Driven Heat Pump Research Articles

Dynamic Simulation of a Solar Electric Driven Heat Pump for an Office Building Located in Southern Italy

Dynamic Simulation of a Solar Electric Driven Heat Pump for an Office Building Located in Southern Italy

A novel adsorption module with fiber heat exchangers: Performance analysis based on driving temperature differences

A main focus of recent R&D on adsorption modules for thermally driven heat pumps and chillers has been to enhance the volume specific power output while maintaining a reasonable coefficient of performance (COP).An adsorption module using a new type of heat exchanger based on aluminum sintered metal fiber structures brazed on flat fluid channels has been developed. The heat exchangers for adsorber/desorber and evaporator/condenser are identically constructed. The adsorption heat exchanger is coated with a silico-alumino phosphate (SAPO-34) by a partial support transformation direct crystallization (PST) [1]. Both components are placed in a vacuum tight housing using a valve-free configuration. Water is used as adsorptive.The experimental characterization of the module shows a high volume specific power (up to 82 W/litre module for cooling, 320 W/litre for heating). Although no heat is recovered between ad- and desorption cycle, a COP of almost 0.4 is reached for cooling and 1.4 for heating.Driving temperature differences are defined for the analysis of the heat exchanger performance. The evaporator/condenser shows extremely good performance with about 240 W/K specific evaporation power per litre of heat exchanger, while the adsorber is limiting the module performance.

Energetic and financial evaluation of a solar assisted heat pump heating system with other usual heating systems in Athens

This study is a manifold energetic and financial comparison of various heating systems. The examined building is a well-insulated building of 100m2 area located in Athens (Greece) and three different heating systems are investigated in order to determine the most suitable technology. The basic idea of this study is to compare a solar driven heat pump space heating system with an air source heat pump heating system and a fan coil heating system driven by solar collectors with an auxiliary electrical heater. Feeding a heat pump with hot water increases the Coefficient of Performance (C.O.P.) because the heat source temperature is higher compared to the case of air source heat pump. The energetic simulation tool of the analysis is the commercial software TRNSYS which simulates the behavior of complex transient systems. Many combinations of collecting area and storage tank volumes are presented because these are the main parameters which influence on a solar heating system performance. A simple sensitivity analysis proved that 25m2 flat plate collectors (FPC) coupled with a storage tank of 1m3 are able to feed the heat pump while 40m2 of solar collectors coupled with a 1.25m3 storage tank lead to solar coverage over 70%. Every system is designed carefully in order to maintain the thermal comfort conditions in high standards. The last part of this analysis is the financial evaluation of the examined technologies in terms of total cost which combines the investment and the operation cost.

Determination of Heat Transfer Characteristics of Solar Thermal Collectors as Heat Source for a Residential Heat Pump

With reducing energy demand and required installed mechanical system power of modern residences, alternate heat pump system configurations with a possible increased economic viability emerge. Against this background, this paper presents a numerically examined energy feasibility study of a solar driven heat pump system for a low energy residence in a moderate climate, where a covered flat plate solar collector served as the sole low temperature heat source. A parametric study on the ambient-to-solarfluid heat transfer coefficient was conducted to determine the required solar collector heat transfer characteristics in this system setup. Moreover, solar collector area and storage tank volume were varied to investigate their impact on the system performance. A new performance indicator “availability” was defined to assess the contribution of the solar collector as low temperature energy source of the heat pump. Results showed that the use of a solar collector as low temperature heat source was feasible if its heat transfer rate (UA-value) was 200 W/K or higher. Achieving this value with a realistic solar collector area (A-value) required an increase of the overall ambient-to-solarfluid heat transfer coefficient (U-value) with a factor 6–8 compared to the base case with heat exchange between covered solar collector and ambient.

Field performance of gas-engine driven heat pumps in a commercial building

The aim of this study is to evaluate the field performance of gas engine driven heat pumps (GEHP) used in a commercial building. Four, 8 TR (cooling capacity) GEHP units were employed to provide air-conditioning to seven thermal zones in a commercial building. The performance of these GEHPs was assessed over a period of 10 months and compared with prior results reported in the literature. Additionally, this study provides a comparative economic analysis of GEHPs and conventional electrical heat pumps. During normal operation, the cooling capacity ranged between 12.3 kW and 19.3 kW. The average COPunit of these systems varied from 0.15 to 0.85 during field operation. The gas engines were found to operate at significantly lower loads than their design capacity, and therefore, produced overall lower efficiencies. Oversized GEHP systems were deployed to meet the low cooling/heating demands attributed to the lower overall field performance. This study demonstrates the importance of sizing the GEHP/HVAC system similar to the load in buildings.

