Wojciech Zienkiewicz

Thermal consideration of a shed Module: MEC10110 - Advanced Energy System Lecturer: Prof. Jorge Kubie Assessment type: Coursework Hand in date: Friday, 28 November 2014 Group ‘J’ Name Matric Course Arkadiusz Tyranski - Meng – Mechanical Aymeric Mommaerts - Beng – Mechanical Robbie Murdoch - Beng – Mechanical Tomasz Sliwinski - Beng – Energy Wojciech Zienkiewicz - Beng – Energy 1 Abstract Investigation of the thermal performance of the shed is presented in the following report. It highlights the importance of determining the optimum thickness of the insulation in order to provide best performance/money solution. Factors such as ventilation losses, sensible and solar gains were considered while providing the following analysis. Number of assumptions had been listed and explained. The work provided helps to reduce the overall energy demand of the shed, and helps to reduce the CO2 emissions which are at a constant rise. 2 Contents Abstract................................................................................................................................. 2 1. Introduction .................................................................................................................... 7 2. General Assumptions ..................................................................................................... 8 3. Technical Work .............................................................................................................. 9 3.1 Design of the shed .................................................................................................. 9 3.2 Heat loss............................................................................................................... 11 3.2.1 Front panel (combined) – Heat transfer for an isothermal vertical plate.......... 11 3.2.2 Side Panel (Combined) – Heat transfer for an isothermal vertical plate.......... 13 3.2.3 Back panel (natural) – Heat transfer for an isothermal vertical plate. ............. 13 3.2.4 Side panel (natural) – Heat transfer for an isothermal vertical plate ............... 14 3.2.5 Roof (combined) – Heat transfer for an isothermal horizontal plate ................ 14 3.2.6 Floor (nautral) – Heat transfer for an isothermal horizontal plate .................... 15 3.2.7 Windows ........................................................................................................ 16 3.3 Solar/Sensible gains and ventilation losses .......................................................... 17 3.3.1 Solar Gains .................................................................................................... 17 3.3.2 Solar gains admitted through single and double glazing ................................ 18 3.3.3 Sensible Gains............................................................................................... 20 3.3.4 Ventilation Losses .......................................................................................... 21 4 Selecting Windows ....................................................................................................... 22 5 Environmental friendly insulations considered.............................................................. 23 5.1 Description of Insolation types .............................................................................. 23 5.1.1 Wool Fibre ..................................................................................................... 23 5.1.2 Cellulose ........................................................................................................ 23 5.1.3 Hemp batts .................................................................................................... 23 5.1.4 Wood Fibre .................................................................................................... 23 5.2 Selecting optimum thickness of the insulation ....................................................... 24 5.3 Payback Time ....................................................................................................... 24 5.4 Final Selection ...................................................................................................... 25 3 6 Regulations .................................................................................................................. 26 7 Results ..................................................................................................................... 28 7.1 Shed breakdown providing U values and heat demand ........................................ 28 7.2 Final Shed Heat Demand and Payback time ......................................................... 29 8 Discussion and limitations ............................................................................................... 30 9 Recommendations .......................................................................................................... 31 10 Conclusion .................................................................................................................... 31 11 References.................................................................................................................... 32 12 Appendices ................................................................................................................... 33 12.1. Excel Clarification .............................................................................................. 33 12.2 Solar Gains ........................................................................................................... 34 12.3 Sensible Gains...................................................................................................... 35 12.4 Ventilation Losses ................................................................................................. 