INDOOR SWIMMING POOL INFORMATION FOR POOL MANAGERS AND OPERATORS A warm body of water, such as a swimming pool, releases enormous amounts of water vapor (and dissolved chemicals) into the air above the water. In an outside swimming pool, the water vapor and contaminants are dispersed in the atmosphere. As long as the make-up water flow rate, chemical treatment flow rate and water heater capacity are appropriate, the pool water temperature and chemistry can be maintained at design levels. Once a building encloses that body of water, things get complicated. The water vapor that escapes into the air must be removed. Adequate amounts of outside air for ventilation and contaminant control must be provided, and the building envelope must be protected from moisture migration. The inside air temperature and relative humidity and the pool(s) water temperature are all interrelated in a complex cycle of dehumidification (and heating or cooling) by the HVAC system; heating and evaporation of the pool water; and infiltration or exfiltration and condensation within the building’s walls and roof. I.
DEFINITIONS: A. Dry Bulb Temperature: The “dry bulb temperature” of air is a measure of the dry heat content of the air (also called "sensible" heat). This is what one normally thinks of as "air temperature" and is easily sensed by a human being. B.
Enthalpy: Air at the same dry bulb temperature but different moisture content has a different total energy content. The “total energy content” is called enthalpy. The more water vapor the air has, the higher its enthalpy, even though its dry bulb temperature is the same. Air that is fully saturated with water vapor (100% relative humidity) contains the maximum amount of energy possible for air at that dry bulb temperature.
C.
Relative Humidity: Relative humidity is a measure of the relative moisture content of air. Air with the same amount of moisture content has different relative humidities at different dry bulb temperatures. Given the same moisture content, air's relative humidity increases as its dry bulb temperature decreases.
D.
Specific Humidity: The total moisture content of air (regardless of its temperature) is measured by “specific humidity” (also called “absolute humidity”). Specific humidity may be measured in pounds of water vapor per pound of dry air.
E.
Dewpoint Temperature: Depending on its temperature, air at a constant specific humidity may have different relative humidities. But that air's “dewpoint temperature” is constant. The dew point temperature is therefore sometimes used to measure specific humidity. The dew point temperature is that dry bulb temperature at which air with a given specific humidity will become fully saturated. In other words, air at its dewpoint temperature is also at 100% relative humidity. Any surface in the pool enclosure building (or Natatorium), which is at a temperature less than or equal to the air’s dewpoint temperature will become wet due to condensation of the water vapor in the air.
The dewpoint temperature defines absolute humidity as well as vapor pressure of the air. F.
Vapor Pressure: Vapor pressure is the partial pressure of water vapor in the air. The higher the moisture content, the higher the vapor pressure. Like any pressure differential, vapor pressure differentials cause water vapor to flow from a location with high moisture (high vapor pressure) to low moisture (low vapor pressure). It is the vapor pressure differentials between the warm, moist Natatorium and the relatively cool, dry outside air that drives damaging moisture into the thermal envelope.
G.
II.
Saturation Vapor Pressure: A vapor pressure at (or above) the saturation vapor pressure will cause excess moisture to condense. A vapor pressure below the saturation vapor pressure will allow a material to “store” or “absorb” moisture without condensing. If the actual vapor pressure is always below the saturation vapor pressure at every point within an assembly, no condensation will occur. Water vapor will flow through the assembly without damaging it.
FACTORS AFFECTING THE RATE OF POOL EVAPORATION: A. The ideal air condition in the Natatorium is a condition that strikes the best balance between bather comfort (not guard or spectator comfort), indoor air quality, and rate of pool water evaporation. 1. In general, bathers are most comfortable at indoor air temperatures between 82º and 88º and relative humidities between 40% and 60% RH. a. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) recommends an air temperature 2ºF above the largest pool temperature (but not greater than 86º). b. See the attached information for Natatoriums, from ASHRAE’s 2011 Application Handbook (below). ASHRAE recommends a narrower space relative humidity range of 50% to 60% for other reasons, including indoor air quality and energy consumption. However higher relative humidity levels may be deleterious to building components and may indirectly affect indoor air quality by promoting mold growth. 2.
