Water Loop Heat Pump Research Articles

Low-grade energy-bus air conditioning system using energy efficient three-fluid heat exchange terminals

Typical air conditioning terminals mainly focus on room temperature control, often neglecting adequate satisfactory room humidity management, resulting in poor thermal comfort. In addition, the direct heat exchange between refrigerant and air in these terminals cannot facilitate free-cooling using natural or waste cooling capacities. This study proposes a low-grade energy bus system that connects three-fluid heat exchange terminals, allowing for simultaneous control of room temperature and humidity. Furthermore, it enables the direct circulation of anti-icing fluid to each terminal for free cooling. Considering an office building in Nanjing, China, as an example, the annual operational performance of the proposed system is numerically studied and compared with two typical systems. The results reveal the following. 1) The three-fluid heat exchange terminals used can accurately regulate the room temperature and humidity, even when there are significant differences in the indoor cooling and dehumidification loads. 2) The annual system coefficient of performance (COP) of the proposed system increases from 3.3 to 3.9, leading to an annual energy saving rate of 14.4% compared to a typical water loop heat pump system in a typical office building in Nanjing, China. 3) Compared to commonly used room air conditioners, the proposed system is more energy-efficient.

Systems of heat pumps in water loop

The paper presents various solutions for water loop heat pump systems. Systems with heat pumps connected by a water loop are an economically attractive proposition. They allow significant savings. In the winter months, they achieve up to 60% energy savings for shopping centers. On an annual basis, they reach up to 23%. It is also important to note the possibility of additional use of "free-cooling" cooling, which allows a significant reduction in operating costs or supplementing with solar panels as an additional heat source. In industrial systems, the potential of water loop heat pump systems allows for significant energy savings and positive environmental aspects.

Welfare maximization with the least subsidy: Pricing model for surface water loop heat pump PPP projects considering occupancy rate growth and coefficient of performance

The surface water loop heat pump (SWLHP) is a renewable energy technology applied to support heating, ventilation and air conditioning (HVAC) systems to address the threat of global warming. However, the operation of SWLHP-PPP projects is challenging because the demand uncertainty brought by occupancy rate growth (ORG) affects SWLHP systems' coefficient of performance (COP), leading to cost uncertainty of the SWLHP-PPP projects. In this paper, we propose an analytical framework to examine how ORG (characterized by the initial occupancy rate, IOR, and the pace of occupancy rate growth, PORG) and COP affect the private sector's and government's pricing and subsidy decisions, respectively. Our findings identify two critical coefficients, the ORG-related coefficient and the COP-related coefficient, which influence the optimal price and government subsidies. Specifically, the optimal price declines with the former but increases in the latter, while the variation patterns of the optimal unit subsidy with respect to these two coefficients are just the opposite. Furthermore, the optimal price's sensitivity to the IOR is relatively stable, whereas that to the PORG decreases in PORG; the optimal unit subsidy and the total subsidy behave similarly. These results caution the private sector and the government to not blindly improve the forecasting accuracy of the PORG as the value of accurate forecasting diminishes with the PORG. Finally, the comparative results show that the lowest total subsidy is afforded by the government when both the COP and ORG are considered.

Optimizing Energy Consumption Strategy of Water-loop Heat Pump

In order to study the influencing factors of energy consumption of water-loop heat pump system, the optimal loop-water temperature strategy is proposed. The multi-variable building load is transformed into circulating water energy only related to water temperature. From Carnot cycle to think of the optimal loop-water temperature strategy, the original water temperature control method is changed. This paper shows that there is a unique circulating water temperature, which can minimize the overall energy consumption under certain building load conditions.

