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Energy and Buildings 45 (2012) 257–263

Contents lists available at SciVerse ScienceDirect

Energy and Buildings

j ourna l ho me p age: www.elsev ier .com/ locate /enbui ld

nergy and water conservation from air handling unit condensate in hot andumid climates

usan Licina, Chandra Sekhar ∗

epartment of Building, School of Design and Environment, National University of Singapore, 4 Architecture Drive, Singapore 117566, Singapore

r t i c l e i n f o

rticle history:eceived 19 October 2011ccepted 13 November 2011

eywords:nergy and water conservationot and humid climateondensate recovery

a b s t r a c t

This study investigates the potential for energy and water sustainability in hot and humid climates byutilizing the condensate captured from large dedicated air handling units (AHUs) for pre-cooling outdoorair in another AHU and subsequently offsetting cooling tower water needs. In such climates, latent loadis large enough throughout the year to produce a substantial amount of condensate, which is typicallydrained away from all the AHUs. In this study, condensate is collected from several AHUs and directedthrough another coil that pre-cools the warm and humid outdoor air which is supplying another AHU,called the condensate assisted pre-cooling (CAP) AHU. During the same time, the cooling towers require

ir handling unitooling tower

considerable amounts of make-up water to replace water losses occurring on a regular basis. The con-densate, including that from the main cooling coil of the CAP AHU, is first supplied to the pre-coolingcoil of the CAP AHU and is then routed through the cooling tower, which significantly reduces potablewater usage and improves cooling tower water chemistry. It is found that condensate production is largeenough to make pre-cooling cost-beneficial with energy savings of approximately 10% and the ability tooffset cooling tower water demand in excess of 50%.

. Introduction

In a time of increasing energy and water demand, engineers willeed to pay more attention to designing innovative energy efficientystems together with conservation of natural resources in ordero minimize their environmental impact.

In hot and humid climates, considerable amount of energy issed in the conditioning of outdoor air, which involves coolingnd dehumidification. Comparing to typical office building, HVACystems in facilities such as hospitals, laboratories or operating the-tres can consume five to ten times more energy [1]. This highernergy use is due to many factors including provision of largemounts of 100% outside air, continuous operation, requirementor stringent internal parameters, high fan energy, etc. At the sameime, imbalance seems to exist between the current cost of waternd the actual value of that water to the society and environment.ven purified and distributed over long distances, water is avail-ble for such a low cost that it usually consumed irrationally, i.e.rreversibly wasted. With this significant energy and water usage,

esigning innovative efficient systems will be essential.

In temperate climates, the amount of latent load is vari-ble throughout the year which implies inconsistent condensate

∗ Corresponding author.E-mail address: bdgscs@nus.edu.sg (C. Sekhar).

378-7788/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.enbuild.2011.11.016

© 2011 Elsevier B.V. All rights reserved.

production. These fluctuations lead to inability to harvest the con-densate continuously year round. On the other hand, in hot andhumid climates, latent load is large enough to produce a reasonableamount of condensate throughout the year. Apart from climaticconditions, important factors that determine whether condensatecollection should be a cost-effective venture include the amount ofoutdoor air required, capacity, number and accessibility of AHUsthat condition outdoor air, location of end user for the condensate,etc.

So far, little has been done in the field of energy recovery fromcondensate. Namek [2] in 2005 raised a question whether the latentload is large enough to produce a sufficient amount of condensatefor pre-cooling of outdoor air that is supplying another AHU. Thestudy which is carried out for different locations across the U.S.showed that pre-cooling of the second airstream might be cost-effective if large amount of condensate is discharged from the firstair stream, and if the mass flow rate of the second air stream issignificantly lower. Also, it is suggested that this system wouldbe more attractive in locations where high wet bulb temperaturesoccur year round.