A minimum amount of outside air is required to dilute the pollutants created by chemical reactions between bathers and swimming pool water. The contaminates of interest are chloramines. Trichloramine vapor (nitrogen trichloride), is the primary pollutant that causes adverse physiological responses in humans. This compound, not chlorine itself, creates the familiar “swimming pool smell” characteristic of natatoriums. Mono- and di-chloramine pollutants primarily affect water quality. ASHRAE recommends a minimum outside air ventilation rate of 0.5 cfm/sq. ft. (pool and deck area). As much of this outside air as is possible should be introduced in the breathing zone – which is near the pool’s surface. However, air movement
across the pool’s surface also greatly increases evaporation rates. The minimum ventilation rate is a starting place for ventilation system design and may be higher or lower depending on likely occupancy, use of water features, etc. Trichloramine is a heavy gas with a density several times that of dry air, it initially accumulates in low-lying places. The lowest place in most natatoriums is the space above the water line and below the deck level – in the “breathing zone” of swimmers. Once this “bubble” of contaminated air “settles” into the below deck air, it becomes very difficult to remove. Natatorium ventilation systems should address this issue to as great an extent as possible. The rate at which trichloramine gas is produced is related to the evaporation rate of the water surface 3.
B.
C.
The rate of evaporation increases with: a. Higher pool water temperatures, b. Higher air velocity across the pool water's surface, c. Splashing or displacement of the water's surface by bathers or water features, d. Lower air dry bulb temperatures and e. Lower air relative humidities.
Each gallon of water that is evaporated from the pool surface requires: 1. A gallon of make-up water (and its associated chemical treatment), 2. Approximately 8100 BTU's of heating energy (through the pool heating water system), and 3. Additional energy to condition the air that accepts the evaporated water. Conditioning may include dehumidification, heating and/or sensible cooling as well as tempering of ventilation air. . Neglecting ventilation, a space without a pool usually requires more space heating than the same space with a pool. The evaporating pool water helps heat the space.
Excessive evaporation rates increase operating costs and put higher levels of trichloramine into the air.
III.
NATATORIUM AIR AND WATER CONDITION GOALS: A.
Water and Air Conditions In general, follow the ASHRAE guidelines: The pool water temperature should be set as low as comfortable for the majority of bathers. Generally, the largest pool in a Natatorium is used for lap swimming and competition and can appropriately be set between 78º and 80ºF. Leisure or Play pools usually have much higher temperatures. The lower the air temperature, the lower the stack effect: Consider a temperature of about 82⁰ in the space (+/-2º over
the lap pool setpoint). 1.
Suggested Air Temperature Setpoints During The Winter In general, a lower air temperature and higher space relative humidity (at the same dewpoint) are desired as the best compromise between bather comfort, pool evaporation rates and protection of the building envelope. However, relative humidity setpoints should not be reduced below 40%RH (to maintain bather comfort and minimize evaporation). In very cold climates (with very dry outside air), proper space depressurization may cause the actual relative humidity to drop below setpoint. This is acceptable for short periods of time as the resultant lower dewpoints help protect the building’s thermal envelope, even if they (temporarily) create less comfortable conditions for bathers. A higher relative humidity (at a lower temperature) is much more comfortable to a wet bather than a higher temperature (at a lower relative humidity). And, lower air temperatures decreases stack effect. An 80ºF largest area pool water setpoint, an 82F space air temperature setpoint and a 45%-55% relative humidity setpoint is usually appropriate for winter-time Natatoriums in the front range of Colorado. An average space condition of 82F and 50%RH equates to a dew point temperature of about 62ºF and will generally be comfortable to pool occupants. A slightly higher temperature setpoint and slightly higher relative humidity setpoint is recommended for roof mounted pool HVAC units (that sense air conditions at the ceiling). Their return air openings are usually higher than the occupied space and the air is usually warmer and moister at the top of the Natatorium. Actual air conditions at the pool deck may be significantly cooler and drier than at the air sensors because of the infiltration of cold, dry outside air at interior and exterior doors – especially if the natatorium is properly de-pressurized.
B.
Outside Air for Ventilation ASHRAE minimum ventilation rates (of 0.5 cfm/sq. ft. of pool & pool deck area) should be maintained. Higher ventilation rates may be required for indoor air quality, humidity control or to offset higher rates of evaporation from water features such as falls, slides, etc.
