Sewage Source Heat Pump System Research Articles

Optimising design and operation of sewage source heat pump: techno-economic and environmental assessment

ABSTRACT Heat pump can be used to recover abundant thermal energy contained in the discharge of municipal wastewater treatment plants. While there are some design standards for common heat pump systems, the design of a sewage source heat pump (SSHP) system is still often based on a fixed heat load and neglects the interdependencies between the equipment sizing and operating parameters. To address the issue that previous design methods have not balanced investment and operational costs well from a global optimisation perspective, this work formulates the simultaneous optimisation of SSHP design and operation as a non-linear programming problem. The proposed model features the consideration of multiple working conditions caused by the impact of ambient temperature variation on the heat load of the SSHP system. The feasibility and potential benefits of the optimised SSHP system are also evaluated by incorporating techno-economic performances and environmental impact analyses into the mathematical framework. A case study is carried out to demonstrate the effectiveness of the proposed methodology. The results show that the total annual cost of the optimally designed and operated SSHP in Harbin could be 9% lower than in Beijing and 39% lower than in Shanghai, suggesting that constructing and running the SSHP system in severe cold regions with great heating demands might be more economical than in less cold regions. The CO2, SO2, and NOx emissions of the SSHP could be approximately 50% less than that of coal-fired boiler heating, and 80% less than that of direct electric heating with coal-fired electricity.

Integration of sewage source heat pump and micro-cogeneration system based on domestic hot water demand characteristics: A feasibility study and economic analysis

The reduction of carbon emissions from building space heating and cooling technology has become a crucial approach in achieving global carbon neutrality. Among these technologies, heat pumps and cogeneration systems are effective methods for carbon reduction in buildings. However, in numerous studies of coupled system operation, few scholars have considered the energy use of domestic hot water. This research investigates the operational feasibility of a sewage source heat pump coupled with a micro-cogeneration system, using a large-scale hotel building as the basis for the study. An economic operation strategy, based on the load characteristics of domestic hot water, is proposed and validated through simulation using TRNSYS software. The results showed that the proposed system can reduce peak power usage by 37 % annually, leading to lower operating costs. The calculations indicate that the proposed system can decrease the annual operating cost by 402,300 CNY compared to a single sewage source heat pump system. The payback period for the proposed system is estimated to be 6 years at the current time-of-use electricity price. Under various energy policy conditions, 71 % of the proposed system’s payback period is less than 20 years. Moreover, the emissions of SO2, NOx, and CO2 are reduced by 73.5 %, 73 %, and 64.8 % respectively. The system offers substantial economic and environmental benefits, and this study can serve as a reference for energy supply systems in cold regions.

Application and Analysis of a Heat Pump System for Building Heating and Cooling Using Extracting Heat Energy from Untreated Sewage

Heat pump technology can extract low-level heat energy from urban sewage to heat or cool buildings, which can alleviate the two major problems of energy shortage and environmental pollution to a certain extent. This paper introduces the principle of wastewater source heat pump technology and summarizes the current common system forms and their key core technologies. The proposed special heat transfer technology for sewage can effectively solve the problem of blockage and corrosion in the process of sewage heat transfer. Taking the system of an office building in Qingdao as an example, the system design parameter is introduced in detail. The operation monitoring of the heating and air conditioning seasons of this project was completed through a data collection system, and various performance parameters of the system were studied and analyzed. The data was obtained using measured data from one year of system operation. The testing results show that the sewage temperature of the heat pump system in winter is approx. 13.5 °C, the hot water supply temperature is approx. 50 °C, the average COP of the unit is 3.95, and the average COP of the system is 2.96. The calculation results show that the heating energy consumption of the heat pump unit is only 50.81% of that of a traditional heating mode coal-fired boiler and 57.57% of that of an air source heat pump system. In summer, the sewage temperature is approx. 22 °C, the cold-water supply temperature is approx. 5.5 °C, the average COP of the unit is 4.45, and the average COP of the system is 3.25. The cooling energy consumption of the heat pump system is 79.39% of the energy consumption of the traditional chiller and 61.56% of the cooling energy consumption of the air source heat pump system. This shows that the sewage source heat pump system has a remarkable energy-saving effect.

