Analysis of Thermal Comfort and Indoor Air Quality in a Mechanically Ventilated Theatre

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Analysis of thermal comfort and indoor air quality

in a mechanically ventilated theatre

M. Kavgic

a,

*, D. Mumovic

a

, Z. Stevanovic

b

, A. Young

a

The Bartlett School of Graduate Studies, University College London, Gower Street, London, WC1E 6BT, England, UK

b

Institute of Nuclear Sciences – Vinca, P.O. Box 522, 11001 Belgrade, Serbia

Received 29 January 2007; received in revised form 10 December 2007; accepted 17 December 2007

Abstract

Theatres are the most complex of all auditorium structures environmentally. They usually have high heat loads, which areof a transient nature as audiences come and go, and from lighting which changes from scene to scene, and they generally have full or nearly full occupancy. Theatres also need to perform well acoustically, both for the spoken word and for music, and as sound ampliﬁcation is less used than in other auditoria, background noise control is critically important. All these factors place constraints on the ventilation design, and if this is poor, it can lead to the deterioration of indoor air quality and thermal comfort. To analyse the level of indoor air quality and thermal comfort in a typical medium-sized mechanically ventilated theatre, and to identify where improvements could typically be made, a comprehensive post-occupancy evaluation study was carried out on a theatre in Belgrade. The evaluation, based on the results of monitoring (temperature, relative humidity, CO2, air speed and heat

ﬂux) and modelling (CFD), as well as the assessment of comfort and health as perceived by occupants, has shown that for most of the monitored period the environmental parameters were within the standard limits of thermal comfort and IAQ. However, two important issues were identiﬁed, which should be borne in mind by theatre designers in the future. First, the calculated ventilation rates showed that the theatre was over-ventilated, which will have serious consequences for its energy consumption, and secondly, the displacement ventilation arrangement employed led to higher than expected complaints of cold discomfort, probably due to cold draughts around the occupants’ feet.

Keywords: Post-occupancy building evaluation; Ventilation rates; Thermal comfort; Indoor air quality; Theatres

1. Introduction

Indoor air quality (IAQ) and thermal comfort are important factors in the design of high quality buildings [1]. Although innovations in air-conditioning and other forms of cooling or ventilation,which can be viewed as technologicalsolutionsto the problem of producing and maintaining energy efficient environmental conditions that are beneficial for human health, comfort and productivity [2], there is often a conflict between reducing energy consumption and creating comfortable and healthy buildings [3]. Unhealthy buildings have been associated with the high prevalence of several symptoms: headaches, dry eyes or throat, itchy or watery eyes, sneezing, blocked and stuffy nose, runny nose, and dry or irritated skin [4].

Theatres are the most complex of all auditorium structures, and often have more than one performance per day.

Furthermore, unlike other building types, the use of opening windows for air intake and extract ventilation is not possible, requiring a different approach. Theatres frequently operate at high occupancy level, and tend to have higher sensible (and latent) heat loads. Air must be distributed over a wide area, both within the auditorium and the stage, with numerous supplies and return registers.

For all these reasons, a post-occupancy evaluation was carried out to gain an in-depth insight into IAQ and thermal comfort within theatres, and to identify speciﬁc problems, which could be used to inform future theatre design.

In order to develop an IAQ post-occupancy evaluation methodology, and as a short review of literature, a number of papers focusing on lecture theatres (there is little useful literature on performance theatres) have been analysed. This was possible as the ventilation design for large teaching and performance theatres follow the same principles with varying degrees of complexity [5].

One study [6], solely based on computational ﬂuid dynamics (CFD) modelling scenarios, showed how this methodology

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Energy and Buildings 40 (2008) 1334–1343

* Corresponding author.

E-mail address:miroslava.kavgic@gmail.com(M. Kavgic).