C.
Space pressurization ASHRAE also recommends that the Natatorium be maintained at a "slightly negative pressure of 0.05 to 0.15 inches of water" (to offset stack effect). In reality, even 0.05”w.c. (measured at the deck) is a very negative building pressure and is difficult
to achieve in most Natatoriums. Only a slight negative pressure differential is required to offset moisture transport via air pressure (about 0.001”w.c. at the affected area). However, this pressure difference must be provided at the highest point in the enclosure. Since stack effect varies with building height, much higher negative space pressurization will be created at the pool deck. The design winter negative space pressurization setpoint should offset anticipated “wintertime average” stack effect (or use a “re-set” control strategy). One should also remember that wind conditions may also influence space pressurization. A negative space pressure differential between -0.03 and -0.09”w.c (as measured near the pool deck) is required to maintain 0.001”w.c. at the ceiling high-point in most high-bay public natatoriums. Negative space pressurization may be re-set based on outside air temperature to save energy, minimize bather discomfort and reduce icing of the pool deck. However, this may allow hot humid air to infiltrate into the upper walls and roof assemblies. Reduced space de-pressurization is not recommended for extended periods of time. D.
Supplemental Space Heat In addition to cool drafts, the proper space pressure relationship to the outdoors may cause icing in the Natatorium where cold outside air encounters moisture. This is especially true at outside doors and windows. Windows, window frames and doors should be properly sealed to minimize this problem. Supplemental heat is often required to offset these cold drafts (and to reduce the potential for icing of the pool deck). Heating strategies that deliver heat radiantly and/or at the deck are most successful.
A Natatorium’s water treatment and heating systems must work in concert with its HVAC system and the building’s thermal envelope. Proper understanding and integration of these factors will maximize occupant health and comfort, minimize building maintenance and increase energy efficiency. Inattention to the influence these seemingly separate systems have on one another is an invitation for trouble.
Attachment: extract from 2011 ASHRAE HVAC Applications Handbook – Chapter 5, “Places of Assembly” (3 pages)
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2011 AS H RAE Handboo k- HVAC Applications
5.6 Storage areas can generally be condi tioned by ex ha ust ing excess air from the main exhibi t hall through these spaces.
NATATORIUM S Environmental Control A natatorium requires year-round humidity levels between 40 and 60"10 for comfort, reasonab le energy consumption, and building envelope protection. The designer must address the following concerns: humidity con trol. room pressure control. vent ilation requirements for air qua lity (ou tdoor and ex haust air). air distribution, duc t design. pool water chemistry. and evaporation rates. A hum id ity control system alon e will not provide satisfactory results if any of these items arc overlooked. Sec Chapter 24 of the 2008 ASHRAE Handbook- H VA C Systems (/lid Equipment for additional dehum idifier appl ication and design information.
Humidity Control People who arc wet are very sensi tive to relative humidi ty and the resultant evaporati on that occurs. Fluctuations in re lative humi dity outside the 50 to 60% range are not recommended. Susta ined levels above 60% can promote factors that reduce indoor ai r qual ity. Relative humi dity levels below 50010 significan tly increase the facili ty's energy consumption. For swimmers, 50 to 60"/0 rh limits evaporation and corresponding heat loss from the body and is comfortable without being extreme. Higher re lat ive humi di ty levels can be destructive to buildi ng components. Mo ld and mi ldew can attack wa ll, floor. and ceiling coverings, and condensation can degrade many building materials. In the worst case, the roof structure could fail because o f corrosion from water condensing on the structure.
Load Est imation Loads for a natatorium include hea t gains and losses from outdoor air, lighting. wa lls. roof. and glass. Internal latent loads are generall y from people an d evapora tion. Evaporation loads in pools and spas are signi fi ca nt relati ve to other load clements and ma y vary widely dependin g on pool features. areas of water and wet deck, water temperature, and acti vi ty level in the pool. Evaporation. The ra te of evaporation can be estimated from empiri cal Equati on ( I). This equa tion is vali d for pools at normal act ivity levels, allowi ng for splashi ng and a limi ted area of wetted deck. Other pool uses may have more or less evaporation (S mith et al. 1993).
