion of waterhrough the skin; Ersw is the evaporative heat loss by regulatoryweating; pa is the water vapour partial pressure in indoor air.

Respiratory heat loss is often expressed in terms of sensible Cres

and latent Eres heat losses. The Cres and Eres can be computed asfollows:

res + Eres = 0.0014M(34 − ti) + 1.73 · 10−5M(5870 − ps) (12)

here ps is the saturated water vapour pressure at the humid oper-tive temperature.

The body’s mechanical efficiency is defined by:

= W

M(13)

The energy balance equation (1) is under the form:

ac = M − W − E − (Cres + Eres) − (C + R) (14)

here Qac is the accumulated heat in body.If Qac = 0, thermal comfort felt by occupants is adequate. When

ac > 0, body temperature rises and the person will have a sense ofarmth, and if Qac < 0, body temperature decreases and the personill have a sense of coldness.

Writing the energy balance equation (14), for Qac = 0, in the form:

− W − E − (Cres + Eres) = Qs = C + R (15)

nd explaining the terms in it with Eqs. (2), (3), (6), (9) and (12), webtain the thermal comfort equation:

(1 − �) − 0.35[43 − 0.061M(1 − �) − pa] − 0.42[M(1 − �) − 58]

− 0.0014M(34 − ti) − 0.0023M(44 − pa)

= 35.7 − 0.032M(1 − �) − th

0.155TRcl= fcl˛c(th − ti)

− 3.96 · 10−8fcl[(th + 273)4 − (tmr + 273)4] (16)

onsidering some parameters as constant in Eq. (16), after it isolved and the solutions graphically represented the comfort dia-rams are obtained. Substituting the thermal comfort equation (16)nto expression of PMV index established by Fanger [9], the pre-icted mean vote index is obtained, for a certain point of the room:

MV = [0.352 exp(−0.042M) + 0.032] × {M(1 − �)

− 0.35[43 − 0.061M(1 − �) − pa] − 0.42[M(1 − �) − 58]

− 0.0023M(44 − pa) − 0.0014M(34 − ti) − fcl˛c(th − ti)

− 3.96 · 10−8fcl[(th + 273)4 − (tmr + 273)4]} (17)

PMV index has the optimum value equal to zero, but accordingo the prescriptions ISO Standard 7730 [10] it is considered that theomain of thermal comfort corresponds to values between −0.5nd +0.5. The use of PMV index is recommended only for values

etween +2 and −2. In Fig. 1 are represented the values of operativeomfort temperature tc (corresponding to index PMV = 0), corre-ated to thermal resistance of clothing (Rcl and Rh), metabolic rateM and metabolic heat production M.

Fig. 1. Operative comfort temperature function of clothing and activity.

The predicted percent dissatisfied PPD is function of PMV indexas follows:

PPD = 100 − 95 exp(−0.0335 PMV4 − 0.2179 PMV2) (18)

The optimal value for PPD index is of 5% [6] and may be obtainedonly using air conditioning systems, with a high automation degree.A relationship between the radiant temperature asymmetry andthe percent dissatisfied was established (Fig. 2). Fig. 2 shows thatpeople are sensitive, to asymmetry caused by an overhead warmsurface than by a vertical cold surface. These data are particularlyimportant when using radiant panels to provide comfort in spaceswith large cold surfaces or cold windows.

On the basis of this mathematical model was elaborated com-puter program COMFORT 1.0 [11], in FORTRAN programminglanguage, which allows both direct computation of PMV and PPDindices in different points of a room, and their comparative analy-sis. It is also possible to determine the mean radiant temperaturein isolated points or in a series of points situated on a straightline.

2.2. Numerical application

The room with geometrical dimensions of 4.4 m × 6 m × 2.7 mfrom Fig. 3 is considered. The following data are known: heat

2

Fig. 2. Variation of percent dissatisfied function of radiant temperature asymmetry.

I. Sarbu, C. Sebarchievici / Energy and

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3.2. Criteria for local thermal comfort

TN

TE

Fig. 3. Room heated.

A comparative study of PMV and PPD indices is performed usinghe computer program COMFORT 1.0 in several points situated on

straight line (discontinuous), at different distances from the win-ow, function of clothing thermal resistance and metabolic rate.

