Sharp JX-9400 Información técnica

5.10 Global heat recovery efficiency versus nominal heat exchangereffectiveness measured in several units 965.11 Seasonal average coefficient of performanc

indoor air quality at a lower energy cost. Once again, measurements may help incommissioning and diagnosing failures.Energy in air handling unitsEnerg

Figure 5.1, a psychrometric chart for air, shows several characteristics ofhumid air. The curves show the water content of air as a function of itstem

Figure 5.2 illustrates the paths of temperature and water content of air forheating and humidifying outdoor air in winter, at 08C and 80 per cent rela

slowly if the air is in contact with massive structures that were cooled downbefore, for example, by strong airing during the cool night.Mechanical co

.From the indoor env ironment, heat loads and solar gains. This way ,common in tropical climates, saves the investment of the heating system,and heati

To improve energy efficiency, mechanical ventilation systems are oftenequipped with heat recovery for recovering the heat contained in exhaust air.This

can be transferred from the warm side to the other. The heat recovery efficie ncyof these exchangers ranges from 60 to 80 per cent, depending on the typ

Placing both fans on the same side results in a large pressure differentialthrough the rotating heat exc hanger, thus increasing leaks. A parasiticreci

The enthalpy flow, H, is the product of mass airflow rate and specificenthalpy, h:H ¼ Qh ð5:5Þwhere  is the density of air.At ambient temperature, a nu

Leakage through heat exchangersSome heat exchangers let some air leak between both air channels. This is inmost cases not expected, since there are ve

7.4 Student distribution for 1, 2 and 5 degrees of freedom comparedto the normal distribution 1587.5 Confidence limit divided by standard deviation ver

rates. If these pressure differentials are significantly larger than the nominalvalues, the wheel should be cleaned.Indication on how to measure pressur

In simplified methods to calculate heating (or cooling) demand of buildings,ventilation heat loss, V, is often calculated by (CEN, 1999, 2007):V¼_mmð

We have mentioned abo ve the following recirculation rates:External Re¼_mmi_mmo_mme¼_mme_mma_mmeð5:20ÞInlet to exhaust Rie¼_mmi_mmrs_mmi¼_mme_mmre

where:x¼_mmx_mmxþ_mmexfð5:32Þis the extraction efficiency, i.e. that part of the air leaving the ventilated volume,which is extr acted through the air

which depend s on all parasitic airflow rates. When there is no external recircu-lation (Re¼ 0), Equation 5.37 simplifies to:G¼ð1  exfÞð1  RxsÞ1  R

Net energy saving and performance indexHeat recovery systems recover thermal energy but use electric energy for thefans. The net energy saving should

Table 5.2 Measured airflow rates with experimental uncertainty band (whenavailable), total and specific fan power in audited unitsAirflow rates (m3/h) Fa

in the three small units, and external recirculation above 20 per cent ismeasured in three large units. These leakages significantly affect heat recover

Best net ene rgy savings in large units (7 and 8 in Table 5.2) are 80,000–90,000 kWh per winter season, but unit 10 actually wastes as much energy.Sma

where: is the density of air,c is the heat capacity of air, is the temperature difference between exhaust air and supply air.The kinetic ene rgy giv

6.6 VOC transfer rate in the experiments performed in both EPFLunits (%) 1236.7 VOC transfer rate in the EMPA experiments 1236.8 General IAQ strategie

consumption of electrical energy by the fan motor, and on the other hand thekinetic energy given to the air in duct.The fan efficiency is the ratio of u

The two ports of this manometer are connected to pressure taps located onboth sides of the fan (see Figure 5.13). Care should be taken to avoid too mu

simultaneously the r.m.s. voltage, U, between phase and neutral point, ther.m.s. current, I, running into each motor coil and the phase shift, ’, betw

on which the frequency, the voltage, the current and the fan motor power canbe displayed.Examples of applicationFan efficiencies were measured on severa

indoor environment quality and health or paying attention to possible damagesto buildings. If a decrease of thermal comfort was implicitly accepted, c

Table 5.4 Uses of energy in buildings, energy saving measures and their effects onindoor environment qualityEnergy use Energy saving measures Impact on

For each variant, the effect of the following changes in design and operation wassimulated:.with 50 per cent recirculation instead of no recirculation;

per day), ventilation strategies have a minor influence on heating energy demand.The air may be either heated by coils in the supply air or by radiator

a rotating heat exchanger (see Chapter 6, ‘Rotating heat exchangers’), has anegligible effect on energy demand.Infiltration or exfiltration through a lea

