Space Heating In Cold Climates Research Articles

Analysis and comparison of innovative PEMFC systems coupled with an ASHP for space heating in cold climates

In this study, two integrated systems are proposed and analysed: an air source heat pump (ASHP) coupled with either high-temperature proton exchange membrane fuel cells (HT-PEMFCs) or low-temperature proton exchange membrane fuel cells (LT-PEMFCs), where the exhaust gases from the PEMFCs are used to increase the external air temperature to the evaporator of the ASHP. The objective is to understand how the proposed systems behave in a cold climate region and determine which of the systems is better to couple with an ASHP for domestic space heating purposes in a cold climate. The novelty of the work lies in the idea of recovering heat from the exhaust gases from the fuel reformer and PEMFCs and mixing them with external air, before sending it to the ASHP as the inlet air. Grey-box models are employed to model the PEMFCs, whereas the hypothesis of the chemical equilibrium of reacting species is considered in the reformer model. Steady state analyses are considered to understand the performances of the proposed systems compared to two different types of furnaces: high-efficiency and mid-efficiency ones. The results indicate that the HT-PEMFCs are the best for the case studied here, with performances up to 100% greater than the mid-efficiency furnace and up to 63% more than the high-efficiency one. A scenario analysis on a simple pay back is also carried out, and the return on the investment costs in the 2024 scenario is about 24 years if compared to the high efficiency furnace and 14 if compared to the mid-efficiency one, whereas the corresponding numbers are 19 and 11 years, respectively, for the 2030 scenario.

Modified transcritical CO2 heat pump system with new water flow configuration for residential space heating

Utilizing air-source heat pumps for residential space heating in cold climates is an important measure for environmental protection and energy conservation. In this paper, a new water flow configuration for water-heating process is proposed for transcritical CO2 heat pump combined with a dedicated mechanical subcooling (DMS) subsystem. In the modified system, the conventional parallel water flow configuration is changed to a new series water flow configuration, in which the CO2 gas cooler is separated into two parts with the condenser of DMS subsystem in the middle. The water is sequentially heated by CO2 gas cooler 1, condenser of DMS subsystem and CO2 gas cooler 2. Through three-stage heating, the uniformity of refrigerant-water temperature difference field is remarkably improved. The evaluations are conducted from energetic, exergetic and economic perspectives. Firstly, the impact of heat transfer area allocation among the three water-heating heat exchangers on system performance is numerically investigated. The results show that the COP of modified system is 1.6%–7.6% higher than that of the existing system. The greater the temperature difference between supply and return water and the higher the ambient temperature are, the more significantly the COP increases. By evaluating heating seasonal performance in three typical cities, energy efficiency of the modified system is increased by 2.4%–6.5%. Besides, the exergy efficiency is also improved by 2.1%–6.6%. As for life cycle cost, the proposed system can save up to 3.7% investment in terms of annual operation.

Performance analysis of indirect-expansion solar assisted heat pump using CO2 as refrigerant for space heating in cold climate

The indirect-expansion solar assisted heat pump (SAHP) is one of the main configurations for SAHP systems. Previous work on this configuration has focused only on one-stage heat pump cycles using traditional refrigerants, which will be phased out in the future. In addition, one-stage heat pumps may not work properly in cold climate regions. To evaluate the performance and understand the potential of indirect-expansion SAHPs using CO2 as a refrigerant for space heating in cold climates, models of an indirect-expansion SAHP with a one-stage transcritical CO2 cycle, with a two-stage transcritical CO2 cycle, and with the presently popular one-stage R410a cycle for space heating in Toronto, Canada were developed using the combined platforms of EES and TRNSYS. Based on these models, the performance variations of the three systems with solar thermal collector area, storage tank volume, and heat pump compressor capacity were simulated, compared, and presented. The comparison of the systems showed that the performance of the two-stage cycle peaked at a much smaller compressor capacity than that of the other cycles – 0.4 m3/h for the two-stage cycle, 0.7 m3/h for the one-stage cycle, and 1.7 m3/h for the R410a cycle. When the three systems operated at the optimal compressor capacity, the free energy ratio (FER) of the two-stage cycle could reach 0.772, which was higher than that of the one-stage cycle by 19.0% and higher than that of the R410a cycle by 11.6% at the given conditions. The potential cost reduction benefits from the smaller compressor and higher FER could make the two-stage cycle more competitive than the other cycles in cold climates.

