Environmental Comparison of Energy Solutions for Heating and Cooling

Abstract

Humanity faces several environmental challenges today. The planet has limited resources, and it is necessary to use these resources effectively. This paper examines the environmental impact of three energy solutions for the heating and cooling of buildings. The solutions are conventional district heating and cooling, a smart energy solution for heating and cooling (ectogrid™), and geothermal energy. The ectogrid™ balances energy flows with higher and lower temperatures to reduce the need for supplied energy. The three solutions have been studied for Medicon Village, which is a district in the city of Lund in Sweden. The study shows that the energy use for the conventional system is 12,250 MWh for one year, and emissions are 590 tons of CO₂ equivalents. With ectogrid™, the energy use is reduced by 61%, and the emissions are reduced by 12%, compared to the conventional system. With geothermal energy, the energy use is reduced by 70%, and the emissions by 20%. An analysis is also made in a European context, with heating based on natural gas and cooling based on air conditioners. The study shows that the environmental impact would decrease considerably by replacing the carbon dioxide intensive solution with ectogrid™ or geothermal energy.

1. Introduction

The greenhouse gas emissions have led to an ongoing climate change, which can have devastating consequences. A considerable source of these emissions is the extraction and transformation of energy. According to the IPCC (Intergovernmental Panel on Climate Change) [1], a good quarter of the global greenhouse gas emissions come from electricity and heat production. Therefore, it is of paramount importance to reduce the use of electricity and heat and, at the same time, increase the share of renewable energy. Smarter energy solutions for buildings can be one way of reaching the climate goals.

Buildings need heating and cooling systems to ensure a comfortable and functioning indoor-air condition. District heating and cooling are system solutions where heat and cold are distributed to customers through a grid [2]. This technology is common in Swedish cities, but the limited reach of the grid means that buildings situated far from the city centre cannot be connected.

A thorough environmental evaluation is necessary to make a well-founded decision about which energy solution is the most beneficial. An environmental evaluation assesses the performance of the energy solution in relation to the energy and climate targets [3,4]. The evaluation gives the opportunity to choose the energy solution that will have a low climate impact in the longer time perspective, that is, a solution in line with the determined environmental goals nationally as well as internationally.

ectogrid™ [5] is one of the approaches to a smart energy solution since ectogrid™ can improve the energy performance of the buildings. ectogrid™ is based on already existing technology for heat pumps, cooling machines, and energy distribution grids, but in a new combination and with new features [6]. The aim of ectogrid™ is to make use of energy that is currently being wasted, thus reducing the demand for additional heat and cold sources [7]. This is achieved through the ability of the heat pumps to transfer the energy, i.e., to allow heat that has been generated from buildings that need cooling to be used in buildings that need heating and vice versa. The buildings are connected via a network with water, which is used as an external heat source.

The aim of this paper is to evaluate the environmental impact of a new energy solution for heating and cooling that is called ectogrid^TM. ectogrid^TM will be compared with two existing technologies, which are conventional district heating and cooling and geothermal energy. The purpose is also to ensure that this study can contribute to an improved understanding of how different energy solutions could interact with each other in the future. The objectives of the study will be achieved through a case study with three energy solutions for heating and cooling in the area of Medicon Village in Lund, Sweden. The studied solutions include conventional district heating and cooling (Case 1), ectogrid™ (Case 2), and geothermal energy (Case 3).

The following aspects are covered in this studied; 1) the energy use, divided by energy carrier, for the three energy solutions; 2) the energy solution that gives the least environmental impact in the case of Medicon Village. The study is based on data for Medicon Village collected in 2015. Economic aspects will not be explored in this paper. Some economic aspects of introducing ectogrid^TM in Germany and the United Kingdom have been studied in [8].

2. Heating and Cooling Buildings

2.1. Conventional Approaches

The principle for both heat pumps and cooling machines is the same. By using additional work to aid the process in the form of electricity, heat can be transferred from an environment of lower temperature to an environment of higher temperature [9]. The machines are often optimized depending on whether a cooling or heating demand shall be fulfilled. The highest efficiency is achieved when there is a demand for both the heat from the condenser and the cold from the evaporator. Machines made to easily shift between fulfilling a heating and a cooling demand are called refrigeration heat pumps [10]. One way of determining how efficiently a heat pump or cooling machine can transform electric power into heating or cooling power is through the coefficient of performance, COP. In a heat pump, the COP for heating is calculated as the ratio between delivered heat power and added electric power, as shown in Equation (1) [10]:

$$CO{P}_{heating}=\frac{P_f+P_k}{P_k},$$

(1)

where P_f is the heat absorbed at the evaporator, and P_k is electricity added to the compressor. In a cooling machine, COP for cooling is calculated according to Equation (2) [10]:

$$CO{P}_{cooling}=\frac{P_f}{P_k}.$$

(2)