6Contaminants inAir Handling UnitsThe purpose of mechanic al ventilation systems is to supply appropriateamounts of clean air and to evacuate vitiated

PreambleThis book includes information already published by the author in scientificjournals and in an Air Infiltration and Ventilation Centre (AIVC) te

DuctsThe duct material and the manufacturing process has the biggest effect on theperceived air quality (Bjo¨rkroth et al., 2000). Depending on the mac

The effect of airflow on the perceived air quality from ducts was relativelysmall and is probably insignificant in normal applications. Increasing theair

Rotating heat exchangersRotating heat exchangers are not themselves sources of contaminants, but theymay transfer contaminants from exhaust to supply

such that a sector of it that contains exhaust air passes first through the purgingchamber. The author has seen wheels turning the wrong way!In additio

Figure 6.7 shows that certain categories of volatile organic compounds(VOCs) are easily transferred by a sorption transfer mech anism. Among thetested

Selecting the panelThe subjects are selected from a group of at least 50 applicants of ages rangingfrom 18 to approximately 35 years old. There is no

The 2-propanone gas is evaporated in the PAP by placing one or more 30 mlglass bottles filled with 10 ml of 2-pr opanone and making different holes in t

.mechanical air supply with filtered air;.mixing ventilation with a certai n minimum ventilation rate.During the tests, the background level of 2-propa

pollution of concentrations of 2-propanone unknown to them by makingcomparison with the milestones. On the third, fourth and fifth days, traininginclud

of Figure 6.10. The concentration of these VOCs in the air is analysed at thefour locations shown in Figure 6.10. Locations C6and C3should be farenoug

IntroductionWhy ventilate?Without ventilation, a building’s occupants will initially be troubled by odoursand other possible contaminants and heat. Hu

Air sampling and analysisAir at the four locations is sampled with a pump through small tubes filled withan adsorbing medium (for example, activated ch

Wal et al., 1998). These lists can inspire a selection of compounds to include inthe mix. However, the total number of compounds should not be too lar

unit, however, was found with the wheel turning in the wrong way, making thepurging sector inactive.The measured ventilation efficiency in the EMPA acad

and rotates at 5 rpm. The diameter of one honeycomb cell is 1.5 mm. The wheelhas no purging sector and the fans are not in their ideal positions. This

Results of all experiments are shown in Tables 6.6 and 6.7.Evidence for adsorptionLeakage and entrained air would result in the same recirculation rat

experiments, the smallest recirculation rates are for limonene. They are close tothe rates that could be expected from leakage or entrained air.At the

unity. The average difference between recirculation rates is 22 per cent, close tothe recirculation rate resulting from internal leakage in the EMPA un

.Strategies that affect the design of the HVA C system – design principles andinnovative design strategies.For both of these categories, IAQ strategies

Table 6.9 Checkpoints in HVAC units in visual inspectionComponent passed failOutdoor chamberAccess door: exists but closed hhChamber is clean (no dirt

Table 6.10 IAQ strategies for filtersDesign OperationPrevent filters from becoming a source of pollutionSelect a low-polluting new filterCondition (bake)

However, when the outdoor temperature excee ds indoor temperatures, it maybe wise to reduce the ventilation rate, only allowing high levels of ventila

Table 6.11 IAQ strategies for ductsDesign OperationPrevent ducts from becoming a source of pollutionUse duct processed withou t oil, and whichdoes not

Table 6.12 IAQ strategies for rotating heat exchangersDesign OperationSelect a wheel equipped with purgingsector and install it with the purgingsector

Notes1E´cole Polytechnique Fe´de´rale de Lausanne (Swiss Federal Institue of Technology ofLausanne).2 Swiss Federal Research Institute for Materials.T

7Common Methodsand TechniquesExpressing concentrations and flow ratesCoherent unitsWhen using equations, such as Equation 2.7, to model ventilation sys

withMM ¼PiMiniPinið7:3Þbeing the average molar mass of the mixture. For dry air,MM ¼ 28:96 g/mole.The relative change in density is then:¼MMMM

In a mixture, every gas, x, occupies the whole volume, V:V ¼nxRTpxð7:8ÞThe relations between mass concentration, Cm, molar concentration, CM, andvolum

