Incoming Cold Water Research Articles

Advanced solutions to improve heat recovery from wastewater in a double heat exchanger

Reducing energy consumption and CO2 footprint in existing buildings without requiring extensive construction work is one of the biggest challenges facing the globe today. Although heating contributes for the majority of energy use in buildings, residential hot water demand is also relatively high, particularly when daily usage is high and especially for certain applications. The use of technologies that recover energy from sources other than fossil fuels to heat water has grown crucial, and one such technology involves recovering thermal energy from wastewater. Typically, heat recovery from wastewater is made to collect any remaining energy from the hot drainage water, and this energy is then applied to heat pumps or to warm up incoming cold water. The paper presents numerical simulations using a SST k-ω turbulence model in order to compare a regular geometry of heat exchanger with a helicoidal one. The second one provides a more turbulent flow that allows an intensification of the outer flow, thus allowing the enhancement of the heat transfer from the inner heated flow to the outer flow.

Comparative Study of Inlet Structure and Obstacle Plate Designs Affecting the Temperature Stratification Characteristics

Temperature stratification between outgoing hot water and incoming cold water is a key factor in diminishing energy loss during the discharging process and maximizing the useful hot water delivered from the tank or enhancing the thermal efficiency of the heating device during the heating process. In this study, the inlet structure and the obstacle plate were designed and modified based on two main factors, the reduction of inlet water velocity and the stipulation of the water recirculation area, to develop temperature stratification through the computational fluid dynamics method. The simulation model’s accuracy was validated against the experimental results. The results showed that using the equalizer as an inlet pipe’s auxiliary device was the best approach for decreasing the inlet water velocity, which resulted in enhancing temperature stratification. The discharging efficiency improved from 77.3% for the original tank model to 86.1% for the tank with equalizer IV model, which meant an additional 45 L of useful hot water was gained from the good temperature stratification storage tank. The installation of the obstacle plate for controlling the turbulence zone could not improve temperature stratification significantly, which resulted in an increase in discharging efficiency by only 4% more than the original tank model.

Numerical analysis of rectangular fins in a PCM for low-grade heat harnessing

Harnessing waste thermal energy from greywater (GW) in non-industrial buildings is becoming necessary to reduce energy demands, make heating/cooling technologies more efficient and to increase the share of renewables in the consumption. Harnessing this low grade energy to heat incoming cold water (CW) linked with phase change materials (PCMs) would decouple demand and supply along with integrating heat recovery with storage in a single unit, unlike technologies of the past.Radially installed rectangular copper fins around the GW and CW pipes of such heat exchanger (HE) enhance the thermal conductivity of the PCM which is the biggest obstacle in this high-impulse application, with the flow rate being high only for a short duration of time. Initially an experimental test rig is used to validate a numerical model as the basis of a sensitivity analysis to find the optimum geometric parameters of the finned HE for this application. A 40 × 90 mm fin with a 10 mm pitch provides complete phase change for both melting and freezing in the constrained time duration of 900s. Compared to a non-finned geometry this optimized fin configuration enhances the effective thermal conductivity of the PCM by a factor of 1.38 for melting and 4.75 for freezing. Although the development of buoyancy induced natural convection vortices are inhibited by fins the eventual heat transfer is enhanced due to a lower overall thermal resistance compared to a non-finned configuration. The GW to CW energy transfer efficiency is 72.4% with higher fluid flow temperature increments, compared to only 47.3% for a non-finned version.

Drain water heat recovery horizontal for energy conservation and reduction of CO2 emissions

One of methods to reduce energy consumption for hot water heating is install of Drain Water Heat Recovery (DWHR) units. The purpose of using this device is to take the thermal energy of the warm drainage water and transfer it to incoming cold water. Many DWHR systems work optimally in a vertical position. Due to the waste water flow in drain pipes. But these requirements are prohibitive to be applied on a large scale of this technology, as many buildings do not have enough space to accommodate the vertical DWHR in their sewage drainage system. This paper presents testing and analysis of the horizontal DWHR system. The result of the test showed the level of effectiveness of the horizontal DWHR unit created by 25.54 percent. Implementation of this technology in regional area, is one of the potential opportunities for energy saving, and reduce CO2 gas emissions.