Rheological measurement of untreated sewage by straight tube

Sewage contains abundant low-grade heat energy, and recycling it using a heat pump system is an effective way to reduce carbon emissions. The particles in sewage will cause untreated sewage to exhibit non-Newtonian characteristics, and accurate rheological measurement is important for sewage transmission and distribution system design. The traditional rotary rheometer deforms, agglomerates, or breaks the solid particles in sewage, which affects the measurement results. Therefore, in this study, a horizontal tube rheological test bench was built for urban sewage. Constitutive equations and viscosity expressions of untreated and prepared urban sewage at different temperatures and particle concentrations were tested. The results show that untreated and prepared sewage conforms to the shear-thinning model of power-law fluids in non-Newtonian fluids even at particle wet mass concentration as low as 0.103%. The flow characteristic index n of sewage is unrelated to temperature, and its influence is mainly reflected in the consistency coefficient k. However, the sewage flow characteristic index n increases with a decrease in particle concentration. In the laminar flow range of 0.02–0.2 m/s, the flow resistance obtained by treating untreated sewage as a Newtonian fluid was approximately 1.36–1.99 times that of the non-Newtonian fluid model, which will result in a larger power system design and higher energy consumption. Under turbulent flow conditions, the drag coefficient of the Newtonian model was approximately 1.13 times that of the non-Newtonian model. This shows that when designing a sewage source heat pump system, the power-law fluid shear-thinning characteristics of untreated sewage must be fully considered, which helps reduce the calculated energy consumption of transportation.

An experimental study on effects of oily content on flow pattern transition over horizontal tubes in a sewage source heat pump system

The spray sewage heat exchanger is better used for sewage source heat pump systems due to its simple structure and good anti-blocking characteristics. To maintain high heat transfer efficiency of using oilfield wastewater, an experimental sewage source heat pump system is built and experimental studies are carried out to investigate the falling film flow patterns of oily wastewater over the horizontal tubes of spray sewage heat exchanger and effects of oily content. The critical spray density for flow pattern transition is clarified based on visualization by high-speed camera, and the influence of spray temperature and oily content are further analyzed. It is found the flow pattern transition is delayed with the critical spray density increased by 3%–12% when the oily content is raised from 0% to 20%, due to the higher temperature reduces the viscosity of the fluid. The critical spray density of flow pattern transition is also influenced by the spray temperature, which reduce the critical spray density from column flow to column-sheet flow from 0.0828 kg m−1 s−1 at 46 °C to 0.0782 kg m−1 s−1 at 65 °C for wastewater of 15% oily content. The tube surface temperature is further analyzed, and different high heat transfer performance regions are specified with a higher range of spray density for oily wastewater.

Summary of Application of Solar Thermal Evaporation Technology in Wastewater Treatment

In view of the current problems of sludge drying, this article mainly proposes a sewage source heat pump + solar heat collection system sludge drying technology, and expounds the feasibility of using sewage source heat pump and solar heat collection system as the heat source for sludge drying. The main principles, the structural characteristics of the main equipment and the operation precautions. It is clarified that this sludge drying method has good expansibility and practicability, and has the value of engineering application and further development.

A Smart Community Waste Heat Recovery System Based on Air Source-Sewage Source Compound Heat Pump

Compared with the traditional hot water production methods, heat pump systems have the unique advantages of high efficiency, energy saving, and eco-friendly, so they have a very good promotion and application prospect. The sewage source heat pump systems can recover the waste heat of high-temperature sewage produced in residential communities, for this reason, this study integrated the proven air source heat pump technology with the sewage source heat pump technology and conducted a research on the smart community waste heat recovery system based on the air-source/sewage-source Compound Heat Pump system (CHP system). In the paper, the design steps and equipment selection flow of the proposed system were given, the waste heat utilization rate of the proposed system was calculated, and the obtained experimental results verified the energy-saving effect of the proposed system, which had provided a reference for the application of the compound heat pumps in other occasions.

Numerical investigation on the longitudinal distribution characteristics of falling film flow outside a vertical tube

In order to design the vertical falling film evaporators applied in the sewage source heat pump systems, a numerical study employing the VOF (Volume of Fluid) method has been carried out to determine the thickness and the wave behavior of falling liquid film outside a vertical tube. The effects of the annular gap, tube diameter, tube length, spray density, viscosity and surface tension are discussed. The simulation results demonstrate that spray density and the fluid viscosity are the two most influential factors affecting the film thickness. Besides, when spray density is larger than 0.100 kg/(m∙s), the film thickness decreases slightly with the increase of the flow distance. So the influence of tube length on film thickness cannot be ignored and it also should be considered in the film thickness prediction model. On the other hand, the tube diameter and the surface tension have little effect on the film thickness. It mainly have a significant impact on the wave amplitude of the liquid film at low flowrate. Besides, the annular gap provides a limited effect on the outlet section of the falling film. On the basis of the simulation results, a new correlation incorporating the tube length is developed to effectively predict the falling film thickness. Compared with the experimental data, it is found that the prediction accuracy of the correlation can be controlled within ±15%. The present research provides a theoretical basis for designing falling film evaporators.

