Inlet Water Temperature Research Articles

Experimental Analysis of Fin Pitch Distance Variation of Adsorber for Adsorption Chiller Performance

The purpose of this study was to study the performance of silica gel-air adsorption chiller on two types of adsorber fins by conducting experiments at several cycle times, namely 500, 600, 700 and 800 seconds with specific mass recovery times, heat recovery times, and also variations on the input of the cooling fluid, so that optimal cycle times can be obtained related to COP and SCP. The adsorber fin-spacing which has more tightly fin distance does not determine the better performance of the adsorber for chiller application because the shorter distance of the fin, the cross-sectional area of the silica gel surface that has initial contact with the adsorbate will decrease so that the performance of the adsorber will decrease. The highest cooling capacity and COP obtained are 3.1 kW and 0.52, respectively. The results are obtained on adsorber with 3 mm fin distance and 700 s cycle with hot water inlet temperature of 79°C, cooling water inlet temperature of 29.4°C and chilled water outlet temperatures of 8.5°C

Experimental and numerical investigation on the charging and discharging process of a cold energy storage for space cooling of buildings

To address the current issue of the difficulty to use the hot outdoor environment during summer nights to provide coolness for phase change materials (PCM) and thus reduce building energy consumption in hot summer areas, a novel cold energy storage unit has been proposed. It replaces the hot outdoor environment with other free or cheap cold sources. An experimental setup is built to investigate the cold storage and release performance of the PCM storage unit. Later, the well-validated numerical model is conducted to further explore thermal performance of the PCM storage unit. The numerical result indicates that the cold storage process can be completed from 64.33 min to 96.56 min when the water inlet temperature varies from 10 °C to 16 °C. Further, during the cold release process, the PCM storage unit can reduce the temperature of the hot air by a maximum of about 8–12 °C when the air inlet temperature ranges from 32 °C to 38 °C. The cold release efficiency is varied between 81.65 % and 96.44 %. In conclusion, the findings provide a promising way for cold storage and space cooling of buildings in hot summer areas through the cold energy storage unit.

Energy, exergy, and exergoeconomic analyses of an air source transcritical CO2 heat pump for simultaneous domestic hot water and space heating

The transcritical CO2 heat pump system experiences significant throttling losses in space heating operation due to the higher temperature of returning water. This paper presents an energy, exergy, and exergoeconomic analyses of an air source transcritical CO2 heat pump integrating a tri-partite gas cooler, which is an effective method to match CO2 temperature glide with water for simultaneous domestic hot water and space heating (DHW+SH) production. A pinch point-based numerical model is developed to find the optimal discharge pressure. This validated model is then utilized to investigate the impacts of water inlet temperature and ambient temperature. Two configurations are examined: one with only DHW supply and the other with DHW+SH supply. The results indicate that combining SH with DHW enhances COP by 7.5% with a 7.9% reduction in discharge pressure at 10 °C ambient temperature and 10 °C water inlet temperature. At a water temperature of 10 °C, exergy efficiency improves by 4%. The compressor accounts for 54%–60% of the total exergy loss. The DHW+SH system exhibits an average exergy destruction reduction of 7.6%. With each 5 °C rise in ambient temperature, the DHW+SH system’s total exergy destruction cost rate decreases on average 7.7% compared to the DHW system. Furthermore, the combined exergy destruction cost rate of GC2 and GC3 in DHW+SH is significantly lower (by 48.2%) than only GC3 in DHW. The exergoeconomic factors of the compressor, gas cooler 2, and gas cooler 3 emphasize the need to decrease their costs to enhance cost-effectiveness.