Results of the numerical solution obtained for the following pairf values: 0.33 clo − 1 met, 1 clo − 1 met and 0.5 clo − 2.8 met, areeported in Table 1.

According to the performed study it was established thatMV index has values closed to zero only for the pair of values

clo − 1 met. For any other pair of values Rcl–iM the percent dissat-sfied people of the thermal comfort would be greater, of 5%.

able 1umerical results of COMFORT 1.0 computer program.

Distance from thewindow [m]

0.33 clo − 1 met 1 clo − 1

tmr [◦C] PMV PPD [%] tmr [◦C]

0 1 2 3 4

1.0 24.43 −1.22 36.28 24.43

1.5 24.86 −1.18 34.37 24.86

2.0 25.34 −1.09 30.18 25.34

2.5 25.67 −1.03 27.45 25.67

3.0 25.78 −1.01 26.56 25.78

3.5 25.70 −1.03 27.20 25.70

4.0 25.63 −1.04 27.77 25.63

4.5 25.55 −1.05 28.43 25.55

5.0 25.37 −1.09 29.92 25.37

able 2xamples of recommended categories for design of mechanical heated and cooled buildin

Type of building or space Category

0 1

Offices and spaces with similar activity (single offices, open-planoffices, conference rooms, auditoriun, cafeteria, restaurants,classrooms); iM = 1.2 met

I

IIIII

Buildings 60 (2013) 410–419 413

3. Thermal comfort criteria for design of heating systems

3.1. Criteria for general thermal comfort

For the design of buildings and HVAC systems the thermal com-fort criteria (minimum room temperature in winter and maximumroom temperature in summer) and required ventilation rates foran acceptable indoor air quality shall be used as input for heatingload. The basis for establishing the criteria is ISO Standard 7730 andthe use of the PMV-PPD indices, as shown in Table 2.

Based on specified type of clothing and activity of the occupantsit is possible to calculate the corresponding ranges of operativetemperature. As an example, thermal design criteria for differenttypes of space with sedentary activity and typical winter clothingare given in Table 2.

The heat emission system must fulfil the requirement that thedifference between the operative temperatures in the warmestposition in the space must be inside the choses temperature range(3–5 K). Especially in a very deep room with a fully glazed fac adethe difference may be critical.

By a simplified design method [12] showed that the maximumoperative temperature difference in a room at an outdoor air tem-perature of −12 ◦C can be calculated according to the equation:

tc2 − tc1 ≤ 0.96Uw (19)

where tc1 is the operative temperature at the coldest position, in◦C; tc2 is the operative temperature at the warmest position, in ◦C;Uw is the average U-value of the facade, in W/(m2 K).

For a typical modern standard window (U = 1.5 W/(m2 K)) thedifference in operative temperature is lower than the criteria,because additional variation in operative temperature will becaused by the control system. If the difference is too large it willbe necessary to position a heat emitter at the fac ade (radiator, floorheating, and convector), change the design of the fac ade, and choosea higher insulation of the fac ade.

Criteria for draft, vertical air temperature difference, radiantasymmetry and surface temperatures will also impact the design

met 0.5 clo − 2.8 met

PMV PPD [%] tmr [◦C] PMV PPD [%]

5 6 7 8 9

−0.18 5.64 24.43 −0.70 15.39−0.13 5.38 24.86 −0.63 13.42−0.07 5.09 25.34 −0.56 11.46−0.02 5.01 25.67 −0.50 10.26−0.01 5.00 25.78 −0.48 9.89−0.02 5.01 25.70 −0.50 10.16−0.03 5.01 25.63 −0.51 10.41−0.04 5.03 25.55 −0.52 10.68−0.06 5.08 25.37 −0.55 11.35

gs.

Thermal comfort indexes Operative temperature range [◦C]

PPD [%] PMV Winter (Rcl = 1 clo) Summer(Rcl = 1 clo)

2 3 4 5

<6 −0.2 < PMV < +0.2 21.0–23.0 23.5–25.5<10 −0.5 < PMV < +0.5 20.0–24.0 23.0–26.0<15 −0.7 < PMV < +0.7 19.0–25.0 22.0–27.0

414 I. Sarbu, C. Sebarchievici / Energy and

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ig. 4. Variation of maximum air velocity in function of window–wall height and-value.

f buildings and HVAC systems [13]. These criteria are included inSO 7730.

