White Paper MCP15-803

8/10/2019 White Paper MCP15-803

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P a g e | 2 MCP15 803 Modine Manufacturing Company September, 2011

Cost of Operation w/ERV but without ERV ByPassMode Cooling Heating Economizer TotalsHours 1787 1443 5530 8760

Operating Cost $ 2,8 64 $ 2,5 81 $ 4,8 39 $ 10 ,2 84Average Cost per Hour = $1.17

Cost of Operation w/ERV and with ERV By PassMode Cooling Heating Economizer TotalsHours 1787 1443 5530 8760

Operating Cost $ 2,864 $ 2,581 $4 ,517 $9 ,962Average Cost per Hour = $1.14

Cost of OperationMode Cooling Heating Economizer TotalsHours 1787 1443 5530 8760

Operating Cost $ 7,2 77 $ 5,7 30 $ 3,8 20 $ 16 ,8 27Average Cost per Hour = $ 1.9 2

DOAS units heating system. If the outside air is warmerthan the exhaust air, the opposite will be true and theentering air will be precooled, thus reducing the energyload on the DOAS units cooling system. In the case oftotal energy (enthalpy) wheels the same scenario can bestated for the transfer of sensible energy, but in additionthe enthalpy wheel is also capable of transferringmoisture. This means the energy wheel can serve as a

dehumidifying component of the system in the summertime, and a humidification component in the winter. Thisis very useful in reducing the latent load on airconditioning systems in hot and humid climates. Insome areas the latent load can be equal to or evengreater than the sensible load of a cooling system.

If the energy recovery system is equipped with aneconomizer air by-pass system (and VFDs on thesupply and exhaust fans) the DOAS unit then becomescapable of supplying outdoor air (ventilation air) directlyto the space without preconditioning the air. The

economizer mode is used when outdoor air conditionsare such that neither mechanical cooling, nor heating ofthe ventilation air is necessary. The use of a by-passsystem allows the fan energy use to be reduced duringthe economizer mode of operation because all of theventilation air does not have to pass through the energywheel, thus the total static pressure drop through theventilation system can be reduced. Because the totalsystem static pressure is reduced, the fan(s) speed canbe reduced via motor VFDs to maintain constant airvolume at the lower static pressure condition and reducemotor energy used.

How Much Energy Can an Energy Recovery SystemSave?The example systems in Figures 2.1 and 2.2 areprovided to demonstrate the magnitude of the potentialenergy savings that can be achieved by incorporating anenergy recovery system into a DOAS ventilation system.The selected location for comparison purposes is

Atlanta, Georgia. The cost of electricity is assumed tobe $.013 per kW, and the cost of natural gas is assumedto be $0.90 per Therm. The average heating, cooling,

and economizer hours are as shown in the operatingcost summaries. The cooling load is 30 Tons.

In the examples shown, the total energy recoverysystem reduces the cost of operation of the DOASsystem by $6,543 or 39% for a system without an energywheel economizer by-pass, and by $6,865 or 40.8% with

an energy wheel economizer by-pass. The greatestsavings comes from the reduction in mechanical coolingat $4,413 per year, and the second greatest is from areduction in the heating costs at $3,149 per year. Duringthe economizer mode the operating costs actuallyincrease due to the additional static pressure in thesystem with the energy recovery wheel versus thesystem without, but even with this difference the total

annual system cost savings is substantial, justifying theadditional year round added system static pressureimposed by the energy recovery system.

Figure 2.1 (1)

Figure 2.2 (1)

VentilationAir Out

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STANDARD DOAS UNIT CONFIGURATION

Total Supply Air System

Static Pressure P = 4.8" w.c.

Supply Fan

BHP = 6.17

72 oF DB 50% RH

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Supply FanBHP = 6.64

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Total P = .926"w.c.

Exhaust FanBHP = 1.09

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(1) Assumed Cooling Efficiency 11.5 EER, HeatingEfficiency 80% Natural Gas

The examples demonstrate that the addition of anenergy recovery wheel reduces the mechanical coolingload of the DOAS system by 20 Tons, and reduces themechanical heating system load by 266 Mbh. These aresubstantial reductions and they make the DOAS system

with energy recovery 39% more efficient than a standardDOAS system.

It is important to note than even though the two systemsare substantially different in comparison to the totalmechanical energy required, they both deliver the sameequivalent heating and cooling capability.

(Detail calculations used to estimate the annual energyuse for these examples can be found in Appendices atthe end of this report.)

How does adding energy recovery affect thesystems cooling efficiency?The units Energy Efficiency Ratio (EER) is a measure ofthe full-load energy efficiency ratio of cooling equipment.It is a measure of the ratio of the input energy required toproduce the output cooling at 100% load conditions.

EER = Cooling out (Btu/Hr) / Energy in(watts)

For example if it takes 24 kW (24,000 watts) of electricityto produce 20 tons (240,000 Btu) of cooling the energyefficiency ratio would be 10.0 Btu/Watt.

EER = 240,000 Btu / 24,000 Watts = 10.0 EER

The EER is determined by applying the standard ANSI/AHRI 340/360-2007 performance rating testconditions which are 95 oF DB outdoor air (air enteringthe condenser) and 80 oF DB/ 67 oF WB air entering theevaporator coil and operating the cooling system at itsmaximum capacity (100% load). The results aremeasured and documented. The total energy in is

measured (in watts), and the total cooling capacityoutput is measured (in Btu/Hr). From this data the EERis calculated.

If this formula is applied to the two systems compared inFigures 2.1 and 2.2 it is found that the standard DOASunit has an EER of 11.5, and the DOAS system with an

energy recovery system has an apparent EER of 29.6,or an energy efficiency ratio improvement in excess of157%.

