The Analysis of Operating Conditions of Geothermal Heat Pump Units

Transcription

1 roeedings World eothermal Congress Bali, Indonesia, 5-9 April The Analysis of Operating Conditions of eothermal Heat ump Units Andrey Red ko, Dyonis Kharlampidi, Sergey avlovsky Kharkiv State Tehnial University of Constrution and Arhiteture (Ukraine), 6, Symska str. 4. Keywords: Heat ump Unit, Coeffiient of eormane, eothermal Heating, Suessively Countelow Heat ump Shemes, Multistage Heat ump Shemes. ABSTRACT Thermodynami peormane of suessively ountelow, multistage and ombined models of heat pump units with regard to their utilization onditions in geothermal heating systems is under study. The numerial simulations of stati operating onditions for suessively ountelow and multistage shemes of heat pump units for geothermal heating systems are arried out. The results of exergy analysis for different tehnologi shemes of hightemperature heat pump units are presented.. ITRODUCTIO eothermal waters are one of the promising soures of thermal energy for heating by means of heat pump units (HUs), e. g. Ogurehnikov (5). reliminary alulations arried out for the refrigerants R4, R45fa, R4b showed that with the inrease of number of units for more than three for the speified operation onditions we annot find any notieable hanges of the value µ /µ. The utilization of several working fluids for eah HU in a sheme is possible. A peuliar feature of suessively ountelow shemes as an objet of regulation is high sensitivity to the hanges of input and output parameters of the heat arrier and geothermal water. Any deviations from speified operating onditions for one HU lead to the hanges of operative parameters of all the other units and onsequently of the whole system. Fig. shows suessively ountelow shemes of the geothermal HU. There are some shemes of geothermal heating system, e. g. Rozenfeld and Serdakov (967), whih provide for HU work in bivalent operation onditions. In this ase HUs heat some of «return» water from a heating system up to the required temperature, the rest part serves as a soure of low-potential heat for HUs. The lower the speified temperature in a heating system is, the more the share of heat utilization of geothermal waters in that sheme is. As a rule a medium-temperature refrigerant is used as working fluid in HUs. With utilization of high-temperature single-omponent refrigerants or nonazeotropi mixture on their basis as working fluids, it is possible to realize monovalent operation onditions of HU work with the diret onversion of low- potential heat from geothermal water. The peuliar feature of utilization of suh a sheme lies in the possibility to redue the onsumption of geothermal water through the seletion of optimal ooling temperature, e.g. Kaminsky (7). It is possible to expand the work range of geothermal heating systems with HUs by means of onnetion of several units in a suessively ountelow sheme. In suh a sheme water heating in a ondenser and ooling of geothermal water in an evaporator are realized in stages, besides every suessive yle happens in a higher interval spae of the refrigerant evaporation and ondensation temperatures. Thus, in speified temperature limits of the basi working yle of HUs the approximation to the Lorenz yle, with typial for this yle anisothermi harater of evaporation and ondensation proesses is reahed. The effiieny of approximation to the Lorenz yle is valued with the ratio of the atual onversion oeffiient µ and the theoretial µ and depends on the number of independent units, e. g. Heinrih, ajork and estler (985) and, see e. g. Ostapenko (6) Figure : rinipal suessively ountelow HU shemes for geothermal heating. - prodution well; - injetion well; - heat onsumer; 4- HU; 5- ondensers; 6- evaporators; 7- irulation pump. Multistage shemes of HUs, onsisting of one ommon ondenser and evaporator and several ompressors onneted suessively, are less sensitive to the hanges of input parameters. Fig. shows multistage of the geothermal HU.. HEAT UM ERFORMACE MODELI Within the limits of this work it seemed rational to develop a alulation tehnique and on its basis to fulfill the analysis of operating onditions of geothermal HUs with different onneting shemes of fundamental equipment elements. The methods of mathematial modeling of HU stati harateristis are traditionally used to solve the task, e. g. Jin and Spilter ().

