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Kuosa M.,Aalto University | Aalto M.,Aalto University | El Haj Assad M.,Australian College of Kuwait | Makila T.,Energianhallinta Tapio Makila | And 2 more authors.
Energy and Buildings | Year: 2014

Plate heat exchangers (PHE) have consolidated their position as key components of modern heating processes. They are widely accepted as the most suitable design for heat transfer applications in various processes, including the field of energy-efficient district heating (DH). This study refers to new DH coupling and control applied to a consumer substation. The concept introduces a new mass flow control model optimising the primary and secondary water streams to achieve remarkably higher temperature cooling in a new low temperature programme with diminished pressure losses. Here the operation of the ring network and the mass flow control in the substation are studied theoretically. A calculation procedure and transient models were constructed for the DH network, building structures, and heating heat exchangers. The PHE and its operation in the substation were studied by means of a corrugated plate model with five vertical parts and 10 elements. Variations in the flow rates, pressure losses, and overall heat transfer coefficients were received for the selected days. As a result almost equal heat capacity flows were found between the hot and cold sides of the PHE with maximum temperature cooling. The key performance factors of the heat exchanger, NTU and effectiveness, were monitored and the mean values obtained were 9.2 and 0.9, respectively. © 2014 Elsevier B.V. Source


Iturralde J.,Aalto University | Kuosa M.,Aalto University | Lampinen M.,Aalto University | Lahdelma R.,Aalto University | Makila T.,Energianhallinta Tapio Makila
Euroheat and Power (English Edition) | Year: 2015

Ring network topology and variable flow control are two improvements in district heating technology that would lead to higher energy efficiency. The ring network represents an alternative topology to the traditional DH distribution networks. The key to success of this topology is the fact that the return line starts at the closest consumer to the heat station and not at the furthest one, in a way that the return water flows in the same direction as the supply water and the total pipe length gets equalized for all the consumers. This leads to an important balancing effect that simplifies the control of the network to a great extent. In the same manner, the centralized single speed pump and control valves are replaced by inverter-controlled variable speed local pumps both on the primary and secondary sides, which has a positive effect on the system. The elimination of the valve related pressure losses results in lower pumping power needs that allow smaller pipe dimensions, lowering investments and operating costs. Source


Iturralde J.,Aalto University | Kuosa M.,Aalto University | Makila T.,Energianhallinta Tapio Makila | Lampinen M.,Aalto University | Lahdelma R.,Aalto University
Applied Thermal Engineering | Year: 2015

The contribution of this paper is to demonstrate experimentally the feasibility of a novel district heating (DH) system that uses a new low-temperature technology based on ring network topology and a mass flow control system. The study is based on several previous works: a theoretical approach to the new concept, an optimization case study and a simulation of a heat exchanger in a consumer substation. The central part of the work is the analysis of a laboratory-scale system with the purpose of proving the usability of the new technology. Series of experimental measurements were conducted with the aid of a simulation model, getting a mean heat exchanger effectiveness of 0.88 as a result. Additionally, non-linear supply and return temperature curves were obtained, which implies higher temperature difference (ΔT) and lower return temperatures. Furthermore, the new mass flow control enables equal flow rates on both sides of the heat exchanger, which improves the heat transfer and allows lower flow rates. These improvements led to the main findings of the research: substantial increase of the overall system efficiency and important savings in operational costs. © 2015 Elsevier Ltd. All rights reserved. Source


Laajalehto T.,Aalto University | Kuosa M.,Aalto University | Makila T.,Energianhallinta Tapio Makila | Lampinen M.,Aalto University | Lahdelma R.,Aalto University
Applied Thermal Engineering | Year: 2014

Heating and cooling have a major role in the energy sector, covering 46% of total final energy use worldwide. District heating (DH) is a significant technology for improving the energy efficiency of heating systems in communities, because it enables waste heat sources to be utilised economically and therefore significantly reduces the environmental impacts of power generation. As a result of new and more stringent construction regulations for buildings, the heat demands of individual buildings are decreasing and more energy-efficient heating systems have to be developed. In this study, the energy efficiency of a new DH system which includes both a new control system called mass flow control and a new network design called a ring network is examined. A topology in the Helsinki region is studied by using a commercial DH network modelling tool, Grades Heating. The district heating network is attached to a wood-burning heat station which has a heat recovery system in use. Examination is performed by means of both technical and economic analysis. The new non-linear temperature programme that is required is adopted for supply and return temperatures, which allows greater temperature cooling and smaller flow rates. Lower district heating water temperatures are essential when reducing the heat losses in the network and heat production. Mass flow control allows smaller pressure drops in the network and thus reduces the pumping power. The aim of this study was to determine the most energy-efficient DH water supply temperatures in the case network. If the ring network design is utilised, the district heating system is easier to control. As a result the total heat consumption within the heating season is reduced compared to traditional DH systems. On the basis of the results, the new DH system is significantly more energy-efficient in the case network that was examined than the traditional design. For example, average energy losses within the constraints (which consist of heat losses, pumping energy, and surplus energy from the heat recovery system) are reduced from 4.4% to 3.1%. © 2014 Elsevier Ltd. All rights reserved. Source


Kuosa M.,Aalto University | Kontu K.,Aalto University | Makila T.,Energianhallinta Tapio Makila | Lampinen M.,Aalto University | Lahdelma R.,Aalto University
Applied Thermal Engineering | Year: 2013

District heating (DH) systems are an inseparable part of the infrastructure in many countries. Today more attention is being paid to energy savings, efficiency improvements, and the replacement of fossil fuels by renewable energy. Research in the field of DH is focused on the supply of areas with low heat demand and low-energy buildings and on an increased share of heat being produced from renewable energy sources. New DH systems are expected to remain competitive in the future. In this study a new DH concept is proposed which is based on mass flow control. The DH system using mass flow control is meant for the concept of a ring network technology where mass flow rates in consumer substations are controlled by pumps with inverters to improve heat transfer. It will replace the traditional DH network and control in which water flow is throttled by control valves. The new control system will enable new temperature curves to be adopted for supply and return temperatures and more significant temperature cooling. First, a new topology and control method is presented. This ring network and the method used to control the flow rate of the primary supply water and its temperature are compared with the traditional technology. This method clearly shows the benefits of the DH applications under consideration. Second, these benefits are demonstrated by mathematical modelling. A simulation model is developed to study the area heating of six single-family houses and two apartment buildings. The static operation on the primary side of the networks is investigated for the most common outdoor temperatures. The numerical results are compared to those achieved with the traditional technology. The new flow rate is 46%, the pressure loss 25%, and the pumping power 12% of their former values in the pipes. The heat losses increase slightly with higher outdoor temperatures. The return temperature is lowest with the new technology. In the future the equipment that consumers will have will be more intelligent. The new technology that is presented allows consumers to adjust their energy consumption more easily by means of fast feedback on outdoor and room temperatures. © 2013 Elsevier Ltd. All rights reserved. Source

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