Applied research on water loop heat pump system based on a novel mechanism of energy conversion

Water loop heat pump (WLHP) has been widely used as a heat recovery system to realize building energy efficiency, but it still was a difficult problem to how to determine the effect of extracting and rejecting heat on water loop, because the unit converted its operation to reverse mode with load changing but the process would have a reverse effect on system operation. In this paper, a novel mechanism of energy conversion is introduced into the WLHP system to solve the problem and its view is presented as follows. First, the operation of WLHP system produces a “Reverse Energy” and it originates from an energy difference caused by the converted unit to water loop and can be used as a quantitative index to illustrate the energy-saving principle of system operation. Second, system operation is a combined effect caused by load change and reverse energy and yields to a nonlinear law due to the dynamic effect of reverse energy, so, it is characteristic of generality and individuality. Third, we can replace building load with circulating water to determine the energy-saving range of system operation and its law, and the idea that the energy carrier is used to solve the problem caused by operation will be of an important significance for a complex system. At last, the impact factors of system operation can be converted into a single function on circulating water by extracting and rejecting heat and the reverse energy is also determined by power equation of circulating water. To validate the previous conclusions and optimize heat pump systems, an office building group with different air-conditioning projects was tested in Tianjin and the results show that the change of system load determines the overall trend of operation, but the effect of reverse energy can reduce the fluctuation caused by load change and energy consumption of auxiliary power to improve operational efficiency, so, the WLHP system can achieve a higher efficiency compared to an air source heat pump (ASHP), in addition, the total energy consumption can further be reduced by building an energy balance between auxiliary heat source and units. These contributions contribute to the development of WLHP system and building energy efficiency.

Demand side management analysis of a supermarket integrated HVAC, refrigeration and water loop heat pump system

Supermarkets are intensive energy consumers because of a high electricity demand, mainly due to refrigeration utilities. Thus, in this work a supermarket integrated HVAC, refrigeration and water loop heat pump (WLHP) system was analyzed according to a demand side management approach, adopting a demand response strategy coupled with real-time pricing predictive rule based controls. The system was modeled with TRNSYS and several DR strategies were applied to both the space heating/cooling and the WLHP to determine the plant configuration with the most effective electricity cost saving. It was found that two setups guarantee the highest economic savings. The first consists of a predictive rule based control applied to the space heating/cooling only, which is basically inexpensive and allows an annual cost saving of 4.06% respect to the baseline configuration. The second, instead, combines predictive rule based controls applied to both the space heating/cooling and the WLHP auxiliary heater, and shows the best performance with the adoption of a 200 m3 water-based thermal energy storage. Respect to the baseline, this configuration provides an annual cost saving of 4.67%.

Analysis on energy efficiency and CO2 emission reduction of an SOFC-based energy system served public buildings with large interior zones

A novel energy system which serves public buildings with large interior zones was proposed in this study. The proposed system integrates a modified water loop heat pump (WLHP) with a natural-gas-fueled SOFC plant. The distributed SOFC plant is employed to complete the conversion from chemical energy to electricity and heat, and the modified WLHP which retrieves the waste heat of the SOFC plant is used for space cooling or heating. A “standards-oriented” model was built, and an “as-designed” approach was adopted to estimate the performance of the WLHP. For understanding the energy saving potential and CO2 emission reduction of the proposed system, a reference system, representative of the general level of energy production and consumption, is brought about for comparison. The IEER (integrated energy efficiency ratio) and CO2 emission trend show that the proposed system offers a much higher primary energy efficiency and realizes an obvious CO2 emission reduction compared to the reference system. Although the estimate of the IEER and CO2 emission reduction is conservative for some imperfections of the built models, the results of this study will still help significantly in guiding China's future CO2 emission reduction efforts.

Demand side management analysis of a commercial water loop heat pump system

Demand side management analysis of a commercial water loop heat pump system

Study and Optimization of Design Parameters in Water Loop Heat Pump Systems for Office Buildings in the Iberian Peninsula

Water loop heat pump (WLHP) air conditioning systems use heat pumps connected to a common water circuit to fulfill the energy demands of different thermal zones in a building. In this study, the energy consumption was analyzed for the air conditioning of an office building in the typical climate of four important cities of the Iberian Peninsula. The energy consumption of one water loop heat pump system was compared with a conventional water system. Two design parameters, the range in the control temperatures and the water loop thermal storage size, were tested. Energy redistribution is an important advantage of the WLHP system, but significant savings came from high efficiency parameters in the heat pumps and minor air flow rates in the cooling tower. The low thermal level in the water loop makes this technology appropriate to combine with renewable sources. Using natural gas as the thermal energy source, a mean decrease in CO2 emissions of 8.1% was reached. Simulations showed that the installation of big thermal storage tanks generated small energy savings. Besides, the total annual consumption in buildings with high internal loads can be reduced by keeping the water loop as cool as possible.