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could be used to investigate IAQ issues in theatres. It attempted to evaluate how two ventilation systems with the same air inlet arrangement, but different systems of air extraction, affected the air speed, temperature and CO2concentration proﬁle inside

the teaching auditorium. The conclusion, not surprisingly, was that the lowest rate of air change leads to the increase of temperature. Furthermore, it was found that CO2concentration

decreases rapidly if the ventilation rate is increased, in this case by the unexpectedly large factor of ﬁve.

A more comprehensive assessment methodology was developed by Cheong and Lau, and applied to audit IAQ and thermal comfort in lecture theatres in the tropics [7]. The suggested IAQ assessment methodology consisted of four stages: (1) preliminary stage (understanding the background of the building), (2) sampling stage (on-site data collection), (3) evaluation stage (data analysis) and (4) recommendation stage (effectively a set of remedial measures). In addition, a questionnaire survey was carried out in the lecture theatre a few weeks prior to the monitoring campaign. However, the overall results suggested that the ventilation system, in this case a full air-conditioning system, was effective in removing indoor air pollutants and achieving reasonable IAQ with 81% of the respondents perceiving that the air quality was acceptable. Another study, again by Cheong et al., has focused on thermal comfort, rather than IAQ, in an air-conditioned lecture theatre in the tropics [8]. In addition to collecting thermal comfort data, the methodology in this paper included the analysis of thermal comfort using computational ﬂuid dynamics. Despite the fact that all the thermal comfort parameters were within the range limit set out in ISO 7730 [9], the occupant survey showed that more than 20% of the occupants were not satisﬁed with thermal comfort. Furthermore, the authors concluded that the VAV air-conditioning system was unable to cope with the peak occupancy load.

A recent study [10] focused on thermal comfort and indoor air quality in a lecture theatre with a 4-way cassette air-conditioning and mixing ventilation system. This showed that increasing the discharge angle from the supply grilles on the cassette unit makes uniformity of thermal comfort worse, but rarely affects IAQ. The above review shows how a range of methodologies can be used to investigate the post-occupancy performance of theatres.

2. Methodology

This study was carried out in a recently refurbished theatre located in the city centre of Belgrade which is characterized by a moderate continental climate. The theatre (Fig. 1), roughly a rectangular box, is 28 m long, 20 m wide, with a floor to ceiling height of 11 m, with a gallery over the rear and sides of the ground floor (or stalls). Around half of the ground floor area is given over to the stage. The auditorium is served by a displacement-type ventilation system. Fresh air is introduced via vortex diffusers, mounted at ground and gallery floor level directly under the seats (SDV01–12 and SDV13–18 in Fig. 1), boosted by a few circular diffusers in the ceiling of the gallery (SDR1 and SDR2 and SDR3 and SDR4). Air is also supplied at

low level from the side walls of the stage (SDG1–3 and SDG4– 6). Extract air is removed by rectangular outlet grilles set into the ceiling over the stalls (RDG01–04) and gallery level (RDG05–09 and RDG10–14)). The post-occupancy evaluation followed a systematic 4 step approach similar to the one described in [7] but further developed for the purposes of this study:

Step 1: walkthrough (review of mechanical drawings, feed-back from occupants including the facility manager, identiﬁcation of areas prone to deterioration of IAQ), Step 2: on-site data collection (continuous monitoring of IAQ and thermal comfort parameters, questionnaire survey), Step 3: modelling (development, analysis and validation of

detailed CFD model using FLAIR, which is based on PHOENICS code [11],

Step 4: data analysis and assessment (statistical analysis of monitored parameters, comparison with standards and/ or regulations).

2.1. Walkthrough (Step 1)

The ﬁrst, and perhaps most crucial step, in preparing for a post-occupancy evaluation of a building is the walkthrough. This helps to clarify the perceived strengths and weaknesses of the building design and to develop a detailed on-site data collection methodology. By interviewing the facility manager and the HVAC engineer, who designed the mechanical ventilation system, potential areas prone to deterioration of indoor air quality can be identiﬁed. In addition, anecdotal stories may provide an insight into the operational performance of the mechanical ventilation system.

