4. Chapter four: Simulation Results, Tehran, US Code (IEEC+FNRC)
4.2. Simulation results and analysis for fixed SHGC
In the first part of this chapter, the influence of both window to wall ratio and window’s U-Value on energy consumption have been studied. Window‘s size ranges from minimum to maximum possible size (10-90 percent) and U-Value ranges from 0.4 to 1.2 following NFRC rates. The building’s energy performance is studied in three outputs of cooling, heating and total consumption. The “total” does not consist of just only cooling and heating, but also artificial lighting and house appliances.
Windows are weak parts of building envelope regarding energy loss, because of their low U-Values. Therefore, in most cases increasing their size means increase in heat transfer through building’s envelope, but since they provide natural light and can help heating spaces in cold times, they would be able to reduce energy consumption of artificial lighting and heating.
In general, and in this series of simulations, required energy for cooling increases by increasing window size and for heating decreases, because of receiving more sun radiant heat through fenestration. Since U-Values of windows are low and extracted from strict codes, they do not have big differences to UV of other parts of envelope, therefore their large size does not result in high amount of heat exchange and energy loss. As an inclusive rule, adding value of thermal transmittance will end to more heat loss and more energy consumption.
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4.2.1. Cooling energy consumption simulation results Variable 01---window’s size: 10% - 90%
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
TEHRAN1-NORTH-SHGC 0.4 UV(0.4-1.2)- COOLING
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
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4.2.2. Cooling energy consumption simulation analysis Variable 01---window’s size: 10% - 90%
Variable 02---window’s U-value: 04 - 1.2 Fixed---SHGC: 0.4
Least variation change: The minimum change in energy consumption graphs, can be seen in the north direction, where 127.78 to 211.60 (83.82 kWh)
Most variation change: The maximum change in energy consumption graphs, can be seen in the south direction, where 135.36 to 352.25 (216.89 kWh)
Notable points:
1. In all four main directions there is Incremental linear graph lines, which imply that increasing window size will result in more energy consumption for cooling of internal spaces.
2. Although higher UV has better performance, but graph’s lines are very close together in both angel and measure, and almost are in accordance to each other.
This shows that disadvantage of rising window size on energy consumption is nearly same in all amounts of UV. The reason is that heat gain through windows is done by Radiation Transmission, not conduction.
3. In north direction, graph shows smaller trend to increase. The reason is less amount of sunlight penetration, in this envelope side, and lower heat gain from sun which needs fewer cooling energy.
4. At the graph of “all dir.”, when W/W ratio gets to higher percentages, we see that progressive slope of the graph lines are declined. It is why the simulation model is one-unit space that has window on all four direction walls; In high window percentages, receiving sunlight gets to very high amount and changing window size has lower influence on it.
Instructions:
For cooling internal spaces, the less size of window has better energy performance, to the extent of daylight need. There is not any preference for increasing window to wall percentage.
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4.2.3. Heating energy consumption simulation results Variable 01---window’s size: 10% - 90%
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
TEHRAN1-WEST-SHGC 0.4 UV(0.4-1.2)- HEATING
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
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4.2.4. Heating energy consumption simulation analysis Variable 01---window’s size: 10% - 90%
Variable 02---window’s U-value: 04 - 1.2 Fixed---SHGC: 0.4
Least variation change: The minimum change in energy consumption graphs, for three directions of east, west and north are almost same: East 628.38 to 909.05 (280.67 kWh), West: 635.82 to 910.82 (275.00 kWh) and North: 792.09 to 1078.17 (286.08 kWh) Most variation change: The maximum change in energy consumption graphs, can be seen in the South direction, where 233.3 to 830.82 (597.52 kWh)
Notable points:
1. Both east and west directions, have similar trends and graphs which decrease slightly and constantly by w/w ratio increase. Having larger windows let more sunshine inside while their low UV prevents heat loss conductivity.
2. In the north direction, there is two opposite graph trends, rising for higher U-Values and failing for lower U-U-Values. Heat gain in building’s windows in north direction is not as much as east and west. Therefore, only in lower UV there is positive heat exchange through windows which means getting more sun’s warmness than transmitting heat from inside to outside.
3. In south it could be seen that numbers have come down considerably by increasing window size. Obviously, it is much sun light in the south that declines need for heating, in particular using these high-quality windows (low UV) that hinder heat transfer to outside.
4. At the graph of “all dir.”, for lower UV it is dropping while for higher UV it comes down then goes up. Large windows having less thermal resistance, although get more solar heat but let more heat transfer through it to outside.
Instructions:
For heating internal spaces, in all four main directions, it is recommended to increase window size for consuming less heating energy, at all amount of UV. The only exception high UV in the north side and all-dir. that smaller windows performance have better performance.
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4.2.5. Total energy consumption simulation results
Variable 01---window’s size: 10% - 90%
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
TEHRAN1-SOUTH-SHGC 0.4 UV(0.4-1.2)- TOTAL
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
TEHRAN1-NORTH-SHGC 0.4 UV(0.4-1.2)- TOTAL
TOTAL ENERGY CONSUMPTION (KWH)
WINDOW TO WALL RATIO (%)
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4.2.6. Total energy consumption simulation analysis Variable 01---window’s size: 10% - 90%
Variable 02---window’s U-value: 0.4 - 1.2 Fixed---SHGC: 0.4
Least variation change: The minimum change in energy consumption graphs, for two directions of east and west are almost same: East 1283.04 to 1440.61 (157.57 kWh) and West: 1331.78 to 1499.14 (167.36 kWh).
Most variation change: The maximum change in energy consumption graphs, can be seen in the South direction, where 938.34 to 1318.97 (380.63 kWh)
Notable points:
1. Both east and west directions, have similar trends and graphs so that changing UV and window size has not great impact on energy consumption. For higher UV energy consumption rises by making windows larger and for lower UV it reduces, whilst for medium UV of 0.8 by increasing w/w energy consumption remains constant. It means that in this range of UV, the amount of energy loss through windows are almost same to energy got by window in the form of heat and light.
2. In the north direction, the general trade is similar to east and west, but slightly more increase of all graphs. Clearly the reason is less solar radiation in the north and lower energy receive. Windows UV is close to other envelope’s part and having large fenestration does not lead to much heat exchange.
3. In south it could be seen that energy consumption amounts have come down considerably by increasing window size. Obviously, it is much sun light and warmness in the south that declines need for heating. In high window sizes, slope of decreasing graphs gets down, by reason of overheating and need to cooling south spaces.
4. If building has window in all directions, the percentage of 30-40 for w/w has best performance while previous decreasing graphs start to increase upward.
Instructions:
In the main, for reducing total energy consumption it is recommended to provide larger windows in south but for other directions there is not strong preference just for higher UV larger windows, and for lower UV smaller windows have better performance.
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