Master of Science Programme in Sociotechnical Systems
Engineering (STS)
Upps al a U niversity log oty peSAMINT-STS; 21001
Degree project 15 credits
June 2021
Sharing Surplus Energy at
Gränby Sports Field
A case study investigating the possibilities for sharing
thermal surplus energy from the ice rinks at the sports
field
Linnea Abrahamsson
Karolina Engström
Rebecca Waldenfjord
Faculty of Science and Technology Uppsala University, Uppsala
Supervisor: Outi Kilkki, Linnea Nedar and Mirja Cedercrantz Subject reader: Fatemeh Johari
Examiner: Joakim Widén
Upps al a U niversity log oty pe
Sharing Surplus Energy at Gränby Sports Field
Linnea Abrahamsson Karolina Engström Rebecca Waldenfjord
Abstract
This project aimed to investigate the existence of thermal surplus energy from the ice rinks at Gränby Sports Field, Uppsala. Furthermore, a secondary goal was to suggest a distribution system for sharing the potential surplus energy.
To fulfil the purpose, each ice rink was modelled in the software IDA ICE. The following ice rinks were considered: buildings A and B, building C and the bandy arena. Data regarding the total heat and cold consumption for each building was collected from the owner, Uppsala kommun Sport- och rekreationsfastigheter AB, and was used to validate the simulation results from the building models.
The results from IDA ICE were presented in graphs that illustrate each ice rink’s total heat and cold consumption, surplus energy and energy balance. However, the results from the models in IDA ICE were not validated within a deviation of a maximum of 10% when compared to the data from Uppsala kommun Sport- och rekreationsfastigheter AB. Hence, the results were analyzed on a general level, which showed that there was a greater need for heating during wintertime, with certain peaks during the coldest months, whereas the cooling is maintained at a relatively stable level throughout the year, but with a slightly greater need in the summer. Further on, there was an identified surplus energy from the ice rinks, in terms of waste heat from the refrigeration systems. During the summer there was a greater amount of surplus heat
generated, caused by the greater cooling demand. Due to not being able to validate the models, complementary calculations of the yearly surplus heat were made with data from Uppsala kommun Sport- och rekreationsfastigheter AB. The surplus heat was 1 200 MWh for buildings A and B, 497 MWh for building C and 1 492 MWh for the bandy arena. No surplus cold was identified within the ice rinks.
The suggested solution for sharing the surplus energy is to implement seasonal thermal storage, due to the similar characteristics in heating and cooling demand for the ice rinks. The stored surplus energy could cover the ice rink’s peaks in heating demand during winter, which is an energy-efficient way would reduce purchased heat from the district heating grid. For further studies, it is of great interest to identify the possibilities of implementing a distribution system similar to the fifth generation district heating as well as seasonal storage, to possibly enable a direct share of energy between all the buildings within the sports field.
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Table of contents
1. Introduction _____________________________________________________ 4
1.1. Purpose _______________________________________________________ 4 1.2. Research questions ______________________________________________ 5 1.3. Limitations and delimitations _____________________________________ 5 1.4. Overview _____________________________________________________ 5
2. Background ______________________________________________________ 6
2.1. Theory _______________________________________________________ 6 2.1.1. Thermodynamics and energy __________________________________ 6 2.1.2. Energy balance in buildings ___________________________________ 6 2.1.3. Surplus energy within a building _______________________________ 8 2.1.4. District heating _____________________________________________ 8 2.1.5. Heating and cooling using heat pumps __________________________ 10 2.1.6. Thermal energy storage _____________________________________ 12 2.2. Existing knowledge within the field _______________________________ 13 2.2.1. Energy efficiency in ice rinks _________________________________ 13 2.3. Gränby Sports Field ____________________________________________ 15 2.3.1. Systems at Gränby Sports Field _______________________________ 16
3. Methodology and data ____________________________________________ 17
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4. Results _________________________________________________________ 23
4.1. IDA ICE models ______________________________________________ 23 4.1.1. Total heat and cold consumption ______________________________ 23 4.1.2. Energy balance ____________________________________________ 25 4.1.3. Surplus energy ____________________________________________ 28 4.2. Simulation results______________________________________________ 29 4.3. Calculated surplus energy _______________________________________ 31 4.4. Sensitivity analysis_____________________________________________ 31 4.4.1. Insulation in the floor _______________________________________ 31 4.4.2. Occupants ________________________________________________ 32
5. Discussion ______________________________________________________ 32
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Nomenclature
HVAC - Heating, cooling, air conditioning systems DH - District heating
3GDH - Third generation district heating 5GDH - Fifth generation district heating 4GDH - Fourth generation district heating HP - Heat pump
COP - Coefficient of performance TES - Thermal energy storage
SeTES - Seasonal thermal energy storage TTES - Tank thermal energy storage PTES - Pit thermal energy storage
ATES - Aquifer thermal energy consumption BTES - Boreholes thermal energy storage LB1 - Air unit 1 in the ventilation system LB2- Air unit 2 in the ventilation system AHU - Air handling unit
VAV - Ventilation with variable flow of air CO2 - Carbon dioxide
FTX - Fan driven supply and exhaust air system with heat recovery FT - Fan driven supply and exhaust air system
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1. Introduction
The present climate goal set by the United Nations 2030 is far from being reached (United Nations Sustainable Development, 2021). Drastic measures need to be taken into action and this demands the entire society to change the way of living. In today's society, enormous amounts of energy are consumed, resulting in untapped residual energy, surplus energy. If the surplus energy could be reused and shared, it could supply the energy demand of entire cities (E-ON, 2021a). Hence, the challenge is to produce and use energy in an efficient way while aiming for improving sustainability in society. Furthermore, the real estate sector is currently responsible for approximately 39% of greenhouse gas emissions and energy consumption in Sweden (Naturvårdsverket, 2020). This percentage needs to be reduced to reach the goals of reducing carbon emission and improving energy efficiency set for 2030. In commercial buildings approximately 70% of the energy consumption is assigned to heating, cooling, air conditioning systems (HVAC) and lighting (Harish and Kumar, 2016). These systems often have thermal energy as a waste product, in the form of excess heat or cold. If this excess energy could be reduced to some extent, a great deal of energy could possibly be saved (Naturvårdsverket, 2020). One way to reduce the energy consumption in
buildings, according to Naturvårdsverket (2020), is to start by looking at districts where buildings could be interconnected. Through a connection between the buildings, the energy surplus that is produced within the area can be shared to meet the different energy needs. This would result in lower energy consumption and therefore less greenhouse gas emission.
Gränby Sports Field is a building complex located in Uppsala consisting of several sports arenas with differing needs of energy supply (Gränby sportfält, 2020). The sports field is owned by the company Uppsala kommun Sport- och rekreationsfastigheter AB, further mentioned as Sportfastigheter. It partly consists of four ice rinks and will soon consist of five ice rinks, since a new ice arena is planned to be built. In municipalities, ice rinks are one of the biggest energy consumers, as they must maintain the ice surface at a proper temperature for players while also striving for a suitable indoor thermal comfort for visitors (Karampour, 2011). Identifying and sharing a surplus of energy, concerning heat and cold, between the different ice rinks at Gränby Sports Field would result in more efficient energy usage which is of interest for Sportfastigheter. For that reason, this bachelor thesis will investigate the possibilities for the implementation of such a distribution system, if there is a surplus of energy to be shared between the ice rinks. The distribution system will also include ways of storing surplus energy if there is no energy demand at that given time.