Combined influence of pore size distribution and surface hydrophilicity on the water adsorption characteristics of micro- and mesoporous silica

Adsorption processes are ubiquitous in nature as well as of great technological importance for gas separation, purification, storage and thermally driven heat pumps. This has led to a strong interest in the fundamental mechanisms governing adsorption phenomena and their exploitation to tailor adsorption systems for specific applications. In particular, the adsorption of water on porous silica exhibits remarkable properties due to the strong polarity of the adsorbate and moderate hydrophilicity of the adsorbent. It is generally accepted that the adsorption of water vapor on porous silica depends upon the concentration of surface silanols and the pore size. In fact, materials with ordered mesopores and a well-defined pore size have been used as model systems to demonstrate that water adsorption occurs predominantly through capillary condensation. While the pore surface chemistry is modified to become more hydrophilic after filling of the pores in these materials, the overall shape of the water adsorption isotherm (Type V) is not significantly affected in subsequent adsorption measurements. The present contribution shows that conservation of the isotherm shape is a unique phenomenon related to ordered mesopores but doesn't apply to materials with a more complex pore structure. For materials with wider pore size distributions including micropores, a synergistic effect of surface hydroxylation and pore size leads to a dramatic change in the water adsorption isotherm after the first adsorption/desorption cycle. In fact, we demonstrate that the water cycling capacity at relative pressures below the onset of capillary condensation increases significantly in these systems. These results contribute to a fundamental understanding of water adsorption in complex systems and have important implications in applications such as adsorption heat pumps where a large water cycling capacity in a specific relative pressure window is required.

Experimental study of a diesel engine heat pump in heating mode for domestic retrofit application

An engine driven heat pump (ENHP) can provide better efficiency compared to electric heat pump (EHP) considering primary energy consumption. The present work aimed to find suitability of diesel engine heat pump as a domestic retrofit application for off or weak gas/electricity network area. For this work, water-to-water heat pump test facility was developed which consisted heat pump, diesel engine and heat recovery arrangements. The system performance was evaluated for 65 °C flow temperature from condenser at three different engine speeds (1600, 2000 and 2400 rpm) and four evaporator water inlet temperatures (0, 5, 10 and 15 °C). The system performance was evaluated by heating capacity, isentropic efficiency, coolant heat recovery, exhaust gas heat recovery and PER. Performance analyses showed that heat recovery contributed 33% in total heat output where heat recovery was in a range of 1.7 to 3.7 kW. PER varied in the range of 0.9 to 1.4 showing good potential in terms of 35–65% primary energy saving and 23–42% CO2 emissions reduction compared to conventional systems. DEHP optimisation showed ability to meet water flow temperature requirement of 65–73 °C by speed variations and heat recovery providing good potential to meet heating demand during winter and summer periods in retrofit settings.

Pinch Analysis Techniques for Carbon Emissions Reduction in the New Zealand Industrial Process Heat Sector

Options for reducing industrial process heat greenhouse gas (GHG) emissions in New Zealand are investigated using the Carbon Emissions Pinch Analysis (CEPA) and Energy Return on Energy Invested (EROI) analysis methods. Renewable sources like geothermal, biomass, biogas from animal waste and heat pumps from renewable electricity are investigated. Results indicate that some regions of New Zealand are well placed to make significant reductions to process heat GHG emissions through shifting from fossil fuel heating to renewable heating without a large increase in energy expended or cost. Reducing GHG emissions below 1990 levels can be achieved by using wood waste and biomass in place of coal (33.3 PJ) and biogas from animal waste in place of natural gas (12.1 PJ) where high temperature heating is required (>90 °C), and renewable electricity driven heat pumps for low temperature heating (<90 °C) in dairy and meat processing industries (7.0 PJ). The expected increase in expended energy is 20 %. Over all the Central North Island of New Zealand has a significant degree of renewable and natural resource convergence and hence is a prime region for creating low carbon emission industries requiring process heat based on renewable energy and agricultural and forestry waste.

