Development of By-pass Blending Station System

Transcription

1 Develoment of By-a Blening Station Sytem. Liu Ph.D., P.E., Ph.D., D. Barne K. Bunz N. Ronerry Architectural Engineering Univerity of Neraka Omaha, Neraka ABSTRACT A new uiling lening tation ytem name y-a lening tation (BBS) ha een eveloe to reuce uiling um energy conumtion in oth itrict heating an cooling ytem. Theoretical invetigation emontrate that the BBS can ignificantly reuce uiling um ower for a tyical cooling ytem when contant water flow i maintaine in the uiling ie. When ifferential reure reet i alie in the uiling ie, more um energy can e ave. The BBS alo reuce the um ize an therefore reult in lower initial ytem cot. A cae tuy wa alo erforme an emontrate 42% of annual chille water um energy aving for contant uiling water flow, an 82% of annual chille water um aving for ifferential reure reetting at Omaha, Neraka. NOENCLATURE C: Contant : water flow rate (GP or kg/) T: Temerature ( F or C) W: Pum ower (kw) Q : Builing loa ratio : Differential reure (Pi or Pa) β: Ratio of the um ower aving over the eign um ower φ: Ratio of the uiling loo ifferential reure over the loo ifferential require uner eign flow. ϕ: Ratio of the lening water flow over the uiling water flow. Sucrit: : uiling : eign, full loa o: Otimal, BBS : itrict ytem, um r: Return : Suly min: minimum INTRODUCTION Ditricting heating an cooling ha een revive ince 1984 in USA [ornhe an Gaten, 1995]. any new itrict heating an cooling ytem have een etalihe an exiting ytem have een exane in recent year. Inutry an feeral government have agree that cooling, heating, an ower (CHP) ytem are a key uort for electric gri of the future; a much a eight gigawatt y the year 2020 [Sweeter, 2002]. any more exiting an new uiling are likely to receive chille water an/or hot water from itrict cooling ytem in the future. When uiling are irectly connecte to the central heating or cooling ytem, lening tation are require. Ditrict cooling or heating ytem often require higher temerature ifference of the uly an return in orer to reuce the uming cot [ASHRAE, 2000]. For examle, the itrict cooling ytem may require the return water temerature e 17 F higher than the uly water temerature. The cooling coil in air-hanling unit (AHU) are often eigne to rie the uly water temerature y 10 or 12 F. When the itrict chille water i irectly ulie to the cooling coil, the uiling return water temerature i often ignificantly lower than the value require y the itrict lant. To maintain the require return water temerature, a lening tation i ue to mix the itrict uly water an the uiling return water. The lening tation control the amount of return water ackflow to the uiling to maintain the return water temerature at the require value y the itrict ytem. Builing en uer are eigne with the ame temerature rie or ro a the itrict ytem, the lening tation are alo require to maintain the contant return water temerature uner artial loa conition. In thi cae, the lening tation ha no function at the eign loa conition. However, the heating an the cooling ytem motly work on artial loa conition. Uner artial loa conition, mot uiling en uer cannot maintain the ame ifferential temerature ince the no-linearity of the Proceeing of the Thir International Conference for Enhance Builing Oeration, Berkeley, California, Octoer 13-15, 2003