Vertical air temperature differences. One of the main features ofradiant floor heating and cooling is the uniform temperature con-dition from floor to ceiling.

Measurements show that floor heating large panel radiatorsnder the window have a very uniform temperature profile. Theore convective systems (Baseboard under window, Warm air sys-

ems, and Back wall) or high temperature water systems have largerifferences in air temperature. The standard [10] requires the ver-ical temperature difference lower than 3 K between feet and headcategory II) and below 2 K (category I).

Radiant temperature asymmetry. A person is most sensitive toradiant asymmetry caused by warm ceiling or cool walls – win-dows. Difficulties may occur by a temperature asymmetry of 5 Kfor warm ceiling and 10 K for cold walls (category II [10]). Usually,the radiators/convectors are placed under the window in orderto avoid the problems. Due to the development of high isolativewindows this is, however, normally not a problem anymore. Also,the maximum radiant temperature asymmetry can be calculatedat the design stage [13] by the equation:

tmr < 3.96Uw (20)

This means that if the fac ade is a standard double glassing, = 2.9 W/(m2 K), the asymmetry will be 11.54 K, which is higher

han the category II criteria of 10 K. For a typical modern standardindow, U = 1.5 W/(m2 K), the asymmetry will be less than 6 K.

Draft. Downdraft from cold surfaces is another factor that maycause discomfort and require a heated surface under the coldwall/window. On the basis of a calculation method, the relationbetween the window height, U-value for the wall/window, out-door air temperature and the maximum acceptable air velocity[10] can be determined [14].

An example is shown in Fig. 4, where the maximum air velocityn the occupied zone 1 m from a cold vertical surface (wall, window)s shown as a function of window–wall height and U-value by anutdoor air temperature of −12 ◦C.

For category II the criteria for the air velocity, taken into accounthe calculated lower air temperature and an assumed turbulencentensity of 20%, is 0.18 m/s. This means that if the window is

standard double glassing, U = 2.9 W/(m2 K), the window should

Buildings 60 (2013) 410–419

not be higher than 1.5 m. For a typical modern standard window,U = 1.5 W/(m2 K), the height could be full room height, 3.5 m.

• Floor surface temperature. In international standards, a floor tem-perature range of 19–29 ◦C is recommended in the occupied zonefor rooms with sedentary and/or standing occupants wearingnormal shoes. This is a limiting factor for the capacity of floorsystems.

For heating, the maximum temperature is 29 ◦C, which at adesign indoor air temperature of 20 ◦C will provide a heat outputof 100 W/m. Seated persons would prefer 1 K higher floor temper-atures and standing persons 1 K lower surface temperatures. In thestandard EN 15377-1, it is acceptable to use 35 ◦C as the design floortemperature outside the occupied zone, that is perimeter until 1 mfrom fac ade.

• Wall temperature. For wall heating, the maximum lies in the range35–50 ◦C. The maximum may depend on the application of thewall heating system. The risk for burns and pain is a skin temper-ature of 42–45 ◦C and depends on the conductivity of the surfacelayer. Surface temperature of a radiator may also be limited. Insome countries it is limited to 55 ◦C. The difference to a wallheating is that the radiator is invisible and people can be warned.

• Ceiling temperature. Requirements to the ceiling surface tempera-ture should not cause a too high radiant temperature asymmetry.The radiant asymmetry depends on the angle factor from a smallplane element to the ceiling and the ceiling temperature.

For a room with the dimensions 2.4 m × 4.8 m and 2.7 m height,the angle factor is 0.42 between the ceiling and a sitting personat the centre of the room. For heating, it is assumed that all thesurfaces other than the heated ceiling will have a temperature equalto a design indoor air temperature of 20 ◦C. The radiant asymmetryfrom a heated ceiling must then be less than 5 K:

0.42 × tceiling + (1 − 0.42) × 20 ◦C − 20 ◦C < 5 K (21)

This means that the limitation is a maximum average ceiling tem-perature of 32 ◦C.

4. The relationship between thermal environment andhuman performance

Since the human performance and work productivity benefitsare quite substantial, they should be considered in conventionaleconomic cost–benefit calculations pertaining to building designand operation.