Item 5 is important mainly if the concentration is relatively high (for example,0.1 per cent or higher). For this reason and to achieve also items 3,

potentially analyse any tracer. Table 7.3 shows their background concentra-tions in outdoor air.It can be seen in Tables 7.2 and 7.4 that no tracer co

Mixing tracer gasesPerfect mixing of tracer gas in the air of the measur ed zone or in the measuredduct is essential when determi ning the airflow rate

maintained under pressure. It is noted, however, that these two conditionscomplicate the experimental arrangement since control leads must extend toth

Measured airflow rates differ from the design values in many ventilationsystems. Figure 0.2 shows the relative differences between measured anddesign out

Sampling methodsSamples of air containing tracer gases need to be taken for analysis. There areseveral sampling methods, each one being adapted to a p

tight caps. Properly used passive samplers adsorb all the tracers that are in theair enter ing the sampler. They are used to obtain a quantity of trac

As an example, for an airflow rate of 100 l/h, that is 28  106m3/s, theminimum pipe inner diameter will be 2.6 mm to have an air speed of 5 m/s.In th

Remember, however, that, in order to achieve good mixing, it is advanta-geous to inject the tracer continuously whenever possible. A series of shortpu

up to several minutes for gas chromatographs or multi-tracer infraredanalysers. Faster analysis will enable more frequent sampling of each zoneand hen

vapour and CO2present at high concentrations in the air. Filters are used tominimize the effect but humidity should be measured simultaneously tosome t

this field. Only ions having a charge-to-mass ratio that corresponds to a givenradio frequency reach an orifice at the end of that path and pass into an

Gas chromatographyA puff of the sampled air is injected into a separating (chromatographic)column, a tube in which adsorbent material is packed. This c

By making the prescr ibed number of strokes of the hand-held bellows, thecorrect amount of air is drawn through the tube. This enables the tracer gase

Linear least square fit of the first kindSuch methods are used to find the coefficients of leakage models of Equations4.1 or 4.2 in fa n pressurization (se

measured recirc ulation rates are compared in Figure 0.3. These are seldom thesame. Even worse: as shown in Figure 0.4, out of 27 units planned withou

Confidence in the coefficientsThe variances on the linear coefficients of the regression of the first kind areusually estimated using the following relation

Regression of the second kindWhen there are uncer tainties in both axes, there is no reason to emphasize the xaxis, and the same procedure can be foll

where "yand "xare the experimental errors on y and x respectively anddeduce a corr esponding value of a using Equation 7.16. This recipe doe

will be obtained, and a correlation between C and n will be found: the larger Cvalues correspond to the smaller n and vice versa. A good identification

the a posteriori information. T his new distributio n:ðzÞ¼C exp 12fðzÞTC1TðzÞþðz  zpÞTC1zðz  zpÞghið7:41ÞFrom this distribution, the z vector

Generally, an instrument does not directly give the required information. Inmost cases, several measurements are combined to obtain the needed value.

domain. The statistical method allows one to obtain more information on thereliability of the results.Because of rando m reading errors and uncontroll

Variance and standard deviationA figure representing the importance of the scattering around the average valueis the mean square deviation or variance:

The confidence interval [c; c] of the normal distribution is obtained bysolving the equation:P ¼ erfðc=ffiffiffi2pÞð7:57Þfor a given value of P.If the norma

more detail in statistical tables such as Zwillinger (2003)) and in mostmathematical software packages.Confidence interval of the Gaussian distribution

the design and measured exfiltration ratios, i.e. parts of the supply air leakingthrough the building envelope in 30 units.Ventilation efficiencyAn efficie

Hence, we can state: ¼hxiIcð7:65ÞP is the probability that the confidence interval contains the ‘true’ value. P ischosen a priori, in practice betwee

the infinitely small increments dxiby the absolute error xiand by summing theabsolute values:yj¼Xi@fj@xixið7:67ÞIf only arithmetical operati

represented by a vector x and a matrix A. The question is: which is theresulting error y on the vector y, which is the vector containing the final r

the partial derivatives are computed as above and we get finally:s2yi; yj¼Xklmnikyljmyns2aklamnþXklikjls2xkxlþXklmnðikyljm jkylimÞs2aklxmð7:7

and the matrix norm is subordinated to the vectorial norm jxj if:jAj¼maxjAxjjxjfor any x 6¼ 0 ð7:85ÞThe subordinated norm is the smallest matrix nor

where 1and nare respectively the largest and the smallest eigenvalues ofAHA. This number is the spectral condition number.Constant absolute errorIf

