Comparison of natural gas driven heat pumps and electrically driven heat pumps with conventional systems for building heating purposes

Electrically driven heat pumps achieve good efficiencies for space heating. If heat pumps are driven directly by a combustion engine instead of an electric motor, losses attributed to the production and transport of electricity are eliminated. Additionally, the use of the combustion engine's heat leads to a reduced temperature difference across the heat pump. This article presents annual efficiencies of these systems and compares internal combustion engine and electrically driven heat pumps in terms of primary energy consumption and CO₂ emissions. Because heat pump performance depends strongly on the heating circuit's flow temperature level, the comparison is performed for air-to-water and geothermal heat pump systems in two cases of maximum flow temperatures (40 °C and 60 °C). These temperature levels represent typical modern buildings with large heating surfaces and older buildings with high-temperature radiators, respectively. In addition to the different heat pump setups, conventional space heating systems are included in the comparison. The calculations show that natural gas-driven heat pumps achieve about the same efficiency and CO₂ emissions as electrically driven heat pumps powered with electricity from the most modern natural gas-fired combined cycle power plants. The efficiency of such systems is about twice that of conventional boiler technologies.     

Economy of exploiting heat from low-temperature geothermal sources using a heat pump

The article describes the economy of exploiting heat from low-temperature geothermal sources for high-temperature heating of buildings using a heat pump. For the exploitation of low-temperature geothermal sources, a two stage heat pump with a heat exchanger was planned. The pump consists of two single stage heat pumps which use different refrigerants at each stage. At stage 1, the calculation of the heat pump is conducted with refrigerant R407c; at stage 2 of the heat pump, the refrigerant R600a is used. The main operational characteristics of a two stage heat pump are presented in the form of diagrams. For the exploitation of heat from geothermal water with a temperature of 45 °C, a profitability evaluation of the investment in the heat pump was carried out, using the method of the net present value. In the research, also the coefficient of profitability and the period of time in which the investment is going to return itself were established.     

Exergoeconomic analysis of the Gonen geothermal district heating system for buildings

This paper presents an application of an exergoeconomic model, through exergy and cost accounting analyses, to the Gonen geothermal district heating system (GDHS) in Balikesir, Turkey for the entire system and its components. This exergoeconomic model is used to reveal the cost formation process and the productive interaction between components. The exergy destructions in the overall Gonen GDHS are quantified and illustrated for a reference temperature of 4 °C. The results indicate that the exergy destructions in the system occur primarily as a result of losses in the cooled geothermal water injected back into the reservoir, pumps, heat exchangers, and pipelines. Total exergy destruction and reinjection exergy of the cooled geothermal water result in 1010 kW (accounting for 32.49%), 320.3 kW (accounting for 10%) of the total exergy input to the Gonen GDHS, respectively. Both energy and exergy efficiencies of the overall Gonen GDHS are also investigated to analyze the system performance, as these efficiencies are determined to be 42% and 50%, respectively. It is found that an increase of the load condition leads to a decrease in the overall thermal costs, which will result in more cost-effective energy systems for buildings.     

广西可再生能源建筑应用工程节能验收要点分析

为更好地指导广西可再生能源建筑应用工程的节能验收,形成可再生能源建筑应用的长效推广机制,建立健全可再生能源建筑应用工程的节能验收体系已至关重要。本文研究针对广西地区可再生能源建筑应用技术特点,开展了可再生能源建筑应用工程节能验收要点分析,获得了广西地区主要的可再生能源建筑应用技术类型,包括太阳能热水系统、地表水源热泵系统、地埋管地源热泵系统和地下水源热泵系统工程的节能验收要点。     

Effect of reference state on the performance of energy and exergy evaluation of geothermal district heating systems: Balcova example