Unlike energy saving strategies, more attention has been paid towater sustainability features. Guz [3] reported that the San Antonio

central library produces 0.06 l/s or 163,500 l of condensate eachmonth from its air handlers, which is used for irrigation purposes.The downtown Rivercenter Mall collects 946 l of condensate perday, which is used to partially offset cooling tower water losses. It

258 D. Licina, C. Sekhar / Energy and B

Nomenclature

ACH air change per hour (h−1)AHU air handling unitCAP AHU condensate assisted pre-cooling air handling unitDOAHU dedicated outdoor air handling unitHVAC heating, ventilation and air conditioningcp specific heat capacity of water (kJ/kg K)mcon production of condensate flow rate (l/s)mamb outdoor air flow rate (m3/s)wamb outdoor air absolute humidity (kg/kg)woff off-coil air absolute humidity (kg/kg)Wc condenser/cooling tower water flow (l/s)Qcon condenser capacity (kW)�T temperature range of condenser/cooling tower (◦C)Wm make up water (l/s)We water loss due to evaporation (l/s)

isb

mwtdtidwwmir

i–EdSr

osctwr

2

2

isiopwbp

The process described is most cost-effective if the latent coolingload from 6 AHUs is large enough to generate sufficient flow of

Wb water loss due to drift (l/s)Wd water loss due to blow down (l/s)

s found that the fastest payback period for condensate recoveryystem is utilizing the water for cooling tower make up, which cane less than a year.

Furthermore, severe drought along the southeast of U.S. in 2007ade a wake-up call for exploring alternative sources of waterhich can be used in more efficient manner. Painter [4] explored

he feasibility of harvesting condensate from large dedicated out-oor AHUs with enthalpy wheel energy recovery, which is usedo offset water consumption for water closets, urinals and cool-ng tower. For the case study, building located in San Antonio isetermined to have an annual condensate production of 7.15 × 106 lhich is enough to completely replace water closets and urinalsater demand, while the excess of 6.12 × 106 l is used to supple-ent landscape irrigation. In case that entire condensate collected

s applied for supplementing the cooling tower water needs, 16%eduction in potable water consumption is estimated.

The water consumption in buildings and its relevance to societys reflected in two present Standards: ASHRAE Standard 189.1-2009

Standard for the Design of High Performance Green Buildingsxcept Low-Rise Residential Buildings; and Standard 191P – Stan-ard for the Efficient Use of Water in Building, Site and Mechanicalystems. Both standards address water efficiency usage, providingequirements for water using systems and condensate collection.

The purpose of this study is twofold: first, to analyse, by meansf a standard coil selection software and heat pipe dehumidificationoftware, one such system related to energy saving potential due toondensate energy recovery and second, water saving potential dueo condensate being directed to replenish cooling tower make-upater requirements, both of which are applied in a hot and humid

egion.

. Methodology

.1. Description of the system

In this study, the recovery medium is cold condensate that is typ-cally drained away from numerous AHUs and routed to the nearestanitary drain. During cooling, air passes through the cooling coilsn six AHUs prior to entering the facility. Each AHU is assigned tone storey, conditioning 10,000 m3/h of 100% outdoor air and 24 h

er day operation, 7 days a week. As air cools, its ability to holdater in the form of vapour decreases. When air is cooled down

eneath its dew point, transition from gaseous phase into liquidhase begins and moisture is released. This condensate then drips

uildings 45 (2012) 257–263

into a collection pan below each unit from which, together withcondensate from the other five units, is drained by gravity to thecollector, placed next to the condensate assisted pre-cooling (CAP)AHU at the lowest floor (Fig. 1). The condensate, including that fromthe main cooling coil of the CAP AHU, is first supplied to the pre-cooling coil of the CAP AHU and then flows directly into the coolingtower basin, thus reducing the amount of required potable waterand improving cooling tower water chemistry. The cold conden-sate is constantly sent to the energy recovery pre-cooling coil via asmall pump.

The first step in this study is to collect annual weather data forseveral cities in south-east Asia region [5]. The average monthlydry bulb temperature and relative humidity data for representa-tive cities are shown in Figs. 2 and 3, respectively. As seen, thehighest and most consistent latent load throughout the year occursin Singapore, which has been chosen as a representative city for thepurpose of this study.

The next step is to determine the absolute humidity values forthe on/off-coil dry bulb temperature and relative humidity. For bothcases without and with heat pipe the assumed leaving conditionsare 16 ◦C dry bulb temperature with a 99% and 60% relative humid-ity, respectively. The psychrometric state points, associated withthe average annual conditions, are shown in Figs. 4 and 5.

