Change-over natural and mechanical ventilation system energy consumption in single-family buildings

The parameters of the outside air in Poland cause that in winter it is reasonable to use a mechanical ventilation equipped with a heat recovery exchanger. The time of spring, autumn, summer evenings and nights are often characterized by the parameters of the air, which allow for a natural ventilation and reduce the electricity consumption. The article presents the possibilities of energy consumption reduction for three energy standards of buildings located in Poland, ventilated by a change–over hybrid system. The analysis was prepared on the assumption that the air–to–water heat pump is the heat source for the buildings

Energy balancing in ground heat exchanger for heat pump systems – a case study with simulations

The negative impact of systems based on fossil fuel on the environment and the desire to promote sustainable development is increasingly encouraging building owners to invest in renewable energy sources. One of the possibilities of using a renewable energy source located in shallow soil layers is a brine-to-water heat pump. Ground energy can be used for both heating and cooling buildings. This article presents the advantages of balancing the supply and energy consumption from the ground for the large heat pump systems. Authors presented a case study and the simulation of the system operation with different cooling load share vs heating load. This was done on the basis of the analysis of data from several years of measurements from the actual installation as well as the simulation in Earth Energy Designer software. The results of the simulations shows that the most advantageous strategy for the operation of the analysed installation is to provide 50 to 75% of the cooling load in relation to the heating load

The influence of thermal load profile of building on the air/water heat pump efficiency simulation

In this paper the authors analysed the impact of the calculation method of the partial load conditions and the accuracy of the energy demand profile on the simulation results of the air/water heat pump operation supplying the heating system. All the analyses results were compared to the results acquired for the real installation of the air/water heat pump located in Poland. The authors assessed the inaccuracy of the unit’s efficiency estimation resulting from the simplified thermal load profile of the air/water heat pump. It has been showed that using the monthly energy demand as the input data gives satisfactory results. Inaccuracy of the monthly simulation results in relation to simulations carried out on the actual hourly energy demand by no more than 7% is acceptable. On average, this deterioration did not exceed 3%

Quasi-dynamic model of the energy efficiency for an air-to-water heat pump

The energy efficiency of air-to-water heat pump operating in an actual heating installation depends on many factors. In order to create a reliable model of the unit, it is necessary to include as many of them as possible. Unfortunately, the most common data provided by heat pump manufacturers are based on tests performed in accordance with the EN 14511 standard [1]. These tests are performed in steady-state conditions and do not provide reliable information on the impact of dynamic effects on the energy efficiency of the device. The solution may be the tests in quasi-dynamic conditions. The article presents the possibility of creating the characteristics of an air-to-water heat pumps based on operational data. The accuracy of the created model has been compared with the characteristics resulting from measurements in steady state conditions. It has been confirmed that dynamic test data, after proper selection, will allow to determine the characteristics of repeatable parameters and this can be an alternative to tests performed in fixed conditions

Quasi-dynamic model of the energy efficiency degradation coefficient for an air-to-water heat pump

Operating in part-load conditions significantly affects the energy efficiency of the air-to-water heat pumps. The currently used method of testing the devices does not provide the necessary data for estimating the degradation of the device’s efficiency in part-load operating mode. The value of the degradation coefficient Cc = 0.9 adopted in accordance with the EN 14825 standard is generally used. However, this value often does not reflect the actual degree of the COP reduction. Hence the new quasi-dynamic model and the calculation approach to the degradation coefficient were proposed. The model reflects the real and overall reduction between the full and part-load COP, not only the energy consumption in the stand-by mode. The estimation was made using the field measurement data of the air-to-water heat pump supplying heat to the low temperature installation. It has been proved that the determination of the main parameter is possible using a relatively small amount of data without losing an accuracy

The impact of the work under partial load on the energy efficiency of an air-to-water heat pump

The energy efficiency of air-to-water heat pumps used for central heating depends significantly on the correctness of the device choice. Under given climate conditions, the temperature of the bivalent point defines the amount of energy supplied from an additional source, usually an electric heater, in periods when the power of the heat pump is too low. Commonly overlooked fact is that excess capacity is also unfavourable and has significant, negative impact on the energy efficiency of such a system. In the article, basing on the measurement data of the real installation of the air-to-water heat pump, a significant decrease in the energy efficiency of the device during periods of low energy demand was shown. The average monthly value of SCOP in the warm months was similar or even lower than in the winter months. The reason of this is the operation of the device under partial load. Although the values of COP were very high in short periods of operation, frequent switching on and off of the heat pump reduced its energy efficiency. Also, the length of operation in stand-by mode, i.e. the length of the periods between successive heating cycles, had negative influence on energy efficiency

