Displacement App Guide

7/27/2019 Displacement App Guide

1/20

DISPLACEMENT VENTILATION

www.titus-hvac.com | www.titus-energysolutions.com

A p p l i c a t i o n G u i d e

clever. creative. comfort.


2/20

Application Guide ...........................................................................................................................................3

Introduction to Displacement Ventilation ................................................................................................3

Air Change Effectiveness .........................................................................................................................3

Typical Applications .................................................................................................................................4

Contaminant Removal .............................................................................................................................4

Benefits & Limitations .............................................................................................................................4

Energy Considerations .............................................................................................................................4

Outlet Characteristics ..............................................................................................................................5

The Adjacent Zone ..................................................................................................................................5

Outlet Choices .........................................................................................................................................5

Heat Sources & Convective Flows ...........................................................................................................6

Space Temperature Gradients & Airflow Rates .......................................................................................6Air Pattern Projection ..............................................................................................................................6

Methods of Evaluation.............................................................................................................................7

Supply Air Connections ...........................................................................................................................7

Acoustical Performance ...........................................................................................................................7

Displacement Ventilation Theory & Governing Equations .......................................................................7

Design Procedure for Displacement Ventilation ......................................................................................9

Design Examples ...................................................................................................................................10

References .............................................................................................................................................16


3/20

Displacement Ventilationwww

. t i t u s -h v a c . c om | www

. t i t u s - en

er g

y s ol u

t i on

s . c om

APPLICATION GUIDE

Displacement Ventilation Design& Application GuideBuildings come in all shapes and sizes and are designedfor any number of purposes. In order to create healthy andproductive environments, air distribution systems must beselected that best meet the goals of designers. There are awide range of choices available, but often one system canbe identi ed as the best solution in terms of cost, comfortand energy. The purpose of this guide is to explain howdisplacement ventilation works, describe recommendedapplications and provide engineering guidance to the systemdesigner.

INTRODUCTION TO DISPLACEMENT VENTILATIONIn order to understand the advantages and limitations of displacement ventilation, its important to understand thedifferences between conventional mixed air distribution andfully-strati ed air distribution.

In mixed air distribution, hot or cold supply air is deliveredat relatively high velocity from ceiling-mounted diffusers.When ceiling diffusers are properly selected and positioned,this high velocity air doesnt result in occupant discomfortbecause it is delivered outside the occupied zone. Thepurpose of the high velocity supply is to create low velocityroom air motion through entrainment. Ideally, this airmotion will thoroughly mix the supply air with the room airresulting in uniform temperature and contaminant levelsthroughout the occupied zone. Internal heat loads andcontaminants are eventually picked up and carried away bythe return air.

In fully-strati ed air distribution, cool supply air is typicallydelivered at reduced velocity from low sidewall diffusers.The supply air is always cooler than the room air, so itquickly drops to the oor and moves slowly across the room.When this slow moving air mass encounters a heat load, itrises and carries the heat and pollutants towards the ceiling.

A layer of warm air forms above the occupied zone due tonatural buoyancy. Internal heat loads and contaminants arecarried away by the return air.

The main differences between these systems are:

Mixed air distribution Suitable for both heating and cooling with a

supply temperature range of 38 to 90F. Air is supplied to the unoccupied zone

at relatively high velocity. Minimizes temperature variations throughout the space. Creates uniform contaminant concentration

throughout the zone.

Fully-strati ed air distribution Suitable for cooling only with a supply

temperature range of 62 to 70F. Air is supplied directly to the occupied

zone at low velocity. Takes advantage of natural air buoyancy

to divide the zone into two regions. Heat and pollutants rise into the upper unoccupied zone. Contaminant concentration is greatly

reduced in the lower occupied zone.

AIR CHANGE EFFECTIVENESS ASHRAE Standard 62.1-2010 Ventilation for AcceptableIndoor Air Quality assigns a zone air distributioneffectiveness value ( E z ) of 1.0 for conventional mixed airsystems and 1.2 for fully-strati ed systems (Table 6-2). This

means that fully-strati ed systems are 20% more effectivethan the best mixed air systems and can provide the samelevel of ventilation with a 16.7% reduction in air volume.This reduces the amount of outdoor air necessary to meetventilation requirements.

