A Guide to an Integrated HVAC System Design for the 21st Century Natatorium

A Guide to an Integrated HVAC System Design for the 21st Century Natatorium

Foreword

Desert Aire has written this document to provide owners,mechanical contractors and engineers with a helpful guideto designing or retrofitting an indoor pool facility.

Just in the past few years there has been a major break-through in understanding the complexity of maintainingthe indoor air quality of a pool facility. is guide tries totie together the many independent elements of a very complexHVAC system, building structure, water loop, facilityprogramming and energy consumption. For too long theseelements were designed independently and rarely was aneffort made to integrate them to create the best indoor poolfor all stakeholders.

It is our expectation that this guide will assist in developingthe dialog to solve problems in existing designs as well asserve as the benchmark for new construction. e guidewill also refer to other documents or industry knowledgeto support creation of final design specifications and theconstruction document.

This guide will be a living document so we welcome theopportunity to receive your feedback on innovations andinnovative thinking that can help produce the highestquality indoor pool facility. Feel free to reach out to anyDesert Aire sales representative or staff member with yourfeedback.

Keith CoursinPresidentDesert Aire Corp.Keith@desert-aire.com

Contents

Overview ..................................................................... 3• e Purpose of the Natatorium• e Goals of HVAC Design

Heating, Cooling and Moisture Load Determination ............................................................ 4

• Air and water temperatures• Relative humidity• Airflow across water• Activity factor• Spectator load• Ventilation load

Condensation and Building Integrity .................... 7• Dew point control• Vapor barrier• Negative pressure• Spectator areas

Swimmer Health Concerns ....................................... 11• Toxic air • Most common airborne contaminants• Source capture solution• Pool chemical usage• Chlorine• Chlorine alternatives• Salt water pools

Proper Airflow Design .............................................. 13• Duct design• Supply air rate

Dehumidification Equipment DesignConsiderations ............................................................ 15

• Dehumidifier system components• Dehumidifier design options • Economizers• Purge mode• Maximizing energy recovery• Integrated with source capture• Low exhaust energy recovery• Installation considerations

Commissioning ........................................................... 22• Factory certified start-up• Facility staff training

Conclusions .................................................................. 22

Overview

The Purpose of the Natatorium

e natatorium is a building that contains one or moreaquatic venues and structures where the general public isexposed to water intended for recreational or therapeutic use.

Although we most oen think of aquatic venues as indoorpool facilities for swimming and diving, they may not onlycontain standing water. The term can be used to describeindoor water parks where the public is exposed to water bycontact or spraying, such as with waterslide landing poolsand spray pads.

A natatorium can be housed in a dedicated building or non-dedicated building such as a school building or fitness club.e natatorium may also house locker rooms, lavatories andoffices. Locker rooms, staff offices and storage rooms shouldnot be part of the pool room mechanical HVAC system.

is design guide focuses on larger natatoriums and aquaticcenters but many of the concepts would apply to smallercommercial and residential indoor pool facilities.

The Goals of HVAC Design

e many ways people use buildings with enclosed pools forrecreational, competitive and health purposes continue toevolve. ese uses place demands on HVAC systems and on thebuildings themselves that weren’t present even a generationago. Fortunately, there are advances in knowledge, under-standing, strategies and technology that meet the challengesof today’s natatorium.

Reflecting the depth and breadth of demands, the scope ofHVAC design considerations for large natatoriums andaquatic centers has expanded in the 21st Century.

Objectives now include protecting the health of swimmers,divers, coaches and spectators; promoting the long-termstructural integrity of the building and supporting systems;and conserving energy, water and water treatment resources.

But there is a guiding principle that applies to HVAC systemdesign no matter the purpose, size and location of thenatatorium: the HVAC system must work in harmony withsystems that control water temperature and water quality.

For engineers who must translate these objectives intodesign goals an integrated, sustainable approach is required.These design goals must reconcile the intensive tasks ofdehumidifying the space, heating and cooling the interior,heating pool water, and meeting outdoor air requirements.

Fortunately, today’s design engineers have access to a rangeof problem-solving equipment technologies and strategies.ese technologies and strategies complement resourcesmade available by professional associations and engineeringsocieties; and the goals manifest in building codes andstandards. For example, the American Society of Heating,Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE)provides guidance and resources for pool room design.

e Model Aquatic Health Code (MAHC), published by theCenters for Disease Control and Prevention (CDC), is amore recent addition to the resources available to mechanicalengineers.

First published in late 2014, the MAHC is a set of guidelinesfor public aquatic facilities. According to the CDC, theMAHC “brings together the latest knowledge based onscience and best practices to help state and local governmentofficials develop pool codes. Pool codes are specific rules thatdesigners, builders, and managers of spas, pools, waterparks,and interactive fountains must follow to keep the fun goingand reduce injuries and illnesses.”

A Guide to an Integrated HVAC System Design for the 21st Century Natatorium

A Guide to an Integrated HVAC System Design for the 21st Century Natatorium

3

e MAHC encompasses traditional aquatic venues such asthose enclosing swimming pools and spas. e MAHC alsocovers contemporary water-containing structures includingwave pools, surf pools, therapy pools and spray pads.

As part of bringing together the best knowledge and practices,the MAHC states the design, construction and installationof indoor aquatic facility air handling systems shall complywith local codes as well as the proven ASHRAE standard62.1 2013, Ventilation for Acceptable Indoor Air Quality.

Together, this matrix of technologies and strategies providesmechanical engineers with essential tools for balancingdiverse operating conditions, seasonal variations and specialevent needs with building codes and standards for theongoing, critical concerns of indoor air quality and relativehumidity.

Heating, Cooling and Moisture

Load Determination

e heating, cooling and moisture loads of a natatorium area product of seasonal variations in outdoor air temperatureand humidity, solar gains and losses as well as the presenceof spectators and bleacher areas.