Microchannel cooling plates with non-uniform airfoil fin arrangement for large-capacity marine battery: An experimental study

In the process of charging and discharging, the heat generation of the battery is uneven, which is more obvious for large-capacity batteries. To maintain the performance of the battery, the thermal management system based on the cooling plate is of critical importance. In this paper, the non-uniform airfoil fins arrangement of microchannel cooling plates for marine large capacity battery thermal management are designed and tested. The cooling performances of the uniform airfoil fins arrangement (UAFA), non-uniform airfoil fins arrangement 1 (N-UAFA 1) and non-uniform airfoil fins arrangement 2 (N-UAFA 2) are experimentally investigated. The maximum temperature (Tmax) and temperature standard deviation (SD) of battery module during charge and discharge process are compared with the variation of the volume flow rate (qv), the cooling water inlet temperature (Tin) and the charge–discharge rate (CR). The experimental results demonstrate that increasing qv and decreasing Tin would contribute to lower Tmax but higher SD. Both Tmax and SD increase with the CR increasing. The cooling effectiveness of the non-uniform airfoil fins arrangement is validated by the reduced Tmax and the robustness in SD control. In particular, the newly designed N-UAFA 2 microchannel could relief the contradiction between cooling capacity and the temperature uniformity. For all the working conditions, the N-UAFA 2 exhibited the best performance. Especially at the CR of 0.5C, the N-UAFA 2 could manage the Tmax and the SD below 36.8 °C and 1.5 °C, respectively.

Numerical investigation of the deep borehole heat exchanger in medium-depth geothermal heat pump system for building space heating

The deep borehole heat exchanger (DBHE) is a vital part in medium-depth geothermal heat pump system (MD-GHPs). In comparison to other forms of heat exchangers, the DBHE has the following outstanding advantages: the small footprints, the little damage to rock as well as the high efficiency. However, numerous DBHE models were fixed variable values such as flow rate or inlet fluid temperature and there were few studies combining the user heating load variation with the temperature fluctuation on the DBHE side. In order to fill this gap, a DBHE heat transfer model with dynamic building heating load constraint is developed. In this heat transfer model, the load boundary condition is the hourly flow rate and the difference in inlet and outlet water temperature, and the outlet water temperature is obtained through iteration. In addition, this model is validated by a building space heating experiment data in Harbin and guaranteed its correctness. The average heat exchange per meter at the coldest heating moment also ensures the viability of MD-GHPs, which is 141.5 W/m. A series of typical coordinates are used to analyze the effect of DBHE on the surrounding rock, and the concept of DBHE recommended insulation length are proposed. One single DBHE with 2000 m burial depth possesses a temperature effect radius of 13.0 m for one heating period. Besides, some critical conclusions are as follows: For the structural parameter, the recommended insulation length is 178 m. For the operating parameter, there is a minimum value for the total power consumption and 18 m3·h−1 is the recommended optimal flow rate in this situation. For the geological parameter, raising the geothermal gradient can dramatically improve inlet fluid temperature (IFT) and outlet fluid temperature (OFT), and enhance the ability of DBHE to carry the building heating load. When maintaining the same IFT at the coldest moment, the geothermal gradient of 0.04℃·m−1 is 1.33 times more capable of carrying loads than the 0.03℃·m−1. This paper can provide basis for a series of DBHE thermal performance in practical space heating engineering applications of MD-GHPs.

Comparative study of various adsorbents for adsorption-based thermal energy storage

Adsorption-based thermal energy storage (ATES) systems can potentially replace conventional heating technologies. This research explores the application of ATES systems for heating, focusing on the performance of various adsorbents using lumped parameter modeling. UiO-66, MOF-801, and their modified counterparts are evaluated alongside silica gel in terms of total and useful energy for end-users. Analysis of the ATES system encompasses Coefficient of Performance (COPh), Specific Heating Power (SHP), and Temperature Lift (ΔT) across different operating conditions. Isotherm characteristics reveal that (CH3)2-MOF-801 and NH-UiO-66 excel in water uptake at low relative pressures (Henry's region), resulting in high total and useful energy density. Notably, higher cooling water flow rates generally enhance Energy Storage Density (ESD) for materials like silica gel, UiO-66, and NH2-UiO-66, albeit at the cost of reduced SHP and COPh. Conversely, lower flow rates can lead to higher temperature lift (ΔT) for specific materials, although with a slight ESD decrease. Adjusting the chilled water inlet temperature typically favors ESD and COPh with higher temperatures while affecting SHP and ΔT differently. Heat source temperature impacts ESD and SHP variably due to isotherm characteristics and dynamic water uptake. The results highlight the superiority of (CH3)2-MOF-801 and N-UiO-66, achieving 91 % and 76 % of total energy density, with 94 kg of (CH3)2-MOF-801 covering 89 % of energy requirements for a single South Korean home annually.