1.1. Purpose
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distribution system for sharing and storing potential surplus energy in order to make the sports field as energy-efficient as possible.
1.2. Research questions
In order to reach the aim of the report the following questions will be answered: ▪ How extensive is the surplus energy in each ice rink at Gränby Sports Field? ▪ What are the heating and cooling needs of each ice rink and how can the surplus
energy meet these needs?
▪ What distribution system is suitable for sharing and storing surplus energy?
1.3. Limitations and delimitations
Limitations in the project have been a lack of data and a limited time frame. These limitations have resulted in some delimitations. In the sharing of surplus energy within Gränby Sports Field, only heat and cold as an energy source was included, which means that sharing electricity between the buildings was not considered. When investigating the sharing of surplus energy, the focus has been on fluid-based distribution systems, since it is the most common (Axell et al., 2009). Furthermore, the indoor temperature was assumed to be regulated according to set conditions and therefore did not result in any surplus energy in the form of air that had higher or lower temperatures than required.
1.4. Overview
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2. Background
In this chapter, background information regarding theoretical concepts (2.1) and previous reports within the field (2.2) is presented, followed by a brief presentation of the buildings included at Gränby Sports Field (2.3).
2.1. Theory
This section aims to present and explain theoretical concepts of how energy flows within a building. The chapter includes theory regarding: thermodynamics, energy balances in a building, surplus energy, systems for heating and cooling and different storage techniques of energy.
2.1.1. Thermodynamics and energy
To develop an understanding of the different heating and cooling systems and how energy flows within a building, the first law of thermodynamics is crucial. This law states that the energy within an object is always conserved, which means that the energy can be neither created nor destroyed (Jones, 2017). Energy can only be converted into other forms of energy. In this project, with a focus on thermal energy, the process of heat exchange between different objects and systems is considered in depth. Heat
transfer is the main energy flow that takes place in buildings, and it includes convection, conduction, radiation and phase change of a substance (Bejan and Kraus, 2003).
Convection is related to the heat transfer through the movement of a fluid by diffusion, in this case, air movement inside and outside the building. Conduction explains the diffusion through the building's envelope, i.e., wall, floor, roof and window. This happens when there is a difference in temperature between indoor and outdoor temperatures. The second law of thermodynamics explains the conduction; entropy causes spontaneous processes in which the medium transfers from hot to cold (Wang, 2009). Heat transfer in the form of thermal radiation is heat gain in the form of solar radiation and lighting, as well as radiation exchange between inside surfaces within the building (Bejan and Kraus, 2003). This results in changes in the temperature of bodies, which depends on the body and if it is absorbing or emitting heat. Finally, the phase change is when a substance changes from liquid to gas and the process absorbs or releases heat. Evaporation from buildings, which has a cooling effect, is also included as a form of phase change.
2.1.2. Energy balance in buildings
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equipment in order to fulfill the specific indoor requirements (Energimyndigheten, 2021). These systems can be integrated and cooperate with each other or work separately.
A building can be considered as a system through which energy flows (Abel, 2000). The energy balance of a building can be described as the energy that is supplied to the building as well as the energy losses from it continuously, as seen in Figure 1. How extensive the energy flow is, largely depends on the local climate impact and the type of building, with respect to its specific properties and requirements of the indoor
environment. The supplied energy to a building includes the contribution of energy from HVAC, hot water usage, occupancy and activity levels, use of appliance and lighting as well as solar radiation (Harish and Kumar, 2016). On the other hand, due to temperature and pressure differences with the ambient environment, certain energy losses from the building are expected. The major part of the energy in buildings is lost through transmission. Transmission losses through the building’s envelope, such as walls, roofs, floors and windows, depending on the specific thermal properties of the construction material. Other energy losses come from infiltration losses, which can happen when opening a window, or ventilation losses, i.e. heat losses. Due to the specific energy balance within a building, the need for heating or cooling is dependent on the circumstances mentioned above (Energimyndigheten, 2021).
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2.1.3. Surplus energy within a building
This report refers to surplus energy as the residual energy that is untapped and originates from a process within a building (Suomalainen and Hyytiä, 2014). An example of such a process is heating or cooling a building where the waste heat from the process of cooling, or vice versa, refers to the surplus energy. Surplus energy is the energy not used in the process, but the energy that is a waste product. Furthermore, surplus energy is delimited to thermal surplus energy, which means that the surplus is either heat or cold.
2.1.4. District heating
District heating (DH) is today, according to E-ON (2021b), the most commonly used source for heating buildings in Sweden. The district heating grid consists of three components which are illustrated in Figure 2, a district heating plant (1), the district heating network (2) and a district heating central unit (3). Fuels like waste and residues from the forest industry are burned in the heating plant. The energy generated when burning the fuels heats water that is transported in insulated pipes under high pressure in the district heating network. In most cases, every building that is connected to the DH system has its own district heating central unit with two heat exchangers, one for tap water and one for the water in e.g. the radiator. The heat exchanger then transfers the energy in the hot district heating water to heat in the building and domestic hot water in taps and showers. When the district heating water has heated the buildings it has
become colder and it is transported back to the district heating plant where the same procedure repeats.
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Sweden (Lund et al., 2021). In the third generation (3GDH), hot water of about 120 ℃ is used, while cooler water at a maximum of 60-70 ℃ is used in the fourth generation (4GDH). The lower temperature results in less loss of energy and also, a bigger amount of surplus energy, can be reused. The fifth generation (5GDH) is defined as a network that operates at a near ground temperature exchanging heat and cold bidirectional, between connected buildings. The system enables a direct share of thermal energy, where the buildings connected to the system can work in symbiosis with each other. Some buildings will be heat or cold dominated during different seasons, and preferably complement other buildings connected to the system with different energy demands. The hot and cold water in the pipes can either be extracted directly during a shorter period of time, or stored during a longer period of time to align with the seasonal heat or cold peak demand. Hence, to facilitate the exchange of the surplus heat and cold during a longer period of time, seasonal storage is part of the system. Further development between the fourth (4GDH) and fifth generation (5GDH) is the implementation of district cooling, which is necessary for sharing the excess cold between the buildings. In 5GDH, each consumer that is connected to the system can also work as a producer, which is illustrated in Figure 3 below (Boesten et al., 2019). Different types of consumers, industry, residents and offices can be heat or cold dominated or balanced over the year. When there is a surplus of heat or cold somewhere in the system, it can either be stored or used by another consumer. The only external energy that is added to the system comes from intermittent sources, like solar panels or wind energy, which makes the fifth district heating 100% renewable. It is beneficial if buildings with different energy needs are implemented into the system, such as a sports arena which has a great amount of residual heat and a public swimming pool which has a great energy demand for heating the water (EKA, 2020).
