Residential CO2 heat pump system for combined space heating and hot water heating

Stene, Jørn

doi:10.1016/j.ijrefrig.2005.07.006

Cited by 149 publications

(82 citation statements)

References 13 publications

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“…Fewer theoretical and experimental studies have been conducted for the performance analysis on CO2 heat pump water heating systems. Some studies have been conducted under steady states: Cecchinato et al have investigated the performance of a water heater by a simulation model in consideration of the influence of inlet water temperature by assuming perfect stratification and mixing in a storage tank [23]; Stene has conducted theoretical and experimental studies on the performance of a heat pump for combined space and water heating in consideration of the influence of inlet water temperature due to heat conduction in a storage tank [24];…”

Section: Introductionmentioning

confidence: 99%

Numerical analysis on performance enhancement of a CO2 heat pump water heating system by extracting tepid water

Ohkura

Yokoyama

Nakamata

et al. 2015

Energy

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Water heating systems each of which is composed of an air-to-water heat pump using CO2 as a natural refrigerant and a hot water storage tank have been developed, and are expected to contribute to energy saving in residential hot water supply.However, the area of tepid water in the storage tank expands because of heat conduction during long time storage, which leads to a degradation of the system performance.One of the ways to reduce the area of tepid water and enhance the system performance is to extract tepid water from the side of the storage tank. In this paper, the performance enhancement of a CO 2 heat pump water heating system with such a revised storage tank is analyzed by numerical simulation. The simulation model developed previously for a conventional system is extended by modifying the model for the storage tank and verifying its validity through experiments. Through a performance analysis using a standardized hot water demand, it is clarified how system performance 2 values of the revised system are enhanced, and especially how the trade-off relationship between the system efficiency and the volume of unused hot water is improved, in comparison with those of the conventional system.

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Section: Introductionmentioning

confidence: 99%

Numerical analysis on performance enhancement of a CO2 heat pump water heating system by extracting tepid water

Ohkura

Yokoyama

Nakamata

et al. 2015

Energy

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“…Some studies have been conducted for the performance analysis on water heating systems (Cecchinato et al, 2005;Stene, 2005;Minetto, 2011). However, few studies have been conducted in consideration of daily changes in the aforementioned conditions.…”

Section: Introductionmentioning

confidence: 99%

“…As a result, the system performance is affected by the operational history on past several days, and changes complexly with days. Therefore, in order to attain the maximum system performance, it is necessary to estimate the daily changes in system performance values accurately in relation to those in the ambient conditions, hot water demand, and operating conditions, and determine the operating conditions optimally based on them.Some studies have been conducted for the performance analysis on water heating systems (Cecchinato et al, 2005;Stene, 2005;Minetto, 2011). However, few studies have been conducted in consideration of daily changes in the aforementioned conditions.…”

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confidence: 99%

Performance Estimation and Optimal Operation of a CO2 Heat Pump Water Heating System

Yokoyama¹

2013

Int. J. Thermo

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IntroductionHot water demand occupies about one-third of the energy consumption in the residential sector in Japan, and energy saving in hot water supply has been an important issue. Under this situation, water heating systems each of which is composed of a heat pump using CO 2 as a natural refrigerant and a hot water storage tank have been developed and commercialized widely (Saikawa, 2004;Hashimoto, 2006). The performance of CO 2 heat pumps has been enhanced dramatically through the technological development of their components such as compressors and gas coolers. On the other hand, importance has also been given to the performance of water heating systems in case they are operated under a daily change in hot water demand.The performance of the CO 2 heat pump only, or coefficient of performance (COP) is affected by the air temperature as well as the inlet and outlet water temperatures. Many theoretical and experimental studies have been conducted for the performance analysis on CO 2 heat pumps (Hwang and Radermacher, 1998;Nekså et al., 1998; Saikawa et al., 1999;Saikawa and Hashimoto, 2001;Nekså, 2002;White et al., 2002;Skaugen et al., 2002;Richter et al., 2003;Yokoyama et al., 2006;Laipvadit et al., 2008;Yan et al., 2010;Sarkar et al., 2010;Yamaguchi et al., 2011). On the other hand, the performance of the water heating system composed of the CO 2 heat pump and storage tank is affected by many conditions. The ambient conditions such as air and feed water temperatures, the hot water demand, and the operating conditions such as startup and shutdown, and outlet water temperature during operation of the CO 2 heat pump affect the inlet water temperature and resultantly the COP through the temperature distribution in the storage tank. In addition to the COP, the storage and system efficiencies, and the volumes of stored and unused hot water are considered as system performance values, and these are also affected by the aforementioned various conditions through the temperature distribution in the storage tank. As a result, the system performance is affected by the operational history on past several days, and changes complexly with days. Therefore, in order to attain the maximum system performance, it is necessary to estimate the daily changes in system performance values accurately in relation to those in the ambient conditions, hot water demand, and operating conditions, and determine the operating conditions optimally based on them.Some studies have been conducted for the performance analysis on water heating systems (Cecchinato et al., 2005;Stene, 2005;Minetto, 2011). However, few studies have been conducted in consideration of daily changes in the aforementioned conditions. In order to investigate the daily changes in system performance values, laboratory and field tests have been tried under simulated and practical hot water demands, respectively. However, hot water demands depend on residential houses, and it takes extremely long time to conduct the tests. Thus, it is not necessarily easy to investigate the ...