Fig. 5 compares the three different relationships between ther-mal sensation and work performance in office buildings developedby Roelofsen [15], Jensen et al. [16] and Lan et al. [17]. It shows thatthere exists thermal sensation for optimal performance: feeling toocold or too warm will negatively affect the performance, though theeffects are not symmetrical around thermal neutrality and they aresomewhat skewed toward a slightly cool sensation.

Using these relationships [18], Table 3 summarizes the potentialeffects of thermal environment on performance for different cate-gories of indoor environment as specified in the standard EN 15251.All relationships show that designing for a lower environmentalcategory will result in reduced performance.

5. Evaluation of olfactory comfort

Comfort and indoor air quality (IAQ) depend on many factors,including thermal adjustment, control of internal and externalsources of pollutants, supply of acceptable air, occupant activities

I. Sarbu, C. Sebarchievici / Energy and Buildings 60 (2013) 410–419 415

Table 3Potential maximum reduction in performance for different categories of indoor environment.

Category accordingto EN 15251

Predicted mean vote (PMV) Maximum performance decrement compared to optimum performance of100% [%]

Lan et al. Jensen et al. Roelofsen

I −0.2 < PMV < 0.2 0.12 0.82 1.44II −0.5 < PMV < 0.5 0.31 1.34 5.48III −0.7 < PMV < 0.7 0.50 1.75 8.42IV PMV < 0.7; PMV > 0.7 >0.5 >1.75 >8.42

Table 4The effect of CO2 concentration on human body.

CO2 concentration Effect

[%] [ppm]

3 30,000 Deep breathing, strong4 40,000 Head aches, pulse, dizziness,

psychic emotions

asi

a3mod

d

clf

c

S

wcf

Table 5Minimum rate of outdoor airflow.

No. Activity Outdoor airflow rate[m3/(h pers)]

0 1 2

1 Intellectual 302 Physical very easy 30

5 50,000 After 0.5–1 h may cause death8–10 80,000–100,000 Sudden death

nd preferences, and proper operation and maintenance of buildingystems. Ventilation and infiltration are only part of the acceptablendoor air quality and thermal comfort problem.

Air composition in living spaces differs from that of the outsideir. Carbon dioxide (CO2) concentration in outside air is between00 and 400 ppm, and in living spaces is of about 900 ppm. Theaximum admitted limit of CO2 concentration in the inhaled air is

f 1000 ppm (Pettenkofer’s number). Table 4 presents the effect ofifferent CO2 concentrations on human body.

Air quality is prevailingly determined by people’s sensations toifferent odorants.

Odorant perception depends, on one side, on objective factors:oncentration and toxicity of air pollutants (bio-effluents), activityevel, outside airflow rate, and on the other hand, on psychologicalactors with subjective character.

The relation between perceived odorant intensity and its con-entration conforms to a power function [19]:

= kCˇ (22)

here S is odorant intensity (magnitude); C is the odorant con-

entration, in ppm; is the exponent (0.2–0.7) of psychophysicalunction; k is the constant characteristic of material.

Fig. 5. Relationships between thermal sensation and relative performance.

3 Physical easy 404 Physical hard 50

The percentage of persons dissatisfied PPD with air polluted byhuman bio-effluent (1 olf) can be calculated from the equations[20]:

PPD = 395 exp (−3.66L0.36p ) for Lp ≥ 0.332 l/s (23)

PPD = 100 for Lp < 0.332 l/s (24)

where Lp is the outside airflow rate, in l/s.The curve (Fig. 6) generated by Eqs. (23) and (24) is based on

experiments involving more than 1000 European subjects [21].Experiments with American [22] and Japanese [23] subjects showvery similar results.

Outdoor air requirement for acceptable indoor air quality haslong been debated. Historically, the major considerations haveincluded the amount of outdoor air required to control moisture,carbon dioxide and tobacco smoke generated by occupants. Theseconsiderations have led to prescriptions of a minimum rate of out-door air supply per occupant.

Tables 5 and 6 present the minimum rate of outdoor airflow peroccupant for different activities, according to European StandardCEN 1752, that also takes into consideration the smokers in venti-lated rooms.

The perceived olfactory sensation depends not only on the pol-lutant source but also to a great extent, on the dilution degree withoutside air.

The olfactory pollution degree of a room is given by:

Ci = Cp + 10G

Lp(25)

Fig. 6. PPD as a function of ventilation rate per standard person (i.e., per olf).