The 5GDH system is a technique that is in early development but has been implemented in Lund, Sweden 2017 (Tidningen Energi, 2020). The project is called Ectogrid and is still under development for the extension. Both commercial buildings and apartments are connected to Ectogrid and the goal of the system is to reduce the energy
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Figure 3. A schematic picture of the fifth generation district heating. Adopted from Boesten et al., 2019.
2.1.5. Heating and cooling using heat pumps
Even though the name can be misleading, a heat pump can both work as a heating device as well as a cooling device (European heat pump association, n.d). The heat pump has four main components: compressor, condenser, expansion device and evaporator, and the fluid that passes through all these components is called refrigerant. The heat from the air outside the pipe is transferred to the colder refrigerant and the heat pump then pushes the cold air into the building's ventilation system, cooling the
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heat that is pumped by a refrigeration system can be used to cover a heating demand, in some cases even 100% of the need (ASHRAE, 2010).
Figure 4. The different components in a heat pump and how the heat pump can deliver both heat and cold. Adopted from Heat Pumping Technologies Program, 2021. The efficiency of a heat pump regarding cooling operation is measured through EER, which stands for Energy Efficiency Ratio (Polarpumpen, 2021). The higher the value of EER, the better the efficiency of the chiller. EER is described in Equation 1. The EER is used to determine the ratio between the cold extracted at the evaporator side, Q, with the power used by the compressor, W. EER has no specific unit.
𝐸𝐸𝑅 = 𝑄
𝑊 (1)
The efficiency of a heat pump regarding heating operation is measured through COP, which stands for Coefficient of Performance (Axell et al., 2009). The higher the value of COP, the better the efficiency of the heat pump. COP is described in Equation 2. The COP is used to determine the ratio between the heat delivered at the condenser side, Q, with the power used by the compressor, W. COP has no specific unit.
𝐶𝑂𝑃 = 𝑄
𝑊 (2)
The relation between COP and EER is determined through Equation 3 below (Equa Simulation AB, 2015).
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2.1.6. Thermal energy storage
Thermal energy storage (TES) can be used to balance the energy demand and reduce the peak demand which will result in an overall increased energy efficiency (Celsius, 2020). There are many possible applications for thermal energy storage including integrating intermittent renewable energy sources like solar panels, storage of heat in building structures and couple waste heat and district heating.
The basic principle of TES is that energy is stored in a storage system to be extracted and used at a later time. This can be described in a cycle of three steps: charging, storing and discharging. What then varies is the size of the storage and the method used for storing the energy. There are three different methods for storing energy which are called: sensible, latent and chemical storage, and the difference between them is mainly the material and the operating temperature. Sensible storage is used by changing the temperature of the storing material, latent storage can be used with the same material as sensible storage but instead of only changing the temperature of the material used for storing, the phase of the material changes (vapor to liquid or the other way around). Chemical storage needs different materials compared with sensible and latent storage, due to that chemical storage occurs on the surface of the storing material and in all cases the heat can either be released or absorbed by the material.
Seasonal thermal energy storage (SeTES) techniques can be used to store thermal energy during a longer period of time, i.e., from months to a season (summer/winter). Four types of SeTES are used worldwide: tank and pit thermal energy storage (TTES and PTES), aquifer thermal energy storage (ATES) and borehole thermal energy storage (BTES).
TTES are tank water storages (Nielsen and Sørensen, 2016). The tanks are up to 12 000
m2 and made out of concrete with a thin steel liner inside and have mainly been
implemented in Germany in connection with solar district heating that has 50% or more solar fractions.
PTES are large water storages (Nielsen and Sørensen, 2016). A large pit is excavated
and the soil is compressed and used as banks. The slope of the pit should preferably be 1:2 if it is allowed by the ground conditions. A plastic liner is used to isolate the soil from the warm water that then is stored in the pit. Lastly, another plastic liner is put over the pit and welded around the margin. The pit is not pressurized which results in a maximum temperature of 95 ℃.
ATES is a system where a couple of wells are connected to the same ground water
reservoir (Nielsen and Sørensen, 2016). In the winter the building has a heating demand and the water from the reservoir is pumped up and cooled down in a heat exchanger. By cooling one side of the heat exchanger, the other side in the heat exchanger will become warmer and this heat is then used for heating the buildings and the cold water is
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buildings in the summer, the water from the reservoir is pumped up but this time heated by the heat exchanger, and the other side of the heat exchanger is used to cool the building.
BTES is a closed system consisting of about ten to hundreds of boreholes, their number
and dimensions depend on geological conditions, the thermal properties of the rock and the need for energy storage (Celsius, 2020). All boreholes are connected to a central well and filled with a U-pipe and soil is used to fill the gaps between the pipes and the surrounding soil. In the summer the liquid in the pipes, which is usually water, is heated and heats the surrounding soil. The heat stored in the rock can then be extracted in the winter when there is a heating need. During the winter the soil is instead cooled by the pipes and the liquid travels in the opposite direction and the stored cold can be extracted in the summer when there is a cooling demand.
All these types of thermal energy storage can be built at a very large scale which
enables significant thermal storage at a relatively low cost, which makes thermal energy storage a cheaper alternative than electricity storage (Nielsen and Sørensen, 2016). The implementation cost of the thermal systems depends on storage materials, operation costs and technical equipment for charging and discharging the storage device.
Insulation is an important parameter for storing thermal energy, due to decreased energy losses, and can therefore be a significant part of the cost. Sensible storage is the
cheapest alternative and the cost decreases with the size of the storage medium, which usually is water. Other TES technologies are not as mature and are largely at the research state. Most systems consist of a 5 000 - 10 000 m3 water container with an energy content of 70-90 kWh/m3 which results in an investment cost of between 50-200 €/m3 of water equivalent and specific investment cost from 0,5-3,0 €/kWh. But, since every TES needs a specific design, there is no “one size fits all”. This, as well as differing boundary conditions and requirements, results in complex cost estimation.
2.2. Existing knowledge within the field
In the following section previous reports within the field of ice rink loads are presented. Energy efficiency measures in ice rinks are presented, as well as an overview of energy demands within the building.
2.2.1. Energy efficiency in ice rinks
When studying the heat loads in ice rinks, the refrigerator system is usually the largest energy consumer in an ice rink with 43% share of the total energy consumption
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Figure 5. The share of each energy consumption in ice rinks. Adopted from Karampour, 2011.
A project called “Stoppsladd” aimed to investigate how hundreds of ice hockey rinks in Sweden could be more energy efficient and was made by the Swedish hockey
association in collaboration with Sweden's Energy and Cold centre (Sveriges energi & kylcentrum AB and Svenska ishockeyförbundet, 2010). This study showed that there was at least 150 MWh surplus heat available each month for some of the ice hockey arenas, which results in a surplus of 1 800 MWh each year. To put this number in perspective, the typical ice rink in Sweden consumes approximately 1 185 MWh energy per year, which means that 66% of the ice rink's energy could be covered by surplus energy (Nicolas, 2009). As a comparison, the most energy-efficient buildings consume 800 MWh each year, while the least efficient buildings consume 2 400 MWh each year. Hence, the difference between the most and the least energy-inefficient buildings is 1 600 MWh.
