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Exhibition and congress halls sustainable design.

INTRODUCTION

Exhibition and Congress halls have a complex and distinguished history that can be traced back to the Middle Ages through a tradition of trade fairs. Flexibility is of paramount importance as these spaces are required to serve a multitude of uses. Exhibitions can range from home decoration shows to major industrial trade fairs, in addition to this spaces could be used for major events including sports and music concerts. Buildings generally have long span roof structures to create high-bay, column free and therefore flexible spaces. This variation in use means that the halls themselves must be adaptable to change in size through sub-division. Space conditioning for comfort and the provision of services must adapt in turn to meet the requirements of a particular event.

Business models for this type of building will be significantly affected by the set up and take down periods for an event. The shorter these can be made then the time between events can be reduced which allows a larger number of events to be held annually. It should also be noted that building systems should allow an event to be held in one part of the building whilst another part of the building is being set up or taken down. Set up and take down periods will also require truck access.

Interaction with local transport hubs is important and maybe integrated with entrance vestibules and foyers housing coach drop off points or Metro stations. A number of ancillary spaces are required. These will include breakout areas, meeting rooms, conference facilities, restaurants and in some instances a hotel. All of these would be designed around the visitors and exhibitors and each space requires differing but extensive building services.

Exhibition and Congress halls are subject to a variety of Heating. Ventilating. Air conditioning and Refrigeration (HVAR) loads depending on the type of function in progress from an industrial exhibition to a book fair and small meetings to large conventions. They can also be used for music concerts or sporting events. It is not possible for a designer to predict every type of function and HVAR loads that are very different in character may be encountered. When an Exhibition hall is used as a meeting room the load will be latent in character and not sensible as is normally the case with exhibitions. The integration of sustainable and flexible (HVAR) building services and their impact are integral to the success of the Center. Establishing the design criteria is key to the successful choice of sustainable and subsequent efficient operation of the HVAR systems. The chosen design criteria also have a major impact on the slectrical supply requited for the facility. Ancillary facilities include restaurants, bars, concession stands, parking garages, offices, television broadcasting rooms, and multiple meeting rooms varying in capacity from small (10 to 20 people) to large (hundreds or thousands of people). Often, an appropriately sized full-scale auditorium or arena is also incorporated. The determination of usage and occupancy information is critical in any plan to design and operate these facilities efficiently and effectively, especially sustainably.

LOAD ASSESSMENT

Exhibition Hall design is driven by the layout of exhibitor booths which commonly use a 10ft x I Oft (3m x 3m) base grid for a single booth. Larger booths are then formed in multiples of the 10ft x 10ft grid. Inclusion of circulation and necessary fire escape routes means that the booth density is around 50-60% of the available space in the hall. Figure 1 illustrates this with aisles equal to one booth width.

[FIGURE 1 OMITTED]

Sensible heat gains to the space from booths can be estimated from the capacity of the electrical supply provided which is typically 4kW* per booth. Distributing this load over the gross area of the hall produces a peak small power density of 66BTU'h.sqft (220W/sqm) based on the booth density. It is clearly unlikely for each booth to draw 4kW of power simultaneously and information analyzed from Exhibition Halls currently operating implies a diversity of 50% during events with the highest loads. This means that the peak continuous cooling load due to small power is 33BTU1i.sqft (I lOW/sqm) which agrees with ASHRAE guidance (1) recommendations although many events could have a much lower demand.

