Issues to improve ground source heat pump units in Korea: Refrigerant application and hot water generation

Refrigerant significantly influences the performance of air-conditioning and refrigeration system as well as it has some environmental issues that need to be considered before selection. These systems can be made eco-friendly, if it is powered by solar energy or low-grade thermal energy and they use environment-friendly refrigerants. In this chapter, low GWP (global warming potential) refrigerants have been explored for the domestic air-conditioning applications. Refrigerants with high GWP are mostly used in environment control applications such as heating, ventilation, air-conditioning (HVAC), and refrigeration systems. Some refrigerants contribute to significant environmental issues and the Montreal Protocol and Kyoto Protocol have been signed to address the threats of ozone layer depletion and global warming potential. To fulfil the commitments of Kyoto Protocol, meanwhile, governments in many countries instituted phase-out plan for the use of environmentally harmful gasses in heat pump systems. For instance, EU MAC Directives, F-gas regulation, and Japan METI directives, which clearly declared their target year to use new refrigerant of GWP below 150 for mobile air conditioner and GWP below 750 for the residential air conditioner. Research interest has been stimulated to find alternative refrigerants with low or ultra-low GWP for energy conservation and environmental sustainability. Hydrofluoroolefins (HFOs) have a very low environmental impact, and thus HFOs are considering as potential candidates to replace the hydrofluorocarbon (HFC) refrigerants such as R410A, a near-azeotropic mixture of difluoromethane (R-32) and pentafluoroethane (R-125) and is commonly used refrigerant in air-conditioning applications. The limited number of pure fluids sometimes cannot meet the excellent heat transfer criteria due to their low volumetric capacity and moderate flammability or toxicity. Mixing of HFOs and HFCs refrigerants, in this case, allows the adjustment of the most desirable properties of the refrigerant by varying the molar fraction of the components. Different combination of mixture presented here cannot be claimed as the best mixture, but it might be a good choice for further study. This chapter focuses on the research trend in finding low GWP refrigerants and its application in different heat pump system considering the system performance, safety, and the overall environmental impact. The conventional vapor compression system, thermally driven adsorption system, and sorption-compression hybrid system have been taken into consideration.

Refrigerant amount detection algorithm for a ground source heat pump unit

This paper describes the research and implementation of ground source heat pump unit remote real-time monitoring system, researches in remote real-time monitoring system's overall design, hardware design, software design and implementation of OPC communication. The host computer takes advantage of the human-computer interaction interface of configuration software to achieve the remote real-time monitoring for ground source heat pump unit's running state; the lower computer uses data collector to intensively collect the data which is measured by field measuring instruments, and to achieve remote data transmission based on Ethernet, and then to carry out the communication between the host computer and the lower computer via OPC technology. The results show that the system achieves remote real-time monitoring of ground source heat pump unit, and is stable, easy to operate and provides a reliable basis for the actual energy saving effect's evaluation of ground source heat pump system.

This paper takes the ground source heat pump unit of a research and development centre in Beijing as the research object. This collected the operation data in the cooling condition and the heating condition respectively. Based on the measured data, this paper calculated the coefficient of performances and the energy efficiency ratio of the unit. The results show that when the active chilled beam is used as the air-conditioning terminal device, the inlet temperature of the heat pump unit is greatly improved. The ground source heat pump unit meets the standard and has a higher energy efficiency ratio; The operation of a single unit is more efficient than that of multiple units at the same time.

Current status of the performance of GSHP (ground source heat pump) units in the Republic of Korea

Hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) are important substitutes for chlorofluorocarbons (CFCs) and halons. HCFCs have a lower Ozone Depleting Potential (ODP) than CFCs and halons, and are therefore considered temporary substitutes, while HFCs have zero ODP. In addition to ODP many halocarbons also have a Global Warming Potential (GWP). We developed this paper three different scenarios, globally as well as for the Netherlands: (1) the ‘London’ scenarios, in which HCFCs and HFCs are used unrestrictedly to replace CFCs and halons. As a result the global warming effect by halocarbons may increase the future. HFCs are found to be the main contributors to future radiative forcing by halocarbons. In the Netherlands the increasing use of HFCs results in a doubling of the release of CO2-equivalents from all halocarbons by 2010 compared to 1990 (assuming a zero GWP for CFCs and halons, to include potential indirect negative radiative effects via stratospheric ozone destruction); (2) the ‘Copenhagen’ scenarios, which consider an additional phase-out of HCFCs, after which the use of HFCs increases. The higher GWPs of HFCs compared to other halocarbons result in an increase of global warming by halocarbons. Dutch CO2 equivalent halocarbon consumption could increase by a factor 2 to 4 after an HCFC phase-out, if no additional measures for HFCs are implemented; (3) the ‘Additional Policy’ scenario, which assumes the use of compounds, that have zero ODP and a relatively small GWP, which are available for most applications. Such additional measures will reduce CO2-eq. halocarbon consumption substantially. The share of halocarbons in total CO2 equivalent emissions in the Netherlands will increase from 3 to 7% to 11% in 2010 (assuming a zero GWP for CFCs and halons). Substitution by low or zero GWP alternatives leads to stabilization of greenhouse gas emissions by 2010 at the 1990 level, while without additional policy for HFCs Dutch greenhouse gas emissions may increase by 10% or more.