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2.3. Gränby Sports Field
Gränby Sports Field is the biggest sports area in Uppsala, where various sports such as ice hockey, ice skating and bandy are practiced (Gränby sportfält, 2020). The first building was completed and inaugurated in 1974 and the remaining buildings were finished in 2010 (Abrahamsson et al., 2021d). The sports field consists of eight different buildings and of those eight, four of them are ice rinks (Gränby sportfält, 2020). The ice rinks will henceforth be referred to as: “building A”, “building B”, “building C” and “bandy arena”. Another ice rink is planned to be built, mentioned as the new ice arena further on, and is illustrated in Figure 6 as the white square above the other ice rinks. The owner of the A, B and C buildings is Sportfastigheter (Abrahamsson et al., 2021 c). Bandyalliansen is the owner of the bandy arena, but Sportfastigheter is monitoring the refrigeration system to cool the ice rink in the arena. Buildings A and B are connected through a passage, as seen in Figure 6. There are solar panels on the roof of building B. The electricity produced by this renewable energy source supplies electricity within the sports field and is therefore not sold to the external grid. There are also four more buildings included at Gränby Sports Field. These are the IFU arena and the UTK arena where sports such as tennis and track and field are practiced, an outdoor track and field arena and the Arena hotel where visitors can stay while visiting Uppsala. These
buildings highlighted as grey in Figure 6 are not considered in the project.
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2.3.1. Systems at Gränby Sports Field
Every building consists of one main area, where there is an ice rink and audience stands (Abrahamsson et al., 2021 c). Buildings A and C also contain another area which includes changing rooms and showers. These two different areas can be classified as thermal zones, where each thermal zone has different operating indoor temperatures. This is managed and maintained through the implemented systems in each building presented as follows.
All the ice rinks are heated by a third generation district heating (3GDH) which is owned by Vattenfall Heat AB, further mentioned as Vattenfall (Abrahamsson et al., 2021d). Each building has a separate connection and subscription to the district heating grid, except for the A and B buildings that have a shared connection. The heat is
generated from a heat exchanger connected to the district heating grid, which is then distributed through the ventilation system (Lundmark et al., 2017). The domestic hot water is heated by district heating as well. The heat regarding the bandy arena from Vattenfall is however not a fully representable value of the total heating demand since Sportfastigheter only monitors the ice rink as a part of the building (Abrahamsson et. al, 2021a). The building is owned and mostly operated by Bandyalliansen. Complementary data from Bandyalliansen regarding heating has not been accessed in this project. Furthermore, each building has a refrigeration system consisting of heat pumps driven by electricity (Abrahamsson et al., 2021b). In the ice rinks, the heat pumps are
functioning to cool the ice rinks and the refrigerant used in the pipes is ammonia. There are three heat pumps connected to the refrigeration system for buildings A and B, which means that they share the same cooling system. The two buildings were built in 1974 but were reconstructed in 2015. During the reconstruction, Sportfastigheter
implemented a heat recovery system in the refrigeration system in order to make the two arenas more energy efficient (Lundmark et al., 2017). A control system,
ClimaCheck, for monitoring the refrigeration system was also implemented at the same time. Some of the heat that is recovered from the refrigeration system is supplied into the ventilation in order to heat the air (Abrahamsson et al., 2021d). The rest of the excess heat is partially used to heat the water that is used to resurface the ice and partially to melt snow gathered from the ice rinks.
Building C and the bandy arena share the same refrigeration system, which consists of four heat pumps (Abrahamsson et al., 2021d). They also operate with ammonia as the refrigerant. The first three supplies the bandy arena with cold, whereas the fourth
supplies building C. Due to a lack of data, there is no information on whether there is an implemented heat recovery system in these buildings.
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whereas other systems often use a constant flow of air. This variable flow leads to lower operation and implementation costs. Furthermore, the system is a pressure independent system and can regulate the indoor climate in rooms individually.
The ventilation systems in buildings A and C are divided into two different subsystems, one system for the main area with the ice rink and one system for the area with the changing room (Abrahamsson et al., 2021b). In the ice rink areas, there is a ventilation system called FT, which is an exhaust and supply air system. Through an air unit called LB1 the ice rinks are heated when needed by the air flow. It also contains a CO2 sensor, which controls the rate of outdoor supply of air into the ventilation and therefore the amount of CO2 in the indoor air. In the changing rooms, there is a ventilation system called FTX, which is a fan-driven supply and exhaust air system with heat recovery. This area is supplied with air through an air unit called LB2, which is connected to a heat exchanger that heats the air. In building B and the bandy arena, there is only a main area and it uses the same ventilation system as for the main area in building A: FT system with a CO2 sensor. Schemes for the ventilation systems in buildings A and B, including air units LB1 and LB2, are presented in appendix C.
3. Methodology and data
This section presents the process of data collection, from available resources as well as earlier studies on the analysis of energy use in ice rinks. In the section, more
information regarding the simulation tool for building energy modelling (3.1) and data collection (3.2) are presented. Furthermore, the method used for calculations of the surplus energy and the development of an energy model for the ice rink is given (3.3). Assumptions needed for the building modeling will also be presented and motivated (3.4). Lastly, a method for sensitivity analysis building models is presented (3.5).
3.1. IDA Indoor Climate and Energy
To simulate the energy consumption for each building, software called IDA Indoor Climate and Energy, IDA ICE, has been used. IDA ICE is a simulation software used for calculating energy consumption for buildings with respect to a set of given
parameters (Equa, n.d.). These parameters include local climate data, materials and construction, system components and requirements, which can be set individually for the buildings simulated. IDA ICE provides a user-friendly environment including geometrical and non-geometrical properties, as well as day lighting and environment including the geometry of the buildings but also geographical conditions (Equa, n.d.). The software has an equation-based approach which enables solving complex
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beginner, the standard and the expert version. This project is based upon an educational license in the standard version, which is a simplified tool for simulations and therefore has limited access to different functional aspects of the software. All parameters that are included in the software are set to default unless otherwise stated. Furthermore, an extension for implementing ice rinks in the models was added. The building model for the A and B ice rinks are presented in Figure 7.
Figure 7. Buildings A and B modelled in IDA ICE.
3.2. Data
In this report, required data from Vattenfall and Sportfastigheter has been collected. The data from Vattenfall elaborate on the heat consumption from the district heating for each ice rink. For buildings A and B the data concerning the refrigeration system was collected through Sportfastigheter’s control system ClimaCheck. Similar data regarding cooling needs of building C and the bandy arena was collected through a compiled excel file from Sportfastigheter, which consisted of data regarding the electricity usage of each compressor in the buildings.