Evaluation of Thermal Stratification Inside a New Model of Spherical Water Storage Tank Using a Computational Fluid Dynamics 6 Degrees of Freedom Solver

Abstract In this work, a computational analysis of a spherical solar hot water storage tank during the discharging process is carried out by using the commercial code ansys-fluent.15. The study investigates a new type of spherical heat storage tank. A hinged baffle is fixed at the tank vertical axis to increase the discharge flow rate without a thermocline layer. The dynamic mesh LAYERING technique is used to update the computational domain during the movement of the hinged baffle. The passive pitching of the submerged baffle is due to the fluid-dynamic loads. This model limits the mixture between hot and cold water regardless of the inlet flow rate. A comparative study between tanks with typical diffusers and the hinged baffle model is considered. The comparison of the computational fluid dynamics results with available experimental data showed a good agreement. Examinations of the temperature contours indicate that for the typical models, the interaction between the incoming cold water and the stored hot water gives rise to a thick thermocline layer where its temperature and thickness are related to the intensity of the mixing process. The suggested model shows high stratification efficiency along the discharging process.

Physical factors influencing phytoplankton abundance in southern Monterey Bay

As the base of almost all marine food webs, phytoplankton play a dominant role in determining the productivity of marine ecosystems. Recent studies have highlighted the dynamic variability of phytoplankton abundance in nearshore ecosystems over synoptic time scales. Therefore, a greater understanding of the physical mechanisms that contribute to this variability is required to assess impacts of current as well as future weather patterns on these ecosystems. In this study, chlorophyll fluorescence data from a nearshore location in southern Monterey Bay was used to identify the timing and duration of increases in phytoplankton concentrations. Regional physical parameters, including wind stress, wave height and water temperature were analyzed to determine what, if any, physical processes are associated with observed blooms. A significant negative correlation between water temperature and chlorophyll (high chlorophyll associated with cold water) was found for the two summer seasons studied (2012, 2013). The timing of high chlorophyll events coincided with relaxations of upwelling favorable wind conditions. Analysis of surface current data suggests that the incoming cold water masses are the result of poleward currents from the south of Monterey Bay. A conceptual model is proposed in which phytoplankton are advected into southern Monterey Bay during wind relaxation events preceded by upwelling events of great enough duration to establish well defined circulation patterns. The reversal of circulation patterns transports cold, phytoplankton-rich water into the bay from south of the Monterey Peninsula. This study demonstrates that wind relaxation events can be an important driver of localized high phytoplankton biomass events on the inner shelf by advecting recently upwelled water into coastal embayments that are relatively sheltered from strong upwelling favorable winds.

Life-cycle impacts of shower water waste heat recovery: case study of an installation at a university sport facility in the UK.

Recovering heat from waste water discharged from showers to preheat the incoming cold water has been promoted as a cost-effective, energy-efficient, and low-carbon design option which has been included in the UK's Standard Assessment Procedure (SAP) for demonstrating compliance with the Building Regulation for dwellings. Incentivized by its carbon cost-effectiveness, waste water heat exchangers (WWHX) have been selected and incorporated in a newly constructed Sports Pavilion at the University of Brighton in the UK. This £2-m sports development serving several football fields was completed in August 2015 providing eight water- and energy-efficient shower rooms for students, staff, and external organizations. Six of the shower rooms are located on the ground floor and two on the first floor, each fitted with five or six thermostatically controlled shower units. Inline type of WWHX were installed, each consisted of a copper pipe section wound by an external coil of smaller copper pipe through which the cold water would be warmed before entering the shower mixers. Using the installation at Sport Pavilion as the case study, this research aims to evaluate the environmental and financial sustainability of a vertical waste heat recovery device, over a life cycle of 50years, with comparison to the normal use of a PVC-u pipe. A heat transfer mathematical model representing the system has been developed to inform the development of the methodology for measuring the in-situ thermal performance of individual and multiple use of showers in each changing room. Adopting a system thinking modeling technique, a quasi-dynamic simulation computer model was established enabling the prediction of annual energy consumptions under different shower usage profiles. Data based on the process map and inventory of a functional unit of WWHX were applied to a proprietary assessment software to establish the relevant outputs for the life-cycle environmental impact assessment. Life-cycle cost models were developed and industry price book data were applied. The results indicated that the seasonal thermal effectiveness was over 50% enabling significant energy savings through heat recovery that led to short carbon payback time of less than 2years to compensate for the additional greenhouse gas emissions associated with the WWHX. However, the life-cycle cost of the WWHX is much higher than using the PVC pipe, even with significant heat recovered under heavy usage, highlighting the need to adopt more economic configurations, such as combining waste water through fewer units, in order to maximize the return on investment and improve the financial viability.