The higher the COP, the more efficient the machine. The COP largely depends on the working temperatures of the machine; the smaller the difference between evaporator and condenser, the higher the COP [9]. Heat pump solutions are getting more and more efficient. Heat pump manufacturers strive to maximize energy efficiency. One way to do so is to provide multiple services by one single unit, for example, to heat water by using residual energy from cooling the building. In this way, even a heating demand is fulfilled without adding external energy [11]. Closed water-loop heat pump systems are used for achieving this. Energy from condensation is transferred through a water loop and given to the evaporation of reversible heat pumps, thus reducing the energy needed to fulfil simultaneous heating and cooling demands in the building [12]. This makes heat pumps an energy-efficient solution in applications where there are different energy needs [11].

Geothermal heat, which is stored in the bedrock, originates from pressure and nuclear reactions at the core of the earth [13]. In a borehole solution, heating and cooling from the rock is utilized in a waterborne system running through several holes that are drilled in the rock [14]. A heat pump or a cooling machine can be used to increase or decrease the temperature level of the extracted energy. The temperature in the boreholes is lowered when the heat is extracted. The size of the temperature drop depends on the heating load, the depth of the boreholes, and the properties of the rock [14]. This can be used for seasonal storage of heat and cold. The temperature in the boreholes is lowered in the winter due to the heat extraction and because of the thermal inertia of the rock. The temperature is still low when summer arrives [15]. The cold borehole storage can be used to cool buildings, whereby heat is restored to the boreholes before the winter. A seasonal storage does not reduce the energy use of the building, but it replaces purchased energy with local geothermal energy [15]. A geothermal energy solution has high investment costs but low running costs and is suitable for buildings with both a heating and a cooling demand [16]. Local geological conditions determine how much power and energy that can be extracted from the boreholes and, thus, the dimension of the system [14].

A district heating system is aimed at making use of resources that would otherwise go to waste. The source of the heat is usually upgraded excess heat from combined heat and power plants or industrial companies. The heat is brought to the customers through a distribution grid with hot water. The size of the grid is limited by losses in the pipes and the density of customers in the area, where customer density needs to be high enough to warrant an efficient system [10]. A certain pressure is necessary to deliver the heat to all customers in the grid [2].

The most common technology today is often referred to as the third-generation district heating and was developed in the 1970s. The supply-side temperature lies between 80 °C and 100 °C and the return temperature lies between 40 °C and 50 °C [17]. The fourth-generation district heating is currently being developed and is characterized by a lower supply-side temperature with a maximum of 70 °C [18] and a minimum of 50 °C. This makes it possible to reduce the grid losses and incorporate sources of low-temperature waste heat and renewable energy. The principles of district cooling are basically the same as for district heating. Water is cooled centrally and distributed through pipes to buildings that need cooling [2]. Because of the low temperatures of the system, a larger mass flow of the water is needed to deliver the same amount of energy, compared to district heating [2].

2.2. ectogrid^TM

The smart energy solution that is described by ectogrid™ [3] is a bidirectional low-temperature district heating system [19]. It was invented by Ph.D. Per Rosén [3]. ectogrid™ consists of the following fundamental parts:

• Grid of pipes connecting the buildings and the components.
• Components in the buildings, mainly heat pumps and cooling machines.
• A passive balancing unit, i.e., a hot water storage tank that evens out daily demand variations.
• An active balancing unit, i.e., an external source of energy, such as a reversible heat pump, district heating or cooling, or geothermal energy.

The buildings have different equipment since their heating and cooling demands are different. A heat pump or cooling machine is the most crucial part of the system. The heat pump uses the warm side of the grid to add heat until the heating demand is met. Similarly, if the building has a cooling demand, the cooling machine uses the cold side of the grid to add cold until the cooling demand is met. The energy transformation becomes more efficient in this way since the temperature interval of the grid suits the heat pumps and cooling machines better compared to using the outside air.

Figure 1 shows the components of ectogrid™. The system consists of a network of pipes with water that transports the heat and the cold between the buildings. This is the same idea as with district heating and cooling. However, where district heating and cooling require four pipes, ectogrid™ uses only two. Instead of having one feeding pipe and one return pipe for heating as well as for cooling, there is only a hot and a cold pipe. This is called the hot and the cold side.

