Domestic Water Heating Research Articles

Waste heat recovery of a wind turbine for poly-generation purpose: Feasibility analysis, environmental impact assessment, and parametric optimization

World energy markets are gradually shifting in favor of wind-based power plants. A decrease in global warming can be attributed to the reduction of dependence on fossil fuels as a result of wind energy. In this regard, utilizing the waste heat from the generator of a wind turbine has recently been considered and only a few studies have been done about it. This shortage has made clear the need for further studies. In the present research, a novel poly-generation system is introduced based on the waste heat recovery of a wind turbine to fill this research gap because the waste energy of a wind turbine has not been utilized for the poly-generation purpose. A novel power-cooling production absorption cycle and a domestic hot water heat exchanger are utilized for this purpose. Also, the produced power in the absorption cycle is sent to a reverse osmosis desalination unit for freshwater production. The considered system is comprehensively studied from energy, exergy, environmental, and exergo-economic standpoints. In the average wind speed of 10 m/s, the exergy efficiency, unit cost of products, reduction in CO2 emission rate, and payback period are seen to be 36.76%, 20.25 $/GJ, 2452801 kg/year, and 2.301 years, which shows its performance is better than the previous studies based on the waste heat recovery of a single wind turbine.

Low thermal conductivity solar domestic water heater

Solar domestic water heaters (SWH) with thermosyphon circulation are the most common commercial applications of solar energy in Mexico. They are also becoming popular in the rest of the world, given their simplicity, good economic returns, and sustainability. Traditionally the solar collector, the piping, and the storage tank are built of copper and steel. However, water quality in many parts of the Mexican Northwest has high mineral contents and, when heated, results in early metal pitting corrosion of SWH parts. Short-lived water heaters are bad promoters of the technology. In this work, a SWH thermoplastic Chlorinated Polyvinyl Chloride (CPVC) is built and tested under real operating conditions in La Paz, BCS, Mexico. The optimal design is detected with the aid of a suitable numerical model. Results reveal that a full SWH-CPVC can be technically and economically convenient for the weather conditions of the Northwestern states of Mexico.

4E performance evaluation of PV, PV/Thermal, and solar domestic water Heater for building integration in the Moroccan country

In this work, an exhaustive global comparison of the performance of three solar systems, namely, the PV, the PV/Thermal, and the Solar Domestic Water Heater (SDWH), was conducted. The energetic, exergetic, environmental, and economic (4E) performances were evaluated to determine the most suitable technology for the needs of the Moroccan building sector. In this framework, two mathematical models for the estimation of the thermal and electrical performances of the solar systems were developed and validated using TRNSYS and Matlab software. The results showed that from an energetic standpoint, the Moroccan building sector is a fertile ground for the three solar systems. With regard to the exergetic performance, the PVT system has a higher total exergy efficiency of 12% compared to 11% for the PV and 3% for the SDWH system. As for the environmental performance, the PVT and the SDWH systems outperform the PV system due to higher energy production, with a minimum of 351kgCO2/year for the PV and a maximum of 1809 kgCO2/year for SDWH. Economically, the results highlighted the high sensitivity of the economic attractiveness of the PVT and SDWH systems to the subsidized gas price; and the importance of a subsidy policy to help ameliorate it. This study could serve as a guideline for stakeholders in the country to recognize the opportunities and challenges facing the integration of solar technology into buildings.