• The heating load is the amount ofheat energy that must be added to thenatatorium to achieve or maintain atarget temperature level. This is oftenconsidered the heat loss calculation andis a dominant factor due to the highinternal design temperature of an indoorpool area.

• The cooling load is the amount of heatenergy that needs to be removed toattain the target temperature. is is theheat gain calculation with solar gain andlighting heat being the most significantportions of this load.

• e moisture load is the amount of moisture that needsto be removed to attain a target relative humidity level.The moisture load has three components: evaporationfrom the water surface; moisture content from theventilation air; and evaporation from spectators.

To calculate heating, cooling and moisture loads to specify andsize HVAC equipment, these loads are expressed as sensibleand latent. Sensible heat and loads are the heat swimmersand building users feel on their bodies and are temperaturesthat can be measured by a thermometer. Latent heat andloads are the energy and heat stored in humidity, a productof its change in state from liquid to gaseous. These twocomponents when combined provide the total system ratingthat the HVAC equipment must be designed to remove.

e overarching goal in managing heating, cooling andmoisture loads is sustainability: ensuring the natatorium cancontinue to fulfill the purposes for which it was built ina safe and cost-effective manner. Related HVAC designconsiderations, as stated earlier, are protecting the health ofswimmers, divers, coaches and spectators; promoting thelong-term structural integrity of the building and supportingsystems; and conserving energy, water and water treatmentresources.

e ASHRAE Applications Handbook provides formulas forcalculating the natatorium moisture load. e factors thatare used in those formulas include the air and water temper-atures, relative humidity, airflow rate across the water, activityfactor, spectator load, and the ventilation load. Each of thosewill be discussed below.

Figure 1. A pool room with an overwhelmed HVAC system.

A pool room that does not maintain the proper temperatureof its air and pool water along with setting the correct relativehumidity range can quickly overwhelm even the best HVACequipment.

4

Relative Humidity

As the equipment centerpiece of natatorium HVAC systems,the dehumidifier controls humidity in pool enclosuresto counter what is created by evaporation, regardless ofoutdoor conditions. is improves indoor air quality andthe comfort of swimmers and occupants. Humidity controlalso protects building structural elements, furnishings, andsupport systems such as lighting.

ASHRAE recommends that the relative humidity in anatatorium be maintained between 50% to 60% relativehumidity. Lower relative humidity increases operation costsdue to increased evaporation and it can lead to swimmerdiscomfort due to evaporative cooling from their bodieswhen exiting the pool. Higher relative humidity increasesthe risk to the building structure.

Airflow Across Water

One of the recent changes in natatorium design is movingaway from designing ductwork to have grilles aimed at thepool water surface. It is now recommended that air be pulledacross the pool water surface at less than 30 feet per minute.All of the air supply should be aimed at exterior walls andwindows and not at the pool. The reasons for this arediscussed in the Source Capture Solution section of this guide.

The ASHRAE formula for the evaporation load of a poolassumes that the air will not exceed 30 fpm. Using the samepool as mentioned above (3,500 sq. . at 82⁰F water and 84⁰Fair) and increasing the airflow across the pool water from 30fpm to 125 fpm will increase the evaporative load by 40%.If the design engineer for that pool uses the standardASHRAE formula for computing the evaporative load buthas air supplied directly across the pool surface, then the dehumidification equipment selected will most likely besubstantially under designed.

Air and Water Temperatures

ere are many combinations of air and water temperaturesbeing utilized in pool facilities and no one condition is morecorrect than the other. erefore the owner must make adecision on what air and water setpoints they will use intheir facility as this will be a key factor in dehumidifier selection. Changing design conditions after the HVACsystems are installed may not be possible.

ASHRAE recommends maintaining the natatorium airtemperature at two to four degrees above the pool watertemperature but not above the comfort threshold of 86⁰F.ere are several reasons for this recommendation. is isan effort to create a design condition that seeks a balance inthe overall dehumidifier sizing and the energy costs associatedwith maintaining the conditions in the space and pool water.In addition, the warmer air temperature will help make theswimmers not feel as cold when leaving a pool.

However, recent changes in the average water temperatureof an indoor pool can make it difficult to maintain the airtemperature higher than the pool water temperature. Ananalysis of commercial pools found that the average poolwater temperature had increased from 82⁰F to 86⁰F between2003 and 2013 due to the prevalence of swim lessons servingthose 10-years-old and younger and vertical swim classes forsenior citizens; both of these swimmer groups desire warmerwater temperatures than recreational or competitive swimmers.

It is very important when designing a dehumidificationsystem for a new or remodeled facility that the pool ownercommunicates to the engineer the desired operating setpoints. Similarly, it is important the engineer communicateto the pool operator the importance of maintaining conditionsin the natatorium and adhering to design set points.

A 3,500 square foot natatorium, designed for 82⁰F poolwater temperature and 84⁰F air temperature will havean evaporation rate of approximately 159 lbs/hr at 55%relative humidity. Raising the water temperature to 86⁰Fand keeping all other factors the same will increase theevaporation rate by 33% to 211 lbs/hr. e dehumidificationsystem designed for the lower water temperature will nowbe significantly undersized to handle the larger load of thewarmer pool water. As mentioned earlier, communicationbetween the engineer and the pool operator is essential whendesigning for a specific evaporative load.

5

be introduced into the indoor pool enclosure. e standardexists to protect the health of natatorium users.

is volume is generally only a small percentage of the totalair volume required by a dehumidification system to maintainthe space humidity. Proper interpretation can also enhanceenergy conservation by reducing the volume of outdoor airrequired to the minimum required by code.

ASHRAE 62.1, table 6.1 provides the following levels ofoutdoor air to the breathing zones listed below.

• Pool & wet deck outdoor airflow Pool and wet deck area (²) x 0.48 (cfm)/(²)

• Remaining floor area outdoor airflow Room (²) – Pool & wet deck (²) – Bleacher (²) x 0.06 (cfm)/(²)

• Spectator/Bleacher outdoor airflow Spectator area (²) x 0.06 (cfm)/(²) + (# of spectators) x 7.5 (cfm)

e interpretation of “wet deck” is sometimes difficult.ASHRAE defines the wet deck as the deck area that becomeswetted during a normal occupied condition. e acceptedpractice is to define the wet deck for a pool as a definedperimeter around the body of water.