416 I. Sarbu, C. Sebarchievici / Energy and Buildings 60 (2013) 410–419

Table 6Minimum outdoor airflow rate for rooms with smokers.

Roomcategory

Outdoor airflow rate [m3/(h pers)]

Withoutsmokers

20%smokers

40%smokers

100%smokers

0 1 2 3 4

A 36.0 72.0 108.0 108.0

wi

6

6c

paatf

cceraSa

tfiioi

cc

c

i

6

oog

c

t

c

Table 7Typical emission from a smoked cigarette.

Type Pollutant Unit [mg]

Particle Particles suspended in air 18

Chemical Carbon dioxide (CO2) 160–550Carbon monoxide (CO) 60

B 25.2 50.4 75.6 75.6C 14.4 28.8 43.2 43.2

here Ci is the indoor air quality, in dp; Cp is the outdoor air quality,n dp; G is the contaminant concentration of the room air.

. Indoor air quality simulation model

.1. General equation for the time evolution of a contaminantoncentration

Consider a single zone compartment, where there is a source ofollution that has gas exchanges with the outside air, and wheren air purifier may be used. Admitting the possibility of depositionnd absorption of the pollutant on the walls and other surfaces, theemporal evolution of a pollutant concentration is modelled by theollowing differential equation [15]:

dc

d�= P

V+ ncp − nc − �d

S

c− Lp

Vcεp (26)

in which c is the instantaneous average contaminant con-entration, in mg/m3; P is the pollutant generation inside theompartment, in mg/h; V is the room volume, in m3; n is the airxchange rate, in h−1, that is, the fresh airflow rate divided by theoom volume; cp is the concentration of the contaminant in outsideir, in mg/m3; �d is the deposition rate of pollutant, in mg/(h m2);

is the surface of deposition, in m2; Lp is the flow rate through their purifier, in m3/h; εp is the efficiency of the air purifier.

The effects of absorption or deposition of the pollutant insidehe compartment and the removal of filtering through the air puri-er system may be considered in a simplified form, reducing the

ntensity of the sources of their value to them. Thus, for purposesr simplification, their terms in the equation may be despised, com-ng:

dc

d�= P

V+ ncp − nc(�) (27)

That integrated for a situation where V, P, cp, and Lp remainonstant, since an initial time instant � = 0, where the initial con-entration c0 = cp, till a generic time instant �, will come:

(�) = ceq + (c0 − ceq) · exp(−n) (28)

n which ceq is the equilibrium concentration.

.2. Equilibrium concentration

The equilibrium concentration ceq, in Eq. (28), is the value thatccurs when it ceases the variation in concentration. Thus, it isbtained equalizing the first member of Eq. (27) to zero, whichives:

eq = cp + P

Vn(29)

hat as n = Lp/V, comes:

eq = cp + P

Lp(30)

Formaldehyde (HCHO) 0.4Total volatile organic compounds (VOC) 3.6

The equations are solved numerically. The outputs of the sim-ulation are instantaneous concentration of the pollutant and thegraphical results of the pollutant concentration time–evolution.

6.3. Metabolic CO2 computation

In recent study [24], the expressions to calculate the volumesof oxygen (O2) and carbon dioxide (CO2) in the human respirationprocess are given, as a function of the metabolic rate and the cor-pulence of the studied person. The volume of consumed O2 is givenby:

VO2 = 0.00276ADM

0.23r + 0.771S

(31)

in which AD is the nude body surface area given by (5), in m2; Mis the metabolic rate, in met (1 met = 58.15 W/m2); r is the ratiobetween the volume of released CO2 and the consumed volume ofO2.; m is the mass of human body, in kg; h is the height of humanbody, in m.

The ratio r usually takes the value of 0.83, but that may vary till1, for a person with a very high metabolic rate (more than 5 met).

Once the volume of O2 has been calculated, the volume ofreleased CO2, for normal metabolic rate cases is computed from:

VCO2 = 0.83 × VO2 (32)

In [25] is presented a software tool for indoor air quality simu-lation.

Typical values of pollutants usually checked in IAQ audits andreleased by one cigarette burning are given in Table 7, which sum-marizes information collected in [26].