Large solar driven heat pump system for a multifamily building: Long term in-situ monitoring

This article presents the monitoring results of an existing large scale system that combines heat pumps with unglazed solar collectors (used for heat production or as heat source for the heat pumps). The system provides space heating and domestic hot water to a new housing complex (∼10,000heatedm2) in Geneva, Switzerland. Detailed monitoring of one of the blocks (∼1000heatedm2, 32 inhabitants) enables to characterise the behaviour of the system (building demand, control strategy, temperature levels) and to determine the energy flows as well as the performance of the system. The results show a very low space heating demand for Switzerland (∼20kWh/m2/yr), and an unusually high domestic hot water consumption (∼50kWh/m2/yr). The measured seasonal performance factor of the system, including backup electric heating and heat source circulation pump, is 2.9 for 2012 (average of 2.5 in winter and 4.4 in summer). This result can partly be explained by the high domestic hot water consumption, which implies a heat production at high temperature. This project is part of IEA SHC Task 44 “Solar and Heat Pump Systems”.

천연가스 열량 변화에 따른 GHP 엔진의 성능 및 배출가스 특성

가스엔진구동 히트펌프(GHP : Gas Engine Driven Heat Pump)의 연료인 천연가스의 열량이 감소함에 따라 국내에서 생산되는 GHP에 미치는 영향을 평가하였다. 저열량가스(<TEX>$9,800kcal/Nm^3$</TEX>)를 연료로 사용하여 엔진 단체 실험 및 GHP 현장평가를 실시한 결과 약간의 출력감소가 확인되었으나 시동성, 운전안정성, 배출가스 특성 등은 거의 변화가 없음을 확인하였다. 따라서 천연가스 열량이 <TEX>$9,800kcal/Nm^3$</TEX>까지 감소하여도 별도의 조정없이 GHP가 정상운전될 수 있을 것으로 판단된다. In general, natural gas is used as GHP(Gas Engine Driven Heat Pump) fuel. On this study, the influences of different natural gas heating value on GHP were evaluated. As a result of engine test & field test using low heating value gas(<TEX>$9,800kcal/Nm^3$</TEX>) as fuel, the engine power was reduced slightly, however the performance of start-up, the stability of operation and the characteristics of emission gas were almost similar. So it is considered that the normal operation of GHP is possible without any tuning when the low heating value(<TEX>$9,800kcal/Nm^3$</TEX>) of natural gas was used as fuel.

Manufacture of dense CAU-10-H coatings for application in adsorption driven heat pumps: optimization and characterization

CAU-10-H displays a highly suitable step-wise water adsorption behaviour for application in adsorption driven heat pumps and chillers. For actual application, manufacturing of coatings of this material on thermally conductive surfaces is highly desired. Direct, single-step, crystallization of CAU-10-H on either metallic or anodized aluminium yields a significant amount of by-product(s) and an inhomogeneous substrate coverage. Although adequate pretreatment of the substrates before crystallization improves the quality of obtained coatings, significant improvements are achieved only when crystal nucleation and growth are separated. More specifically, application of a reactive seeding approach with anodized aluminium leads to full coverage of the substrate surface, high MOF loading and high purity of the crystalline phase, homogeneous layer thickness, narrow crystal size distribution, and good stability in repeated water adsorption–desorption cycles.

Crystals for sustainability – structuring Al-based MOFs for the allocation of heat and cold

The special water adsorption behaviour of CAU-10-H makes it ideal for application in adsorption driven heat pumps and chillers.

Experimental Study of the Gas Engine Driven Heat Pump with Engine Heat Recovery

Gas engine driven heat pumps (GEHPs) represent one of practical solutions to effectively utilize fossil fuel energy and reduce environmental pollution. In this paper, the performance characteristics of the GEHP were investigated experimentally with engine heat recovery. A GEHP test facility was set up for this purpose. The effects of several important factors including engine speed, ambient temperature, condenser water flow rate, and condenser water inlet temperature on the system performance were studied over a wide range of operating conditions. The results showed that the engine waste heat accounted for about 40–50% of the total heat capacity over the studied operating conditions. It also showed that engine speed and ambient temperature had significant effects on the GEHP performance. The coefficient of performance (COP) and the primary energy ratio (PER) decreased by 14% and 12%, respectively, as engine speed increased from 1400 rpm to 2000 rpm. On the other hand, the COP and PER of the system increased by 22% and 16%, respectively, with the ambient temperature increasing from 3 to 12°C. Furthermore, it was demonstrated that the condenser water flow rate and condenser water inlet temperature had little influence on the COP of the heat pump and the PER of the GEHP system.