(1 )
""here wp -
evaporation ofwater,lblh
A - area of pool surface, n2
Y - latent heat required to change water to vapor al surface waler temperature, Btullb
P.. - satW1ltion vapor pressure taken al surface water temperalure, in. Hg P. - satW1ltion pressure at room air dew poinl, in. Hg ,, - air velocity over water surface. rpm T a ble 1 Typical Na ta torium Desig n C onditions
AI,
Trpe or Pool Recreational Therapeutic Competition Diving Elderly swi mmC:11I Hotel Whi rlpooUspa
Wal ~r
Relatin Tt mperaturt, OF Ttmpt'ratu ~, OF Humidi ty, 75 t085 80 to 85 78 to 85 80 to 85 84 to 90 82 to 85 80 to 85
75 to 85 85 to 95 76 to 82 80 to 90 85 to 90 82 to 86 9710104
50 1060 50 1060 50 1060 50 to 60 50 to 60 50 to 60 50 to 60
Uni ts for the constant 95 are Btul(h · ft2·in. Hg). Un its for the constant 0.425 are Btu· minf(h· ft)· in. Hg). Equation (I) may be modified by mUl tiply ing it by an activity fac tor Fa to alter the estimatc of evaporation rate based on the leve l o f activity supported. For Yvalues o f about 1000 Btullb and Vvalues ranging from 10 to 30 fpm. Equation (I) can be reduced to
(2) The following activit y factors should be applied to the areas of specific feat ures, an d not to the entire welted area: Typtof Pool Baseline: (pool unoccupied) Residential pool Condom inium Thcrapy Hotel Public, schools Whirlpools. spas Wavc:pools. water slides
Typical Acthity Factor (F. )
0.5 0.5 0.65 0.65
0.8 1.0 1.0 l.S (minimum)
The e ffective ness of contro ll ing the natatorium environment depends on correct esti mation of water evaporation rates. Applying the correct activity factors is ex tremely important in detennining wat er evaporation rates. The difference in peak evaporalion rates between pri vate pools and act ive public pools of comparable size may be more than 100%. Actual operating tempera tures and relative humidity condi tions should be established before design. How the area will be used usua ll y dictat es design (Table I). Air temperatures in public and institutional pools are recom· mended to be maintained 2 104° F above the water tempera ture (but not above the comfon threshold of 86° F) for energy conservation through reduced evaporation and to avoid chill effects on swi mmers. Competition pools that host swim meets have two di sti nct operating profiles: ( 1) swim meets and (2) nonnal occupancy. It is recommended that both be fully modeled to evaluate the facilit y's needs. Al though swim meets tend to be infrequent, the loads duri ng meets are oft en considera bl y higher than duri ng normal opera tions. To model the swim meet load accu rat ely, it is recom mended that the designer know the nu mber of spectators, number of swi mmers on the deck, and operating conditions required d uring the meets. The operator may request a peak re lati ve hum idity of 55%, which has a significant impact on total loads. A system designed for swim mect loads should also be designed to operate for considerable portions o f the year at part loads. Water parks and water feature (s lides, spray cannons, arches, etc.) loads are not full y covered by this chapter. It is recommended that the dehumidification load generated by cach water feature be calculated individually. The water toys' manufacturers should be contacted to provide specifica tions to allow for proper load determination. Due to the concentrated nature of the loads in these facilities, it is recommended that more suppl y air and outdoor ai r be used in these faciliti es compared to. what is recommended for traditional pools.
Venti lat ion Requirements
-I.