With ectogrid™, every building can take or give energy to the grid to fulfil its heating or cooling demand, meaning that there is no predetermined direction of the flow in the pipes. If demand for heat dominates in many buildings, cooled water is pushed towards the cold pipe, thus moving towards the thermal storage tank. If demand were to change so that the demand for cold is higher, water in the cold pipe would move towards the buildings. This also means that the temperature of the water in the pipes will not be constant, but instead vary within certain intervals; hence the name ectogrid™, i.e., an ectothermic system. Daily variations in heating and cooling demand are controlled by a thermal storage tank connected to the grid. Depending on how much hot and cold water that is sent to the tank, the temperature in the tank will vary between an upper and a lower limit. When the lower limit is reached, heat must be added to the system. When the upper limit is reached, heat must be removed. This is done by the active balancing unit, which can have several solutions. The active balancing unit could be a hybrid net connected to district heating, district cooling, or a gas boiler. It could also be a standalone system with geothermal energy or reversible air-source heat pumps.

ectogrid™ is a low-temperature system with temperatures ranging between 16 °C and 40 °C on the hot side and between 6 °C and 30 °C on the cold side. The temperature difference between the sides is set to 10 °C. The pipes are not insulated and can, therefore, take up or release energy to the surrounding ground. The system uses small circulation pumps, which consider that there is no predefined direction of the flow in the system. This means that exactly the necessary flow is created and losses through choking are minimized. In the ectogrid™ system, the energy is balanced internally within the building, between buildings in the system, and in the thermal storage tank. Balancing means that the system utilizes the heat pumps to provide multiple services to both fulfil a heating and cooling demand at the same time. The balancing is made internally within the connected buildings when there is a simultaneous heating and cooling demand. In those cases, the energy added to and subtracted from the grid is cancelled out. When there is an overall dominating heating or cooling demand in the system, energy is needed from the thermal storage tank. If a dominant demand just lasts for a shorter period, the variations are balanced within the tank, and no external energy is needed.

2.3. Perspectives on Energy Solutions

There are arguments both in favour of and against heat pumps and district heating from an energy efficiency perspective. Electricity is characterized by high exergy, meaning that most of the energy is used for the desired purpose, resulting in low losses and high energy efficiency [2]. Losses occur when electrical energy is transformed into thermal energy, which is an energy form characterized by low exergy. Heat pumps use electricity to create heat, which can be questioned, as the energy resources are not used in the most efficient way [20]. From an exergy point of view, district heating is an energy-efficient solution since heat is used for heating.

In the third-generation district heating, the temperatures and pressure need to be adjusted to deliver the right temperature to the customer at the end of the system. With the fourth-generation district heating, the development is moving towards lower temperatures. The limitations of the fourth generation are that it is mainly suitable for new or renovated buildings with similar demands and that it has low compatibility with district cooling [21]. Ultra-low temperature district heating uses distributed heat pumps to fulfil heating demands, thus making it easier to adapt to buildings with varying demand. Cold district heating uses distributed heat pumps and cooling machines together with a waterborne grid to fulfil both heating and cooling demands. For heat pumps, the development is moving towards using the ability of heat pumps to produce heating and cooling at the same time in order to increase the efficiency [11]. The development in the different areas coincide in ectogrid™, which is sometimes called the fifth-generation district heating [2]. Using a bidirectional low-temperature network and balancing heating and cooling demand on a district level takes advantage of the development in the different areas.

2.4. Environmental Impact

It is not always easy to instantly and intuitively understand which alternative is the best for the environment. Therefore, methods for quantifying environmental impact are essential. Usually, there is no fully objective way to measure; instead, the results depend on the perspective, system boundaries, and allocation methods used. The perspective that is adopted also influences whether marginal or average values are used in calculations of environmental impact. This greatly affects the results of the evaluation. Marginal electricity values are based on the electricity produced in the plant with the highest running cost. This plant is the last to be started and the first to be turned off. Average electricity values are based on an average of the electricity production during a historical period. Similarly, there are also marginal and average values for district heating. In the Nordic electricity mix, the marginal production is often considered to be Danish coal condensing power, but in reality, the marginal production varies during the year [22]. The emission factor can differ up to 100 times between different kinds of electricity production; thus, the choice of factor for electricity has a large influence on the results of an environmental evaluation [4]. The factor that is selected depends on the perspective used, as well as what those performing the environmental evaluation want to present [22].