2 Red ko, Kharlampidi and avlovsky Motion patterns of geothermal waters in a water-bearing stratum at work of a prodution well and absorption well are shown in Fig. and Fig. 4. Figure : rinipal multistage HU shemes for geothermal heating. - prodution well; - injetion well; - heat onsumer; 4- HU; 5- ondenser; 6- evaporator; 7- irulation pump. The alulation of HU stati harateristis provides for speifiation, as initial data, of the geometri parameters of evaporator, ondenser, ompressor, binding piping of basi equipment and also the initial temperatures of heat-arriers and their flow rates. For the suessively ountelow shemes with more than two HUs the alulation has one peuliar feature. Figure : atterns of geothermal waters inflow to a vertial prodution well. In the sheme onsisting of, for example, three units the temperature of inlet «return» water in the first HU in water heating and the temperature of inlet geothermal water in the third HU are known. The outlet temperatures of heatarrier and geothermal water in the seond HU whih atually determine operating onditions of the rest units are not known. For multistage shemes onneted suessively aording to the refrigerant, the parameters of inlet steam in the seond and third ompressors are unknown.. The Calulation of the Thermal Water Intake eormane The well prodution rate of a hydrodynamially peet well is found from the equation, e. g. Shterenliht (99) gwt w w H h =,6k () Rw lg r where k is the filtration oeffiient, m/s; H is the apaity of a water-bearing stratum, m; h w is the depth of water in the well when there is no pumping out, m; r w is the radius of a well, m; R w is the range radius of a well, m. With the start of pumping out the water level in the well and around it beomes lower. The distane R w beyond the limits of whih there is no hange of head pressure an be found from / R w = S k () where S is the lowering of water level during pumping out, m. The equation () an also be used for the alulation of injetion well. Figure 4: atterns of geothermal waters outflow from a vertial injetion well. The weighted average temperature of thermal water intake is assumed as speified (rated) temperature of geothermal water t gw reeived at thermal water intake whih omprises two and more wells t gw t = gw gw + t gw gw + gw t gw where t gw, t gw, t gwk are the temperatures at wellheads, C; gw, gw, gwk are the geothermal well prodution rates, kg/s.. The Calulation of the Heat ump eormane.. The tehnique of alulation of a suessively ountelow geothermal HUs onneting sheme The heating apaity, withdrawn from geothermal water in HU evaporator, and orresponding to it HU ooling apaity are found from the equations gwk gwk gwk () = gw gw( tgw t) η (4)

3 Red ko, Kharlampidi and avlovsky. = (5) q where is the mass flow of a refrigerant in the yle, kg/s; q is the speifi ooling apaity in the yle, kj/kg; t is the evaporation temperature of a working fluid, C; t gw is the inlet temperature of geothermal water into the evaporator; η is the evaporator ooling oeffiient. At the alulation of operation parameters of the first HU, aording to the motion of a low-potential heat-arrier, the temperature t gw = t gw. The evaporator ooling oeffiient η is ke F e gw gw η = e (6) where k e F e is the intensity of heat transfer in the evaporator, kw/k. The intensity of heat transfer in the evaporator is found from the equation, e. g. Wang and Barnet () As is known, e. g. Koshkin (989), while hanging operating onditions some part of HU ooling apaity is spent on ooling of the evaporator (if t is dropping). In the ase, when HU ooling apaity is inreasing, t is also inreasing. Changes of ooling apaity are analyzed as follows: = M (4) e e T where M e and e are the mass and the heat apaity of the evaporator; T is the hange of evaporation temperature. The same equation an be used for the ondenser = M T (5) where M and are the mass and the heat apaity of the ondenser; Τ is the hange of ondensation temperature. At the preseleted theoretial displaement of the ompressor V th the mass flow of a refrigerant is equal to k F e + e = gwt +. (7) V (6) = thλ ν The heating apaity withdrawn from the HU ondenser into the heating system is found from = q (8) = ) wtwt ( tk twt ηс (9) where q is the speifi heating effiieny in the yle, kj/kg; t is the ondensation temperature of a refrigerant, C; t wt is the inlet water temperature in the ondenser; wt is the