Analysis of the ground-source heat pump operation with various heat-carrier fluids in the lower heat source

In the paper the analysis of the operation of ground-source heat pump with various heat-carrier fluids circulating in boreholes was made. The authors considered several aspects related to the heat-carrier fluid selection (freezing point, heat transfer capabilities, toxicity, pumping costs). The lower heat source analysis had been performed in Earth Energy Designer (EED) software. The analyses’ results reliability was assured by the ground-source model calibration made basing on the measurement data from on-site test stand. Analyses were performed for four heat-carrier fluids (two kinds of propylene glycol solutions – standard and with lower viscosity, water and nanofluid (water + CuO)) and in four variants of thermal load (design and actual loads both with and without active regeneration). It had been concluded that temperature of none of the fluids would drop under 0°C if the system was operated under actual thermal load. For design thermal load there would be a risk of the water freezing but it may be minimized by active regeneration or lower heat source enlargement by 20% (in analyzed case) each rising the mean fluid temperature by around 1.0-1.5 K. The use of other fluid in place of standard propylene glycol solution will give pumping energy savings

Domestic hot water consumption in multi-apartment buildings

The article presents the analysis of the hot water consumption in apartment buildings. This study was conducted basing on the data gathered from 626 apartments during two following years. By statistical analysis of the collected data, the correlation between the DHW consumption and both the size of the apartments and the number of occupants in the dwellings was evaluated. The dependencies between the hot water consumption and these two parameters were calculated. The results were compared to the data available in the literature. The article lists the areas of the greatest inaccuracies in the calculations basing on the available indicators and proposes an alternative method that corrects them. The results were used to develop a calculation model for daily hot water usage in multi-apartment buildings

Analysis of the ground-source heat pump operation with various heat-carrier fluids in the lower heat source

In the paper the analysis of the operation of ground-source heat pump with various heat-carrier fluids circulating in boreholes was made. The authors considered several aspects related to the heat-carrier fluid selection (freezing point, heat transfer capabilities, toxicity, pumping costs). The lower heat source analysis had been performed in Earth Energy Designer (EED) software. The analyses’ results reliability was assured by the ground-source model calibration made basing on the measurement data from on-site test stand. Analyses were performed for four heat-carrier fluids (two kinds of propylene glycol solutions – standard and with lower viscosity, water and nanofluid (water + CuO)) and in four variants of thermal load (design and actual loads both with and without active regeneration). It had been concluded that temperature of none of the fluids would drop under 0°C if the system was operated under actual thermal load. For design thermal load there would be a risk of the water freezing but it may be minimized by active regeneration or lower heat source enlargement by 20% (in analyzed case) each rising the mean fluid temperature by around 1.0-1.5 K. The use of other fluid in place of standard propylene glycol solution will give pumping energy savings

Detailed Analysis of the Causes of the Energy Performance Gap Using the Example of Apartments in Historical Buildings in Wroclaw (Poland)

This paper presents the results of measuring and calculating the final energy consumption for heating and domestic hot water preparation in six apartments located in pre-war tenement houses in Wroclaw (Poland). The calculations were carried out based on energy models of dwellings calibrated with measurement data. Calculation variants were characterized by seven internal parameters (indoor air temperature, heat transfer coefficient by transmission through the internal partition, internal heat gains, air exchange multiplicity in the dwelling, domestic hot water consumption, and domestic hot water temperature and cold water temperature) and two external parameters (outdoor air temperature and insolation). By comparing calculations with measurements, the energy performance gap (EPG) values associated with each parameter were determined. The presented results indicate how much of the differences could be attributed to weather conditions and how much to other factors. It is quite common for the influence of some factors to cancel out the influence of others. Identifying and understanding the real causes of the energy gap may allow for the proposal of better retrofitting solutions or appropriate financial support to households at risk of energy poverty. It is important to note that only in-depth interviews with residents and measurements, such as those carried out in this case, allow such situations to be identified in detail