Ventilation may be regulated based upon occupancy toestablish an expanded range and sequence of operation thatmaintains acceptable indoor air quality. When the facility isunoccupied, outdoor airflow may be closed. During normaloperation, outdoor airflow can be set to a minimumcode-approved level. When a swim meet creates higher-than-normal occupancy an increased outdoor airflow maybe engaged.

As a means of ensuring indoor air quality and providingfor system accuracy and flexibility, a Volatile OrganicCompound (VOC) sensor should be installed as part of theventilation control system. VOCs can build up in a pool roomthat has become busy in a short amount of time and foran extended period. The VOC sensor ca n overrideprogrammed setpoints that don’t reflect current conditionsand call for the ventilation system to increase outdoor andexhaust airflow.

Activity Factor

Another factor in the formula for finding the natatoriumevaporative load that an engineer needs to consider is thepool usage. e ASHRAE formula gives an activity factorbased on the type of pool, ranging from an unoccupiedbaseline for any pool of 0.5 up to an activity factor of 2 orgreater for a water park. Different activity factors are givenfor condominiums, therapy pools, hotels, public pools, spas,and water parks. Underestimating the activity factor canhave substantial consequences. A public pool, school, orYMCA has an activity factor of 1. By adding water featuressuch as a wavepool or waterslide the evaporative load forthat pool can double.

It is very important for the architect, engineer, and pooloperator to discuss any water features that might be addedto a public pool that is not considered to be a water park.Any remodeling of an existing pool must take into accountthe capacity of the present dehumidification equipmentbefore adding water features.

Spectator Load

Spectators are not the swimmers using the pool or the pooldeck, but rather the fully clothed observers in a separatearea. For spectator areas an additional amount of airflowneeds to be introduced, when spectators are present,to enhance their comfort and the quality of air around them.ASHRAE recommends an airflow rate of between 6 to 8 airchanges per hour over the spectator area. e evaporativeload of the spectators must also be taken into considerationwhen calculating the total load. Swimmers are not consideredas part of the spectator load.

Ventilation Load

e local building ventilation code protects public healthand safety by providing minimum safeguards and standardsfor ventilation. Most codes have a set amount of outdoor airthat must be brought into the pool area with factors basedon the pool surface area, the swimmer drip area, andspectator areas.

Most local codes are based on ASHRAE Standard 62.1, theindustry accepted ventilation code for indoor air quality,which defines the minimum volume of outdoor air to

6

We will be discussing in the duct design section the properamount of airflow that is necessary to prevent condensationbut it is important that all external areas be completelywashed with airflow. In the photo o n the following page(Figure 3) you can see that the lower areas of the windowsdid not receive adequate airflow and are fogged; while theupper areas did receive the proper airflow and they are clear.is was solely an issue of air distribution and not dehumid-ifier operation. is is an area where the engineer mustcommunicate with the architect. Whenever there are largeglass areas there must be adequate air distribution to keepthese surfaces above dew point to prevent condensation inwinter months.

Condensation and

Building Integrity

While the design of the building does not fall under theresponsibility of the mechanical engineer, it is a key HVACsystem component. e engineer and the architect must bein communication on construction materials that will influencethe size and capacity of the HVAC system through the heatgain and heat loss of the structure; the location of the vaporbarriers; the quality and quantity of the doors and windowsin the natatorium; and, controlling humidity within theentire structure with proper vapor barriers. Nowhere is thiscommunication more important than the area of condensationand building integrity.

75

70

65

60

55

50

45

40

Dew

Point

Tem

pera

ture

°F

30% RH 40% RH 50% RH 60% RHPercent Humidity

Condensation Dew Point

Space Temp.

Figure 2. Condensation dew point for a natatorium.

Dew point control

All external walls, windows, and doors must be kept abovethe dew point in order to prevent condensation. Condensationcontrol is essential to maintaining building integrity. As canbe seen in the graph above (Figure 2), the dew point for anatatorium is fairly high. That means any surface that hasa temperature below the natatorium dew point will seecondensation form.

Over time, if condensation is allowed to form, the acidiccontent of the condensation can destroy key buildingfeatures such as doors, windows, fixtures and, in the worst-case scenario, can destroy a building.

7

Figure 3. Examples of condensation and poor air distribution.

Vapor Barrier

A vapor barrier is a material or film thatprevents moisture migration or penetration.Moisture will travel from high moisturecontent air to low moisture content air. Innon-pool room building designs, the vaporbarrier is located on the outside of the building’sinsulation. Location is dependent upon yourgeographical location but in general the vaporbarrier should be placed on the side where thehighest moisture is present. Because of the highmoisture load insid e a pool room, the vaporbarrier is required to be on the inside of thestructure in all North American locations.

Figure 4 shows white chalking on the outside ofthe brick building. e white chalking iscaused by moisture from the pool room pene-trating the brick, a result of having no vaporbarrier installed on the inside of the wallstructure.

If the facility is in a cold climate and thetemperature outside is below freezing and aproper vapor barrier is not installed, moisturewill condense inside the wall cavity. Once conden-sation occurs inside the wal l cavity theremaining insulation value is lost and theproblem will get worse. Condensation inside awall cavity may also prompt decay or mold to thebuilding structure.

Figure 4. Example of natatorium without vapor barrier

showing white chalking on building exterior.

8

Similarly, all windows and doors need to have a very tightseal to prevent moisture migration. e photo below (Figure5) shows a facility that did not seal the wall to roof interface.Higher moisture content pool room air migrated to the roofand building envelope, condensed into water and then froze,forming icicles.

