Dynamic Thermal Modelling of an Office Building

Dynamic Thermal Modelling of an Office Building

Executive Summary

Virtual Environment (IES) was used to help improving the design of the building performance by developing several properties of different materials within the building. This report looked into changing materials of a certain building such as glazing area, construction data and infiltration in order to demonstrate the building peak heating and cooling loads. The model was built on the base case analysis and allocated to be in Heathrow, London. In addition, it is used as offices building. Numerous changes in the building’s properties materials were carried out in order to decrease the peak heating and cooling loads of this building. The changes were then taken into consideration in the overall design so that it can aid to achieve the building’s thermal performance.

Table of Contents

1. Introduction

1.1. Aims and Objectives

1.2. Approach taken

2. Base Case Analysis

3. Design Development

3.1. Glazing

3.2. Building Fabric

3.3. Infiltration

4. Design Proposal and Recommendations

5. Conclusion

6. References

7. Appendix

List of Figures

Figure 1: model with glazing of 30%

Figure 2: Construction Data for Case Base model

Figure 3: Room heating and Boiler loads for the base case model

Figure 4: Room Cooling Load in each month along the year for Case Base Model

Figure 5: Solar gain for three different rooms (Base Model)

Figure 6: Room heating and Boiler loads (20% glazing)

Figure 7: Room Cooling Load in each month along the year (20% glazing)

Figure 8: Solar gain for three different rooms (20% glazing)

Figure 9: Room heating and Boiler loads (brickwork thickness 35mm – roof insulation 250mm)

Figure 10: Solar gain for three different rooms (Building Fabric)

Figure 11: Room heating and Boiler loads (with 0.450 AC/h max flow infiltration)

Figure 12: Room cooling load (with max filtration of 0.450 AC/h)

Figure 13: room heating and boiler loads for the proposed building design

Figure 14: Room cooling load for the proposed building design

Figure 15: Solar gains in the three different rooms for the proposed building design

1.    Introduction

Energy Demands is a significant factor in terms of cooling and heating of an office building. Minimizing this energy consumed has been taken in consideration. Mainly, if a building allocated in extreme winter climate condition, where the heat inside the building seeks to move out. While, if the building was allocated in hot climate condition then the heat wants to move in which can have a huge impact on the design performance (Liberte, 2015) and also the buildings’ thermal masses are largely based on glazing and the construction of the walls. A various tools can be used to investigate the performance of a building, which can provide the dynamic behaviour and also establish results so that can be used to optimise the thermal performance.

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1.1.           Aims and Objectives

The aiming of this report is to investigate a three storey building in term of load demands and to analyse the influence of construction data and heat gains on building’s thermal performance using IES software. The objectives in this report is to evaluate the effects of changing the properties of the materials of the building in term of load demands. Also to verify a new ideas that can help to improve the building performance and decrease the heating and cooling loads. Finally, presenting an overall proposal design building that can have an optimising thermal performance and require less energy demands.

1.2.           Approach taken

Firstly, a base case model will be completed and carried out to do some analysis in order to improve the peak heating and cooling loads. Secondly, a several parameters material of the building model will be changed such as glazing, infiltration and building fabric in order to have an idea how the heating and cooling loads are affected. Finally, proposal design building will be provided as results of the investigation that have been carried within the second stage.

2.    Base Case Analysis

This part of the study looks at a three-storey cubic building and each storey of the building has nine offices room with each room of a size 4x4x4 m³. The building has been implemented in in the UK climate and this factor will not change throughout the entire project. Modifying the construction data and heat gains, due to that a several calculations were carried out. The purpose is to compare how the building’s thermal performance is affected.

Firstly, Figure 1 shows the glazing used in the building of 30% of the entire external walls. The change of glazing has a huge effect in the building’s fabric heat loss and solar heat gain. The glazing will be changed later in the study to compare the results.

In addition, several calculations were undertaken in order to make sure that the building, case base model, preformed sufficiently in terms of energy output as well as to give a determination of the physical processes by plotting heating and cooling loads.

Figure 2 below shows a table of the construction data for the case base model.