Experimental data analysis and dimensionless exergy levels in a commercial stratified thermal storage

The continuously rising demand for renewable energy sources within the energy system has highlighted the need for technologies capable of mitigating the impact of renewable energy intermittency and addressing the generation-demand mismatch in the system. Thermal energy storage (TES) emerges as a versatile storage medium with a wide range of applications, spanning from solar energy utilization and power peak shaving to the storage of industrial waste heat. In this study, data collected from an operating commercial stratified tank are used to validate a 2-D axisymmetric CFD model. Temperature profiles are collected throughout one month with a one-minute refresh rate. The model replicating the tank is generated in COMSOL Multiphysics® and validated by emulating the registered charging phases of the real storage. The model is then employed to optimize the stratification capability of the tank, by varying the logics applied to pinpoint optimal values of both inlet water temperature and velocity. The study aims to maximize the exergetic efficiency of the system using dimensionless exergy, a parameter often utilized in literature to identify the ability of the storage to generate and preserve optimal temperature stratification. Finally, the experimental dimensionless exergy has been evaluated for the aforementioned temperature profiles.

Study on the optimization of heat loss during operation of air source heat pump based on entransy theory

Existing research on the analysis heat pump operation generally focuses on the efficiency of doing work while ignores heat loss in the transfer process. Hence, heat pumps are often studied based on theory of minimum entropy production. However, this theory is rarely applied to optimizing heat transfer process with?out heat work conversion. Taking the air source heat pump hot water supply sys?tem of a hotel building as an example, this paper simulates the heat production, power and COP of the air source heat pump during operation based on the the?ory of entransy and entransy dissipation proposed by Professor Zengyuan Guo. The findings show that heat pump operates best at inlet water temperatures of 293 K and 298 K, with a COP of 4.8. In the water at a temperature of 298 K, water temperature can be adjusted by the function of heating capacity between 30 kW and 40 kW to minimize the system?s entransy dissipation, where the system?s unit power consumption reaches its minimum at 9 kW, corresponding to an entransy dissipation of 245.4 kJK. This study provides a good research idea to optimize the thermal power conversion process using the theory of entransy and entransy dissipation.

Experimental investigation on cooling tower performance with Al<sub>2</sub>O<sub>3</sub>, ZnO and Ti<sub>2</sub>O<sub>3</sub> based nanofluids

<p>This study deals with an experimental investigation of the thermal performance of a prototype mechanical wet cooling tower with a counter flow arrangement. Different volume concentrations ranging from 0.18 to 0.50 vol.% of stable Al oxide (Al<sub>2</sub>O<sub>3</sub>), Zn oxide (ZnO), and Ti oxide (Ti<sub>2</sub>O<sub>3</sub>) nanoparticles of 80, 35, and 70 nm diameter were considered. Water was taken as a base fluid, and the experiment was carried out at 60, 70, and 80 ℃, respectively, in laboratory conditions. The study revealed that an increase in the volume concentration of the nanofluids increased the cooling range, cooling efficiency, convective heat transfer coefficient, tower characteristic called number of transfer unit (NTU), and effectiveness of the cooling tower compared with water at the same mass flow rate and inlet temperature. However, increasing the volume concentration increased the viscosity of the nanofluids, leading to an increase in friction factor. For instance, for 0.18% volume concentration of ZnO, at an inlet water temperature of 66.4 ℃ and water/air (L/G) flow ratio of 1.93, the cooling range increased by 3.62%, cooling efficiency increased by 33.3%, and NTU increased by 50.5% compared with fresh water (FW).</p>

Energy and economic analysis of a sub-cooler based vapor injection transcritical CO2 heat pump for space heating