Energy study in water loop heat pump systems for office buildings in the Iberian Peninsula

The energy consumption is analyzed for the air conditioning of an office building in four important cities of the Iberian Peninsula. A water loop heat pump (WLHP) system is compared with a conventional water system. Energy redistribution is an important advantage, but significant savings come from heat pumps high efficiency parameters and minor air flow rates in the cooling tower. Even using natural gas as energy source, 8.1% decrease of CO2 emissions is reached, but additional important reduction can be easily obtained by using a solar thermal energy system as energy source.

Energy benefit assessment of a water loop heat pump system integrated with a CO2 commercial refrigeration unit

The improvement of energy efficiency and the use of environmentally friendly working fluids are key elements of current European policies. Supermarkets are intensive energy consumers and approximately the 40% of their annual energy consumption is for refrigeration. Direct emissions of greenhouse gases associated with the use of high Global Warming Potential (GWP) refrigerants, and the indirect impact on the environment related to high electrical energy consumption, make shopping malls not sustainable buildings. This paper analyses the energy saving potential of integrated supermarket air conditioning and refrigeration systems using a Water Loop Heat Pump system (WLHP). A basic CO2 booster commercial refrigeration system, applied to cold rooms and display cabinets, is considered. Heat recovery from the refrigeration circuit is performed in the heating season, while in the cooling season a dry cooler on the water loop allows heat rejection to outdoors. The building and all systems are modelled in the Trnsys environment taking into account the hourly weather data, the simulated daily profiles of the cooling and heating load demand and the request from refrigerated food storage equipment. Such a model allows a thorough understanding of the potential for energy savings with heat recovery solutions.

Theory of energy level and its application in water-loop heat pump system

It is a difficult problem to how to determine the reverse energy caused by units to water loop when a water-loop heat pump (WLHP) is in cooling and heating simultaneous mode, which not only has a great impact on energy-saving rate but also decides the use of auxiliary heat source in winter. This paper presents a theory of energy level to improve the research on WLHP system by using the relationship among building, circulating water and units. In this theory, the circulating water replaces building load as a new method to convert the reverse energy into energy change of circulating water and the equation of energy level also is built to determine the energy-saving range of WLHP system and report the capacity model of auxiliary heat source for all building types. An office building with different auxiliary powers is tested to analyze system operation characteristic and the effect of auxiliary heat source on unit and system and the results validate previous conclusions and suggest that an energy balance should be considered between units and auxiliary power to improve overall operation.

Application Analysis of Water Loop Heat Pump System Energy Conservation of a Sports Training Center

A sports training center training venues and office building adopting water loop heat pump system (WLHPS) are taken as examples, combined with the practical problems in design and operation, to analysis the operation characteristics of the air conditioning system and its advantages and disadvantages, and the energy saving operation strategy is put forward to further reduce energy consumption.

Research on the application of water-loop (tank) heat pump systems in catering buildings

The use of thermal energy in catering buildings is normally mishandled and causes significant waste of thermal energy. To increase the efficient use of energy and decrease the total amount of a catering building’s energy consumption, independent thermal systems should be integrated. If thermal systems are integrated, coupling utilization of thermal energy will be possible, and the primary energy input of a building will be utilized to a greater extent. To implement this concept, a water-loop (tank) heat pump system is necessary and its most important aspect is the design of the thermal storage tank (serving as the water-loop). In this paper, a typical catering building has been selected, and the building’s thermal service systems (processes) are studied in detail. The amount and state of the current thermal energy utilization within each service system is analyzed, and a specific integrated thermal system model is suggested. The research work conducted for this study is based on simulations, such as building thermal load simulations (DesignBuilder software), characteristic simulations of the water-loop heat pump system (TRNSYS software), optimal dimensions and thermal characteristic simulations of the thermal storage tank, etc. The energy consumption characteristic analysis and the technical and economic analysis of the entire building model are discussed, and the optimal scheme for process allocation and optimal operation mode are also presented in this paper. Based on the analytical results (including simulation of building thermal load, simulation of systematic energy consumption, performance analysis of the system, economical analysis, and exergy analysis), the advantages of the system model are demonstrated.