In this paper, we undertake a parametric study to investigate how varying reference temperature from 0 to 25 °C will affect the energy and exergy efficiencies of the Balcova geothermal district heating system (BGDHS) and develop two significant correlations (with a correlation coefficient of 0.99) that can be used for predicting the efficiencies. The exergy losses in the overall BGDHS are quantified and illustrated using exergy flow diagram particularly for a reference temperature of 11.4 °C for comparison purposes. This reference temperature is taken as an average value of the ambient temperatures measured during the past 5 years for the day of 2nd January to reflect the actual situation. The results show that the exergy losses within the system occur mainly due to the losses in pumps, heat exchangers, reinjection sections of the geothermal water back into reservoir and pipeline, and account for 1.75%, 8.84%, 14.20%, and 28.69%, respectively. In addition, we study energy and exergy efficiencies to determine the possibilities to improve the system, and energy and exergy efficiencies of the system are found to be 42.36% and 46.55%, respectively, for 2nd January 2004.     

地源热泵--建筑节能新技术

在建筑供热空调中采用热泵技术可以有效地提高一次能源利用率，减少温室效应气体CO2和其他大气污染物的排放。本文阐述了利用热泵供热比锅炉直接燃烧供热节能的原理，对主要的热泵供热形式，特别是地源热泵的技术特征、适用范围和经济性作了较详细的介绍。     

Experimental performance analysis of a solar assisted ground-source heat pump greenhouse heating system

Ground-source heat pumps (GSHPs), also known as geothermal heat pumps (GHPs), are recognized to be outstanding heating, cooling and water heating systems, and have been used since 1998 in the Turkish market. Greenhouses also have important economical potential in Turkey’s agricultural sector. In addition to solar energy gain, greenhouses should be heated during nights and cold days. In order to establish optimum growth conditions in greenhouses, renewable energy sources should be utilized as much as possible. It is expected that effective use of heat pumps with a suitable technology in the modern greenhouses will play a leading role in Turkey in the foreseeable future.The main objective of the present study is to investigate to the performance characteristics of a solar assisted ground-source heat pump greenhouse heating system (SAGSHPGHS) with a 50 m vertical 1 × 1/4 in. nominal diameter U-bend ground heat exchanger using exergy analysis method. This system was designed and constructed in Solar Energy Institute of Ege University, Izmir, Turkey. The exergy transports between the components and the destructions in each of the components of the SAGSHPGHS are determined for the average measured parameters obtained from the experimental results. Exergetic efficiencies of the system components are determined in an attempt to assess their individual performances and the potential for improvements is also presented. The heating coefficient of performances of the ground-source heat pump unit and the overall system are obtained to be 2.64 and 2.38, respectively, while the exergetic efficiency of the overall system is found to be 67.7%.     

A study on modeling and performance assessment of a heat pump system for utilizing low temperature geothermal resources in buildings

Low and moderate geothermal resources are found in most areas of the world. A very efficient way to heat and air-condition homes and buildings is the utilization of ground source heat pumps (GSHPs), also known as geothermal heat pump (GHPs), to obtain heat energy from low temperature geothermal resources.     

Building signatures: A holistic approach to the evaluation of heating and cooling concepts

A sustainable and environmentally responsible building concept aims at a high workplace comfort, a significantly reduced heating and cooling demand, a high-efficient plant system, and the use of renewable energy sources to condition the built environment. This paper presents a comprehensive analysis of the heating and cooling concepts of 11 low-energy buildings in terms of energy use, efficiency and occupant thermal comfort. All buildings investigated employ environmental energy sources and sinks – such as the ground, ground water, rainwater and the ambient air – in combination with thermo-active building systems. A limited primary energy use of about 100 kWh_prim/(m²_neta) as a target for the complete building service technology (HVAC and lighting) was postulated for all buildings presented. With respect to this premise, a comprehensive long-term monitoring in high time resolution was carried out for two to five years, with an accompanying commissioning of the building performance. Measurements include the useful heating and cooling energy use, auxiliary energy use for the hydraulic system, as well as end and primary energy use, occupant thermal comfort and local meteorological conditions. A new methodology is proposed for a holistic approach to the evaluation of heating and cooling concepts, which not only considers the occupants thermal comfort, but also the useful energy consumption and the efficiency of the generation, distribution and delivery of heating and cooling energy.     