The Chinese government has considered the transcritical CO2 heat pump (TCHP) as a promising solution for space heating with the goal of “carbon peaking” and “carbon neutrality.” Considering the convenient implementation and the performance improvement, the vapor injection technique should be taken into consideration. This paper presents the experimental and simulation investigation of the SCVI TCHP prototype with energetic and economic analysis. Under the design condition, the SCVI technique could improve the peak COP by 5.02 % with a 10.11 % improvement in heating capacity. Compared to the direct electric heater solution, the annual operation cost was reduced by 11966CNY, 29.03 % higher than the Base TCHP. The payback period was decreased from 8 to 6.9 years due to the application of vapor injection. The effect of ambient temperature on the system performances was evaluated based on the experimental data. As the simulation progressed, a control strategy optimizing both the discharge and the medium pressure was developed, and the influence of inlet and outlet water temperature was studied.

Use of Ionic Liquid as Crystallization Inhibitor in Water-Lithium Bromide Absorption Chiller

Chillers are used in commercial buildings and industrial plants to provide air conditioning, refrigeration, and process fluid cooling. There are two basic types of chiller cycles: vapor compression and sorption. Sorption chillers are available as either absorption or adsorption designs, depending on the state of the sorbent. Absorption chillers use fluid refrigerants and absorbents (liquid or dissolved), while adsorption chillers employ a solid sorbent (typically silica gel) in combination with a fluid refrigerant. Among the former category, the use of highly hygroscopic LiBr salt as absorbent in combination with H2O as refrigerant comprises LiBr-H2O absorption chillers. Such chillers possess cooling capacities ranging from a few kilowatts (kW) to megawatts (MW) which match with small residential to large scale commercial or even industrial cooling needs. One of the major debilitating factors associated with LiBr-H2O absorption chillers is crystallization. A crystallization event causes a loss of cooling and requires de-crystallization by applying external heat, which results in extensive down-time and requires redundancy designed into a chiller plant. We investigated the use of the imidazolium-based ionic liquid, 1-butyl-3-methylimidazolium bromide ([BMIm]-Br), as crystallization inhibitor additive to LiBr-H2O in the ratio 1:19 [BMIm]-Br:LiBr. It was found that under the operating boundary conditions of 27°C/9°C (cooling water inlet temperature/chilled water outlet temperature), the LiBr-H2O absorption chiller can be operated without modifications and with around 10 K higher heating water inlet temperatures when adding [BMIM]-Br before crystallization occurs compared to pure LiBr-H2O solution. When using the [BMIM]-Br ionic liquid, the refrigeration capacity of the absorption chiller under the above operating conditions and at 85°C heating water inlet temperature exhibited 10% increase after optimizing the solution flow, that lead to higher outputs, such as lower cooling water temperatures. By adding the [BMIM]-Br to the aqueous lithium bromide solution the operating range of the absorption refrigeration system could also be extended to resorption mode, which allows refrigeration below 0 °C. Thus, there is an excellent potential for a significant extension of the application range of LiBr-H2O chillers, e.g. in the field of food cooling and refrigeration processes. Figure 1

Investigation of effect of cooling water characteristics on flue gas condensation along vertical tube heat exchanger

Flue gas condensing heat exchangers obtain the highest thermal efficiency of power boilers through the recovery of sensible and latent heat of condensation from flue gases containing certain amount of water vapor. Many parameters influence the operation of economizers, among them the amount of water vapor in the flue gas and cooling water parameters. This paper presents experimental results obtained for various local parameters of vertical tube bundle economizer when the flue gas water vapor mass fraction is 6 % and 14 % and when different cooling water inlet flow rates and temperatures are applied. The results showed that the change in the water flow rate had negligible effect on variation of the local flue gas and cooling water temperature along heat exchanger. However, its effect on the condensate flux and the local Nusselt number was significant. The cooling water temperature and, especially, water vapor mass fraction had a great impact on the average Nu number, but the effect of the flue gas Re number was less evident. It was determined that there exists a ratio of cooling water to flue gas mass flow rate, where the operation of the economizer is optimal in terms heat transfer and condensation efficiency.