(The term apparent EER is used here because, thereare currently no nationally recognized rating standardsfor rating cooling systems with energy recovery. There isan ARI guideline, Guideline V - Guideline for Calculating

the Efficiency of Energy Recovery Ventilation and ItsEffect on Efficiency and Sizing of Building HVACSystems, but this guideline is not a rating system and itclearly states in Paragraph 1.1.1 of the guideline underIntent; This guideline is intended for the guidance of theindustry, including engineers, installers, contractors andusers. It provides a means for calculating the impact ofapplied energy recovery equipment on the energyefficiency of the heating, ventilating and air-conditioningsystem at a single selected operating condition. Theguideline is not a rating system for Energy RecoveryVentilation(ERV) Equipment, nor does it provide a

means of estimating annual energy use.)

Doesnt the addition of an energy recovery systemadd static pressure to the system, and isnt this anoperating cost penalty, particularly when energyrecovery is not n eeded (economizer mode)?The answer is yes if only the motor horsepower of thesystem is being analyzed, but that is not the proper wayto analyze the system. The main point of adding energyrecovery is to reduce the overall energy consumption ofthe system. Therefore if the value of the heating andcooling energy recovered is in excess of the addedmotor horsepower energy employed, there is a netpositive effect for the system. In most cases, the heatingand cooling energy recovered will far outweigh theadded cost of the increased motor horsepower in thesystem, even when the economizer mode of operation isconsidered.

In the earlier examples it was assumed that the DOASunits were operating 24/7 in Atlanta, Georgia and thatthe mode of operation was 1787 hours of cooling, 1443hours of heating, and 5530 hours in economizer mode.

It can be seen that the hours of operation in theeconomizer mode far exceed the cooling and heatingmode hours. The example also shows an increase inoperating cost in the economizer mode of $1,019annually with the addition of the energy recovery system.However, because the heating and cooling energysavings are so great relative to the added motor


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Comparison of Energy Recovery Utilizing Bypass Air and Remix After WheelBased on AHRI 1060 Standard Cooling Conditions of 95DB/79WB Supply and 75DB/63WB ExhaustAtlanta, Georgia cooling hours = 1787

(1,2) Cost of (1,2) Cost of Energy

(5)(6) Energy Energy Air Side Wheel (1) Value of Air Side Wheel Wheel Energy Motor Motor Energy

Wheel / Mot or Mot or Rot at ion Rot at ion Re cove re d O pe rat ion O pe rat ion R ecove re dBypass CFM P BHP kW Motor HP Motor kW kW/Hr per Ho ur pe r Hour per Hour

Case 1 50%/50% 8000 0.431 1.76 1.313 0.250 0.187 55.52 $0.190 $0.027 $7.22Case 2 75%/25% 8000 0.665 2.68 1.999 0.250 0.187 73.80 $0.289 $0.027 $9.59Case 3 100%/0% 8000 0.912 4.40 3.282 0.250 0.187 87.95 $0.474 $0.027 $11.43

(4) Annual(4) Annual Motor

Cost of Operat ionMot or Cost as %

Wheel / Operation of CoolingBypass CFM Savings

Case 1 50%/50% 8000 $246.65 1.91% $0.00Case 2 75%/25% 8000 $359.55 2.10% $4,134Case 3 100%/0% 8000 $570.61 2.79% $7,211

(1) Assumes cost of electricity to be $0.13 / kW Hour(2) Assumes 90% Efficient motors(3) Based on average cooling hours for Atlanta, Georgia(4) Assumes 24 hour operation, 365 days a year. Includes heating, economizer, and cooling modes of operation.(5) Motor HP includes both supply and exhaust ai r side of energy recovery system. (6)

Based on using twin 15" Dia. x 15" W DWDI forward curved centrifugal fans.

$20,433$10.93

Increased Savings over

50/50 Bypass

Method

(3) AnnualCooling Energy

CostAvoidance

Energy Costs)$12,651$16,784$19,862

Cooling Energy

$7.00$9.28

Ne t Annual Cooling

Energy CostAvoidance

(Energy Recovered lessAnnual Motor

Cost Avoidanceper Hour(Energy

Recovered lessMotor Energy)

$12,897$17,144

horsepower required to deliver these savings, the netenergy increase during the economizer mode is wellworth the investment.

The additional annual energy investment of $1,019during the economizer mode is greatly offset by thesystem savings of $6,543 in total energy savings(assuming an economizer mode air bypass is not in the

system). If an economizer air bypass is added (toreduce the system static pressure load during theeconomizer mode of operation) the added motorhorsepower energy cost is only $697 annually during theeconomizer mode of operation and the systems annualenergy savings are improved further to $6,865. In thiscase, adding the economizer mode air bypass improvesthe overall energy savings by 4.9% ($6865 - $6543 $6,543).

Can some of the air in the system permanentlybypass the energy recovery wheel to reduce the

system static pressure? Would this improve theoverall system efficiency?

A simple calculation of the potential energy savings canbe made to show that bypassing any amount of airaround the wheel to reduce the system static pressureduring the heating or cooling energy recovery modes ofoperation has a negative effect on the overall system

efficiency. The table below shows the change in energyrecovery potential based on varying amounts of bypassand remix air. The calculations show that it is far moreefficient to recapture as much cooling energy as possiblethrough the wheel because the total availablerecoverable energy in the exhaust air far offsets anyadded motor horsepower required to capture thatenergy. It might be thought that the reduction in air

across the wheel might improve the wheel efficiency,and to some extent it does, but the improvement inwheel efficiency can never overcome the loss ofpotential recoverable energy in the bypassed air.