Moisture does not have to travel only to the outside of thebuilding to cause damage. Adjacent interior rooms, suchas offices, are typically maintained at 75ºF and approximately40% RH. Because this air has a lower moisture content, themoist air in the pool room will travel to these interior rooms.All pool room partitions needan appropriate vapor barrier ormoisture damage will happenbetween the walls.

Negative Pressure

Natatoriums should be main-tained at a negative air pressure(0.05 to 0.15 in. of water) relativeto the outdoors and adjacentareas of the building to preventthe forming of condensation inthe wall and ceiling interstitialspaces; and to prevent the dispersalof chloramines, other noxiousfumes and moisture to otheroccupied spaces in the building.e space pressurization schememust be maintained during everyhour of the year and for all possibleoperating conditions.

To maintain the favorable negative air pre ssure, HVAC systemsuse static and active methods of pressure control to providethe correct proportions of return air and outdoor air.

Static methods employ pressure sensors to measure airflows(differential pressure) across HVAC system components. Forexample, a dehumidifier’s evaporator coil, exhaust blowerand reheat coil. Dampers respond to the measurementsthrough an automated control system, opening or closing todeliver the correct amount of air to the equipment or space.

One active method of pressure control that meshes well withautomatic control systems, as well as energy efficiency

Figure 5. Example of natatorium with improper seals

showing moisture migration and icicle formation.

systems for worst-case scenarios, low exhaust systems maybeoversized or running constantly if not modulated. On theother hand, if sensors measure an air pressure or air con-taminant level that is not within the tolerances for properindoor air quality, the VFDs can increase the exhaust volumein concert with dampers.

To promote the negative pressurization function of theHVAC system, the natatorium must be separated fromadjacent spaces by effective partitions and air barriers. eseinclude tightly gasketed doors and sealed cracks in theframes of doors and windows.

9

objectives, is using either a Variable Frequency Drive (VFD)or an Electronically Commutated Motor (ECM) for the exhaust air stream. This may be installed in new or retrofitinstallations. VFDs and ECMs reduce or increase the speed of the fan to match the load and real-time needs of thenatatorium’s negative pressure requirements. ey willspeed up or slow down the exhaust air to maintain thedesired negative pressure.

VFDs and ECMs also deliver pressure control benefits ifinstalled as part of chloramine low exhaust systems. Becausemechanical engineers must specify HVAC equipment and

e ASHRAE 62 ventilation standard also requiresthat HVAC systems introduce additional outdoorair into the space during spectator events. As notedearlier, the standard requires a ventilation air volumeof 0.06 cfm/2 for the dedicated spectator areaplus 7.5 cfm per spectator during times whenspectators are present. is is in addition to theventilation rate for the pool and wet deck.

In event modes, HVAC systems and equipmentincrease outdoor air volumes as a percentage of airsupplied to the space. e dehumidifier’s ventilationdamper will open to a greater position to introducethe required amount of event air. The exhaustsystem will then respond to maintain the propernegative pressure setpoint. is is a higher rate thanthe occupied mode setting, providing the requiredvolume for pool plus spectators. HVAC equipmentsuch as dehumidifiers can increase the amount offresh and exhaust air by rebalancing dampers andexhaust fans.

Because spectator occupancy is not constant inmost facilities, the scheduling programs of buildingmanagement systems can reduce the energy costsrelated to conditioning spectator areas.

To increase the comfort of fully clothed spectators manybuilding owners and HVAC engineers choose to separate thespectator load by using dedicated outdoor air systems(DOAS) that flush spectators with clean, fresh air. ese canbe designed to supply an air temperature that is approxi-mately two degrees less than air supplied to the pool space.

A DOAS allows for independent control of temperature andduct placement. is independence can reduce energy costscompared to HVAC systems that would serve combinedpool and spectator areas. When spectators are not presentthe DOAS recirculates air to provide dehumidification of airwithin spectator areas.

10

Figure 6. Building pressurization.

Locker rooms, dressing rooms and food preparation spacesalso need to be maintained at negative pressures with respectto their adjacent spaces, but they must be positive relative tothe pool space. Chemical storage areas however, need tohave negative pressures with respect to the pool space andall other spaces. Chemical storage areas must also have theirown exhaust systems to prevent moisture and airbornechemicals from coming into contact with each other.

Spectator Areas

Natatoriums and aquatic centers with spectator areasrequire multi-level strategies from mechanical engineers andtheir HVAC systems. Spectators may not be present at alltimes when the building is being used by swimmers. If aswim meet brings in spectators, loads increase. Spectators canimpact the temperature of the space and create additionalinternal moisture through breathing and perspiration.

In fact, the chemical smell results from the interaction ofthe chlorine disinfectants with perspiration, urine, oilsand organic materials from swimmers. Chloramines arechemical compounds formed from the reaction of chlorinedisinfectants with the ammonia in perspiration and sweat.When there is a pool smell present or swimmers getreddened, bloodshot eyes, there is actually not enoughchlorine present.

Figure 7. Dedicated Outdoor

Air System (DOAS) for spectator area.

Swimmer Health Concerns

Toxic Air

In natatoriums, the presence of “pool smell” or chlorineodors is oen confused with the use of chlorine disinfectantsadded to pool water to destroy germs that can give swimmersdiarrhea, earaches and athlete's foot. When the smell buildsup and accumulates at the pool or deck level, it can irritatethe eyes, lungs and skin of swimmers and occupants. echemicals that are associated with these smells have a toxicityfactor and should be removed in a manner that does notcause more swimmer discomfort or a higher evaporative load.

Outdoor Air

Supply Air

Return Air

DOAS

Return Air

11

ere are three chloramine by-products of the disinfectionprocess. Monochloramines and dichloramines are predom-inately waterborne and can be removed by ultraviolet (UV)and other sanitation systems. Trichloramine, which is alsoknown as nitrogen trichloride, becomes almost instanta-neously airborne and does not stay in the water long enoughto reach the UV or surge tank protection systems. Since it isapproximately four times heavier than air it stays at the poolsurface and is then inhaled by swimmers moving throughthe water.

