evaluat<strong>in</strong>g <strong>the</strong> air exchange rate with<strong>in</strong> <strong>the</strong> build<strong>in</strong>gs. The methods used to measure <strong>the</strong>ventilation per<strong>for</strong>mance <strong>of</strong> <strong>the</strong> build<strong>in</strong>g are described <strong>in</strong> this section.Build<strong>in</strong>g location and sit<strong>in</strong>g can <strong>in</strong>fluence <strong>the</strong> ventilation <strong>for</strong> a naturally ventilated build<strong>in</strong>g, but<strong>the</strong> focus <strong>of</strong> <strong>the</strong> assessment was on <strong>the</strong> build<strong>in</strong>g itself and <strong>the</strong> <strong>in</strong>ternal conditions. The w<strong>in</strong>dowgeometry proved to be a challenge. The effect <strong>of</strong> w<strong>in</strong>dow geometry has been studied to a limitedextent (Heiselberg 1999, 2001) but not specifically <strong>for</strong> <strong>the</strong> top hung awn<strong>in</strong>g-type w<strong>in</strong>dows thatare used <strong>in</strong> <strong>the</strong> prototype build<strong>in</strong>g. The awn<strong>in</strong>g-type w<strong>in</strong>dows are h<strong>in</strong>ged at <strong>the</strong> top, and are keptopen by friction at <strong>the</strong> h<strong>in</strong>ge. These w<strong>in</strong>dow types are used both <strong>for</strong> <strong>the</strong> smaller, upper w<strong>in</strong>dowsas well as <strong>for</strong> <strong>the</strong> lower, large occupant controlled w<strong>in</strong>dows. A method <strong>for</strong> determ<strong>in</strong><strong>in</strong>g <strong>the</strong>airflow rate <strong>of</strong> <strong>in</strong>com<strong>in</strong>g air and exhaust air had to be developed because natural ventilation <strong>in</strong>build<strong>in</strong>gs relies on external conditions to provide fresh air and remove <strong>in</strong>ternal heat ga<strong>in</strong>s, andw<strong>in</strong>d speed and direction can change quickly. This characteristic <strong>in</strong>creases <strong>the</strong> complexity <strong>of</strong>evaluat<strong>in</strong>g ventilation effectiveness. Part <strong>of</strong> <strong>the</strong> complexity lies <strong>in</strong> <strong>the</strong> effective open<strong>in</strong>g area <strong>of</strong><strong>the</strong> w<strong>in</strong>dow; it has both a horizontal area, as well as two vertical pieces, that can all affect <strong>the</strong>total airflow rate. Initially velocity measurements were taken <strong>in</strong> <strong>the</strong> horizontal plane us<strong>in</strong>g handheldhot-wire anemometers, as that dimension was determ<strong>in</strong>ed to be <strong>the</strong> largest contributor to<strong>in</strong>com<strong>in</strong>g and outgo<strong>in</strong>g airflow <strong>for</strong> <strong>the</strong> w<strong>in</strong>dow.The stack vents were a key design characteristic that had to be considered when evaluat<strong>in</strong>gventilation per<strong>for</strong>mance. The fans <strong>in</strong>tegrated <strong>in</strong> <strong>the</strong> stack vents were <strong>in</strong>cluded <strong>in</strong> <strong>the</strong> assessment.Hot-wire anemometers were used to measure <strong>the</strong> air velocity just outside <strong>the</strong> louvers from <strong>the</strong>exterior and just below <strong>the</strong> fan <strong>in</strong> <strong>the</strong> <strong>in</strong>terior. Measurements were taken under two conditions;with <strong>the</strong> fans on and <strong>of</strong>f. In addition, smoke pencils were used when tak<strong>in</strong>g measurements at <strong>the</strong>exterior to determ<strong>in</strong>e <strong>the</strong> direction <strong>of</strong> <strong>the</strong> airflow.Ano<strong>the</strong>r method employed to determ<strong>in</strong>e <strong>the</strong> ventilation rate <strong>of</strong> <strong>the</strong> prototype build<strong>in</strong>g was <strong>the</strong>monitor<strong>in</strong>g <strong>of</strong> carbon dioxide (CO 2 ) levels with<strong>in</strong> <strong>the</strong> occupied spaces us<strong>in</strong>g a Tel-Aire carbondioxide sensor, comb<strong>in</strong>ed with a HOBO® H8 series data recorder. Measur<strong>in</strong>g CO 2 can be used todeterm<strong>in</strong>e air exchange rates, and to evaluate <strong>in</strong>door air quality. Several groups have def<strong>in</strong>edmaximum acceptable levels <strong>of</strong> CO 2 <strong>for</strong> <strong>of</strong>fice spaces. Levels above 1,000 ppm can lead tolethargy and headaches (ems, 2004). However, both <strong>the</strong> United States OSHA (OccupationalSafety and Health Association) and <strong>the</strong> United K<strong>in</strong>gdome BSRIA (Build<strong>in</strong>g Services Researchand In<strong>for</strong>mation Association) have def<strong>in</strong>ed maximum exposure limits to be 800 ppm over aneight-hour period <strong>for</strong> <strong>of</strong>fice areas. The CO 2 level is dependent on <strong>the</strong> ventilation distribution,occupant density, and amount <strong>of</strong> outside air be<strong>in</strong>g <strong>in</strong>troduced <strong>in</strong>to <strong>the</strong> space (ASHRAE 2001).When evaluat<strong>in</strong>g <strong>the</strong> <strong>in</strong>door environment with respect to occupant health, ASHRAE suggeststhat an <strong>in</strong>door level <strong>of</strong> CO 2 650 ppm above <strong>the</strong> outside level is representative <strong>of</strong> an air exchangerate <strong>of</strong> 20 cubic feet per m<strong>in</strong>ute, with an occupant density <strong>of</strong> 100 