The use of synthesized refrigerants has several environmental concerns. The most widely used substances like hydro fluorocarbons (HFCs), chlorofluorocarbons (CFCs) and hydro chlorofluorocarbons (HCFCs) have either high global warming potential (GWP), high ozone depletion potential (ODP) or long atmospheric life time. With the growing demand of healthier atmosphere, the study of other alternative substances is very important. This paper presents theoretical thermodynamic performance analysis of hydrocarbon based domestic vapour compression refrigeration system. Propane (R-290), isobutane (R-600a) and butane (R-600) were used. Then, the results were compared with the performance of currently most commonly used tetrafluoroethane (R-134a). These hydrocarbons have zero ODP and very negligible GWP. Different parameters, like coefficient of performance (COP), refrigeration effect, compressor work input and compressor discharge temperature were investigated. Evaporator and condenser temperatures, subcooling, superheating and compressor isentropic efficiency were the variables used for this study. MATLAB software has been used in the mathematical analysis. COP values were found comparable to that of R134a. All the hydrocarbons investigated gave beyond 150% refrigeration effect compared to R-134a for the same mass flow rate. But this was at the expense of higher compressor work input. This research also revealed that the compressor discharge temperature is much lower for R-600a and R-600. Generally, these hydrocarbons showed that they are a good alternative to R134a based on the thermodynamic point of view.

Application and Analysis for Ground Water Heat Pump System of a University in Tianjin

Natural refrigerants have gained significant interest due to environmental reasons. Among different natural refrigerants such as water, air, and ammonia, Carbon dioxide (CO2) is the main candidate to replace commonly used hydrofluorocarbon (HFC) refrigerants in air-conditioning compressors due to its environmental benefits. One of the main advantages of implementing CO2, from an environmental point of view, lies in its relative low global warming potential (GWP) which is three orders of magnitude lower than commonly used HFC refrigerants. Coupled with the new refrigerants is also the need to use some form of protective coatings on the tribopairs. In this study unlubricated (presence of CO2 refrigerant only) experiments were performed to evaluate the tribological performance of three different polymeric-based coatings deposited on Durabar G1 gray cast iron disks. Specifically, Fluorolon 325, Impreglon 1704 PEEK, and PEEK/Ceramic/ PTFE blends were tested against 52100 hardened steel pins. Results showed lower friction coefficient and wear in the Fluorolon 325 case compared to the Impreglon 1704 PEEK and PEEK/Ceramic/PTFE coatings. These results are comparable with earlier studies using PTFE-based coatings [1].

Exergetic modeling and assessment of solar assisted domestic hot water tank integrated ground-source heat pump systems for residences

The heat transfer performance of a ground heat exchanger (GHE) directly influences the operational performance of a ground source heat pump (GSHP) system. The fluid temperature within the GHE is constrained by the protective temperature limits of the GSHP unit. Specifically, the inlet water temperature has an upper limit in summer and a lower limit in winter. These temperature limits further affect the heat exchange efficiency between the GHE and the surrounding soil. In this study, an experimental station featuring a single U-shaped GSHP system was constructed, and a three-dimensional model of the system was developed. Experiments were conducted by operating one or two GHEs to investigate the heat transfer per unit well depth and the matching relationship between cooling capacity and indoor load when the inlet water temperature of the heat pump unit approaches its summer and winter limits. In summer, when operating a single GHE, the heat transfer per unit well depth reached 134.4 W/m at an inlet temperature of 45 °C. When the cooling supply just matched the cooling load demand, the heat transfer per unit well depth was 131.5 W/m. However, prolonged operation led to a scenario where the cooling supply could no longer meet the load demand. In winter, operating a single GHE resulted in a heat transfer per unit well depth of 43.95 W/m at an inlet temperature of 5 °C. These results indicate that when the number of heat exchangers is insufficient, the inlet water temperature of the heat pump unit may reach or exceed the limit value, leading to decreased unit efficiency. Additionally, inadequate heat exchange between the GHE and the soil results in insufficient cooling or heating capacity, failing to meet the indoor load requirements.