water flow through HU ondensers, kg/s. The ooling oeffiient for the HU ondenser η is defined from k F wt wt η = e () where k F is the intensity of heat transfer in the ondenser, kw/k. The intensity of heat transfer in the ondenser is found from the equation, e. g. Kempiak and Crawford (99) k F =.5 4wt () The evaporation and ondensation temperatures in the seond and following approximations are alulated from the equations: t = tgw () gwgwη t = twt + () wtwtη where ν is the speifi volume of refrigerant vapor at sution in the ompressor, m /kg. Under the ondition of isoenthalpi nature of the proess in the HU expansion valve, the flow of a refrigerant through the throttle is defined from, e. g. Chernyvsky (6) = ϖf p ( ) (7) in where f is the flow area of the throttle, m ; ω is the efflux oeffiient; in is the fluid density before the HU expansion valve, kg/m³; and are the ondensation and evaporation pressures, ka. The volumetri effiieny of the ompressor an be presented as, e. g. Morozuk (6) λ = λ с λ wt (8) where λ is the volumetri effiieny oeffiient taking into aount the effet of «dead spae» m λ = (9) where is the relative value of «dead spae» =,5,5; m is the polytropi exponent of the reverse expansion from «dead spae», m =,,5. The oeffiient λ wt in the formula (8), taking into aount the volumetri losses whih were aused by vapor throttling in valves, vapor heating from the ylinder walls during the sution proess, flow from the ompression hamber to the sution hamber, is defined from the expression: su sup su Tsup T + T λ wt = () αt + β

4 Red ko, Kharlampidi and avlovsky where Τ sup su is the total superheating of a refrigerant at the sution in the ompressor; T and T is the evaporation temperature and ondensation temperature of a refrigerant, K; α =,; β =,5 are the oeffiients taking into aount the working fluid influene. The ompressor adiabati apaity is = l () a m where l m is the ompression work in the ompressor k k k dis l m = ν () k su The oeffiient of peormane for the whole suessively ountelow onnetion sheme of three HUs is equal to µ = n= el n= + aux (9) where aux is the power spent on the drive of auxiliary equipment. Fig. 5 shows the alulation blok diagram of HU stati harateristis. where k is the adiabati exponent; su and dis are the sution and disharge pressures respetively, ka. Considering pressure losses in the sution Ρ su and disharge Ρ dis pipelines and the ompressor valves, the values su and dis are found from the following relations: = () su su dis = + (4) m dis The values Ρ su and Ρ dis are defined onsidering reommendations of the work, e.g. Bratuta, Sherstyk and Kharlampidi (7). The isoentropi apaity of the ompressor is i η a = (5) i where η i is the isoentropi effiieny fator of the ompressor. In the general ase, the value η i an be determined using the empirial dependene, e. g. Morozuk (6) η = λ,5t (6) i wt + The power apaity onsumed by the ompressor eletri motor from the network el is as follows: i Vth p fr + i el = (7) ηel. m where η el.m is the effiieny fator of the eletri motor, η el.m =,85,9; p i fr is the average indiator pressure of frition, p i fr = 5 ka. The atual oeffiient of peormane of HU is µ = (8) el Figure 5: Calulation blok diagram of HU stati harateristis. To hek funtion ability of the tehnique we arried out the alulation of HU operating onditions where the following geometri and metering harateristis were represented: V th =, m /s; F =, m ; F e =,6 m ; wt =,5 kg/s; gw =,75 kg/s. A new safe for ozone refrigerant R45fa was regarded as working fluid. With regard to the alulation of a suessively ountelow sheme onsisting of three HUs, in the first approximation, besides t and t, t gw and t wt are also speified, whih, subsequently, are defined more preisely aording to heat balanes of evaporators and ondensers. Fig. 6 and 7 represent the generalized relations for and obtained at different t, t, t wt, t gw. The relation µ = f(t gw, t wt ) is presented in Fig. 8. Table represents the alulation results of peormane of a suessively ountelow sheme onsisting of three HUs. 4

