Realistic Analysis of Air Conditioning Technologies Prakash Dhamshala 1

Transcription

1 Realistic Analysis f Air Cnditining Technlgies Prakash Dhamshala 1 Abstract - This paper deals with the use f a cmputer cde, Transient Analysis f Building Lads and Energy Technlgies (TABLET) develped by the authr fr the analysis f varius air-cnditining technlgies. Cnventinal techniques such as thermstat setback r energy recvery as well as emerging technlgies such as dedicated utside air Systems (DOAS) and distributed energy systems with turbine inlet air cling can be cnsidered by use f hurly weather data fr varius cities acrss the natin. The utility f such cdes is illustrated with cst savings resulting frm use f a DOAS system. Fr the purpse f such analysis, a cmmercial building with realistic electrical, ventilatin, lighting and air cnditining lads are assumed. The cde estimates the hurly building lads, energy requirements and annual energy cst fr any f the abve mentined technlgies as selected by the user emplying the existing energy csts fr the cities evaluated. The cde is windws based develped in the Visual Basic language t facilitate easier interactin fr the user. Students wh used this cde were extremely pleased t have the greater insights and significance f the technlgies cnsidered. Keywrds: DOAS, heat pump, air-cnditiner, energy recvery device, building lads Intrductin Sftware is emplyed by the practicing engineers. Althugh the results f using these The energy cnsumptin f a cmmercial building is primarily due t peratin f heating, ventilatin and aircnditining equipment (HVAC) and that cnsumed by the secndary equipment such as lights, ther electrical equipment, cmputers, cpiers, Xerx machines, etc,. The energy csts is directly related t the energy cnsumptin f the HVAC equipment, which depends upn several factrs such as the type f equipment, prvisins fr energy recvery r imprving the efficiency f energy utilizatin, the weather cnditins existing n the utside f the building, and finally n the unit csts f energy which may vary with time during the day r frm seasn t seasn. The energy efficiency f mst f the HVAC equipment vary with lads that depends upn the type f building envelpe structure and weather cnditins utside fr a given hur. The thermal cnditins f cnditined air stream cming ut f the HVAC equipment are adjusted t meet the energy demand f the building fr the given hur. The basic mechanism f heat transfer thrugh the building envelpe is truly transient in nature that is affected by the thermal strage capacity f the building materials utilized in the cnstructin f rf, walls and windws. In rder t simplify the calculatins invlved in sizing the HVAC cmpnents, the industry [1] emplyed the cling lad temperature difference (CLTD) methd. This methd is nt helpful in evaluating the energy cnsumptin f the equipment ver a perid f seasn r year. Alternate methd such as BIN methd is used but it will nt yield accurate results. Inaccuracies in these methds arise due t lack f using the mre detailed hurly weather data as well as pr accunting f thermal strage effects, as is dne in sme f the available cmmercial sftware are very accurate, but it requires cnsiderable amunt f experience n the part f the users f such prgrams. In a three hur first curse in HVAC field, it is very difficult t cver such materials in ne semester. The authr has develped a few user friendly cmputer prgrams [-7] t illustrate the effect f thermal strage as well as the mre accurate hurly weather data fr a given city. Such prgrams are very useful in prviding the greater insights int the design prblems in additin t understanding the significance f the technlgies cnsidered as well as in btaining the mre accurate results using realistic data. 1 Prfessr f Mechanical Engineering, Cllege f Engineering and Cmputer Science, The University f Tennessee, Chattanga, 615 McCallie Ave, Chattanga, TN 37403