Design screening and analysis of gas-fired ammonia-based chemisorption heat pumps for space heating in cold climate

Abstract Thermally-driven ammonia-based chemisorption heat pumps (CSHP) have the potential to provide high-efficiency space heating in cold climates. Using the reversible chemical bond between sorbent salt and ammonia, CSHP thermochemically pumps heat from the cold ambient to the end-uses of space heating at 50 °C. The heating coefficient of performance (COP) of a CSHP is largely dependent on the selection of the sorbent salts, cycle configuration, and the system operation. This study uses a thermodynamic model to investigate the performance of six CSHP system configurations, including four single-effect and two double-effect cycles. The feasibility and performance of 121 available NH3/salt reactions are studied for each configuration. The thermal COP of the cycles and the primary energy COP of the gas-fired CSHP systems are evaluated assuming 50 °C supply temperature for building space heating and the optimal system designs are identified. The highest thermal COP for single-effect and double-effect cycles under −25 °C ambient temperatures are predicted to be 1.22 and 1.57, respectively. The corresponding primary energy COPs are above 1.0 and 1.15, which are 30% higher than condensing furnaces and is sustained into the same cold temperatures.

Multi-objective optimisation of a seasonal solar thermal energy storage system for space heating in cold climate

Seasonal solar thermal energy storage (SSTES) system is a promising technology to minimise greenhouse gas emissions (GHGE) by harnessing solar energy for space heating applications. The SSTES system in this study includes double U-tube borehole heat exchanger, ground-coupled heat pump and evacuated tube solar collectors. The aim of this investigation is to optimise the design variables of a SSTES system for space heating in cold climate locations. Six cold climate locations were studied namely: Lukla (Nepal), Dras (India), Sivas (Turkey), Harbin (China), Ulaanbaatar (Mongolia), and Verkhoyansk (Russia). The optimisation variables considered are the total solar collector area and total borehole length. There are three separate optimisation investigations: two single-objective and one multi-objective for the SSTES system. The first investigation is to minimise total life cycle greenhouse gas emissions and the second investigation is to minimise total life cycle cost included cost of GHGE. The third investigation is to minimise both life cycle cost of SSTES system and cost of GHGE (multi objectives). The simulation model was developed using TRNSYS 17 and the Multi-Objective Building Optimisation (MOBO) tool was applied for optimisations. The optimal set of design variables and the corresponding value of the objective function were determined for each single-objective optimisation investigation. Pareto front for each location was also identified for the multi-objective optimisation investigation. The technical and financial performance were also analysed and presented.

Simulated performance of a borehole-coupled heat pump seasonal solar thermal storage system for space heating in cold climate

The performance of a seasonal solar thermal energy storage system for space heating in cold climates was investigated. The system includes a double U-tube vertical borehole thermal energy storage integrated with a ground coupled heat pump and evacuated tube solar collectors. A validated TRNSYS model for six cold climate locations: Lukla, Dras, Sivas, Harbin, Ulaanbaatar and Verkhoyansk was applied. The hourly typical metrological year (TMY) data of each location was used. The house model for each location was based on the typical local dwelling. The annual heating loads per unit floor area (GJ m−2) was found in the range of 0.71–2.59 (1.71, 1.79, 0.71, 1.19, 1.45 and 2.59 for Lukla, Dras, Sivas, Harbin, Ulaanbaatar and Verkhoyansk respectively). The sizes of the system components such as solar collector area, borehole length, number of borehole and heat pump capacity were determined for each location. The analysis covered both heat charging and discharging. It was found that the average ground temperatures were stable in each location with solar charging. However, if the system was not charged by solar energy, the average ground temperatures were decreased over the years. The seasonal compressor heating coefficient of performance coefficient of performance were found to be more than 5.8, that shows the potential benefit of the system. The proposed system could fulfil more than 93% of the space heating demand in all selected locations. The results of the study reveal the potential benefits of utilising seasonal solar thermal energy storage system in cold climate locations.