2.2. On-site data collection (Step 2)

It should be noted that the on-site data collection strategy consists of two parts: (1) monitoring and (2) assessment of thermal comfort and health as perceived by the occupants.

2.2.1. Monitoring strategy

Measurements were carried out at several locations in the occupied zone within the auditorium, over two successive evenings during a performance. Three sampling points, MPP1– 3 (Fig. 1), were selected in the occupied space with point 4 in an outdoor location. These measurements were carried out during two theatre performances at carefully selected locations in order to ensure a good representation of human exposure to thermal comfort and IAQ. It should be noted that sampling point MPP1 was located at the balcony near an outlet, while sampling points MPP2 and 3 were placed approximately at head height. The following parameters were measured: carbon dioxide concentration (CO2), air temperature (T ), wall surface

temperatures (T w), relative humidity (RH) and air speed. All

parameters were measured at 5-min interval for the duration of the whole performance. The 5-min interval was chosen to see how the breaks in the performance (which last approximately 20 min) will affect carbon dioxide concentration proﬁle in the

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auditorium, since the pertinent source of CO2is human beings.

The thermal comfort and IAQ in the auditorium were assessed using the following parameters:

 predicted mean vote index (PMV),

 percentage of people dissatisﬁed index (PPD),

 draught rate index (DR),

 mean age of air (AGE) and

 ventilation effectiveness (Ev).

Deﬁnitions of these parameters can be found elsewhere [12,13]. The rate of change in concentration of CO2depends on

the concentration of CO2in the in-ﬂowing air, the concentration

in the out-ﬂowing air and the internal generation rate. From this, the following equation can be derived for the calculation of ventilation rates during the occupied and unoccupied periods using the monitored values of CO2 [14]:

C ðt Þ ¼C exþ G Qþ



C inÀC exÀ G Q



eQt =V (1)

whereC (t ) is the internal concentration of CO2(ppm) at time

t (s), C exis the external concentration of CO2(ppm),Gis the

generation rate of CO2 (m 3

/s), Q is the internal–external exchange rate (m3 /s), C in is the initial concentration of

CO2 (ppm), and V is the volume of the auditorium (m 3

). Note that in this case the inter-zone effects between the auditorium and surrounding internal spaces are neglected. Although not entirely accurate, this assumption was possible as the vast majority of the auditorium is facing the outdoor environment.

2.2.2. Assessment of thermal comfort and health as perceived by occupants

The assessment of thermal comfort and health as perceived by occupants was carried out during the interval of each play, on both days. Audiences were requested to complete the questionnaire pertaining to thermal comfort (see Appendix A). The questionnaire was divided into sections, namely users’ gender and health, perceived environmental conditions, and other aspects of the auditorium environment such as cleanliness and odour. This was to assess the users’ observation of IAQ and investigate how people, perhaps with health problems, such as sinusitis or asthma, react to the existing indoor environment. The assessment of the thermal comfort and IAQ was based on the audience’s votes on thermal sensation, humidity and air movement in the auditorium. A 3-point scale was used to evaluate thermal impression and sensation of comfort regarding humidity, air temperature, and air speed. Although the capacity of the auditorium was 500 people, a total of 100 questionnaires were distributed on each day. Sixty-ﬁve on the ﬁrst day and 75 on the second day were completed and returned. The dominant gender was female (approximately 90%). Prior to the survey, the subjects would have been in their seats for between 1 h and 2 h, depending on the play. Since it was summer, the clothing ensemble consisted of light cotton shirts, trousers, blouses and skirts.

2.3. Modelling strategy (Step 3)

A 3D ﬂow model was set-up using the incompressible steady state Navier–Stokes equations coupled with the k-e_turbulence

model, continuity equation and the conservation equation for carbon dioxide concentration, as summarised in Table 1. The

Fig. 1. Location of the measuring points in the auditorium (MPP1–3).