2 Thery The estimatin f the annual r mnthly energy requirements f a building t maintain it at cmfrtable cnditins require the knwledge f building lads fr each hur f the year. Hurly lads are estimated typically, since the weather data is available fr mst f the cities n an hurly basis. The weather data cllected fr each city reflects the histrical average fr a perid f 0 t 30 years. Transfer functin methd takes int accunt the thermal strage effect f the slar energy, ccupants, lights and equipment. Heating lad is the rate f heat transfer typically per hur frm the building t the utside, while cling lad refers t that frm utside t the inside f the building. The types f lads are further classified int sensible and latent lads. The sensible lads ccur due t difference in temperatures that cnsists f cnvective and radiatin cmpnents, while the latent lads ccur due t difference in humidity levels which are instantaneus. The estimatin f radiatin cmpnent f sensible lad is cmplicated due t thermal strage effect. Fr instance, the heating r cling lad Q can be cnsidered as the respnse f a building r rm t the effects that the temperature f the space ( ), the temperature f the envirnment utside ( T ), r adjining spaces, and the slar heat transfer rate ( sl ), etc. have n that building r rm. The temperature f the space, the temperature f the envirnment utside, r adjining spaces, the slar heat transfer rate, heat energy frm ccupants, equipment, and lighting Ti, T, Q& sl, etc are knwn as the driving terms. The Transfer Functin Methd (TFM) calculates the respnse f a system by making three assumptins (i) all functins f time are represented as sum f series f values at regular time steps ( hurly in this case). (ii) the respnse f a system is a linear functin f the driving terms and f the state f the system. (iii) the respnse at time t can depend nly n the past, nt n the future. T i Q & ( ) A linear series relatinship between the respnse term y t and the driving term u t can be represented as y = a y + a y + K + a y + b u + b u + b u + K b u t ( ) ( ) (1) 1 t 1 t t t n t n t 0 t 1 t 1 t t t + m t m t where the time step t = 1 hur and a1 t an and b0 t b m are cefficients that characterize the system that take int accunt the thermal inertia r strage effects f the materials and are called transfer functin cefficients. Equatin (1) can be generalized t take int accunt several driving terms. The slar radiatin and utside air temperatures are tw driving terms that affect the heat gain int the building. A term called sl-air temperature (T e ) is defined t take int effect bth the utside air temperature T and slar radiatin I t and is expressed as: T e = T α I + h t ε R h () α = absrptance f surface fr slar radiatin I t = ttal incident slar lad btained frm actual measured values ε R h α h = lng wave radiatin factr = -7 F fr hrizntal surfaces; 0 F fr vertical surfaces = surface clr factr = 0.06 fr light clrs and 0.05 fr dark clrs The slar incident slar lad as given by I t can be btained frm the measured slar data at a given lcatin in terms f varius terms invlving slar incident angle (θ i ), declinatin angle (δ), slar azimuth angle (ǿ s ), the slar zenith angle (θ s ), the surface azimuth angle (ǿ p ), and surface tilt angle (θ p ), surface latitude angle (λ) and finally the hur angle.

3 The reader may refer t the reference [8] t see the rientatin f these angles. The declinatin angle (δ) can be given as, ( n + 10) Sinδ = Sin 3.45 Cs (3) where, n is the day f the year with January 1 being n = 1. The hur angle (ω) can be estimated in terms f slar time (t sl ) frm, ( t sl 1 h) ω = (4) 4 h The slar zenith angle (θ s ) can be estimated frm, Cs θ s = Cs λ Cs δ Cs ω + Sin λ Sin δ (5) Nw, the slar azimuth angle (ǿ s ) in terms f slar zenith angle (θ s ) as fllws Csδ Sinω φ s = (6) Sinθ Finally, the slar incident angle (θ i ) is given by s Cs θ i = Sin θ s Sin θ p Cs (ǿ s - ǿ p ) + Cs θ s Cs θ p (7) where, ǿ s is the slar azimuth angle given by Equatin (6) while the surface azimuth angle ǿ p is the angle made by the surface nrmal with suth directin. The tilt angle f the surface θ p is the angle f inclinatin f the surface with lcal hrizntal surface. Nw the ttal incident slar lad I t is the sum f (i) (ii) (iii) I t the slar direct radiatin (I dir ) incident nrmal t the surface the slar diffuse radiatin (I dif ), the diffuse radiatin is the radiatin scattered frm the surrundings and the dust particles present in the atmsphere. the slar radiatin reflected frm the grund 1+ Csθ p 1 Csθ p = I dir Csθi + I dif + I gl, hr ρ g (8) where, I gl,hr is the glbal hrizntal radiatin incident n the hrizntal surface. The weather statins in many majr cities recrd hurly data cnsisting f I dir, I dif, I gl,hr, the ambient air temperature, the dew pint temperature, the relative humidity, wind speed and directin, clud cver factr and many ther data. The research scientists btained the average f 5 t 30 years f such data and call this data as the typical meterlgical year (TMY) fr that city. Use f such data prvides a mre accurate slar lads.

4 Cnductive Heat Gain The cnductive heat gain ( r lss), & Q cnd, t at time t thrugh the rf and walls can nw be expressed as: Q & cnd, t = d n Q& cnd, t n t + A bn Ts, t n t Ti cn (9) n 1 n 0 n 0 where A = area f the rf r wall, can be in units f m r ft. t = time step, which is 1 hur. T = sl-air temperature f utside surface at time t s, t n t b n, c n, d n are the cefficients f cnductin transfer functin and the values f these cefficients fr different types f rfs r walls cmmnly emplyed in building industry are listed in reference [1]. The cmputer cde develped by the authr has these values in its memry and prvides the apprpriate values fr the materials chsen by the user f the prgram. t = hur fr which calculatin was made t = time interval (1 hr) n = number f hurs fr which and values are significant, typically fur A = area f element under analysis The heat gain int the building des nt translate int the building lad instantaneusly. Cling Lad The ttal cling lad, Q t is given as Q = Q + Q t rf sc (10) ( v q + v q + v q + K ) ( w Q + w Q + K) t i i t, i t t, i t 1 t t t t Q = rf i= 1, (11) (, j ) Q sc = q c j= 1 where: Q rf = sensible cling lad frm heat gain elements having radiant cmpnents. v and w = rm transfer functin cefficients, listed in [1] selected per element type, circulatin rate, mass, and/r fixture type. q t = each f i heat gain elements having a radiant cmpnent; selected apprpriate fractins fr prcessing. t = time interval (1 hr) Q sc = sensible cling lad frm heat gain elements having nly cnvective cmpnents. q c = each f j heat gain factrs having nly cnvective cmpnent ( q c, n ) n= 1 (1) Latent Q = (13) q c = each f n latent heat gain elements. The abve equatins are presented here t prvide the glimpse f what is invlved in the calculatins f heat gains and cling lads. The cde iterates fr abut six times fr each hur f the ttal 8760 hurs in a year and it further iterates the Equatin (11) fr anther six times fr each hur f the ttal 8760 hurs in a