Most Common Airborne Contaminants

e top four airborne disinfection byproducts are listed below.

• Nitrogen trichloride

• Cyanogen chloride

• Trihalomethane

• Hydrogen cyanide

e way these byproducts move from the pool water to theair is through a process similar to evaporation. If the air hasa lower concentration of the byproduct than the water (lowerpartial pressure), then it migrates from the water to the air.As noted earlier, traditional chemical treatment systems donot remove these byproducts from the water.

Source Capture Solution

Source capture strategies and technologies have evolved towhere they can assist in removing the byproducts from thefacility, improving the quality of the air and water. eyshould be used in any natatorium designed to hold a largenumber of swimmers or swimmers who will be in the waterfor long periods of time.

These source capture strategies employ bench, drain orwall-mounted systems positioned along the sides and decksof pools. They work in concert with code-mandated ductdesigns and ventilation standards that deliver supply air. esupply air is pulled over the water surface at a rate not toexceed 30 fpm so that contaminated air is moved toward alow exhaust point, in this case the source capture systems.e contaminated air is exhausted directly outdoors.

ese low exhaust source capture strategies minimize andprevent the recirculation of chloramines and other airbornepollutants, helping maintain the quality of supply air to the breathing zone in the pool and deck area. The absenceof chloramines and corrosive pollutants also helps protectnatatorium equipment and other HVAC system components.

Pool Chemical Usage

a. Chlorine

e question is oen asked as to why chlorine is used if theoff-gassing is so bad for humans. e answer is simple: thegood far outweighs the bad. Chlorine is put in the water tokill microorganisms and bacteria. If done properly, it doesan excellent job. e chlorine in the pool water breaks downinto hypochlorous acid and hypochlorite ions. Both willinstantaneously attack and kill any microorganism or bacteriathey come in contact with by attacking the lipids in their cellwalls. is is the positive outcome of putting chlorine in poolwater.

However, chlorine also reacts with sweat, skin cells, urine,and other organic compounds found in water to create thedisinfectant by-products such as trichloramine andcyanogen chloride. It is these airborne by-products that canbe hazardous to one’s health if not removed properly.

b. Chlorine alternatives

There are alternatives to using chlorine as the primarysanitizer in a pool, if local codes allow. Bromine is the secondmost used disinfectant. Bromine can be as effective aschlorine in killing bacteria although the dosage has to behigher. In addition, bromine is a less powerful oxidizer thanchlorine and thus is not as effective as chlorine in eliminatingswimmer waste products. For this reason, oxidizers such asmonopersulfate are oen used in conjunction with bromineand can be more expensive in large pools.

12

c. Salt water pools

Salt water pools have become popular among swimmersbecause of the soer feel of the water. It can be popular withpool operators because salt is safer to store than chlorine.

However, a common misperception is that this is a chlorinefree environment. e reality is that a salt water pool is alsoa chlorine pool. e salt system works by sending pool waterthrough a salt cell with metal plates. ese plates receive anelectrical charge and the electrolysis produces chlorine. Asthe water returns to the pool it will now have chlorine andhypochlorous acid in it, the same as in a regular chlorinatedpool although the concentrations may be less.

e design engineer and pool operator must use cautionwith a salt water pool since the salt in the water can conductlow level electrical current that can cause a galvanic reactionif separate metal components are not on the same earthground connection.

If a pool water condenser is being specified for a dehumidifierserving a salt water pool then it should also be specified thatthe water condenser’s inlet and outlet connections are wiredback to the electrical box to connect to the common earthground.

Proper Airflow Design

e Overview section of this guide noted how natatoriumsand aquatic centers create a challenging application environmentfor air handling systems. ese systems must move significantvolumes of air to control temperature, humidity and pressure.The speed of airflow created, location of ductwork thatdelivers the airflow, and nature of construction materialsalso play roles in providing acceptable indoor air quality forswimmers; and protecting the building and its equipment.

e designer can use either fabric duct or metal to meet theobjectives of proper air distribution. Each has its own meritsand comes down to personal preferences.

The American National Standards Institute (ANSI) hasaccredited the Sheet Metal and Air Conditioning ContractorsNational Association (SMACNA) as the lead standards-setting organization for HVAC duct design and construction.

The SMACNA standards for duct systems address ductconstruction and installation, indoor air quality and energyrecovery. HVAC Duct Construction Standards - Metal andFlexible is the third and current edition recommended foruse by design professionals as well as the HVAC SystemsDuct Design, 4th edition.

Duct design

Supply air ductwork should form a “U” around three sidesof the pool. is provides for airflow that travels across or“washes” windows and outside walls with dry supply air. eductwork configuration also raises the temperature of theinside surface while flushing it with the lowest dew point airin the facility. e duct size and dimensions should followthe SMACNA design standards or the design guidelinesprovided by the fabric duct manufacturers.

As noted in the condensation section, proper airflow onexterior walls, windows, and doors eliminates or minimizescondensation that can be caused by the high humidity andhigh temperature levels of an indoor pool facility coming incontact with a cold surface. Depending on the window andwall surface area, the flow of dry supply air is set at 3 to 5cfm per sq. .

HVAC engineers locate return air and exhaust air grilles onthe fourth side or wall of natatoriums. High and mediumheight grill locations work best for the return air. e higherlocations optimize the recovery of the higher temperatureand humidity containing air since hot, humid air rises.This also keeps the air returns f rom being blocked by poolfurniture and spectator stands. High returns should be asclose to the ceiling as possible; medium returns 6 to 8 feetabove the pool deck and spectator levels.

is combination of the "U" shaped supply air and fourthwall return air provides the best solution to utilize a sourcecapture exhaust air technique (see Figures 8 and 9).

13

Figure 9. Plan view of duct design.

High & MediumReturn Air

Low Source Capture Exhaust

Supply Air

Supply Air

HighReturn

Medium HeightReturn

Low Source Capture Exhaust

ExhaustOutdoor Air

Figure 8. Top view of duct design.