During the work procedure, the data required for modelling each building was collected. The following parameters were acquired when creating the model: building location, the climate data for the specific location, building construction data and materials, heat plant characteristics, the HVAC system and subsystems and building operating hours. The data was acquired through several contact persons at Sportfastigheter and was collected continuously through digital meetings, emails, phone calls and specific access to the company’s customer portal at Vattenfall. The data used for the building
modelling can be found in appendices, where building modelling materials used for all buildings is found in appendix A and the blueprints for each building is found in
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3.3. Methodology
From Sportfastigheter’s excel file, the compressor electricity usage data regarding building C and the bandy arena was used to calculate the cold consumption for the two buildings with help of Equation 1, presented in section 2.1.5. The EER for each
compressor was calculated according to Equation 3, also presented in section 2.1.5. The COP was set to 3, with consideration to the default value in IDA ICE (Equa,n.d.). This resulted in a value of 2 for the EER coefficient.
The building models were created in the software IDA ICE where specific input parameters were collected and considered, as mentioned in section 3.2. Information regarding these parameters can be found in the appendices D, E and F for each building model. Each building was, as earlier mentioned, divided into different thermal zones which required different indoor temperatures. The ice rink unit was implemented into the main area in each building and the refrigerant was chosen to ammonia, due to the information given in the interview with Sportfastigheter, see section 2.3.1. In order to obtain thermal comfort, ideal heaters and coolers were implemented in every area, except for the main area in building B. The ideal heaters were run by district heating and ideal coolers were run by electricity. Through the building modelling, the hour-by-hour simulation of each building was possible and resulted in graphs regarding the annual energy consumption, surplus energy and energy balance within the buildings. In order to validate the model, the output data regarding the energy consumption of each ice rink was compared with the data of heating and cooling from Vattenfall and Sportfastigheter, aiming for a deviation of maximum 10%.
3.3.1. Buildings A and B
Table 1 shows the yearly heat and cold consumption for buildings A and B. The data for the heat consumption comes from district heating supplied by Vattenfall during the time frame May 2019 to May 2020, and the data for the cold consumption comes from the control system ClimaCheck and has the same time frame from May 2019 to May 2020. The waste heat from the refrigeration system, during the same period, is stated in
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Table 1. Yearly waste heat, heat recovery and total heat and cold consumption for buildings A and B.
Waste heat Heat recovery Heat consumption Cold consumption
1 664 MWh 465 MWh 645 (+465) MWh 1 420 MWh
3.3.2. Building C
From the portal on Vattenfall and an excel file from Sportfastigheter the yearly heat and cold consumption for building C can be gathered, which is shown in Table 2. The time period for the heat consumption is from February 2020 to February 2021. The data regarding the cold consumption was gathered from February 2020 to February 2021. There is no data available on whether there is any heat recovery system in the building. The chosen time period for the data depends on the limited access of data, since the excel file from Sportfastigheter only contains measures between 2020 and 2021.
Table 2. Yearly heat and cold consumption for building C.
Heat consumption Cold consumption 572 MWh
3.3.3. The bandy arena
The yearly heat consumption for the Bandyarena could be found on Vattenfall during the time period February 2020 to February 2021. The cold consumption for the Bandyarena was found in the same excel file from Sportfastigheter as the cold
consumption for building C, for the same time period February 2020 to February 2021. The heat and cold consumption are shown in Table 3. There is no data available on whether there is any heat recovery system in the building. The chosen time period for the data depends on the limited access of data, since the excel file from Sportfastigheter only contains measures between 2020 and 2021.
Table 3. Yearly heat and cold consumption for the bandy arena. Heat consumption Cold consumption
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3.3.4. Calculations of surplus energy
When identifying the surplus energy of each building there was some variation in the collected data that affected how each calculation proceeded. For the A and B building, there was data available at ClimaCheck which presented the total amount of waste heat from the refrigeration system on a yearly basis and how much of this excessive heat was recovered for the same period, which was presented in section 3.3.1. The difference in value between these two resulted in the heat that was not used and therefore was defined as the surplus energy for these two buildings during the chosen time period.
For building C and the bandy arena, the data regarding the refrigeration system was acquired from the compiled excel file from Sportfastigheter. Potential heat recovery in these buildings was not considered due to the lack of data regarding implementation of such a system. That led to the decision that all excessive heat from the refrigeration system in building C and the bandy arena was considered as a surplus of energy from the buildings. In order to calculate the total waste heat, Q, from each refrigeration system, Equation 2, in section 2.1.5, and the electricity usage of the compressors in the compiled excel file was used. As earlier mentioned, the default value for COP was used and had a value of 3. This resulted in the total surplus of energy from building C and the bandy arena.
3.4. Assumptions
Because of the lack of data some assumptions were made for all the buildings. This regarded indoor and ice surface temperature, lighting, occupants in the building, hot water consumption, air leakage and ventilation system. The following assumptions include all the buildings, the A and B buildings, building C and the bandy arena, unless otherwise stated. The indoor temperature for the main area was set to 5-8°C according to a report made by the Swedish association which stated temperature specifications for ice arenas in Sweden (Svenska ishockeyförbundet, 2014). A temperature of 20-21°C was set in the changing rooms according to research about suitable comfort indoor temperature for regular buildings (Polarpumpen, 2013). The ice temperature was set to -4℃ (Karampour, 2011). To set the power consumed by the lights in the building a report regarding lighting specifications depending on the type of ice arena manufactured by the Swedish ice-hockey association was used as a reference, and the power
consumption was chosen to 10 000 W and 400 lux for each zone respectively (Sveriges energi & elcentrum AB and Svenska ishockeyförbundet, 2010).
The hourly number of occupants in the building depends on a couple of different aspects. All the buildings are used for training and games, but due to certain
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weekday was 325 people and 400 people during the weekend (Ramboll, 2019). This number included people who visited the arena for public ice skating, but again, due to the pandemic, no public ice-skating was considered in the number of occupancy in this report. The remaining occupants are only hockey and bandy practitioners. When not including the public ice skating a number of 240 occupants during a weekday and 312 occupants during a day in the weekend were assumed (Håbo Kommun, 2021). The estimation of the hot water consumption was based on the consumption of water in the showers in the building. This parameter, as well as the occupancy of the buildings, is affected by the regulations set by the government due to Covid-19, which resulted in the assumption that the showers were not being used during the chosen time period
(Folkhälsomyndigheten, 2021). Due to the Swedish Public Health Agency
(Folkhälsomyndigheten) regulations and therefore reduced numbers of occupants, doors and windows were assumed to be closed during the simulations in IDA ICE. Further on, the default ventilation system in IDA ICE was used for all the buildings.
3.5. Sensitivity analysis
In the software IDA ICE, multiple parameters can be changed. This leads to endless possibilities when designing buildings and therefore the software and its parameters need a sensitivity analysis in order to state the credibility or discredibility of the models created. The sensitivity analysis identifies the key parameters in all the models as well as the parameters with lower to no impact of the results, to get an understanding of what parameters influence the results. The investigation was performed on all building
models presented in the report.