In the examples below it is shown that the horsepowerrequirement for passing 100% of 8,000 cfm through atypical energy wheel recovery system is 4.65 bhp.Reducing the wheel air throughput by 25% will reducethis system horsepower to 2.93 bhp, a difference of 1.72bhp. The annual savings in motor operating cost is only$211, but the loss in potential cooling energy recovery

savings is $3081. This difference is substantial, and iseven greater when the heating energy recovery savingsare added to the scenario. Conclusion, do not bypassany air when in the heating or cooling energy recoverymodes of operation. Only bypass air when in theeconomizer mode.

Table 4.1 Bypass and Remix Versus Through theWheel


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(1,2) (1,3) Increased(1,2) Cost of (1,4)

Net Annual

(5)(6) Energy Energy Cost of Energy Net Annual Energy

Energy Mechanical Energy Air Wheel Whee l (1) Cost of Air Side Wheel Energy Cooling Cost

Wheel Cooling Wheel Side Air Side Rotat ion Rotat ion Energy Motor Motor Cost Energy AvoidanceDia. Reduction P Motor Motor Motor Motor Recovered Operation Operation Avoidance Cost w/ Larger

(Inches) Tons (" w.c.) BHP kW HP kW per Hour per Hour per Hour Per Hour Avoidance Wheel46 14.5 0.842 1.98 1.477 0.250 0.187 $6.61 $0.234 $0.030 $6.35 $11,344

52 16.6 0.547 1.36 1.015 0.250 0.187 $7.58 $0.161 $0.030 $7.39 $13,211 $1,867

Oversized Wheel vs Maximized Wheel ScenariosBased on AHRI 1060 Standard Conditions of 95DB/79WB Supply and 75DB/63WB ExhaustAtlanta, Georgia cooling hours = 1787

Energy

WheelDia. Enthalpy

(Inches) Cfm WB oF WB oF (Btu/Lb) %RH Btu/Hr % Effec. Btu/Hr % Effec. Btu/Hr % Effec.

46 5000 95 79 42.44 49.89 75,874 71.3% 97,664 63.1% 173,538 55.2%52 5000 95 79 42.44 49.89 83,037 77.9% 115,994 74.9% 199,031 63.4%

Table 5.1 Benefits of Upsizing Savings Calculations

Latent Sensible

Energy Recovered and Energy Recovery EffectivenessSupply Air Conditions

Total

What are the effects of increasing the energyrecovery transfer area? Improved systemsefficiencies? Lower system pressure drops?There are two advantages of increasing the effectivearea of the energy recovery medium in the systemdesign stage. The first is increased efficiency of the

recovery system, and the second is lowering of the totalstatic pressure in the system. Often designers minimizethe size of the energy recovery system in order to keepfirst costs low. But this can lead to false economies.Designers need to address the Total Cost of Ownership(TCO) as well as first installed cost. After all, mostmechanical systems are expected to have a usefuloperating lifetime of 15 to 20 years and cumulativeenergy savings over this period of time can besubstantial. As an example consider the followingscenarios.

Two energy recovery wheels are available, a 46diameter wheel, and a 52 diameter wheel. The top endcapacity of the smaller wheel is 5,500 cfm. The largerwheel has a rated top end capacity of 8,000 cfm. Theventilation requirement for this scenario is 5,000 cfm.Should the use of the larger wheel be investigated?

Table 5.1 shows that increasing the wheel size from 46to 52 boosts the systems efficiency by nearly 15%(55.2% to 63.4%). At the same time the systems staticpressure is reduced by 0.3 w.c. which results inlowering the systems break horsepower requirementsby 0.62 bhp. These two system changes result in anadditional estimated annual cooling savings of $1,867

per year by using the 52 wheel instead of the 46 wheel.Over 15 years, without adjusting for inflation, the totalaccumulated savings increase is $28,005. These areadditional savings over what the 46 wheel wouldprovide. The additional equipment cost for the largerwheel is likely to have a price differential in the range ofonly $2,000 to $3,000. (The payback for the additionalequipment cost is in the range of 1.1 to 1.6 years.)

Conclusion, maximize the recovery systems efficiencyand minimize the recovery systems pressure dropwhenever possible. Additional comparisons can be

found in Appendix D for other air volumes. It can beseen that greatly oversizing does have limitations, suchas diminishing returns and longer payback periodsdepending on the efficiency sweet spot of anyparticular wheel, but the benefits of up upsizing shouldalways be investigated.


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8/15


When looking at energy recovery systems, energywheels are not the only choice, there are also static plateheat exchangers, thermal heat pipes, and run-around finand tube systems among others. Depending on theapplication these differing technologies are viableoptions, but remember these systems are generallysensible only heat transfer systems and do not transfermoisture. This may make it difficult to meet the

ASHRAE mandates of changing 50% to 60% of the totalenthalpy of the outdoor air supply equal to 50%-60% ofthe difference between the outdoor air and return air atdesign conditions. Thus it is important to look forsystems that can transfer both sensible and latentenergy.

Static plate systems, as well as thermal heat pipes andrun-around system are generally not as compact asenergy wheels and therefore may be more difficult toemploy. They do have the advantage of no movingparts (providing they do not incorporate damper style

frost protection systems), and they can be completelysealed between the exhaust and supply air streams.This is important when it is desirable to recover energyfrom non-reusable exhaust air sources.

Also look for systems that have relatively lowmaintenance requirements and have easy maintenanceaccess. Over the course of time some cleaning of theenergy recovery surface will be inevitable to maintain theeffectiveness of the recovery system. Easy access andor/slide out access to the recovery medium can keepmaintenance cost to a minimum.

What is the difference between sil ica gel wheels andzeolite wheels ?Up to now, sorption rotors existing on the marketworking under the principle of adsorption were usuallymade of silica gel or zeolite coating.