Dynamic Heating System of Multiphase Flow Digester by Solar-Untreated Sewage Source Heat Pump

The traditional biogas heating system has the disadvantages of a low energy efficiency ratio and high energy consumption. In this study, a solar-untreated sewage source heat pump system (SUSSHPS) was developed for heating a 12 m3 multiphase flow digester (MFD) in Suining, China. To investigate the operating effects, two modes were defined according to the solar fractions in different regions. On the basis of experimental data, thermodynamic calculations and operating simulation analysis were performed, and the solar collector area (Ac) and the minimum length of the sewage double-pipe heat exchanger (lmin) for the two modes were calculated. The results indicated that the Ac and lmin of mode 2 were larger than those of mode 1 at different solar fractions. Additionally, the results suggested that mode 1 can be used at a solar fraction of <0.33, and mode 2 can be used at a solar fraction of >0.5. Moreover, a comprehensive evaluation of different biogas heating systems was performed. Two evaluation methods were used for modeling calculations, and the results of the two methods were consistent. The SUSSHPS had the largest comprehensive evaluation value among the four systems. The proposed SUSSHPS can play a significant role in improving current biogas heating systems and promoting the development of biogas projects.

Design of remote monitoring system for sewage source heat pump based on PLC and GPRS

In this paper, the remote monitoring system of sewage source heat pump is designed and developed by using the scheme of PLC + configuration software. According to the technological process of sewage source heat pump system, the communication between PLC and heat pump unit and variable frequency water pump is realized by RS485 bus. The upper computer human-computer interaction software of sewage source heat pump control system is developed, and the system operation is realized. The functions of line data monitoring, remote control of units and transducers are tested and verified. The results show that the system can achieve the expected functions and run well.

Experimental study on liquid flow fields in de-foulant hydrocyclones with reflux ejector using particle image velocimetry

Hydrocyclone has been extensively used in various separation processes. For example, in the sewage source heat pump system, a De-Foulant Hydrocyclone with Reflux Ejector (DFHRE) can fully use the kinetic energy of its overflow to suck its underflow and flush away the foulants flowing out with the underflow. Our previous experiments in 2018 showed that the reflux ejector could prevent the underflow orifice from blocking, and reducing the suction angle could increase the separation efficiency by approximately 10% whereas decreasing its energy consumption markedly. To date, however, its mechanism is still unclear. Therefore, in this study, we used the Particle Image Velocimetry (PIV) method to study the flow field in DFHREs with different suction angles and compared it with that in the traditional hydrocyclone without reflux ejector. Results indicated that, in all the tested DFHREs, there was a negative-axial-velocity area in the center of hydrocyclones, which was not found in the center of the tested traditional hydrocyclone. The negative axial velocity produced by the overflow-suck-underflow decreased with increasing suction angle whereas increased with increasing inlet velocity. The split ratio and total pressure drop of the DFHRE are respectively and approximately 18.5% and 28.3kPa greater than those of the traditional hydrocyclones at the suction angle of 30°. This proved that the experimental performance of the sewage suction ejector used in hydrocyclone, that is, the suction effect of the reflux ejector and the separation efficiency of DFHRE were the best at the suction angle of 30°. Besides, the obtained change of flow field caused by the reflux ejector provided a new idea for enhancing hydrocyclone separation.

Experimental and theory investigations on falling film flow characteristics and heat extraction performance of spray heat exchanger for sewage heat pump system