5 Lads due t Ventilatin and Infiltratin Air The building lads due t ventilatin and infiltratin are instantaneus, they dn t have the radiatin cmpnent in them and they are given as q sensible latent =. 10 ( T T ) 1 Q (14) ( W Wi i q = 4840 Q ) (15) q ttal =. 5 ( h h ) 4 Q (16) i where: Q = sum f ventilatin airflw as per ASHRAE Standard 6 and infiltratin cfm T, Ti, = utside, inside air temperatures, F W, W i, = utside, inside air humidity rati, lb (water) / lbm d.a h, h i, = utside, inside air enthalpy, Btu/lbm d.a Latent Q = ( q c, n ) n= 1 q c = each f n latent heat gain elements. The space heat lad will be the summatin f the lads frm each f the abve. The maximum values f hurly heat gain and lss represent the building peak cling and heating lads, respectively. Dedicated Outside Air System (DOAS) Standard HVAC system takes a mixture f utdr air and return air, cnditins it, and then returns it t the building space at the desired temperature and humidity levels. In rder t maintain a space at specified temperature and humidity levels, the cling system, r chiller, has t cl dwn the mixture f utside and return air t a much lwer temperature well belw the dew pint f the mixed air t remve r dehumidify the excess misture t the desired levels. T accmplish this, the cmpressr r air-cnditiner cnsumes greater pwer t maintain a lw evaprating r cil temperature. Typically, near the peak cling lads, the air temperature is reduced t a very lw value after the required dehumidificatin takes place within the cling cils. The reheating f the dehumidified air is frequently dne, s that the temperature f the supply air t the space is at a cmfrtable level. In certain applicatins and gegraphical regins, the cst f reheating can be significant. Energy csts assciated with air-cnditining the utside air can be increased further if the building ccupancy is nt unifrm in each zne f the building. A Dedicated Outdr Air System (DOAS) is a cnstant air vlume system that is designed t deliver the required amunt f air t each space r zne f the building evenly. This system cmplies 100% with ASHRAE Standard 6. DOAS unit requires abut 0 t 30% less utdr air and als can prvide 100% f the space s latent lad, when needed. With the DOAS unit, the sensible cling and heating is perfrmed separately. The sensible cnditining is decupled frm the latent cnditining f the air. The sensible cnditining f the air can be perfrmed effectively and ecnmically by circulating the chilled water thrugh panels r cils imbedded in the ceiling and walls f the building. The radiant heating r cling frm the panels r wall cils can be supplemented with the cnditined fresh air frm the DOAS unit t the space r zne and is delivered thrugh a smaller duct system frm the DOAS. The energy cst savings resulting frm use f the DOAS unit is attributed primarily t the fllwing factrs: It uses the ptimal (minimum) amunt f ventilatin air and als cmplies 100% f ASHRAE Standard 6. (17)