14

Dehumidification Equipment

Design Considerations

Dehumidifier system components

At a minimum, the natatorium dehumidifier is an air handlersized to remove the moisture in a natatorium at a rate equalto the evaporation rate of the pool water plus (or minus) thesummer ventilation air load.

Desert Aire SelectAireTM dehumidifiers for natatoriums andaquatic centers go above and beyond the standard air handlerdefinition. Desert Aire SelectAireTM dehumidifiers meet theintegrated requirements of natatoriums and their owners toprotect the health of building users, maintain ideal temperatureand humidity levels, promote the structural integrity of thebuilding and its contents, and conserve energy.

Desert Aire SelectAireTM dehumidifiers are refrigerant-typedehumidifiers providing closed loop systems that effectivelytransfer both latent and sensible heat from an indoorenvironment to a variety of alternate heat sinks.

Engineers and architects should choose duct materials andconstruction methods that are suitable for environmentsthat are humid, wet and where airborne chemicals arepresent. Moisture and chemicals attack ducts, grilles, registers, diffusers and equipment enclosures. Fabric duct,galvanized steel or aluminum is used for above grade duct,PVC for below grade. Special epoxy paint is used to improvecorrosion resistance on galvanized steel, aluminum ductsand 316 stainless steel. Aluminum or plastic is the materialof choice for grilles, registers and diffusers.

Supply air rate

Supply air should be delivered at a constant rate in order tocontinuously wash the walls, windows, and doors. e rate ofsupply air should not be lowered during unoccupied hours.

To provide sufficient air to flush the walls and windows,prevent stratification and deliver air down to the breathingzone, ASHRAE Applications Handbook recommends the airchange rates listed below.

• 4 to 6 air changes per hour for pools with no spectator areas

• 6 to 8 air changes per hour for pools with spectator areas

• 4 to 6 air changes per hour for therapeutic pools

It should be noted that these are air changes within theroom. e outdoor air ventilation rate is considered undera different formula as noted earlier in this guide.

Another strategy to address indoor air quality concerns arelow velocity/high volume fans. ese can be included innatatorium HVAC system designs to provide airflow to ceilingareas that would be difficult for the supply ductwork toreach. ey should not be used in the down flow configurationas this can impact airflow across the pool surface.

15

Figure 10. SelectAireTM (top) and AuraTM DOAS (bottom) dehumidifiers.

Figure 11. Refrigeration schematic without pool recovery.

A water heater coil may be added as an additional heatsink. This component is generally a tube in tube heatexchanger that allows water to absorb the heat from thehot refrigerant. A diverting valve controls whether therefrigerant goes to the air reheat coil or the water heater coil.In most applications the air reheat coil has priority. Figure 13. Refrigeration schematic with all modes.

When the remote condenser is utilized, the cool air from theevaporator coil does not get reheated. The air leaving thedehumidifier is cooler than the entering air. e total airconditioning capability is a function of the latent and sensibleload in the room.

For applications where an air-cooled remote condenser isnot practical, such as a long line set, a refrigerant to waterheat exchanger and a fluid cooler can be used to meet thespace cooling needs.

Dehumidifier design options

When planning a dehumidifier application there are severalkey specifications that must be considered.

First, how much moisture must be removed from thenatatorium? is is generally calculated in pounds per hourof water. Once a size is selected, then a decision on what heatsinks are appropriate must be made. Answers to the heatsink question will then dictate whether an air-cooled orwater-cooled unit is selected and if a remote condenser orfluid cooler is required.

Figure 12. Refrigeration schematic with pool recovery.

ere are several different water sources for this heat sink.Examples include pool water, spa water, potable water, coolingtower water and hydronic heat water. e actual water heatercoil is selected to be compatible with the water source used.Materials used include copper, cupronickel, ChlorinatedPolyvinyl Chloride (CPVC), titanium or stainless steel.

An air-cooled remote condenser may also be added to thedehumidifier. is would only be used when all other heatsinks for recovery of heat have been exhausted. is becomessimilar to a standard air conditioner by adding a condenseroutside of the conditioned space.

Water Condenser

Water Flow

Compressor

Evaporator Reheat

Water Condenser

Water Flow

To RemoteCondenser

Compressor

Evaporator Reheat

Compressor

Evaporator Reheat

When all other heat sinks have satisfied the respectivesetpoints, then a valve diverts the hot refrigerant outsidewhere the remote condenser dissipates the heat to thesurrounding environment. is condenser must be sized tothe dehumidifier to ensure proper charging and operation.

A reheat or condenser coil is present in all Desert Airedehumidifiers and is the most common heat transfermethod. e condenser or combination of condensers mustbe sized for the total heat of rejection (THR) of the system.

16

Simulations typically show that an economizer-equippeddehumidifier for an indoor pool will not provide operational“economy”. is is due to the significant energy penalty ofthe full-sized blowers and their low Energy Efficiency Rating(EER) in the cooling and dehumidification modes. It willcost more money to operate the economizer-equippeddehumidifier compared to other dehumidifiers.

Purge mode

Many design engineers and pool operators require a purgemode. is allows the room to be quickly purged of indoorair and replaced with outdoor air. In all cases this purgingoccurs during unoccupied hours.

e Model Aquatic Health Code recommends the purgemode be set at a minimum of twice the code requiredoutdoor air rate. e Desert Aire SelectAireTM system canprovide up to 50% of the total airflow when in the purgemode.

A common design mistake is to schedule 100% outdoor airfor purge. e difference in time between a full purge of anatatorium space at 100% as compared to 50% is usuallyabout 20 minutes or less. However, the backup space heatermust be double the size to handle the full heating requirementof a 100% purge that happens on a design load winter day.is will add substantial equipment cost plus an increasedstructural load.