Figure 1. Mixed Air System

Figure 2. Fully-Strati ed System


4/20

Displacement Ventilation

4

w w w

. t i t u s -

h v a c . c o m

| w w w

. t i t u s - e n e r g y s o

l u t i o n s . c o m

A P P L I C A T I O N

G U I D E

APPLICATION GUIDE

TYPICAL APPLICATIONSIdeal applications for displacement ventilation often involvelarge open spaces with tall ceilings. These include but arenot limited to:

Theaters and performance halls Meeting rooms and lecture halls Restaurants and cafeterias Hotel lobbies and atriums Shopping malls Gymnasiums Casinos Museums and exhibit halls Classrooms Airport terminals and train stations

CONTAMINANT REMOVAL

Displacement ventilation can be a very effective strategyfor removing contaminants from room air, because fully-strati ed systems take advantage of the fact that airbornepollutants are generally lighter than air. The naturalbuoyancy of tobacco smoke and human respiration allowthese pollutants to rise above the breathing zone in plumesto the upper zone that forms below the ceiling. This upwardmigration of pollutants effectively increases concentrationsin the unoccupied upper zone while reducing concentrationsin the breathing zone.

A couple of important considerations: Displacement ventilation is not recommended forspaces where hazardous chemical spills could occur.In the event of a spill, a displacement ventilationsystem is likely to cause noxious fumes to be drawnfrom the oor and brought up to the breathing level,thereby increasing the possible hazard to occupants.

In rare situations where contaminants are heavier thanair, accommodations should be made to allow someportion of the room air to be extracted at a lower level.

BENEFITS AND LIMITATIONSTypical bene ts of displacement ventilation include:

Improved removal of airborne contaminants. Greatly reduced energy requirements to

cool occupied spaces in mild climates. Reduced ventilation air requirement due to

increased air distribution effectiveness. Very low diffuser noise levels. Reduced comfort complaints due to drafts.

Although displacement ventilation is well-suited for a widevariety of applications, the following spaces may be better

served by mixed air systems: Spaces with ceiling heights lower than 9 ft. Spaces with occupied zone heat loads

in excess of 30 Btu/hr-ft 2. Spaces furnished with cubicles or other partitions. Spaces with ceiling heights lower than 10 ft that may

be subject to signi cant room air disturbances. Applications involving contaminants that are heavier

and/or colder than room air in the occupied zone.

ENERGY CONSIDERATIONSDisplacement ventilation can reduce energy use in severalways:

Increased economizer hours due to increasedsupply temperatures in comparison toconventional mixed air systems.

Chiller ef ciency increases due to lesser dehumidi cationat higher water supply temperatures.

Figure 3. Contaminant Distribution in a Mixed Air System

Figure 4. Contaminant Distribution

in a Fully-Strati ed System


5/20



. t i t u s - en

er g

y s ol u

t i on

s . c om

APPLICATION GUIDE

OUTLET CHARACTERISTICSDisplacement ventilation requires outlets that supply airat extremely low velocities, (typically 50-70 fpm). Theseoutlets are typically located low on a sidewall or at thebase of a column. The low average face velocity generallyresults in rather large diffuser panels. Since the outletsare located adjacent to the occupied zone and within easyreach of room occupants, they have the following specialrequirements:

Should be elevated above the oor to preventdamage from cleaning equipment.

Construction and nishes must be ruggedenough to prevent damage through accidentalor intentional occupant contact.

Should provide a concealed and tamperproof means of air pattern adjustment.

Face panel must be removable for cleaningand adjustment of air pattern controllers.

THE AD JACENT ZONEThe area immediately adjacent to a displacement ventilationoutlet is known as the adjacent zone. This is any area inthe occupied zone where local air velocities exceed 50 fpmat a height 1 in above the oor. Although this clear zone canoften be in an aisle or corridor without creating potentialcomfort problems, stationary occupants should never belocated within the adjacent zone. Cool air that drops froma sidewall diffuser and travels across the oor can easily besensed by stationary occupants at the ankle level.

It is important to note that all Titus displacement ventilationdiffusers are supplied with adjustable air pattern controllersas standard equipment. The ability to adjust the shape of the air pattern and the adjacent zone can be of great bene twhen dealing with furniture, occupants and obstructionsespecially in smaller spaces.

OUTLET CHOICESDisplacement ventilation diffusers are available in a widerange of styles and sizes. Unlike conventional ceilingdiffusers, the size and placement of displacement ventilation

diffusers require early coordination with architectural

professionals for successful project integration. Generallyspeaking, displacement diffusers can be ducted from aboveor below or plenum-supplied.

All Titus displacement diffusers include: Adjustable air pattern controllers. Air balancing tap. Removable face plate. All metal construction (galvanized steel and aluminum). Standard #26 white powdercoat nish. Optional telescoping duct cover (not applicable to DVR1). Optional 2-3/4 or 4 inch mounting

base (not applicable to DVR1).