From which, using the method described in Chapter 1, ‘Zone by zonesystems of equations’, we get the airflow rates to and from each zone [m3/h]shown in

ReferencesAeschlimann, J.-M., C. Bonjour and E. Stocker, eds, 1986, Me´thodologie et Techniquesde Plans d’Expe´riences: Cours de Perfectionnement de l

Brown, S. K., M. R. Sim, M. J. Abramson and C. N. Gray, 1994, Concentrationsof volatile organic compounds in indoor air: A review, Indoor Air, vol. 4,

Hakajiwa, S. and S. Togari, 1990, Simple test method of evaluating exterior tightnessof tall office buildings, in E. M. H. Sherman, ed., ASTM STP 1067,

When assess airflows in buildings?Ventilation performance should be checked early to detect potential problemsand to optimize the overall performance o

Presser, K. H. and R. Becker, 1988, Mit Lachgas dem Luftstrom auf der SpurLuftstrommessung in Raumlufttechnischen Anlagen mit Hilfe der Spurgasmethode

Sandberg, M. and C. Blomqvist, 1985, A quantitative estimate of the accuracy of tracergas methods for the determination of the ventilation flow rate in

Annex AUnit Conversion TablesIntroductionSI units are used throughout this book. Non-SI units are, however, of generaluse in air infiltration and venti

AreaName Symbol m2cm2sq in sq ft sq yd1 square metre m21 104 1550 10.7639 1.195991 square centimetre cm21041 0.3937008 0.0328084 0.010936131 square i

PressureName Symbol Pa mbar mm H2OinH2O psi1 Pascal Pa 1 0.01 0.102 0.004 145.037  1061 millibar mbar 100 1 10.2 0.422 14.5037  1031 mm water colu

Annex BGlossaryItems in italics are additional entries in the glossary.Age of the air (or age of a contaminant)Average time period since the fresh air

adventitious openings), caused by pressure effects of the wind and/or theeffect of differences in the indoor and outdoor air density.Air infiltration char

Building componentGeneral term for any individual part of the building envelope. Usually appliedto doors, windows and walls.Building envelopeThe total

Constant concentration techniqueA method of measuring ventilation rate whereby an automated sy stem injectstracer gas at the rate required to maintain

Distribution effectivenessRatio of the average tracer gas or contaminant concentration to the concentrationthat could be reached, at equilibrium, in th

Ventilation and Airflow in Buildings

effectiveness of the ventilation in appropriately distributing the air in the venti-lated space or in evacuating contaminants emitted at a given locati

Fan pressurizationGeneral term applied to any technique involving the production of a steadystatic pressure differential across a building envelope or

Indoor air pollutionPollution occurring indoors from any source, i.e., from outside as well as insidethe building.Infrared gas analyserInstrument used

MixingThe degree of uniformity of distribution of outdoor air or foreign material in abuilding.Mixing fanSmall electric fan used to aid the mixing of

Piston-type ventilationSee displacement flow.Pitot tubeAnemometer measuring the difference between the pressure in a tube facingthe flow, in which the flo

Reductive sealing methodA method of determining the leakage of specific building comp onents bypressurizing the building and recording the leakage chan

Site analysisApplied to any tracer gas measurement technique where tracer gas concentrationsand air exchange rates are determined directly at the meas

Turnover time of a contaminantRatio of the mass of contaminant con tained in an enclosure to the mass flow rateof the contaminant source in this enclos

Indexabsolute error, 154active ways, 78adsorption, 123age matrix, 10age of the air, 39, 42, 174airage of, 39, 42, 174changeefficiency, 40leakage rate, 6

conductance, 176confidence interval, 28, 149, 154,155conservation equation, 1, 7, 177constant concentration, 3, 12, 176constant injection rate, 3, 12,

1995, 2003). This can, however, be avo ided by appropriate design and main-tenance. Chapter 5, ‘Energy effect of IAQ measures’, lists the sources andca

air change rate, 67and heat recovery, 89area, 67, 178characteristics, 180coefficients, 60, 64heat exchangers, 88visualization, 69least square fit, 27, 14

tracer gas (Continued)injection, 21mixing of, 137pulse injection, 4, 12, 182sampling, 22techniques, 12trained panel, 113transfer of contaminants, 10un