Key features and benefits of Desert Aire SelectAireTM

dehumidifiers include meeting ventilation codes; exhaust airrecovery; ventilation air flexibility; pool water condensercapabilities; integration with a source capture system;and, latent and sensible energy recovery. Return of thecondensate to the pool water system is also available wherecodes allow.

Desert Aire dehumidifiers integrate all ventilation aircomponents through the dehumidifier to ensure the correctproportions of return air, supply air, exhaust air and outdoorair; and to maintain a negative pressure in the space.

Because conditioned air returning to the dehumidifier contains sensible energy in the form of heat and latentenergy in the form of humidity, there is an opportunity toincur energy savings before conditioned air is exhaustedfrom the HVAC system.

Economizers

Building designers often ask mechanical engineers toinclude in their system designs HVAC equipment withenergy efficiency features such as economizer functions.ey want the new buildings to comply with ASHRAE 90.1,a standard that provides minimum requirements for energyefficient designs for buildings. HVAC equipment in thisclassification includes air conditioners, heat pumps, furnacesand boilers.

Including dehumidifiers in this classification is a commonmistake. The code specifies that any air conditioner witha supply air volume greater than 5,000 cfm utilize aneconomizer in most weather zones.

Dehumidifiers are not in the same equipment classificationas air conditioners, because they function mostly in thedehumidification and heating modes; not air conditioningmodes. erefore ASHRAE 90.1 does not directly apply tothe pool room dehumidifier.

Nevertheless, to meet building owner requests and meetlocal codes, dehumidifiers with economizer features do existand may theoretically be suitable for some climates undercertain conditions. When certain weather and enthalpyconditions are present, outdoor air may be able to supply thecooling and dehumidification requirements for the poolfacility.

17

Other systems that use passive heat exchangers cannotrecover latent energy during the majority of the operationand the amount of sensible recovery is dependent on theoutdoor temperature. In addition, their actual recoveryeffectiveness is variable as it changes based on the temperaturedifferential. Passive heat exchangers require additional fanenergy and cannot take full advantage of free outdoor aircooling unless bypass dampers and controls are installed.

SelectAireTM systems have a constant rate of energy recoverywhen activated and are always controlled automaticallybased on the zone condition.

Integrated with source capture

If natatorium HVAC designs include chloramine source captureevacuation systems such as the FreshAire Evacuator®, DesertAire dehumidifiers can provide all of the ventilation air,including what is required for operation of the FreshAireEvacuator®.

Desert Aire’s SelectAireTM control system modulates theFreshAire Evacuator® exhaust speed based on the requiredmode of operation. e SelectAireTM dehumidifier can varythe volume of outdoor air and exhaust air based on the levelof contaminants within the natatorium.

Maximizing energy recovery

Desert Aire employs techniques and designs to maximizerecovered energy. The dehumidifiers achieve energyefficiency without weighing down the equipment with fansystems and motors designed for introducing and exhausting100% outdoor air. is system also saves substantial energycompared to an outdoor air system during non-occupiedperiods due to not having to exhaust all of the latent energyfrom the building while bringing in outdoor air that needsto be heated.

Desert Aire’s SelectAireTM system has two exhaust airdampers. One is upstream of the evaporator coil and one isdownstream. is special design feature allows SelectAireTM

dehumidifiers to take advantage of two basic thermody-namic principles while not impacting the sensible coolingcapacity of the units: exhaust air at its coldest point; and,exhaust air at its warmest point.

When the space requires heating, air is exhausted after theevaporator coil to recover the energy contained in theexhaust air prior to its discharge. In the cooling mode,air that is warm and humid is exhausted before theevaporator coil.

SelectAireTM systems use the principle of a heat pump torecover energy in the heating mode by operating one of thetwo circuits in conjunction with exhaust air. As previouslynoted, exhaust air consists of two energy components:sensible and latent. e cold evaporator coil absorbs both ofthese components. In addition to this energy, the energyrequired to operate the compressors is returned in the formof heat. is option provides high coefficient of performance(COP) efficiency to the exhaust air recovery cycle.

The SelectAireTM method is the most efficient method torecover the total energy of the exhaust air. Since the airflowsand loads are maintained through the special airflow controlsequence the amount of recovery can be optimized.

18

Outdoor Air

Supply Air

SelectAire™ Dehumidifier

Dehumidifier Exhaust

High Return Air

Medium Height Return Air

EvacuatorExhaust Air

RecoverAire™Energy Recovery

FreshAire Evacuator®

Source Capture Exhaust

Wash windows, walls and doors with supply air to prevent condensation(see pages 13, 15)

Airborne pollutants drawn into FreshAire Evacuator® Exhaust(see pages 12, 18)

Figure 14. Integration of dehumidifier with low exhaust

energy recovery.

19

The key to this integration is the use of a VOC sensingelement that can detect when interior levels of chemicalssuch as chloramines are present. is is similar to the use ofCO2 sensors in general ventilation applications but sincethe main source of contamination is a volatile organiccompound, the VOC sensor is more appropriate for thepool environment.

is provides the ability to optimize the volume of exhaustair required with the energy cost of doing so and ensures asuitable pool environment for the occupants. If the VOCsensor is not included in the installation, the SelectAireTM

dehumidifier will exhaust all air without optimizing its volume.

The following table (Figure 14) shows an example of theflexibility of the Desert Aire SelectAireTM control systemto meet the IAQ needs for pool rooms at various levels of occupancy.

Desert Aire's RecoverAireTM system has been designed tomeet the challenges of the low exhaust system and interfacesdirectly with the SelectAireTM system to allow easy field set-upand balancing. Exhausting too much air is an energy waste,but since every application is different the SelectAireTM

/RecoverAireTM tandem provides the end user with thecontrol to optimize the volume of air in all 5 modes ofoperation. is capability balances the volume of outdoorair to ensure proper IAQ while minimizing the cost of treatingthis outdoor air.

Installation considerations SelectAireTM dehumidifiers can be installed either indoorsor outdoors. Units intended for outdoor installation are factoryequipped with additional insulation, heavy-duty weathersealing and special rain hoods mounted on the outside airintake. When required they can also be installed on roofcurbs that permit bottom return and supply air to meetHVAC design specifications.