Through-chip microchannels for three-dimensional integrated circuits cooling

Cooling high-power electronics in multilayer integrated circuits (ICs) is challenging for existing cooling methods. In this work, we designed through-chip microchannels (TCMCs) that cross the entire chip perpendicularly to the layers, with water circulating inside to provide direct cooling to each layer. TCMCs are organized in a square array where the pitch and radius of the microchannels are explored. Our computational fluid dynamics (CFD) simulations show that a pitch ∼ 10 μm and a radius ∼ 1 μm optimize the cooling performance to support a power higher than 104 W/cm2 while the maximum temperature rise remains below 60 K with a water inlet temperature of 300 K. We show that the cooling properties do not change with the number of layers for a given chip thickness which provides flexibility to the functional design of the chip. Though manufacturing may be challenging, TCMCs offer a new way for chip cooling that could provide a leap forward in the performance of multilayer 3D ICs and high-power electronics.

Development and experimental study of a compact silica gel-water adsorption chiller for waste heat driven cooling in data centers

In recent years, data centers have experienced rapid construction, leading to a significant surge in energy consumption, and cooling systems have emerged as prominent energy consumers of data centers. Among the cooling technologies, liquid cooling allows higher cooling circuit temperatures and provides potential for heat recovery. As a thermally driven cooling technology, adsorption refrigeration systems offer an alternative way to compression refrigeration systems by utilizing low-grade waste heat from liquid-cooled circuits to produce chilled water for air-cooled components. In this study, a compact silica gel-water adsorption chiller is developed for a small modular data center and experimentally investigated under extremely low driving temperatures. Under the typical summer conditions with the hot/cooling/chilled water inlet temperatures of 50 °C/30 °C/23 °C, the adsorption chiller achieves the cooling power of 4.9 kW and the COP of 0.50. When the cooling water inlet temperature changes from 32 °C to 24 °C, both the cooling power and COP show significant improvements, from 3.04 kW to 10.50 kW and from 0.44 to 0.66, respectively. Moreover, the increase of the hot water inlet temperature from 48 °C to 56 °C can enhance the cooling power to some extent, while the chilled water inlet temperature has little influence on the performance. The experimental results demonstrate the feasibility and performance of the developed adsorption chiller in data center waste heat driven cooling. Besides, potential adsorbents and possible optimization strategies are presented for performance improvement based on adsorption potential method.

Experimental Investigation of Chilled and Hot Water Inlet Temperature, and Mass Flow Rate Influence on Energy and Exergy Efficiency in a Prismatic Adsorbent Bed Cooling Systems

Adsorption technologies offer a promising solution for managing high electricity demand in building by leveraging waste heat recovery and renewable energy sources. The prismatic adsorbent bed adsorption water cooling system investigates energy and exergy analyses for cooling application. With hot water temperature of 80 °C, cooling water inlet temperature 30 °C, and chilled water inlet temperature 14 °C, the system achieves an energy efficiency of 45.2% while demonstrating an energy storage density of ≈340 kJ kg−1. As a result, the exergy efficiency reaches 12.2%, and the mass fraction at the end of the adsorption process is a significant value of 0.13kgadsorbate/kgadsorbent. Increasing the water mass flow rate in the evaporator results in a decrease in exergy efficiency, while simultaneously causing an increase in energy efficiency. With an increase in the chilled water inlet temperature of the evaporator and the hot water inlet temperature of the adsorbent bed, there is an increase in the energy storage density, energy efficiency, and exergy destruction due to irreversibility and losses. According to this study, the impact of the chilled water inlet temperature on the energy and exergy performances of the evaporator is more significant compared to the effect of the water mass flow rate.