Figure 3 shows a graph for the room heating load and boiler load with values of about 12.93 KW and 13.10 KW, respectively. This means that the coefficient of the boiler will be more due to the room heating plant sensible loads. The graph above is only showing the heating loads on Monday in the week of the January. In addition, it was plotted using the data construction shown in Figure 2. The difference between the boiler load and room heating load is because the system is not perfectly efficient.

Another factor has been investigated for the case base model, which is the cooling loads. It is considered at various times along the year. Figure 4 below shows that the cooling sensible load is considerably at the highest level during August with a value of 28.65 KW. This is due to overall temperature during the month as it is considered to be high and also due to the solar gains.

Furthermore, due to the orientation of the building, certain rooms within the office building will have more solar gain as they are facing the sunlight. The chart below shows the solar gain developed for three different room. These rooms allocated in the third floor. From Figure 5 below it can be easily said that room 003 has the largest amount of solar gains compared to the other rooms. This is due to that the room has larger glazing area than room 002 and it is facing the south side. Furthermore. This clearly state that the orientation of the building and the area of the glazing are an important factors in term of providing the most effective heating and cooling loads.

3.    Design Development

This part of the study looks at different strategies that may help to improve the performance of the office building. Changing of various parameters of the building will be carried in order to influence the design of the building. However, there are certain parameters will remain the same such as the lighting, occupants and the areas of the rooms and the building. Each parameters changed will be analysed in details as this can help to appraise the finest building in terms of energy demands.

3.1.           Glazing

The first parameter considered to be changed is glazing, as it is an important tool that have the ability to determine the solar gain and the heating and cooling loads (Greenspec, 2018). This means changing the glazing of the base model will have an impact on the solar heat gain as well as heating and cooling loads. As large window will enter more light during the summer period, but this will depend on orientation factor of the building. While less light will entre if small wide windows used. Due to this a glazing is reduced from 30% to 20%.

The above graph, Figure 6, shows that there is decreasing in the boiler load and heating load comparing to the base model in Figure 3. It shows that the boiler load has reduced from 13.10 KW, in the base model, to 11.12 KW in the developed model with 20% glazing.

While in term of cooling load, the graph below shows that the peak cooling load has decreased from 28.65 KW to about 24 KW. Moreover, the cooling load for each month is decreased compared to the cooling load in the base model. This data shows that the U-value has also decreased. Furthermore, less energy will be stored in the building and as a result of this the boiler will produce more work to maintain the ideal temperature inside the building.

As the glazing area is reduced, this will lead to reduce the solar heat gain as shown in Figure 8 below, where the peak solar gain for room 003 has reduced from 4.2 KW to 2.8 KW. The reduction of heat not only during winter period also during summer time. Hence, the cooling loads will be decreased. In other words, reducing the area of the glazing can help to make the boiler do less work to keep the room temperature at comfort zone.

3.2.           Building Fabric

Another factors considered to be changed in this part is building fabric. This can help to see the boiler and chiller response. One of the changes made in the thickness of the external wall (Brickwork) from 10mm to 35mm. This showed that the value of the thermal mass has increased from 35.5 kJ/( m^2.K) to 59.1 kJ/( m^2.K) , which means that changing the temperature for the specific material will require more energy. This change also can lead to have an effective building in term of the heating and cooling loads. In addition, another factor of the building fabric changed, which is the roof insulation thickness. It increased from 154.4mm to 250mm. The thermal mass didn’t change, but the U value significantly dropped from 0.1801 W/m^2.K to 0.1144 W/m^2.K (SeeAppendix). Decreasing the U value can lead to slowing the travel of the heat through the material and this can be better in term of overall building perform, for instance in winter period.

Load calculations were carried out in order to see and compare the results with the base model.  Figure 9 shows that the boiler load decreased from 13.10KW to about 12.53KW, which means that the boiler will do less work, compared to the base, in order to warm the rooms.