The flow characteristics of sewage directly affect the technical and economic performance of sewage-source heat pump systems in heat extraction from sewage. To prove there is significant improvement in heat extraction from sewage with the spray heat exchanger for sewage heat pump system (SHPS): (1) The flow states of the falling film on and between the multiple horizontal tubes were investigated experimentally. The correlations of Reynolds number (range from 100 to 600) and the tube distances to the flow were derived; (2) A model was developed for the falling film flow state analysis of the horizontal elliptical tube of the spray heat exchanger using the ellipse plotting method, which was constructed using approximately three circular arcs. The laser-induced fluorescence technology was used to measure the horizontal tube falling film thickness of water. This experiment focused on the film thickness distribution characteristics of Al-brass tubes with outside diameters of 19 mm and 25.4 mm in column flow with the tube spacing ranging from 20 mm to 40 mm and the Reynolds number (Re) ranging from 184 to 368. The images of the gas-liquid interface were captured with a digital camera. The image processing technology was used to quantitatively describe the liquid film thickness around the horizontal tube. The comparisons between the falling film thickness calculation results and experimental data were in good agreement for the variation of the angle of the elliptical surface and the specific liquid rate. Furthermore, a novel correlation was developed to describe the Nusselt number which was subjected to the examined tube shapes; (3) The heat extraction performance of SHPS with spray heat exchanger was experimentally investigated. The temperature of the sewage ranged from 10 to 30℃. The heat supply, input power, COP, and output water temperature of the condenser of the SHPS were discussed. The results of the proposed calculation method were in conformity with the experimental data and gave good predictions with maximum deviation being lower than 8.6%. Thus, the proposed method is helpful in improving the design and the performance of the SHPS.

Numerical study on heat transfer of oily wastewater spray falling film over a horizontal tube in a sewage source heat pump

Sewage heat exchanger is the key equipment of oily sewage source heat pump system, which has great influence on its performance. Among many kinds of heat exchangers, the spray heat exchanger has the advantages of simple structure, high heat transfer efficiency, good operability and anti-blocking ability. Therefore, it can be used in a sewage source heat pump to recover energy from the oily wastewater. However, the heat transfer and flow characteristics of oily wastewater spraying in the heat exchanger are different from the ordinary sewage heat pump system. Hence, it’s necessary to investigate the heat transfer of oily wastewater spray falling film on horizontal tube for better application. In this paper, a three-dimensional numerical model was established for a spraying heat exchanger in the oily sewage source heat pump system, and a mixture of water and glycerin was used to simulate the oily wastewater. The VOF model was used to track the liquid-gas interface of oily wastewater spray falling film over a horizontal tube in the heat exchanger, and the effects of different glycerin content, heat flux, spray density, tube diameter, liquid distributor height and spray temperature on the heat transfer coefficient were investigated. To further understand the mechanism of heat transfer inside the film, the temperature distribution inside the liquid film was obtained and analyzed. The results show that: (1) the heat transfer characteristic can be divided into three regions around the tube; (2) the local heat transfer coefficient decreased with increase of glycerin content in the thermal developing region; (3) the local heat transfer coefficient increased with the increase of the spray density and spray temperature, decreased with the increase of the tube diameter and was little affected by heat flux in the thermal developing region, and the increase in the liquid distributor height caused increase of local heat transfer coefficient in the upper part of the tube.

Fault Detection Method Using Multi-mode Principal Component Analysis Based on Gaussian Mixture Model for Sewage Source Heat Pump System

This paper presents an algorithm for fault detection of a sewage heat pump system by designing multi-mode principal component analysis with Gaussian mixture model. If the heat pump system fails, the loss of energy and time is enormous, therefore the fault detection of the system is important. For this purpose, this study proposes a fault detection method using multi-mode principal component analysis with Gaussian mixture model. The data were clustered into multi-mode of Gaussian on principal component subspace. Based on the multi-model, the values of Hotelling’s T2 and SPE were calculated and used for the fault detection as indexes that are compared performance with clustering model using k-means and k-medoids algorithm as well as conventional PCA. Actual data of the sewage heat pump were used to verify the proposed method. The results of the fault detection performance show that the proposed model shows the best performance of fault detection among the conventional, k-means, and k-medoids PCA models.

Field Test Analysis of a Urban Sewage Source Heat Pump System Performance

The sewage flow rate of the urban drainage system is relatively large and generally stable, its sewage temperature range varies relatively lightly and maintains 10~15℃ in winter. The sewage in the drainage system can be the low grade thermal source for building heating and cooling. Sewage source heat pump technology can efficiently extract or discharge the amount of heat from the sewage in the drainage system for building heating or cooling. The field test of the actual operation thermal performance of the sewage source heat pump were carried out and investigated. The sewage source heat pump system were continuously measured for 72 hours. Based on the test datum, the average COP of the heat pump was 4.5. The relationship between energy consumption of system and energy consumption of transportation are analyzed. The analysis shows that the pump of this system cannot match the load change well and the use of variable frequency pump can improve the energy efficiency of the system. Before the use of the sewage source heat pump system, the traditional coal-fired boiler and air-cooled chiller are the heating and cooling system of this building. Compared with the traditional coal-fired boiler and air-cooled chiller, the advantages of sewage source heat pump system in energy saving, economy and environmental protection are analyzed. The results show that: Compared with the original system, direct heat exchange type sewage source heat pump system can save 53% of the primary energy consumption, reduce the annual operating cost by 11%, increase the initial investment by a factor of 14.3%, and the payback period of incremental investment is about 4.7 years. This method not only has better energy saving, saving capital benefit, but also can reduce the local pollutant emission, and has better environmental emission reduction benefits.