37 Figure 1- Shed dimensions 9 Figure 2 - Shed orientation and wind 10 Figure 3- Top view of the shed 10 Figure 4 - Combined Convection 11 Figure 5- Thermal Resistance Series Diagram 12 Figure 6 - Boundary Layer 12 Figure 7 - Natural Convection 13 Figure 8 - Roof Combined 14 Figure 9 - Floor natural 15 Figure 10- Double Glazing 16 Figure 11 - Losses vs Gains SG 19 Figure 12 - Losses vs Gains DG 19 Figure 13 - Comparison of Ventilation Losses 21 Figure 14 - Optimum Insulation Thickness 24 Figure 16 - Actual Heat Demand Comparison between sheep wool and no insulation 29 Table 1 - Front Panel 13 4 Table 2 - Side Panel 13 Table 3 - Back Panel Natural 14 Table 4 - Side Panel 14 Table 5 - Roof 15 Table 6 - Floor 15 Table 7 - Monthly Heat Demand SG/DG windows 18 Table 8 - Sensible gains summary 20 Table 9- Typical values for air change per hour (data from 3rd year energy notes) 21 Table 10- Payback Time Windows 22 Table 11 - Annual Heat Demand / Cost of Demand 24 Table 12 - Energy Savings and payback time of insulation 24 Table 13-Maximum U values for building insulation envelop; (Act, The Building (Scotland) Regulations 2004 Handbook, 2004, p. 469) 27 Table 15 - Summary - no insulation 28 Table 16 - Summary - sheep wool 28 Table 17 - Final Payback Time of Insulation 29 Table 18- Monthly ventilation losses with no insulation 37 Table 19 - Monthly ventilation losses with insulation 37 5 Symbol SI Unit Quantity 𝑅𝑎𝐿 Rayleigh Number ̅̅̅̅𝐿 𝑁𝑢 𝑁𝑎𝑡𝑢𝑟𝑎𝑙 Nusselt Number, Natural ̅̅̅̅𝐿 𝑁𝑢 𝐿𝑎𝑚𝑖𝑛𝑎𝑟 Nusselt Number, Laminar ̅̅̅̅ 𝑁𝑢𝐿 𝐶𝑜𝑚𝑏𝑖𝑛𝑒𝑑 Nusselt Number, Combined ̅ ℎ𝑖 𝑊/𝑚2 𝐾 Heat transfer coefficient, Inside ̅̅̅ ℎ𝑜 𝑊/𝑚2 𝐾 Heat transfer coefficient, Outside 𝑞 𝑊/𝑚2 Heat flux 𝑇𝑖 ℃ Temperature, Inside 𝑇𝑜 ℃ Temperature, Outside 𝑇𝑓𝑖 𝐾 Film Temperature, Inside 𝑇𝑓𝑜 𝐾 Film Temperature, Outside 𝑅𝑒 Reynolds Number ℎ̅𝑐𝑎𝑣 𝑊/𝑚2 𝐾 Heat transfer coefficient, Cavity 𝑅𝑡,𝑇 𝑚2 𝐾/𝑊 Total Thermal Resistance 𝑈 𝑊/𝑚2 𝐾 Total Heat Coefficient 𝑄𝑙𝑎𝑚 𝑊 Heat Transfer, Laminar 𝑄𝑇𝑢𝑟𝑏 𝑊 Heat Transfer, Turbulent 𝑄𝑇𝑜𝑡 𝑊 Total Heat Transfer ℎ̅𝑙𝑎𝑚;𝑡𝑢𝑟𝑏 𝑊/𝑚2 𝐾 Laminar and Turbulent Heat Transfer Coefficient l 𝑊/𝑚 𝐾 Thermal conductivity, window l’ 𝑊/𝑚 𝐾 Effective thermal conductivity 𝑅𝑠𝑖 𝑚2 𝐾/𝑊 Internal surface resistance 𝑅𝑠𝑒 𝑚2 𝐾/𝑊 External surface resistance 𝐿2𝐷 𝑊/𝑚 𝐾 Thermal coupling of coefficient 𝑙𝑡𝑏 𝑚 Linear thermal bridge 𝑑𝑗 𝑚 Glass pane, thickness 𝑈𝑔 𝑊/𝑚2 𝐾 Total heat transfer, glass pane 𝑈𝑓 𝑊/𝑚2 𝐾 Total heat transfer, frame 𝐴𝑓 𝑚2 Total area, frame 𝐴𝑔 𝑚2 Total area, glass ψ 𝑊/𝑚 𝐾 𝑈𝑤 𝑊/𝑚2 𝐾 Linear thermal transmittance combined glass and frame Total heat transfer, Window 6 1. Introduction In today's world, the huge and increasing demand on energy is mostly composed of fossil fuel gas, oil and coal. These resources are not infinite, environmentally friendly and the cost of extracting them is at a constant rise. The aim of this project is to provide a recommendation for insulating a shed. This will be achieved by looking at the energy performance of the shed, the environmental impact of the insulation type and the economic feasibility. 7 2. General Assumptions In order to provide the calculations shown in the report, some general assumptions were made: - Steady state flow, temperature does not vary with time - Heat flux is the same through the fabric of the shed, 𝑞𝐼 = 𝑞𝐶 = 𝑞𝑜 - Temperature of air inside the shed = 19ºC - Wind-speed of 3 m/s - Wind direction East-West - The shed is standing on a concrete foundation - The study uses Glasgow as data reference; outside air temperature is taken as the average monthly temperature. - The orientation of windows in the shed is assumed south to obtain maximum solar gains - Natural convection was considered inside the shed. - For natural convection to occur inside the shed, it is assumed that there are no ventilation losses presented for calculation purposes - The ventilation rate is not affected by the insulation type. It is also assumed that changing from single glazed windows to double glazed windows have no effect on the ventilation rate. - For the roof, front and one side panel, combined convection was considered. For the side panel facing west and the back panel facing north, only natural convection was considered. This is because it is assumed that the shed is well sheltered from those sides, assuming no external wind. This can be seen in Figure 2. - It is assumed that the shed is used for 3hrs/weekdays resulting in total usage time of 60hrs per month. - The contact resistance was neglected as the overall resistance of the material stack dominates the thermal resistance. - The external heating is provided by electric heater - Cost of electricity is taken as 11.15 pence per kW/h 8 3. Technical Work 3.1 Design of the shed The shed is a timber construction with water prof barrier on the roof. The dimensions of the shed are specified in Figure 1 Front/Back Pane Length 2.62m Front/Back Panel Height 2.26m Side Panel Length 2.09m Side Panel Height 1.73m Window Length 0.5m Window Height 0.5m Figure 1- Shed dimensions The inclination angle of the roof is 66° (total of 132°). The thickness of the wooden walls along the entire construction is 12mm. The windows are single glazed, measuring 500mm by 500mm. The shed is standing on the concrete foundation, which improves moisture, water and frost protection. The thickness of the wall will increase by 60mm due to addition of the insulation material (50mm) and OSB board (10mm). OSB board will provide the cover for insulation and trap the air inside to increase insulating properties. 