Additional sensible heal gains will also occur due 10 occupancy, lighting and fabric loads. An allowance of 4.7BTU/h.sqft (l5W/sqm) should be made for gains from lighting to maintain a background illuminance of 3001ux. Fabric loads with modern building standards should not exceed 9.3BTU/h.sqft (30W/sqm). but should be calculated for each project. Accurate occupancy and usage information is critical in any plan to design and operate such a facility efficiently and effectively. The flexibility of usage is demonstrated in Figure 2 showing plans for a hall set up for various functions. For an exhibition. ASHRAE guidance [I] recommends an average occupancy of one person per 44sqft <4sqm) of the gross exhibition hall area (around one person per 22sqft (2sqm) of aisle). For conferences and concerts the occupant density is likely to increase to 22sqft (2sqm) per person throughout the whole space. Gains generated by occupants will also vary according to the type of event. During an exhibition the average occupant will generate 23.3BTU'h.sqfi (75W/sqm) of sensible heat and BTU/h.sqfi (55W/sqm) latent heat, however a music concert with dancing means that occupants could be generating 27.9BTU/h.sqfi (90W.-sqm> of sensible heat and 49.6BTU;h.sqrt (l60W/sqm) of latent heat.

[FIGURE 2 OMITTED]

Table 1 summarizes the design heat loads that may be incurred, it can be seen that significant variations in both sensible and latent loads should be expected. This further demonstrates the flexibility required in the design of systems. Peak Loads are seldom experienced because large power-consuming equipment will not be used at all shows or continuously. Alternative loads of very different character may be encountered. In general Exhibition loads will be dominated by sensible heat gain whereas for concerts latent loads are much more significant.
Table 1: Exhibition Hall Loads-BTU/h.sqft (W/sqm)

Load Type              Exhibition      Conference  Music Concert

Small Power        4.65-34.1 (15-110)    15.5(50)       21.7(70)

Lighting                     4.65(15)    1.55 (5)       1.55 (5)

Occupant Sensible             5.9(19)    11.8(38)         14(45)

Occupant Latent              4.3 (14)    8.7 (28)      24.8 (80)

Fabric Loads                 9.3 (30)    9.3 (30)       9.3 (30)

Total Sensible     24.8-53.6 (80-173)     38(123)      46.5(150)


COMFORT

It is important to have an index for comfort that takes into account heat transfer by radiation, conduction, convection and evaporation. This will also be influenced by our type of clothing and air movement. One method for estimating comfort at particular conditions is the Predicted Mean Vote (PMV) method. However a simpler indicator used by ISO, ASHRAE and CIBSE [2] is 'Operative Temperature' which considers air and radiant temperatures. In a room without draughts the air velocity due to natural convection is assumed as 0.1 m/s and the operative temperature relationship becomes:

Operative temperature [T.sub.o] = ([T.sub.a] + [T.sub.r]) /2

This indicates that for normal design conditions, air and mean radiant temperature are of equal importance. In lightweight buildings, fabric will respond quickly to the room air temperature so the air. mean radiant and occupant temperature will be similar when conditioned by an air system.

Given the large surface areas of buildinjj fabric that exist in exhibition halls there is the potential these may be used to control radiant temperature of the space and hence improve operative temperatures. This could be through the introduction of thermal mass or some form of surface heating-cooling system. Large span roofs for exhibition halls tend to be lightweight to reduce costs and hence surface cooling/heating is simpler to integrate. However the influence of thermal mass with its influence on comfort can delay or reduce the point at which IIVAR plant is operated.

Operative temperature does not account for humidity which is a major factor, particularly where occupancy rates are intense as with Exhibition and Congress halls. Designs should fully consider the effect of humidity on comfort rather than simply adopting a wide humidity range of 30-70% which is common in systems design. The influence of moisture on people is one of the least understood of all the comfort factors. There is a direct relationship between air temperature and humidity. Research evidence indicates that at low temperatures of 68 [degrees] F 20 [degrees] C a higher relative humidity of 65% is the condition at which people feel most comfortable. Current trends have sought to relax air temperatures to reduce energy consumption and allow buildings to operate passively which means in order to provide healthy and comfortable moisture conditions a lower relative humidity is required.

Generally lower humidity means that occupants can tolerate higher air temperatures. Lower humidity will also provide,1 healthier environment. The World Health Organization [3] recommends a level of 7 g'Kg as optimum which translates to a temperature of 73.4 [degrees] F 23 [degrees] C at 40% relative humidity. We should therefore seek to control the absolute level of humidity rather than the relative level of humidity. Low temperature air systems arc helpful in this regard.