6 The pumping pwer f cnditined air thrugh the ducts is cnsiderably reduced due t lwer air flw rates. The latent lads are cmpletely handled by the DOAS unit s that the sensible lads can be handled by the sensible chiller units perating at higher evaprating temperatures, and thus at peak efficiency levels. Radiant panel cling and heating f the buildings t meet the sensible lads can be very cst effective due t reductins in capital csts assciated with larger ducts, larger fans, and lw pumping cst f water as cmpared t that f air. Additinal csts savings are pssible due t the use f enthalpy and heat wheels. The purpse f this investigatin is t assess the ptential energy cst savings resulting frm use f integrated DOAS unit with CRCP and energy recvery wheels at varius climatically different regins within the U.S Descriptin f DOAS System The DOAS unit cnsists f a separate heat pump unit in parallel with a sensible chiller as shwn in Figure 1. In additin t DOAS unit, the Figure 1 als shws an enthalpy wheel and a heat wheel. The enthalpy wheel allws the transfer f bth latent (misture) and sensible (heat energy) between the tw air streams flwing thrugh it, while the heat wheel allws nly the transfer f heat energy due t temperature difference between the streams. The heat wheel placed dwnstream f the DOAS unit prvides the free reheat energy t the dehumidified air leaving the DOAS system. The enthalpy wheel will be very effective during the cling seasn by cling and dehumidifying the incming utside fresh air with the utging exhausted air. In certain applicatins, especially with greater latent lads caused due t large number f ccupants, the enthalpy wheel will be cunter prductive in winter by transferring the misture t the incming fresh air and thus increasing the latent lads. The dashed lines indicates the typical winter peratin, while the slid lines shw the air streams during the cling seasn. The dtted lines indicate the ht r chilled water flw t the CRCP f the building space. A Typical Operatin in Cling Seasn The exhaust air frm the building space at state 6 enters the heat wheel and heats up the dehumidified air leaving the DOAS system at state 4. The exhaust air leaving the heat wheel at state 7 splits int tw streams. The stream at state 9 has the same mass flw rate as that f the incming fresh air at state 1 and enters the enthalpy wheel t partially dehumidify and cl the utside air, while the flw rate at state 8 is mixed with the fresh air leaving the enthalpy wheel t prvide a larger required flw rate t the DOAS system. This is required in the event f having a larger latent lad. The minimum flw rate required by the heat pump f the DOAS system is frequently larger than the minimum required t meet the ASHRAE Standard-6. The added mass flw rate f the DOAS unit abve that required fr prper ventilatin nly increases the sensible capacity f the DOAS system thus reducing further the lads n the sensible chiller. A Typical Operatin in Heating Seasn If latent lads are zer r negligible: The utside fresh air picks up the heat energy frm the exhaust air frm the building space in the heat wheel, after mixing with the added re-circulated return air it enters the DOAS system fr additinal sensible heating. If latent lads are negative (Humidificatin Required): The utside fresh air can pass thrugh the enthalpy wheel and after mixing with the added re-circulated return air it enters the DOAS unit fr additinal sensible heating, if required. If latent lads are psitive in:

7 The fresh utside air will bypass enthalpy wheel and passes thrugh the DOAS system fr dehumidificatin, this situatin adds t the sensible heating unit, but can recver a certain amunt by passing thrugh the heat wheel. q sl q tl W c,das DOAS System 14 enthalpy wheel dehumidified air 5 building space utside air 11 heat wheel heating seasn cling seasn chilled water W c,sc chilled water supply chilled water return frm radiant panels ht water Q fuel sensible chiller ht water heater ht water supply Figure 1 Schematic f a Typical DOAS System Estimating the energy cst savings resulting frm use f DOAS unit bils dwn t determining the perating cst thrugh the pwer supplied t the DOAS unit (W c,das ) and the sensible chiller (W c,sc ) unit alng with the pumping csts f the chilled water and the air-duct systems as shwn in the Figure 1. T determine the W c,das and the W c,sc the fllwing equatins are gathered first based n fundamental laws f the energy balance and heat exchanger analysis. The energy balance n the enthalpy wheel gives, m c p (t 1 t ) = ε s m c p (t 1 t 9 ) r, t = t 1 - ε s ( t 1 t 9 ) (18) m h fg (ω 1 ω ) = ε l m h fg (ω 1 ω 9) r ω = ω 1 - ε l ( ω 1 ω 9 ) (19) where ε s = the sensible effectiveness f the enthalpy wheel. ε l = the latent effectiveness f the enthalpy wheel. m = mass flw rate f the utside air assumed t be minimum f the tw streams. c p = the specific heat at cnstant pressure f the air streams assumed t be