Optimum compressor cylinder volume ratio for two-stage compression air source heat pump systems

With the outstanding performance potential and excellent modulation capacity, the Two-Stage Air Source Heat Pump (TSAHP) may become a substitute for fossil fuels for space heating in cold climates. In TSAHP, the design cylinder volume ratio is closely related to the evaporating and condensing conditions and will determine the average heating seasonal coefficient of performance (COP¯). In this paper, based on weather data and a two-step optimization approach, a volume-ratio selection method was presented. Eight typical cities in the cold region of North China were selected for demonstrating the impacts of the optimum cylinder volume ratio at different outdoor design temperatures on COP¯. The results show that the appropriate outdoor design temperature is between −4 °C and −8 °C, and the corresponding design cylinder volume ratio is between 2.0 and 2.1. The COP¯ with the volume ratio of 2.0 is 10.3% and 17.6% higher than that with the volume ratio of 3.0.

Potential application of glazed transpired collectors to space heating in cold climates

Although unglazed transpired collectors (UTC) succeed in industrial ventilation applications, solar fraction is very low when they are used in space heating in cold climates due to the lower exit air temperature. Considering the potential for glazed transpired collectors (GTC) using recirculated air for space heating applications in cold climates, a mathematical model is developed for predicting the thermal performance of GTC. Simulation results show that although glazing results in optical loss, it could decrease convective heat loss resulted from high crosswind velocities effectively. For a solar radiation of 400W/m2, an ambient temperature of −10°C, and a suction velocity of 0.01m/s, the exit air temperature of GTC is higher than that of UTC for crosswind velocities exceeding 3.0m/s. By comparison with a conventional flat-plate solar air collector operating under the same conditions, the thermal performance of GTC shows a significant improvement. For a five-storey hotel building located in the severe cold climate zone of China, case study shows that the annual solar fraction of the GTC-based solar air heating system is about 20%, which is two times higher than that of the flat-plate collector-based system and nearly nine times higher than that of the UTC-based system respectively. Hence, an enormous amount of energy will be saved with the application of GTC to space heating in cold climates.

LCC analysis for energy-saving in residential buildings with different types of construction masonry blocks

Space heating in cold climates requires large quantities of heat energy to be spent. Therefore, considerable energy-savings can be obtained using construction wall materials with low thermal conductivity in the buildings. In this study, an economic analysis (LCC analysis) was performed in order to estimate the optimum thickness, saving and pay-back period which minimizes the total cost including the masonry material and the energy consumption costs. The LCC analysis was carried out for external walls of buildings in Afyonkarahisar, Turkey. Considering long term and current outdoor air temperature records, degree-days (DD) values were used, and the variation of annual energy requirement of the building was investigated for various masonry (product) types for per unit area. Masonry products were block elements with one, two, three and four row-hollows, hollow-brick and aerated concrete. As the fuel types, fuel-oil, natural gas, coal and electricity were considered in the analysis. The functional unit of the LCC was the use of 1 m 2 of the building's living area over 50 year's period. As a conclusion, the highest energy-saving was obtained by the use of hollow blocks with 4 rows. Moreover, the most suitable fuels for all climate zones appear to be electricity and fuel-oil. But, the natural gas is a better choice when the atmospheric pollution is an important consideration.

Non-convective roof pond with movable insulation for passive solar space heating in cold climates

A roof pond may be rendered non-convective by increasing the viscosity of its water with suitable thickeners like natural gums or polymers. The thermal performance of such a non-convective roof pond system covered by movable insulation during the night is investigated for passive solar space heating in cold climates. The analysis is based on the solution of the heat conduction equation for temperature distribution in the roof pond system subjected to periodic solar radiation and atmospheric air on one side and in contact with room air at constant temperature (corresponding to air-conditioned rooms) on the other side. The day-to-night change of insulation has been represented by a rectangular step function variation of the heat transfer coefficient at the pond surface. An explicit solution for the temperature distribution satisfying appropriate boundary conditions has been derived to obtain the heat flux entering the room. It is found that the proposed system is quite suitable to provide the heating need in cold climates, and the thermal storage behaviour of this system is much better than a convective roof pond system with movable insulation.

Comparison of 100 per cent solar heated residences using active solar collection systems

Several residences designed with active solar collection systems to provide 100% space heating in cold climates (greater than 3000/sup 0/C - days) are compared. Some of the features desirable in a 100% solar space heated residence are identified, including high energy conservation standards, use of passive gain through proper window orientation, and use of high efficiency collectors. (SPH)