5 Red ko, Kharlampidi and avlovsky. Table eormane of a Countelow Sheme Consisting of Three HUs arameters HU HU HU Heating apaity, kw Refrigerating apaity, kw Figure 6: Change of ompressor refrigerating apaity and evaporator power apaity subjet to t at different t gw and t wt. - ompressor produtivity; - evaporator refrigerating apaity. Inlet temperature of geothermal water into the evaporator, C Evaporation temperature of refrigerant, C Outlet temperature of geothermal water from the evaporator, C Condensation temperature of refrigerant, C Inlet water temperature in the ondenser, C Outlet water temperature from the ondenser, C 7,6 5,6 5, The Tehnique of Calulation of a Multistage eothermal HU Sheme The alulation of harateristis of a multistage HU is a oordination of the harateristis of its separate elements. On the one hand, the volumetri apaity of all the stages must be equal to the refrigerant flow rate appropriate to heat load on the evaporator. On the other hand, the ompressor produtivity must orrespond to the ondensation pressure whih goes with the ondenser heating effiieny and the heat arrier parameters of a heating system. Figure. 7: Change of ompressor produtivity and ondenser power apaity subjet to t at different t and t wt. - ompressor produtivity; - ondenser power apaity. Despite the equality of flow rates through all the ompressors in a multistage sheme, the values of speifi vapor volumes at sution in eah ompressor are different. Therefore, it is neessary to oordinate the work of eah stage onsidering intermediate pressure. For a three-stage HU there are two levels of intermediate pressures whih divide the range of working pressures from to into three stages of ompression. The first stage is from to int, the seond stage is from int to int and the third stage is from int to. Thus, taking into aount reommendations of the work Morozuk (6), we an put down then int int = = = (9) int int int = () Figure 8: Coeffiient of peormane µ = f(t gw, t wt ). int = () 5

6 Red ko, Kharlampidi and avlovsky The oeffiient of peormabe for a three-stage HU is µ = n= + el aux () Table represents the alulation results of power apaity of the ompressors of a three-stage HU for the following geometri and metering harateristis: ΣV th =,6 m /s; F = 9, m ; F e = 5, m ; wt =,5 kg/s; gw =,75 kg/s. Table. Calulation of ower Capaity of the Compressor Drive of a Three-Stage HU. Compressor stage ower apaity of ompressor drive el, кw t wt, ºC t gw = 6 C stages,964 4, 4,7 5,8 stages 4,79 4,589 5, 5,45 stages 4,79 4,67 5,87 5,659 t gw = C stages,559,96 4,78 4,648 prodution well and an injetion well. The methods of water prodution from the well and water injetion into the well, inluding its design and proessing equipment, an be seleted with the employment of existing projets, e.g. Murawyev (978). The partiular feature of operation for all geothermal designs omprising doublet well systems (one prodution well and one injetion well) is strongly marked unsteady harater of hydrauli proesses in the initial period of operation of thermal water prodution system. The analysis arried out in the work, e. g. Razakov (7), showed that before entering quasisteady operation of the system at first fast pressure drop in the outlet of prodution well and pressure rise in the injetion well our, besides, the intensity of water flow onsiderably hanges. Conerning HU, hanges of thermal water flow will lead to hanges of its most operation parameters, espeially in a suessively ountelow operation design. In this onnetion it is reasonable to offer the onfiguration of HU tehnologial sheme whih would allow to ompensate this defiieny. Fig. 9 shows a ombined design of geothermal heat supply with HU, onsisting of two units. The first, aording to thermal water flow diretion, HU operates in a simple single-stage yle, where the refrigerant R45fa serves as working fluid; the seond HU operates in a two-stage yle, the sheme of whih inludes an intermediate heat exhanger and isobutane R6а serves as refrigerant. Evaporators in the ombined sheme are onneted suessively, ondensers are onneted parallel. stages,744 4,9 4,548 4,97 stages,76 4,9 4,589 5,9 t gw = 7 C stages,69,55,868 4,8 stages,5,77 4, 4,5 stages,96,78 4,8 4,66 The analysis of alulation results showed that under other equal onditions the sensitivity of µ to the hanges of input parameters of geothermal water and heat arrier of a heating system for a three-stage HU sheme is less than for a suessively ountelow sheme. The average value of µ for a suessively ountelow sheme and also the ooling value of geothermal water in HU evaporators are higher. These fators allow to reommend a suessively ountelow HU sheme for the projets with a low well prodution rate.. COMBIED SCHEME OF EOTHERMAL HEAT SULY