8 cnstant fr bth streams. t = the temperature at the state indicated by the subscript. ω = the humidity rati at state indicated by the subscript. h fg = enthalpy f vaprizatin assumed t be cnstant fr bth streams. The temperature and humidity rati f the mixture f the tw mist air streams at state 8 and state is given by, mad cp t7 + m cp t t3 = (0) ( m + m ) c ad p m h ω + m h ω ad fg 7 fg ω 3 = (1) ( m + mad ) hfg where m ad = the mass flw rate f the added re-circulated air thrugh the DOAS system. It may be nted that the temperature at states 7, 8 and 9 are the same as that at state 7. The perfrmance f the DOAS unit r any air-t-air heat pump r air-cnditiner depends primarily n the air flw rate thrugh the evapratr, the utside air temperature and the wet-bulb temperature f the air entering the evapratr cil. Fr a given air flw rate thrugh the heat pump, the sensible (q s ) and ttal cling capacities (q t ) are primarily dependent upn the ut side air temperatures (t ) and the wet-bulb temperature (t w3 ) f the air entering the evapratr cil as shwn belw. q s = f 1 ( t w3, t ) q t = f ( t w3, t ) and the latent capacity, q l = q t - q s where, f 1 and f are empirical relatins that can be develped by curve fitting the data frm the manufacturer s catalg fr the heat pump emplyed in the DOAS unit as shwn in the Figure 1. The fllwing equatins are develped fr a mre efficient heat pump recently intrduced int the market: t t 8.16E 06t twi twi3 q t = 1000 () t twi twi t E 05t ln( twi3) (ln( twi3)) q s = 1000 (3) E 05 t ln( twi3) t twi twi3 W c, c = (4) t twi twi3 where t wi3 = the wet-bulb temperature f the air entering the DOAS unit, and W c,c = pwer supplied t the cmpressr, while in cling mde. The abve three equatins give the cmputatinal relatins fr the ttal and sensible cling capacities and the Equatin (4) is fr the required cmpressr pwer while the heat pump is wrking in a cling mde. The heating capacity and the cmpressr pwer t the heat pump in the heating mde is dependent upn the dry-bulb temperature f the utside air and that f the return air t the cndenser fr a given air flw rate, as shwn by the fllwing tw equatins. q heat { t t t t E 05 t } 4.1E 07 t 5 = (5) 1000 r 3 0

9 tr t t E 05t tr t E 05 t E 06 t W (6) c, h = 3 where t r = the dry-bulb temperature f the return air t the cndenser, and W c,h = pwer supplied t the cmpressr, while in heating mde. The energy balance acrss the DOAS system gives, qs t4 = t3 (7) m c d d p fg 3 ql ω 4 = ω3 (8) m h where m d = mass flw rate f the mist air flwing thrugh the DOAS system. Since the Equatins (4), (5) and (6) invlve the wet-bulb temperature f the mist air at the state 3, the fllwing Equatin [9] can be emplyed t determine iteratively the wet-bulb temperature at state 3, prvided the dry-bulb temperature and humidity rati at state 3 are knwn. ( tw3 ) ωs3 0.4 ( t3 tw3 ) ϖ 3 = (9) t3 tw3 The energy balance n the heat wheel gives, m d c p ( t 5 t 4 ) = m d c p ( t 6 t 7 ) r t 4 = t 5 - ( t 6 t 7 ) (30) t 7 = t 6 + ε s (t 6 t 4 ) (31) where ε s = the effectiveness f the sensible heat wheel. The abve equatins frm Equatin 18 t 31 invlve 14 unknwns namely t, t 3, t w3, t 4, t 5, t 7, t 9, ω, ω 3, ω s3, ω 4, q s, W c,das, W c,sh. All f the abve 14 unknwns are time dependent and can be slved by the fllwing methdlgy. Cmputatinal Methdlgy It is assumed that the system is perating with minimum duct lsses r gains and the mass flw rates are such that balance flw cnditins exist in the enthalpy and heat wheels during their peratin. The sensible and latent effectiveness are assumed t be cnstant at 0.7 and 0.65, respectively, under all cnditins. The energy csts, electric cnsumptin and demand csts are assumed t be cnstant ver the year. The DOAS unit is emplyed in a medium sized cmmercial building f flr area 4000 ft (371.6 m ) with 66 peple wrking during the day with W/ft (1.53 W/m ) f lighting lad and a ttal f 5 kw f equipment and the nrmal lads assciated with ht water cnsumptin and an infiltratin rate f 0.1 ACH. The lads during the nn-ffice hurs, weekends and hlidays are set at minimum values with a realistic thermstat setbacks. Using the hurly weather data f the city, the hurly (q s, q t, q l, W c,das, W c,sc and Q fuel ) and peak building and equipment lads are estimated by use f TABLET cmputer cde develped based n transfer functin methd. The energy csts assciated with the HVAC system cnsists f the cst f pwer supplied t the DOAS unit (W c,das ), the cst f pwer supplied t the sensible chiller unit (W c,sc ), the fuel cst assciated with heating unit (Q fuel ) and the cst assciated with pumping the fluids as shwn in Figure 1. The energy csts are evaluated fllwing the prcedure described fr a typical cling perid as fllws: 1. The latent lad f the building is btained t check, if latent cling is required, that the latent rate f heat extractin is the same as latent lad f the building and is equated t the latent capacity f the DOAS unit. The latent heat capacity f the unit is btained frm Equatins (3) and (4), which are functins f the utside air temperature, t, and the wet-bulb temperature, t w3, f the entering air. Using the Newtn-Raphsn technique, the wet-bulb temperature, t w3, is btained