Moisture content this low is fairly extreme particularly considering the fact that Exhibition Halls are not occupied daily by the same occupants. Operative temperatures of 75.2 [degrees]F (24 [degrees]C) and 50% relative humidity arc appropriate as this gives a PMV of 0 to-I-.5 depending on air movement. It is also worth noting that occupants at a rock concert will have more relaxed expectations of internal comfort than visitors to a trade show.

The new 2010 ASIIRAC Standard 55 allows designers with a detailed understanding to propose dramatically different systems through more careful consideration of influencing factors. Choosing the best of the three compliance methods for the project is essential. These changes empower designers and operators alike to implement high performance concepts.

VENTILATION AND AIR DISTRIBUTION

Air distribution systems must control internal loads to provide the target comfort criteria outlined above. The design of these systems is key to reducing energy consumption as far as practical to provide a sustainable solution.

Good indoor air quality (IAQ) is important for a comfortable and healthy indoor environment and is a prerequisite of ASHRAE 189.1 [4]. Consequently green and sustainable rating systems place great emphasis on maintaining acceptable IAQ. Outdoor air rates requirements arc generally defined by the need to dilute and remove indoor contaminants. Local codes for ventilation must be referenced whenever available although specific Codes relating to these types of facilities arc hard to find. ASHRAE 62.1 [5] docs not list guidance for exhibition halls. Guidance in ASHRAE [I] handbooks is limited to information pertaining to occupant densities of 40 to 50sqfl (3.7 to 4.6sqm) per person.

The large height of Exhibition Halls means that the volume of air per person is high which is favorable for the reduction of odours as shown by work conducted by Yaglou. Riley and Coggins [6]. This is due to the dilution of pollutants such that where the volume of a space is in excess of 500cuft per person the outdoor air flow rates can be reduced by approximately 60% when compared to the outdoor air flow rates required where a person occupies 100 cult.

The approach taken in this paper has been to consider the latent gain produced by occupants. Table 2 shows the ventilation rates required to maintain the required humidity assuming that air is supplied with a dew point of 9 [degrees] C. The reason for this strategy is to allow outdoor air systems to provide the required dehumidification to the space during a latent load when sensible loads arc unpredictable. Table 2 also shows the ASHRAE standard 62.1 recommendation for conference halls. ASHRAE 189.1-2009 indicates that rates should be increased by 30% over ASHRAE 62.1 guidance. It can be seen that the proposed exhibition halls rates per person arc more than 30% larger than those for a conference and as such should comply with both standards. Local codes should be checked to ensure that the rates proposed here arc sufficient for vehicular access to the halls that is required during set up/take down.
Table 2: Outdoor Air Load for Exhibition Hall

             Exhibition  Conference        Units

Occupant       43.5 (4)     21.7(2)  [sqft.sup.-1]
Density                              ([sqm.sup.-1])

Outdoor air  9.37 (4.4)   5.3 (2.5)  cfm (1/s) per
per person                           person

Outdoor air  0.06 (0.3)  0.06 (0.3)  cftn/sqft (1/s)
per area                             per sqm

Total per       12(5.6)   6.6 (3.T)  cfm (1/s) per
person                               person

Total per    0.36(1.82)  0.30(1.55)  cfm/sqft (1/s per
sqm                                  sqm)


Cooling loads arc dominant in Exhibition Halls due to high internal loads. The large spaces in question will require a number of air handling units which can be divided into ODA (outdoor air) supply units and recirculation units. Dedicated ODA units with integral energy recovery systems should provide ventilation that will meet dehumidification requirements of an exhibition which allows recirculaticn systems to be de-activated when sensible gains arc low. Recirculation systems provide additional sensible cooling. During conferences and concerts recirculation units can also be operated to provide some latent cooling due lo increased load from higher occupancies. This will be accompanied by a relatively predictable rise in sensible load which will avoid tiele need for reheat in this system. Recirculation systems are likely to be simple large scale fan coil style units. The use of dedicated outdoor air systems for latent loads does also allow potential for a radiant cooling system. The ability to operate outdoor air units alone with or without heating and cooling is important for ventilating the space during sei-up when vehicle access is required without recirculation.