Environmental concerns are driving regulations to reduce the use of hydrofluorocarbons (HFCs) with high global warming potential (GWP) as refrigerants in heat pumps. CO2 is an attractive alternative refrigerant because is it 'environmentally friendly' in terms of 'direct' emissions, with GWP = 1, and no ozone depletion potential (ODP). However, CO2 heat pumps generally have a lower efficiency than HFC-based systems, and therefore have higher 'indirect' emissions, related to generating the electricity that powers them. The indirect emissions dwarf the direct emissions for most heating, air-conditioning and refrigeration applications, so it is critical for the equipment to operate with high efficiency. CO2 air-source heat pumps (ASHPs) provide cooling with particularly low efficiency at high ambient temperatures where the CO2 operates in a transcritical cycle. Using CO2 in a ground-source heat pump (GSHP) offers the potential to overcome the low efficiency since a GSHP operates with lower heat-rejection temperature (for cooling), enabling the system to operate some of the time in a more-efficient subcritical cycle. This report details the laboratory tests of a prototype residential liquid-to-air ground-source air conditioner (GSAC) using CO2 as the refrigerant. The tests were performed in an environmental chamber and followed the ISO 13256-1 standard for rating GSHPs. The CO2 GSAC operated either in a subcritical or a transcritical cycle, depending on the entering liquid temperature (ELT). The test results included the coefficient of performance (COP), capacity, sensible heat ratio (SHR), and pressures. The system incorporated a liquid-line/suction-line heat exchanger (LLSL-HX), which was estimated to cause a COP penalty of (0 to 2) % for ELTs ranging (10 to 25) C, and benefit of (0 to 5) % for ELTs ranging (30 to 39) C. The CO2 system was compared to a 'low-cost', commercially-available R410A-based GSHP. With ELTs ranging (10 to 39) C the CO2 system cooling COP ranged (7.3 to 2.4), whereas the R410A system values ranged (6.1 to 3.2). At the 'standard' rating condition (ELT 25 C), the CO2 GSAC cooling COP was 4.14 and the R410A GSHP COP was 4.57. At 'part-load' conditions (ELT 20 C) both systems had a COP of ?4.92. Further effort is needed to increase the CO2 system efficiency at ELTs greater than 20 C, since it underperformed the R410A system in that temperature range.

Worldwide use of high global warming potential (GWP) hydrofluorocarbon (HFC) refrigerants for space conditioning and food storage results in significant equivalent greenhouse gas (GHG) emissions. This is further exacerbated in developed countries by the current transition from hydrochlorofluorocarbon (HCFC) refrigerants to HFC refrigerants. Under the Kigali amendment to the Montreal Protocol, the proposed phase-out of currently used HFC and HCFC refrigerants has initiated a re-evaluation of some pre-existing refrigerants as well as the development and evaluation of new refrigerants. Making the ideal refrigerant selections for heating, ventilation, air-conditioning, and refrigeration (HVAC&R) applications is thereby difficult in an already overabundant refrigerants market. In this paper, a study of key parameters required of a good refrigerant is conducted, followed by the analysis of refrigerants desired and refrigerants used in two major sectors of the HVAC&R industry, namely commercial refrigeration and residential air-conditioning and heat pumps. Finally, keeping in consideration the global environmental regulations and safety standards, a recommendation of the most suitable refrigerants in both sectors has been made.

The effect of the hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC) refrigerants on the environment through the attack of its halogen contents-chlorine and fluorine, on the ozone layer and the toxic nature of such refrigerants, has paid the attention of researchers to work towards getting suitable alternatives using hydrocarbons (HC) or its blends with HFC refrigerants. This study was centered on getting a suitable retrofit of R-134A with a good coefficient of performance (COP) and low global warming potential (GWP) using the blends of R-290 and R-600 HCs for use in refrigeration systems. An experimental testing rig was developed by assembling various measuring devices to the operational points of a vapor compression refrigerator. A mixture design was developed using the simplex lattice design (SLD) of design expert software 11.0. The response variables considered were COP and GWP. The experimental design was meticulously followed using 1kg for each refrigerant run, and the temperature and pressure values at the operating points were noted. From the results obtained, blend A had the highest COP of 2.5 and the highest GWP value of 3.93. Blend D had the lowest value of C.O.P. of 1.33, while blend B had the lowest value of GWP of 3.51. Also, the optimal blend was achieved at a mixture factor of 59% R-290a and 41% R-600. The response values obtained at this optimal mixture level were COP-2.05182 and GWP – 3.59. Therefore, the optimal blend obtained would be a better retrofit to R-134a and could be used in refrigeration systems.

Various binary mixtures of carbon dioxide and hydrocarbons, especially propane or ethane, as alternative natural refrigerants to Chlorofluorocarbons (CFCs) or Hydro fluorocarbons (HFCs) are presented in this paper. Their environmental performance is friendly, with an ozone depletion potential (ODP) of zero and Global-warming potential (GWP) smaller than 20. The capillary tube performance for the alternative refrigerant HFC HCand mixed refrigerants have been widely studied. However, studies that discuss the performance of the capillary tube to a mixture of natural refrigerants, in particular a mixture of azeotrope carbon dioxide and ethane is still undeveloped. A method of empirical correlation to determine the mass flow rate and pipe length has an important role in the design of the capillary tube for industrial refrigeration. Based on the variables that effect the rate of mass flow of refrigerant in the capillary tube, the Buckingham Pi theorem formulated eight non-dimensional parameters to be developed into an empirical equations correlation. Furthermore, non-linear regression analysis used to determine the co-efficiency and exponent of this empirical correlation based on experimental verification of the results database.