In Sweden, a certificate of origin is given for electricity produced from renewable sources. This certificate can be traded to assure that the purchased electricity comes from a renewable source [23]. When performing an environmental evaluation using historical data, both [23] and the Heating Market Committee [3] recommend using the Nordic countries, excluding Iceland, as the limitation of the electric system. The electricity grid in these countries is connected, and there is a common electricity market, Nord Pool. The Swedish Energy Market Inspectorate reports the CO₂ emissions for Nordic residual electricity each year. The residual electricity mix represents the electricity that remains when electricity that is marked as renewable has been subtracted. This is the electricity that customers receive if they do not make an active choice of electricity production source. Since the residual mix has a lower share of renewable energy, it usually has a lower environmental performance than the total electricity production [23]. The environmental impact cannot be evaluated fully through one indicator alone, but one fundamental factor is climate impact. Both the Heating Market Committee [3] and [24] emphasize climate impact as the most important parameter of an environmental evaluation. Climate impact is calculated using factors derived from life-cycle assessments. Emission factors can be found at different levels of detail, ranging from a specific green-house gas emitted from the burning of a certain fuel to CO₂ equivalents per energy carrier or per district heating grid. This information together, with the energy use of a specific customer (e.g., representing a building), gives the climate impact caused by that customer.

3. Case Studies

Medicon Village is a science park situated in Lund in Sweden. In Medicon Village, there are more than 1600 people working at more than 120 different organisations and companies with businesses in medical science and life science [25]]. The properties cover an area of 80,000 m² [25]. The current energy solution in Medicon Village is district heating and district cooling, with an annual demand of 10 GWh heat and 4 GWh cooling [25]. ectogrid™ has been implemented for the first time in Medicon Village as a pilot project and is expected to be finalized during 2020 [25]. Fifteen buildings will be connected, but the buildings will be connected to the district heating and cooling system in Lund as a backup. Every building will be equipped with a heat pump and a cooling machine, which will be dimensioned for 50% of the power demand. This means that 90% of the heat demand and 85% of the cooling demand will be covered, based on data from the hourly measured energy use in Medicon Village during 2015. The remaining demand will be covered by district heating and cooling. Figure 2 shows the components of ectogrid™ in Medicon Village.

The ectogrid™ system in Medicon Village will contain 400 m³ water divided on 250 m³ in the pipes and 150 m³ in the tank. The pipes will be made of polyethylene, and the size of the diameter will be different for different buildings, depending on the energy demand of the building. The active balancing unit will consist of a reversible heat pump.

In this study, environmental evaluations are done for three energy system solutions in Medicon Village. In Case 1, the energy use and environmental impact are calculated for the conventional district heating and district cooling. This is the current energy solution in Medicon Village. In Case 2, the energy use and environmental impact are calculated for an ectogrid™ system. Case 3 is a fictive case to evaluate the option of using heat pumps and cooling machines. To use geothermal energy as the energy source for the heat pumps is, in this case, the most reliable assumption [26].

4. Method

4.1. Calculations of Energy Use

The calculations are made hourly and divided into district heating use and electricity use for each of the three cases. The aim of the calculations is to obtain the sufficient amount of energy needed to meet the heating demand of 10 GWh and the cooling demand of 4 GWh [25]. The method considers the different components of the different energy solutions, including their energy losses. The calculations are performed with a method based on Microsoft Excel [27].

Some assumptions have been made for the calculations. The first assumption is that the internal system components for heating and cooling use the same amount of energy for all the different systems. That makes it possible to neglect the energy use of the components in the calculation. Another assumption is that the energy use for some distribution and circulation pumps are neglected.

Only the pumps that will distribute energy between the energy source and the buildings are included in the calculations. In Case 1 and this particular network, the energy supplied to the pump is assumed to be 1.5% of the total energy use [28]. In that case, the pumps are used to deliver the district heating and cooling from the production place. In Case 2 and Case 3, the energy supplied to the pump is estimated to be 1.0% of the total energy use [28]. There are several reasons why the supplied energy to the pump is estimated to be lower in Case 2 and Case 3. In Case 1, higher pressure and more energy are needed to ensure the desired flow to all the customers in the network. In Case 2 and Case 3, the energy source is closer to Medicon Village. The pumps are situated in connection with the components in the system and only use the amount of energy needed to deliver the desired flow. All pumps are assumed to work all the year with the same load.

The effects of the position of the polyethylene pipes used in the ectogrid™ system are neglected in the calculations. It is assumed that the distance between the pipes and the distance between the air and the pipes will not affect the heat transfer to and from the pipes. When using electricity in electrical components, the electrical energy will be converted into heat, as said in the second law of thermodynamics [29]. In this study, it is assumed that all heat is utilized in the system.

