• Energy Research
• 2016-2025close

Abstract The use of pre-set thermostatic radiator valves (TRVs) contributes to the reduction of energy consumption and the increase of the energy efficiency of the existing heating systems in buildings. However, there are limited long-term experimental studies that document the level of energy savings achieved by the use of TRVs, quantified for three different options of their utilisation. Long-term field data were collected over several heating seasons from nine existing multifamily residential buildings organized into three groups characterized by different modernization activities using TRVs. The first group includes the cases where the buildings are equipped with TRVs without hydraulic balance of the heating system with pre-set TRVs; the second group encompasses buildings that were already equipped with TRVs and then a hydraulic balancing of the heating system was performed by means of a pre-set; finally, the third group of buildings considers the simultaneous installation of TRVs and hydraulic balancing of the heating system using pre-set TRVs. The energy savings ranged between 7.1% and 23.3%, depending on the range of modernization activities using TRVs with or without hydraulic balance. The payback time was less than 2.5 heating seasons in all cases.

Increasing the level of energy efficiency and using renewable energy sources in the design and existing buildings is an important aspect in minimizing the carbon dioxide emissions and mitigating the climate changes. One of such solutions may be the application of a heating system using residential thermal stations (RTSs) for heating and hot water preparation individually in the premises of a given building. The main purpose of this paper was to analyze long-term filed research results on the energy consumption and efficiency of heating systems in a dormitory (building B1) and two multifamily buildings (building B2 and B3) equipped with residential thermal stations (RTSs) that are used for supplying individual dwellings with heat, as well as hot and cold water. An additional aspect of the analysis is a presentation of the structure of total energy consumption for particular purposes in the analyzed buildings and the possibilities to increase the share of renewable energy sources using solar thermal collectors for supporting the analyzed heating system.

Nowadays, the attention of designers and service providers is especially focused on energy efficiency and integration of renewable energy sources (RES). However, the knowledge on smart devices and automated, easily applicable algorithms for optimizing heating consumption by effectively taking advantage of solar heat gains, while avoiding overheating, is limited. This paper presents a simple method for taking into account the influence of solar heat gains in the form of solar radiation for the purposes of forecasting or controlling thermal power for heating of buildings. On the basis of field research carried out for seven buildings (five residential buildings and two public buildings) during one heating season, it was noticed that it was justified to properly narrow down the input data range included in the building energy model calculations in order to obtain a higher accuracy of calculations. In order to minimize the impact of other external factors (in particular wind speed) affecting the heat consumption for heating purposes, it was recommended to consider the data range only at wind speeds below 3 m/s. On the other hand, in order to minimize the impact of internal factors (in particular the impact of users), it was suggested to further narrow down the scope of the input data to an hour (e.g., 10–14 in multi-family residential buildings). During these hours, the impact on users was minimized as most of them were outside the building.

Abstract The energy efficiency of existing buildings may be increased by using new control techniques of their heating systems, especially if such methods are validated and easy to install. Hence, short-term forecasting of heat power demand is needed, in order to optimize their operation. This work presents a simple, new method of short-term forecasting of heat power for space heating, which may be easily applied in existing buildings. The method is first presented and then validated with two case studies, a multifamily building and a school, using hourly data from three heating seasons. It was found that beyond the outdoor meteorological parameters the accuracy of the method is improved by including the equivalent indoor temperature as the parameter related to the effect of the building occupant behavior. Accordingly, the resulting mean absolute percentage error of the predicted heat demand using the proposed prediction method was 3.2% and 12.0% for the two buildings. Compared to a simple model of the heat poser demand that is based only on the outdoor temperature error was lower by 61.4% and 43.2% for two buildings respectively. In addition, five profiles of equivalent indoor temperature were proposed in order to select the most accurate one for a specific building. This method may be also used in the process of predictive control of heating systems, because the external and internal parameters are measurable and predictable, which will contribute to more energy efficient systems in existing and new buildings.

Abstract Smart control of energy supply to the existing buildings may increase their energy efficiency. However, to the best of the authors’ knowledge, there are no simple, general, automated, widely applicable and accurate methods for the creation of energy model of the building, which may be used to calculate the actual energy consumption of a heating system or for their prediction. This work presents a new simplified method for generating the energy characteristics of buildings and their heating systems, without the influence of occupants. The method requires as input only the actual heat supplied to the heating system and the local outdoor weather conditions (i.e. temperature, wind speed and solar insolation) of a building. The output is a building energy model in terms of an equivalent outdoor temperature. It was found that when determining the correction due to the wind, the data from the night hours (e.g. from 11.00 p.m. to 4.00 a.m.) should be used in order to exclude the impact of solar radiation and minimize the interaction of users. On the other hand, the correction due to the influence of solar radiation should be obtained using data with low wind speeds and time periods from 10.00 a.m. to 2.00 p.m. on weekdays for residential buildings or from 10.00 a.m. to 2.00 p.m. on the weekend for public buildings in order to minimize disruptive effects of wind speed and the impacts from occupants. This method may be used to generate a simple building energy model and to accurately determine the duration and the amount of heat power supplied to a building for space heating, for periods when the impact of occupants and other internal heat gains are kept to a minimum.