Peak loads vs. cold showers: the impact of existing and emerging hot water controllers on load management

ABSTRACT Electric Hot Water Cylinders (HWCs) offer considerable Demand Side Management in Aotearoa New Zealand, which can provide load management and increase integration of renewable electricity. In this work, scenario analyses are conducted to simulate the impact on Low Voltage transformer load and demand fulfilment of four HWC controller types: setpoint (the default in Aotearoa New Zealand), ripple, smart-power, and smart-thermostat. All controllers reduce peak electricity demand by 14-34% from setpoint, where 34% is the maximum possible reduction with hot water control. Unmet demand, which indicates insufficient hot water and can lead to negative outcomes such as cold showers, is increased by 120% and 12-69% by ripple and smart-power control, respectively, and decreased by 7-31% by smart-thermostat control. Average thermal losses are 2.25 kWh/day for the setpoint controller, and between 2.20-2.76 kWh/day for other controllers. Smart-power controllers demonstrate demand deferral, shifting peak electricity loads to shoulder loads, while smart-thermostat controllers demonstrate demand deferral and valley filling, shifting peak loads to times of lowest demand and smoothing load distribution. Overall, smart controllers improve load management performance with little-to-no increase in unmet demand or thermal losses. Thus, smart controllers are a viable option for Demand Side Management in Aotearoa New Zealand. Abbreviations and Nomenclature: DHW: Domestic Hot Water; DLC: Dynamic Load Control; DSM: Demand Side Management; EV: Electric Vehicle; GHG: Green House Gas; HV: High Voltage; HWC: Hot Water Cylinder; LDC: Load Duration Curve; LV: Low Voltage; MV: Medium Voltage; NZD: New Zealand Dollar; PV: PhotoVoltaic; TOU: Time Of Use; UD: Unmet Demand; WTP: Willingness To Pay; A: WTP function coefficient; B: WTP function coefficient; Cp: specific heat of water [J/kg/K]; Ctrans: cost imposed by the transformer; HWsuff: ratio of hot water sufficiency; Kloss,h: thermal losses for cylinder h [W/K]; Kmix: thermostatic mixing valve factor; m: WTP function coefficient; Ptotal: transformer power demand [W]; Pcap: transformer capacity [W]; Ph: Household power demand [W].; PHWC: heater element power [W]; Pop: Transformer limit for Type3 controller [W]; QDHW: heat loss from DHW use [W]; Qloss: heat loss from standing losses [W]; th: time horizon [s]; Tamb: ambient temperature [K]; THWC: temperature of the HWC [K]; Tin: water inlet temperature [K]; Tmin: minimum temperature before fulfilment failure; Tout: water outlet temperature [K].; Tset: temperature setpoint of the HWC controller [K]; V ˙ : flow rate of hot water from the HWC [L/s]; Vavail: available DHW in the HWC [L]; VDHW: volume of hot water draw [L]; VDHW,expected: expected time weighted demand; VDHW,expected,max: maximum expected DHW demand; VHWC: volume of the HWC [L]; wf: time weighting function; ρ: density of water [kg/m3].

Numerical Analysis of the Boiling Heat Transfer Coefficient in the Flow in Mini-Channels

Abstract This paper deals with boiling heat transfer in the flow of water through an asymmetrically heated horizontal rectangular mini-channel. The mini-channel was made by gluing three transparent glass plates and a copper block. Through the glass window, the variable along the length of the mini-channel two-phase flow structures were recorded to determine local values of the void fraction. Four resistance heaters were attached to the copper block, powered by direct current, generating the heat initiating the flow boiling inside the channel. During the experiment, the following were measured: water volumetric flow rate, inlet pressure with pressure drop, inlet and outlet water temperature, copper block temperatures at three points inside its body, voltage and current supplied to the heaters. Stationary and laminar fluid flow with low Reynolds numbers were assumed in the mathematical model of heat transfer in selected elements of the measuring module. The temperature distributions in the copper block and flowing water were described by the appropriate energy equations: the Laplace equation for the copper block and the Fourier–Kirchhoff equation with parabolic fluid velocity for the flowing water. These equations were supplemented with a set of boundary conditions based on measurement data; moreover, data from experimental studies were the basis for numerical calculations and their verification. Two-dimensional temperature distributions of the copper block and water were calculated with the Trefftz method (TM). The main objective of this study was to determine the heat transfer coefficient on the contact surface of the copper block and water, which was calculated from the Robin boundary condition. The results of the calculations were compared with the results of numerical simulations performed using the Simcenter STAR-CCM+ software, obtaining consistent values. Computational fluid dynamics (CFD) simulations were verified based on experimental data including void fraction and temperature measurements of the copper block and flowing water.