Finally, the amount of condensate produced from the dehumid-ification process is calculated using mass balance equation:

mcon = mamb(wamb − woff ) (1)

Heat transfer between the droplets of moisture and the waterinside of cooling coil is governed by conduction. It is expected thatthe temperature of the condensate collected below the coolingcoil will approach the surface temperature. The actual measure-ments of condensate temperature are conducted for the same givenconditions. The average temperature of condensate obtained is11.8 ◦C; however, the adopted value of the condensate temperatureis 12.5 ◦C as the highest recorded value during 24 h measurement(Fig. 6). Condensate collected does not account for any heat gainduring transport to the pre-cooling coil. Therefore, in hot and humidclimates, the enthalpy the discharged condensate is low enough tobe used in an energy recovery process.

2.2. Energy recovery process

The process of energy recovery is analysed in two differentways using two different simulation softwares. The first analysis,by means of SPC 2000 standard cooling coil selection program [6],include the energy recovery pre-cooling load for systems usingconventional DOAHUs without possibility of maintaining stringentrelative humidity parameters. Typical facilities using such a sys-tem are food preparation centres, laundry facilities, some industrialfacilities and storages. The second analysis, performed using SPCHPD heat pipe dehumidification software [7], is energy recoveryanalysis of system using DOAHU in conjunction with heat pipedevice. This system enables maintaining stringent internal param-eters which are required by facilities such as laboratories, cleanrooms, rare book libraries, operating theatres and animal housefacilities. In this case, heat pipe device is integrated only in upper 5AHUs, while the CAP AHU in which energy analysis is conducted iskept without heat pipe device.

condensate which is inherent in a humid climate and occurs year-round (high wet bulb temperatures), and if there is no additionalenergy used in pump, i.e. the condensate from the upper AHUs isdrained by gravity to the energy recovery pre-cooling coil.

D. Licina, C. Sekhar / Energy and Buildings 45 (2012) 257–263 259

OAHU

2

nlotcai

Fr

Fig. 1. Scheme of condensate energy recovery system using 6 D

.3. Water recovery process

The quantity of condensate collected at design condition doesot necessarily correspond to the total amount of condensate col-

ected throughout the course of a year. This is a function of the rangef distinctive conditions that exist over the course of the year. Since

he uniform high wet bulb temperature occurs year round and theondensate is collected from system that conditions 100% outdoorir and operates 24/7/365, it is not necessary to make adjustmentsn the amount of condensate collection predictions.

ig. 2. Monthly average dry bulb temperature for several cities in south-east Asiaegion.

s with cooling tower water recovery (drawing is not to scale).

Figs. 7 and 8 show monthly average condensate productionpotential for Singapore, Bangkok, Kuala Lumpur and Manila, with-out and with heat pipe strategy, respectively.

The condensate collected, after recovering energy in the pre-cooling coil of the CAP AHU is routed to cooling tower sump. In orderto determine cooling tower’s annual make-up water consumption,

the condenser heat rejection part was first calculated. The chillerload, which is determined by adding cooling loads of all six AHUs,is oversized by 20% as most water chillers are larger than needed tomeet maximum load conditions. Once the chiller load is calculated,

Fig. 3. Monthly average relative humidity data for several cities in south-east Asiaregion.

260 D. Licina, C. Sekhar / Energy and Buildings 45 (2012) 257–263

tlte

W

Fh

Fig. 6. Temperature of the condensate discharged from the cooling coil during 24 hmeasurements.

Fig. 4. Psychrometric state points of the air passing through the cooling coil.

he cooling tower’s total heat rejection load is 1.2 times the chilleroad due to energy used in compressor. Finally, water flow throughhe condenser and cooling tower is calculated using the followingquation:

c = Qcon

cp · �T(2)

ig. 5. Psychrometric state points of the air passing through the cooling coil andeat pipe device.

Fig. 7. Monthly average condensate production potential for different cities withoutheat pipe strategy.

where �T represents the difference between inlet water tempera-ture and outlet water temperature of cooling tower.

Water make-up (Wm) requirements for a cooling tower consistsof the sum of water loss due to evaporation, drift loss, and blowdown. Evaporation loss can be estimated by:

We = 0.00085 · 1.8 · Wc · �T (3)

As the evaporated water in the cooling tower is in a pure vapourstate, it leaves its dissolved solids behind, thus raising the con-centration in the circulating cooling water. To prevent the solid

concentration of the water from becoming too high, and thereforeprotecting the condenser, cooling tower and equipment, a portion

Fig. 8. Monthly average condensate production potential for different cities usingheat pipe device.