WITH HU atural onditions of the most Ukrainian geothermal soures pratially eliminate appliation of the flowing tehniques sine known sites are haraterized by limited supply of natural thermal fluids and by small water prodution in the setion of water-bearing reservoirs, e. g. Razakov (7). Thereby, at utilization of low-potential heat it is neessary to organize operation of two wells: a Figure 9: Combined sheme of geothermal heat supply with HU and thermodynami yle of two-stage HU with refrigerant R6a in - i diagram. Сm- ompressor at low pressure side; Cm- ompressor at high pressure side; C- ondenser; E- evaporator; R- reeiver; IHE- intermediate heat exhanger; TV, TV- throttling valves; МW- modular unit of water leaning; - pump; HS- heating system; HW- system of hot water supply; W- prodution well; IW- injetion well The priniple of ombined sheme operation is the following. Some part of thermal water at temperature of 4 С enters the evaporator of the first, aording to water flow diretion, HU where it is ooled to the temperature of 6

7 Red ko, Kharlampidi and avlovsky. 6 С, the other part of it after passing the modular unit of water leaning omes to the ondenser inlet of HU where it is heated up to 7 С, after that water is delivered to the system of hot water supply. In the evaporator of the seond, aording to water flow diretion, HU deeper water ooling happens, after that thermal water enters the injetion well. In the ondenser of HU heating of thermal water up to the temperature of С is aomplished. HU realizes the two-stage yle where after the stage of low pressure (Cm) ompressed vapor R6a enters the intermediate heat exhanger (IHE) and there it is ooled. In the same heat exhanger superooling of refrigerant ondensate oming from the ondenser (C) is arried out. For the purpose of more omplete ooling of superheated steam before sution to the seond stage ompressor (Cm), after the throttling proess in the ontrol valve (TV) some part of liquid refrigerant flow is injeted. At the same time not only the vapor from Cm undergoes the proess of ompression in Cm but also the vapor formed during the proess of boiling in IHE. At the thermodynami parameters alulation of the ombined sheme the following data were taken. Temperatures of the yle for HU: Т = 5 С; Т = 8 С; steam superheating Т sh = 7 С; superooling Т s = С; = 7 kw; =,58 kw. For HU: Т = С; Т = 95 С; superooling in the ondenser Т s = 5 С; intermediate pressure int =,87 Ма; saturation temperature appropriate to intermediate pressure Т int = 6 С; ooling temperature in intermediate heat exhanger Т IHE = 7 С; steam superheating before sution into Cm Т sh = 5 С; steam superheating before sution into Cm Т sh = 5 С; heat apaity of a low-potential soure = кw. While studying HU operation onditions it is to estimate reliably their thermodynami peetion with the help of a detailed analysis of exergy losses in its elements. Relative value of exergy destrution in the element is χ = E Dk E Dk () where Е Dk is exergy destrution in the element under study, kw; Е Dk is total value of exergy destrution in the unit elements, kw. The destrution figure of exergy applied to HU is found from δ = el EDk + τ where τ is the Carnot fator for evaporator. Exergi weight of the element is ξ = τ (4) E Dk (5) where τ is the Carnot fator of the ondenser. Exergy effiieny is η ех = сτс + τ el (6) Table represents the alulation results of exergy destrution in the elements of HU (refrigerant R45fa) and HU (refrigerant R6a) whih are inluded in the ombined sheme. Table. The alulation of exergy destrution in the HU elements for different shemes HU element Е Dk, кw χ, % δ, % ξ, % Combined sheme HU (R45fa) Evaporator,78 5,9,7,57 Compressor,4 6,9, 7,94 Eletri motor,4,, 4,9 Condenser,88 6, 8,6,7 Throttle,7,5 7,6,4 HU (R6a) Evaporator,69, 5, 8,56 Compressor,5, 4,77 7,99 Eletri motor,99 4,44,88,4 Intermediate heat exhanger,,9 5,89 9,87 Compressor,7 6,4,6 4,9 Eletri motor,4 4,66,97, Condenser 5,9 6,4, 8,7 Throttle,87 7, 7,5, Throttle,8,6,55,59 Exergi effiieny η ех =,66 Single-stage HU (R6a) Evaporator 6,7 5, 7,67 6,7 Compressor 9,96,6,5 4,8 Eletri motor,5 8, 4, 8,76 Regenerative heat exhanger,6 6,4, 8,8 Condenser,86 8,79 4,4 9,6 Throttle 8, 8,9 9,46,6 Exergi effiieny η ех =,457 7