M. Kavgic et al. / Energy and Buildings 40 (2008) 1334–1343

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physical model of the theatre was simulated with approximately the same geometrical configuration as the real auditorium. The geometric model consists of three groups of ‘‘objects’’: (1) the auditorium shell, (2) the HVAC ‘‘objects’’ (diffusers, grilles, etc.) and (3) the heat sources (lighting, occupants, etc.). Most of these objects are already defined in the FLAIR library (building orientated CFD based on PHOENICS code) [11]. However, as the shape of the gallery was too complex, a 3D solid model of the gallery was created in AutoCAD and imported into FLAIR. The vortex diffusers were simulated at floor level of the main auditorium and gallery and the round diffusers similarly in the ceiling of the side gallery, and grille/nozzle diffusers were simulated on the lateral walls of the stage. The under-seat round vortex diffusers were actually approximated as squares. The heat source representing the audience was defined as 3D rectangular objects with specific heat, water vapour and CO2

emissions, as appropriate to human beings. The lighting was

set-up as an array of 3D rectangular heat source objects deﬁned to generate 19.6 kW of heat in total.

A number of cells, specifically, 140Â153Â75, were set-up in the x, y and z directions, respectively. In other words, the whole theatre domain was divided into approximately 1.6Â106 finite volumes (or cells). In every cell, all physical parameters, thermal comfort indices as well as indoor air quality parameters, were deduced. Since the surface tempera-tures of the ceiling, floor and internal walls, measured with an infra-red sensor, were found to be 238_{C, 22}8_{C and 24}8_C,

respectively, at the beginning of the monitoring period, these values were input as boundary conditions in the CFD analysis. Note that it was assumed that these values were constant for the duration of the performance, which is not an unreasonable assumption. The boundary conditions applied to air inlets and outlets are shown in Tables 2 and 3, respectively. Internal heat and mass sources are summarised in Table 4.

Table 1

Summary of the mathematical model

General transport equation@iðrU iFÞ À@iðrG F@iFÞ ¼S F

Equation F G F S F

Continuity 1 0 0

Momentum U j veff À@ jP+bg j(T ÀT ref )

Energy T veff =s T 0

CO2mass fraction Y CO₂ veff =s CO₂ 0

H2O mass fraction Y H₂O veff =s H₂O 0

Turbulence kinetic energy k veff =s k Pk +Gk Àe

Dissipation rate e v_eff=s e_s r(e / k )(C e1Pk +C e3Gk ÀC e2e)

Pk =nt (@k U i+@iU k )@k U i;Gk =bgiat (@iT )

neff =n+nt ;nt =C mk 2

/ e; a_t=n_t / s _T,b= 1/ T _ref

s k ,s e,s CO₂,s H₂O,s T ,C e1,C e2,C e3C m= 1.0, 1.314, 0.9, 0.9, 0.9, 1.44, 1.92, 1.44, 0.09

Table 2

Air inlet boundary conditions of theatre HVAC air supply system

Supply diffusers Number of

elements Temperature (8_C) Humidity (kg/kg) Total volume ﬂow rate (m3_/h) CO2volume fraction (ppm) Ground level Vortex 312 20 0.008654 15650 350 Round 8 20 0.008654 1600 350 Gallery level Vortex 120 20 0.008654 6450 350

Mean stage level

Grille 6 20 0.008654 6000 350

Table 3

Air outlet boundary conditions of theatre HVAC return air system

Return diffusers Dimensions (mm) Number of elements Effective area (m2₎ _{Pressure drop (Pa)}

Gallery ceiling

Grille 1025Â525 10 0.269 2

Mean stage ceiling

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3. Data analysis and assessment (Step 4)

In this section the collected and analysed data are discussed. Thermal comfort and IAQ are examined, with exploration of the physical parameters such as air temperature, relative humidity, air speed and CO2concentration. The developed CFD

model of the theatre has contributed to further analysis of the spatial distribution of airﬂow patterns, temperature gradients, levels of relative humidity and ventilation effectiveness inside the occupied zone. All these data are correlated with the results of the assessment of thermal comfort and health as perceived by the occupants.