4.1.1. Case 1—Electricity and Heat Use

In Case 1, the use of electricity and heat connected to the district heating and cooling in Medicon Village has been calculated. The aim of the calculations is to find the amount of energy that can meet the heating and cooling demand of 10 GWh and 4 GWh, respectively. Hourly values for the district heating have been calculated in relation to:

• Heat demand
• System losses
• District cooling production
• Distribution pumps
• District cooling pumps

Hourly values for the electricity have been calculated in relation to:

• District cooling production
• District cooling pumps
• District heating pumps
• Energy losses
• Heat generated by the district cooling pumps

Hourly values of the heat demand for the different buildings in Medicon Village are used to estimate the total district heating demand. The system losses, as a result of the transmission losses from the pipes, are estimated to 10% of the delivered district heating [2,28]. The use of district cooling for the different buildings in Medicon Village is calculated in the same way as for the use of district heating. System losses are estimated to 5% [28] of the delivered district cooling. The losses are caused by heat transmission from the surrounding ground and the circulation pumps. The electrical energy demand for the pump needed to obtain the water pressure in the pipes is set to 1.5% of the delivered district cooling [28]. The district cooling is produced by reversible heat pumps. The heat pumps have a COP value of 3 [28], which is used to determine the electricity use of the pumps. The COP value is assumed to be constant over the year. The production of district cooling generates the same amount of heat. This heat has a temperature of about 70–80 °C and can be used for district heating [28]. The heat generated from the total district cooling production corresponds to 5.6% of the total district heating production. The same portion of the district cooling allocated to Medicon Village is, therefore, estimated to be available as district heating.

4.1.2. Case 2—Electricity and Heat Use

In Case 2, the use of electricity and heat for the ectogrid™ system in Medicon Village is calculated. As in Case 1, the aim of the calculations is to meet the heating and cooling demand of 10 GWh and 4 GWh, respectively. Hourly values have been calculated and divided into district heating in relation to:

• Heat demand
• System losses
• District cooling production
• Distribution pumps
• District cooling pumps

Hourly values have also been calculated as electricity use or savings in relation to:

• Internal balancing
• Remaining energy demand
• Active balancing unit
• Circulations pump
• Energy transmissions to the ground
• District cooling production
• District cooling pumps
• District heating pumps
• Energy losses
• Heat generated by the district cooling pumps

In the model, the heat and cooling demand for Medicon Village during 2015 [25] is used as the starting point for the calculations. From the diagrams of the power demand of the buildings, the sizes of the heat pumps and the cooling machines have been decided from an economic perspective. District heating and district cooling cover the rest of the demand. Hourly values of the electricity needed for the heat pumps and the cooling machines have been calculated by the COP value. The COP value changes depending on the working temperatures for the unit. Data sheets from the suppliers have been used to find how the COP value correlates to the temperature at the supply temperature in the radiator system.

The energy supplied to or removed from the thermal storage tank $\left(\Delta Q\right)$ causes a temperature change $\left(\Delta T\right)$ within the tank. The change is calculated with Equation (3) [29], where $m$ is the mass, and $c$ is the specific heat capacity:

$$\Delta Q=m\ast c\ast \Delta T.$$

(3)

In the ectogrid™ system in Medicon Village, the temperature difference is set to 10 °C between the hot and cold side and is used to calculate a corresponding energy flow concerning the tank [30]. The active balancing unit is activated when the temperature in the tank reaches the maximum or minimum value. The electricity needed to the tank depends on the energy demand and the COP value of the units in the system. The COP value of the tank has been decided in the same way as for the heat pumps and the cooling machines.

Since ectogrid™ is built with non-insulated pipes, there is an energy transmission $Q$ between the pipes and the ground. The energy transmission can be controlled based on the temperature chosen for the ectogrid™, i.e., $T_{net}$. Equations (4)–(6) [31] have been used to calculate the transmissions from the system, where $U$ is the heat-transfer coefficient, and $A_y$ is the outer area of the pipe. The other parameters that have been used are explained in

Table 1. Parameters for the calculation of the energy transmission from ectogrid^TM.

Parameter	Explanation	Value
$R_i$	Inner diameter of the pipe (m)	0.090
$R_y$	Outer diameter of the pipe (m) [32]	0.103
$L$	Length of the pipe (m)	5000
$k$	Thermal conductivity (W/mK) [33]	0.465

.

$$Q=U{A}_y\left(T_{net}-T_{ground}\right),$$

(4)

$$\frac{1}{U}=\frac{R_{y}ln\frac{R_y}{R_i}}{k}$$

(5)

$$A_y=2\pi R_{y}L+2\pi R_y{}^2$$

(6)

Values for $T_{ground}$ for the summer and the winter have been obtained from simulations of district heating systems in the area around Malmö [17]. The values that have been used in this study are $T_{ground}=8 °\mathrm{C}$ for the summer and $T_{ground}=3 °\mathrm{C}$ for the winter.