D. Licina, C. Sekhar / Energy and Buildings 45 (2012) 257–263 261

Table 1Summary of the condensate energy recovery analysis without heat pipe using SPC2000 software.

Cooling coil Pre-coil

Air side dataAir on DB temp. (◦C) 27.5 27.5Air on RH (%) 84 84Air off DB temp. (◦C) 16 24.7Air off RH (%) 99 98Air flow rate (m3/h) 10,000 10,000Duty (kW) 101.2 9.36Face velocity (m/s) 2 2Air pressure drop (Pa) 131.5 175.4Fluid side dataFluid on temp. (◦C) 6 12.5Fluid off temp. (◦C) 12 24.3Flow rate (l/s) 4.03 0.19Max pressure drop (kPa) 50 50Physical dataFin material/type Al 0.15 louvre Al 0.15 louvreCoil type Water WaterTube diameter (mm) 12 12Tubes high 28 28Finned height (mm) 1070 1070Finned length (mm) 1300 1300Fin density (Fins/in.) 14 14

ow

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Table 2Summary of the condensate energy recovery analysis with heat pipe using SPC HPDsoftware.

Cooling coil Pre-coil

Air side dataAir on DB temp. (◦C) 27.5 27.5Air on RH (%) 84 84Air off DB temp. (◦C) 16 24.7Air off RH (%) 60 98Air flow rate (m3/h) 10,000 10,000Duty (kW) 147.7 10.99Face velocity (m/s) 2 2Air pressure drop (Pa) 319 175.4Fluid side dataFluid on temp. (◦C) 6 12.5Fluid off temp. (◦C) 12 ◦C 21.2Flow rate (l/s) 3.34 0.28Max pressure drop (kPa) 50 50Physical dataFin material/type Al 0.15 louvre Al 0.15 louvreCoil type Water WaterTube diameter (mm) 12 12Tubes high 28 28Finned height (mm) 1070 1070Finned length (mm) 1300 1300Fin density (Fins/in.) 14 14No. rows 8 4

No. rows 3 4

Savings (%) 9.3

f the water is drained off for disposal and replaced with cleanater:

b = We − (C − 1) · Wd

C − 1(4)

here C is cycles of concentration as the ratio of solids dissolvedn the circulation water to solids dissolved in the make-up water.rift is entrained water in the tower discharge vapours which isstimated at 0.0002 times condenser water flow [8].

. Results and discussion

.1. Energy recovery process

The results of the condensate energy recovery analysis with-ut and with integration of heat pipe device are presented inables 1 and 2, respectively. Both tables give the summary of theonfiguration and operating parameters of the cooling coil at theverage annual weather conditions in Singapore.

As seen in Table 1, operating a coil at the average annual capac-ty (101 kW), together with other AHUs will cause production of.19 l/s of condensate which is pumped into a pre-cooling coil.ecent studies show that cooling coils with lower face velocity1–1.2 m/s) can be superior to that of the conventional cooling coiln terms of achieving the desired temperature and enhanced dehu-

idification performance due to its ability to maintain low surfaceemperature that results in more condensation from the moist air9,10]. In this case, for adequate moisture removal to occur, faceelocity is kept at 2 m/s resulting in 9.3% pre-cooling energy sav-ngs.

Heat pipes are viewed as sensible heat recovery devices; how-ver, they can also be utilized for latent cooling applications. Usingeat pipe strategy it is possible to enhance dehumidification per-

ormance by pre-cooling of the hot and humid outdoor air, so thatff-coil conditions are at substantially lower dew point tempera-ure than would otherwise be plausible using conventional system

Figs. 4 and 5). This implies a greater amount of condensate on theooling coil surfaces. As seen from Tables 1 and 2, the amount ofondensate discharged from AHUs using heat pipe strategy is 47%igher compared to the case without heat pipe device. However,

Savings (%) 10.9

this will not proportionally affect pre-cooling energy savings, asthe maintaining of low relative humidity implies higher cooling coilcapacity. Another reason is increased condensate flow through thesame geometry of pre-cooling coil, which will cause lower outletcondensate temperature from the pre-cooling coil.