As flexibility is of key importance underfloor air distribution is not appropriate for Exhibition Halls as the Location of air supplies would impose restrictions on floor layouts. An over head air distribution strategy is therefore preferred. Conventional overhead strategies use diffusers to supply air and rely on momentum jets to 'throw* air into the occupied zone. The height of "exhibition halls allows an alternative solution which uses buoyancy driven flow. Low temperature air supplied at high level will descend due to negative buoyancy. This thermal syphonic system of air distribution will find the heat loads and provide an even temperature gradient throughout the hall. The driving mechanism is buoyancy; intense heat sources will create a plume of hot air which rises to high level This air is then replaced by cool air which has descended from tiig.li level maintaining comfortable conditions. With conventional mixing which relies on driving air at a heat load it is virtually impossible to deal with the variety and number of hot spots and unacceptable temperature gradients may occur.

Figure 3 showsaCFD simulation of a syphonic air distribution system in relation to a number of hot spots in a notional hall. It can be observed that temperatures around the heat loads are only around 0.56-1.1 [degrees]F (1-2 [degrees]C) warmer than the main body of the mall. Physical modeling in a thermal water bath was also used to ensure effective oneration. Cold nlumes were observed to be drawn towards a localized heat source as required as a c

[FIGURE 3 OMITTED]

The thermosyphonic system has a number of advantages:

* High level displacement air distribution systems have the benefit of being suitable for low temperature air. which can increase the cooling capacity per litre of air by up to twice that of normal air conditioning systems. Thus considerably reducing fan power. Variable volume control should be used to further reduce energy consumption.

* No need 10 reheai air after dehumidification.

* Less mechanical equipment means lower capital costs.

When fixed seating is required this solution is still appropriate as supply air is well mixed before entering the occupied zone. Heat plumes from occupants will ensure that there is a continuous turnover of air in the occupied zone maintaining a fresh environment. If the building is specifically used for conferences with permanent seating then an analysis of energy consumption to compare overhead thermal syphonic systems with underlloor displacement systems is required. The importance of mean radiant temperature in this type of space must not be forgotten, especially if the internal surfaces of the proscenium are almost entirely lined with participants unlike more conventional prosceniums where the audience may be surrounded by cooler walls.

Figure 4 shows fabric ducts which are perfect for distribution of low temperature air integrated at high level on a recent design project. Fabric should have some porosity to prevent condensation forming on the surface as air bleeds out. I f all air is supplied by porosity then the duct may eventually become blocked with dust so around 80% of the air is supplied through lower resistance nozzles.

[FIGURE 4 OMITTED]

There are also occasions when the space is used for equipment that produces an unusual amount of fumes or odours, such as restaurant or printing industry displays. It is helpful to build seme Hues into the structure to duct these fumes directly to the outside, alternatively specialised local re-circulatory systems may be imported.

It has been discussed already that due to high internal heat loads Exhibition Halls are driven by a demand for cooling. In order to reduce energy consumption it is important to establish the potential for free cooling during the design stage and specify air distribution systems accordingly. Free cooling refers to the use of outdoor air directly to purge heat from a space.

Free cooling can be investigated through consideration of the balance temperature in the following equation. This is the external temperature at which cooling provided by a particular flow rate of outdoor air is sufficient to offset heat gains in the space and maintain the required internal temperature of 75.2 [degrees] F 24 [degrees] C discussed earlier.

Balance Temperature TB = Ts - (Internal Gains)/(UA+pcv)

Figure 5 shows the variation in balance point for varying small power loads. Table 1 is used for all other loads. It is clear that in all cases the high internal loads mean that some refrigeration cooling is always likely to be required for this type of building unless internal temperatures are relaxed. This shows that for an average internal load of around 15.7btu/hr.sqft (50W'sqm) the building is self heating and requires refrigeration down to temperatures below 32 [degrees]F (0 [degrees]C). Increasing the flow rate raises the temperature at which free cooling can operate. These balance points should be considered along with weather data for a location to establish the number of hours where operation in this mode is feasible and the optimum ventilation rate for the system above minimum requirements. Consideration should be given to the additional fan power required if higher flow rates are to be used. It is also possible to use natural ventilation for free cooling which could potentially be integrated with the smoke ventilation strategy for the hall to reduce capital costs by sharing components.