Air Quality. Outdoor air venti lation rates prescribed by AS HRAE SfUlldard 62.1 are intended to. provide acceptable air qua lity conditions for the average pool usi ng chlorine for primary disinfec tion. The ven tilation requirement may be excessive for private pools and installations with Io.w use, and may also prove inadequate for high-occupancy public or water park installations. A ir quali ty problems in pools and spas are often caused by water quali ty problems. so simply increasing ventilation rates may prove both expens ive an d ineffec tive. Water qualit y conditions are a direct
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5.7
Places of Assembly function of pool use and the type and effectiveness of water disinfection used. Because indoor pools usua lly have high ceilings, temperature stratification and stack effect (see Chapter 16 of the 2009 ASHRAE Handbook-Fundamentals) can have a delJimental effect on indoor air quality. Careful duct layout must ensure that the space rece ives proper air changes and homogeneous air quality throughout. Some air movement at the deck and pool water level is essential to ensure acceptable air quality. Complaints from swimmers indicate that the greatest chloramine (see the section on Pool Water Chemistry) concentrat ions occur at the water surface. Children are especially vulnerable to the ill effects of chloramine inhalation. Exhaust air from pools is rich in moisture and may contain high levels of corrosive chloramine compounds. Although most codes allow pool air to be used as makeup for showers, to ilets, and locker rooms, these spaces should be provided with separate ventilation and maintained at a positive pressure wi th respect to the pool. Pool and spa areas should be maintained at a negative pressure of 0.05 to 0.15 in. of water relative to the outdoors and adjacent areas of the building to prevent chloramine odor migration. Active methods of pressure contro l may prove more effective than sta tic balancing and may be necessary where outdoor air is used as a pan of an active hum idity control strategy. Openings from the pool to other areas should be minimized and controlled. Passageways should be equi pped with doors wi th automatic closers and sweeps to inhibit migration of moisture and air. Exhaust air intake gri lles should be located as close as possible to the warmest body of water in the facility. Warmer waters and those wi th high agitation levels off gas chemicals at higher rates compared to traditional pools. This also allows body oils to become airborne. Ideally these polluta nts should be removed from close to the source before they have a chance to diffuse and negatively impact the air qua lity. Installations with intakes di rectly above whirlpools have resulted in the best air qual ity. Air Deli\'ery Rates. Most codes req ui re a minimum of six air changes per hour, except where mechanical cooling is used. This rate may prove inadequate for some occupancy and use. Where mechanical dehumidification is provided, air delivery rates should be established to maintain appropriate condi tions of temperature an d humidity. The following rates are typica ll y desired: Pools with no spectator areas Spectator areas Therapeutic pools
4 to 6 air changes per hour 6 to 8 air cha nges per hour 4 to 6 air cha nges per hour
Outdoor air delivery rates may be constant or variable, depending on design. Minimum rates, however, must provide adequate dilution of contaminants generated by pool water and must maintain acceptable ventilation for occupancy. Where a minimum outdoor air ventilation rate is established to protect against condensation in a building's structural elements, the rates are typica lly used for 100"10 outdoor air systems. These rates usually result in excessive humidity levels under most operating conditions and are generally not adequate to produce acceptable indoor air qua lity, especially in public facilities subject to heavy use. Duel Design Proper duct design and installation in a natatori um is critical. Failure to effectively deliver air where needed can result in air qua lity problems, condensation, stratification, and poor equipment performance. Ductwork that fails to deliver airflow at the pool deck and water surface, for example, can lead to air quality problems in those areas. The following duct construct ion practices apply to nata toriums: Duct materials and hardware must be resistant to chemical corrosion from the pool atmosphere. Stainless steels, even the 316 series.