To calculate the total heat transmissions from the ectogrid™ system, the problem has been divided into two scenarios, one when the heat transfer is favourable for the system, and another when the heat transfer is unfavourable for the system. The heat transfer during the summer is favourable since there is a heat overload in the system. In that case, the heat transfer has been calculated for 40 °C on the warm side and 30 °C on the cold side. The transferred energy that is favourable has been calculated for the hours during the year when the temperature in the tank is 40 °C. When energy is transferred to the ground, less electrical energy is needed to the balancing unit.

The heat transfer during the winter is unfavourable for the system when there is a heat demand within the system. In that case, the heat transfer has been calculated for 16 °C on the warm side and 8 °C on the cold side. The transferred energy that is unfavourable has been calculated for the hours during the year when the temperature in the tank is 6 °C. When energy is transferred to the ground, in this case, more electrical energy is needed for the balancing unit. The heat transfer is assumed to be negligible during the hours when the tank neither has the maximum temperature or the minimum temperature. The electrical energy used or saved as a result of the influence of the ground has been calculated as depending on the COP value of the balancing unit.

4.1.3. Case 3—Electricity and Heat Use

In Case 3, the electricity use connected to a geothermal energy solution in Medicon Village is calculated, with the aim of meeting the heating and cooling demand of 10 GWh and 4 GWh, respectively. This energy solution is constructed together with E.ON [26]. Hourly values have been calculated and summarized as electricity use in relation to:

• Heat pumps for heat production
• Heat pumps for cooling production
• Circulation pump
• Cooling machines
• Coolers

The heat pumps have been dimensioned, as in Case 2, for 50% of the maximum heat power demand, and the rest of the heat demand is covered by electricity. The cooling machines have been dimensioned for the total heat power demand. The total cooling power demand needs to be fulfilled by cooling machines during the periods when no free cooling is available. The hourly electricity use of the heat pumps is calculated from the dimensioned power of the heat pumps and the COP value. The cooler has the same purpose as the active balancing unit during the summer, and because of that, the electricity use is assumed to be the same. The COP value has been calculated in the same way as for the other cases, but, in this case, the evaporating temperature is represented by the geothermal temperature. The geothermal energy is affected by the delivered energy to the buildings, which varies depending on the heat and cooling demand. The geothermal temperature has been set to 4 °C from January to March and October to December. For April to June, the temperature has been set to 10 °C, and for July to August, the temperature has been set to 15 °C. These temperatures represent the average geothermal temperature for these months. Information about the COP value for different evaporating temperatures has been given by [34]. The cooling demand is covered most of the year by free cooling, which, in the calculations, represents a COP value of 30. The cooling machines are necessary to use when the geothermal temperature has increased above 12–13 °C and do not have any cooling potential. In the calculations, it is assumed that there is no free cooling potential from July to August. During these months, a COP value of 4 is used.

4.2. Quantification of the Environmental Impact

Climate impact is calculated using factors derived from various life-cycle assessments. These factors can be found at different levels of detail, ranging from a specific green-house gas emitted from the burning of a certain fuel to CO₂ equivalents per energy carrier or per district heating grid. The Nordic electricity mix gives a value of the climate impact that is not affected by the electricity sale and just the production [35]. This value has been used in this study because it takes into account the emissions of the total electricity production. The emission factor concerning the district heating is declared by Kraftringen [36] every year.

The climate impact is formulated as CO₂ equivalents per kilowatt hour used by ectogrid™, which includes methane, nitrous oxide, and carbon dioxide. This information multiplied by the amount of energy used gives the climate impact caused by each case. The emission factors are shown in

Table 2. Emission factors for electricity and district heating.

Energy Carrier	Emission Factor (g CO2 equivalents/kWh)
District heating, Lund [37]	31.0
Nordic electricity production mix [35]	131.2

.

5. Results

5.1. Energy Use for the Different Cases

Figure 3 shows the annual energy use for Case 1, Case 2, and Case 3. The energy use has been calculated according to the procedures described in Section 4, including 4.1.1, 4.1.2, and 4.1.3. The calculations show that the energy use of Case 1 amounts to 12,250 MWh, which is the highest of the three cases. The electricity use for Case 1 is, however, the lowest. The energy use of Case 2 is considerably lower and represents a reduction of 61% compared to Case 1. The energy use for Case 3 is reduced further and represents a reduction of 70%. The results for Case 1 and Case 2 can be verified by [25], where approximately the same energy amounts are obtained for the conventional district heating and cooling system and ectogrid^TM and, also, a similar relative difference in energy use between the two cases.

Figure 4 shows the climate impact quantified in the number of CO₂ equivalents for a year. The procedure for the calculations is explained in 4.2, and the emission factors for the electricity and district heating are shown in Table 2. Case 1 has the highest emissions with 590 tons of CO₂ equivalents. Case 2 reduces the CO₂ equivalents by 12% compared to Case 1, and Case 3 reduces the CO₂ equivalents by 20%. The percentage reduction in emissions for Case 2 and Case 3, compared to Case 1, is less than the corresponding percentage reduction in energy use (see Figure 3).