Comparison of Real and Forecasted Domestic Hot Water Consumption and Demand for Heat Power in Multifamily Buildings, in Poland

Determining the demand for heat power for domestic hot water preparation is necessary to perform a building energy assessment. For this, we need to predict domestic hot water consumption. Considering the number of factors influencing domestic hot water consumption, it is difficult to develop a highly accurate methodology. The aim of the study was to compare the real domestic hot water consumption and heat power for its preparation with the values calculated based on the available prediction methods in multi-family buildings. The analysis was carried out based on annual monitoring (2021 year) of domestic hot water consumption and the actual demand for heat power in eight multi-family buildings located in Grudziądz, in Central Poland. The results of these measurements were compared with the values determined based on the available methodologies for forecasting the demand for heat power and domestic hot water consumption: Sander’s, Recknagel’s, the standard method and the method according to Polish regulations from 2008 and 2015. The real average demand for heat power for domestic hot water was 89.8 ± 8.5 W/person, 211.2 ± 13.7 W/apartment and 4.8 ± 0.3 W/m2, and the daily domestic hot water consumption was 26.7 ± 3.6 dm3/person·day, 62.6 ± 5.8 dm3/apartment·day and 1.4 ± 0.1 dm3/m2·day. The real demand for heat power for domestic hot water was lower than that determined by the analyzed methods. The values obtained from the modified standard method based on Standard PN-92/B-01706/A1: 1999, with mean relative error of 10.5 ± 4.1%, were the closest to the real values. The current ordinance method (Regulation 2015) is characterized by an error of 45.4 ± 10.2%. The predicted domestic hot water consumption using the current ordinance was the closest to the real consumption. On average, it was higher by 7.7 ± 5.0%.

Experimental investigation and performance evaluation on a direct expansion solar-air source heat pump system

Solar energy is the most important renewable energy source for achieving carbon neutrality. The problem of steady and efficient operation must be promptly addressed due to the inconsistent and variable nature of solar energy. This research proposes a multifunctional heat pump using the R417A refrigerant, which combines a direct expansion solar heat pump (DXSHP) with an air source heat pump (ASHP), resulting in a direct expansion sola-air source heat pump (DX-S/AS-HP). The system could operate in three modes: combined cooling and heating, domestic water heating, and space heating. The performance of solar heat pump and air source heat pump in different modes was compared, and the switching logic of different modes was developed accordingly, and the performance of the system at different working temperatures was analyzed. The results demonstrate that in combined cooling and heating mode, the system's average comprehension coefficient of performance (COP) could approach 6.0. In DX-SHP mode, the average COP for domestic water heating and space heating is 3.94 and 4.25, respectively, which is greater than the air source heat pump in similar working conditions. Switching from DX-SHP to ASHP for domestic water heating is only necessary when solar irradiation is less than 300 W m − 2, while switching to ASHP for space heating is only necessary when solar irradiation is absent. The greater the working temperature, the lower the COP. While the working temperature has little effect on thermal collecting efficiency.

Effect of hydrogen-blended natural gas on combustion stability and emission of water heater burner

To study the effect of hydrogen-blended natural gas on the combustion stability and emission of domestic gas water heater, a test system is built in this paper, taking a unit of the partial premixed burner commonly used in water heaters as the object. Under the heat load of 0.7–2.3 kW, the changes of flame shape, burner temperature and pollutant emission of natural gas with hydrogen volume ratio of 0–40% are studied with independent control of primary air supply and mixing. The results show that: with the increase of hydrogen blending ratio, the inner flame height increases firstly and then reduces, while the change of burner temperature is opposite. The maximum inner flame height and the minimum temperature of the burner both appear at the hydrogen blending ratio of 10–20%. It can be seen that the limit of hydrogen blending ratio which can maintain the burner operate safely and stably under rated heat load is 40% through the maximum temperature distribution on the burner surface. The CO emission in the flue gas gradually decreases with the increase of hydrogen blending ratio, while the NO x emission fluctuates slightly when the hydrogen blending ratio is less than 20%, but then decreases gradually.