are readily attacked by chlorides and are prone to pilling. They require treatment to adequately perform in a natatori um environment. Galvanized steel and aluminum sheet metal may be used for exposed duct systems. If galvanized duct is used, steps should be taken to adequately protect the metal from corrosion. It is recommended that, at a minimum, the galvanized ducts be properly prepared and painted with epoxy-based or other durable paint suitable to protect metal surfaces in a natatorium environment. Note that galvannealed ductwork is easier to weld and paint than hot-dip galvanized, but galvannealed is more susceptible to corrosion if left bare. Cenain types o ffabric duct (ainight) with appropriate grilles sewn in are also a good choice. Buried ductwork should be constructed from nonmetallic fiberglass-reinforced or PVC materials because of the more demanding environment. Gri lles, registers, and diffusers should be constructed from aluminum. They should be selected for low static pressure loss and for appropriate throws for proper air distribution. Supply air should be directed aga inst envelope surfaces prone to condensation (glass and doors). Some supply air should be direeted over the water surface to move contaminated air toward an exhaust point and control chloramines released at the water surface. However, air movement over the pool water surface must not exceed 30 fpm [as per the evaporation rate wp in Equation (1»). Return air inlets should be located to recover warm, humid air and return it to the ventilation system for treatment, to prevent supply air from shon-circuiting and to minimize recirculat ion of chloramines. Exhaust air inlets should be located to maximize capture effectiveness and minimize recirculation of chloramines. Exhausting from directly above whirlpools is also desirable. Exhaust air should be taken directly to the outdoors, through heat recovery devices where provided. Filtration should be selected 10 provide 45 to 65% efficiencies (as defined in AS HRAE Standard 52.1) and be installed in locations selected 10 prevent condensalion in the filter bank. Filter media and suppon materials should be resistant to moisture degradalion. Fiberglass duct liner should not be used. Where condensation may occur, the insulalion must be applied to the duct exterior. Ai r systems should be designed for noise levels listed in Table 42 of Chapler 48 (NC 45 10 50); however the room wall, floor, and ceiling surfaces should be evaluated for their reverberalion times and speech intelligibility. Envelope Design Glazing in exteri or walls becomes susceptible 10 condensalion when the outdoor lemperature drops below the pool room dew point. The design goal is to maintain the surface temperature of the glass and the window frames a minimum of 5F above the pool room dew point. Windows must a llow unobstructed air movement on inside surfaces, and thermal break frames should be used 10 raise the indoor temperature of the frame. Avoid recessed wi ndows and protruding window frames. Skylights are especiall y vulnerable, and require atlention to control condensation. Wall and roof vapor retarder designs should be carefully reviewed, especially at wa ll-to-wall an d wa ll-Io-roof j unclures and at window, door, skylight, an d duct penetrations. The pool enclosure must be suilable for yea r-round operation at 50 to 60% relative humidity. A vapor retarder ana lysis (as in Figure 12 in Chapler 27 of the 2009 ASHRAE Handbook-Fundamentals) should be prepared. Failure to install an effective vapor reta rder will result in condensation forming in the structure, and pOlentially serious envelope damage. Pool \Valer Chemistry Failure to mai ntain proper chemistry in the pool wate r causes serious air quali lY problems and deterioration of mechanical systems and building components. Wate r treatment equipment
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5.8 and chem icals should be located in a separate, dedicated, wellventilated space that is under negative pressure. Pool water treatment consists or pri mary disinrection, pH control, water filtration and purging, and water heating. For rurther inronnation, rerer to Kowalsky (1990). Air quality problems are usually caused by the reaction or chlorine wi th biological wastes, and particularly with ammonia, which is a by-prod uct orthe breakdown or urine and perspiration. Chlorine reacts with these wastes, creating chloramines (monochloramine, dichloramine, and ni trogen trichloride) that are commonly measured as combined chlorine. Adding chemicals to pool water increases total contaminant levels. In high-occupancy pools, water contaminant levels can double in a single day or operation. Chlorine's efficiency at reducing ammonia is affected by several ractors, including water temperature, water pH, total chlorine concentration, and level or dissolved solids in the water. Because or thei r higher operating temperature and higher ratio or occupancy per uni t water vol ume, spas produce greater quantities or air contaminants than pools. The ro llowing measures have demonstrated a potential to reduce chloramine concentrations in the air and water: Ozonation. [n low concentrations, ozone has substantially reduced the concentration or combined chlorine in the water. [n high concentrations, ozone can replace chlorine as the primary disinrection process; however, ozone is unable to mai ntain sufficient residual levels in the water to maintain a latent biocidal effect. This necessitates mai ntenance or chlorine as a residual process at concentrations oro.s to 1.5 ppm. Water Exchange Rates. High concentrations or dissolved solids in water have been shown to directly contribute to high combined chlorine (chloramine) levels. Adequate water exchange rates are necessary to prevent the buildup or bio[ogical wastes and their oxidized components in pool and spa water. Conductivity measurement is an effective method to control the exchange rate or water in pools and spas to effectively maintain water qual ity and minimize water use. In high-occupancy pools, heat recovery may prove useru[ in red ucing water heating energy requirements.
