Case 3

Purpose of case three is to simulate the most luxurious house with the most equipment generating energy loads. This case also has the most energy generation potential with a more extensive storage system. An air-air heat pump is added to help with heating and provide cooling during summer if necessary. The cooling is set to start if the zone temperature goes over 22 C. Size of the heat pump is defined in the simulations by defining the heating capacity to 4.5 kW. Cooling capacity is auto-calculated to match the needed cooling. Also, COP is set to 3 for heating. A backup electrical baseboard system auto-sized by the software is added to ensure enough heating even on the coldest days.

The room illumination is kept at 500 lux as more would be too bright to use continuously.

No specific other electrical equipment is chosen compared to case 2 as the increased amount of equipment can be simulated by increasing the total energy consumption of other equipment. The increased equipment could include gaming consoles, PC, more TVs, and more kitchen appliances. The increased consumption puts the total to 3500

kWh/a. This approximation is based on the data from the electricity usage of residential living in 2007. (Adato 2011)

For energy generation, maximum capacity for solar panels is used, assuming that they can only be installed on the roof. The total area of solar panels is 54m²; this area can fit approximately 27 panels, making 8.1 kW in total capacity. Energy generation from wind energy is added with at 3kW wind turbine for electricity generation on winter months.

More turbines could also be added, but there might not be enough room on the plot for multiple wind turbines. Storage system size is kept at 16 kWh.

5 SIMULATION RESULTS

The main results studied from the different cases include energy consumption and generation and changes during the year. Another essential result to study is the use of energy storage systems. The three different cases are compared to each other to determine how different equipment levels affect the feasibility of an off-grid system. The result also shows that the energy generation systems alone enable off-grid use around the year and, if not, show the main reason. Using the model, different variables like the weather and storage size can be changed to test the effects on the results. The results are also compared to practical studies of energy and load generation of houses to confirm that the simulation results can be trusted to be a close enough representation of the real world.

5.1 Electricity consumption

In fully electrified houses, the electricity consumption consists of heating, cooling, and other equipment. Heating uses the most electricity. The second most electricity is used for water heating, although electricity for other equipment can come close depending on the number of devices and the use level. The following figure shows the total electricity usage of the three different cases during the year.

Figure 11. Electricity consumption changes during the year of all three study cases.

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From figure 11, it is visible that the most significant energy loads are generated during the winter months due to lower outside temperatures. In the summer months, for cases 1 and 2, the only load is generated due to electrical equipment and lights. The notable spikes in the summer come from the use of sauna on Saturdays. In winter, it is not as noticeable due to increased total consumption. Cases 1 and 2 mostly have similar electricity consumption during winter as the energy needed for heating is constant for all cases, and they both use baseboard heating.

The third case differs most from all the other cases as the heating method is changed from only baseboards to heat pump and baseboards. The change is most clearly visible from the summer month graphs as the electricity consumption in the third case is highest due to cooling done by the heat pump. Also, the electricity usage is similar or lower to other cases during the winter months even though case 3 has the most electrical equipment. The consumption is lower due to the heat pump using less electricity to generate the heat needed than baseboards. This change is due to the heat pump having higher COP compared to the baseboards. The reason for case 3 still having close to the same electrical consumption during winter is the most extensive consumption caused by other equipment.

The total electricity consumption for case 1 is 8900 kWh for case 2, 9800 kWh, and for case 3, 10600 kWh. According to an approximation tool from Vattenfall, the approximated electricity consumption per year for a 60 m2 house with electricity heating is 8700 kWh. This result shows that the total simulated consumption seems reasonable compared to data gathered by Vattenfall. The Vattenfall approximation tool uses the average electricity consumption values from Finnish houses. (Vattenfall 2020)

The differences between the cases are as expected with the set parameters. The simulation could be improved by adding more complexity to the model. For example, the electricity used by the baseboards is too great because no radiative heat is simulated. Heating demand could be approximated better by modelling the airflows by doing a more complex HVAC model for the house. Another aspect not taken into account is the heat produced by electrical equipment. For these reasons, the modelled electricity consumption is

probably slightly higher than what would be reached in reality. Also, in case 3, the COP of 3 set for the heat pump is quite conservative. With a more efficient heat pump, the amount of electricity needed for heating would lower case 3. The results still show well the difference a heat pump makes on the needed amount of electricity.

The current results give a rough approximation of the electricity consumption and the changes in the electricity demand. This accuracy can help design an off-grid system where electricity consumption of equipment doesn't drastically change daily. When considering an off-grid system with more changes in electricity demand by equipment, a more accurate electricity use schedule for different equipment would help find possible problem points caused by spikes in the load. At the moment, the results show that an electric sauna stove could be a problem for the off-grid system if the sauna is used on a day when the system entirely relies on storage systems.