9 To summarize the modified shed, the wall is composed of three sections: o OSB board (Inside) o Insulation Material (Middle) o Timber (Outside) It also contains a desk, shell and a chair for office use purposes. As shown below in Figure 2, the wind is blowing from East to West. The North and West walls are enclosed. Figure 2 - Shed orientation and wind As shown in Figure 3, after modification of the shed the insulation decreases the total volume of the room but does not restrict the space available for the occupant. Figure 3- Top view of the shed 10 3.2 Heat loss 3.2.1 Front panel (combined) – Heat transfer for an isothermal vertical plate. Figure 4 - Combined Convection In order to undertake this analysis, further assumptions had to be stated: - For calculation purposes cross wind is assumed - There will be forced convection occurring on the outside of the panel resulting in a combined convection - All specifications for this panel are taken from wholesaler’s website. The dimensions can be found in Figure 1- Shed dimensions (Anon., 2014) The surface of the front plate is considered as isothermal vertical plate and the external surface is affected by the cross wind. The free convection of the inside air flows parallel to the surface similar to the free convection of an external plate. This implies that inside conditions can be treated the same as outside. As the heat travels towards the roof, the material of the shed begins to conduct and the heat transfers through the material. Free convection occurs on the external side of the shed and the forced convection created from the crosswind merges with the free convection resulting in combined convection. The process described above is summarised in Figure 4. The same process applies when dealing with non-insulated panel. The only difference is that the overall thickness of the panel is lower resulting in a lower thermal resistance which implies higher heat loss. This heat transfer analysis applies for 4 of the 7 components respectively, front panel, window, side panel and roof. 11 1/hi LOSB/kOS Lins/kins Ltimber/ktimber 1/ho Figure 5- Thermal Resistance Series Diagram Figure 5- Thermal Resistance Series Diagram shows the resistances in series and the effect the materials stack has on the temperature. A large drop in temperature can be seen from T 2 to T3. Figure 6 - Boundary Layer The critical length of the boundary layer seen in Figure 6 - Boundary Layer in the coldest month is calculated to be larger than the length of the front panel (2.2m, blue line) therefore the boundary layer is considered laminar. 𝑅𝑒 = 𝑈 ∗ 𝑥𝑐𝑟 = 5 ∗ 105 𝜈 Transpose for 𝑥𝑐𝑟 𝑥𝑐𝑟 = 5 ∗ 105 ∗ 𝜈 5 ∗- = = 2.48𝑚 𝑈 3 12 The abbreviated results for the front panel are shown in Table 1 - Front Panel. Total results can be found in the excel spreadsheet in the folder ‘insulation’ labelled ‘Front Panel’. Table 1 - Front Panel Comparison table - Front panel Average Annual U (W/m²K) Average Annual Q (W) Average Annual Heat Demand (kW/h) 3.2.2 No insulation- Wood fibre- Hemp batt- Cellulose- Sheep Wool- Side Panel (Combined) – Heat transfer for an isothermal vertical plate The same methodology used for the front panel has been applied to the side panel using the relevant dimensions. The air flow of 3m/s was considered an updraft and was used to calculate the forced convection resulting in combined convection. Table 2 - Side Panelsummaries the results of the side panel. Table 2 - Side Panel Comparison table - Side Panel No insulation Wood fibre Hemp batt Average Annual U (W/m²K- Average Annual Q (W- Average Annual Heat Demand (kW/h- 3.2.3 Cellulose- Sheep Wool- Back panel (natural) – Heat transfer for an isothermal vertical plate. Figure 7 - Natural Convection Looking at the orientation of the shed presented in Figure 2 - Shed orientation and wind it can be seen that the shed is well sheltered from external wind hence the assumption is made that only free convection occurs. The methodology and shed dimensions are exactly the same as the front panel but due to the assumption made above forced convection do not merge with 13 free convection. Figure 7 shows that without wind, the boundary layer is parallel to the external surface of the panel. Table 3 - Back Panel Natural Comparison table - Back Panel Natural No insulation Wood fibre Hemp batt Average Annual U (W/m²K- Average Annual Q (W- Average Annual Heat Demand (kW/h- 3.2.4 Cellulose- Sheep Wool- Side panel (natural) – Heat transfer for an isothermal vertical plate The methodology for the side panel (natural) is exactly the same as the back panel using relevant panel dimensions. Table 4 summarises results. Table 4 - Side Panel Comparison table - Side Panel No insulation Wood fibre Hemp batt Average Annual U (W/m²K- Average Annual Q (W- Average Annual Heat Demand (kW/h- 3.2.5 Cellulose- Sheep Wool- Roof (combined) – Heat transfer for an isothermal horizontal plate Figure 8 - Roof Combined As shown on Figure 8 - Roof Combinedthe inclination is greater than 60° therefore the internal and external surfaces are considered to be horizontal planes. The combined convection process of the external surface it shown in Figure 8 - Roof Combined. The critical length has been calculated to be 2.48m (red line) which is smaller than the overall length of the roof resulting in a mixed boundary layer as shown in Figure 6. 14 Table 5 - Roof Comparison table - Roof No insulation Wood fibre Average Annual U (W/m²K) Average Annual Q (W) Average Annual Heat Demand (kW/h) 3.2.6 Hemp batt Cellulose Sheep Wool - - - - - 4.70 3.03 3.03 3.04 3.06 Floor (nautral) – Heat transfer for an isothermal horizontal plate Figure 9 - Floor natural The heat transfer occuring at the floor is considered free convection. Lateral lossses are neglected and the floor was only treated as a composite wall. Table 6 - Floor Floor Average Annual U (W/m²K) Average Annual Q (W) Average Annual Heat Demand (kW/h) No insulation- For all the components described below, to obtain the results, data for average temperature in Glasgow was used. For the floor, ground temperature for Glasgow was considered. 