Figure 6. Standard Air Patterns

Figure 7. Adjusted Air Patterns

Figure 5. The Adjacent Zone


6/20


6

w w w

. t i t u s -

h v a c . c o m

| w w w




G U I D E

APPLICATION GUIDE

Figure 8. Heat Plume

Stratificationlevel

Upper zone

Convection plume Return

Lower zone

Heat/contaminant source Temperature, F

Stratification S e t p

o i n t

Supply0

HEAT SOURCES AND CONVECTIVE FLOWS

The ow of convective heat is essential in establishing afully-strati ed system. As heat moves from warmer surfacesto the cooler surrounding air, the buoyancy of the airincreases and the heat rises to create strati cation in theoccupied zone. This upward air motion driven by convectionalso results in room air entrainment that results in a largerheat plume. Although radiant heat sources do not directlyaffect these convective heat plumes, they may increaseplume formation by increasing surface temperatures of heatsources.

The characteristics of individual convective heat plumes maybe in uenced by each of the following:

Size and shape of heat source Amount of heat available Air motion surrounding heat source Temperature gradient in the space

Convective heat plumes will continue to rise until they reacha room level of equal temperature.

SPACE TEMPERATURE GRADIENTS AN D AIRFLOW RATESDisplacement ventilation diffusers supply conditioned air athigher cooling temperatures (typically 62 to 70F) and lowerdischarge velocities (less than 70 fpm) than ceiling diffusers.Since the supply air is always cooler than the room air, itcan be said to cascade from the diffuser face to the oor.

The negative buoyancy of the cooler air causes it to moveat the oor level until it reaches a source of convective heat. As the supply air warms, its buoyancy increases to createa heat plume that rises to the upper mixed zone below theceiling.

The distance from the oor to the upper mixed zone isknown as the shift height. Since the design goal of adisplacement ventilation system is to create temperaturestrati cation throughout the occupied zone, it is critical thatthe shift height is greater than height of the occupied zone.Lower shift heights may be acceptable in situations whereall occupants are seated.

AIR PATTERN PROJECTION

Although displacement ventilation is typically supplied froma low sidewall, the resulting room pattern is very differentfrom a conventional sidewall grille. Because the supply air iscooler than the room air and is discharging at low velocity,it immediately drops to the oor. The air moves across theoor in a thin layer typically no more than 6-8 inches high.The diagrams above show why displacement ventilation isonly recommended for cooling applications.

This air pattern tends to stretch out and cover the entireroom, even if the room shape is irregular. Obstructions suchas partitions or furniture resting directly on the oor can

result in coverage gaps, but the air pattern will rejoin itself much like uid passing around an object.

Displacement diffusers can typically provide coverage intoa room that is up to six times the length of the adjacentzone. Internal heat load concentrations actually help toextend the projection of a displacement system by drawingthe air across the room. Large rooms can be supplied fromthe side walls so long as the distance from the diffuserface to the furthest projection is no more than 30 ft. Whenroom dimensions exceed 30 ft in length or width, it is bestto place displacement diffusers on more than one wall. Byplacing diffusers on opposing walls, rooms up to 60 ft canbe supplied from side walls. Another solution for large rooms

is to place 360-degree diffusers throughout the interiorspace.

Figure 9. Discharge Air Patterns


7/20



. t i t u s - en

er g

y s ol u

t i on

s . c om

APPLICATION GUIDE

METHODS OF EVALUATION A successful displacement ventilation design shouldprovide a supply air ow rate to meet the thermalgradient pro le of an occupied space in accordance with

ASHRAE comfort guidelines. ASHRAE Standard 55-2010 Thermal Environmental Conditions for Human Occupancy recommends that vertical temperature differential betweena seated occupants ankle and head regions (roughly 4 to43 in) should be no more than 5.4F to deliver acceptablecomfort to 95% or more of the occupants. For a stationarystanding person same guideline would apply over anelevation range of 4 to 67 in.

SUPPLY AIR CONNECTIONSDisplacement ventilation diffusers are usually supplied byductwork and they can be supplied from either above orbelow.

Optional telescoping duct covers are availableto hide otherwise visible supply ductwork for a clean nished appearance.

Optional mounting bases (2-3/4 or 4 inch) arerecommended to prevent possible damage dueto traf c and oor cleaning equipment. Thesemounting bases are also recommended to simplifyinstallation when air will be supplied from below.

It is also possible to supply displacement ventilationdiffusers from a pressurized plenum.

Care must be taken to insure that thesupply plenum is tightly sealed.

In a properly designed supply plenum,pressures should be equal throughout andbalancing dampers should not be required.

ACOUSTICAL PERFORMANCELike any building space, those supplied by displacementventilation create an acoustical environment withcontributions from air handlers, terminal units, diffusersand structure-borne sound. Properly sized and selected

displacement ventilation diffusers are rarely the cause of noise complaints because they operate at low pressure and

low velocity and therefore do not generate audible noise.The catalog sound performance rating of a displacementdiffuser is usually expressed in terms of a noise criteria (NC)level based upon a typical space with room absorption of 10 dB in each octave band per ASHRAE Standard 70-2006(Appendix D).