10 iteratively. Once the wet-bulb temperature is cmputed, ne can determine the sensible capacity, q s, and cmpressr pwer W c,c f the DOAS unit frm Equatins (3) and (4).. Since the heat wheel des nt transfer any misture between the streams, and humidity ratis at states 6, 7, 8 and 9 are the same as that f the building space als knwing the latent effectiveness f the enthalpy wheel, ne can determine the humidity rati (ω ) frm the Equatin (19) and, ω 3, frm the Equatin (1). 3. Knwing the humidity rati ω 3 and the wet-bulb temperature, t w3, at state, 3, ne can find the actual dry-bulb temperature, t 3, f the mist air entering the DOAS unit by using the Equatin (9). 4. The exit temperature, t 4, f the mist air frm the DOAS unit can be btained frm Equatin (7) as the sensible capacity f the DOAS unit is estimated frm the Equatin (3) frm the knwledge f t w3 and t. 5. Knwing the sensible effectiveness, ε s, f the heat wheel, and the temperature t 4 and t 6 ne can determine the exit temperature, t 7, f the exhaust air frm Equatin (31). 6. Recgnize that temperatures at state 7, 8 and 9 are the same, i.e t 7 = t 8 = t Finally, the supply air temperature, t 5, can be estimated frm Equatin (13). 8. One can determine the crrected sensible lad f the building by adjusting the sensible cling prvided by the DOAS unit. 9. The pwer required by the sensible chiller is btained frm the crrected sensible lad and characteristics f the sensible chiller. Fr simplicity, it is assumed that a centrifugal chiller perating at a higher evaprating temperature can have an average, COP, f 7, and hence the pwer supplied t the sensible chiller, W c,sc, is btained by dividing the crrected sensible lad with the average COP. 10. In heating seasn, the heating lad is met by circulating the ht water prduced in the ht water biler as shwn by the dtted lines and the heating capacity, q heat, and the cmpressr pwer supplied t the heat pump f the DOAS unit is btained frm the utside air temperature, t, and the return air temperature, t r, f the space frm Equatins (5) and (6), respectively. The fuel supplied t the ht water heater is btained by dividing the heating lad f the hur with the biler efficiency. The fuel cst wuld be the prduct f the fuel supply and fuel cst fr the hur. Results The results btained frm detailed cmputer simulatins fr several gegraphical lcatins are listed in the Table 1. These cst savings are btained frm detailed cmputer simulatins using the same cst structure fr the fuel and electric demand the energy cst and cnsumptin charges in rder t assess the influence f different climatic cnditins f the varius regins. It may be nted that savings are related nly t perating cst and takes n accunt f ptential capital cst savings r additinal charges. Fr instance, fr the city f Hustn, the peak cling lad is reduced by mre than 4 tns f capacity, which may amunt t a reductin f nearly $ 4000 in the capital cst f the chillers. There exist a reductin f the capital cst f duct cnstructin and fan sizes due t reduced air flw rates. It has been reprted that the ceiling space f an integrated DOAS unit can reduce by nearly 50 percent due t smaller size ducts. The energy cst savings resulting frm use f varius technlgies and fr varius cities are shwn in Figure -7. Cnclusins and Recmmendatins The results f shwn in Table 1 shw that the integrated DOAS unit with CRCP and the energy and heat recvery wheels has a significant ptential f reducing the capital as well as perating csts as cmpared t cnventinal systems. The size f the building chsen fr this investigatin is relatively small as cmpared t the average size f a cmmercial building in the U.S. Based n the magnitude f the energy cst savings as a result f the applicatin f the DOAS units, applicatin f DOAS unit has a ptential t be a significant cst-effective technlgy in the near future f HVAC industry. The Figures -7 shw the significance f each technlgy in prviding energy cst savings. Students indicated in a survey that the prgram is very simple and user friendly and prvided a mre realistic analysis tl t evaluate each technlgy, and allws t get greater insights int each f the technlgy

11 cnsidered and the factrs that influence the energy cst savings. It is recmmended that the materials presented in this paper shuld be prvided t the students alng with such cmputer cdes in rder t understand the quantitative impact f each energy savings technlgies and als t appreciate the imprtance f using mre detailed methds such as thse illustrated in this paper. The materials presented in this paper helps students t get familiar with the detailed apprach f estimating the building lads and als t the varius current energy efficient r recvery technlgies.