15 3.2.7 Windows The calculations for the windows have been calculated based on ISO- as well as on the class notes. The ISO standard includes both, the glass thermal transmittance (UG) and the frame thermal transmittance (Uf) but the class notes omit the frame transmittance. The glass thermal transmittance has been calculated three times: a) Calculations based on ISO10077 standard for a double glazing window with the dimensions of 4-9-4mm as shown in Figure 10. As shown in the excel tab ‘WindowISO10077’ and also following the EN673 (ISO), the thermal transmittance of the glass (Ug) for the double window has been determined as 2.53W/m2K. It should be noted that EN673 does not take in account the temperature but the internal and external surface resistance respectively Rsi and Rse. Figure 10- Double Glazing ISO10077 estimates the glass transmittance (Ug) at 2.6 for ‘one pane coated’ for a window dimension of (4-9-4 mm) with air as the insulating gaz. b) The thermal transmittance of glass has also been determined as 1.48 W/m2K considering the window as a composite wall and natural flow inside and outside. As discussed in the general assumptions, the flow should be considered to be forced convection resulting in higher heat transfer coefficients (hi,ho) and thus higher thermal transmittance. Comparing the heat transfer coefficients between natural and combined convection, the heat transfers coefficients for combined are about 3 times higher. By multiplying the natural heat transfer coefficient by 3 to simulate a combined convection the thermal transmittance of glass has been determined as 2.05 W/m2K which converges towards the ISO value. 16 c) The thermal transmittance has also been taken as 5.6W/m2K (Anon., 2012) for a single glazing window. The thermal transmittance of the frame (Uf) has been determined next. The technical drawings of the shed did not include any dimensions concerning window frame size hence dimensions were assumed as shown in the excel tab ‘Window-ISO10077’. Once both, the glass (Ug) and frame (Uf) thermal transmittance have been determined the overall heat loss through the window (Uw) can be calculated as: Following the standard the overall heat lost (Uw) has been determined for the three cases. 3.3 Solar/Sensible gains and ventilation losses 3.3.1 Solar Gains Solar gains are those admitted to the building through windows and fenestrations. Solar gains are greater for single glazed windows than for double. However, the design specific heat load will be greater for a building with single glazed windows. To provide a comparison of the shed performance, when considering single and double glazing, solar gains must be considered. Data included in Solar Gains provides a monthly breakdown of the solar gains admitted to the building through single and double glazing. As stated in general assumptions the shed is only used for 3 hours per day. Rough approximations were used to determine the solar gains. These include:  Taking daily solar gains provided by Tom Grassie and dividing them by 24 to obtain a value per hour. This value was then multiplied by 3 to achieve the total amount of solar energy in the time period when the shed will be used. This assumes that the solar irradiation admitted to the building is constant throughout the day, which is not true.  After the above estimation was implemented, the number obtained was multiplied by 20, in order to obtain the total monthly solar energy admitted to the shed in the time when it is used. As before, this is not accurate as the solar irradiation changes every day. 17 Excel Spreadsheet which enables to determine the exact value of the solar irradiation, for each hour of the day, for 365 days was obtained from Tariq Muneer. As the group has agreed, amount and detail of work required to determine these parameters exceeded the allocated time. The solar gains are very small and will not have a great impact on the final results. 3.3.2 Solar gains admitted through single and double glazing Table 7 represents data obtained for single and double glazed windows. Table 7 - Monthly Heat Demand SG/DG windows Base Temperature Month January February March April May Jun July August September October November December Annual Heat Demand SG Annual Heat Demand DG Annual Gains SG Annual Gains DG Monthly Heat Demand (kW/h) 19 C Average Temp ( C ) Heat Demand Single (kW/h) 3,5 2,08 3,3 2,10 5 1,88 7,4 1,55 10,1 1,19 12,9 0,82 14,2 0,64 14,2 0,64 12,2 0,91 9,5 1,27 5,4 1,82 3,9 2,02 Heat Demand Double (kW/h) 1,14 1,15 1,03 0,85 0,65 0,45 0,35 0,35 0,50 0,70 1,00 1,11 16,94 9,-,87 28,14 From the above table it can be seen that the total annual amount of solar gains exceed the annual heat demand in both single and double glazing windows. This analogy can be miss directing as the amount of solar gains admitted for summer months offsets the demand for winter months. Further comparison providing a monthly breakdown, representing solar gains against losses is provided in the Figure 11 and Figure 12. 18 Single Glazing- Losses (Sg) kW/h Gains (Sg) kW/h Figure 11 - Losses vs Gains SG Double Glazing- Losses (Dg) kW/h] Gains (Dg) kW/h Figure 12 - Losses vs Gains DG It can be seen that amount of gains during summer, is greater that the losses through both single and double glazing. This will result in offsetting the heat demand for the summer months, and as proven in further calculations, it will contribute for making the shed selfsustained when heating is considered. 19 3.3.3 Sensible Gains Sensible gains are heat inputs to the building that are derived from the occupants and from equipment used. The shed consist of only one occupant, with a small number of appliances, resulting in overall sensible taken as 11 kW/h. Results are summarised in Table 8, Calculations carried to obtain the results are summarised in the Sensible Gains. Providing a value for sensible gains is very difficult as it requires a lot of assumptions to be stated but the data provided is closely related to the notes provided by Tom Grassie. Table 8 - Sensible gains summary Component Rating (W) Heat Gain per 3 hours (W/h) Heat Gain per 20 days (kW/h) 15 54 1.080 20 72 1.440 Laptop 52.5 30 0.6 Printer 80 3.3 0..66 390 7.800 Desk Lamp with Fluorescent bulb Lamp with Fluorescent bulb (x1) Occupant Total 10.986 20 3.3.4 Ventilation Losses Ventilation rate can be different for different areas in the house. For the simplicity, it can be assumed as 1, but in the Table 9, there are some typical values of ventilation