Energy Considerations Natatoriums can be a major energy burden on raci lities, so they represent a significant opponunity ror energy conservation and recovery. ASHRAE Standard 90. [ offers some recommendations. Several design solutions are possible using both dehumidification and ventilation strategies. When evaluating a system, the seasonal space conditions and energy consumed by all elements should be considered, including primary heating and cooling systems, ran motors, water heaters, and pumps. Operating conditions ractor significantly in the total energy requirements or a nata tori um. Although occupant comrort is a primary concern, the impact or low space temperatures and relative humidity levels below 50% (especially in winter) should be discussed with the owner/operator. Reductions in either room air temperature or relative humidity increase evaporation rrom the pools, thus increasing the dehumidification requirements and increasing pool water heating costs. Natatoriums with fixed outdoor air ventilation rates without dehumidification generall y ha ve seasonally fluctuating space temperature and humidity leve[s. Systems designed to provide minimum ventilation rates without dehumidification are unable to mai ntain relative humidity condi tions within prescribed limits. These systems may racilita te mold and mi ldew growth and may be unable to provide acceptable indoor air quality. Peak dehumidification loads vary with activity levels and duri ng the cooling season when ventilation air becomes an addi tional dehumidification load to the space.
2011 ASH.RAE Handbook- HV AC Applications FAlRS AND OTIIER TEMPORARY EXHIBITS Occasionally, large-scale exhibits are constructed to stimulate business, present new ideas, and provide cultural exchanges. Fairs or this type ta ke years to construct, are open rrom several months to several years, and are sometimes designed considering ruture use or some buildings. Fairs, carnival s, or exhibits, which may consist or prerabricated shelters and tents that are moved rrom place to place and remain in a given location ror only a rew days or weeks, are not covered here because they seldom req ui re the involvement orarchitects and engineers.
Design Concepts One consultant or agency should be responsible ror selling unironn utility service regulations and practices to ensure proper organization and operation or all exhi bits. Exhi bits that are open onl y during spring or rail months require a much smaller heating or cooling plant than those open during peak summer or wi nter months. This inronnation is required in the earliest planning stages so that system and space requirements can be properly analyzed.
Occupancy Fair buildings have heavy occupancy during visiting hours, but patrons seldom stay in anyone building ror a long period. The length or time that patrons stay in a bui lding detennines the airconditioning design. The shorter the anticipated stay, the greater the leeway in designi ng ror less-than-optimum comrort, equi pment, and duct layout. Also, whether patrons wear coats and jackets while in the building influences operating design conditions.
Equipment and Maintenance Heating and cool ing equipment used solely ror mai ntaini ng comrort and not ror exhibit purposes may be secondhand or leased, ir available and or the proper capacity. Another possibility is to rent the air-conditioning equi pment to reduce the capital investment and eliminate disposal problems when the rai r is over. Depending on the size or the rair, length or operation time, types or exhibitors, and rair sponsors' policies, it may be desirable to analyze the potential ror a centralized heating and cool ing plant versus individual plants ror each exhibit. The proportionate cost or a central plant to each exhibitor, including utility and maintenance costs, may be considerably less than having to rurnish space and plant utility and maintenance costs. The larger the rair, the more savings may result. [t may be practical to make the plant a showcase, suitable ror exhibit and possibly added revenue. A central plant may also ronn the nucleus ror commercial or industrial development orthe area after the rair is over. Ir exhibitors rurnish their own air-conditioning plants, it is ad visable to anal yze shortcuts that may be taken to reduce equipment space and maintenance aids. For a 6-month to 2-year maximum operating period, ror example, tube pull or equipment removal space is not needed or may be drastically reduced. Higher ran and pump motor power and smal ler equipment are pennissible to save on initial costs. Ductwork and piping costs should be kept as low as possible because these are usually the most difficult items to sal vage; cheaper materials may be substi tu ted wherever possible. The job must be thoroughl y analyzed to eliminate all unnecessary items and reduce all others to bare essentials. The central plant may be designed ror short-term use as well. However, ir it is to be used after the rair closes, the central plant should be designed in accordance with the best practice ror [onglire plants. It is difficult to detennine how much or the piping distribu tion system can be used effectively ror permanent installations. For that reason, piping should be simply designed initially, prererably in a grid, loop, or modular layout, so that ruture additions can be made easily and economically.