1Airflow Rates in BuildingsThis chapter intends to help the reade r to measure airflow rates and air changerates in buildings and room s, independently

outdoor environment is then:dmdt¼ I þ CoQoi CiQioð1:1Þwhere:m is the mass of tracer gas in the zone (kg);I is the injection rate of the tracer gas (k

This solution can be simplified, depending on the way the tracer isinjected.Tracer decay, no injectionA suitable quant ity of tracer gas is injected to

Constant concentrationUsing an electronic mass flow controller monitored by the tracer gas analyser,the concentration of tracer gas can be maintained c

Applying again the integral mean value theorem, we get:m ¼ Qs;ið0Þðtf0CðtÞdt with 0 <0< tfð1:20ÞCombining Equations 1.18 and 1.20, we get:Qið

concentration C (Ciindoors and Cooutdoors) by:Qe¼SCi Coð1:22Þwhere S is the CO2source strength, i.e. about 20 l/h. The equivalent outdoorairflow rate

do not change during the measurement campaign. This section describes waysof interpreting the records of tracer gas injection rates and concentration

where:mikis the mass of tracer gas k in zone i;Iikis the injection rate of tracer gas k in (or just upwind of ) zone i;Cjkis the concentration of trac

C contains the differences in mass concentrations Cik C0kof gas k in zone i.I is the matrix containing the mass flow rates Iikof the tracer, k , in zon

Properties of the flow matrixThe total outdoor airflow rate to each zone, i, is easily obtained by summing thecolumns of the flow matrix:Qi0¼XNj ¼1Qijð1:

sums of the  matrix are the mean age of air in the corresponding rooms:hii¼XNj ¼1ijð1:38ÞThis relation enables the measurement of the room mean ag

The air mass conservation (Equat ion 1.23) is rewritten as:q0i¼ TiXNj ¼0qijð1  ijÞTjXNj ¼1qjið1  ijÞþViTidTidtð1:43ÞThese last two systems includ

.The long-term integral method, generally used with passive sources andsamplers, also gives a biased estimate of the average airflow rate. Since themea

.Constant injection used with long-term direct solution is simpler to use andmay give, under certain conditions, unbiased estimates of an average airfl

2Airflow Ratesin Air Handling UnitsAir handling units are designed to supply new air to the ventilated zone and toextract vitiated air from this zone.

placed in the flow, for example a nozzle, Venturi or sharp-edged orifice (ISO,2003). Alternatively, the air speed can be measured directly at a number o

 is the reduction ratio, which is the ratio of the smallest diameter to thediameter of the pipe.The flow may be restricted with an orifice plate, a noz

from 0.05 to 5 m/s, and are well suited for speeds of 1–5 m/s, which are typical inventilation ducts.Helix anemometers measure the rotation speed of a

BUILDINGS|ENERGY|SOLAR TECHNOLOGYVentilation and Airflow in BuildingsMethods for Diagnosis and EvaluationClaude-Alain RouletLondon.Sterling, VA

Assuming that no trac er is lost in between, the mass balance of the tracer gasis, at steady state:I ¼ðC  C0ÞQ ð2:3Þwhere:C is the tracer concentrati

The methods described in the section on ‘Measurement of airflow rate in aduct’ (above) may of course be used to measure the ai rflow rates through grill

In principle, the method described above in ‘Tracer gas dilution’ can beapplied to each branch of a duct network. However, this requires as manytracer

expected tracer gas concentration of tracer k:Ik¼ CkQ01ð2:5ÞSampling points for concentration measurementsTracer gas concentrations are measured at se

bringing additional tracer into the analyser, thus biasing the concentrationmeasurement. To avoid this, use different colours for injection and samplin

gas conservation equations can be rearranged so as to obtain one system ofequations per node, giving all airflow rates entering in this node. At steady

recirculated air passes through a leak between extract and supply parts of theair handling unit or through a purpose-installed duct. Alternatively, ve

Node 2, return I11¼ðC11 C31ÞQ12þðC61 C31ÞQ62þðC71 C31ÞQ72ð2:10Þ0 ¼ðC12 C32ÞQ12þðC62 C32ÞQ62þðC72 C32ÞQ720 ¼ðC13 C33ÞQ12þðC63 C33ÞQ62þðC73 C3