rate for different areas in the house: Table 9- Typical values for air change per hour (data from 3rd year energy notes) Area Kitchen Bathroom Room Hall Ventilation Rate (a.c/hr) 2 1.5 0.5 1.5 This data indicates a typical value taken when considering the ventilation losses in the house. Due to the shed’s fabric, consisting of many air gaps, it can be estimated that the overall ventilation rate would be greater from these specified for the house. The ventilation rate is in order of 5.5 a.c/h without insulation and 3.5 a.c/h with insulation. In order to obtain ventilation losses in kW/h, degree days had to be considered. Data summarised in Ventilation Losses show a monthly breakdown of ventilation losses for the shed with and without insulation. Figure 13 provides comparison of ventilation losses with and without insulation. Ventilation Losses (wiht and without insulation- No Insulation kW/h With Insulation kW/h Figure 13 - Comparison of Ventilation Losses 21 4 Selecting Windows In order to provide further analysis of the shed, the window type which will be considered has to be determined. Table 10 shows the energy savings and payback time when considering replacement of already installed single glazing to double glazing windows. Table 10- Payback Time Windows Single Glazing 258.55 Actual Heat Demand Energy Savings (kW/h) Price of Electricity (£) Cost of Installing DG window (£) Money Saved (£)/year Payback 0.1115 Double Glazing- To provide payback calculations, annual heat demand had to be considered. Non insulated shed was used for the calculation purposes. This methodology is true for all insulation types as the difference in the heating demand will remain the same when analysing windows. All ventilation losses and gains were considered. Greater number of solar gains admitted through single glazing windows, and also due to the assumption that the ventilation losses are not affected by the type of glazing, the difference of the annual heating demand for single and double glazing units is very small. This implies that the overall energy savings are also very small, which provides a very high payback time of 276 years. This payback time seems very unrealistic, but considering overall heat demand for the shed in order of 286,66 kW/h and energy savings of 14.91 kW/h (1,66 pounds) per year it can be justified. The conclusion taken from that analysis implies that the payback time for double glazed windows will reduce, when considering bigger buildings consisting of greater areas of glazing and also greater heat demands. It can also be stated that replacement of single glazed windows for double glazed windows will have an environmental impact on the shed related to installation, manufacturing and transportation. Life cycle analysis will be required to justify this statement, but from previous experiments undertaken for different subject and consultation with Tariq Muneer allow this statement to be made. 22 5 Environmental friendly insulations considered 5.1 Description of Insolation types 5.1.1 Wool Fibre Wool fibres (Thermal conductivity 0.042W/mK) are hygroscopic by nature and will have a moisture weight content of up to 35%, dependent on the relative humidity of the surroundings. While absorbing this moisture, wool releases energy in the form of heat, thus raising the temperature of its surrounding areas. By naturally releasing this moisture in the warmer seasons, wool creates a cooling effect in the surroundings. It does not slump or reduce in thickness over the years unlike polyester or fiberglass. It takes up to 15% less energy to produce when compared to fiberglass and it is fully biodegradable. (EcoMarchent,- Cellulose Loose cellulose insulation made from recycled newspaper combined with a mineral fire retardant offers a sustainable and cost effective way to insulate floors and lofts as well as the walls. With an installed density of 40kg/m3 cellulose has a high thermal performance (Thermal conductivity 0.039W/mK) and also improves sound control of the building. It fills the smallest gaps, even around wiring and does not encourage the growth of fungi, mould or bacteria while providing cheap insulation solution. (EcoMarchent,- Hemp batts Hemp batts is a natural fibre thermal insulator (thermal conductivity of 0.040 W/mK.) which contains 95% of natural hemp and 5% of recycled adhesive binder (although content proportion may vary). It is highly sustainable insulation (2 tonnes of CO2 taken away for one tone of hemp harvest), which comes from waste straw from hemp harvest. Easy application and durability makes it attractive solution for shed insulation. (EcoMarchent,- Wood Fibre Wood fibre batts come from sustainable forestry and have a heat capacity of more than twice that of mineral wool (Engineering tool box). The heat capacity of a material, tells us how much thermal energy is stored in a material. Higher the heat capacity, the greater the thermal inertia, which means that it is harder to get the temperature to change. Wood fibre batts are easy to install and can be applied on walls, roofs and floors. Thermal conductivity of 0.040 W/mK and its heat capacity gives very good overall thermal performance. (EcoMarchent, 2014) 23 5.2 Selecting optimum thickness of the insulation In order to determine the optimum thickness of the insulation which will be used for the shed, analysis of how the heat loss changes accordingly to the insulation thickness was undertaken. This is summarised in Figure 14 Figure 14 - Optimum Insulation Thickness The curve presented in the Figure 14 - Optimum Insulation Thicknessshows that change in thickness from 0-50mm provides the greatest heat loss difference (65W). The heat loss difference between 50-100mm is almost four times lower (20W). Because of the market availability and the results obtained from the above figure, 50mm of insulation thickness was selected as appropriate. 