The models in IDA ICE are all similar to each other, in the way that all buildings are ice rinks with the same requirements on the indoor climate. Hence, the same parameters for each building model were analysed. The analysis was done by changing one of the chosen parameters at a time to then compare the new result with the given result of the models respectively. The parameters chosen for investigation in the sensitivity analysis were insulation on the floor and occupants within the building. The insulation in the floor was chosen due to the fact that it had a low U-value compared to the U-value, for example the walls. The U-value of material corresponds to the thermal transmittance, i.e. the rate of heat transfer through a certain material (Merrriam-Webster, 2021). The occupants were chosen as a parameter due to the current pandemic which has had an impact on reduced occupancy in public areas. Details regarding the changes for the given parameter will be presented down below and the results will be presented in the results chapter below, in section 4.4.
3.5.1. Insulation in the floor
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transmittance. Hence, a higher U-value was obtained by using less insulation on the floor. The change was done on the floor connected to the main areas in each building and not for the floor in the changing room areas.
3.5.2. Occupants within the building
To evaluate the sensitivity of the chosen parameter, a change in the number of occupants was made. The number of occupants was changed from 20 occupants per hour to 40 occupants per hour, in the main area. The change of the parameter, resulting in a 100 % increase, was chosen due to the certain circumstances of the pandemic and aimed to investigate the impacts of a more crowded space.
4. Results
In the following section, the results for each simulated building in IDA ICE are presented. The results section is divided into subsections, where the IDA ICE models, and relevant graphs for energy within the buildings, are presented in section 4.1. In section 4.2, the simulation results regarding total heat and cold consumption for each building model is presented, whereas a subchapter presenting the calculated surplus for each building is presented in section 4.3. Further on, a sensitivity analysis is made in section 4.4, where certain input parameters were changed in order to get an
understanding of how this impacts the achieved results in the building models.
4.1. IDA ICE models
The following section presents the results obtained from the IDA ICE building models. The results are presented as follows: total heat and cold consumption, energy balance and surplus energy. In the models for buildings A and B, the simulations concern the time period of May 2019 to May 2020. For building C and the bandy arena, the results concern the time period of February 2020 to February 2021.
4.1.1. Total heat and cold consumption
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Figure 8. The total amount of heat and cold consumption for buildings A and B during the time period May 2019 - May 2020, as well as a zoom-in plot illustrating the
consumption for the first week simulated.
Figure 9. The total amount of heat and cold consumption for building C during the time period February 2020 - February 2021, as well as a zoom-in plot illustrating the
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Figure 10. The total amount of heat and cold consumption for the bandy arena during the time period February 2020 - February 2021, as well as a zoom-in plot illustrating
the consumption for the first week simulated.
In all graphs, the cold consumption from the refrigeration system, i.e. the evaporators, is maintained at a relatively stable level throughout the whole year. There is a slight increase in cooling demand during the warmer summer months, whereas the cooling demand decreases during the winter months. For the heat consumption, there is a greater need during the winter months which is illustrated by the red curve, i.e. the ventilation heating coil. There are peaks in heating, especially during the coldest winter months in each graph. During summer-time, the heat consumption is reduced due to the warmer weather outside.
4.1.2. Energy balance
In the following section, the energy balance within the main area in each building model is presented. The different colored lines correspond to the different parameters affecting the energy balance, mentioned in each graph. Figures 11 and 12 present the energy balances within the ice rink areas in buildings A and B. There is no ideal heater
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Figure 11. The energy balance for the ice rink area in building A during the time period May 2019 - May 2020.
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Figure 13. The energy balance for the ice rink area in building C during the time period February 2020 - February 2021.
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There is supplied energy, as well as energy losses, from each building model presented in the corresponding graphs. Most supplied energy and energy losses in the graphs are maintained at a constant level during the simulated year. There is however a correlation between the purple mechanical supplied air, i.e. supplied energy, and the grey envelope and thermal bridges, i.e energy loss, for the areas in building B, C and the bandy arena. During the winter months, there is a greater amount of energy loss from the building from the envelope and thermal bridges compared to the summer months, which is seen as a decrease in the graphs. The mechanical supplied heated air is also increasing for the same time period. A similar correlation can be found for building A, whereas there is an increase of energy supplied from the ideal heating units in the red line, when there is a decrease of energy from the envelope and thermal bridges.
4.1.3. Surplus energy
There is an identified surplus energy from the ice rinks, in terms of waste heat from the condensers in each corresponding refrigeration system. No surplus cold was identified for the buildings. Figures 15, 16 and 17 present how the identified surplus heat in each building model varies throughout the year. In all graphs, the amount of surplus heat is increasing and consequently resulting in a major surplus heat generated during the summer months. However, the amount of surplus heat is decreasing during winter time. In Figure 15 below, the total amount of surplus heat from buildings A and B is
presented. Figures 16 and 17, presents the total amount of surplus heat from building C and the bandy arena.
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Figure 16. The amount of surplus heat for building C during the time period February 2020 - February 2021.
Figure 17. The total amount of surplus heat for the bandy arena during the time period February 2020 - February 2021.
4.2. Simulation results
30
implemented even though such a system exists. To validate the heat consumption for the model in IDA ICE with the data from Vattenfall, the heat recovered from
ClimaCheck was added to the heat consumption data at Vattenfall.
Table 4. The total heat and cold consumption for the building models calculated in IDA ICE.
Building Total heating Total cooling
A and B 1 467 MWh
1 468 MWh
C 321 MWh 314 MWh
The bandy arena 979 MWh 788 MWh
The purpose of validating each building model in IDA ICE is to determine whether the models are representative of the ice rinks at Gränby Sports Field or not. Furthermore, the goal is to have a deviation of maximum 10% for the heat and cold consumption compared with the corresponding data acquired from Vattenfall and Sportfastigheter. The deviation between the simulation results from IDA ICE and the collected data is presented accordingly, in Table 5 below.
Table 5. The heating and cooling deviation for each building model. Building Heating deviation Cooling deviation
A and B 32.1%
3.3%
C 43.9% 5.2%
The bandy arena 301% 20.7%
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regarding heat consumption since the data only concerns the ice rink in the bandy arena and not the entire building.
4.3. Calculated surplus energy
In this section, the calculated surplus energy for all the buildings are presented. The surplus for buildings A and B were calculated through the data acquired from
ClimaCheck and concerned the time period of May 2019 to May 2020. The surplus for building C and the bandy arena were calculated through the compiled excel file from Sportfastigheter and concerned the time period February 2020 to February 2021. The results are presented in Table 6.
Table 6. Showing the calculated surplus heat for buildings A and B, building C and the bandy arena.
4.4. Sensitivity analysis
In this section, the results of the sensitivity analysis are presented. The results of each building are presented as a percentage of how much the heating and the cooling demand is changed by changing the parameters. Through this result, an analysis can be made in what parameters have a greater impact on the models in IDA ICE.
4.4.1. Insulation in the floor
Here the results for the parameter insulation in the floor are presented for each building modelled in IDA ICE, by changing the U-value from 0.15 W/m2K to 0.5 W/m2K. The results are shown in Table 7 below.