This system of 27 equations when combined with the system of Equation 2.9can be solved in various ways to provide the six main airflow rates andpotenti

Simplest wayA method providing all airflow rates with the simplest solutions – henceprobably the least sensitive to measurement errors – is given below

First published by Earthscan in the UK and USA in 2008Copyright # Claude-Alain Roulet, 2008All rights reservedISBN-13: 978-1-84407-451-8Typesetting by

withQ46¼ TðP; 1ÞffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðC402 C42Þ2I252þ I252ðC2402þ C242ÞðC402 C42Þ4sð2:28

The bias resulting from the alias with Q72is not taken into account in theconfidence interval. If tracer 4 is used, we get:Leakage to node 2Q72¼ðC32 C

orQ04ffi Q24ðC3k C4kÞðC4k C0kÞ¼ Q12ðC6k C1kÞðC6k C3kÞðC3k C4kÞðC4k C0kÞð2:41ÞQ04¼TðP; 1ÞðC4k C0kÞ2ffiffiffiffiffiffif04pð2:42Þwheref04¼ðC6k C3kÞ2ðC3k C1kÞ

with k 6¼ 2(k ¼ 4 is not recommended here).Q76¼TðP; 1ÞC7k C6kffiffiffiffiffiffif76pð2:52Þwheref76¼ Q226C23kþ Q246C24kþðQ26þ Q46 Q76Þ2C26kþðC3k C6kÞ2Q226þð

Planning toolThere are many types of air handling units, and, from our experience, each newmeasurement poses new problems. It is hence impossible to p

Leaks in the heat exchanger, as well as in the return air channel, weredetected with this measurement. Measurement in three other identical unitsin th

concentrations are in volumetric ratios. It is not possible with only one tracerinjected into the ventilated space to differentiate between outdoor air

with ¼nð1  RÞ1  R þ ið2:63ÞThe theoretical exponential can be fitted to the experimental points, as shownin Figure 2.11 depicting an actual experi

The recirculation airflow rate can then be calculated using:Q62¼ Q24 Q12ð2:66ÞwithQ62¼ TðP; 1ÞffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiQ224þ Q212qffi TðP ; 1Þffiffiffiffiffiffi

withR ¼QQffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffið1 þ RÞpð2:73ÞOr method CR ¼ 1 Q12Q24withR ¼ffiffiffi2pQQð1  RÞð2:74Þassuming that the relative error Q=Q is the same for bo

ContentsList of Figures and Tables viiPreamble xiiIntroduction xiii1 Airflow Rates in Buildings 1Single-zone measurements 1Application to buildings, mu

3Age of Air andVentilation EfficiencyThe airflow patterns should, in principle, be organized in order that new airis brought to the head of the occupants

However, the more time a small volume of air spends in a room, the more itwill be contaminated by pollutants.Since there is a large number of air part

constant. In rooms with complete mixing, the room mean age of air equalsthe nominal time constant, and the air exchange efficiency is 50 per cent.Short-

corresponding to the nominal time constant. The air exchange efficiency inthis very theoretical case is 100 per cent. At 99 per cent air exchange effi-cie

assumes that the tracer gas behaves the same as the air: no adsorption andsame buoyancy, which is the case if the tracer concentration is small. It ca

To interpret the recorded tracer gas concentrations and obtain the age ofair, the background (or supply) concentration should first be subtracted froma

The local mean age of air at any location is the integral (or zero moment)of the probability distribution:r¼ 0¼ð10FrðtÞdt ð3:8ÞThe first moment of th

where:Fjis the probability distribution at time t ¼ j t,Step-up case Fj¼ 1 Cð t0þ jtÞCð1ÞDecay case Fj¼Cðt0þ j tÞCð t0Þð3:16ÞN is the last measure

withFj¼ TðP; 1ÞffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiCeðjt þ t0ÞCeðjt þ t0Þ2þCeðjt þ

a displacement ventilation system, as shown in Figure 3.6. The conferenceroom is 8 m by 10 m wide and 3 m high. It is completely embedded in an old,ma