5.3 Payback Time Payback time of four different isolation types are provided in Table 11 and Table 12 Table 11 - Annual Heat Demand / Cost of Demand No insulation Wood Fibre + OSB Hemp Batt + OSB Cellulose + OSB Sheep Wool + OSB Annual Heat Demand - No Gains (kW/h) Cost of demand (£- Table 12 - Energy Savings and payback time of insulation Wood Fibre + OSB Hemp Batt + OSB Cellulose + OSB Sheep Wool + OSB Energy Savings (kW/h- Isolation Cost (£- 24 Money Saved (£- Payback Time (years- When calculating the heat demand and the payback time, solar and sensible gains were not included as it will not affect the presented comparison. It can be seen on Table 12 - Energy Savings and payback time of insulation that the difference in energy demand and energy savings is very small, and that only cost of insulation has an impact on the payback time. The high payback time results from small energy demand resulting in small energy savings. 5.4 Final Selection Decision matrix was constructed in order to help with selection of the optimum insulation type. It can be seen below: Total weighted - Case II Total weighted - Case III Total weighted - Case IV 3 3 3 3 5 0.7 0.7 0.7 0.7 Payback Time 4 3 4 4 2 0.3 0.3 0.3 0.3 Environmental impact 4 4 5 5 5 0.9 0.9 1.1 1.1 Ease of installation 4 4 2 4 3 0.5 0.5 0.3 0.5 Health impact Fire risk 5 4 5 3 4 3 4 4 4 4 0.9 0.7 0.9 0.5 0.7 0.5 0.7 0.7 23 4 3.7 3.6 4 III-Cellulose I- Wood fibre IV-Sheep Wool Energy Savings II-Hemp Batts Total weighted - Case I Different Insulation Requirements Weight Grand total points - - - 4 RANKING 2 3 4 1 Scale 5 better 3 same 1 worse 25 All of the above insulation have good overall thermal performance. Their thermal conductivity ranges between- W/mK. Although wood fibre bats have the highest heat capacity, every insulation could be considered in different terms of properties. Bearing in mind initial sustainability aspect of materials, sheep’s wool and hemp bats come from fast growing sources while cellulose comes from easy to obtain, everyday use products. Even though wood bats are obtained from sustainable forestry, it takes a very long time to replenish them but they are easy to recycle. All of the products show fire retardant properties and meet fire resistance classification requirements of Euroclasses (Commission 2000/147/EEC). Sheep wool is covered with titanium based treatment, called “Thorlan”, which protects the material against insects. It is also a 100% natural product and while absorbing the moisture it releases the heat to the surroundings. During summer months this will have an opposite effect and will provide cooling. Technically each of the considered materials could be used to insulate the shed, but after evaluating the decision matrix, and by looking at the description provided above, sheep wool was selected as the best suitable insulation type. 6 Regulations The initial use of the shed was not intended as an office hence the shed was not designed to be heated and did not have to comply with ‘The Building (Scotland) Act 2003 and The Building (Scotland) Regulations 2004 Handbook in relation to Climate change (Scotland) Act 2009’ as it is part of an exception of this standard: (a) Non-domestic buildings which will not be heated, other than heating provided solely for the purpose of frost protection. The shed is now being converted to an office hence during the heating season (October to April) the shed will use some heater to keep the inside temperature at 19°C as stated in our general assumptions. Heating buildings not primarily designed to be heated will adversely affect energy efficiency and because of this, the most demanding of measures are recommended when conversion occurs. When converting an unheated building (shed) into a heated building (office) the same standards to those for an extension to the insulation envelope should be achieved. (Act, n.d., p. 473) 26 Table 13 shows the maximum U-values for building elements of the insulation envelope complying with BS EN ISO 8990:1996 –‘Thermal Insulation’. Table 13-Maximum U values for building insulation envelop; (Act, 2004, p. 469) Measurements/Calculations of U-values should also comply with BS8990 and be determined for a steady-state thermal transmission. BS8990 defines the ‘U-values’ as a measure of how much heat will pass through one square metre of a structure when the temperatures on either side of the structure differ by 1 degree Celsius (expressed in W/m2K). Table 13 summarises the U-values for the shed considering a temperature difference of 1°C. The assumed temperature difference (ΔT) in the calculations is well above ΔT=1°C specified in the regulations. Comparing the maximum U values for building insulation envelop; (Act, 2004, p. 469) is only possible after assuming new interior and outside temperature to obtain satisfactory maximum 1° difference. From the results obtain from Table 14 and Table 15 for which the annual average temperature was used, it can be seen that the U value calculated not exceed the stated ones in regulations and because they are close to them it is hard to assume but optimistically can be said that they are comply with maximum U values. U value of the roof (0.81) is the exception as it does exceed the specified regulations of 0.35. 27 7 Results 7.1 Shed breakdown providing U values and heat demand Table 14 and Table 15 represent the U-value for every component of the shed and also provide the annual heat demand. Table 14 - Summary - no insulation Component Side Panel (Natural ) Side Panel (Combined) Back Panel (Natural) Front Panel (Combined) Windows Roof Floor Total Shed Heat Demand (kW/h) NO INSULATION Average U value Average Annual Heat Loss (W/m²K) (Q) ( W- Annual Heat Demand (kW/h- 273.52 Table 15 - Summary - sheep wool Component Side Panel (Natural ) Side Panel (Combined) Back Panel (Natural) Front Panel (Combined) Windows Roof Floor Total Shed Heat Demand (kW/h) Insulation - Sheep Wool (k=0.042 W/mK) Average U value Average Annual Heat Loss (W/m²K) (Q) ( W- Annual Heat Demand (kW/h- 126.13 The average U value has been calculated for every month as the average temperature changes resulting different U values. As expected, the panels open to the wind have higher heat losses than the one obstructed. The roof has the highest U-value and the biggest area (5.91m2) resulting in highest heat losses. 