Environmental Impact Evaluation and Economy Analysis of Air-Conditioning Cold and Heat Source Based on TEWI Index

TEWI (total equivalent warming impact) index, a comparatively scientific method to evaluate the environmental impact of air-conditioning cold and heat source, is introduced. Taking some engineering in Hunan Province for example, the TEWI analysis was performed on the environmental impact assessment of four air-conditioning cold and heat source plans. Also the first investment and energy consumption were analyzed. The results indicate that: water loop heat pump unit, due to investment recovery period with only 2.9 years and carbon emission reduction up to 22.68%, has significant economy and environmental protection, which is followed by water source heat pump; the screw chilled water units plus gas boiler is poor. Gas direct-fired machine has certain economic advantage, but its environmental performance is general. Among four schemes, the proportion of indirect effects of CO2emissions from fossil fuels used to generate energy to operate the equipment throughout its lifetime are all larger, respectively is 95.1%, 95.2%, 100% and 89.9%. It fully showed the importance of developing clean and renewable energy, reducing energy consumption and increasing performance coefficient of refrigeration and air conditioning device.

Design and Economic Analysis of Air Conditioning System with Water Loop Heat Pump of Office Building in Hot Summer and Cold Winter Zone

Design and Economic Analysis of Air Conditioning System with Water Loop Heat Pump of Office Building in Hot Summer and Cold Winter Zone

Buildings dynamic simulation: Water loop heat pump systems analysis for European climates

In this paper, a purposely designed code for the performance analysis of the Water Loop Heat Pump (WLHP) systems is presented. Hourly, daily and seasonal energy system consumptions, operating economic costs and environmental impact assessments are dealt with. For the scope of comparison, the performances of two reference HVAC system are investigated too. For the computation of the building heating and cooling requirements, a suitable dynamic performance simulation model is being developed. All the relevant algorithms are implemented in MATLAB®. A case study of an office building undergoing simulation in different European climatic areas is being presented. Here, different building thermal features are considered. In order to maximize the system performance an additional optimization procedure to the operating devices temperatures is carried out. Results show that primary energy savings and avoided CO 2 emissions of the WLHP system vary in relation to the compared reference systems and can be obtained only in several European weather zones. The feasibility of the WLHP system strongly depends on electricity and natural gas national costs.

Optimizing energy consumption of a water-loop variable-speed heat pump system

Abstract Water-loop heat pump (WLHP) systems have been widely used for decades. The most appealing feature of WLHP is its capability of handling simultaneous heating and cooling demands in a building and recovering heat generated from zones in cooling. The typical heat sink and source are cooling tower and boiler. WHLPs discussed in this paper are equipped with a variable-speed compressor; the cooling tower comes with one variable-speed fan; and the boiler has a continuously-adjustable capacity. This paper analyzes how the energy efficiency of individual component responds to variations in loop water temperature; demonstrates that there exists a unique loop-water temperature that minimizes overall energy consumption given a certain building load; proposes a practical strategy to find the optimal temperature in a real-time manner.

Energy Analysis and Optimization of a Water-Loop Heat Pump System

A water-loop heat pump system consists of a set of water-source heat pumps that are connected with a closed-loop water network, which allows heat to be injected into or extracted out of the loop water. Such a configuration is able to meet simultaneous heating and cooling demands with a heat recovery capability. This paper analyzes the impact of loop water temperature on energy performance of individual heat pumps and the whole system, demonstrates that there exists a unique loop water temperature that minimizes overall power consumption of the configuration under discussion, and proposes a strategy to find the optimal temperature, which can be implemented in a real-time application. Simulations have been conducted to verify that a significant energy savings can be achieved over conventional practice.

06/01732 Conception of combination of gas-engine-driven heat pump and water-loop heat pump system: Lian, Z. et al. International Journal of Refrigeration, 2005, 28, (6), 810–819

06/01732 Conception of combination of gas-engine-driven heat pump and water-loop heat pump system: Lian, Z. et al. International Journal of Refrigeration, 2005, 28, (6), 810–819