Measurement methods 59Determining the leakage coefficients 63Corrections for standard conditions 65Ways of expressing the airtightness 66Airtightness of

efficiency was doubled, and the mean age of air was maintained despite areduction of the ventilation rate – and of energy use – by a factor two.Mapping

straightforward, takes time and has its cost, the theory of experimentaldesign (Box et al., 1978) may help in providing a maximum of informationthroug

for which seven coefficients must be determined. Table 3.2 summarizes theminimum number of measurements needed.Location of the measurement pointsAn impo

The criteria described below are used to establish the most efficientdesign.Criteria for location of the measurement pointsThe model matrix MFirst, let

If 2is the experimental variance of the measured variable v, the variance2(ve) of the estimated variable is:2ðveÞ¼rTðMTMÞ1r2ð3:36ÞA variance func

As mentioned above, the experimental domain is about 20 per centsmaller than the measured space, samples of air being taken at least 0.1 timesthe char

can be added to obtain a minimum design for a quadratic model, which has acondition number of 6.3 (see Figure 3.9).The 2-D full factorial design with

the points 8, 5 and 2 can be deleted (in that order) giving finally a designhaving 12 points and a condition number of 4.8. Finally, deleting two morep

Example of applicationThe age of air was mapped in the conference room after the improvement,first in the empty room, and then with ten occupants sitti

4AirtightnessWhy check airtightness?Controlled airflows, having adequate flow rate and passing at the appropriatelocations are essential for good indoor

List of Figures and TablesFigures0.1 Design and measured outdoor airflow rate per person in12 buildings xv0.2 Relative difference between measured and d

ventilation rate. Maintaining air quality requires an increase in supply air,leading to energy wastage.Checking the airtightness of a building envelop

column) and the airflow rate through the fan is measur ed using any of thefollowing methods:.The airflow rate through a fan depends on the pressure diffe

Inverting this relationship gives the airflow rate resulting from a pressuredifferential:q ¼b þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffib2 4app2að4:3ÞBy fitting one of t

flow rates at each pressure using the method described in section ‘Determiningthe leakage coefficients’, below.Components that can usually be sealed incl

experiments is performed, enough equations can be written to compute theairflows through the various measured parts for each pressure step.For that pur

its absolute temperature, and as long as the pressure differential remains smallwith respect to the atmospheric pressure:q ¼ qmTTmð4:5Þwhere T and Tmar

intervals. If the coefficients a and b are known, the airflow coefficient C and theexponent n are calculated using:C ¼ expðaÞ and n ¼ b ð4:11ÞThe Etheridge

Using the subscript o for these standard conditions and no subscript for themeasurement conditions, then:Co¼ Coð2n 1Þoð1 nÞð4:15Þwhere  is

Virtual air change rateBy dividing the airflow rate at conventional pressure by the internal volume ofthe tested enclosure gives a virtual leakage air

in order to create a pressure difference large enough to minimize influencesfrom wind and temperature differences on the results. This pressure differen-t

3.1 Ventilation modes with typical airflow patterns and airchange efficiencies 413.2 Typical probability density curves for the age of the air 413.3 Typi

The overall airtightness of the structure and the size of the available fangovern the maximum volume of enclosure that may be pressurized. Even iflarg

case, the airtightne ss is not good enough and cold air enters the inhabited spacethrough cracks between wooden panels.The stack effect methodThis simp

there is a priori only one neutral plane at the height z0. The neutral plane is thegenerally horizontal plane in the building or part of it where the

measuring the air speed at several locations and integrating over the wholeopening or using a tracer gas.gQgþ tCtpðztÞnþðznzrbdðrCrpðzrÞnÞ¼0 ð4:2

top of the opening to observe the flow direction. The neutral level is locatedbetween the ingo ing and outgoing flow directions. Sensitivity can be incr

that Ti> To, by:Q ¼ QAToTi1=21 znH3=2znH3=2ffi QAð1  aÞ3=2 a3=2ð4:29Þwith a ¼znHwhere znis the height of the neutral level.The opening area

example, using plastic sheeting and adhesive tape. Inflated balloons are alsowell suited to seal circular ducts.Tracer gas injection and air sampling t

upstream end of the duct and its concentration is measured at both ends to givethe flow rate at each.The leakage of the whole supply or exhaust network

5Measurements and MeasuresRelated to Energy Efficiencyin VentilationEnergy in buildingsEnergy uses and indoor environment qualityEnergy is used in build

Passive and active ways to get high quality buildings.Passive ways are architectural and constructive measures that naturally providea better indoor e