[FIGURE 5 OMITTED]

SYSTEMS

Having established internal loads, comfort criteria and air distribution equipment site wide loads including those from ventilation can be established and a central plant equipment strategy established.

The plot on the left in Figure 6 shows the variation in total load for a typical exhibition centre building (sensible plus latent) for a day each month through the year. Key points to note are:

[FIGURE 6 OMITTED]

* The variation from summer to winter in this instance is in the order of 20%.

* Daily variations are around 80% in the summer and 60% in winter.

* This is when the building has a high power intensity exhibition, lower loads will cause further variation.

HVAR equipment is costly, as well as being expensive to run and maintain, especially when megawatts of healing and cooling are involved as will be the case with these Centers. The efficiency of the electrical network that supplies them with energy is also a major factor (hat must be considered. Thus should the operational HVAR equipment be selected for the peak, average or something less?

One way of dealing with (be imponderable variation in load is to utilize thermal storage both building mass (fabric) and the more traditional utilizing water and or ice. The effect of thermal storage on the cooling load is demonstrated in the profile above. Figure 6.

There are formulae that will provide the answer: a detailed analysis of the heating and cooling load is required utilizing daily, weekly and annual profiles in order to arrive at a solution that will suit a particular project. It is equally important to establish both base and peak loads.

Incorporating thermal storage into the design will also provide resilience, for when an exhibition is booked it is impossible to cancel due to the refrigeration equipment being down! The thermal storage will also provide ability to meet loads in excess of design albeit for a shorter duration.

Refrigeration including thermal storage

Selection of refrigeration system is very dependent on the anticipated load profile and geographical location but whatever system is finally selected it should incorporate thermal storage to manage the considerable variation in load as well as maximizing on the downtime on load to minimize the installed electrical capacity for refrigeration equipment, figure 6 shows the potential for ice thermal storage to reduce peak installed chiller plant to around 60% of the peak load required.

The use of thermal storage and in particular ice as the storage medium for cooling facilitates the use of high temperature differential water circulation systems and distribution low temperature air systems, both of which contribute to lower parasitic energy use and is therefore beneficial to operators.

Combined heating, cooling and power systems are also a potentially important contender for projects of this nature and can be integrated with the thermal storage systems discussed to maximize the load factor on the engine.

Electrical load profiles

Thermal energy, 'hut and cold' is now gaining currency because of the growing awareness of its potential to store electrical energy, providing flexibility and adding efficiency as well as resilience. The important part is (he interaction of the storage medium with the system, how it behaves with the pattern of (he demand and the generation, plus consideration of the input energy. All these enable electrical energy to be stored as thermal energy and a delay in its use created, IE store the heat and or coolth and then discharge it lateral a different rate. Flexible demand is about shifting the lime of use of energy rather than focusing on reducing the overall consumption. This shift in demand will ideally lead to a potentially lower carbon generation mix [7] and more efficient electrical energy supply system.

Electrical energy can be stored as thermal energy within the IIVAR system when the building is unoccupied during the night or set up to be used when required.

The smart electrical grid of the future will control these thermal stores to manage the demand on the grid and implement energy farming to maximise the utilization of renewable energy generation.

Building mass thermal storage

Building mass (fabric) thermal storage should also be considered as part of the energy story. This activates thermal mass inherent in the structure which is not usually exposed to the space. Energy stored in building fabric can be utilized for both pre-cooling and healing dependent upon location and requirement. It is possible to store approximately u\077ton'sqft (25W sqm) of energy for pre-cooling by circulating outdoor air through the structural slab at night [91. Il is also possible lo store heat from the exhibition during the day into the structural slab for healing at night and or pre heating the space for tie following day.