2 ICEBO 2003, Develoment of By-a Blening Station Sytem coil heat tranfer. Unfortunately, the ifferential temerature i often maller uner the artial loa conition. The lening tation are often eigne an ue for ractical reaon. For examle, the lening tation may e ue to maintain uiling comfort when a uiling ha ignificant water alance rolem. Blening tation i require for oth contant water flow an variale water flow ytem in orer to maintain require return water temerature. ASHRAE [2000] recommen intalling uiling circulation um on the uiling return water line an intalling a y-a to connect the return an the uly line. Thi eign ha two rawack: (1) the um eign flow mut e the ame a the total uiling flow although the return water flow for mixing i much le than the total water flow, an (2) the um will have to rovie the entire hea require y the water circulation in the uiling loo, although the rimary loo may have the require ifferential reure availale. Thi aer firt icue the ASHRAE recommene lening tation eign, an then reent an innovative lening tation ytem name a y-a lening tation (BBS). The um energy moel are eveloe an uquently ue to comare the energy erformance. A cae tuy i finally reente uing the actual uiling ata to emontrate the otential annual um energy aving. EXISTING BUILDING BLENDING SYSTES Figure 1 reent the chematic of a tyical uiling lening tation ae on ASHRAE (ASHRAE Hanook Sytem, 2000). The lening tation conit of a control valve on the uiling uly ie, a y-a line, an uiling circulation um. Figure 1: Schematic of Exiting Builing Blening Station The control valve (Valve-1) i eigne or electe to conume the rimary loo ifferential reure. Very often, ecial reure throttling evice are eigne to ait the control valve to conume the exceive ifferential reure rovie y the itrict ytem. The y-a ie rovie the hyical a of the return water ack flow. The um i eigne or electe ae on the eign water flow an the uiling loo reure lo uner the uiling eign water flow. During normal oeration, the control valve (Valve-1) locate on the chille water uly conume the entire ifferential reure rovie y the itrict ytem an i moulate to maintain the require return water temerature from the uiling. If the uiling return water temerature i lower than the require value, the control valve will cloe more to allow more return water ackflow an vice vera. The valve maintain the reure at the uly ie (1) rather than on the return ie (2) thu allowing the water from the uiling return to e lene with the uly from the central lant. The um run at full ee an ue the ame amount of um ower regarle of the loa conition. Thi ytem rovie goo control over the T require y the itrict ytem. However, everal imrovement can e erforme on thi ytem. Firt, the ifferential reure rovie y the itrict ytem may e ue ince it i wate y the control valve. Secon, the water flow through the um may e reuce ince the return water ack flow i ignificantly le than the uiling circulation rate. An innovative ytem name y-a lening tation (BBS) i eveloe to imrove the lening ytem erformance y imlementing thee feature. BY-PASS BLENDING STATION (BBS) Figure 2 how the chematic for the rooe BBS eign. The um are locate in the y-a line. VFD are ae to the um. A ifferential reure enor i ae to the uiling loo. The enor can either e intalle at the en of the loo or at the entrance to the uiling loo. The control valve (Valve-1) i eigne an electe ae on uiling circulation an maller ifferential reure, which equal the ifference of the maximum availale itrict loo ifferential reure an the maximum uiling loo reure lo. The um eign water flow equal the maximum return water ackflow rate, which can e ignificantly le than the uiling eign water flow 2 Proceeing of the Thir International Conference for Enhance Builing Oeration, Berkeley, California, Octoer 13-15, 2003

3 ICEBO 2003, Develoment of By-a Blening Station Sytem rate. The um hea equal the uiling loo reure lo. W C, = (1) W o = C, (2) Notice that the water flow rate i a variale in Equation 2 for the BBS ytem. To correlate the flow with eign flow an water temerature, an energy alance analyi i erforme. Figure 2: Schematic Diagram of the BBS Sytem Figure 3 reent the flow alance in a lening tation. Equation 3 tate that the energy of the uiling uly water equal the um of the energy of the rimary uly water an ackflow water. Equation 4 tate that the uiling energy conumtion equal the itrict ytem energy lo. During normal oeration, Valve-1 i moulate to maintain the uiling et oint eening uon the loa require y the uiling. The um ee i controlle to maintain the require return water temerature. If the return water temerature i lower than the et oint, the VFD ee u the um to increae the uiling uly water temerature, an vice vera. In the BBS ytem, the rimary loo ifferential reure i fully ue to circulate the rimary water. The um i only ue to circulate the ackflow water. Therefore, the BBS ytem ue much le um ower than the exiting ytem. The amount of um ower aving een on the amount of water re-circulation. Le water circulation reult in more um ower aving. The BBS ytem allow the uiling ifferential reure reet an variale flow ue to the ue of VFD. Imlementing an otimal uiling ifferential reure reet can reult in ignificant aitional um aving. It i imortant to note that the BBS ytem can only e eigne an intalle where the ifferential reure of the itrict loo i higher than the uiling loo reure lo. Energy Performance Analyi The um ower i roortional to the rouct of the water flow an the um hea when the imact of the um efficiency i ignore. Therefore, the um ower of the ae ytem an the BBS ytem are exree uing Equation 1 an 2 reectively. Figure 3: Schematic Diagram of Water Balance T, r + ( ) Tc, = T, (3) T T ) = ( T T ) (4) ( r From equation 3 an 4, the water ackflow i exree a: = T T, (5) T r T To introuce equation 5 into equation 2, the um ower of the BBS ytem i euce a: T T W = o C P, (6) T r T If the contant uiling circulation i aume for oth the exiting an the BBS ytem, the otential um ower aving can e exree a the ratio of the um ower aving over the eign um 3 Proceeing of the Thir International Conference for Enhance Builing Oeration, Berkeley, California, Octoer 13-15, 2003

