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The heat pump soil-water efficiency design for a research laboratory of the Transilvania University of Braşov-study case
IOAN LUCIAN CÎRSTOLOVEAN1), MIRCEA HORNEŢ1)
GEORGE DRAGOMIR 1), PARASCHIVA MIZGAN 2) 1) Buildings Services Department Transilvania University of Braşov
5th Turnului Street, Brasov ROMANIA
[email protected], [email protected],[email protected], http://www.unitbv.ro/constructii/en
2) Civil Engineering Department Transilvania University of Braşov
5th Turnului Street, Brasov ROMANIA
[email protected], http://www.unitbv.ro/constructii/en Abstract: - In the IRDT of the Transilvania University of Braşov there have been implemented in a research laboratory a soil-water heat pump and a consumer a radiation heating system called heated concrete – the thermal agent for the heated concrete is produced by the soil-air heat pump The structure of the envelope was designed in such a way as to respond to the Directive which requires cuts on the energetic consumption of buildings. The accumulation of heat in ceiling / floors will ensure an efficient overtaking without any thermal variations of highest values during the heating period. The efficiency of a heating installation which has as heat source a thermal pump needs to be estimated with a view to establishing the amortization period of the initial spending. The variation of the external temperature has a direct effect on the efficiency of the thermal pump since the functioning efficiency of the thermal pump is influenced by the thermal load of the building, that at its turn, depends on the exterior temperature. Key-Words: - heat pump, thermal fields,heated concrete, geothermal energy 1 Introduction The determination of performance rates for heat pumps is largely standardised throughout Europe on the basis of the EN 14511. Energy Performance Buildings Directive (2010) required nearly zero-energy buildings. Article 9 states that Member States shall ensure that by the end of 2020, all new buildings are nearly zero –energy buildings[1]. The building, research laboratory, where the heat pump was implemented, studied in this paper, has a reduced head necessary. The structure of the envelope was designed in such a way as to respond to the Directive which requires cuts on the energetic consumption of buildings. In this way, it was possible to use as source for the production of the thermal agent a soil-water heat pump. The heat naturally accumulated in the crust triggers what is called geothermal energy. The soil has the property of accumulating and maintaining solar energy for a alonger period of time, which leads to an almost
constant level of the heat source throughout the whole year [2], [3],. The energy is captured by the soil, either directly under the form of radiations, or indirectly under the form of heat from rains or air. The heating system by low temperature radiation also called „heated concrete” represents a simple solution to be used in building elements as heating objects radiators, the heat transfer from the heating objects to rooms being done mostly by radiation. The thermal agent pipes, as heat transporters, are inserted in the concrete at the level of floors, respectively, the floors of the rooms, the temperature of the thermal agent being under 30° C[7]. 2 Problem Formulation The projection and positioning of the installation of geothermal collectors in
Recent Advances in Environmental Science
ISBN: 978-1-61804-167-8 49
combination with the heat pump was made by having the following data [11]: 1.The heating necessary and the performance factor, 22kw and COP 4, vaporization capacity 16.5 kw. 2.The volumetric flow of the heat pump, 4400 l/h. 3.The specific earth-extraction capacity , 15 W/m². The geothermal tubes are double profile U, placing scheme is Fig.1. The characteristics for a tube are :
• Lenght -100ml • The tube tipe is Pe Xa De 32x2.9
with 0.531 l /m. • The agent quantity for a tube is-
218 l.
Fig 1 Placing scheme of the thermal collectors The heat necessary for the heating of the building is of 54 kw, calculated with SR EN 1907/1[8]. Fig. 2 presents the variation of the heat necessary for the heating with exterior temperatures:At -22 º C the heat necessary is of 35,5kW, and at -2 º C the heat necessary is of 19,8 kW.
Fig.2 Thermal load variation with external temperature
The fuel consumption, natural gases, of the 60 kW boiler situated in the central heating room as background source, for the same exterior temperatures is represented in the follwoing graph, fig 3:
Fig 3. Gas consumption diagram
The connection between the thermal load of the heat pump for different values of the agent’s parameters obtained in the secondary of the heat pump and the exterior temperature is represented in fig. 4. The diagram was obtained by drawing the two curves:
• The curve for the heat necessary of the building;
• The load curve of the heat pump.