Measured values of the thermal comfort parameters are tabulated in Tables 5 and 6. Figs. 2–4 present the monitored results at sampling location 1 (MPP, see Fig. 1). Relative humidity in the occupied zone was between 58% and 67%, and between 57% and 65%, respectively, on the 2 days and is shown in Fig. 2. Mean relative humidity was 56% and 55%, respectively. Air temperatures in the auditorium on both days were between 24.68_{C and 26.6}8_{C and between 24.2}8_{C and}

26.78_{C, respectively. The mean air temperatures were 25.9}8_C

and 25.58_{C, respectively, with a standard deviation of 1}8_C.

Note that the monitored air temperature on a number of occasions exceeded the higher limit of the acceptable range set by ISO Standard 7730 [9]. A close examination of the

temperature curves in Fig. 3 showed that due to greater attendance, air temperatures on the ﬁrst day were slightly higher than on the second day. The main temperature peaks occurred when the audience was entering a little before 19:30 h,

Table 4

Internal heat and mass sources in theatre HVAC load sources

Parameters

Sensible heat (W/person) Latent heat

(W/person) Total heat (W/person) Total number of persons Humidity source (g/h person) CO2source above outdoor air (ppm) Heat from lights (W) Ground occupants 60.5 55 115.5 332 55 450 0 Gallery occupants 60.5 55 115.5 132 55 450 0 Mean stage 60.5 55 115.5 3 (average) 55 450 19600 Table 5

Measured air temperatures in the occupied zone for day1/day2

Locations Minimum air

temperature (8_C) Maximum air temperature (8_C) Mean air temperature (8_C) 1 24.6/24.2 26.6/26.7 25.8/25.4 2 25.1/24.5 25.9/25.9 25.6/25.4 3 25.6/24.8 26.3/25.9 26.1/25.7 Table 6

Measured RH in the occupied zone for day1/day2

Locations Minimum relative

humidity (%) Maximum relative humidity (%) Mean relative humidity (%) 1 58.3/57.5 67.3/64.8 62.2/61.0 2 43.7/44.4 51.0/49.8 47.8/46.7 3 48.4/56.4 61.0/60.2 57.0/58.3

Fig. 2. Relative humidity proﬁles at MPP1.

Fig. 3. Air temperature proﬁles at MPP1.

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and when it was applauding and cheering during the performance, and while vacating the auditorium.

The two CO2 concentration curves in Fig. 4 correspond

closely. Furthermore, as the audience entered an abrupt build-up of concentration was perceived, while there was a gradual decay as they settled down. Other rapid decays and increases in the CO2concentration were due to the intervals, when most of

the people moved to the lobby. Finally, the third CO2 peak

happened at the end of the performance when the audience was applauding, cheering and leaving the theatre. Measured CO2

concentrations ranged between 599 ppm and 1041 ppm and between 587 ppm and 949 ppm, respectively for the 2 days, with an average concentration of 744 ppm on the ﬁrst day and 734 ppm on the second day. The only time the CO2

concentration exceeded 1000 ppm, was at the beginning of the performance, and sincethis was for such a short period (note that the CO2 levels shown in the diagram are averaged over a

period of 5 min), it is probably of no great concern as the recommended threshold values relate to a 2 h exposure [15]. Moreover, since this is a cabaret theatre, the audience was

involved in cheering, which inﬂuenced the increase of air temperature and CO2 concentration. However, the calculated

ventilation rates have shown that the theatre was mostly over-ventilated which may have consequences for its energy consumption. The calculated ventilation rates averaged over the period of duration of the performance was 14.5 l/s.p and 15.5 l/s.p for days 1 and 2, respectively which is around 50% greater than the recommended level of 10 l/s.p [16].