Numerical investigation of the Castle of Zena energy needs and a feasibility study for the implementation of electric and gas driven heat pump

In this work a numerical investigation of the energy needs of the Italian historical building Castle of Zena (XXIII century) and a feasibility study for the retrofit of its HVAC plant is presented.About the building envelope behaviour two types of numerical analyses have been performed. First of all, free floating conditions (no temperature control) have been considered, in order to evaluate the building envelope performance through the adaptive comfort approach. During almost the 50% of the summer season the internal temperature is above the upper limit of the comfort range, therefore a cooling plant is needed. Secondly, an ideal temperature control has been considered, in order to calculate the annual energy needs for space heating (around 164kWh/m2/year) and cooling (around 5kWh/m2/year).Regarding the HVAC retrofit, due to the historical constraints, it has been decided to use a fan coil emission system linked to a heat pump appliance. Four combination have been analysed, combining two type of heat pump (compression and absorption) with two type of heat source (air and water). Neglecting the control, emission, storage and distribution sub-system energy needs, there are two systems with the lowest primary energy consumption: the EHP-WS and the GAHP-WS (around 130kWh/m2/year), followed by the GAHP-AS (around 147kWh/m2/year) and the EHP-AS (around 180kWh/m2/year). From the economic point of view the EHP-WS has the shortest pay-back time, 7 years, also thanks to the use of the existing well. However, excluding the water source, only the GAHP is economically feasible. Lastly, a significant reduction of greenhouse gas emission (CO2) could be obtained replacing the EHP-AS with the GAHP-AS (−26%), the EHP-WS (−28%) or the GAHP-WS (−34%).

Performance analysis, model development and validation with experimental data of an ICE-based micro-CCHP system

The ICE technology applied to micro-CHP is a mature technology, with certain equipment established in the market. The integration of chillers in micro-cogeneration systems can be used to develop micro-CCHP systems with high overall efficiencies and high potential for integration in buildings. Studies of the behavior of these machines are necessary to develop models that simulate the micro-CCHP system under different weather conditions in different building configurations. This paper presents a micro-CCHP with heat recovery based on a Honda gas engine. The system incorporates a heat pump to meet the need for air conditioning. To analyze the behavior of the tri-generation system and its capabilities, a fully functional prototype is built and tested in the laboratory under different operating modes. The obtained results from the experimental data reveal that the maximum electrical efficiency is 7.63% and it is obtained when the heat pump is off and engine is operating at low speed. The higher performance of the gas engine driven heat pump is 10.79% and it is achieved when the engine is running at high speed. A model of the system is developed using TRNSYS software components and validated using the experimental data obtained during testing of various operating modes. The main contribution of this paper is focused on the applied methodology of tests, model, and validation through simulation. The proposed methodology includes experimental validation of the CCHP model using the TRNSYS energy simulation software. The features of this model make it appropriate for use as a stand-alone system in building simulations to produce electricity, DWH, heating and cooling.

Modeling and Experimental Investigation of an Oil-Free Microcompressor-Turbine Unit for an Organic Rankine Cycle Driven Heat Pump

Domestic heating and cooling will more and more have to rely on heat pumps (HPs) in order to support a more rational use of primary energy consumption. The HP market is mainly dominated by electrically driven vapor compression cycles and by thermally driven sorption processes. The drawback of electrically driven vapor compression cycle is their dependence on an electrical grid and the fact that they increase the winter or summer electricity peak demands. Hence, a thermally driven vapor compression cycle would offer substantial advantages and flexibility to the end user for heating and cooling applications. This paper presents the investigation of an oil-free compressor-turbine unit (CTU) used for a thermally driven HP (TDHP) based on the combination of a HP compression cycle and an organic Rankine cycle (ORC). The CTU consists of a radial inflow turbine and a centrifugal compressor of the order of 2 kW each, directly coupled through a shaft supported on gas lubricated bearings. The CTU has been tested at rotor speeds in excess of 200 krpm, reaching compressor and turbine pressure ratios up to 2.8 and 4.4, respectively, and isentropic efficiencies around 70%. Comparisons between the experimental data and predictions of models, that are briefly described here, have been carried out. A sensitivity analysis based on the experimentally validated models shows that tip clearance, for both compressor and turbine, and surface roughness of the compressor are key parameters for further improving performance.

Experimental investigation of a Thermally Driven Heat Pump based on a double Organic Rankine Cycle and an oil-free Compressor-Turbine Unit

This paper presents the experimental investigation of a concept of Thermally Driven Heat Pump (TDHP), based on the coupling of a vapor compression heat pump cycle and an Organic Rankine Cycle (ORC). The studied concept uses a single stage centrifugal compressor directly coupled to a single stage radial inflow turbine. The shaft is rotating on gas bearings, which allows the system to be oil-free. Like most of the other TDHP's, this system has the advantage to work with a variety of fuels or heat sources like wood pellets, natural gas, solar heat, geothermal heat or waste heat. A prototype using R134a as working fluid and with a heating capacity of about 40 kW has been developed. The results of the first tests are presented.