If the pre-cooling coil is designed so that the leaving temper-ature of the condensate approaches the dry bulb temperature ofincoming air, it is possible to obtain even greater energy savings.That can be achieved by simply increasing the number of rows,which is in our case limited to 4. On the other hand, installationof pre-cooling coil in the CAP AHU refers to additional local pres-sure drop of 175.4 Pa which will result in slightly higher fan powerconsumption.

It is to be noted that 10.9% energy saving in the CAP AHU isachieved only due to condensate recovery process. Saving relatedto pre-cooling and reheating of air using heat pipe device in upper5 AHUs are much larger comparing to the conventional systemusing heaters due to the stringent thermal requirements. Resultsobtained using SPC HPD software show 24% energy conservationdue to pre-cool and reheat processes; however, focus of this studyis held on savings due to condensate recovery process.

From the aspect of practical application, several buildings inSingapore are considered that would be appropriate to host the sys-tem analysed with heat pipe strategy. Only facilities where 100%outdoor air is required without any recirculation, such as facili-ties for housing animals for life-science laboratories or operatingtheatres in hospitals, are taken into consideration. This group offacilities require strict indoor conditions that include 100% outdoorair during the 24 h of operation with a maximum relative humid-ity of 60% and a temperature of 22 ◦C (±2 ◦C) [11]. For one suchfacility with the minimum outdoor ACH of 4, it is found that thesystem analysed would be sufficient to provide adequate indoorparameters for building with approximately 3500 m2 area.

3.2. Water recovery process

The results of the condensate water recovery analysis withoutand with integration of heat pipe device at the average annualweather conditions in Singapore are shown in Table 3.

262 D. Licina, C. Sekhar / Energy and B

Table 3Summary of the condensate water recovery in cooling tower using strategies with-out and with heat pipe.

Without heat pipe With heat pipe

Circulating water flow (l/s) 38.68 53.94Cycles of concentration 6 6Temperature range (◦C) 5 5Evaporation (l/s) 0.296 0.413Drift loss (l/s) 0.059 0.082Blow down (l/s) 0.008 0.011Total make-up water (l/s) 0.363 0.506Condensate produced (l/s) 0.19 0.28

6 6

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Annual production (l) 6 × 10 8.83 × 10

Savings (%) 52.3 55.3

After passing through the pre-cooling coil, condensate is drainedy gravity to the cooling tower basin where it is used to partially off-et make-up water losses from evaporation, blow down and drift.n the case without using heat pipe device, condensate is able toffset 52.3% of total make-up water requirements, while savingsre slightly higher using heat pipe strategy (55.3%). In this study,t is assumed that the cooling towers are located at a lower ele-ation than the AHUs; therefore, no additional pumping energy isequired (Fig. 1). In the most unfavourable case, when the cool-ng tower is located on the roof of the building, additional pumpingnergy would be required. For the building height of 25 m and pumpfficiency 60%, total pump energy of 0.1 kW is required.

In majority of the cases, peak condensate production and peakake-up water demand will occur at the same time, thus form-

ng a convenient feedback loop. As a high quality source of water,ondensate can be routed directly to the tower with no need forreatment. Because of the removal of minerals during the evapo-ation process, condensate is similar in water quality to distilledater. In condensate, suspended solids, salinity and turbidity are

ow and the pH is neutral to slightly acidic. It is important to keepir conditioning equipment as clean as possible in order to ensurehat condensate stays uncontaminated. Due to its low-mineral con-ent, condensate increases the cycles of concentration achievablen cooling towers.

There are many other benefits provided by condensate recoveryystem that are not quantified in this paper:

The condensate discharged from pre-cooling coil is slightly coolerthan usual make-up water (in Singapore 28 ◦C), thus loweringthe condenser water temperature and cooling tower fan energyrequired for final heat rejection.The system improves cooling tower water chemistry and isexpected to reduce overall chemical treatment costs due to thenearly distilled quality of water.If condensate collected is utilized, it will not become part of thesewerage cost or have to be treated by the on-site waste treat-ment plant.

As a possible alternative, cooling coil condensate could be uti-ized for irrigation purposes, sometimes coupled with rain waterapture and reuse system. An attractive aspect related to hot andumid climates is that the condensate flow is available even in arought periods when there is a high need for irrigation. However,ondensate recovery for irrigation purposes is high-priced, becausef necessity to provide additional storage and water pressurizingystem. Due to nearly distilled quality of water and reasonably inex-ensive piping and equipment, the most cost-beneficial venture is

chievable using cooling tower and such usage should be a firsthoice when designing a system.