This paper presents the results of the questionnaire survey conducted on both days, when a total of 100 questionnaires were distributed each day to the audience. On the ﬁrst day 65, and on the second 75 were completed and returned. Fig. 5 shows the percentage of respondents who complained that they had suffered from a particular physiological symptom. Overall a total of 63% claimed they had suffered from one or more symptoms. The most prevalent symptoms are related to nasal and respiratory organs, dry or watering eyes, and headaches. Unexpectedly, a signiﬁcant number of respondents claimed they suffered from asthma. A total of 58% felt that thermal comfort and indoor air quality were satisfactory, while 16% stated that the air was too cold (Fig. 6). The reason many people complained about cold air, given a mean air temperature in the comfort zone (25.58_{C) on both days, could be due to an}

inherent problem with the displacement ventilation arrange-ment where cold (and fresh) air is located at the lower zones, near the occupants’ feet and ankles. The measured air speed at the supply diffusers, imbedded directly under the seats, was indeed 0.3 m/s which could lead to unpleasant draughts, since 0.25 m/s is the recommended upper limit for comfort for a sedentary person. The incoming temperature at the under-seat vortex diffusers was 188_{C which was 6}8_{C below the design}

temperature of 24Æ1.58_{C. It should be noted that 8% of}

respondents claimed the air was too dry even though the mean relative humidity, on both days, was 55%. It is interesting to note that many of the people who complained about dry air were those with dry or irritated throat symptoms.

To validate the model the numerical probes, i.e. the cells used to predict the conditions in the simulation study, were located at the same positions as the sampling points used during the monitoring campaign. Based on the differences between the

Fig. 4. CO2concentration proﬁles at MPP1.

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two sets of values, it was concluded that the air temperature, relative humidity and volume fraction of carbon dioxide were being predicted with acceptable accuracy. A comparison between measured and simulated data is given in Table 7.

Figs. 7 and 8 show the predicted thermal stratiﬁcation and ﬂow pattern in the auditorium and indicate that the air movement is taking place in the ideal displacement ventilation manner. Cold and fresh air is located at the lower zones of both ground and gallery levels, while the hotter air moves to the

upper zones (Fig. 7). The ﬁelds of air temperature and relative humidity obtained are roughly homogeneous. The average values were between 24.78_{C and 47% at the ground level and}

between 258_{C and 46.7% at the gallery level. Detailed analysis}

of the air ﬂow pattern in the auditorium (Fig. 8) indicates that the air speeds may cause cold draughts around the occupants’ feet. This further underpins the statement that the displacement ventilation arrangement employed led to higher than expected complaints of cold discomfort, probably due to this factor.

Fig. 6. Physical parameters: percentage of respondents who complained about a particular environmental problem.

Table 7

Comparison of measured and numerical (simulated) data

Probe location: ﬁrst exhaust diffuser Air temperature (8_C) _CO₂_{volume fraction (ppm)} _{Relative humidity (%)}

Measured data 25.40 795.0 61.0

Numerical data 25.65 738.8 45.4

Relative error 1.0% over predicted 7.0% under predicted 25.6% under predicted

Fig. 7. Predicted thermal stratiﬁcation in the middle-vertical cross-section.

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Unfortunately, the questionnaire did not contain a question related to cold draughts around occupants’ feet. The range of PMV was from À1.0 to +1.0 (Fig. 9). However, the occupied zones of the ground ﬂoor and gallery were of A class (À0.2<PMV>+0.2). The higher PMV values occurred in the micro zones near the back walls of the ground and gallery levels, respectively. In the occupied zones the mean age of air had the averaged values of approximately 50 s and 100 s at the ground and gallery levels, respectively. Clearly, as expected, the mean age of air in the lower part of the auditorium (ground level) was much less than that in the upper part (gallery level),

by a factor of nearly two. The average AGE across the whole auditorium was 30 s. Ventilation effectiveness Ev deﬁned by CO2 mass fractions was in the range of 0.9–1.0 and therefore

satisﬁes the criteria deﬁned by CIBSE Guide A [17].