Experimental and simulation study of an automobile cooling system: Performance improvement using passive flow control

The performance of an automobile cooling system has substantial impacts on the engine's efficiency, fuel consumption, and CO2 emission. In this novel experimental and numerical investigation, a combination of full three-dimensional car simulation, and one-dimensional modeling of the radiator along with the results of road tests on two car models, namely Vehicle A (the base car) and Vehicle B, was used to evaluate and compare the performance of the vehicles' cooling systems. The effects of implementing a passive flow control as well as changing the angle and geometry of the air deflectors on the cars' performance were investigated. The simulation utilized the K-epsilon (k-ε) turbulence model, while the experimental section involved standard road cooling tests. The results show that modifying the air deflectors in Vehicle B enables quick cooling of the system by controlling the air flow rate moving toward the radiator, which increased the air mass flow rate through the condenser and the radiator by 13% and 21%, respectively. Also, the radiator inlet water temperature decreased by about 1.9 °C, and the fuel consumption was reduced by approximately 0.5% under the New European Driving Cycle (NEDC) conditions, which decreased the greenhouse gas emissions, namely CO2 by about 0.9%.

Waste heat recovery of air conditioning on thermal efficiency enhancement of water heater

Air conditioning units are used to deliver comfortable air in households for the daily life of humans. This generates waste heat into the surroundings, that can cause global warming. This study investigated the thermal performance of water heaters recovering waste heat from air conditioners. A double-tube heat exchanger was installed between the compressor and the condenser to recover heat from the air conditioner. The inlet water temperature ranges from 15 °C to 40 °C, mass flow rates range from 2.5 L/m – 12.5 L/m, and water heater power input of 880 W – 3520 W is investigated. The results showed that water heaters have high thermal efficiency at low water mass flow rates. The waste heat of the air conditioner was recovered, which increased the thermal efficiency of the water heater by 12 % – 180 %, higher than the conventional type by approximately 50 %. The inlet water temperature ranges from 15 °C to 25 °C, and the input power range from 880 W to 1760 W has a significant impact on the thermal efficiency of the water heater. The energy consumption of the air conditioner decreased significantly when it was integrated with the heat recovery system. In addition, the water mass flow rate affected the energy consumption of the air conditioner. This study provides guidelines for improving the thermal efficiency of water heaters to reduce carbon dioxide emissions and heat rejection from air conditioners, leading to a reduction in global warming.

TRNSYS MODEL OF THE COMBI BOILER DOMESTIC HOT WATER CIRCUIT WITH A FOCUS ON THE PARAMETER DEFINITION OF THE PLATE HEAT EXCHANGER

Combi boilers used for both space and domestic hot water heating are one of the common household appliances. Modelling the domestic hot water circuit of a combi boiler for the preliminary evaluation of the laboratory testing is of crucial importance since it decreases the time, cost, and energy spent on the trials. There are various modelling approaches established by the authors of this paper. Domestic hot water circuit of the appliance is modelled previously making use of the Transient System Simulation Tool (TRNSYS 18) and a good agreement is achieved with the experimental and numerical data for the economic mode simulations. The drawback of the current TRNSYS model is the dependence on the experimental data for some of the parameter definitions of the components selected from the TRNSYS library, i.e. UA (multiplication of the overall heat transfer coefficient and the heat transfer area) input of the plate heat exchanger and heat retention effect of the heat cell block. In this paper, a constant value is assigned to the parameter definition of UA instead of a time dependent varied profile. Mean absolute errors covering the steady-state and transient operating regions for the domestic hot water inlet and outlet temperature difference in economic mode simulations stay nearly the same around 0,46°C, 0,82°C, and 0,53°C for 5 l/min, 7 l/min, and 8,7 l/min, respectively, under constant and variable UA approaches. Comfort operating scheme model is established with a couple of experimental data as of the principal application of the constant UA approach. Mean absolute error of the overall domestic hot water inlet and outlet temperature difference profile decreases to 0,5°C in the comfort mode simulation.