ft 2 per person (ASHRAE 1997).Occupant com<strong>for</strong>t is also affected by higher CO 2 levels, with 20 percent <strong>of</strong> people dissatisfied atCO 2 concentrations <strong>of</strong> 650 ppm above <strong>the</strong> outdoor level (Liddament, 1996). In <strong>of</strong>fices, carbondioxide levels are primarily due to <strong>the</strong> respiration <strong>of</strong> <strong>the</strong> occupants. Initially <strong>the</strong> CO 2 andtemperature monitor was place outside, away from <strong>the</strong> build<strong>in</strong>g <strong>in</strong> order to record <strong>the</strong> externalconditions as a basel<strong>in</strong>e. Then <strong>the</strong> CO 2 sensor was placed at desk level, away from directexposure from an occupant, <strong>in</strong> <strong>the</strong> second floor <strong>of</strong>fice area and data recorded every fifteenm<strong>in</strong>utes over <strong>the</strong> twelve-month monitor<strong>in</strong>g period. On site visits, <strong>the</strong> number <strong>of</strong> people <strong>in</strong> each<strong>of</strong>fice area was logged over <strong>the</strong> period <strong>of</strong> <strong>the</strong> day and compared to <strong>the</strong> data recorded <strong>for</strong> that day.50
F<strong>in</strong>ally, airflow visualization was <strong>in</strong>cluded as part <strong>of</strong> <strong>the</strong> assessment <strong>of</strong> <strong>the</strong> build<strong>in</strong>g to improveunderstand<strong>in</strong>g <strong>of</strong> <strong>the</strong> characteristics <strong>of</strong> natural ventilation <strong>in</strong> <strong>the</strong> build<strong>in</strong>g design. Smoke pencilswere used <strong>for</strong> localized flow patterns throughout <strong>the</strong> build<strong>in</strong>g. These experiments proved to beuseful supplemental <strong>in</strong><strong>for</strong>mation <strong>in</strong> determ<strong>in</strong><strong>in</strong>g <strong>the</strong> airflow paths at <strong>the</strong> <strong>in</strong>let conditions, with<strong>in</strong><strong>the</strong> occupied space and atrium, and at <strong>the</strong> exhaust, but cannot be quantified reliably outside <strong>of</strong>laboratory conditions. Ano<strong>the</strong>r method with ‗neutrally buoyant‘ helium balloons was used totrack <strong>the</strong> airflow patterns with<strong>in</strong> <strong>the</strong> build<strong>in</strong>g. The neutrally buoyant balloons were made neutralat a selected height, which corresponded with a specific temperature. When <strong>the</strong> balloon wouldmove to an area <strong>of</strong> a different temperature, it would oscillate until reach<strong>in</strong>g <strong>the</strong> neutraltemperature aga<strong>in</strong> (Glicksman 2004). The balloons were <strong>the</strong>n released near <strong>the</strong> <strong>in</strong>let w<strong>in</strong>dows,and allowed to travel with<strong>in</strong> <strong>the</strong> build<strong>in</strong>g. The balloons normally ended up near <strong>the</strong> ro<strong>of</strong> <strong>of</strong> <strong>the</strong>atrium, <strong>the</strong> warmest location with<strong>in</strong> <strong>the</strong> build<strong>in</strong>g. However, this method did not producerepeatable results <strong>for</strong> specific streaml<strong>in</strong>es. The balloons were able to follow larger, macroscopicflow patterns with<strong>in</strong> <strong>the</strong> space, but had difficulty with low velocity airflow and detailed flowpatterns visible us<strong>in</strong>g <strong>the</strong> smoke pencils.3.3.1.3 Energy UsageThe occupancy schedule and energy usage pr<strong>of</strong>ile can be determ<strong>in</strong>ed by monitor<strong>in</strong>g <strong>the</strong> energyconsumption and usage patterns with<strong>in</strong> a build<strong>in</strong>g. The more detailed <strong>the</strong> meter<strong>in</strong>g <strong>of</strong> <strong>the</strong> electricenergy us<strong>in</strong>g equipment, <strong>the</strong> more thorough is <strong>the</strong> understand<strong>in</strong>g <strong>of</strong> <strong>the</strong> build<strong>in</strong>g energyper<strong>for</strong>mance. For <strong>the</strong> prototype build<strong>in</strong>g, not only <strong>the</strong> overall energy usage, but also a substantialamount <strong>of</strong> detailed monitor<strong>in</strong>g was completed. This detailed monitor<strong>in</strong>g <strong>in</strong>cluded data collectionon each floor level by orientation, miscellaneous build<strong>in</strong>g services, lifts, atrium fans andexternal/outside lights to determ<strong>in</strong>e <strong>the</strong>ir energy consumption. The energy usage <strong>for</strong> each floorcould not be separated out <strong>in</strong> more detail, e.g. lights versus plug loads, due to problems with<strong>in</strong>stallation <strong>of</strong> <strong>the</strong> data loggers <strong>in</strong> <strong>the</strong> electrical closets. Current transducers (CTs) were also<strong>in</strong>stalled on <strong>the</strong> actuators <strong>for</strong> <strong>the</strong> boiler so that <strong>the</strong>re was a measure <strong>of</strong> how <strong>of</strong>ten <strong>the</strong> boilers were<strong>in</strong> operation and <strong>the</strong>ir schedule <strong>of</strong> operation. Enernet K-20 electric energy data loggers were<strong>in</strong>stalled along with CTs <strong>of</strong> various sizes rang<strong>in</strong>g from 50 amps to 500 amps to capture energyusage data. CTs were <strong>in</strong>stalled on each <strong>of</strong> <strong>the</strong> three phases <strong>for</strong> each sub-system. Though <strong>the</strong> datawere recorded over <strong>the</strong> eighteen-month period, <strong>the</strong>re was still a 10 percent marg<strong>in</strong> <strong>of</strong> errorbetween <strong>the</strong> monitored data and <strong>the</strong> monthly energy bills. S<strong>in</strong>ce <strong>the</strong>re were a limited number <strong>of</strong>locations to <strong>in</strong>stall <strong>the</strong> K-20s, it is assumed that not every load was measured. Additionally, <strong>the</strong>total energy consumption was not recorded due to <strong>the</strong> limitation <strong>in</strong> size <strong>of</strong> CTs available and <strong>the</strong>location <strong>of</strong> <strong>the</strong> <strong>in</strong>com<strong>in</strong>g power supply. As a validation <strong>for</strong> <strong>the</strong> recorded data, energy us<strong>in</strong>gequipment and systems were <strong>in</strong>ventoried by a walk-through assessment <strong>of</strong> Houghton Hall <strong>for</strong>comparison.3.4 Issues with Assess<strong>in</strong>g a <strong>Natural</strong>ly Ventilated Build<strong>in</strong>gOverall naturally ventilated build<strong>in</strong>gs are more difficult to assess than <strong>the</strong>ir mechanicallyventilated counterparts, as <strong>the</strong>y have more temperature variation, vary<strong>in</strong>g ventilation rates thatare dependent on environmental conditions and w<strong>in</strong>dow geometry and less controlled airflowpatterns. This requires additional attention when determ<strong>in</strong><strong>in</strong>g air exchange rates, and <strong>in</strong> this case,<strong>the</strong> development and construction <strong>of</strong> a device to fit completely over <strong>the</strong> w<strong>in</strong>dow to obta<strong>in</strong> moreaccurate volume flow rate measurements.51
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Monitoring data collected from the
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By default, there was no accounting
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40-location card inserted into the
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6.5 ExperimentsTo evaluate the mode
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modified to determine the impact of
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Figure 39. Two Heated Zone ModelWit
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minute interval, the model was assu
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Figure 42. Cross-Section of Wind-Ge
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Table 25. Wind-Assisted Ventilation
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Figure 44. Heaters and Zones for a)
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Height from Floor (m)Height from Fl
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Where V is the outlet velocity, A o
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Table 32. Conduction Heat Loss for
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a) Air Modelb) Water ModelFigure 50
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Height from Floor (m)The temperatur
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Height from Floor (m)In the atrium
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First NorthUpper Window 0.17 m/s -0
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Height from Floor (m)the column at
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Height from Floor (m)Height from Fl
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Height from Floor (m)3.53.02.52.01.
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was less than 12 percent. These val
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Table 39. Variation of Outlet Wind
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temperature of the air was the same
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3.532.521.55m/s4m/s3m/s2m/s1m/s1.5m
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The average and exhaust internal bu
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uoyancy case the air from the groun
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160
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windows of naturally ventilated bui
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difficult to select the boundary co
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simulations are able to do would al
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Bordass, W.T., A.K.R. Bromley and A
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Linddament, M. 1996. Why CO2? Air I
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172
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MODEL: K20-8SERIAL: 10047RECORDER_I
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2 Boiler-3 50.00 C1 N1 1.0 ON ON OF
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|PW|DESCRIP |KW |KWH|KVA|KVH|------
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2:5 ;day_ofYr17:P30 ;EOT = 0.000075
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2:3136:P30 ;DUM2 = -0.040891:-4.089
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Five Windows Open: Upper versus Low
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25 cm / 3 m 24.33 26.62 22.68 22.93
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25 cm / 3 m 24.07 25.26 22.65 22.78
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Two Stacks Open Temperature Stratif
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Stacks Closed Temperature Stratific
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0.6 20.56 20.67 20.94 21.22 21.41 2