7. Computation of outside airflow rate and indoor airquality control

7.1. Mathematical model

Computation of outside airflow rate in a room can be performedfunction of:

– number of occupants, keeping CO2 concentration under the max-imum admitted level, according to Romanian Norms [27];

– number of occupants and room surface, according to GermanNorms [28];

– indoor air quality, according to European Standard CEN 1752,described below.

Ventilation efficiency εv is a criterion for energy and fan per-formances. This is used to evaluate a ventilation system and isdefined by following expression:

εv = ci − cp

czl − cp(33)

where ci is the contaminants concentration in exhausted air; cp

is the contaminants concentration in supply outside air; czl is thecontaminant concentration at breathing level.

I. Sarbu, C. Sebarchievici / Energy and Buildings 60 (2013) 410–419 417

Table 8Indoor air quality, Ci .

Room category Ci [dp] Percentdissatisfied [%]

0 1 2

A 1.0 15B 1.4 20C 2.5 30

Table 9Outside air quality, Cp .

No. Air source C [dp]0 1 2

1 Mountain, sea 0.052 Locality, fresh air 0.13 Locality, mean air 0.24 Locality, polluted air 0.5

Table 10Contaminants quantity from the occupants, Goc .

No. Contaminants source Goc [olf/pers]0 1 2

1 Adults resting, if the percentage of smokers is:0% 120% 240% 3100% 6

2 Adults, if metabolic rate is:Reduced (3 met) 4Medium (6 met) 10High (10 met) 20

I

L

w

G

iii((T

t

L

wi

TC

Table 12Outside airflow rate Lp and air exchange rate, n.

Computation norm Method Lp [m3/h] n [h−1]0 1 2 3

CEN 1752Air quality – parquet floor 2306 8.54Air quality – PVC floor 8494 31.46

I5 Number of occupants 330 1.22

3 Children:Children under school age (2.7 met) 1.2Pupils (1–1.2 met) 1.3

The outside airflow rate Lp, in l/s, can be computed function ofAQ from equation:

p = 10G

(Ci − Cp)εv(34)

here

= Goc + Gob (35)

n which G is the contaminants concentration of room air, in olf; Cis the indoor air quality, in dp (Table 8); Cp is the outside air quality,n dp (Table 9); Goc is the contaminant quantity from the occupantsTable 10); Gob is the contaminants quantity from room objectsbuilding elements, furniture, carpets, etc.) having the values inable 11.

The outside airflow rate Lp, in m3/h, can be computed and func-ion of hygienic sanitary conditions follows as:

P

p =

(ci max − cp max)εv(36)

here P is the power of the indoor pollutant source, in mg/h; ci maxs the maximum admitted concentration of the most critical con-

able 11ontaminants quantity from room objects, Gob .

No. Building destination Gob [olf/m2]0 1 2

1 Offices 0.02–0.952 Schools 0.12–0.543 Kindergarten 0.20–0.744 Meeting rooms 0.13–1.325 Houses 0.05–0.10

DIN 1946Surface of the room 600 2.22Number of occupants 660 2.44

taminant of room air, in mg/m3; cp max is the maximum admittedconcentration of the most critical contaminant of outside air, inmg/m3.

To determine the variation in time of the contaminants concen-tration ci in indoor air two hypotheses are assumed:

– constant pollution in time, where the balance equation within aninfinitesimal time interval d� is:

Lpcp d� + P d� − Lpci d� = V dci (37)

where V is the volume of room.Integrating Eq. (37), with the initial condition ci = cp, for � = 0, we

obtain:

ci = cp + P

Lp[1 − exp(−nx)] (38)

where n is the air exchange rate.

– instantaneous pollution at moment � = 0; consequently, the con-taminant initial concentration is given by the equation:

co = P

V(39)

The balance equation for d� infinitesimal time interval is:

Lpcpd� − Lpcid� = Vdci (40)

Integrating Eq. (40) with the initial condition ci = co, for � = 0, isobtained following expression:

ci = cp − co exp(−nx) (41)

The computer program COMFORT 2.0 [16], elaborated in FOR-TRAN programming language, allows to determine the outsideairflow rate and air exchange rate for the ventilation of a roomand the variation in time of contaminants concentration of roomair both on the basis of the mathematical model described aboveand on some national norms (I5, DIN 1946), as well as to analyzethe influence of different parameters on these characteristics.