Thermoelectric Power Generation from Waste Heat of Natural Gas Water Heater

Abstract Waste heat is a viable source of recoverable energy in both industrial anddomestic scenario. One of the methods to convert waste heat to electrical power is byusing thermoelectriccells.In this paper, a power generation unit consist of 60 TECs was designed, fabricated and tested with the aim to recover the waste heat from domestic natural gas water heater. In the conceptual design, the waste heat from the flue is transferred to the hot water reservoir by using heat pipes (with fins). The cold water is entering to the power generation unit and serving as coolant for the TECs and thus at the same time, the cold water is preheated prior entering to the burner and this unit as a cogeneration system. In the experiment, the power generation unit was tested in a hot water bath at varying hot water temperature (50 °C -100 °C) and different cold water flow rates, ranging from 11 LPM to 33 LPM. With 60 TECs, the power generation unit has generated the electric power at the minimum of 3.9 W and a maximum 42.4 W under maximum flow rate, with the aforementioned range for hot water temperature and incoming cold water at 19.5 °C, which corresponds to typical scenario for hot water heating system.

Financial analysis of the implementation of a Drain Water Heat Recovery unit in residential housing

One of the ways of diminishing energy consumption for hot water heating is the use of Drain Water Heat Recovery (DWHR) units. The aim of the use of these devices is thermal energy recovery from warm drain water and transferring it to incoming cold water. This paper presents the calculation model that allows the estimation of the financial efficiency of the project involving the construction of a shower Drain Water Heat Recovery system in a single-family dwelling house. The presented method of investment risk assessment can be used for decision making by individual users, designers and others. The study of the financial performance was carried out for the various parameters of the installation and the different heat recovery system configurations. From investors point of view the most beneficial option of heat recovery system installation is the system in which preheated water is fed to both the hot water heater and shower mixing valve. Additionally, it was proved that obtained financial results are affected by showering time and water consumption. DWHR units will be therefore particularly beneficial to apply in case of swimming pools, sports facilities or fitness clubs, where high rotation of users is observed.

Residential Drain Water Heat Recovery Systems: Modeling, Analysis, and Implementation

This paper describes the design and environmental improvements that can be achieved using drain water heat recovery systems (DWHR) to reduce the energy consumption associated with residential showering. DWHR systems transfer heat from hot drain water to the shower's incoming cold water stream, thus reducing the demand on the hot water heater. There are various DWHR systems available that differ in heat exchanger type, cost, and performance. This article focuses on designing a flat plate and gravity fed heat exchangers for a range of residential showering conditions. This is useful since there currently is no peer-reviewed published data on the effectiveness of DWHR, nor is there published research considering the emissions reductions that can be achieved with realistic DWHR systems. The governing equations for heat exchangers are used to model empirical data and to derive implementation recommendations for DWHR design. The model is validated using a prototype flat plate heat exchanger and test stand under varying flow rates and temperatures. A Monte Carlo simulation of the results showed that DWHR could save an average $74 a year for homes with natural gas water heaters and $160 a year for homes with electric water heaters. This corresponds to 0.3 metric tons and 1.5 metric tons of CO2offset per home per year for natural gas and electric water heaters, respectively. The results are compiled and organized into a software program that allows consumers to input their household showering habits and location to get an estimate of their CO2, energy, and cost savings to determine if they should install a DWHR system.

Colonization of hospital water systems by legionellae, mycobacteria and other heterotrophic bacteria potentially hazardous to risk group patients.

Occurrences of legionellae and nontuberculous mycobacteria were followed in water systems of a tertiary care hospital where nosocomial infections due to the two genera had been verified. The aim was to examine whether their occurrence in the circulating hot water can be controlled by addition of a heat-shock unit in the circulation system, and by intensified cleaning of the tap and shower heads. One hot water system examined had an inbuilt heat-shock system causing a temporary increase of temperature to 80 degrees C, the other was an ordinary system (60 degrees C). The heat-shock unit decreased legionella colony counts in the circulating hot water (mean 35 cfu/l) compared to the ordinary system (mean 3.6 x 10(3) cfu/l). Mycobacteria constantly present in the incoming cold water (mean 260 cfu/l) were never isolated from the circulating hot water. Water sampled at peripheral sites such as taps and showers contained higher concentrations of legionellae, mycobacteria, and mesophilic and Gram-negative heterotrophs than the circulating waters. The shower water samples contained the highest bacterial loads. The results indicate the need to develop more efficient prevention methods than the ones presently used. Prevention of mycobacteria should also be extended to incoming cold water.