Opportunities for reversible chillers in office buildings in Europe

Europe with more than 600 millions of square meters of air-conditioned office buildings offers an opportunity to save energy and reduce CO₂ emissions by reconverting chillers into reversible heat pumps in office buildings. One of the questions asked in the framework of the IEA ECBCS Annex 48 is how to assess the energy saving potential and how to identify the most interesting building cases. The methodology proposed here is based on the simulation of office buildings representative of the building stock. The energy consumption has been simulated for different office building types in five European climatic zones on the one hand with boilers for heating and chillers for cooling, and on the other hand with reversible chillers plus back-up boilers. The results of the simulations in terms of energy consumption allow us to assess the primary energy savings and CO₂ emission reduction in Europe by reconverting chillers into reversible heat pumps. The results show that the potential of annual primary energy savings and annual CO₂ emission reduction are about 8 TWh_PE and 3 millions of tons of CO₂ in Europe-15. Even if the temperature level in terminal units can be solved using the cooling coil instead of the heating coil, a back up boiler turns generally out to be required for the coldest days in the year or when simultaneous heating and cooling demands occur.     

An experimental study on the performance of enthalpy recovery system for building applications

In recent years, the attention of researchers has been focused on energy conservation demands due to the environmental impact of energy consumption throughout the built environment and global warming issue. Heat or energy recovery is one of the main energy-efficient systems that has been approved to overcome this problem. However, in conventional heat or energy recovery for building applications, only sensible energy has been recovered and neglecting the latent energy. In this work, enthalpy recovery system has been developed and the performances of sensible and latent energy have been investigated experimentally. The efficiency of close to 66% has been achieved for sensible energy and the latent energy efficiency was nearly 59% gained. Comparison of efficiency with effectiveness-NTU method showed both were in good agreement. Recovered energy was achieved up to 167 W at 3.0 m/s air velocity with 4.3 °C temperature difference.     

An aquifer thermal storage system in a Belgian hospital: Long-term experimental evaluation of energy and cost savings

Over a three years period, an aquifer thermal energy storage system was monitored in combination with a heat pump for heating and cooling of the ventilation air in a Belgian hospital. The installation was one of the first and largest ground source heat pump systems in Belgium. Groundwater flows and temperatures were monitored as well as the energy flows of the heat pumps and the energy demand of the building. The resulting energy balance of the building showed that the primary energy consumption of the heat pump system is 71% lower in comparison with a reference installation based on common gas-fired boilers and water cooling machines. This corresponds to a CO₂-reduction of 1280 ton over the whole measuring period. The overall seasonal performance factor (SPF) for heating was 5.9 while the ATES system delivered cooling at an efficiency factor of 26.1. Furthermore, the economic analysis showed an annual cost reduction of k€ 54 as compared to the reference installation, resulting in a simple payback time of 8.4 years, excluding subsidies.     

Primary energy and comfort performance of ventilation assisted thermo-active building systems in continental climates

This article presents a simulation study comparing the primary energy and comfort performance of ventilation assisted thermo-active building systems (TABS) relative to a conventional all-air (VAV) system in a compact office building featuring good thermal envelope performance, heat recovery, and solar gain control for the continental climate of Omaha, Nebraska with pronounced heating and cooling periods. TABS heating is accomplished using a geothermal heat pump and TABS cooling using a geothermal heat exchanger without an additional vapor compression cycle required. It was found that the coordination of the TABS and VAV systems is crucial, i.e., supply air temperature and active layer temperature setpoints and reset schedules greatly affect the performance of the overall system. The small contribution of TABS in the heating case shows the need for the adaptation of the ventilation system configuration to the TABS system. Annual cooling energy demand for the ventilation assisted TABS is higher than for the pure VAV system, which is due to lower occupied period room operative temperatures and thus a higher comfort provided. While a 4% useful energy penalty for the combined TABS/VAV was recorded, the VAV case requires 20% more delivered energy than the TABS case because of the displacement of compressor driven coil loads with low-exergy cooling through the ground heat exchanger in the TABS case. A primary energy intensity of 189 kWh/m² a was recorded for the TABS case; in contrast, the conventional all-air (VAV) equipped building incurs a primary energy intensity of 229 kWh/m²a, which represents a penalty of 20%. Clear advantages of the TABS approach can be observed with respect to thermal comfort: during summer cooling periods, the mean radiant temperature of the TABS case is on average 2 K below that of the VAV case. Moreover, the VAV system is associated with a fairly constant predicted mean vote (PMV) value of 0.75, which is quite warm, while the TABS equipped system reveals an average of 0.56, which results in only 12% instead of 17% of people dissatisfied. Based on these results, ventilation assisted thermo-active cooling systems appear to be a very promising alternative to conventional all-air systems offering both significant primary energy as well as thermal comfort advantages provided the TABS is mated with low-exergy heating and cooling sources.     