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“…Hence the annual heating demand for SHW has a higher share of the total heating demand in new houses. The SHW ratio 1 usually ranges from 20 to 45% in new and low-energy houses (Stene, 2005). Therefore, SHW production is an interesting case study in 2 Chapter 1 Introduction order to make the process more efficient and have a great impact on the total energy consumption.…”

Section: Motivationmentioning

confidence: 99%

“…Works like (Cecchinato et al, 2005;Nekså et al, 1998;Nekså, 2002;Rieberer et al, 1997) has shown high efficiency of these cycles at water temperature lifts even higher than 50K. Stene (2004) discussed the existence of the gas cooler pinch point and the effect of the rejection pressure control for CO2 heat pump water heaters. Figure 1.3 illustrates the result of increasing the rejection pressure from 85 bar to 110 bar for a CO2 heat pump water heater, where water is heated up from 5ᵒC to 70ᵒC.…”

Section: The Transcritical Co2 Cyclementioning

confidence: 99%

High capacity heat pump development for sanitary hot water production

Mocholi¹

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L'home viu d'emocions, no del seu currículum Kilian Journet i AcknowledgmentsEn primer lloc volia donar-li les gràcies als meus directors de tesis, José Gonzálvez i Emilio Navarro, perquè sense ells aquest treball no haguera sigut possible. Gràcies per donar-me l'oportunitat de treballar en el projecte Europeu NxtHPG, per tot el que m'heu ensenyat, pels bons consells i per les hores que hem passat analitzant els resultats o especulant sobre algun problema concret.Gràcies als meus companys del IIE, sobretot a tots aquells que en alguna mesura han participat en aquest projecte, en especial a José Miguel, Carla, i Alex, amb qui he passat moltes hores barallant-nos amb sensors, vàlvules d'expansió i altres aparells del dimoni. També volia nomenar a Estefania, qui continuarà amb el treball d'aquesta tesi, i amb qui, juntament amb Emilio, hem passat unes quantes hores donant-li voltes i repensant els cicles termodinàmics.Gràcies també als participants del projecte Europeu "Next Generation of Heat Pumps working with Natural fluids", de qui també he aprés moltes coses.Des d'una perspectiva més personal, volia començar nomenant a aquells que varen començar amb mi aquesta aventura universitària, en especial a Ausiàs, i com no a Guillermo, a qui vaig conéixer en la cua per a la matrícula d'industrials, i que 10 anys després hem viscut tantíssimes coses junts.To those guys who I met during my two years in Denmark and we became friends for life, the Xafaets: Andrea, Cristian and Niccolo.Als meus amics d'infància, d'adolescència, edat adulta, i segur que vellesa, Irak, Gabi (Pollo), i com no Jorge (Puxi) amb qui he compartit tantes hores de confidències, moments bons i roïns, però sobretot reconfortants.A Marinna, o meu sol do meio-dia, perquè el seu somriure ja m'alegra el dia, per tots els projectes que tenim i perquè amb ella sempre podré dir cueca.Per últim volia donar-li les gràcies a la meua família. Als meus germans Gabi i José, qui m'ha fet tio de les xiquetes més boniques del món, Olga i Núria. A ma Mare, perquè és una lluitadora, però sobretot una somiadora, en part li dec a ella la meua forma de ser. Però si he de dedicar aquesta tesi a algú, és a ell, a l'home del somriure permanent, a qui li dec l'altra part de la meua forma de ser, a mon Pare.iii AbstractHeat pumps have been identified as an efficient alternative to traditional boilers for the production of sanitary hot water (SHW). The high water temperature lift (usually from 10ᵒC to 60ᵒC) involved in this application has conditioned the type of used solutions. On the one hand, transcritical cycles have been considered as one of the most suitable solutions to overcome the high water temperature lift. Nevertheless, the performance of the transcritical CO2 heat pump is quite dependent on the water inlet temperature, which in many cases is above 10ᵒC. Furthermore, performance highly depends on the rejection pressure, which needs to be controlled to work at the optimum point in any condition. On the other hand, for the subcritical systems, subcooling seems to be c...

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Residential CO2 heat pump system for combined space heating and hot water heating

Cited by 149 publications

References 13 publications

Numerical analysis on performance enhancement of a CO2 heat pump water heating system by extracting tepid water

Numerical analysis on performance enhancement of a CO2 heat pump water heating system by extracting tepid water

Performance Estimation and Optimal Operation of a CO2 Heat Pump Water Heating System

High capacity heat pump development for sanitary hot water production

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