Occurrence of heterotrophic bacteria and fungi in cold and hot water distribution systems using water of different quality

The microbiological quality of cold and hot water samples of 67 Finnish buildings was studied. Most of the buildings were apartment buildings receiving their cold water from municipal groundwater or surface water plants. Disinfection with chlorine was applied in all the surface water plants and 33% of the groundwater plants. Water samples in buildings were taken from incoming cold water, from the hot water main just before and after the heat exchanger, and from a tap or shower in an apartment. The viable counts of mesophilic bacteria and fungi and total cell counts were higher in cold than in hot water samples. In hot water, the microbial counts were higher in samples from taps and showers than from the mains. In taps and showers, the decrease in hot water temperature probably increased the microbial numbers. Thermophilic bacteria appeared with high numbers in all the hot water samples, but thermophilic fungi were found in only one sample. Bacterial biomass and mean cell volume were greater in processed surface water than in processed groundwater samples. Disinfection with chlorine reduced the viable plate counts, although the chlorine concentration was extremely low in the water samples studied.Key words: heterotrophic bacteria, fungi, distribution system, groundwater, surface water.

PWR pressurizer modeling

A series of experiments have been performed which help to provide fundamental understanding of the phenomena which are important to the analysis of a PWR pressurizer. The transients considered include insurges to a partially-full tank, outsurges, insurges to a tank with hot walls, empty tank insurges, and combined insurges and outsurges. The experiments include the effects of noncondensable gases, and free surface heat transfer. These experiments provide a data base from which recommendations are made for calculating such phenomena, as: (i) stratification of the hot water and incoming cold water, (ii) wall condensation, (iii) flashing, (iv) rainout, (v) suppression of flashing, (vi) wall conduction, (vii) the effect of noncondensable gases on wall heat transfer, and (viii) free surface heat transfer. From these experiments a general model of a PWR pressurizer has been developed. It will predict the pressure-time behavior of a PWR pressurizer during a variety of transients. The model has been benchmarked against the low pressure experiments of this study and a single full scale pressurizer transient experiment. The most significant finding is the pool in the pressurizer remains stratified during an insurge transient so that practically no heat transfer to the cold insurge liquid occurs. Wall heat transfer can be significant for insurge transients, however.

Isolation of Legionella pneumophila from the cold water of hospital ice machines: implications for origin and transmission of the organism.

Although the mode of transmission of L. pneumophila is as yet unclear, the hot water distribution system has been shown to be the reservoir for Legionella within the hospital environment. In this report we identify a previously unrecognized reservoir for L. pneumophila within the hospital environment, ie, the cold water dispensers of hospital ice machines. The cold water dispensers of 14 ice machines were cultured monthly over a 1-year period. Positive cultures were obtained from 8 of 14 dispensers, yielding from 1 to 300 CFU/plate. We were able to link the positivity of these cold water sites to the incoming cold water supply by recovering L. pneumophila from the cold water storage tank, which is directly supplied by the incoming municipal water line. This was accomplished by a novel enrichment experiment designed to duplicate the conditions (temperature, sediment, stagnation, and continuous seeding) of the hot water system. Our data indicate that significant contamination of cold water outlets with L. pneumophila can occur. Although no epidemiologic link to disease was made, the fact that the primary source of a patient's drinking water is from the ice machines warrants further investigation of these water sources as possible reservoirs.

Electrical Automatic Water Still

MESSBS. BAIRD AND TATLOCK (LONDON), LTD., 14 Cross Street, Hatton Garden, E.C.I, have put on the market an interesting electrically heated automatic water still. The smaller size, which costs £6 13s. 6d, produces four pints of distilled water an hour with a consumption of 1,500 watts. The still is designed to allow easy access to all parts, a great advantage when hard water is used. It is fitted with an automatic safety device to cut off the current should the water supply fail, and there is heat interchange between the incoming cold water and the outgoing steam.