Instrumentation strategies for energy conservation in broiler barns with ventilation air solar pre-heaters

At the present consumption rate, world fossil-fuel reserves are expected to be depleted by 2050 unless their consumption is optimized and supplemented with renewable energy sources. The objective of this project was to evaluate the performance of a simple data acquisition system installed to conduct an energy balance and identify energy saving strategies in two commercial broilers barns with ventilation air solar pre-heaters. Located near Montreal, Canada, the two identical barns were instrumented for inside and outside air conditions, ventilation rate and energy recovery by the solar air pre-heaters. Whereas the temperature, relative humidity and radiation sensors were reliable, inside air temperature stratification complicated energy balance analyses and broiler heat production rate calculations. Lack of room air mixing resulted in the loss of 25 and 15% of the generated heater load and recovered solar energy. The proper monitoring of all environmental conditions required their measurement every 5 rather than 20 min. Instead of using a data transmission service found to be unreliable in rural areas, all data loggers were downloaded onto a portable computer every 45 days during regular instrument maintenance. Accordingly, room air mixing is recommended to facilitate energy balance studies and improve the efficient use of heating energies.     

Arsenic accumulation in irrigated agricultural soils in Northern Greece

The accumulation of arsenic in soils and food crops due to the use of arsenic contaminated groundwater for irrigation has created worldwide concern. In the Chalkidiki prefecture in Northern Greece, groundwater As reach levels above 1000 μg/L within the Nea Triglia geothermal area. While this groundwater is no longer used for drinking, it represents the sole source for irrigation.This paper provides a first assessment of the spatial extent of As accumulation and of As mobility during rainfall and irrigation periods. Arsenic content in sampled soils ranged from 20 to 513 mg/kg inside to 5-66 mg/kg outside the geothermal area. Around irrigation sprinklers, high As concentrations extended horizontally to distances of at least 1.5 m, and to 50 cm in depth. During simulated rain events in soil columns (pH = 5, 0 μg As/L), accumulated As was quite mobile, resulting in porewater As concentrations of 500-1500 μg/L and exposing plant roots to high As(V) concentrations. In experiments with irrigation water (pH = 7.5, 1500 μg As/L), As was strongly retained (50.5-99.5%) by the majority of the soils. Uncontaminated soils (< 30 mg As/kg) kept soil porewater As concentrations to below 50 μg/L. An estimated retardation factor R_f = 434 for weakly contaminated soil (< 100 mg/kg) indicates good ability to reduce As mobility. Highly contaminated soils (> 500 mg/kg) could not retain any of the added As. Invoked mechanisms affecting As mobility in those soils were adsorption on solid phases such as Fe/Mn-phases and As co-precipitation with Ca. Low As accumulation was found in collected olives (0.3-25 μg/kg in flesh and 0.3-5.6 μg/kg in pits). However, soil arsenic concentrations are frequently elevated to far above recommended levels and arsenic uptake in faster growing plants has to be assessed.     