Waste heat recovery of two solar-driven supercritical CO2 Brayton cycles: Exergoeconomic analysis, comparative study, and monthly performance

The waste heat from a supercritical Brayton cycle has a great potential to be recovered. However, there is a lack of research regarding the utilization of these cycles in multi-generation systems. In addition, different multi-generation systems based on supercritical Brayton cycles have not been compared in the literature. In the present study, two multi-generation configurations based on two supercritical Brayton cycles, namely regenerative (configuration 1) and recompression (configuration 2), are proposed and compared from thermodynamic and exergoeconomic standpoints. In both configurations, an organic Rankine cycle, a domestic hot water heat exchanger, and an LiCl-H2O absorption refrigeration system are employed to convert the waste heat of the two supercritical Brayton cycles into useful energy. Meanwhile, a thermoelectric generator is used instead of a condenser for efficient waste energy recovery of the organic Rankine cycle. The generated electricity by the organic Rankine cycle and thermoelectric generator is used to generate hydrogen in a proton exchange membrane electrolyzer. In addition, a direct integration method is employed to integrate the two supercritical Brayton cycles with a solar power tower as the heat source. The final results regarding the net output power, exergy efficiency, and economic performances of the two configurations reveal the superiority of configuration 2 over configuration 1. Net output power and exergy efficiency of configuration 2 are 6.55 MW and 4.06% points higher than configuration 1. Moreover, total cost rate and unit cost of products for configuration 2 are 0.4 $s-1 and 10.03 $GJ-1 lower than configuration 1. On the other hand, cooling, heating, and hydrogen rates of configuration 1 are respectively 2.93 MW, 4.23 MW, and 2.84 kgh-1 higher than configuration 2. Moreover, the monthly analysis of the two systems for Dhahran city (26.3°N/50.2°E) as a case study indicates that the best thermodynamic performance of the systems is achievable in February, June, and July.

FARKLI EĞİM AÇILARINDA GÜNEŞ KOLLEKTÖRLERİNİN ENERJİ VE EKSERJİ ANALİZİ: ERZİNCAN İLİ ÖRNEĞİ

Güneş kollektörleri kullanım suyu ısıtma uygulamalarında sıklıkla kullanılmaktadır. Tasarım aşamasında güneş kollektörlerinin en uygun eğim açısında konumlandırılması güneş enerjisinden verimli faydalanılması için önemlidir. Bu çalışmada, Erzincan ilinde konumlandırılan bir güneş kollektörünün eğim açısının aylık/günlük ortalama ışınım değerlerine, su çıkış sıcaklığına, enerji ve ekserji verimlerine etkisi teorik olarak incelenmiştir. Optimum güneş kollektörü eğim açısının en yüksek ve en düşük değerlerinin Aralık ve Haziran aylarında sırasıyla 63° ve 0° olduğu görülmüştür. Erzincan için önerilen (27.14°) ve hesaplanan eğim açıları için günlük ortalama saatlik ışınım değerleri karşılaştırılmış olup en büyük değişimin Ocak ayında %26 olduğu görülmüştür. Buna ek olarak, güneş kollektörünün enerji ve ekserji verimleri hesaplanmış olup optimum eğim açıları için en yüksek verimleri sırasıyla %74.2 ve %9.7 olarak belirlenmiştir.

A study on data-driven hybrid heating load prediction methods in low-temperature district heating: An example for nursing homes in Nordic countries

In the face of green energy initiatives and progressively increasing shares of more energy-efficient buildings, there is a pressing need to transform district heating towards low-temperature district heating. The substantially lowered supply temperature of low-temperature district heating broadens the opportunities and challenges to integrate distributed renewable energy, which requires enhancement on intelligent heating load prediction. Meanwhile, to fulfill the temperature requirements for domestic hot water and space heating, separate energy conversion units on user-side, such as building-sized boosting heat pumps shall be implemented to upgrade the temperature level of the low-temperature district heating network. This study conducted hybrid heating load prediction methods with long-term and short-term prediction, and the main work consisted of four steps: (1) acquisition and processing of district heating data of 20 district heating supplied nursing homes in the Nordic climate (2016–2019); (2) long-term district heating load prediction through linear regression, energy signature curve in hourly resolution, providing an overall view and boundary conditions for the unit sizing; (3) short-term district heating load prediction through two Artificial Neural Network models, f72 and g120, with different prediction input parameters; (4) evaluation of the predicted load profiles based on the measured data. Although the three prediction models met the quality criteria, it was found that including the historical hourly heating loads as the input to the forecasting model enhanced the prediction quality, especially for the peak load and low-mild heating season. Furthermore, a possible application of the heating load profiles was proposed by integrating two building-sized heat pumps in low-temperature district heating, which may be a promising heat supply method in low-temperature district heating.

