Actual Heat Demand Research Articles

Adjusting heat demands using the operational data of district heating systems

The main objective of this study is to investigate variations and peak values of actual heat demand profiles in a centralized district heating (DH) network. Operational heat data is utilized to discover that almost no weather correlation exists during warm months when supply temperatures exceed 60 °C; thermal inertia of buildings affects their behavior differently in terms of needed space heating; and thermal energy storage (TES) units can be important assets for improving the performance of DH networks. To draw such concluding remarks, two approaches namely scaling design heat demand and the weighted moving average (WMA) are used. Analysis of heat demand profiles reveals that the fourth generation DH (4GDH) shows promise in the Russian context. It is also observed that the discrepancy between the projected and the actual values is 7–14% higher than average, and the variation of temperature in the supply line is 1.5 times that in the return line. Through designing TESs or DH plants using more precise heat demand data, DH operator is able to reduce the energy price by lowering infrastructure costs. By implementing WMA strategies and incorporating advanced control techniques, it is also possible to save 40%–50% energy per year, which results in lower energy fees for the end-users.

Heat demand forecasting in District Heating Network using XGBoost algorithm

Forecasting an hourly heat demand during different periods of district heating network operation is essential to optimize heat production in the CHP plant. The paper presents the heat demand model in the real district heating system with a peak load of 200 MW. The predictive model was developed with the use of the machine learning method based on the historical data. The XGBoost (Extreme Gradient Boosting) algorithm was applied to find the relation between actual heat demand and predictors such as weather data and behavioral parameters like an hour of the day, day of week, and month. The method of model training and evaluating was discussed. The results were assessed by comparing hourly heat demand forecasts with actual values from a measuring system located in the CHP plant. The RMSE and MAPE error for the analysed time period were calculated and then benchmarked with an exponential regression model supplied with ambient air temperature. It was found that the machine learning method allows to obtain more accurate results due to the incorporation of additional predictors. The MAPE and RMSE for the XGBoost model in the day-ahead horizon were 6.9% and 8.7MW, respectively.

A Heat Demand Load Curve Model of the Swiss National Territory

This paper presents a bottom up model simulating the hourly heat demand load curve for space heating and domestic hot water production for Swiss buildings listed in the national building and dwelling register. The model was calibrated on the actual heat demand load curves of several building types and predicts the demand as function of external temperature and solar irradiation. In addition, it includes stochastic deviations to accurately reproduce the aggregated load of large building groups. Using a climatic database covering the whole Swiss territory, the model takes account of the diverse weather conditions and climate types. The aggregated simulated load curve is compared with the measurements from a large district heating network, demonstrating that key indicators such as peak load and ranked loads are very well reproduced. To disseminate the results, a GIS database was setup that estimates the aggregated heat demand load curve for any portion of the Swiss national territory. The proposed approach addresses the challenge of large territorial scale simulation using only limited information available on its building stock. The model can be easily adapted to generate load curves for other EU regions provided the required information is available for the building stock.

Actual energy performance of student housing: case study, benchmarking and performance gap analysis

While recent studies have shown an important gap between design and real energy use of multifamily buildings, this study analyses the energy performance gap for student housing. A very high energy performance (VHEP) student residency was analysed in detail, followed by a comparison of energy and water consumption with student residencies and other dwellings in Geneva. The analysis shows that for this VHEP residency the limit values according to the actual thermal regulations and MINERGIE label are exceeded: actual heat demand is 98 MJ/m2.a for heating (without double-flow ventilation) and 116 MJ/m2.a for hot water while the MINERGIE-index is 137 MJ/m2 (38 kWh/m2.a). Nevertheless, its thermal energy consumption (IDC=224 MJ/m2.a) is similar to other VHEP buildings, and half of Geneva's average values. The study points to factors which highly influence real performance of VHEP buildings and concludes that there is a huge optimisation potential during use phase of a building.

A method of determining the thermal power demand of buildings connected to the district heating system with usage of heat accumulation

The paper presents a new method of determining the thermal power demand of buildings connected to the district heating system, which included the actual heat demand and the possibility of balancing the thermal power using the thermal storage capacity of district heating network and internal heat capacity of buildings. Moreover, the analysis of the effect of incidence of external air temperature and duration of episodes with the lowest outdoor temperatures on the thermal power demand of district heating system was conducted.

Façade-integrated Massive Solar-thermal Collectors Combined with Long-term Underground Heat Storage for Space Heating

This work shows how façades of industrial buildings can be used as a heat source for a heat pump heating system. Opaque sections of the building skin are formed by façade-integrated massive solar-thermal collectors (FMSC) in order to collect solar radiation and heat from the ambient air. By means of a building-integrated long-term storage (BLTS), the heat collected during the summer period is conserved for utilization during the heating season. Depending on the current ambient conditions and the actual heat demand, different operating modes are to be applied: In part load with favorable external conditions the space heating demand is covered by direct use of the FMSC heat output. With rising heat demand and lower heat gain from ambient, heating is accomplished by a heat pump with FMSC or BLTS as heat source. With regard to architectural restrictions, FMSC surfaces have to be operated at temperatures above the dew point, avoiding formation of condensate or frost at the building surface. The performance of the system is modeled by means of TRNSYS, relying to available model types for the system components. The model of the core component, i.e. the FMSC, has been validated by a laboratory measurement. A design study has been carried out for an industrial building with a foot print of 1,300 m2 and an annual heating demand of 82,000 kWh. Key aspect of the investigation is the identification of the most efficient system composition, characterized by the required size of collector area and heat storage volume.

Method for reducing excess heat supply experienced in typical Chinese district heating systems by achieving hydraulic balance and improving indoor air temperature control at the building level

A common problem with Chinese district heating systems is that they supply more heat than the actual heat demand. The reason for this excess heat supply is the general failure to use control devices to adjust the indoor temperature and flow in the building heating systems in accordance with the actual heat demand. This results in 15–30% of the total supplied heat being lost. This paper proposes an integrated approach that aims to reduce the excess heat loss by introducing pre-set thermostatic radiator valves combined with automatic balancing valves. Those devices establish hydraulic balance, and stabilize indoor temperatures. The feasibility and the energy consumption reduction of this approach were verified by means of simulation and a field test. By moving the system from centrally planned heat delivery to demand-driven heat delivery, excess heat loss can be significantly reduced. Results show that once the hydraulic balance is achieved and indoor temperatures are controlled with this integrated approach, 17% heat savings and 42.8% pump electricity savings can be achieved. The energy savings will also have a positive environmental effect with seasonal reductions of 11 kg CO2, 0.1 kg SO2, and 0.03 kg NOx per heating square meter for a typical case in Harbin.

OPTIMAL DIMENSION OF A RESERVOIR FOR TEMPORARY STORAGE OF HEAT SURPLUSES FROM COMBINED HEAT AND POWER IN ARTIFICIAL LIGHTED GREENHOUSES

Producing electricity with on-site combined heat and power, to feed artificial lighting implies the production of large amounts of waste heat. Quite often the heat production exceeds the actual heat demand of the greenhouse. Thus combined heat and power induces heat surpluses. However, in a large span of time (yearround), reject heat from combined heat and power is less than the heat demand of an intensive utilized greenhouse. Thus, periods with surpluses must be considered temporary and storage of these surpluses for future use is advantageous. Another potential source of heat surpluses is the boiler, when its exhaust gases are used for carbondioxide enrichment of the greenhouse air. Carbondioxide addition is requested during the day, whereas the heat, associated with this way of CO2-production is mostly not required during the day. A buffer can store the heat produced during the day for use during the night. To determine the energy consumption and canopy growth of a greenhouse with artificial lighting, combined heat and power, CO2-enrichment of the canopy ambient and a heat storage facility a simulation model was built. In this paper the energy saving obtained by heat storage facilities with different dimensions is discussed. Comparison of the benefits with the costs related to the storage facility gives a possibility to determine an optimal storage capacity. It will be demonstrated that the amount of carbondioxide addition has a significant effect on the optimum storage capacity.