The measurements undertaken to evaluate the indoor environment in the auditorium were discussed in line with the recently introduced standard EN15251:2005 [16]. The evaluation of the category of the auditorium was based on temporal and spatial distribution of the theatre temperature, air speed and representative CO2 samples taken from different

zones. Taking into account the recommended criteria for the

Fig. 9. Predicted PMV distribution in the middle-vertical cross-section. Fig. 8. Predicted air ﬂow pattern in the middle-vertical cross-section.

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thermal environment [16], the parameters related to thermal state of the body as a whole belong to the categories A (À0.2<PMV<+0.2) and B (PPD<10%). The local discomfort indices such as draught rate (DR<15%) and the vertical air temperature difference (DT <10%) fall into the categories A and C, respectively. However, it has to be highlighted that in the micro zones near the backward walls of ground and gallery levels all parameters deteriorated sig-niﬁcantly (PPD>15%, À1.0<PMV<+1.0, DR<25%,

DT >10%) falling below the requirements for the category C. Note that the calculated ventilation rates averaged over the period of duration of the performance (approximately 15 l/s.p) are higher than the recommended design ventilation rates for both low-polluting building (approximately 11 l/s.p) and non low-polluting building (approximately 12 l/s.p) leading to the conclusion that the theatre was mostly over-ventilated which will have consequences for the energy consumption of the theatre.

4. Conclusions

To analyse the level of indoor air quality and thermal comfort in a typical medium-sized mechanically ventilated theatre, and to identify where improvements could typically be made, a comprehensive post-occupancy evaluation study was carried out on a theatre in Belgrade. The evaluation, based on the results of monitoring (temperature, relative humidity, CO2, air speed and heat ﬂux) and modelling (CFD)

as well as the assessment of comfort and health as perceived by occupants, has shown that for most of the monitored period the environmental parameters were within the standard limits of thermal comfort and IAQ. However, the post-occupancy evaluation of the theatre has highlighted the following issues:

 Firstly, the calculated ventilation rates have shown that the theatre was mostly over-ventilated which will have con-sequences for the energy consumption of the theatre. To optimize the energy consumption of the ventilation system, while maintaining adequate IAQ, a CO2 operated control

system for the ventilation system could be incorporated in the existing system.

 Secondly, although average air temperatures were mostly in the comfort region, a larger than expected number of people complained of cold discomfort. In a displacement ventilation system, supply air is introduced to the space near the ﬂoor level, at low velocity, at a temperature only slightly below the desired room temperature, typically say, 28_{C. In this case,}

however, the incoming temperature at the under-seat vortex diffusers was 188_{C, which was 6}8_{C below the design}

temperature of 24Æ1.58_{C, while the air speed was 0.3 m/s.}

Where air speeds in buildings are greater than 0.15 m/s, the resultant temperature should be increased from its ‘still’ air value to compensate for the cooling effect of the air movement. The required elevation to the dry resultant temperature to take account of an air speed of 0.3 m/s is approximately 1.58_{C [17]. The high air speed and large} _D_t

found here, in addition to the usual ﬂuctuations, which occasionally occur in any temperature controlled ventilation system, appear to be the main reasons for complaints of cold draughts.

 Thirdly, it has been shown that the ventilation system was capable of maintaining the IAQ at an acceptable level. The only time the CO2concentration exceeded 1000 ppm, was at

the beginning of the performance, and since this was for such a short period, it is probably of no great concern as the recommended threshold values relate to a 2 h exposure.

This study has shown that post-occupancy evaluation, using the techniques described, is key to maintaining adequate thermal comfort and IAQ in theatres, while ensuring that energy consumption is minimised. The techniques can be easily used by both HVAC engineers and facility managers.

Appendix A. Questionnaire M. Kavgic et al. / Energy and Buildings 40 (2008) 1334–1343

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[16] CEN/TC 2005 Criteria for the Indoor Environment including thermal, IAQ, light and noise, European Standard CEN 156/EPBD/TC ver. 2.1. [17] CIBSE Guide A: Environmental Design, London, UK: The Chartered