While this typical space effect has been used for manyyears to estimate the sound level of a diffuser serving asmall of ce, this certainly isnt the typical environment inwhich displacement ventilation is employed. Since we areoften dealing with much larger spaces and taller ceilings,a different method must be employed to better estimatesound levels. A space effect for each octave band can becalculated based upon the size of the room and the distancebetween the source and observer using the followingequation per AHRI Standard 885-2008:

Space Effect = 25 10 log (ft) 5 log (ft 3) 3 log (Hz)

Where:

ft = Distance between the source and observerft3 = Room volumeHz = Octave band center frequency

When considering sound contributions from multiplediffusers, we can logarithmically add or multiply, but thisis typically unnecessary. In large spaces, diffusers arerarely close enough together to contribute to the overallroom sound level. As a general rule for smaller spaces, it isadvisable to select diffusers for an NC level that is 10 pointslower than the desired room sound level. This has the effectof masking the sound contribution of the diffusers in thebackground sound level. For larger spaces, the NC levelof the diffuser is less critical because the room effect is somuch greater.

DISPLACEMENT VENTILATION THEORY AND GOVERNINGEQUATIONSThe following material is based on ASHRAE researchproject RP-949 that resulted in the ASHRAE publication

System Performance Evaluation and Design Guidelinesfor Displacement Ventilation (2003). This summary isintended to brie y explain the theory behind displacement

ventilation. For a more detailed explanation including thederivation of each equation, the original publication is highlyrecommended.

The design air volume supplied by a displacementventilation system must be capable of meeting both thecooling and minimum ventilation requirements for a givenspace. In order to determine the cooling design air volume,the type, location and magnitude of all heat loads must beidenti ed. These loads can be classi ed as:

Heat generated by occupants, desk lampsand of ce equipment, Qoe (Btu/h)

Heat generated by overhead lighting, Q l (Btu/h) Heat from the exterior wall and window surfaces

including transmitted solar radiation, Qex (Btu/h)

Figure 10. Maximum Temperature Differentialsfor Acceptable Thermal Comfort


8/20


8

w w w

. t i t u s -

h v a c . c o m

| w w w




G U I D E

APPLICATION GUIDE

A weighting factor must be applied to each of these loadsto properly approximate the effect of each type of loadentering the region between the head and the feet of a seated occupant. Based on ASHRAE research, theseweighting factors are:

Occupants, desk lamps and of ce equipment, oe = 0.295 Overhead lighting, l = 0.132 Exterior wall and window surfaces including

transmitted solar radiation, ex = 0.185

The heat transfer to the region of interest can therefore becalculated by the following equation:

T hf C pV = oeQoe + l Q l + exQex

Where:

T hf = temperature differential between thehead and foot level of occupant (F)

= air density under standard conditions (lb/ft 3) C p = speci c heat of air at constant pressure (Btu/lb-F) V = supply ow rate (ft 3/h)

Since:

V = nHA

Where: n = the required air change rate (ach) H = space height (ft)

A = oor area (ft 2)

The heat transfer equation can be simpli ed to:

T hf = ( oeQoe + l Q l + exQex ) / ( C pnHA)

ASHRAE Standard 55-2010 recommends that for goodthermal comfort the temperature difference between thehead and foot level of a standing person should not exceed5.4 F. In a strati cation zone, assume that the temperaturegradient will be less than 1 F/ft. Since the verticaltemperature gradient between a seated persons head(3.6 ft) and a standing persons head (5.6 ft) is generallyless than that between the ankle level (0.3 ft) and seatedpersons head (3.6 ft), any design that meets the seatedrecommendations should also be suitable for a standingperson.

The same equation can be used to calculate the requiredventilation rate:

n = ( oeQoe + l Q l + exQex ) / ( T hf C p HA)

The cooling air volume (cfm), V h, for a typical of ceenvironment can then be calculated using the followingequation:

V h = nAH/60

Substituting the ventilation rate, n, into the equation yields:

V h = (0.295 Qoe + 0.132 Q l + 0.185 Qex)/( T hf C p)

With the following assumptions: T hf = 3.6 F (for a seated occupant) = 0.075 lb/ft 2

C p = 0.24 Btu/lb-F

This equation can be simpli ed to:

V h = 0.076 Qoe + 0.034 Q l + 0.048 Qex

This equation is very useful for typical applications involvingseated occupants.

The required ventilation rate can be determined by

consulting ASHRAE Standard 62.1-2010. This standardprovides recommended ventilation rates for variousroom occupancies and applications (Table 6-1). Theserecommendations involve the minimum ventilation rates inthe breathing zone based upon both occupant density andoor area.