12 Table 1 Perfrmance Characteristics f DOAS Unit at Varius Lcatins City Eqpm Number Lad f kw Occupants Peak H. Lads Tns (kw) Tt heating/ latent Atlanta / 3.5 (44.3) / (1.3) Atlanta / 3.5 (DOAS) (44.3) / (1.3) Peak C. Lads tns a (kw) Tt cling / latent / 4.3 (65.6) / (15.1) 15.4 / 1.8 (54.) / (6.3) Max Elec. Demand (kw) E b. Demand Cst $/yr Energy Cst Cnv $/yr DOAS Cst $/yr % diff c 710 1, , Chattanga 5 Chattanga (DOAS) 5 Chicag 5 Chicag (DOAS) 5 Hustn 5 Hustn (DOAS) / 3.6 (46.7) / (1.7) / 3.6 (46.7) / (1.7) / 3.8 (56.5) / (13.4) / 3.8 (56.5) / (13.4) / 3.5 (43.1) / (1.3) / 3.5 (43.1) / (1.3) 19 / 4.8 (66.8) / (16.9) 15.3 / 1.8 (53.8) / (6.3) 18.3 / 4.3 (64.3) / (15.1) 15.1 / 1.9 (53.1) / (6.9) 0.1 / 6 (70.7) / ((1.1) 15.8 /.3 (55.6) / (8.1) , , , , , ,6 33 L. A / / , (7.4) / (10.) (54.4) / (9.1) L. A (DOAS) / / , (7.4) / (10.) (49.6) / (5.3) New Yrk / / , (49.) / (13.4) (6.) / (10.6) New Yrk (DOAS) / 3.8 (49.) / (13.4) / 1.6 (53) / (5.6) , a- rf: 3 in,w/4 l.cnc deck sus ceiling, walls: 4 l.w.cnc blck, w/1 in face brick, b- first 50 kw demand free, but penalizes by $ 9.89 /kw and energy cst f $ 0.06/kWh c- based n perating cst nly

13 Cmparisn f Energy Cst Savings Due t Use f Mre Insulative Materials fr Varius Cities Cmparisn f Energy Cst Savings Due t Use f the Thermstat Night Set-Back System fr Varius Cities Ttal Energy Csts ($/yr) Mre Cnductive Mre Insulative Ttal Energy Csts ($/yr) Cnventinal Night Set-Back 0 Atlanta Chicag Hustn L.A New Yrk Phenix 0 Atlanta Chicag Hustn L.A New Yrk Phenix Building with 50 peple, Eqpm Lad:5 kw; Lighting: W/ sq.ft Building with 50 peple, Eqpm Lad:5 kw; Lighting: W/ sq.ft Figure. Energy Cst Savings due t Mre Insulative Materials Figure 3. Energy Cst Savings due t Night Set-Back Cmparisn f Energy Cst Savings Due t Use f Energy Recvery System fr Varius Cities Cmparisn f Energy Cst Savings Due t Use f DOAS System fr Varius Cities Ttal Energy Csts ($/yr) Atlanta Chicag Hustn L.A New Yrk Phenix Cnventinal Energy Recvery System Ttal Energy Csts ($/yr) Atlanta Chicag Hustn L.A New Yrk Phenix Cnventinal DOAS Building with 50 peple, Eqpm Lad:5 kw; Lighting: W/sq.ft Building with 50 peple, Eqpm Lad:5 kw; Lighting: W/sq.ft Figure 4. Energy Cst Savings due t Energy Recvery Systems Figure 5. Energy Cst Savings due t Use f DOAS Systems Cmparisn f Varius Energy Savings Technlgies fr Hustn,TX Annual Energy Csts ($/yr) Cnv Insul NSB Ecn E.Rec DOAS Building with 50 peple, Eqpm Lad: 5 kw; Lighting: W/sq.ft Figure 6. Energy Cst Savings due t Varius Technlgies

14 a n, b n, and c n are cefficients f cnductin transfer functin c p = the specific heat f mist air (J/kg. 0 C). f 1 = a mathematical functin that relates the sensible capacity t entering wet-bulb temperature and utside air temperature. f = a mathematical functin that relates the ttal capacity t entering wet-bulb temperature and utside air temperature. h = cnvective heat transfer cefficient fr utside air, W/m.K h fg = enthalpy f vaprizatin (J/kg). I dif = diffuse slar radiatin, W/m I dir = direct slar radiatin, W/m I t = ttal slar radiatin, W/m I gl,hr = glbal slar radiatin n a hrizntal plane, W/m m ad = mass flw rate f additinal re-circulated mist air thrugh DOAS system (kg/s). m d = mass flw rate f mist air thrugh the DOAS system (kg/s). m = mass flw rate f the mist air frm the utside (kg/s). q heat = heat capacity utput f the heat pump (kw). q l = latent cling capacity f the heat pump (kw). q s = sensible cling capacity f the heat pump (kw). q t = ttal cling capacity f the heat pump (kw). Q = vlumetric flw rate f air, L/s r cfm Q rf = sensible cling lad frm radiant prtin (W) Nmenclature Q sc = sensible cling lad frm cnvective prtin (W) T i, t i = mist air temperature at state, i ( 0 C ). T, t = utside air temperature ( 0 C ). T e = sl-air temperature ( 0 C ). t n = dry bulb temperature at state, n ( 0 C) t w3 = wet-bulb temperature f mist air at state, 3 ( 0 C ). W c,c = pwer supplied t the cmpressr f heat pump in cling mde (kw). W c,h = pwer supplied t the cmpressr f heat pump in heating mde (kw). W c,sc = pwer supplied t the cmpressr f the sensible chiller (kw). Greek Letters α = absrptance f slar energy δ = declinatin angle λ = latitude angle ε = emittance f utside surface ω = hur angle θ i = slar incident angle θ p = surface tilt angle θ s = slar zenith angle ρ g = reflectance f grund surface Φ s = slar azimuth angle ε s = sensible effectiveness f heat r energy wheel. ε l = latent effectiveness f energy wheel. ε s = sensible effectiveness f secndary heat wheel. ε t = ttal effectiveness f energy wheel. ω i = humidity rati f a mist air at state, i ω si = humidity rati f a saturated mist air at state, i