(1)Silica gel is silicon dioxide (SiO2). It is a naturallyoccurring mineral that is purified and processed intoeither granular or beaded form. As a desiccant, it has anaverage pore size of 24 angstroms and has a strong

affinity for moisture molecules. The silica gel will pull inmoisture at temperatures up to 220F (105C). Astemperature goes above 100F, the rate of moisturepickup will slow down but the silica gel will still work.

(1)Silica gel performs best at room temperatures (70 to90F) and high humidity (60 to 90% RH). Silica gel hasa wide range of pore sizes and therefore has the

capability of adsorbing compounds other than water. Therelative order of absorbability is: water, ammonia,alcohols, aromatics, diolefins, olefins and paraffins.When the potential for multicomponent adsorption ispresent, expect the more strongly adsorbed compounds,such as water, to displace the more weakly held ones.

(1)Molecular sieve is the best desiccant based on

technical performance characteristics. Its ability toadsorb moisture, in this case water vapor, is sopronounced that it can remove trapped H 20 moleculesfrom a fully saturated silica gel bead, which in turnchanges the silica gel back to its original Cobalt bluecolor.

(1)Molecular sieves are synthetic porous crystallinealuminosilicates which have been engineered to have avery strong affinity for specifically sized molecules. Thedefinitive feature of the molecular sieve structure, ascompared to other desiccant medias, is the uniformity of

the pore size openings.

(1)There is no pore size distribution with molecularsieves, as part of the manufacturing process the poresize on the molecular sieve particles can be controlled.The most commonly used pore size is 4 angstroms (4A)although 3 angstroms (3A), 5 angstroms (5A) and 10angstroms (13X) are available. This distinctive featureallows for the selection of a molecular sieve productwhich can adsorb water vapor yet exclude most othermolecules such as volatile organic compounds (VOCs)which may or may not be present in air stream.

(1)For example: 3A molecular sieve's structure allowswater vapor adsorption but excludes most hydrocarbons.3A is good for ammonia (NH3), water vapor (H2O) andpolar liquids. 4A molecular sieve has a slightly higherwater vapor capacity.

(1)Molecular sieves can trap water vapor to temperatureswell past 225C in some cases, and due to its highaffinity for water vapor, molecular sieve is able to bringthe relative humidity (RH) in environments down to as

low as 1% RH.(1) Although molecular sieve is slightly higher in cost perunit due to its extremely large range of adsorptivecapabilities and high capacity at low relative humidity it isoften the best value.


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(1) Source Sorbent Systems on line presence of IMPAKCorporation, 2011. Desiccant TypesOver the years silica gel wheels have been, rightly orwrongly, purported to be susceptible to germ formationor formation of odors because of their large pore size.Zeolite rotors have smaller pore diameters and thereforeare less susceptible to these concerns, but they havetraditionally been comparatively worse in terms of

performance. In the past this disadvantage was mostlycompensated for by applying a thicker desiccant coatinglayer which resulted in higher pressure losses throughthe wheel.

With the advent of synthetic nano-zeolite technology theproblem of applying a thicker coating and the resultanthigher pressure drop has been eliminated as the size ofthe nano-zeolite particles are clearly smaller comparedto other Zeolites. In consequence the adsorption kinetics(speed of adsorption and desorption) is much higher asthe distance to the pore is smaller. Additionally the

number of particles is higher and therefore the totalsurface area is larger.

The Klingenburg enthalpy wheel used in the AtherionERM module uses the Klingenburg patent pendingsynthetic nano-zeolite technology for improvedperformance and enhanced product reliability.

Where can energy recovery sy stems be applied?Most exhaust air streams are good targets for theapplication of energy recovery systems. ANSI/ASHRAEStandard 62.1 - Ventilation for Acceptable Indoor AirQuality defines four different air quality classifications,they are; Class 1 : Air with low contaminant concentration, lowsensory-irritation intensity, and inoffensive odor. Class 2 : Air with moderate contaminant concentration,mild sensory-irritation intensity, or mildly offensive odors.Class 2 air also includes air that is not necessarilyharmful or objectionable but that is inappropriate fortransfer or recirculation to spaces used for differentpurposes. Class 3 : Air with significant contaminant concentration,

significant sensory-irritation intensity, or offensive odor. Class 4 : Air with highly objectionable fumes or gasesor with potentially dangerous particles, bioaerosols, orgases, at concentrations high enough to be consideredharmful.The standard further advises which classes of air maybe recirculated under certain conditions. The followingrecommendations are include in ASHRAE 62.1.

Energy Recovery. Class 2 Air may be re-designated asClass 1 air in the process of recovering energy when it isdiluted with outdoor air such that no more than 10% ofthe resulting airstream is Class 2 air. Class 3 Air may bere-designated as Class 1 air in the process of recoveringenergy when it is diluted with outdoor air such that nomore than 5% of the resulting airstream is Class 3 air.

Recirculation Limitations - When the Ventilation RateProcedure of ASHRAE 62.1 is used to determineventilation airflow values, recirculation of air shall belimited in accordance with the following requirements.Class 1 Air - Class 1 air may be recirculated ortransferred to any space.Class 2 Air - Class 2 air may be recirculated within thespace of origin. Class 2 air may be transferred orrecirculated to other Class 2 or Class 3 spaces utilizedfor the same or similar purpose or task and involving thesame or similar pollutant sources. Class 2 air may berecirculated or transferred to Class 4 spaces. Class 2 air

shall not be recirculated or transferred to Class 1spaces. Note: Spaces that are normally class 1 may beidentified as Spaces ancillary to class 2 spaces and assuch classified as Class 2 spaces as permitted in Table

A.Class 3 Air - Class 3 air may be recirculated within thespace of origin. Class 3 air shall not be recirculated ortransferred to any other space.Class 4 Air - Class 4 air shall not be recirculated ortransferred to any space nor recirculated within thespace of origin.