Abstract The application of regulation valves in new and existing buildings allows for proper hydraulic balance of the heating system and in this way it may increase the energy efficiency of heating installation. Unfortunately, to the best of authors’ knowledge, there are no long-term field studies that present the level of energy savings achieved by means of commonly used valves in engineering practice, such as thermostatic radiator valves (TRVs), under risers differential pressure control valves (DPCVs), pressure independent balancing radiator valves (PIBRVs), as well as a combination of them. This article presents the results of field research conducted during 6 heating seasons in 16 multifamily buildings assigned to four groups, depending on the type of heating system modernization. The buildings in the first group had existing on-off valves located near the radiator that were replaced with TRVs, and hydraulic balancing of the heating system was performed by means of a pre-set. The second group of buildings was characterized by the installation of DPCVs under the risers of heating installation which was already equipped with TRVs; the third group encompasses the buildings with simultaneous installation of TRVs and DPCVs. The final group consisted of buildings in which the existing TRVs were replaced by pressure independent balancing radiator valves. The energy savings were calculated based on average heat consumption before and after modernization and ranged between 14.6% and 23.8%, depending on the type of the installed valves or their combination. The calculated payback time for the analyzed modernization actions was in the range between 1.4 and 4.9 heating seasons.

Abstract Energy consumption for domestic hot water (DHW) preparation is one of the main components of the energy balance of the existing and newly designed buildings. However, based on the number of existing buildings and the related opportunities to improve energy efficiency, an important issue is to propose effective and low cost methods that allow to reduce the heat consumption in existing domestic hot water systems and are fast in the implementation. This article presents the results of an experimental research conducted in 12 objects (9 multifamily buildings and 3 thermal substations) assigned to three groups (A, B and C), depending on the analyzed feature of the domestic hot water system. The objects in the group A were analyzed in detail (each 1 h during one full heating season) in order to clearly show the amount of the heat used for circulation of hot water. The group B of objects characterized by the installation of temperature control valves (TCVs) under the risers of circulation installation. The third group consisted of the objects in which the temperature of hot water was decreased during the night hours. The objects from group B and C were analyzed over 8 years. The share of heat losses associated with the circulation of hot water in the total heat consumption supplied for its preparation was in the range from 56.7% to 70.5% for the Group A objects. On the other hand, the energy savings were calculated using different methodologies and for the recommended one they ranged from 8.5% to 49.5% for group B objects and from 6.0% to 14.4% for group C objects.

Abstract Thermal renovation of existing buildings is one of the most popular actions to decrease the energy consumption for heating and cooling. However, to the best of the authors’ knowledge, there are no long-term field studies that present the influence of hydraulic rebalancing of the heating system after the thermal renovation of the building’s envelope on the level of achieving the calculated energy savings. This work presents the results from a field study that collected data on actual operational energy over several heating seasons, from 11 similar multifamily buildings in Poland. All buildings were thermally renovated by insulating their envelope, while for some of them the works were completed by a hydraulic rebalance of their heating system. The modernization activities were implemented with a different sequence. For another group of buildings, the hydraulic balancing of the heating system was not performed after the envelope thermal renovation. This offered an excellent opportunity to compare the actual energy performance of the renovated buildings and quantify the achieved energy savings resulting from different practices. Energy audits were performed in all buildings in order to calculate the energy use of the buildings before and after the renovations. These estimates were then compared with the actual energy savings from the monitored energy use for all renovated buildings. Accordingly, the actual energy savings range between 8.8% and 74.8% of calculated energy savings, depending on the different renovations. The actual payback time for the analysed modernization actions was longer than the calculated one, ranging between 3.1 and 104.8 heating seasons.

AbstractThis work presents the results of experimental studies on the energy performance of an evacuated solar collector, heat pipe type, consisting of 24 tubes, over the period of 2 months. The solar collector with a gross area of 3.9 m2 is part the solar hot water test system located in Lublin (Poland). The effect of the weather conditions and operating parameters on the thermal and exergy efficiencies of the evacuated tube solar collector has been defined. The solar irradiation per month for July amounted to 80 kWh/m2, and for August, it equalled 112.8 kWh/m2. The average thermal gain was found to be in July 163 W/m2 and in August 145 W/m2, respectively. For the considered study period, the average value of energy yield in the solar collector was obtained at the level of 4.28 MJ/(m2·d). The average monthly energy efficiencies of the solar collector in July and August were 45.3% and 32.9%, respectively, while the average monthly exergy efficiencies reached 2.62% and 2.15%, respectively. Increasing the wind speed to 0.86 m/s decreases the thermal efficiency and the exergy efficiency by 67% and 41%, respectively.