15 References 1. ASHRAE Handbk f Fundamentals American Sciety f Heating, Refrigeratin and Air-cnditining Engineers, Atlanta, GA 001. Energy Cst Savings due t Use f Energy Recvery System with Dedicated Outside Air Systems (DOAS), Seminar presented ASHRAE Annual Meeting in Kansas City, MO June Energy Cst Savings with Use f DOAS Systems in Varius Cities in U.S paper t be presented at ASME Wrld Cngress, Washingtn D.C, Nv A Multi-Purpse Thermal Design Prject that Wrks by Prakash R. Damshala and Rbert Bailey, published in The Internatinal Jurnal f Mechanical Engineering Educatin, vl 30, N, April, Thermecnmic Analysis f Cgeneratin System fr HVAC Applicatins in Cmmercial and Industrial Buildings by Prakash R. Damshala and James Nathan Pugh M.S thesis cmpleted in August A Cmputer Design Prject fr an Energy Recvery System by Prakash R. Damshala, a paper presented at ASEE sutheastern cnference held at Charlestn, SC in April Numerical Analysis f Slar Strage (Trmbe) Wall fr Identifying Optimal Energy Recvery Cnditins by Prakash R. Damshala and Rbert Bailey, a paper presented at ASEE sutheastern cnference, April 000 at Blacksburg, Virginia. 8. ASHRAE Handbk f Fundamentals, chapter 30. American Sciety f Heating, Refrigeratin and Air-cnditining Engineers, Atlanta, GA Heating and Cling f Buildings by J.F. Kreider., and A. Rabl, McGraw-Hill publicatin, 1994, New Yr, N.Y Prakash R. Dhamshala The authr is a prfessr f mechanical engineering at the University f Tennessee, Chattanga.He btained his M.S frm University f Miami, Fl and Ph.D frm Gergia Tech, GA. He has been teaching thermal science curses in thermdynamics, heat transfer, thermal systems and air-cnditining and refrigeratin curse at this schl fr ver 0 years. He is a member f ASHRAE, ASME and frmer member f ASEE. He is active in reviewing and publishing papers fr ASEE, ASHRAE and ASME. Appendix These instructin illustrate the prcedure t evaluate the energy cst savings ptential f varius advanced energy technlgies. Yu interact with a single screen cntaining several windws and buttns and is divided int six znes A, B, C, D, E and F. The data such as utside air dry bulb temperature, relative humidity, ambient pressure, direct, diffuse and ttal slar radiatin n hrizntal and nrmal planes are inputted frm the files cntaining in the cde nce user select a city. The user will prvide data n building envelp and lad prfiles during the wrking, and ff-days and hlidays, and time f use energy csts. The fllwing prcedure may be emplyed t btain the simulatin results. 1. Select the city in windw A. Select the rf # 8 in area B 3. Select the wall #8 in area B fr East, Suth, West and Nrth walls

16 4. Select # 1 fr flr, NE, SE,SW and NW walls 5. Selectin the ptin "Off" fr Ecnmizer, Energy Recvery and DOAS systems in area C 6. Select the ptin "Off" fr CHP system and press the buttn # 1t calculate the building peak lads 7. When yu see the peak lad values in windws in area D, then press the buttn # t estimate the HVAC equipment lads 8. When yu see the message "Dne" in the windw X, press the buttn # 3 t calculate the energy csts 9. Once yu see the results in windw E, yu have a chice f printing the results by pressing the buttn # 4 r see the bar chart f mnthly energy csts by pressing the buttn # 5 (Yu may print the chart if needed, prvided the cmputer is cnnected t a printer) r see the temperature and building lad prfile n peak cling day by pressing the buttn # 6 r see the pie chart f varius building energy csts by pressing the buttn # If yu want t rerun the prgram with CHP unit, then select the ptin "n" fr the CHP system, enter the ttal annual energy cst frm windw E f the cnventinal system withut CHP int the windw "Y" then press the clear buttn # 8 and finally press buttn # Repeat steps 7 thrugh 9 1. Yu can repeat the abve prcedure fr varius cities by selecting the city in windw A r fr varius energy csts scenaris as shwn in windw area F