Energy storage is an important technology for managing load and energy consumption
At the beginning of May, at the initiative of the KPT (the Technology Transfer Committee, Danube Chapter, which includes Slovenia) the ASHRAE organisation in cooperation with the KGH SMEITS and the Engineering Academy of Serbia organised a seminar entitled Ice Banks in the Era of Sustainability. The lecture was given by W. P. Bahnfleth from the Department of Architectural Engineering at the Pennsylvania State University, who explained a few interesting facts about ice banks.
Lately, one often encounters the term sustainable development, which was defined by the United Nations (Our Common Future 1987, United Nations, Brountkand Commission) as follows: “Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.”
Cold Energy Storage Units
The last two decades of the 20th century were significant for the advancement of the use of TES systems (Thermal Energy Storage) in the USA as well as Europe. In the field of air handling, cold energy storage units (ice banks) were one of the key technologies in the programme for managing energy and energy systems by consumers. Gradually, as the trend of designing economical systems grew and focused on designing sustainably suitable systems, the question arose of whether cold energy storage (CES) - ice banks could be used to an advantage. Most significantly, there is the question of whether cold energy storage can affect the consumption of primary energy, the CES economy without encouragement and the role of CES in achieving net zero energy buildings.
Cold Energy Storage:
- is the generation of cooling energy at a certain time that is used at a different time
- reduced peak load
- increased utilization factor
The so called “load factor” (LF) indicates what the utilization of our cooling system is. The higher the LF, the smaller the system and the higher the system’s effectiveness. CES increases the LF, at the consumer’s side as well as in the electricity grid. The typical load factors (LF) vary depending on the building type and, at the consumer’s side, amount to:
- 60 to 80 per cent industry,
- 40 to 60 per cent institutions,
- 25 to 35 per cent commercial buildings.
If the load factor is examined on the side of the electricity production/grid, the load factors are low, approximately 50 to 60 per cent, and by raising the LF on the consumer’s side, the LF on the side of the electricity supplier is also raised.
Advantages of CES
Besides the known advantages of the CES (cold energy storage) system and the lower operating costs of the system, the advantages also include lower costs of investments into parts of the systems (smaller chillers, smaller pipelines, smaller cooling towers). An often overlooked advantage is also the reduced electrical power input of the system, which affects both the investment costs and the operating costs (lower flat-rate for lower power input). The CES system also enables a different design and engineering of the system, and lower costs can be ensured by a low temperature system (+1 to +5 degrees Celsius) and the increase of dT on the side of water and air.
However, there is still the question of how “green” and sustainable CES technology is. It is necessary to evaluate and identify the potential of CES in terms of “green” and sustainable technology.
CES can be a sustainable technology in several respects: energy consumption (site energy) and energy generation (source energy).
By producing ice in the CES, the evaporation temperature is lowered, but in combination with a lower condensation temperature (cooler night air) and low-temperature system, a positive effect can be achieved. The utilization rate and the related savings of a system with CES compared to a system without it on the consumer’s side results in up to 10.3 per cent less electricity consumption of the chiller in the CES system, and also 21.3 per cent less electricity consumption when filling the CES system compared to a system without CES.
Thus, by monitoring various types of buildings before installing the CES system and after the results showed an average energy savings of 15 per cent (ranging from 5 to 44 per cent).
Also interesting is the impact CES has on improved utilization rates on the side of electricity generation, which is indirect as it affects the constant consumption of the electrical energy. Thus generation in hydroelectric power plants (HPP), nuclear power plants (NPP), thermal power plants (TPP), gas-fired power plants (GPP) as well as generation based on renewable sources (solar energy, wind energy, tide etc.) is performed in a favourable band or when the renewable source is available. In this way, on the electricity generation side, it is possible to achieve savings similar to the savings on the consumer’s side, depending of course on the type of electricity generation.
It is up to us to use CES in practice
The conclusion that arose from study and years of research into systems with and without CES is that energy storage is an important technology for managing load and energy consumption. If suitably applied, energy storage can contribute to sustainability in several respects. Cold energy storage is not only financially/economically efficient but is also energy efficient: lower electricity consumption and the related positive effects in terms of a “green” sustainable technology.
The challenge we have to overcome is to understand the current and new technologies in terms of sustainable development and to correctly use them in practice.