Energy flexible heat system for buildings by integration of in-house heat stations
MetadataShow full item record
The objective of the work was to develop a method for calculation of potential energy and cost saving by better utilization of available excess power and energy capacity in existing heat stations. Better utilization of available excess power and energy capacity is done by integrating existing heat stations into one merged heating system. The results from the calculations can then be used in cost-benefit analysis to investigate the profitability of such measures. Basis for the study was a report about installed over capacity in a group of heat stations in Narvik, Norway. This report concluded that it could be possible to integrate and coordinate nearby buildings into one larger system. It was assumed that by doing so the installed capacity could be utilized in a more efficient manner by operating a single boiler, or combination of boilers, with installed capacity matched to the current power demand. Such alteration between available boilers was assumed would give less intermittent boiler operations. A part of the work investigated the influence of heat loss in distribution systems on the overall boiler efficiency. The results showed that arranging distribution in such way that the heat loss can be utilized can have significantly impact on the resulting energy consumption. When calculating the need for purchased energy based on the net energy demand in the building, the calculation routine is conducted "backwards" compared to ordinary energy calculations. For such reversed calculations it is necessary to know the boilers efficiency. The efficiency can be determined by experience or rule of thumb, but it can also be calculated. These two methods are compared. The result demonstrated the importance of using calculated real efficiency when selecting boilers in an energy flexible heat system. The results from the work investigating energy and costs influence of oversized boilers were unambiguous. Compared to situations where the boilers were dimensioned according to prevailing design techniques, oversized boilers lead to more intermittent operation with decreased boiler efficiency as a result. From the study it is evident that correct dimensioning of boilers is of outmost importance when engineering new heat systems. For 50% oversized system, the excess energy consumption was in the range of 5-30% depending on control regime before integration. Resulting excess energy cost was between 5% and 60%. Multiple buildings with in-house heat stations were modeled in the MATLAB/Simulink environment. The goal of the study was to investigate the hypothesis that integration of heat stations would result in reduced energy consumption and cost. A boiler selection routine for multiple boiler operations was developed and implemented in the systems. Boiler configurations were selected based on lowest running cost for each hour. Based on the energy requirement in each building, the need for purchased energy was calculated. These systems were individually simulated under various climatic conditions for one consecutive year with regard to energy consumption and energy cost. Four versions, from 0-60% oversized, of the heat stations were simulated for each building. Later the in-house heat stations were integrated into one larger energy flexible heat system, and the simulations were repeated. The results were then compared. The same mechanism as observed in previous work was observed. The integration led to more efficient operations with reduced energy consumption and cost as a result. Based on the work it should be clear that there is a potential for energy and cost savings by integration of multiple in-house heat stations into one energy flexible heat system. Buildings and heat stations come in numerous variations, configurations and under various climatic conditions. It has therefore not been possible to find general relationships that explain the savings. All situations/configurations must be evaluated separately. However, all case studies indicated that integration of heat stations is both feasible and profitable. Rate of savings depend to a large degree on how many buildings are being integrated and types of energy equipment installed. The results from the case studies with conventional boilers indicate an energy savings potential in the range of 5-13%, and cost savings between 12-21%.