8 Red ko, Kharlampidi and avlovsky The estimation of thermodynami peetion of the singlestage HU with regenerative heat exhanger (refrigerant R6a) is given for the omparison. Calulation of the single-stage HU was arried out for the same heating effiieny and at the same inlet and outlet parameters of evaporator and ondenser as for the ombined sheme. Some reommendations of literature, e. g. Yantowsky and ustovalov (98), were used to define exergy losses. The refrigerant parameters haraterizing system state of equilibrium with environment were taken at Т env = 7 К. As table shows, for a ombined sheme exergy effiieny is 8% higher than for a single-stage one. As for the absolute value of exergy destrution in the elements a ombined sheme also has some advantage in omparison to a single-stage one. Exergy losses in the ondenser are the exeption. For a ombined sheme they are a little higher than for a single-stage sheme. This an be explained by higher value of the Carnot heat transfer fator for a singlestage sheme (τ =,44) in omparison to a ombined sheme where that value is τ =,5. It should be noted that exergy losses in the ondenser mostly depend on losses in the ompressor and are predetermined by the proess of thermodynami yle. The alulation of relative harateristis χ, δ, ξ allowed to reveal the most impeet elements in eah sheme. For the single-stage HU suh an element is a regenerative heat exhanger and for the ombined sheme it is the ompressor of HU. COCLUSIO The introdued relations and alulation tehnique let analyze different thermodynami operation onditions of HU and also to selet rational arrangement of its tehnologi sheme onsidering operation onditions of thermal water intake system and parameters of heat-transfer agent of heating system. REFERECES Ogurehnikov L. A.: eothermal Resoures in the ower Engineering, International Sientifi Journal Alternative Energy and Eology, (), (5), Rozenfeld L. M., and Serdakov. S.: The rospet to Use Heat umps for the Effetiveness Inrease of Utilization of Low otential Heat Carrier, Chemial and Oil Equipment,, (968), 6-. Kamisky O. V.: The Effetiveness Inrease of the Industry and Deentralized Heating System on the Basis of Alternative Energy Supply. Abstrat of the Thesis for a Candidate of Tehnial Sienes Degree on rofession Code "Tehnial Thermo-physis and Industrial Heat-and-ower Engineering". Odessa State olytehnial University, Odessa, (7). 8 p. Heinrih., ajork H., and estler W.: The Heat ump Installation for the Heating and Hot Water Supplying. Mosow. Stroyizdat, (985), 5 p. Ostapenko O..: Vapor Compression Heat ump Installations in Heat Supply Systems. Abstrat of the Thesis for a Candidate of Tehnial Sienes Degree on rofession Code "Tehnial Thermophysis and Industrial Heat-and-ower Engineering". ational University of Food Tehnologies, Kyev, (6). p. Jin H. A., and Spilter D. J.: arameter Estimation Based Model of Water-To-Water Heat umps for use in Energy Calulation rograms. ASHRAE Transations, 8, (), -7. Shterenliht D. V.: Hydraulis, Vol.. Mosow, Energoatomizdat, (99), 67 p. Wang S. W., Wong J., and Barnet S.: Mehanisti Model of Centrifugal Chillers HVAC System Dynamis Simulation. roeedings CIBCE. Building Serv. Eng. Res. & Teh. (), (), 7-8. Kempiak M. J., and Crawford R. R.: Three-zone steadystate modeling of a mobile air-onditioning ondenser. ASHARE Transations. 98(), (99), Koshkin..: Refrigerating Units. Leningrad, Masheenostroenie, (985), 5 p. Chernyvsky S. A.: Development and Investigation of the Regulated Throttling Devie. Abstrat of the Thesis for a Candidate of Tehnial Sienes Degree on rofession Code The Mahinery and Devies, roesses of Refrigerating and Cryogeni Tehnis, Air Conditioning and Life Support Systems. Makhahkala, (6), 8 p. Morozuk T. V.: The Theory of Refrigeration Mahines and Heat amps. Odessa, egoziant, (6), 7 p. Bratuta E.., Sherstyk V.., and Kharlampidi D. Kh.: The Analysis of the Influene Hydrauli Resistane of Reduing Fitting and Tubs On the Effetiveness Refrigeration Mahines. Integration Tehnologys and Energy Saving,, (7), 6-. Razakov A.: Thermo-physial roesses Under the Forming and Utilization of eothermal Resoures. Abstrat of the Thesis for a Dotor's Degree in Tehnial Siene on rofession Code "Tehnial Thermo-physis and Industrial Heat-and- ower Engineering". Institute of Tehnial Thermophysis. Ukrainian ational Aademy of Siene, Kyev, (7). 4 p. Murawyev V. M.: The Exploitation of Oil and gas boreholes. Mosow. edra, (978), 448 p. Yantowsky E. I., and ustovalov Y. V. Vapor Compression Heat ump Installations. Mosow. Energoizdat, (98), 44 p. 8