Building Surplus heat
A and B 1 200 MWh
C 497 MWh
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Table 7. The increase of energy demand, due to changing the insulation in the floor.
Building Increase
(compared to earlier results)
A and B Total heat: 0.0%
Total cold: 0.0%
C Total heat: -2.9%
Total cold: 1.5%
The bandy arena Total heat: -1.3% Total cold: 0.3%
4.4.2. Occupants
In Table 8 below, the results for the change of the parameter occupants per hour are presented for each building modelled in IDA ICE, by changing the occupancy from 20 to 40 occupant per hour.
Table 8. The increase of energy demand, due to changing the occupancy per hour.
Building Increase
(compared to earlier results)
A and B Total heat: -7.9%
Total cold: -4.4%
C
Total heat: -7.8% Total cold: 5.4%
The bandy arena
Total heat: -3.5% Total cold: 0.8%
5. Discussion
33
consumption in section 4.1.1, there is an identified need for cooling throughout the whole year, with special emphasis in the summer, as well as an even greater heating demand during the winter months. This result is supported by and aligns with Karampour's theory regarding ice rink heat loads (2011) found in section 2.2.1. According to Karampour, there is a constant need for cooling to maintain a proper temperature at the ice surface as well as a seasonal need for heating the changing rooms and areas for visitors to achieve thermal comfort, which increases during winter due to colder weather. Further on, the graphs representing the energy balance show a
correlation between the supplied energy and the energy losses within the buildings. During the winter months, there is a greater amount of heat loss which leads to an increased amount of supplied heat, in order to maintain the assumption regarding the indoor requirements of 5-8℃ within the ice rinks. All graphs illustrate a stable energy balance, which according to Harish and Kumar (2016), means that proper thermal comfort within the areas is maintained.
Furthermore, the results section presented an identified surplus heat. According to European heat pump association (n.d.), there is waste heat from the condensers when the heat pumps are cooling through the evaporators. Such a correlation can be identified between the condensers in the surplus graphs, in section 4.1.3, and the evaporators in the total heat and cold consumption graphs, in section 4.1.1. When the need for cooling increases during the summer months, through the evaporators, there is also an increased amount of surplus heat, through the condensers. Hence, during winter there is a
decrease in the surplus heat, because of the decrease in need of cooling. Consequently, there is mainly surplus heat generated during the summer months. As presented in the results section, there is no surplus cold identified for the ice rinks. This is explained due to the fact that all the buildings are connected to, and heated by, the district heating grid operated by Vattenfall. Therefore, there is no excess cold from the heating system at Gränby Sports Field, since the waste energy, according to E-ON (2021b), is transported back to the district heating plant.
Since the models were not fully validated, complementary calculations for the surplus energy were done through the data received from ClimaCheck and the excel file from Sportfastigheter, presented in Table 7 in section 4.3. As mentioned in the study
“Stoppsladd '' by Svenska Ishockeyförbundet (2010), there are ice rink arenas that have approximately 150 MWh of surplus heat available each month. This aligns with the calculated surplus heat in this report and therefore substantiates the following discussion regarding the sharing of the identified surplus energy within the sports field.
5.1. Sharing surplus energy
34
other buildings within the sports field that need heating, for example, IFU arena or the UTK arena. Another suggestion is to use all the generated surplus energy to heat the new ice arena that is not yet built. Based on the result, which showed that the surplus energy from the buildings each year was generally greater than their yearly heating demand, the surplus from all the buildings would most definitely cover the yearly heating demand for the new arena at Gränby. In that case, the new arena would not need to be connected to the district heating grid, and the heating demand for the new arena could be completely supported by the surplus heat from the other ice rinks. These are examples of how to use the surplus heat identified from the ice rinks.
When analysing the sharing of surplus heat between the buildings at Gränby Sports Field, a suggestion is to consider a fifth generation district heating system, 5GDH. Lund et al. (2014), states that 5GDH enables direct sharing of both heat and cold, seasonal storage and renewable energy sources to supply energy to the buildings connected to the grid. For a direct sharing of surplus heat generated from the ice rinks to be profitable, the surplus from one building needs to align with the heating demand from another building, to make use of the surplus energy. The total heating and cooling graphs in the results section indicated that all the ice rinks had the same characteristic behaviour, with a greater cooling demand in the summer and greater heating demand in the winter. If an implementation of a direct share of heat between only the ice rinks would be relevant is therefore questionable.
In the unlikely case that a direct share of surplus energy between the ice rinks would be beneficial, a system similar to the 5GDH presented by Boesten et al. (2019) would be suggested, except for the cold water loop due to not identifying a surplus cold. The components that would be included in the system are: a hot water loop, heat pumps, solar panels and seasonal storage. The concerned buildings would be connected to a hot water loop, distributing the surplus heat, with a heat pump connected to each building. The heat pump could either heat the water in the pipe to a preferable or required temperature or operate as a cooling device to cool the building, according to the
European heat pump association. Additionally, building B has solar panels implemented on the roof which could be used as a renewable energy source to supply external energy to the system. In the suggested system of 5GDH at Gränby Sports Field, another
important component is seasonal storage, which will be discussed in detail further down in this section.
In the other case, where a direct share of energy between the ice rinks would not be beneficial, the possibilities to connect an external building with a different heating and cooling need to the 5GDH system could be investigated. An example of such a building that could work in symbiosis with the ice rink arenas is a public swimming pool where the water constantly needs to be heated, which is a solution presented by Lund et al. The system would be similar to the previously presented suggestion, including all the
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could be included as well since the public swimming pool, according to Lund et al., will generate excess cold when heating the water through heat pumps.
Even though there are uncertainties if a direct share of surplus energy would be
beneficial at the sports field, which is a key part of a 5GDH system, a suggestion could be for the seasonal storage to work independently, to store the surplus heat, and not as a part of a 5GDH system. This could cover heat peak demands for each ice rink during winter, which would reduce the amount of purchased energy from the external district heating grid according to the Celsius project (2020). Seasonal thermal energy storage is suitable at Gränby Sports Field because of its ability to store energy during one season, in this case, the summer, to be used later during another season when the buildings need heating, in this case, the winter. Which one of the four different seasonal thermal
storage techniques, TTES, PTES, ATES and BTES, that was presented in the
background section 2.1.6, is the most preferable and doable storage technique depends on this specific case. The Celsius project highlighted the importance of adjusting the chosen storage technique to the specific situation, therefore no solution fits all.
All storage techniques, except TTES, are dependent on the characteristics of the ground, and can only be implemented if the ground is suitable for the given technique, according to the Celsius project. ATES and BTES presume that it is possible to drill in the ground, and PTES presumes a large area of land that can be excavated. TTES also presumes a large land area, but the tanks are completely above ground, which also results in the storage being visible. This can be a disadvantage compared to the other storage
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5.2. Reliability and sources of error
When analysing the reliability of the results in this report, concerning building models and calculations, previous studies can substantiate the results obtained. As an example, the calculated surplus energy at first seemed extensive when compared to the energy consumed. However, when gathering information about ice rinks and the surplus energy from previous reports, such as the project “Stoppsladd” mentioned in section 2.2.1, the value seemed more reliable. On the other hand, as proven in the results section, neither of the models are validated when it comes to heating. This error is most likely caused by the lack of data regarding the buildings and the assumptions made due to this, which will be further discussed below. Even though the simulation results from IDA ICE did not result in fully validated models, the software has been an asset in this project. The software has enabled building modelling, simulations, values for relevant parameters, as well as removing the human factor from the calculations.