The breathing zone outdoor air ow (cfm), V bz , can becalculated using the following equation:

V bz = ( R p x P z ) + ( Ra x A z )

Where: R p = people outdoor air rate from Table 6-1 (cfm/person)

P z = zone population (#) Ra = area outdoor air rate from Table 6-1 (cfm/ft

2) A z = zone oor area (ft

2)

ASHRAE Standard 62.1-2010 also de nes air changeeffectiveness ( E z ) of various types of air distribution systems(Table 6-2). While the best mixed air system with ceilingdiffusers can only achieve a rating of 1.0, displacementventilation systems achieve a 1.2 rating. This means thata displacement ventilation system can meet ventilationrequirements with 16.7% less air volume than a mixed airsystem. Be aware that local code requirements may be morestringent than the minimum standards recommended by

ASHRAE and may not differentiate between system typesand air change effectiveness.

The zone outdoor air ow requirement (cfm), V oz , can becalculated as:

V oz = V bz / E z

Where: E z = air change effectiveness from Table 6-2

The supply air volume (cfm), V , will be larger of either thecooling air volume (cfm), V h, or the zone outdoor air owrequirement (cfm), V oz . Be aware that if a dedicated outdoor

air system (DOAS) is employed, then supply air volume,V , would consist of 100% outdoor air. If return air is being


9/20



. t i t u s - en

er g

y s ol u

t i on

s . c om

APPLICATION GUIDE

mixed with outdoor air, supply air volume, V , must containenough outdoor air to meet the zone outdoor requirement,V oz .

The supply air temperature, T s, is always cooler than theroom temperature, T sp, and can be calculated by based onthe air temperature at the oor level, T f .

T f = T sp - T hf

And:

T s = T f f Q t / (60 C pV )

Where: f = dimensionless temperature calculated

by Mundts formula (1992)

Q t = total cooling load in space (Btu/h) V = supply air volume (cfm)

f = 1 / ((60 VC p / A)((1 / r ) + (1 / cf )) + 1 )

Where: r = radiant heat transfer from ceiling to oor (Btu/h-ft

2-F) cf = convective heat transfer from oor

surface to the room air (Btu/h-ft 2-F)

Assuming that heat transfer coef cients r and cf are equalto 0.9 Btu/( h-ft2-F) and that T hf should be less than 3.6

B F fora seated occupant, this equation can then be simpli ed to:

T s = T sp 3.6 (( AQ t ) / (2.59 V 2 + 1.08 AV ))

The exhaust air temperature, T e, can be calculated as:

T e = T s + ((Q t ) / (1.08 V ))

DESIGN PROCEDURE FOR DISPLACEMENTVENTILATIONThe following design procedure is patterned on thatprovided in an ASHRAE publication entitled SystemPerformance and Design Guidelines for Displacement

Ventilation (2003). It was developed based upon the ndingof ASHRAE Research Project RP-949.

Step 1 Calculate the Total Cooling LoadThe total cooling load, Q t , is the sum of the heat loads:

Q t = Q oe + Q l + Q ex

Where: Qoe = Heat generated by occupants, desk

lamps and of ce equipment (Btu/h) Q l = Heat generated by overhead lighting (Btu/h) Qex = Heat from the exterior wall and window surfaces

including transmitted solar radiation (Btu/h)

Step 2 Check for Excessive Heat LoadDisplacement ventilation is generally not recommended for

internal heat loads greater than 30 Btu/ft 2.

Q t / A 30 Btu/ft2

A = L x W

Where: A = oor area (ft 2) L = room length (ft) W = room width (ft)

Step 3 Calculate the Cooling Air VolumeThe cooling air volume, V h, can be determined from heatloads with weighting factors applied:

V h = 0.076 Qoe + 0.034 Q l + 0.048 Qex

Step 4 Calculate the Zone Outdoor Air ow for AcceptableIndoor Air QualityThe zone outdoor air ow requirement (cfm), V oz , and thebreathing zone outdoor air ow (cfm), V bz , can be determinedfrom ASHRAE Standard 62.1 (Tables 6-1 and 6-2) and thefollowing equations:

V bz = ( R p x P z ) + ( Ra x A z )

Where: R p = people outdoor air rate from Table 6-1 (cfm/person) P z = zone population (#) Ra = area outdoor air rate from Table 6-1 (cfm/ft

2)

A z = zone oor area (ft 2)

V oz = V bz / E z

Where: E z = air change effectiveness from Table 6-2 = 1.2

Step 5 Determine the Supply Air VolumeThe supply air volume, V , will be larger of either the coolingair volume, V h, or the zone outdoor air ow requirement, V oz .

Step 6 Calculate the Supply Air TemperatureThe supply air temperature, T s, can be calculated as:

T s = T sp 3.6 (( AQ t ) / (2.59 V 2 + 1.08 AV ))

Where: T sp = room temperature (F)

Step 7 Calculate the Exhaust Air TemperatureThe exhaust air temperature, T e, can be calculated as:

T e = T s + ((Q t ) / (1.08 V ))

Step 8 Select Supply Diffuser(s)


10/20


0

w w w

. t i t u s -

h v a c . c o m

| w w w




G U I D E

APPLICATION GUIDE

DESIGN EXAMPLE - PRIVATE PERIMETER OFFICEThis a small private of ce measuring 12 ft by 10 ft by 9 ft (Lx W x H). The of ce is equipped with a computer, a monitor,a small printer and a desk lamp. The 12 ft long wall includesexterior glass. The room will be supplied by a dedicatedoutdoor air system (DOAS).

Assume: Occupancy = 1 Load per person = 250 Btu/h Overhead lighting load = 2 watts/ft 2 = 6.826 Btu/h-ft 2

Computer load = 65 watts = 222 Btu/h Monitor load = 30 watts = 102 Btu/h Small printer load = 30 watts = 102 Btu/h Desk lamp load = 40 watts = 137 Btu/h Solar and glass load = 4.0 Btu/h-ft 2

Step 1 Calculate the Total Cooling LoadQ t = Q oe + Q l + Q ex




Qoe = person + computer + monitor + small printer + desk lamp = 813 Btu/hQ l = overhead lighting load x oor area = 819 Btu/hQex = solar and glass load x exterior wall area = 432 Btu/h

Q t = 2064 Btu/h

Step 2 Check for Excessive Heat LoadDisplacement ventilation is generally not recommended forinternal heat loads greater than 30 Btu/ft 2.

Q t / A 30 Btu/ft2

A = L x W


Q t / A = 17.2 Btu/ft2


V h = 0.076 Qoe + 0.034 Q l + 0.048 Qex

V h = 110 cfm

Step 4 Calculate the Zone Outdoor Air ow for Acceptable

Indoor Air QualityThe zone outdoor air ow requirement (cfm), V oz , and the

breathing zone outdoor air ow (cfm), V bz , can be determinedfrom ASHRAE Standard 62.1 (Tables 6-1 and 6-2) and thefollowing equations:

V bz = ( R p x P z ) + ( Ra x A z )

Where: R p = people outdoor air rate from

Table 6-1 = 5.0 cfm/person P z = zone population (#) = 1 Ra = area outdoor air rate from Table 6-1 = 0.06 cfm/ft

2

A z = zone oor area (ft2)

V bz = 12.2 cfm

V oz = V bz / E z


V oz = 10.2 cfm


V = 110 cfm


T s = T sp 3.6 (( AQ t ) / (2.59 V 2 + 1.08 AV ))

Where: T sp = room temperature = 72 F

T s = 63 F


T e = T s + ((Q t ) / (1.08 V ))

T e = 80 F

Step 8 Select Supply Diffuser(s)The best diffuser for this application would be a single ush-mounted wall unit handling 110 cfm. It should ideally belocated away from the desk on an opposite wall dischargingparallel to the window. Care should be taken in a spacethis size to ensure that the depth of the adjacent zone isless than 3-4 ft. Since the sound level in a private of ce isrecommended not to exceed a sound level of NC35, thediffuser should be selected for NC25 or less. See Figure 11 forexample of diffuser layout.


11/20



. t i t u s - en

er g

y s ol u

t i on

s . c om

APPLICATION GUIDE

DESIGN EXAMPLE - OPEN PLAN INTERIOR OFFICEThis is an open plan of ce for customer service

representatives. The of ce is furnished with workstations toaccommodate up to sixteen employees and measures 40 ftby 40 ft by 12 ft (L x W x H). Each workstation is equippedwith a computer, a monitor and a desk lamp. There is also asingle large printer that is shared. The room will be suppliedby a conventional air handler that will mix return air withoutdoor air.


Computer load = 65 watts = 222 Btu/h Monitor load = 30 watts = 102 Btu/h Large printer load = 110 watts = 375 Btu/h Desk lamp load = 40 watts = 137 Btu/h





Qoe = (16) people + (16) computers + (16) monitors + (1)

large printer + (16) desk lamps = 11751 Btu/hQ l = overhead lighting load x oor area = 10922 Btu/hQex = 0 Btu/h

Q t = 22673 Btu/h


Q t / A 30 Btu/ft2

A = L x W

Where: A = oor area (ft 2) L = room length (ft)

W = room width (ft)

Q t / A = 17.2 Btu/ft2

Step 3 Calculate the Cooling Air VolumeThe cooling air volume, Vh, can be determined from heatloads with weighting factors applied:

V h = 0.076 Qoe + 0.034 Q l + 0.048 Qex

V h = 1264 cfm


V bz = ( R p x P z ) + ( Ra x A z )



2


V bz = 176 cfm

V oz = V bz / E z


V oz = 147 cfm


V = 1264 cfm

Since the air handler will be mixing return air with outdoorair, we must calculate the required percentage of outdoor airto satisfy the zone outdoor air requirement, V oz .

V oz / V = 12%


T s = T sp 3.6 (( AQ t ) / (2.59 V 2 + 1.08 AV ))

Figure 11. Design Example - Private Perimeter Of ce


12/20


2

w w w

. t i t u s -

h v a c . c o m

| w w w




G U I D E

APPLICATION GUIDE


T s = 65 F


T e = T s + ((Q t ) / (1.08 V ))

T e = 81 F

Step 8 Select Supply Diffuser(s)There are many different diffuser selections that could work well in this space. Flat front or bow-fronted diffusers eitherush-mounted or surface-mounted would be best. The exactmodel choice comes down to appearance and architectural

limitations. The best arrangement would be to place pairs of diffusers on opposite walls such that they discharge downthe aisles between work stations. This would require fourdiffusers each handling 316 cfm, selected for an adjacentzone with a depth of less than 4-5 ft. This should beadequate to achieve coverage to the center of the room.Since the ideal sound level for an open plan of ce is NC40,the diffusers should be selected for NC30 or less. See Figure12 for example of diffuser layout.

DESIGN EXAMPLE - PERIMETER CONFERENCEROOMThis is a conference room with an exterior window. Theroom is equipped with a computer and a projector and isintended for a maximum occupancy of twelve. It measures30 ft by 15 ft by 10 ft (L x W x H). The window is locatedon the longest wall. The room will be supplied by aconventional air handler that will mix return air with outdoorair.


Computer load = 65 watts = 222 Btu/h Projector load = 200 watts = 683 Btu/h Solar and glass load = 4.0 Btu/h-ft 2



lamps and of ce equipment (Btu/h)

Q l = Heat generated by overhead lighting (Btu/h) Qex = Heat from the exterior wall and window surfacesincluding transmitted solar radiation (Btu/h)

Qoe = (12) people + computer + projector = 3905 Btu/hQ l = overhead lighting load x oor area = 3072 Btu/hQex = solar and glass load x exterior wall area = 1200 Btu/h

Q t = 8177 Btu/h


Q t / A 30 Btu/ft 2

A = L x W


Q t / A = 18.2 Btu/ft2

Step 3 Calculate the Cooling Air VolumeThe cooling air volume, V h, can be determined from heat

loads with weighting factors applied:V h = 0.076 Qoe + 0.034 Q l + 0.048 Qex

V h = 459 cfm


V bz = ( R p x P z ) + ( Ra x A z )



2


V bz = 87 cfm

V oz = V bz / E z

Where: E

z = air change effectiveness from Table 6.2 = 1.2

Figure 12. Design Example - Open Plan Interior Of ce


13/20



. t i t u s - en

er g

y s ol u

t i on

s . c om

APPLICATION GUIDE

V oz = 72.5 cfm


V = 459 cfm


V oz / V = 16%


T s = T sp 3.6 (( AQ t ) / (2.59 V 2

+ 1.08 AV ))


T s = 64 F


T e = T s + ((Q t ) / (1.08 V ))

T e = 80 F

Step 8 Select Supply Diffuser(s)The best choice for this application would be a pair of 90-degree air pattern diffusers located on the interiorcorners of the room. Each diffuser will handle 230 cfm andshould be selected for an adjacent zone no deeper than4-5 ft. Since the typical sound level for a conference roomshould not exceed NC30, the diffusers should be selected forNC20 or less. See Figure 13 for example of diffuser layout.

DESIGN EXAMPLE - INTERIOR BREAKROOMThis is a breakroom without windows. The room is equippedwith a water cooler, a coffee machine, a microwave oven,an ice maker, a refrigerator, a cold beverage machine, and asnack machine. It measures 40 ft by 32 ft by 12 ft (L x W x

H). The room will be supplied by a conventional air handlerthat will mix return air with outdoor air.