ASHRAE 62.1 also includes information and tables thatenable a designer to classify the air based on the pointof origin and anticipated contaminants. Basically onlyClass 4 air may not be recirculated under anycircumstances.

When energy recovery wheels are employed, the wheelsrotate through both the supply air stream and theexhaust air stream, thus there is a potential for crosscontamination, however small. For this reason energyrecovery wheels may be restricted for use with exhaust

air streams whose space of origin is defined as Class 4.In these cases, static plate, fin & tube run-around, orthermal heat pipe systems may be considered, eventhough they may sacrifice the latent heat recoverypotential in the exhaust air stream. In all other cases,energy wheels are acceptable when applied under theRecirculation Limitation guidelines presented earlier.


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What type of controls should be considered forintegration of the energy recovery system to theDOAS unit?The controls for the energy recovery wheel should becapable of determining whether or not the unit should beoperating in the energy recovery mode or theeconomizer mode. The best way to accomplish this is touse enthalpy sensors that monitor both the outside air

(on wheel) and the supply air (off wheel) conditions.Based on the feedback from these sensors, calculationscan be made via a unit microprocessor control orbuilding management system which can define whichmode of operation is appropriate.

Consideration should be made for monitoring the airpressure drop across the energy wheel to provide anearly detection system in the event of wheel fouling. Inaddition a method of monitoring the wheel rotation isdesirable to make sure the wheel is actually rotatingwhen called to do so. This prevents the possibility of a

broken wheel drive belt not being noticed. Other itemsmight include air flow proving switches, dirty filterswitches, etc.

In cold climates the recovery system will need someform of frost control, and in extreme cold the system mayalso require an outside air preheat capability.

SummaryBecause Dedicated Outdoor Air Systems (DOAS units)are operated under extreme entering air conditions it ispreferable to pretreat (temper) the outdoor air as muchas possible before it reaches the HVAC systemsmechanical heating and cooling components. Doing thiswill substantially reduce the loads on these componentsand will allow downsizing the mechanical heating andcooling components. The nature of the application ofDAOS units makes these systems ideal targets forincorporating energy recovery capabilities.

Benefits of Adding Energy Recovery to DOASSystems

Reduced DOAS operating cost (up to 40% or

more savings) Increased system cooling EER (up to 150% or

greater improvement) Reduced mechanical cooling and heating

equipment size.

Energy Recovery Applic ation Checks

Always consider the use of energy recoverywhen specifying Dedicated Outdoor AirSystems.

Select the system that maximizes the energyrecovery effectiveness of the system whilemaintaining the lowest pressure drop throughthe system.

To accomplish the previous check, investigate

up-sizing the energy recovery wheel. Theadded savings will often far exceed any first costincreases and can result in surprisingly shortenergy-system investment paybacks.

Never bypass exhaust and supply air around theenergy recovery system outside of economizermode, in an attempt to reduce system motorhorsepower. The savings in reduced motorhorsepower will rarely compensate for the lossof potential energy recovered in the exhaust airstream.

Select a system that allows for filtration of both

the supply and exhaust air streams. This willhelp reduce fouling of the energy wheel whichwill help maintain the effectiveness of thesystem and reduce maintenance costs.

Remember, most exhaust air streams aretargets for energy recovery. Exhaust air needsto be replaced with make-up air or ventilation air.

A DOAS unit is designed for this specificapplication. Remember energy recovery wheelsare applicable to ASHRAE Class 1 through 3 airsteams.

Remember that ASHRAE Standards 90.1 and189.1 define energy recovery in terms of totalenthalpy. Whenever possible, select an energyrecovery system that is capable of recoveringboth sensible and latent energy.

Maximize the energy recovery system byselecting equipment that can bypass much or allof the supply and exhaust air while operating inthe economizer mode to reduce annualoperating costs. It is not uncommon foreconomizer hours of operation to exceed energyrecovery hours. Energy recovery economizer air

bypass or other system control is a requirementof ASHRAE Standards 90.1 and 189.1.

Use enthalpy sensors to monitor both theoutside air (air on the wheel) and supply air (airoff the wheel) to allow optimization of the energyrecovery system.

Provide frost control protection and/or systemsin cold climates.


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Comparison of DOAS Cooling System Performance in Atlanta, Georgia. Standard System vs System with Energy Recovery Cooling load hours = 1787 Heating Load Hours = 1443 Total Hours in a Year = 8760

STANDARD AIR CONDITIONING SYSTEM PERFORMANCETabel 1 Standard Air Conditioning System Performance

Tons of Energy Cost per Hour Annual AnnualEnthalpy Enthalpy Mechanical EER Used @ $.13 per Cooling Energy

CFM DB oF WB oF % RH (Btu/Lb) DB oF % RH (Btu/Lb) Cooling (kW) kW Hour Hours Cost5000 95 79 49.89 42.44 72 50 26.43 30.0 11.5 31.3 $4.07 1787 $7,277

Table2 Estimated Portion of Operating Costs Contributed to System Supply Fan During Cooling ModeAssumed Cooling Annual

TSP Energy Load Operating(" w.c.) BHP kW Efficiency Cost / kW Hours Cost

4.8 6.41 4 .8 90.0% $0.13 1787 $1,234

AIR CONDITIONING SYSTEM PERFORMANCE WITH 52" TOTAL ENERGY RECOVERY WHEELTable 3 Wheel Performance