Proper installation of the dehumidifier into the total HVACsystem takes careful planning. All of the heat available fromthe dehumidification process is derived from the compressorand the conversion of latent energy through refrigerationtechnology.

With a seasonally fluctuating moisture load or maintenancecondition, such as the draining of the natatorium pool,supplemental pool heaters must be added to compensate forthe lack of heat from dehumidification. In the same manner,the dehumidifier must also include an auxiliary form ofspace heating. is can be in the form of an integral electric,hot water coil, or a gas heater downstream of the blower.

Figure 15. Example of SelectAireTM Dehumidifier airflow configuration.

Low exhaust energy recovery

A properly functioning system will not recirculate the airbeing removed from the low exhaust system; otherwise thesystem would reintroduce the highly concentrated chemicalsback into the space. A perceived negative for this is exhausthas a significant energy content that is bypassing therecovery capability of the SelectAireTM dehumidifier.To minimize this loss, a Desert Aire RecoverAireTM air towater heat pump recovery system should be installed inplace of a basic exhaust air blower. By using a high coefficientof performance (COP) heat pump, the system can recover upto 75% of the heat loss of the pool.

Mode ofOperation

UnoccupiedNormal Occ.Event Occ.

Maximum Occ.

Purge (no cmpr)

Low E/A

2,2002,2002,2004,400

4,400

Total E/A

2,2004,4005,2008,800

11,000

SA E/A

02,2003,0004,400

6,600

Total OSA

1,8004,0004,8008,400

10,600

20

Another factor requiring attention is condensateremoval from the dehumidifier. Some local codesstate that condensate must be plumbed to a drain;but many allow the return of the condensate to thesump upstream of the filter and chemical feedsystem. e volume of recovered water can besignificant and can equal the entire volume of thepool per year.

is should be a consideration on a natatoriumdesigned to achieve high levels of recognitionunder the Leadership in Energy & EnvironmentalDesign (LEED) green building certificationprogram. To recover the condensate water thedehumidifier employs a gravity drainage system.An unpressurized drain connection or a condensatepump then returns the condensate upstream ofthe sump.

Many older natatoriums with indoor mechanical rooms didnot take into consideration that the dehumidification systemwould need to be replaced during the life of the facility. eremoval of the failed system is the easiest part of the retrofitproject while moving the new dehumidifier into themechanical room can be quite challenging. Desert Aireoffers a solution to this problem through the sectioning ofour SelectAireTM Series dehumidifiers. Desert Aire workswith the customer to determine the maximum size andweight of the largest section that can be moved into themechanical room. is information is used by Desert Aire

Figure 17. SelectAireTM sectioned unit ready for shipment .

21

Figure 16. Example of SelectAireTM sectioned unit with doors removed.

engineering to create a sectioned SelectAireTM Series unitthat meets the performance needs of the natatoriumwhile taking into consideration the logistical problemscaused by mechanical room access. Refer to Figures 16 and17 for examples.

e key features of Desert Aire sectioned units include thefollowing:

• Refrigeration valves provided when sectioning of refrigeration circuits is required

• Wiring harnesses with mating connectors and terminal strips to distribute power through the unit

• Flanged edges and gaskets for sealing sections

Commissioning

A design process that includes an integrated approach to thenatatorium’s HVAC system should include commissioning.Commissioning encompasses a set of techniques andprocedures to check, inspect and test each operationalcomponent of the system to confirm everything is workingtogether as designed.

e system must be completely tested to verify airflow rates;negative pressurization; operation during all modes of occupied and unoccupied states; space heating and cooling;humidity control; water heating; and integration with thesource capture system.

Factory certified start-up

Due to the complexities of a natatorium’s HVAC design, thestart-up of a Desert Aire SelectAireTM system should be doneby either factory technicians or local technicians certified ashaving been factory-trained by Desert Aire.

Facility staff training

The equipment startup and commissioning processshould include training of the natatorium maintenance staff.e maintenance staff should have a basic understanding ofHVAC and pool dehumidification systems. is trainingshould include the pool room design conditions, generaloverview of the sequence of operation, and navigation of thedehumidifier’s operating control user interface. is trainingshould also include the scheduling setup of Unoccupied,Occupied and Event modes.

Other natatorium personnel, such as aquatic directorsand lifeguards, should be advised of the design conditionsof the pool room and the importance of maintainingthese conditions.

Conclusions

The new ways people use natatoriums and indoor poolfacilities place demands on HVAC systems and buildingsthat weren’t present just a few years ago.

In addition to working in harmony with systems that controlwater temperature and water quality, the HVAC system forthe 21st Century natatorium must protect the health ofbuilding users; promote the long-term structural integrityof the building and supporting systems; and conserveenergy, water and water treatment resources.

Today there is a matrix of strategies, technologies andindustry resources to provide building owners, mechanicalcontractors and engineers with solutions to these challenges.

As a key component of HVAC systems and their designs,Desert Aire SelectAireTM dehumidifiers help meet the holisticneeds of natatoriums and aquatic centers. A Desert Aire systemproperly removes humidity to promote greater comfort, protect structural integrity, improve indoor air quality andconserve resources.

For more information on meeting the HVAC design chal-lenges of your 21st Century natatorium, contact Desert Aireat the address below.

Desert Aire Corp.N120 W18485 Freistadt RoadGermantown, WI 53022 USA www.desert-aire.com sales@desert-aire.comTelephone: (262) 946-7400 FAX: (262) 946-7401

22

N120 W18485 Freistadt Road

Germantown, WI 53022 USA

www.desert-aire.com sales@desert-aire.com

Telephone: (262) 946-7400 FAX: (262) 946-7401

030 2019/01

OPTIMIZING SOLUTIONS THROUGH SUPERIOR DEHUMIDIFICATION TECHNOLOGY