. Fig. 4. Variation of heat load of Heat Pump with external temperature at different external
temperature At the intersction of the two curves, the bivalent temperature has been obtained. 3. Problem Solution Further on, we will illustrate how the heat provided by the implemented heat pump, B121[11], can ensure the heat load of the building by means of the heated concrete heating system. We have analyzed
Recent Advances in Environmental Science
ISBN: 978-1-61804-167-8 50
the capacity of the pump at external temperatures ranging between -4 and 10º C for a number of hours ( the bin method – hourly frequency of the external temperature [5]) as it results from the table below:
Tab 1.External temperature and number of hours
The heated concrete system requires low parameters in the thermal agent ( 35º C). From the technical file of the pump [11] we have extracted the parameters: COP standard, integrated thermal capacity, absorbed electric load. The efficiency of the heat pump depends on the thermal load of the building. The testing conditions of the thermal pumps whose results provide their capacity curve depending on the external temperature are different from the conditions characteristic to real functioning [10]. When the thermal capacity of the heat pump exceeds the heat necessary of the building, the pump begins to enter a cycle: these successive starts and stops will be the more frequent that the difference between the already mentioned two values is greater . “The heat pump will suffer a diminution of its heat providing capacity. As a consequence the diminished providing capacity of the heat DPC will result after applying a diminution factor DF on the values obtained at the testing of the capacity of the heat pump QPT in the conditions of a stationary regime on the test desk” [10 ].In Fig.6. there is the diminished characteristic of the heat pump due to the calculated cycle for each temperature interval and for a degradation coefficient of 0,25 recommended for their heating regime [9],[10].
Fig 5.Heat capacity adjusted and real COP of Heat Pump
The heat provided by the pump in real simulation conditions is illustrated in fig.6
Fig 6. Heat produce by Heat Pump
Tab 2.Thermal energy produce by heat pump
By comparing the quantity of energy provided by the pump with the real load of the building, it results
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ISBN: 978-1-61804-167-8 51
that when the external temperature varies between -4 º C and 10 º C ,Tab 2, we notice that the heat pump can cover the heat necessary of the building, therefore, it does not require the intervention of the gas heating boiler.
Fig 7. Real COP variation of heat pump 4 Conclusion 1.One can notice that there is only one point, the one of equilibrium, Fig 5, (corresponding to an external temperature) for which the capacity of the heat pump equals the heat necessary of the building. 2.The heat pump ensures the heat necessary for heating for external temperatures between -4 and 10 º C and it can register good results for external temperatures of -7,-8 º C 3.The analyzed building has a thermal protection which confers thermal stability to rooms ( low variation of the confort temperature ) 4.The heated concrete heating system can ensure the heating of the building by a thermal agent provided by the pump at low parameters under climatic conditions specific to the Brasov area, thermal agent 35 º C. 5.The COP of the heat pump is situated between 3,4 and 4,7. This COP recommends the use of this equipment for the heating of buildings when external temperatures varies between 10 º C and – 10 º C Fig 7. References: [1] www.rehva.eu/rehva-european journal. [2] JOHNSTON,W.,NARSILIO,G.A,.,COLLS,S.,
Energing Geothermal Energy technologies.KSCE journal of Civil Engineeing (2011)15(4):643-653. DON 10.1007/s 12205-011-0005-7
[3] CÎRSTOLOVEAN,L. (2009),Contributions concerning the fulfillment of the performance by quality in the development and achievement of the installations for buildings.Phd
Thesis,University Technical “GHe Asachi” Iasi.
[4] ENERGUIDE,Heating with Heat Pump, Natural resources Canada’s Office of Energy Efficiency ISBN 0-662-37827-x.2004
[5] ASHRAE Fundamentals HandBook, Chapter 31.2001.
[6] LAZZARIN,R,BUSATO,F.,NORO,M.,Heat pumps in refurbishment of existing buildings-december 2012.
[7] BJARNE,W.,O.Operation and control of thermally activated building systems(TABS),The REHVA European Journal,Vol.48, ISSUE 6,December 2011.
[8] SR EN 1907/1.Method for calculation of the heat design heat load.
[9] BOIAN,I.Dezvoltare durabila. Instalatii pentru constructii bazate pe energie regenerabila. ISBN 978-973-635-978-1.
[10] BOIAN I.,FOTA S.Evaluarea performantei termice a pompelor de caldura in conditii climatic diverse.CIBv 2009
[11] VIESSMANN srl.Design instruction for Heat Pumps
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