Development of a novel flexible multigeneration energy system for meeting the energy needs of remote areas

This paper introduces a flexibility concept in development of a novel multigeneration energy system driven by a renewable energy heat source. Nevertheless, the energy system can be upgraded to a highly productive system by incorporating other subsystems for achieving more production such as domestic hot water and freshwater. A novel design is proposed for a system comprising organic Rankine cycle, absorption compression heat pump, liquid natural gas to natural gas converting system, domestic water heater, and humidifier-dehumidifier desalination to exploit the Sabalan geothermal source for multigeneration purposes. Due to its high-efficient and environmentally friendly characteristics, n-pentane is utilized in the organic Rankine cycle. Also, the Ammonia-water is employed in the absorption compression heat pump subsystem. Energy, exergy, and thermoeconomic analysis is conducted on the plant along with multi-objective optimization based on the parametric study of key variants. According to the results, the novel step-by-step flexibility analysis can give a wide viewpoint to the designers to make the best multiple plant. The results of multi-objective optimization indicate that the freshwater production increases from 0.803 kg/s to 0.834 kg/s, the capacity of the domestic water heater rises from 1254 kW to 1265 kW, and the net output power surges up by 137.96 kW. However, the heating production falls from 1276 to 1088 kW. Furthermore, the total energy and exergy efficiencies increase by 6.43% and 4.47% with a 2.08 $/GJ reduction in the unit cost of the product.

Measures for Assessing the Effectiveness of Investments for Electricity and Heat Generation from the Hybrid Cooperation of a Photovoltaic Installation with a Heat Pump on the Example of a Household

In recent years, one of the key postulates in the European Union’s policy has become the development of renewable energy sources. In order to achieve the desired synergy effect, the idea of combining two selected sources of energy appeared. This article presents a technical and economic analysis of a hybrid connection of a ground source heat pump with a photovoltaic installation. Taking into account the heat demand of the building, a ground heat pump with a catalog nominal heating power of 25 kW was selected. This article presents the problem of the economic profitability of using a hybrid combination of a heat pump and photovoltaic panels in domestic hot water and central heating systems. The justification for the use of such heat sources in these installations is due to global trends and the gradual departure from conventional energy sources such as oil or gas boilers. This paper presents the economic and ecological results of using the pump heat connected together with photovoltaic panels. In the economic analysis, with the assumed installation costs related to the use of the considered heat pump and PV, two parameters commonly used in the investment analysis (static and dynamic) were used, namely, the simple payback period and the net present value of the investment. For the adopted assumptions, the usable area of the facility and the number of years of use were indicated, at which the investment in question is competitive with other alternative investment interest methods and will start to bring tangible benefits. The performed analysis also has measurable environmental benefits in the form of a reduction in carbon dioxide emissions at the level of 2893 kg/year into the atmosphere. The presented solution will help future investors understand the investment profitability mechanism for their households.

Small-Scale Combined Heat and Power Systems: The Prospects for a Distributed Micro-Generator in the ‘Net-Zero’ Transition within the UK