Currently fabric storage methods do not provide control of humidity, research into various building materials is establishing that this may be possible as most building materials can act as absorbents and adsorbents. Thus with building cycling regimes it may be possible to provide limited passive humidity control thus reducing loads on a central plant.

[FIGURE 7 OMITTED]

Renewable technologies

The discussion above focuses on energy demand reduction which is the most economical strategy for reducing environmental impact. However Exhibition Flails do lend themselves to renewable energy technologies.

Large roof areas in relation to floor areas means that solar photovoltaic energy can make a significant impact on the building energy consumption. Sites which are on the outskirts of cities may lend themselves to medium sized wind turbines which could also provide to a significant energy contribution. These contributions are a particularly large percentage of a buildings energy demand because the building is used at peak capacity for a relatively small percentage of the year while energy can be generated continuously and stored.

The above renewable technologies should be considered in conjunction with the thermal systems during design. As renewable technologies tend to be unpredictable in output due to their energy source, ie: sun, wind etc. If high solar radiation is incident when building demand is low then energy can be stored thermally. Conversely when the building is operating on a cloudy day the thermal storage can be discharged to make up for the missing solar power without increasing demand on the grid.

CASE STUDIES

Information and ideas presented here have referenced some recent Exhibition Hall design projects which are outlined below. Both buildings are shown in Figure 8.

[FIGURE 8 OMITTED]

Cairo Expo City

* 1,100,000sqft (100.000sqm) of exhibition halls, with four main halls each sub-divisible.

* The main hall is multi-purpose with facilities also to hold music concerts.

* 4.000 Seat Auditorium housed in a separate building complete with breakout spaces and ancillary facilities.

Messehalle Berlin

* 325,000sqft (30,000sqm) of Exhibition Halls, sub-divisible into 11 halls including a multipurpose hall and convention facilities for 9,000 people.

* The building includes ancillary and office administration facilities.

NOMENCLATURE

[T.sub.o]= Operative Temperature

[T.sub.a]= Air Temperature

[T.sub.r]= Radiant Temperature

ODA= Outdoor Air

[T.sub.B]= Balance Temperature

V = Air Supply

p = Air Density

C = Air Specific heat Capacity

[T.sub.s] = Space Temperature

UA = Fabric Heat Loss Constant

REFERENCES

(1.) ASHRAE Handbook Applications. Chapter 4. 2007

(2.) ASHRAE Standard 55.1

(3.) World Health Organisation: The right to healthy indoor air. Bilthoven Nederlands May 2000

(4.) ASHRAE Standard 189.1

(5.) ASHRAE Standard 62.1

(6.) C.P. Yaglou, EC. Riley and D.I. Coggins: Ventilation Requirements. ASH&VETransactions, Vol 42 1936.

(7.) Klauss, Roots and Pfaftlin: History of the changing concepts of ventilation requirements. ASHRAE Journal February 2011.

(8.) Brian Warwicker, Dan Cash: Energy Farming in the USA, 2010

(9.) B. Warwicker: New cooling for old buildings. RIBA Journal May 1995.

(10.) Brian Warwicker: Low temperature air and ice storage. CIBSE Journal February 1989.

(11.) Brian Warwicker: Low humidity air and air conditioning. CIBSE Journal November 1995

(12.) CIBSE Technical Memorandum TM 18: Ice Storage. 1994

Professor Brian Warwicker Fellow ASHRAE

Dan Cash Affiliate Member ASHRAE

Brian Warwicker was a special professor at the school for the Built Environment at Nottingham University. UK, Private consultant.

Dan Cash is a consulting engineer for Breathing Buildings Ltd.
COPYRIGHT 2012 American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2012 Gale, Cengage Learning. All rights reserved.

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Author:Warwicker, Brian; Cash, Dan
Publication:ASHRAE Transactions
Article Type:Report
Geographic Code:1USA
Date:Jan 1, 2012
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