Tons of Enthalpy Enthalpy Enthalpy Recovered

CFM DB oF WB oF % RH (Btu/Lb) DB oF WB oF % RH (Btu/Lb) DB oF WB oF % RH (Btu/Lb) Cool ing5000 95 79 49.89 42.44 75 63 51.63 28.8 79.4 67.45 54.3 31.9 19.8

Table 4 Mechanical Cooling PerformanceTons of Energy Cost per Hour Annual

Enthalpy Enthalpy Mechanical EER Used @ $.13 per Energy

CFM DB oF WB oF % RH (Btu/Lb) DB oF % RH (Btu/Lb) Cooling (kW) kW Hour Cost5000 79.4 67.45 54.3 31.9 72 50 26.43 10.3 11.5 10.7 $1.39 $2,486

Table 5 Added Energy Load for Increased Static Pressure Load of Energy Wheel System & Wheel Rotation Motor (1)

Added Total Total Wheel Total Total

Exhaust Duct Added Added Rotation Added Added

CFM P (" w.c.) Fan HP Fan kW Fa n HP Fan kW Fan HP Fan kW Motor kW HP Motor kW5000 1.047 0.62 0.463 1.09 0.813 1.71 1.276 0.1865 1.96 1.5

(1) Exhaust P includes wheel plus 0.5" w.c. for added exhaust ai r ductwork

Cooling Cost perLoad kW

CFM Hours Hour Dollars Percent5000 1787 $0.13 $7,277 $4,413 60.6%

(1) Assumes 90% efficienct motors

Table 7 Comparison of Apparent EER of A/C System w/ Energy Recovery versus Standard A/C SystemSystem

Mechanica Recovered Total kW /Hr Cost/Hr EER

Standard A/C System 30.0 0 30.0 31.3 $4.07 11.5A/C System w/ Energy Recovery System 10.3 19.8 30.0 12.2 $1.58 29.6

APPENDIX A Cooling Savings Estimate

WheelRotation

Motor HP0.25

Entering Air Design Condi ti ons Suppl y Air Design Conditons

EnergyWheel

P (" w.c.)0.547

Supply Side (1) Exhaust Side

Entering Air Design Condi ti ons Suppl y Air Design Conditons

Outside Air Design Condi ti ons Bui ldi ng Exhaust Air Design Condi tons Wheel Leaving Air Conditions

Supply Fan Motor

(1) Total (1) Added Motor Operating Costs

Table 6 Added Energy Cost for Increased Static PressureLoad of Energy Wheel System & Wheel Rotation Motor

Table 7 Comparison of A/C System w/ Energy Recovery versus Standard A/C System

Savings w/ A/C

157.51%

Added Motor

kW1.6 $2,864

Energy Cost For

ERV During Cooling$377.42

Std A/C A/C w/ ERV

Tons of Cooling Energy Used

System w/ ERV

PercentEER Improvement

The following calculations were used to compare the operating cost of a typical 5000 cfm dedicated outdoor air ventilation system installed in Atlanta, Georgia and operating 24/7 without an energy recovery system, and with an energy recovery system during the cooling mode of operation. The calculations show that the addition of the energy recovery module reduces the operating cost by 60%.


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Cooling load hours = 1787 Heating Load Hours = 1443 Total Hours in a Year = 8760

STANDARD DOAS HEATING SYSTEM PERFORMANCETabel 1 Standard Heating System Fuel Usage

Heati ng Uni t Heati ng Annual Therms Cos t of AnnualEAT LAT Capaci ty Effi c iency Capaci ty Hea ting Used per Natural Ga s Fuel

CFM DB oF DB oF MBH Output MBH Input Hours Year per Therm Cos t5000 18 72 291.6 80.0% 364.5 1443 5,260 $0.90 $4,734

Table2 Estimated Operating Costs of System Supply Fan DuringHeating Mode

Assumed Heating Annual Annual Annual TotalTSP Energy Running Operating Fuel Electric Operating

(" w.c .) BHP kW Effi c iency Cos t / kW Hours Cost Cost Cost Cost4.8 6.41 4.8 0.9% $0.13 1443 $997 $4,734 $997 $5,730

DOAS HEATING SYSTEM PERFORMANCE WITH TOTAL ENERGY RECOVERY WHEELTable 4 Energy Wheel Heat Recovery Performance

Enthalpy Enthalpy Enthalpy Recovered

CFM DB oF WB oF % RH (Btu/Lb) DB oF WB oF % RH (Btu/Lb) DB oF WB oF % RH (Btu/Lb) Heat (MBH)5000 18 16.75 80 5.99 75 63 51.63 28.8 57.4 49.42 61.8 19.95 314.1

Table 5 Mechanical Heating System Requirement Mec ha ni ca l Uni t Mec ha ni ca l Ann ua l Ther ms Cos t of Annual

Enthalpy Enthalpy Heating Load Efficiency Heating Load Heating Used per Natural Ga s Fuel

CFM DB oF WB oF % RH (Btu/Lb) DB oF % RH (Btu/Lb) MBH Output MBH Input Hours Year per Ther m Cos t5000 57.4 49.42 61.8 19.95 72 50 26.43 78.8 80% 98.6 1443 1,422 $0.90 $1,280

Table 6 Added Energy Load for Increased Static Pressure Load of Energy Wheel System & Wheel Rotation Motor (1) Added Total Total Wheel Total Total

Exhaust Duct Added Added Rotation Added Added

CFM P (" w.c.) Fan BHP Fa n kW Fan HP Fan kW Fan HP Fan kW Motor kW HP Motor kW5000 0.926 0.62 0.463 1.09 0.813 1.71 1.28 0.1865 1.96 1.5

(1) Exhaust P includes 0.47 " w.c. for energy wheel an d 0.5" w.c. for added exhaust ai r ductwork