Small-scale combined heat and power (micro-CHP or mCHP) plants generate heat in the process of localised electricity production that can usefully be captured and employed for domestic space and water heating. Studies of the relative merits of three alternative network-connected mCHP plants are reviewed based respectively on an Internal Combustion engine (ICE), a Stirling engine (SE), and a Fuel Cell (FC). Each plant will, in most cases, result in lower carbon dioxide (CO2) emissions, relative to those from the most efficient condensing boilers. In addition, they lead to operational cost savings for the consumer, depending on house type. However, their capital costs are presently more expensive than a conventional boiler, with the FC being prohibitively so. The ICE and SE variants display the greatest economic and environmental benefit. Nevertheless, the performance and costs associated with these innovative technologies have rapidly improved over the last decade or so. Comparisons are also made with heat pumps that are seen as a major low-carbon competitor by the United Kingdom (UK) Government. Finally, the potential role of micro-CHP as part of a cluster of different micro-generators attached to contrasting dwellings is considered. The review places mCHP systems in the context of the UK transition pathway to net-zero CO2 emissions by 2050, whilst meeting residential energy demand. However, the lessons learned are applicable to many industrialised countries.

An evaluation of domestic electric water heaters for frequency control

Maintaining the frequency of a power system close to its nominal value (50 Hz or 60 Hz) is critical, which comes mainly from generators and flexible loads in traditional power systems. Direct load control (DLC) is a method to control controllable loads for power system optimization. In general, it is used to reduce or shave peak demand. Nonetheless, DLC also can be used to provide frequency control services. Domestic electric water heater (DEWH) is an important kind of controllable load, which takes a high percentage of domestic electric power consumption and has a large thermal energy storage capacity. Hence, DEWH can be a prime candidate for DLC. This study proposes a framework to provide frequency control service with DEWHs. A virtual battery pack system (VBPS) is introduced to be equivalent to the capacity of DEWHs, and a series of measurable indicators are proposed to show the capacity of the VBPS when providing frequency control services. An adaptive criterion is applied to classify controllable DEWHs, which helps to maintain end-user comfort. The performances of the proposed frequency control method during normal and contingency conditions are verified through case studies in CYME.

Impact of Solar Thermal Energy on the Energy Matrix under Equatorial Andean Context

Low-temperature solar thermal energy is a viable and mature alternative to reduce the use of fossil fuels for domestic hot water heating. The impact of the inclusion of this technology in the energy matrix in the Andean city of Cuenca, Ecuador, is analyzed. In Ecuador, liquefied petroleum gas (LPG) is currently used to heat water due to the high state subsidy, with a cost of 0, 11 USD for an LPG kg compared to the international price of 1.18 USD a Kg of LPG in 2021. Sustainability indicators show that the urban energy matrix would be minimally affected by a high penetration of solar thermal systems. The indicators that are positively affected are related to energy self-sufficiency, emissions, and employment at the expense of an increase in the cost of energy. Moreover, the analysis of the impact on consumption exclusively in the residential sector shows that liquefied petroleum gas consumption would drop from 73 to 64%, mainly because the liquefied gas is used in cooking. However, the change in technology is limited by the subsidized cost of liquefied petroleum gas, which makes the adoption of this technology difficult in the current state

Energetic, economic, environmental and climatic analysis of a solar combisystem for different consumption usages with PSI method ranking

Using solar systems is increasing due to oil shortage, environmental effects, and renewability. Solar thermal combisystems use the energy taken to provide for both domestic hot water (DHW) and space heating (SH), which is under investigation by energy researchers. This study uses a dynamic energy analysis of the solar system to evaluate the solar parameters. Also, the environmental and economic effects of using solar systems are discussed. The study is done on four different consumption usages in four different climates of Iran. Energy simulation shows that hot & humid climates, office, and mall usages have the largest solar fraction (minimum of 95.2, 38.5, and 35%, respectively). The lowest optimal collector surface area belongs to a hot and humid climate with 4–21.5 m2 and office usage with 4–159 m2. Also, collector efficiency decreases with higher collector area amounts. 20-year economic analysis shows that the net present value of hospital usage with a maximum of $2216.8, cold climate with a maximum of $768.4, and hot & humid climate with a maximum of $2765.9 are the most affordable. The environmental analysis illustrates that CO2 emission avoidance is highest in hospital usage with a maximum of 1924.5 kg, residential usage with a maximum of 1707.8 kg, and hot & dry climate with a maximum of 1349.2 kg. Lastly, the preference selection index (PSI) method is used to rank all application possibilities, which shows that using systems is highly recommended in cold, hot & humid climates with the best ranks of 1 and 3 and hospital usage with the best rank of 1.