Technology and Economic Analysis of Sewage Source Heat Pump Combined Type District Heating Method

This paper puts forward a kind of compound district heating method for* recycling waste heat of wasting water for building heat supply. The way is to the sewage treatment plant and the district heating plant in combination with heating operation, through the sewage source heat pump system for recycling the sewage heat energy for urban heating system returns water preheating. Research results show that compared with the other two heating methods, under the same heat loading, the sewage source heat pump combined type district heating method has the advantages of high energy consumption, low operation cost, distance from heating and good suitability.

Experimental investigation of convective heat transfer from sewage in heat exchange pipes and the construction of a fouling resistance-based mathematical model

In sewage-source heat pump systems, the properties of sewage flow and heat transfer in heat exchange pipes and the growth characteristic of fouling resistance are very important design parameters of sewage heat exchangers. A test system is set up to investigate the convection and heat transfer properties of original sewage in the heat exchanger tube in practical engineering. The growth process, growth related influencing factors and the growth law of fouling in the sewage-source heat pump system are obtained by analyzing the test data. By analyzing the experimental data, the fouling resistance based model for the heat transfer from sewage flowing in a horizontal pipe is built. The model shows that the fouling resistance is distributed asymptotically and the asymptotic time is inversely proportional to the square of the initial flow velocity. In addition, the asymptotic value showed a linear and decreasing relationship with initial flow velocity. This mathematical model for fouling resistance provides an important theoretical basis for the optimal design of sewage heat exchangers.

The operation characteristics of sewage source heat pump system and the analysis of its thermal economic benefits

The paper focuses on practical ways of water intake in the raw sewage source heat-pump system and the application of the new type heat-exchanger, and gives an analysis on its hydraulic regime of its heat-supply. The experimental data shows that the system operates well and the coefficient of performance approximates to 4.0. The actual cost of the sewage-source heat pump system is about ¥16.77/m2, and the yearly saving cost is about ¥444000, which proves a great energy-saving effect. According to its operation, it gives an analysis about its unit exergetic cost from the prospective of thermal economy. The calculation result shows that the unit exergetic cost in intermediate pump is the highest, and the average value is 7.8W/W.

Using Thermal Shock to Inhibit Biofilm Formation in the Treated Sewage Source Heat Pump Systems

Treated sewage source heat pump systems can reuse the waste energy in the treated sewage. However, biofilms in the heat exchangers decrease the system efficiency. This work investigates the feasibility of thermal shock at accessible temperatures in heat exchangers for biofilm inhibition. Bacillus subtilis biofilms were formed on coupons and in a miniaturized plate heat exchanger. Thermal shocks at different temperatures (50–80 °C) for different exposure times (1–60 min) were used to treat the biofilms. The results showed that thermal shock had a significant bactericidal and biofilm inhibition effect, and the effect was enhanced as the temperature and the exposure time increased. Data fitting of the biomass showed that temperature had a more significant influence on the biofilm inhibition effect than exposure time. The results of the heat exchanging experiments showed that high temperature thermal shock could significantly mitigate the heat transfer deterioration caused by the biofilms, indicating that thermal shock could be used as a viable biofilm inhibition approach for heat exchangers.

The Measured Analysis of Heating Performance of The Sewage Source Heat Pump System of a University in North China

The energy crisis and environmental pollution has become a major problem facing the people. As a green energy-saving technology, the sewage source heat pump system not only makes full use of the rich water resources, but also conducive to environmental protection. In this passage, we take an sewage source heat pump system of a university as the research object, test the Sewage temperature, supplying and returning water temperature of heat pump unit and the Indoor hot and humid environment indoor, in the measure of the use of ultrasonic flowmeter, temperature recorder and power quality analyser. Analyze the cop value of sewage source heat pump system, determine the operating characteristics of sewage source heat pump system, analyze the effect of the sewage source heat pump system so that we can make full use of the sewage source heat pump technology is better used in other buildings.