7.2. Numerical application

It is considered that an A category room with geometricaldimensions 10 m × 10 m × 2.7 m, where there are 11 persons hav-ing an intellectual activity, and smoking is forbidden. Productionrate of CO2 for the occupants is of 15 l/(h pers) and CO2 concentra-tion in outdoor air has the value of 350 ppm. The floor finishing ismade of parquet floor or PVC.

A comparative study for computation of outside airflow rate andindoor air quality control according to the European Standard CEN1752 and national norm I5 and DIN 1946 is performed using the

computer program COMFORT 2.0.

The values obtained for the outside airflow rate and the airexchange rate are reported in Table 12. In Fig. 7 is represented thevariation of outside airflow rate function of the indoor and outdoor

418 I. Sarbu, C. Sebarchievici / Energy and Buildings 60 (2013) 410–419

F

ai

phtt

8p

rai

cftcu

ig. 7. Variation of outside airflow rate function of outdoor and indoor air quality.

ir quality. Fig. 8 shows the variation in time of CO2 concentrationn room air.

From Table 12 it is to be seen that the outside airflow rate com-uted according to norm I5 has the smallest value, leading to theighest values of CO2 concentration of room air. This CO2 concen-ration determines a state of strong tiredness and head aches forhe occupants.

. Influence of carbon dioxide on human performance androductivity

Air temperature is the commonly used indicator of thermal envi-onment and productivity. Another cause that produces discomfortssociated with indoor air temperatures beyond the comfort limits the dioxide carbon concentration [29].

It is considered that air is contaminated when the content ofarbon dioxide ranges between 0.1 and 0.15%, which correspondsor a concentration of 1000 ppm and 1500 ppm. Becomes harmful to

he body starting from a concentration of 2.5%. Normal air contentsorbon dioxide in ranges of 0.032% and 0.035%, reaching 0.04% inrban centres.

Fig. 8. Time variation of CO2 concentration.

Fig. 9. Outside airflow rate depending by admitted CO2 concentration. 1-expired air;2-underground rooms; 3-industrie maximum concentration; 4-offices maximumconcentration; 5-Pettenkofer’s number; 6-outdoor air.

Measurements of carbon dioxide concentration in a natural ven-tilated classroom through leaks had shown that in 10–15 min theconcentration reaches values over 1000 ppm, and after 45 min val-ues to 2500 ppm.

The sedentary human body approximatively releases 15 l/h ofcarbon dioxide. For not exceeding the maximum concentration itis has to be assured a fresh airflow rate Lp for each person:

Lp = Q

ci max − cp max= 15000

1500 − 400= 12. 5m3/(h × pers) (42)

in which: Q is the CO2 emission of human body, in cm3/h; ci max isthe maximum admitted CO2 concentration for indoor air, in ppm;cp max is the maximum admitted CO2 concentration for outside(fresh) air, in ppm.

In Fig. 9 is illustrated in a nomogram the outside airflow ratedepending by maximum admitted CO2 concentration.

Taking into account the overlapping of contaminant, an insani-tary environment, correlated with a high temperature reduces evenmore the human productivity. Even if only in these two aspects(temperature and CO2 concentration) the VAC specialists have theduty to convince over the need to assure these two parameters byusing air–conditioning systems.

9. Conclusions

Computer models developed offer the possibility of detailedanalyses and predictions on thermal and olfactory comfort in build-ings, being of a real use for the design and research activity and inthe environmental studies.

Results show that the microclimate in rooms influences not onlythe comfort but also the health of the occupants, and preservingthe comfort parameters at the optimal values is the mission of theengineer for designing and operating of HVAC systems.

The indoor environment is influenced by the way the equip-ments are designed, produced and operated. That is why it isnecessary to decide upon the equipments that are able to give theproper microclimate conditions, permanently observing the elim-ination of all secondary effects (professional illnesses) that havenegative influences upon human health.

In addressing the relationship between building energy effi-

ciency and IAQ, one needs to consider more than just outdoor airventilation rates as the sole link between these critical goals.

High performance buildings should provide better IAQ condi-tions than those existing in current buildings, and many strategies

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I. Sarbu, C. Sebarchievici / Ener

ill not conflict with energy efficiency. As more experience andnformation are generated, the goal of truly high performance,ustainable and healthy buildings will be more fully realized inractice.

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