Important factors that determine whether condensate recov-ry system should be considered are the quantity of required

uildings 45 (2012) 257–263

outdoor air, accessibility of air handlers, number and size of theunits that condition outdoor air, climatic conditions including loca-tion of cooling tower or other potential user. Apart from systemsusing DOAHUs, spaces that require large quantities of outdoor airon an ongoing basis are favourable for collection of condensate.Other evident candidates are facilities like shopping malls, wherea high degree of air exchange is present. A building that has a cool-ing tower placed on site is another obvious choice for reusing thecollected condensate.

Climatic conditions are important factors in determining thecondensate production potential, as well as the significance of thewater to the community. With growing population water demandwill continue to rise, which will lead to limited supply of fresh andclean water even in humid regions that are rich in water.

4. Conclusions

The analysis performed shows that the production of conden-sate from six large DOAHUs is sufficient to be effectively used for theenergy recovery process with 9.3% savings in case without heat pipeand 10.9% savings using heat pipe strategy. The inherent recoveryof the totally free “cool energy” from the outside air to pre-cool theincoming hot and humid outdoor air provides an attractive overallenergy efficient option.

Although HVAC energy use is often the primary focus, anotherimportant part of sustainability is water conservation. It is shownthat water conservation strategy can be coupled with energy effi-cient features to provide a better overall building design. In hot andhumid climates, the potential for generating substantial amountsof water is available and should be pursued. With high quantities ofhot and humid outside air and 24 h per day operation, it is possibleto provide over 50% reduction in potable water necessary for cool-ing tower make-up and to increase cooling tower efficiency due tothe introduction of a water source that has virtually no hardnesswith a very low content of total dissolved solids.

This paper has a focus only on DOAHUs that require large quan-tities of outdoor air on an ongoing basis.

Nevertheless, systems that are predominantly used usuallyoperate with both outdoor and recirculated air. Therefore, thesetypes of systems should be considered for implementing the pro-posed system. In addition, regulations that require condensate tobe discharged into a sewer should be changed to allow for otheralternative uses. All commercial buildings using high capacity air-conditioning units should examine the feasibility of redirecting allcondensate drain water to a common point where it could be eas-ily captured. Other facilities that require strictly controlled indoorair parameters like technology manufacturing or pharmacy storageare convenient candidates for condensate recovery and should beencouraged to install condensate capturing system.

Adopting the attitude that water is going to be the next “oil” likecommodity and understanding that the reuse potential for conden-sate makes it much too valuable to simply be drained away is properapproach that can help in managing a very precious and necessaryresource.

References

[1] United States Environmental Protection Agency and Federal Energy Man-agement Program, Laboratories for the 21st Century: An Introduction toLow-Energy Design, 2000.

[2] R. Namek, Pre-cooling ventilation outdoor air, by heat exchange with coolingcoil condensate discharge, Engineered Systems Magazine (March) (2005).

[3] K. Guz, Condensate water recovery, ASHRAE Journal 47 (6) (2005) 54–56.

[4] F. Painter, Condensate harvesting from large dedicated outside air-handling

units with heat recovery, ASHRAE Transactions 115 (2) (2009) 573–580.[5] ASHRAE Handbook – Fundamentals, Climate Design Information, 2009.[6] SPC 2000: Version 5.5, Coil Selection Software, S&P Coil Products Limited,

United Kingdom, 2011 (free download from www.spcoils.com).

and B

[10] S.C. Sekhar, A comparison of cooling coil energy performance of twodifferent strategies in an operating room in a hot and humid climate,

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[7] SPC HPD: Version 4.3, Heat Pipe Heat Recovery Selection and Rating Soft-ware, S&P Coil Products Limited, United Kingdom, 2011 (free download from

www.spcoils.com).

[8] D.W. Green, R.H. Perry, Perry’s Chemical Engineers’ Handbook, 8th ed., 2007.[9] S.C. Sekhar, L.T. Tan, Optimization of cooling coil performance during opera-

tion stages for improved humidity control, Energy and Buildings 41 (2) (2009)229–233.

[

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11] ASHRAE Handbook – HVAC Applications, Health-Care Facilities, 2011.