5.2. Environmental Evaluation for Higher Emission Factors

This section shows how the choice of emission factors for Sweden affects the environmental evaluation. It also investigated how the environmental impact would change if ectogrid™ replaces a common energy solution in a country on the European continent.

5.2.1. District Heating

In Lund, most of the district heating is produced by biofuels, and 5% is produced by fossil fuels. Malmö, a city situated 20 km southwest of Lund, uses more fossil fuels, natural gas, and waste to produce their district heating. This leads to a higher emission factor in Malmö than in Lund. It is, therefore, interesting to compare the climate impact for Medicon Village in the district-heating system of Lund with a Medicon Village that would be situated in the district-heating system of Malmö.

Table 3. Emission factors for the district heating systems in Lund and Malmö [37].

District Heating System	Emission Factor (g CO2 equivalents/kWh)
Lund	31.0
Malmö	127.0

presents the emission factors for the two district heating systems.

Figure 5 shows the climate impact for Medicon Village in the district-heating systems of Lund and Malmö. The electricity is still calculated as Nordic electricity mix. The result shows that for Case 1, the emissions are much higher when the district heating is delivered from Malmö (red bar), compared to Lund (blue bar) because of the higher emission factor for Malmö. If ectogrid^TM is introduced in Malmö, the red bar for Case 2, the emissions are reduced by 61% compared to Case 1.

5.2.2. Electricity

As mentioned in Section 2.4, the climate impact for the electricity can be evaluated in different ways depending on the choice of perspective for allocating emissions. The three perspectives selected for this study are Nordic residual electricity, Nordic electricity mix, and wind power. The emission factors for the three perspectives are shown in

Table 4. Emission factors for different scenarios.

Scenario	Emission Factor (g CO2 equivalents/kWh)
Nordic residual electricity [38]	336.4
Nordic electricity mix [35]	131.2
Wind power [24]	15.2

. The factors depend on the amount of fossil fuels that are allocated to the electricity production.

The results in Figure 6 show that Case 1 has the lowest impact when the emissions from the electricity production are high (i.e., the emission factors for the Nordic residual electricity). When the emissions from the electricity production are lower (i.e., the emission factors for the Nordic electricity mix and wind power), Case 2 and Case 3 are more favourable.

The low energy use is a result of the ectogrid™ technology, which enables a reduction in energy use in areas with both heating and cooling demands. Case 3 has the lowest impact because geothermal solutions have the potential to store energy in the ground in order to decrease the energy supply to the system.

A combination of a geothermal energy solution and ectogrid™ would probably be the most energy-efficient solution with the lowest climate impact. Looking into the future, when more electricity will probably be produced by renewable energy sources, solutions with low electricity use will be favourable from an environmental point of view.

5.2.3. A European Context

In a European context, it is likely that the heating demand is met by local gas boilers, and the cooling demand is met by air-conditioners [39]. The emission factors in this example represent the European electricity mix [40] and the combustion of natural gas [41]. These are presented in

Table 5. Emission factors for the European residual electricity mix and natural gas.

Scenario	Emission Factor (g CO2 equivalent/kWh)
European electricity mix [40] Combustion of natural gas in a local boiler [41]	522.0 227.0

. The demand profile for Medicon Village has been used in the comparison.

The results of the calculations can be seen in Figure 7. The case denoted as gas and air-conditioners indicates that the heating demand is met by gas in local boilers and the cooling demand is met by air-conditioners with a COP value of 3. The total emissions are considerably larger for all the cases compared to the results shown in Section 5.1, Section 5.2.1 and Section 5.2.2. If the solution with gas boiler and air-conditioners can be assumed to represent the current situation in many places in Europe, there are possibilities to reduce the emissions through implementing ectogrid™ or geothermal systems.

The results of the case study with the Swedish conditions show that emissions can be reduced by 70 tons of CO₂ equivalents by implementing ectogrid™ and by 115 tons of CO₂ by implementing a geothermal solution, compared with the emissions from district heating and district cooling (see Figure 4). At the same time, this analysis demonstrates that a shift to ectogrid™ and geothermal energy in a European context can give even larger reductions. By changing from the gas boiler and air-conditioner solution to ectogrid™, 990 tons of CO₂ equivalents can be saved. By changing to a geothermal solution, 1250 tons of CO₂ equivalents can be saved. This corresponds to reductions of 24% and 33%, respectively. In central Europe, where there is often a larger cooling demand than in Sweden, there are potentially better balancing opportunities that can be exploited by ectogrid™ to reduce the demand for supplied energy.