关于太阳能辅助水源热泵系统联合冬季供暖的研究

随着我国能源的紧缺和环保意识的加强,太阳能、浅层地热能作为可再生能源,越来越受到人们的重视。但无论是太阳能系统,还是水源热泵系统,单独运行时均有一定的局限性,两者联合运行的应用很少。通过实际工程分析,太阳能系统与水源热泵系统可以联合工作,并可达到预期的室内空调温度;对太阳能系统与水源热泵系统联合运行的运行费用做了技术分析,证实这种联合模式节能效果十分明显。     

A parametric study on the exergoeconomic assessment of a vertical ground-coupled (geothermal) heat pump system

An exergoeconomic model of a vertical ground-source heat pump residential heating system presented in this study uses exergy and cost energy mass (EXCEM) methods. The data obtained from a ground-source heat pump (GSHP) residential heating system installed at the Solar Energy Institute, Ege University, Turkey, are utilized for calculations at different reference temperature values in the range 0–25 °C. The performance of the geothermal heat pump residential heating system is evaluated to indicate how exergoecomic parameter values change with system. We also undertake a parametric study to investigate how varying reference temperatures will affect the exergoeconomic analysis of the GSHP system. A correlation between the ratio of thermodynamic loss rate to capital cost and reference state temperature is developed.     

Development and experimental validation of a high-temperature heat pump for heat recovery and building heating

The performance of a high-temperature heat pump unit using geothermal water for heat recovery in buildings is experimentally evaluated. The unit consists of a twin-screw refrigeration compressor, a condenser, an evaporator and an oil cooling system. The effect of the cooled oil temperature on the performance of the heat pump unit is experimentally investigated. Results show that the unit stably produces outlet hot water at a constant temperature of 85 °C and performs well in a wide range of high-temperature conditions with a high energy efficiency ratio. The results also indicate that the key to improving the performance of a high-temperature heat pump unit often depend on the selection of proper cooled oil temperature. The optimum cooled oil temperature is 50-65 °C when the condensing temperature is above 70 °C. At these temperatures, the oil cooling system can increase the energy efficiency ratio of the heat pump by 6.3%.     

Performance and sustainability assessment of energy options for building HVAC applications

In this study, a building with a volume of 351 m³ and a net floor area of 117 m² is considered as a case study with the indoor and exterior air temperatures of 20 and 0 °C, respectively. For the heating applications, four options are studied with (1) a heat pump, (2) a condensing boiler, (3) a conventional boiler and (4) a solar collector, which are driven by renewable and non-renewable energy sources. An energy and exergy analysis is employed to assess their performances and compare them through energy and exergy efficiencies and sustainability index. Energy and exergy flows are investigated and illustrated. Also, the energetic and exergetic renewability ratios are utilized here along with sustainability index. The results show that overall exergy efficiencies of heat pump, condensing boiler, conventional boiler and solar heating systems are found to be 3.66, 3.31, 2.91, and 12.64%, while the sustainability index values for the four cases considered are calculated to be 1.039, 1.034, 1.030 and 1.144, respectively. So, solar collector-based heating system gives the highest efficiency and sustainability index values.     

Application range of thermally activated building systems tabs

This paper presents application range and functionality of thermally activated building systems (tabs). Tabs are increasingly used for energy efficient and economical cooling and heating of commercial buildings. Thereby, the building structure is used as thermal storage allowing the use of renewable energy sources. Based on a simulation study for a typical office building the aspects of thermal comfort, maximum permissible heat gains in the room and the re-cooling of the building mass are analysed. It is shown that depending on the maximum permissible daily room temperature amplitude with tabs typical heat gain profiles with peak loads up to around 50 W/m² floor area can be managed. However, the transitional (mid-season) periods with already high solar gains and still restricted comfort range, in most cases will be decisive for the dimensioning of tabs, thus limiting maximum loads to lower values. The results also show that processes on the room side are almost unaffected from the processes on the supply side. In the cooling case, this allows for the re-cooling period of the fabric being extended to 24 h a day with accordingly “high” supply temperatures and peak load reductions of up to 50%. The results given may serve as orientation guide whether a tabs may be applicable in a specific building, and provides relevant parameters for the dimensioning of tabs.