Additionally, the cooling load has decreased slightly along each month. The peak cooling load decreased from 29 KW to around 28 KW (See the graph in Appendix). However, this small change in the cooling load, due to the change of the brickwork and roof insulation thicknesses, can lead to a have a high level of efficiency and comfort for the building.

Figure 10 below shows the solar gains for rooms has been decreased comparing to the base model solar gains. This means less heating can enter through the building due to the thickness changes, thus aiding the building to achieve its energy demands.

3.3.           Infiltration

Air Infiltration also known as air leakage. It refers to the uncontrolled air entering the building. The cause of this might be due to wind pressure or openings, cracks and gaps within the external fabric of the building and it is considered significantly important factor in term of heating and cooling loads in the building (Marsh, 2010).

The maximum flow infiltration in the building were set to 0.250 AC/h in the base model. This, however, has been increased to 0.450 AC/h. This showed a huge increase in the boiler load as it had increased from 13.10 KW to 15.33 KW. It also effects the sensible load as it had increased from 12.93 KW to 15.13 KW as shown in Figure 11 below.

Moreover, there was slight increasing in the peak cooling load from 28.65 KW to 29.62 KW as shown in Figure 12.

These increases are due to the amount of air entering the building. This will require the boiler and the chiller to do more work in order to provide comfortability for the occupants and maintain the indoor temperature of the building in winter and summer periods.

4.    Design Proposal and Recommendations

Finally, it is safe to conclude the main findings that have been found during the analysis of the material properties of the building to ensure that the overall building’s energy performance at ideal level. The list below shown the material properties that have been selected in the design proposal:

-          Reducing the glazing area to 20%

-          Increasing the brickwork thickness, for external wall, to 35mm.

-          Roof insulation has been increased to 250mm.

-          Finally, increasing in the insulation of the external wall to 90mm

As the main target in the report was to reduce the heating and boiler loads plus the cooling loads. The graph below shows the heating and boiler loads, using the selected materials, for the final proposal building design analysis.

This shows that the room heating and boiler loads have been decreased dramatically comparing with the base model, in Figure 3, from 12.93 KW to about 10.56 KW and from 13.10 KW to around 10.56KW, respectively. Also the gap between the room heating load and boiler load lines has been decreased. This means that the building is more efficient comparing to the base model.

Additionally, the cooing load has decreased, as shown in the graph above, where the value of the peak cooling load decreased from 28.65KW, in the case model, to 22.98KW. This means that the chiller load will do less work to maintaining the building temperature especially in summer period.

Finally, the solar gains have been dropped down in the proposal design as shown in the above, however, the shape of the graph is still the same as the base model in Figure 5. The peak solar gain in room 003 has decreased from 4.20KW to 1.25KW. Similarly with room 001 and 002 as they decreased comparing with the base model. This means that in term of energy demands the building now able to perform efficiently.

5.    Conclusion

In conclusion, improvements that have been made in the base case model helped to achieve an excellent thermal loads such as thickness of roof insulation and brickwork. The changing factors in the building played a significant role in determining the best energy efficiency. These improvements also helped to reduce the use of the boiler and chiller loads within the building. Therefore, such a design can be put forward for the proposal using these improvement such as reducing the glazing and increase the thickness of certain parameters of the construction data.

6.    References

• Greenspec, 2018. Windows: Heat loss and Heat gain. [Online]
  Available at: http://www.greenspec.co.uk/building-design/windows/
  [Accessed 20 Nov 2018].
• Liberte, M., 2015. The 8 Rules of Building Performance. [Online]
  Available at: http://constructioninstruction.com/building-resources/building-science-videos/the-8-rules-of-building-performance/
  [Accessed 19 Nov 2018].
• Marsh, A., 2010. Air Infiltration Definition. [Online]
  Available at: http://performativedesign.com/definition/air-infiltration/
  [Accessed 20 Nov 2018].

7.    Appendix

1-      base model values in the roof such as

U-value and Thermal mass

2-      Changing in the values of the roof due to changing in the thickness of the roof insulation

3-      Brickwork thickness change lead to change in U-value and Thermal mass

4-      Cooling room graph due to change in thickness of roof insulation and brickwork.