Compressor-assisted thermochemical sorption integrated with solar photovoltaic-thermal collector for seasonal solar thermal energy storage

• Compressor-assisted thermochemical sorption energy storage with solar PV/T system. • Thermal and electrical energy simultaneously stored in summer, discharged in winter. • Identify the optimal operating condition of solar PV/T coupled with the storage unit. • Chemisorption cycle using SrCl 2 achieves 100% solar fraction for domestic heating. • Higher compression ratio leads to positive effect on the life cycle of PV cells. This paper studied the performance of a compressor-assisted thermochemical sorption energy storage (CATSES) system with a solar photovoltaic-thermal collector (PV/T) to support the domestic space and hot water heating. The heat from the PV/T drives endothermic desorption, whilst the electricity from the PV/T powers the compressor to assist the low-temperature desorption. The main aim of this study was to demonstrate that the integrated system can flexibly and maximally utilise solar energy, and store solar energy in a high energy–density system with minimum loss over long-term storage. The parametric investigation on the CATSES system using SrCl 2 /NH 3 working pair was conducted for a case study in the city of Newcastle upon Tyne in the UK, which has long wintertime with high heating demand. Two different system operation modes (Case 1 and Case 2) with different strategies of solar energy usage (direct usage / storage) were studied. By using 30 m 2 PV/T collector with the CATSES reactor that contains 22 m 3 (450 kg/m 3 ) composite adsorbent and a compressor with 11.5 compression ratio, the system that operated Case 1 could achieve 100% solar fraction of annual heating demand. The achieved material-based energy storage density was around 0.6 GJ/m 3 and the storage efficiency was 0.88 with the net electricity consumption of 180 kWh (around 5% average consumption of an ordinary UK household). The system that operated Case 2 stored less heat than that of the Case 1 but was able to output more electricity.

Modelling and analysis of a complete adsorption heat pump system

• An adsorption heat pump system for domestic water heating is proposed; • The physical model for the complete adsorption heat pump system is presented; • Detailed analysis of the temperature, pressure, and uptake in the adsorbent bed; • Time evolution of the system’s variables over five complete cycles; • Simulation of the whole adsorption heat pump system’s performance. Adsorption heat pumps (AHPs) can play a significant role in the future energy transition policies. However, the technology still needs to be matured and further research is still necessary. In this paper, the detailed model of a whole AHP system for domestic water heating is presented aiming to fulfil the literature gap for models that can simulate the dynamics of these complete heating systems, while maintaining a high level of modeling detail for the adsorbent bed. The model integrates all the main components of the AHP system, namely the evaporator, the condenser, the heater, the water reservoir and the adsorber. The adsorber is modeled by a 2D distributed parameter model with dynamic boundary conditions since the evaporator and condenser’s temperatures vary in a cycle as well as from cycle to cycle. The novel model obtains the detailed temperature, pressure, and uptake fields in the adsorbent bed when integrated in a complete AHP system. Real scale AHP systems should not be accurately modelled by lumped-parameter models due to the heterogeneities on the temperature, pressure, and uptake in the adsorbent bed. The time evolution of the system’s variables over five simulated cycles is obtained, as well as the coefficient of performance (COP) and specific heating power (SHP) of the whole system. For working conditions suitable for domestic water heating the system’s COP is 1.35 and the SHP is 79.3 W.kg −1 .s −1 .