28 7.2 Final Shed Heat Demand and Payback time After all of the above calculations were conducted, providing optimal thickness of insulation, insulation type and also the window selection, final calculation for heat demand of the shed can be provided. It is summarised in Figure 15 Heat Demand No Insulation vs Sheep Wool- No Insulation Heat Demand (kW/h) Sheep Wool Heat Demand (kW/h) Figure 15 - Actual Heat Demand Comparison between sheep wool and no insulation Table 16 provides final payback time for the insulation type selected. Table 16 - Final Payback Time of Insulation No Insulation- - Annual heat Demand (kW/h) Cost of Demand (£) Energy Savings Money Savings Isolation Cost Payback Time Sheep Wool- As previously discussed, the payback time is considerably high. This is because the difference between the heat demand is small, resulting in small energy savings. 29 8. Discussion and limitations Results presented above are final, but this does not imply that they are correct. Due to a great number of limitations and assumptions made, these results needs to be examined very carefully and critically commented on. It is known that natural convection will not occur due to doors and windows being opened throughout the day and also due to the shed fabric containing air gaps. This implies that ventilation losses should be associated. For calculation purposes the inside conditions were assumed to be natural convection only. In addition, the heat inside the shed is assumed to be isothermal which is not realistic as the temperature will vary at different levels in the shed. Hot air would rise and accumulate under the roof while cooler air would drop down to the floor. If the flow inside the shed was treated realistically implying forced convection, the heat transfer coefficients would be greater resulting in higher heat loss. This implies that the calculated heat demand is under-estimated. As Table 15 shows the roof has the lowest annual U value meaning that with hot air rising the heat losses would be even greater. Obtaining the heat demand using the average daily temperature is also not accurate as the temperature considered should be the temperature for the hours when the shed is being used. This assumption has an important impact on ΔT and would increase significantly the heat demand of the shed if used during cold hours. The payback time for the insulation was approximately 11 years. Realistic conditions would result in higher heat demand hence reducing the payback time of the insulation. This factor should be taken into consideration with a careful approach. It can be seen that there is no heating requirement during summer months for both insulated and non-insulated conditions. During winter months the heat demand is approximately 3 times greater without insulation. 30 9. Recommendations  To obtain more realistic results further analysis has to be taken which will not assume ideal conditions,  When dealing with larger heat demands and larger areas of glazing, double glazed windows could be considered, for the shed, replacement of single glazed windows is not cost effective, and the payback time exceeds the lifetime of the shed. Therefore, it is recommended not to replace windows,  Sheep wool is recommended for the insulation material,  50mm of insulation is recommended as it provides cost effective reduction of heating load. Also, market availability of insulation limits the thickness to 50mm and 100mm.  When the shed is built, the orientation of the shed should be considered to provide sheltering when possible and to maximise solar gains. This will reduce the overall heating demand.  Carpets on the floor would increase insulation hence resulting in lower heat demand  Painting the external surface of the walls in black color would result in higher solar radiation absorption hence lower heat demand. 10. Conclusion From the report it can be concluded that installing insulation is a very effective way of decreasing the heat demand. The overall annual energy demand was reduced by almost 2/3. The relative long payback time of up to 12 years can be interpreted differently. When moderate use of the shed is considered the payback time significantly decrease. For environmental conscious person, the payback time would be neglected as the invested cost is around £260, this amount is compensated by positive contribution to environment and the idea of sustainability. Further analysis in a form of life cycle assessment should be undertaken to determine the exact environmental impact of the shed, insulations and windows. Ventilation losses are almost half of the heat demand but the solar and sensible gains have a considerably high impact and help to counterbalance the heat demand. Several assumptions had to be stated to evaluate appropriate data which helped to understand importance of small aspects while calculating heat demand for the shed. The project feasibility can be improved by applying recommendations given. 31 11. References Act, S. G., 2004. The Building (Scotland) Regulations 2004 Handbook, s.l.: s.n. Act, S. G., n.d. s.l.: s.n. Alisdair, M., 2014. Electrical design engineer at GDM partnership [Interview] -). Anon., 2012. [Online] Available at: http://www.doubleglazing.com/windows/double-glazing-benefits/energy-efficiency/ Anon., 2014. Shedwarehouse. [Online] Available at: http://www.shedswarehouse.com/id-10377OXFORD_6ft_x_8ft_Premier_Reverse_Tongue_and_Groove_Apex_Shed_Higher_Ridge_(12mm_Tan dG_Floor_and_Roof).aspx [Accessed-]. ASHREA, n.d. ASHREA Handbook- Fundamentals. Cdr edition ed. 2011: ASHREA. box, E. t., 2011. www.engineeringtoolbox.com. [Online] Available at: www.engineeringtoolbox.com/heat-gains-lights-d_709.html [Accessed-]. EcoMarchent, 2014. www.ecomerchant.co.uk. [Online] Available at: www.ecomerchant.co.uk Jan F. Kreider, P. S. C. A. R., 2010. Heating and Cooling of Buildings. 