6. Discussion

6.1. Some Aspects of the Data

The calculations of the energy use are based on measurements of the heating and cooling used by each building in Medicon Village. In order to obtain more information regarding the energy use of the different energy systems, data for Case 1, Case 2, and Case 3 have been prepared in different ways. For Case 1, the energy company Kraftringen [28] has shared data on the district heating and cooling network. Data were given in the form of ratios (percentages) between the energy used by the pump and the energy delivered to the pump. Similar percentages for energy losses are given by [2], which indicate that the values obtained from [28] can be seen as representative data. Data have also been given in the form of actual data on produced district heating and district cooling. For Case 2, the data are based on how E.ON [30] intends for the system to function, based on the conditions of the different system components and the laws of thermodynamics [29]. For Case 3, the system is approximated, based on reasonable assumptions with the support of expertise in geothermal solutions [26].

Another important parameter is COP. COP values have been derived from datasheets from manufacturers of heat pumps and cooling machines. These theoretically-calculated COP values probably do not exactly match the actual values, but they can be assumed to be reasonable assumptions for the calculations.

6.2. Analysis of Environmental Impact

The environmental evaluation shows that the geothermal energy solution has the lowest climate impact. This is because of the advantage of storing energy in the ground. ectogrid™ has the second lowest climate impact because of the increased capacity of the heat pump when both a heating and a cooling demand can be fulfilled simultaneously. Even if the conventional district heating and cooling uses a lot more energy than ectogrid™ and the geothermal solution, the climate impact does not differ that much between the cases. The reason is that it is favourable from an environmental perspective to use heat for heating instead of electricity. Another possibility would be to combine ectogrid™ with a geothermal solution by replacing the active balancing unit. This makes it possible to balance the energy demand between different seasons and decrease the energy supply to the system. In further work, it would be interesting to evaluate this combination from an environmental perspective.

The use of renewable energy resources for electricity and district heating production increases continuously. This will lead to a lower climate impact for all three cases. Combinations of existing energy solutions with new, more efficient energy solutions (e.g., ectogrid^TM) could lead to even more environmentally friendly energy solutions for buildings. The analysis from a European perspective shows that the potential for reducing the climate impact, by using more energy efficient solutions in buildings, is high in Europe.

6.3. Wider Perspective

The results from this study cannot necessarily be transferred to other areas with other conditions. District heating is a favourable solution from an exergy point of view in areas that are characterized mainly by a heat demand. ectogrid™ is a more efficient solution when the buildings have diverse heating and cooling demands with balancing potential. A geothermal solution is energy efficient, but disadvantages include the requirement for specific ground conditions and also high implementation costs. Different conditions in different areas make it profitable to develop different types of of energy solutions. There are several systems that are adapted to the conditions and demands of the future. In this study, ectogrid™, cold district heating, and efficient heat pump solutions are some examples. The fact that electricity production heads towards using more renewable energy sources, with lower emissions, makes it more acceptable to use electricity for heating. More renewable electricity production means more intermittent energy, which leads to a need for energy solutions that can use the electricity when it is available.

With this energy evolution, it will be advantageous to use heat pumps for heating and cooling, because heat pumps can use electricity efficiently to eliminate diverse energy demands. Another advantage is that they can use available intermittent energy by utilizing the thermal inertia of the buildings. The ongoing energy evolution changes the focus of how to evaluate an energy solution. That is, from having an exergy perspective to instead having an energy resource perspective.

7. Conclusions

The results of this study indicate that the geothermal solution should be the best for Medicon Village from an environmental point of view (see

Table 6. Summary of results.

Case	Energy Use (MWh)	Emission (tons of CO2 equivalents)
Conventional district heating and cooling Smart energy solution for heating and cooling (ectogrid™)	12,253 4713	590 510
Geothermal energy	3612	470

). However, as the geothermal solution is fictitious, it is also the case with the most uncertainties in the calculations. The ability of the geothermal solution to store energy in the ground between seasons has advantages from an energy perspective. Even though a smart energy solution, according to ectogrid^TM, does not use seasonal storage, energy use does not differ substantially compared to the geothermal solution. A possible improvement of the solution for Medicon Village could be to combine ectogrid™ with a geothermal solution in order to take advantage of both the balancing of energy between buildings and the seasonal storage. This could result in a system with very low energy use.

The study can hopefully give an increased understanding of how energy solutions can interact with each other. More options for heating and cooling will increase the possibility to choose the energy solution that is best suited to different needs and conditions of different areas. In this way, we can fulfil our heating and cooling demand while at the same time minimize the environmental impact.