4 ICEBO 2003, Develoment of By-a Blening Station Sytem ower. Accoring to equation 1 an 6, the um ower aving i euce a equation 7. W T T o β = 1 = 1 = 1 ϕ W T T r (7) The uiling lening ratio can e correlate with the uiling loa ratio an the minimum lening ratio. Equation 8 i eveloe y erforming energy alance analyi. ( 1 min ϕ = 1 Q ϕ ) (8) Where: T, T ϕ min = T T (9) R The minimum lening ratio i the lening rate when uiling ha full loa. The minimum lening ratio een on the itrict an uiling eign water temerature, eign air conition, an the coil roertie. To introuce equation 8 into equation 7, the um ower aving i exree uing the minimum lening ratio an the uiling loa ratio. ( 1 ϕ min β = Q ) (10) When the BBS ytem i ue, the ifferential reure reet may e ue to reuce the um ower. Auming contant reitance characteritic of the uiling water loo, the uiling loo water flow can e correlate uing the ifferential reure et oint. = (11) The um flow rate for the BBS ytem i then exree y equation 12 ae on equation 5. T T = (12) T r T Introucing Eq. (11) into Eq. (12), the um flow rate,, i: Inerting Eq. (13) into Eq. (2), give the um ower for the new lening tation uner variale uiling reure lo conition: 2,, ϕ W o = C (14), Finally, the otential um ower aving i exree y equation [ 1 ( 1 )] β = 1 φ Q ϕ (15) Where: min φ = (16) Equation 10 how that the um ower aving een on the uiling loa ratio an the minimum lening ratio when the contant loo flow i ue. Equation 15 how that the um ower aving een on oth the uiling loa ratio an the uiling loo ifferential et oint. Figure 4 how the theoretical um energy aving ratio ( β ) of the BBS ytem veru the uiling chille water uly temerature for variou uiling loa. The minimum lening ratio i aume to e 10%. At contant ifferential reure et oint or contant uiling water flow, φ =1, the um ower aving increae a the uiling loa increae. When the uiling ifferential reure reet i ue, the um ower aving i much higher. For examle, the um ower aving i increae from 36% to 70% when the ifferential reure i reet from 100% to 60% uner 40% of the uiling loa. The lower ifferential reure can e ue uner lower uiling loa ratio. Bae on the theoretical reult reente in Figure 4, the um ower aving can e maintaine at higher than 50% all time. Therefore, the BBS can reuce uiling um ower y at leat 50% when the ifferential reure reet i roerly imlemente. The otimal uiling ifferential reure reet an it imact will e reente in a earate aer. The otential annual energy aving i emontrate in the next ection uing a cae tuy. 3 = T T R T T (13) 4 Proceeing of the Thir International Conference for Enhance Builing Oeration, Berkeley, California, Octoer 13-15, 2003