1 ed. s.l.:s.n. 32 12. Appendices 12.1. Excel Clarification On the attached CD, a folder containing five excels spread-sheets can be found: 1. Heat Transfer calculations 2. Summary of the calculations 3. Losses and gains heat demand 4. Insulation market research 5. Insulation justification 1. Heat transfer calculations The heat transfer calculations have been split into seven sections respectively, front panel, window, side panel, back panel, roof and floor. Six sections composed of two sheets that describe the heat transfer without insulation and with insulation. The seventh section presents the calculations for the floor. The structure of each spread sheet except windowiso10077 is as follows: - Inside Calculation - (Insulation Calculation) - Outside Calculation - (Combined) - Results - Data sheet section Each sheet contains its own data sheet section as parameters are changing dependent upon the panel. The datasheet section also contains a thermophysical properties table used for interpolating. The first tab contains a macro. First a suitable value should be inputted in the “outside temperature cell” then pressing the button will iterate and provide a summary of results. Note that, after the macro is run the assumed temperature is defined as 18.9, this value ensures when the macro is run for a second time that the Rayleigh number is positive. As the macro redefines the assumed internal wall temperature, the results are incorrect except for the summary. The macro was initially planned to be available for every tab, but due to time restriction it was only implemented once. 33 12.2 Solar Gains Area of Window (m²) Month January February March April May Jun July August September October November December 0.5 Passive Gains Single South 90° (kW/h per m² per day- Total passive gains/year (kW/h) Area of Window (m²) Month January February March April May Jun July August September October November December Passive Gains 3h/day for month/ area- 0.5 Passive Gains Double South 90 (kW/h per m² per day- Total passive gains/year (kW/h) 34 Passive Gains 3h/day for month/ area- 12.3 Sensible Gains Assumptions:  Two fluorescent 20W bulbs, equivalent to two 100W bulbs  Desk lamp with fluorescent 15W bulb Using fluorescent fixtures: 𝑞𝑒𝑙 = 𝑊 ∗ 𝐹𝑢𝑙 ∗ 𝐹𝑠𝑎 Fsa - Special allowance factor for fluorescent bulbs recommended value: 1.20 (ASHREA, n.d.) Ful – Light use factor W- Wattage  20𝑊 ∗ 1 ∗ 1.20 = 24𝑊 24𝑊 ∗ 3ℎ = 72𝑊ℎ/𝑤𝑜𝑟𝑘𝑖𝑛𝑔𝑑𝑎𝑦(3ℎ)  15𝑊 ∗ 1 ∗ 1.20 = 18𝑊 18𝑊 ∗ 3ℎ = 54 𝑊ℎ/ 𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑑𝑎𝑦 (3ℎ) Sensible and Latent Heat Gains from occupant: Table 1, “Representative Rates at Which Heat and Moisture Are Given Off by Human Beings in Different States of Activity” from ASHREA Fundamentals gives data for the heat gains from a male office worker doing light seated work. (ASHREA, n.d.) 130𝑊/ℎ 130𝑊 ∗ 3 = 390𝑊ℎ/𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑑𝑎𝑦 (3ℎ) Total Heat Latent Heat Sensible Heat 130 W 45 W 70 W Appliances Heat released by computers, printers and other office appliances can be significant and should be considered in heat gains calculations. “There is a considerable uncertainty in the 35 estimated heat gain from appliances owing to the variation in appliances and the varying usage schedules. “ (Jan F. Kreider, 2010) According to Heating and Cooling of Buildings a realistic approach is to take 50% of the total nameplate ratings to show peak heat gain during maximum usage of the appliances, therefore: 𝑄𝑔𝑎𝑖𝑛 = 0.5 ∗ 𝑄𝑛𝑎𝑚𝑒𝑝𝑙𝑎𝑡𝑒 𝑟𝑎𝑡𝑖𝑛𝑔 Actual heat output from laptop can be calculated from OHMS law. -Li-ion battery, 10.8 V, 5-6 A 𝑃(𝑊) = 𝐸 ∗ 𝐼 10.8 𝑉 ∗ 5,5 𝐴 =- 𝑊 52.54 ∗ 0.5 = 26.27𝑊 ∗ *Some of that energy is converted to chemical energy not heat. A fair assumption of 10W of Heat can be generated during moderated work of the laptop. (Alisdair, 2014) Printer (laser): 80W (assuming 10min/ 3h working day operation) 80𝑊 ∗ 0.5 = 40𝑊 40𝑊 = 3.3 𝑊ℎ/ 𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑑𝑎𝑦(3ℎ) 12∗ *Value for Printer has to be added separately (only 5min operation time, 1/12 of and hour) Total heat gains from Lights, occupant and appliances 24𝑊 + 18𝑊 + 30𝑊 + 130𝑊 = 185.3𝑊 185.3𝑊 ∗ 3ℎ = 546𝑊ℎ + 3.3𝑊ℎ (𝑝𝑟𝑖𝑛𝑡𝑒𝑟) = 549.3𝑊ℎ/ 𝑑𝑎𝑦 𝑇𝑜𝑡𝑎𝑙 𝑝𝑒𝑟 𝑑𝑎𝑦: 549.3𝑊ℎ/ 𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑑𝑎𝑦(3ℎ) Total month kWh (20 days each 3h): 0.549 ∗ 20 = 11 𝑘𝑊ℎ 36 12.4 Ventilation Losses To calculate the air change specific heat loss, certain air change per hour for the whole shed needs to be assumed. As mentioned in general assumptions, the air change per hour is in order of 5.5 for no insulation and 3 with insulation. To determine the ventilation losses, volumetric flow rate/sec (m3/s) was obtained. This multiplied by density, (1.2 kg/m3 at 20 C) gives the mass flow rate. Mass flow rate multiplied by specific heat capacity (Cp = 1.0007 kJ/kg.K at 293K) gives the ventilation heat loss rate in kW/K. Table 17- Monthly ventilation losses with no insulation No Insulation Base Temperature Month January February March April May Jun July August September October November December 19 C Average Temp ( C ) Degree Days Monthly Heat Demand (Jules) Heat Demand (kWh) Annual Heat Demand 3,5 3,3 5 7,4 10,1 12,9 14,2 14,2 12,2 9,5 5,4 3,9 153,90 - -,-,-,-,-,-,-,-,-,-,-,-,97 18,87 19,12 17,05 14,12 10,84 7,43 5,84 5,84 8,28 11,57 16,56 18,39 kw/h Table 18 - Monthly ventilation losses with insulation Base Temperature 19 Average Temp ( C Month ) January 3,5 February 3,3 March 5 April 7,4 May 10,1 Jun 12,9 July 14,2 August 14,2 September 12,2 October 9,5 November 5,4 December 3,9 Annual Heat Demand 83,95 With Insulation C Degree Days Monthly Heat Demand (Jules- -,-,-,-,-,-,-,-,-,-,-,-,80 kw/h 37 Heat Demand (kWh) 10,29 10,43 9,30 7,70 5,91 4,05 3,19 3,19 4,52 6,31 9,03 10,03