Cost perHeating kW Std Heating

CFM Hours Hour Dollars Percent5000 1443 $0.13 $5,730 $3,149 55.0%

(1) Assumes 90% efficient motors

APPENDIX B Heating Savings Estimate

Design Conditions

Outside Air Design Conditions Building Exhaust Air Design Conditons Wheel Leaving Air Conditions

Comparison of DOAS Heating System Performance in Atlanta, Georgia. Standard System vs System with Energy Recovery

Entering Air Design Conditions Supply Air Design Conditons

Supply Fan Motor

Table 3 Estimated Operating Costs of Heating System During Heating Mode

Energy Supply Side (1) Exhaust Side WheelWheel Rotation

P (" w.c.) Motor HP0.426 0.25

Table 7 Added Energy Cost for Increased Static Pressure Table 8 Comparison of Heating System w/ Energy Load of Energy Wheel System & Wheel Rotation Motor Recovery versus Standard System

(1) Total Added (1) Total Added Operating Costs Saving with HeatingSystem w/ ERV

1.6 $304.76 $2,581

Motor Energy Cost For

kW ERV During Heating

Heating System with

Energy Recovery

The following calculations were used to compare the operating cost of a typical 5000 cfm dedicated outdoor air ventilation system installed in Atlanta, Georgia and operating 24/7 without an energy recovery system, and with an energy recovery system during the heating mode of operation. The calculations show that the addition of the energy recovery module reduces the operating cost by 55%.


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Comparison of DOAS Heating System Performance in Atlanta, Georgia. Standard System vs System with Energy Recovery Cooling load hours = 1787 Heating Load Hours = 1443 Total Hours in a Year = 8760

Total System Static Pressure and HP Assumptions for Standard System.Table 1 Standard System Fan(s) Operating Costs During CoolingSupply & Supply Exhaust (1) Total Fan Cooling AnnualExhaust TSP TSP Motor Power Energy Runn ing Operating

CFM (" w.c.) BHP kW Efficiency (" w.c.) BHP kW Efficiency kW Cost / kW Hours Cost 5000 4.8 6.41 4.8 90.0% n/a 0 0.0 90.0% 5.31 $0.13 1787 $1,234

Table 2 Standard System Fan(s) Operating Costs During HeatingSupply & Supply Exhaust (1) Total Fan Heating AnnualExhaust TSP TSP Motor Power Energy Runn ing Operating

CFM (" w.c.) BHP kW Efficiency (" w.c.) BHP kW Efficiency kW Cost / kW Hours Cost 5000 4.8 6.41 4.8 90.0% n/a 0 0.0 90.0% 5.31 $0.13 1443 $997

Table 3 Standard System Fan(s) Operating Costs During Non Heating/Cooling HoursSupply & Supply Exhaust (1) Total Fan Non Htg/Clg AnnualExhaust TSP TSP Motor Power Energy Runn ing Operating


Table 4 Total Standard System Fan(s) Annual Operating CostsSupply & Supply Exhaust (1) Total Fan Total AnnualExhaust TSP TSP Motor Power Energy Runn ing Operating


Total System Static Pressure and HP Assumptions for System with Energy Recoverybut Without Energy Recovery Wheel BypassTable 5 System with Energy Recovery Supply Fan(s) Operating Costs During CoolingSupply & Supply Exhaust (1) Total Fan Cooling AnnualExhaust TSP TSP Motor Power Energy Runn ing Operating

CFM (" w.c.) BHP kW Efficiency (" w.c.) BHP kW Efficiency kW Cost / kW Hours Cost

5000 5.23 7.03 5.2 90.0% 0.926 1.09 0.8 90.0% 6.73 $0.13 1787 $1,564

Table 6 System with Energy Recovery Supply Fan(s) Operating Costs During HeatingSupply & Supply Exhaust (1) Total Fan Heating AnnualExhaust TSP TSP Motor Power Energy Runn ing Operating

CFM (" w.c.) BHP kW Efficiency (" w.c.) BHP kW Efficiency kW Cost / kW Hours Cost 5000 5.23 7.03 5.2 90.0% 0.926 1.09 0.8 90.0% 6.73 $0.13 1443 $1,263

Table 7 System with Energy Recovery Fan(s) Operating Costs During Non Heating/Cooling Hours and Without Energy Wheel BypassSupply & Supply Exhaust (1) Total Fan Non Htg/Clg AnnualExhaust TSP TSP Motor Power Energy Runn ing Operating


Table 8 Energy Recovery Wheel Motor Supply & Supply Exhaust (1) Total Fan Total AnnualExhaust TSP TSP Motor Power Energy Runn ing Operating

CFM (" w.c.) BHP kW Efficiency (" w.c.) BHP kW Efficiency kW Cost / kW Hours Cost 5000 n/a 0.25 0.2 90.0% n/a n/a n/a 90.0% 0.21 $0.13 3230 $87

Table 9 Total System with Energy Recovery Supply Fan(s) Annual Operating CostsSupply & Supply Exhaust (1) Total Fan Total AnnualExhaust TSP TSP Motor Power Energy Runn ing Operating


Exhaust Fan Motor

Exhaust Fan Motor

Exhaust Fan Motor

Exhaust Fan Motor

Exhaust Fan Motor

Exhaust Fan Motor

Exhaust Fan Motor

Exhaust Fan Motor

Exhaust Fan Motor

Supply Fan Motor

Supply Fan Motor

APPENDIX C Air Side Fan Energy Calulations

Supply Fan Motor

Supply Fan Motor

Supply Fan Motor

Supply Fan Motor

Supply Fan Motor

Supply Fan Motor

Energy Wheel Rotation Motor

The following calculations were used to compare the air side motor operating costs of a typical 5000 cfm dedicated outdoor air ventilation system installed in Atlanta, Georgia and operating 24/7 without an energy recovery system, and with an energy recovery system during the cooling, heating, and economizer modes of operation. The calculations show that the addition of the energy recovery module without air bypass adds $1,701 to the air side fan operating costs, and the addition of the energy recovery module with air bypass adds $1,379. Therefore the system with the air bypass reduces the added air side fan cost of operation by $322 or 18.9% compared to a system without air bypass.