Energy Efficient Integration of Heat Pumps into Solar District Heating Systems with Seasonal Thermal Energy Storage

Solar district heating (SDH) with seasonal thermal energy storage (STES) is a technology to provide heat for space heating and domestic hot water preparation with a high fraction of renewable energy. In order to improve the efficiency of such systems heat pumps can be integrated. By preliminary studies it was discovered, that the integration of a heat pump does not always lead to improvements from an overall energy perspective, although the operation of the heat pump increases the efficiency of other components of the system e. g. the STES or the solar collectors. Thus the integration of heat pumps in SDH systems was investigated in detail.Usually, the heat pumps are integrated in such a way, that the STES is used as low temperature heat source. No other heat sources from the ambience are used and only that amount of energy consumed by the heat pump is additionally fed into the system. In the case of an electric driven heat pump, this is highly questionable concerning economic and CO2-emission aspects. Despite that fact the operation of the heat pump influences positively the performance of other components in the system e. g. the STES and makes them more efficient. If the primary energy consumption of the heat pump is lower than the energetic benefits of all other components, the integration makes sense from an energetic point of view.A detailed assessment has been carried out to evaluate the most promising system configurations for the integration of a heat pump. Based on this approach a system concept was developed in which the integration of the heat pump is energetically further improved compared to realised systems. By means of transient system simulations this concept was optimised with regard to the primary energy consumption. A parameter study of this new concept has been performed to identify the most sensitive parameters of the system.The main result and conclusion are that higher solar fractions and also higher primary energy savings can be achieved by SDH systems using heat pumps compared systems without heat pumps.

Solar Thermal Trigeneration System in a Canadian Climate Multi-unit Residential Building

This paper presents the comparison of several solar thermal, cogeneration and thermally driven heating/cooling central plant systems implemented into a typical mid-rise apartment, located in Calgary, Alberta, Canada. TRNSYS is used to model the system and predict the primary and secondary energy consumption, greenhouse gas (GHG) emissions and annual utility costs of the various systems and compared to the base case. The highest annual utility cost and GHG emission savings was attained by operating a cogeneration device in priority in a solar thermal, cogeneration with absorption heat pump plant, predicting a 21% reduction in the annual utility cost and a 16% reduction in GHG emissions. The system however has a higher secondary energy consumption, 10% above the base case. Operating the solar thermal collectors in priority over the cogeneration unit in the same central plant the greatest primary and secondary energy savings were attained achieving 16% and 18% savings compared to the base case. GHG emission savings of 16% was predicted with both operating strategies. Comparing this system to a cogeneration only system, secondary energy savings of 36% are predicted demonstrating the benefit of adding solar thermal collectors and a thermally driven heat pump to a cogeneration system. Extending the operating period of the solar thermal and cogeneration system by adding a thermally driven chiller did not yield significant primary energy, secondary energy, GHG emission or utility cost savings over a heating only system. This is attributed to extended operating period of the single stage boiler with poor part load performance. Finally, due to the low natural gas utility costs and higher electricity rates, the systems operating the cogeneration system in priority always resulted in the highest utility cost savings and the addition of solar thermal and thermally driven heating/cooling had limited economic benefit.

System modeling and building energy simulations of gas engine driven heat pump

To improve the system performance of a gas engine driven heat pump system, an analytical modeling and experimental study has been made by using a desiccant system in cooling operation (particularly in high-humidity operations) and suction line waste heat recovery to augment heating capacity and efficiency. The overall performance of a gas engine driven heat pump system has been simulated with a detailed vapor compression heat pump system design model. The modeling includes (1) a gas engine driven heat pump cycle without any performance improvements (suction liquid heat exchange and heat recovery) as a baseline (both in cooling and heating mode), (2) a gas engine driven heat pump cycle in cooling mode with a desiccant system regenerated by waste heat from the engine incorporated, and (3) a gas engine driven heat pump cycle in heating mode with heat recovery (recovered heat from engine). According to the system modeling results, by using the desiccant system, the sensible heat ratio can be lowered to 40%. The waste heat of the gas engine can boost the space heating efficiency by 25% at rated operating conditions. In addtion, using EnergyPlus, building energy simulations have been conducted to assess annual energy consumptions of the gas engine driven heat pump in 16 U.S. cities, and the performances are compared to a baseline unit that has a electrically driven air conditioner with the seasonal coefficient of performance of 4.1 for space cooling and a gas furnace with 90% fuel efficiency for space heating.