On Slowing Climate Change with Ecological, Thermo-Active Building Systems

In the early days of energy conservation(1980s) several countries took the need for energy efficiency seriously enough to sponsor some demonstration buildings. For instance, a US university design concept was built in Regina, Canada in1978. The Saskatchewan Energy Conservation house [1s]demonstrated a new, passive technology. It had super-insulated and airtight walls, large windows on the south facade, evacuated solar pipes for domestic water heating, and a heat recovery ventilator. Despite of all the technology demonstrated there, as Bomberg et al [2] explains, the passive measures were not accepted in the Canadian marketplace because the builders modified the heating system and thereby changed the air flow pattern in the house. The 1995, German passive house was accepted in marketplace because the built system could be duplicated as it was demonstrated. In this case, saving from the elimination of expensive boiler were used to improve the level of thermal insulation and air tightness. These developments led to acceptance of a few points from building science [2-4], namely: (1) any building is a system, (2) a design team should work together starting with the conceptual stage, (3) heat, air, and moisture flows are not separable, and their interactions must be recognized, (4) excellent air tightness and a high-level of thermal insulation are required in all climates.

Thermal energy storage properties, thermal conductivity, chemical/and thermal reliability of three different organic phase change materials doped with hexagonal boron nitride

Myristic acid (MA), Lauric Acid (LA) and Polyethylene Glycol (PEG) are promising organic Phase Change Materials (PCMs) for Thermal Energy Storage (TES). However, low thermal conductivity (TC) negatively affects their heat transfer efficiency during the heat storage/release periods in TES systems. In this regard, hexagonal Boron Nitride (h-BN) was chosen as a filler for TC enhancement. The present study targets to improve the TC of MA, LA and PEG by adding h-BN nanoparticle at different weight amounts, 0.5, 1.0, 1.5 and 2 %, along with a systematic examination of other chemical and thermal properties. Scanning electron microscopy (SEM)/Energy dispersive X-Ray spectroscopy (EDX), Fourier-transformed infrared (FTIR) and X-Ray diffraction (XRD) analysis results demonstrated that the dispersion of h-BN in the PCMs was fairly homogeneous and had no damaging influence on their chemical/crystalline structures. Differential scanning calorimetry (DSC) results indicated that the addition of h-BN (2wt%) marginally shifted their phase change temperatures and slightly decreased the LHS capacities compared to pure PCMs. The h-BN/PCM composites exhibited good chemical stability and thermal reliability after 500 heating/cooling cycles. The addition of h-BN (2 wt%) resulted in 1.40, 1.27 and 1.30 times-enhancement in TC values of MA, LA and PEG, respectively. This improvement was also displayed in the T-History curves. All findings revealed that 2 wt% h-BN addition could be enough for satisfactory TC enhancement without affecting the LHS properties of the selected PCMs significantly. Thus, h-BN enhanced PCMs could be used for thermal management of electronic equipment, solar collectors, solar PV systems and domestic water heating systems etc.

Field Measurement of Central CO2 Heat Pump Water Heater for Multifamily Retrofit

Domestic hot water heating of multifamily buildings accounts for a substantial portion of the energy load of existing buildings. This load is made up of both the energy required to produce hot water and the energy needed to maintain the temperature of the heated water within a building’s distribution piping so that heat can be promptly delivered to building occupants as needed. Properly designed heat pump water heater (HPWH) systems have the ability to improve efficiency in both water heating and temperature control operations. Further, CO2 heat pump technology reflects a shift away from traditional refrigerants and toward refrigerants with low global warming potential (GWP). In this paper’s case study, a design consisting of multiple CO2 heat pump water heaters (commonly used in single-family homes) with a novel “swing tank” was proposed to meet the demand for domestic hot water heating and recirculation loop temperature maintenance. The proposed design was applied to the retrofit of a 60-unit, low-rise, multi-family building located in the Pacific Northwest of the United States. The purpose of this paper is to verify the performance of the system including the proposed “swing tank” in a centralized SHW system using CO2 HPWH. It also provides practical information and lessons learned from the retrofit project. Long-term monitoring data showed that the system had a coefficient of performance (COP) of three or greater and provided an average of 20 gallons of hot water per day per apartment. The results of this work indicate that residential-scale CO2 HPWH equipment and a “swing tank” design can efficiently provide domestic hot water heating and temperature maintenance for mid-sized multifamily buildings.