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Total System Static Pressure and HP Assumptions for System with Energy Recoveryand With Energy Recovery Wheel BypassTable 10 System with Energy Recovery Supply Fan(s) Operating Costs During CoolingSupply & Supply Exhaust (1) Total Fan Cooling AnnuaExhaust TSP TSP Motor Power Energy Running Operatin


Table 11 Standard System Supply Fan Operating Costs During HeatingSupply & Exhaust (1) Total Fan Heating AnnualExhaust TSP TSP Motor Power Energy Running Operatin


Table 12 Standard System Supply Fan Operating Costs During Non Heating/Cooling Hours and With Energy Wheel BypassSupply & Exhaust (1) Total Fan Non Htg/Clg AnnuaExhaust TSP TSP Motor Power Energy Running Operatin


Table 13 Energy Recovery Wheel Motor Supply & Supply Exhaust (1) Total Fan Total AnnuaExhaust TSP TSP Motor Power Energy Running Operatin

CFM (" w.c.) BHP kW Efficiency (" w.c.) BHP kW Efficiency kW Cost / kW Hours Cost 5000 n/a 0.25 0.2 90.0% n/a n/a n/a 90.0% 0.21 $0.13 3230 $87

Table 14 Total System with Energy Recovery Supply Fan(s) Annual Operating CostsSupply & Exhaust (1) Total Fan Total AnnuaExhaust TSP TSP Motor Power Energy Running Operatin

CFM (" w.c.) BHP kW Efficiency (" w.c.) BHP kW Efficiency kW Cost / kW Hours Cost 5000 5.1 7.06 5.3 90.0% 5.3 90.0% 11.78 $0.13 8760 $7,430

(1) Assumes 90% efficient motors

Exhaust Fan Motor

Exhaust Fan Motor

Exhaust Fan Motor

Exhaust Fan Motor

APPENDIX C Air Side Fan Energy Calulations (Continued)

Exhaust Fan Motor

Supply Fan Motor

Supply Fan Motor

Supply Fan Motor

Supply Fan Motor

Energy Wheel Rotation Motor


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Oversized Wheel vs Maximized Wheel ScenariosBased on AHRI 1060 Standard Conditions of 95DB/79WB Supply and 75DB/63WB ExhaustAtlanta, Georgia cooling hours = 1787

Energy

WheelDia. Enthalpy

(Inches) Cfm WB oF WB oF (Btu/Lb) %RH Btu/Hr % Effec. Btu/Hr % Effec. Btu/Hr % Effec.

46 5000 95 79 42.44 49.89 75,874 71.3% 97,664 63.1% 173,538 55.2%52 5000 95 79 42.44 49.89 83,037 77.9% 115,994 74.9% 199,031 63.4%46 4000 95 79 42.44 49.89 64,006 75.1% 86,686 70.0% 150,692 60.0%52 4000 95 79 42.44 49.89 69,242 81.3% 99,856 80.6% 169,098 67.3%46 3000 95 79 42.44 49.89 50,934 79.7% 72,354 77.9% 123,288 65.4%52 3000 95 79 42.44 49.89 54,431 85.1% 80,827 87.0% 135,258 71.8%

(1,2) (1,3) Increased(1,2) Cost of (1,4) Net Annual

(5)(6) Energy Energy Cost of Energy Net Annual Energy

Energy Mechanical Ene rgy A ir Wheel Wheel (1) Cost of Air Side Wheel Energy Cooling CostWheel Cooling Wheel Side Air Side Rotat ion Rotat ion Energy Motor Motor Cost Energy Avoidance

Dia. Reduction P Motor Motor Motor Motor Recovered Operat ion Operat ion Avoidance Cost w/ Larger(Inche s) Tons (" w.c.) BHP kW HP kW per Hour per Hour per Hour Per Hour Avoidance Wheel

46 14.5 0.842 1.98 1.477 0.250 0.187 $6.61 $0.234 $0.030 $6.35 $11,344 52 16.6 0.547 1.36 1.015 0.250 0.187 $7.58 $0.161 $0.030 $7.39 $13,211 $1,86746 12.6 0.660 1.58 1.179 0.250 0.187 $5.74 $0.187 $0.030 $5.53 $9,873 52 14.1 0.431 1.12 0.836 0.250 0.187 $6.44 $0.132 $0.030 $6.28 $11,224 $1,35046 10.3 0.484 1.22 0.910 0.250 0.187 $4.70 $0.144 $0.030 $4.52 $8,084 52 11.3 0.318 0.90 0.671 0.250 0.187 $5.15 $0.106 $0.030 $5.02 $8,966 $883

(1) Assumes cost of electricity to be $0.13 / kW Hour(2) Assumes 82% Efficient motors(3) Based on average cooling hours for Atlanta, Georgia(4) Net energy cost avoidance is calculated as energy recovered less motor energy cost for operation of recovery system.(5) Motor HP includes both supply and exhaust ai r side of energy recovery system.(6) Based on using a 27" Dia. Backward Inclined Air Foil Plenum Fan.

Appendix D Benefits of Upsizing Savings Calculations

Latent Sensible

Energy Recovered and Energy Recovery EffectivenessSupply Air Conditions

Total

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