Water cooler load = 350 watts = 1195 Btu/h Coffee machine load = 1000 watts = 3413 Btu/h Microwave oven load = 200 watts = 683 Btu/h Ice maker load = 400 watts = 1365 Btu/h Refrigerator load = 700 watts = 2389 Btu/h Cold beverage machine load = 800 watts = 2730 Btu/h Snack machine load = 250 watts = 853 Btu/h





Qoe = (40) people + water cooler + coffee machine +microwave oven + ice maker + refrigerator + cold beveragemachine + snack machine = 22628 Btu/hQ l = overhead lighting load x oor area = 8737 Btu/h

Q t = 31365 Btu/h

Qex = 0 Btu/h


Q t / A 30 Btu/ft2

A = L x W


Q t / A = 24.5 Btu/ft2


V h = 0.076 Qoe + 0.034 Q l + 0.048 Qex

V h = 2017 cfm

Figure 13. Design Example - Perimeter Conference Room


14/20


4

w w w

. t i t u s -

h v a c . c o m

| w w w




G U I D E

APPLICATION GUIDE

Step 4 Calculate the Zone Outdoor Air ow for AcceptableIndoor Air QualityThe zone outdoor air ow requirement (cfm), V oz , and thebreathing zone outdoor air ow (cfm), V

bz , can be determined

from ASHRAE Standard 62.1 (Tables 6-1 and 6-2) and thefollowing equations:

V bz = ( R p x P z ) + ( Ra x A z )



2


V bz = 354 cfm

V oz = V bz / E z

Where: E z = air change effectiveness from Table 6.2 = 1.2

V oz = 295 cfm


V = 2017 cfm


V oz / V = 15%


T s = T sp 3.6 (( AQ t ) / (2.59 V 2 + 1.08 AV ))


T s = 65 F


T e = T s + ((Q t ) / (1.08 V ))

T e = 80 F

Step 8 Select Supply Diffuser(s)There are many possible choices, but large open spacescan be easily served with 360-degree air pattern diffuserslocated away from the walls. Although four diffusers each

handling 504 cfm might work, six diffusers each handling

336 cfm would result in shorter throws and smaller adjacentzones. Sound levels in cafeterias and breakrooms areseldom critical, but selecting the diffusers for NC25 or less isadvisable. See Figure 14 for example of diffuser layout

DESIGN EXAMPLE - ELEMENTARY SCHOOLCLASSROOMThis is a school classroom with an exterior window. Theroom is equipped with a computer and a projector and isintended for a maximum occupancy of one teacher and (25)students. The room is equipped with (5) computers, (5)monitors and a projector. It measures 30 ft by 30 ft by 10 ft(L x W x H). The room will be supplied by a conventional airhandler that will mix return air with outdoor air.

Assume: Occupancy = 26

Load per person = 250 Btu/h Overhead lighting load = 2 watts/ft 2 = 6.826 Btu/h-ft 2

Computer load = 65 watts = 222 Btu/h Monitor load = 30 watts = 102 Btu/h Projector load = 200 watts = 683 Btu/h Solar and glass load = 10.5 Btu/h-ft 2



lamps and of ce equipment (Btu/h)

Q l = Heat generated by overhead lighting (Btu/h) Qex = Heat from the exterior wall and window surfaces


Qoe = (26) people + (5) computers + (5) monitors +projector = 8803 Btu/hQ l = overhead lighting load x oor area = 6143 Btu/hQex = solar and glass load x exterior wall area = 3150 Btu/h

Q t = 18096 Btu/h


Figure 14. Design Example - Interior Breakroom


15/20



. t i t u s - en

er g

y s ol u

t i on

s . c om

APPLICATION GUIDE

Q t / A 30 Btu/ft2

A = L x W


Q t / A = 20.1 Btu/ft2


V h = 0.076 Qoe + 0.034 Q l + 0.048 Qex

V h = 1029 cfm


V bz = ( R p x P z ) + ( Ra x A z )



2


V bz = 368 cfm

V oz = V bz / E z


V oz = 307 cfm


V = 1029 cfm


V oz / V = 30%


T s = T sp 3.6 (( AQ t ) / (2.59 V 2 + 1.08 AV ))


T s = 66 F


T e = T s + ((Q t ) / (1.08 V ))

T e = 82 F

Step 8 Select Supply Diffuser(s)Perimeter classrooms are typically arranged with the

instructors desk at one end of the room, the student desksin rows facing the teacher and windows perpendicular desk rows. The most common diffuser arrangement for this roomlayout would require a diffuser on each side of the teachersdesk discharging down the side aisles. Each diffuser wouldhandle 515 cfm and the adjacent zone depth should be nomore than 4-5 ft. Since sound levels in elementary schoolclassrooms are critical to the learning environment and arerecommended not to exceed NC25-30, the diffusers shouldbe selected for NC15 or less so as not to be heard. SeeFigure 15 for example of diffuser layout.

Figure 15. Design Example - Elementary School Classroom


16/20


17/20



. t i t u s - en

er g

y s ol u

t i on

s . c om

NOTES


18/20


19/20



. t i t u s - en

er g

y s ol u

t i on

s . c om

NOTES


20/20

clever. creative. comfort.

605 Shiloh Plano TX 7

ofce: 972.212.4ax: 972.212.

email: titus@titus-hva

Displacement App Guide

Documents

Transcript of Displacement App Guide