5 ICEBO 2003, Develoment of By-a Blening Station Sytem Pum Saving Ratio =0.2 =0.4 =0.6 =0.8 = Loa Ratio Figure 4: Simulate um energy aving ratio veru the uiling loa ratio an the ifferential reure ratio (The minimum lening ratio i aume to e 10%) CASE STUDY The cae tuy i a 500,000 quare feet meical facility locate at Omaha, Neraka. The facility ha 34 AHU. The AHU were eigne to rie the chille water temerature from 42 F to 52 F. The uiling i connecte with the itrict ytem through a traitional lening tation. The itrict cooling ytem rovie chille water temerature at 39 F an require return water temerature e higher than 57 F. Figure 5 reent the meaure hourly chille water conumtion veru the amient air temerature. When the outie air temerature i lower than 30 F, the chille water conumtion i negligile. When the outie air temerature reache 100 F, the hourly chille water energy conumtion i a high a 25 Btu/hr. In orer to ue in metho to analyze the annual otential um energy aving, the imlifie loa rofile i generate uing the etaile hourly meaure ata. The loa ratio i calculate a the ratio of the average loa in the in over the maximum cooling loa (25 Btu/hr). The numer of hour in each in i taken from ASHRAE in ata [Degelman 1984]. Figure 6 reent the loa ratio, the ifferential reure reet ratio, an the ower aving ratio againt the amient temerature. The cooling loa ratio increae from 5% to 95% when the amient temerature increae from 30 F to 100 F. The ifferential reure ratio wa etermine a the Chille Water Conumtion (Btu/hr) quare of the uiling loa ratio rovie it i higher than 0.4. The minimum ifferential reure ratio i et a 0.4. Bae on the theoretical moel, the um ower aving ratio i etermine uner oth contant uiling flow an the ifferential reure reet conition. When the contant uiling water flow i maintaine, the um ower aving ratio i lightly le than the uiling loa ratio ince the 10% minimum lening ratio i aume. When the ifferential reure reet i imlemente, the um ower aving ratio varie from 76% to 89%. Uner artial loa conition, the BBS can ignificantly increae the um ower aving Amient Temerature (F) Figure 5: eaure Hourly Chille Water Energy Conumtion veru the Amient Air Temerature in the Cae Stuy Builing Ratio Power Saving With DP Reet Differential Preure Ratio Loa Ratio Power Saving Ratio W/O DP Reet Amient Temerature Figure 6: Loa Ratio, Differentia Preure Reet Ratio, an Pum Power Saving Ratio veru the Amient Air Temerature 5 Proceeing of the Thir International Conference for Enhance Builing Oeration, Berkeley, California, Octoer 13-15, 2003

6 ICEBO 2003, Develoment of By-a Blening Station Sytem Figure 7 reent the accumulate um oerating hour an the accumulate um energy aving againt the amient air temerature. The um energy aving wa etermine a the rouct of the um ower aving an the numer of hour oeration in each in. The eign um ower i 200 h. When the amient temerature ecreae from 100 F to 52 F, the accumulate um oerating hour are 4,723 hour. The accumulate um energy aving are 296 Wh (42%) if the ifferential reet i not ue. When the ifferential reure reet i ue, the accumulate um energy aving are 593 Wh (84%). If the electricity rice i aume to e $0.08/kWh, the annual energy cot aving are $23,680 for the contant uiling water oeration, an $47,440/yr for ifferential reure reet. When the amient temerature ecreae to 32 F, the accumulate chiller oeration time i 7,185 hour. The accumulate um energy aving are 320 Wh (30%) for contant uiling flow an 873 Wh (82%) for ifferential reure reet. The otential annual energy cot aving are $25,600/yr for contant uiling water flow oeration, an $69,840 for ifferential reure reet. Oviouly, the BBS ytem rovie a very attractive energy retrofit for the cae tuy uiling. Accumulate Oeration Hour With DP Without DP Oeration Pum Energy Saving (Wh) CONCLUSIONS The BBS ytem ha een eveloe. It intall the um in the uiling y-a line an ue a VFD on the um. The BBS ytem ha maller um an rovie ower of the recirculation water only. A cae tuy emontrate a minimum 42% annual um energy aving when contant uiling water flow i maintaine. When the ifferential reure reet i imlemente, the annual um energy aving can e a high a 84%. The actual energy aving may e lightly lower in actual eign oeration ince the moel analyi i not account for the VFD ower lo. It mut e ointe out that the BBS ytem cannot e imlemente in lace where the rimary loo ifferential reure i le than the uiling loo reure lo. REFERENCES ornhe G. an Caten T. R., 1995, Innovation in Ditrict Heating an Cooling an Thir Economic Imact, ASHRAE Tran., 1995, Vol. 101, Part 1, Sweeter R., 2002, Technical, Economi an Regulatory Challenge to Intalling Eight Gigawatt of New CHP for Builing Sytem, ASHRAE Tran., 2002, Vol.??, art 2,.??-??. ASHRAE, 2000, ASHRAE Hanook 2000, HVAC Sytem an Equiment, ASHRAE, Atlanta, GA. Degelman, L., Bin Weather Data for Simlifie Energy Calculation an Variale Bae Degree Day Information, Deartment of Architecture, Texa A& Univerity, College Station, Texa Amient Temerature (F) Figure 7: Accumulative Pum Oerating Hour an Accumulate Pum Energy Saving veru Amient Temerature ACKNOWLEDGEENT Author woul like to thank. Derrick eitorial aitance. 6 Proceeing of the Thir International Conference for Enhance Builing Oeration, Berkeley, California, Octoer 13-15, 2003