The major source of error in the building modelling is based on lacking data regarding the sports field and it's internal systems. This includes data regarding occupancy, domestic hot water use, materials e.g. walls, energy consumptions of heat pumps and heat recovery as well as ventilation systems. The lack of data resulted in assumptions and generalizations, which probably caused the deviation in the results. Furthermore, the fact that ClimaCheck only is implemented in buildings A and B and not the others, as well as the excel file only concerning building C and the bandy arena, resulted in assumptions and generalizations when calculating the surplus energy for each building. Due to all buildings being unique, regarding implemented systems and geometry, they also have different energy needs and requirements, which means that a generalization most likely will cause errors in the results. A further source of error was the lack of compiled and explained data, i.e. metadata. The purpose of metadata is to understand how the data has been compiled and measured. In some cases, mainly when handling the data in ClimaCheck, the metadata was deficient. This led to interpretations and necessary assumptions to proceed with the project, which might have influenced the results. An example of such an assumption was when compiling the data from
ClimaCheck, where the data was assumed as accumulative. However, without the data from ClimaCheck or the excel file, the assumptions and generalizations would probably deviate even more from the correct values. For that reason, the data accessed from ClimaCheck and the excel file is a strength in this project. To conclude, this project has shown the importance of open data and metadata, such as explanations and transparency of what the data regards.
5.2.1. Sensitivity analysis
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discussion of the sensitivity analysis results. A bigger time scope would allow research into why this error occurred.
The first parameter, “insulation in the floor”, was not found to be a sensitive parameter, because of the minor percentual change in heating and cooling demand for building C and the bandy arena. When changing the insulation of the floor, the heat consumption decreased while the cold consumption increased slightly. This can be explained through theory from Bejan and Kraus (2003) in section 2.1.1, in combination with the climate data for Uppsala. The average temperature in the ground, collected from the climate data for Uppsala, is often higher than the wanted temperature of the ice rink. This means that the ground supplies heat into the building, by conduction through the floor, and therefore less insulation results in less heating demand. Moreover, this causes an increased demand for cooling to maintain thermal comfort, which is indicated through the results of the parameter and aligns with the energy balance theory from Harisch and Kumar, in section 2.1.2.
The second parameter, “occupancy”, was found to be more sensitive. An increase of 100% of the parameter resulted in a decrease in heating demand for each building. The decrease in the heat consumption is substantiated by Harish and Kumar, as a higher occupancy within the building results in more heat supplied into the building, which naturally lowers the heat consumption. Regarding the cold consumption, a slight increase was found for the two buildings. This aligns with the theory mentioned above, as the need for cooling increases when there is more heat from the occupants within the building, to maintain thermal comfort.
Even though sources of error are demonstrated, general trends in the sensitivity analysis can be identified which is supported by the theory regarding thermodynamics as well as theory regarding energy balance within buildings, found in section 2.1.1 and 2.1.2 respectively. The sensitivity analysis shows that even a minor change in one of the parameters can have a great impact on the result, which affects the reliability of the model. This emphasizes the importance of obtaining valid data to create a model that is true to reality.
6. Conclusion
38
MWh for building C and 1 492 MWh for the bandy arena. No surplus cold was identified, due to the connection to the district heating grid, which results in all the residual energy being distributed back into the district heating plant.
Due to not being able to validate the building models in IDA ICE, the heat and cold consumption of the ice rinks have been analyzed on an overall level. In the results section, similar characteristic energy demand for all ice rinks could be identified. There is a greater need for heating during wintertime, with certain peaks during the coldest months, whereas the cooling is maintained at a relatively stable level throughout the year, but with a slightly greater need in the summer. There are several possible solutions for using the surplus heat, but a deeper investigation of the building's thermal energy needs is needed to determine if an implementation of a system similar to 5GDH would be beneficial in the long run. As a result of the surplus heat mainly being produced during summertime as well as the ice rinks having a similar energy demand, the optimal solution right now is to implement seasonal thermal storage. The stored surplus heat could cover the ice rink’s peaks in heating demand during winter, which would reduce purchased heat from the district heating grid in an energy-efficient way.
To conclude, there is an extensive amount of surplus heat at Gränby Sports Field and this report has shown the potential in storing this surplus energy, in terms of seasonal storage that enables future energy usage when needed. Furthermore, the report has highlighted the importance of open data, with respect to improving transparency of data.
6.1. Further studies
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References
Abel, E. (2000). Byggnaden som klimatsystem. Chalmers Tekniska Högskola, Göteborg
Abrahamsson, L. et al (2021a) Email to Johan Larsson (2021-05-06) Abrahamsson, L. et al. (2021b) Email to Jan Åkerlund (2021-04-10) Abrahamsson, L. et al. (2021c) Email to John Hamberg (2021-04-09)
Abrahamsson, L. et al. (2021d) Zoom-interview with Jan Åkerlund (2021-04-20) Alberg Östergaard, P., Arabkoohsar, A., Bach Nielsen, Tore., Gudmundsson, O., Lund, H., Vad Mathiesen, B., Werner, S.(2021), Perspectives on fourth and fifth generation district heating, Energy, Volume 227.
ASHRAE. (2010), Ice rinks chapter 44 in ASHRAE Refrigeration Handbook, American Society of Heating, Refrigerating and Air-Conditioning Engineers: Atlanta
Axell, M., et al. (2009) Distribution av kyla och värme i bostäder och lokaler, SP Sveriges Tekniska Forskningsinstitut: Borås
Bejan, A., Kraus, A.D. (2003), Heat transfer handbook. John Wiley & sons, INC.: Hoboken.
Boesten, S., Dekker, S., Eijdems, H.,Wilfried, I (2019), 5th generation district heating and cooling systems as a solution for renewable urban thermal energy supply, serial number, Advances in Geoscience: Netherlands
Celsius (2020), Thermal Energy Storage. Available online:
https://celsiuscity.eu/thermal-energy-storage/ (2021-05-06)
E-ON (2021a), Det är dags att börja dela energi – för en hållbar stad. Available online:
https://www.eon.se/om-e-on/innovation/ectogrid (2020-04-19)
E-ON (2021b), Vad är fjärrvärme?. Available online:
https://www.eon.se/fjarrvarme/vad-ar-fjarrvarme (2021-05-05)
EKA (2020), Ta till vara värmen som alstras och återvinn i en hållbar helhetslösning. Available online: https://www.ekanalys.se/copy-of-natural-refrigerants (2021-05-17) Energimyndigheten (2021), Byggnadens energibalans. Available online:
