Energy efficiency measures - Residential - Passive solar heating / Canada (Muskoka Airport)
Case study assignment
You are designing a "winterised" cottage and retirement home for a couple who is looking for a low maintenance property that can be left unoccupied for reasonably long periods in the winter. Your clients have been investigating high performance windows and are debating between high performance insulating glazing units (IGUs) in an insulated frame, and "superwindow" IGUs in a less insulating but good quality wood frame. You would like to show them a comparison of these options.
The high performance IGU is double-glazed with a single low-e film plus argon gas fill. The "superwindow" IGU is triple-glazed with double low-e films and double argon fill. Both upgrade windows are to be compared with a standard double-glazed IGU in a wood frame.
Site information
The cottage will be built near the village of Dorset, east of the city of Huntsville, Ontario, Canada. The closest weather station is Muskoka Airport, a little over 60 km to the southwest. The house is set in a mixed deciduous forest with the front facing due south. The west side is comparatively clear and some trees have been cleared from the front of the house, but in general the shading is quite heavy. Winter shading is 50% at the front, 15% at the left side, 70% at the right, and 70% at the back. Summer shading is 0% at the front, 10% at the left side, 80% at the right, and 80% at the back.
The heating system is a propane-fired forced air furnace with a setback thermostat that keeps a minimum temperature when the house is empty; it has a seasonal efficiency of 92%. The cottage is not air-conditioned.
The window sizes, orientations and number of units are provided in the table.
The house has a conditioned area of 175 m² including the basement. It has high levels of insulation in the roof and walls, but low thermal mass. The internal gains are low and are estimated from the electricity bills to be 9.6 kWh per day.
Case study assignment
You are designing a "winterised" cottage and retirement home for a couple who is looking for a low maintenance property that can be left unoccupied for reasonably long periods in the winter. Your clients have been investigating high performance windows and are debating between high performance insulating glazing units (IGUs) in an insulated frame, and "superwindow" IGUs in a less insulating but good quality wood frame. You would like to show them a comparison of these options.
The high performance IGU is double-glazed with a single low-e film plus argon gas fill. The "superwindow" IGU is triple-glazed with double low-e films and double argon fill. Both upgrade windows are to be compared with a standard double-glazed IGU in a wood frame.
Site information
The cottage will be built near the village of Dorset, east of the city of Huntsville, Ontario, Canada. The closest weather station is Muskoka Airport, a little over 60 km to the southwest. The house is set in a mixed deciduous forest with the front facing due south. The west side is comparatively clear and some trees have been cleared from the front of the house, but in general the shading is quite heavy. Winter shading is 50% at the front, 15% at the left side, 70% at the right, and 70% at the back. Summer shading is 0% at the front, 10% at the left side, 80% at the right, and 80% at the back.
The heating system is a propane-fired forced air furnace with a setback thermostat that keeps a minimum temperature when the house is empty; it has a seasonal efficiency of 92%. The cottage is not air-conditioned.
The window sizes, orientations and number of units are provided in the table.
The house has a conditioned area of 175 m² including the basement. It has high levels of insulation in the roof and walls, but low thermal mass. The internal gains are low and are estimated from the electricity bills to be 9.6 kWh per day.
Financial information
The feasibility study, development, design/engineering, and overhead costs are part of the basic design and construction cost of the house and are fixed regardless of the type of window.
The base case windows are estimated to cost $175/m² for the front and $200/m² for the other three sides, the difference being due to the large proportion of fixed windows for the front. A local window supplier estimates the installed cost of the double-glazed high performance windows to be $275/m² ($260/m² for the front) and the installed cost of the triple-glazed system to be $320/m² ($300/m² for the front). For the base case and double-glazed windows, assume installation costs of $100/m², while for the triple-glazed window assume $110/m² installation costs.
Propane costs $0.48/litre. The inflation rate is 2% and the fuel cost escalation rate is assumed to be 5%.
The structure is designed to last 100 years, but the window system is expected to last only 30 years. The house is being financed with a conventional mortgage, with a down payment of 26%. The term of the mortgage is 20 years at an interest rate of 8.5%. Because the windows are part of the house and not a separate "energy project", the discount rate is no different than the basic cost of borrowing for the mortgage.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
Results
In 1995 a couple planning an early retirement approached home designer Roger Algie to prepare a design for a new cottage. The building, which would eventually become their year-round residence, would be on a wooded site on the shore of Lake of Bays, near the village of Dorset, Ontario, Canada. The couple's son was a professional engineer in the window business and he advised them to do more than the minimum if the cottage was truly to become a permanent residence.
The couple listened to the advice and built a house to R-2000 standards. The house has mechanical ventilation and double layers of gypsum board built into the walls to dampen the daily temperature swings that are part of a passive solar design approach.
One question that arose during design was the whether standard double-glazed insulated glazing units (IGUs) in a wood frame should be upgraded to either high performance IGUs (with argon fill, a low-e coating and an insulated fibreglass frame) or triple-glazed "superwindows" (with double argon fill, double low-e layers, and high quality wood frame).
The couple chose the high performance double-glaze IGUs. The house has now been operating satisfactorily for about 4 years.
System description
The window and door IGUs installed in the house are double-glazed with low-e, argon fill, and an insulating spacer. The operable windows are vinyl sliders with a U-value of 1.96 W/(m²-ºC) and a SHGC (solar heat gain coefficient) of 0.41. The fixed windows are fibreglass frame picture windows with a U-value of 1.85 W/(m²-ºC) and a SHGC of 0.63. There are three 1.8 m fibreglass glazed sliding doors with a U-value of 1.59 W/(m²-ºC) and a SHGC of 0.31.
Lessons learned
The big picture
In the final analysis, the windows for the cottage were selected based on availability, comfort, and perceived long-term value. The chosen windows have performed well and deliver good value for their cost.
In the winter of 2000 monitoring equipment was used to assess the ability of the house to gain and store solar heat. The results of the monitoring show that a building with the right windows, good insulation and proper thermal mass can very nearly heat itself such that pipes do not freeze over the winter, even if not designed to be freeze resistant and not specially tuned for passive solar gain. This demonstrates an additional value for high performance windows: maintenance requirements for seasonal buildings can be significantly reduced with appropriate design and materials.
Photo
Cottage on a Wooded Site, on the Shore of Lake of Bays, Ontario, Canada
References
The feasibility study, development, design/engineering, and overhead costs are part of the basic design and construction cost of the house and are fixed regardless of the type of window.
The base case windows are estimated to cost $175/m² for the front and $200/m² for the other three sides, the difference being due to the large proportion of fixed windows for the front. A local window supplier estimates the installed cost of the double-glazed high performance windows to be $275/m² ($260/m² for the front) and the installed cost of the triple-glazed system to be $320/m² ($300/m² for the front). For the base case and double-glazed windows, assume installation costs of $100/m², while for the triple-glazed window assume $110/m² installation costs.
Propane costs $0.48/litre. The inflation rate is 2% and the fuel cost escalation rate is assumed to be 5%.
The structure is designed to last 100 years, but the window system is expected to last only 30 years. The house is being financed with a conventional mortgage, with a down payment of 26%. The term of the mortgage is 20 years at an interest rate of 8.5%. Because the windows are part of the house and not a separate "energy project", the discount rate is no different than the basic cost of borrowing for the mortgage.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
- The results are relatively sensitive to the insulation level. This reflects the two ways in which windows affect the heating requirements: solar heat gains and thermal losses. The triple-glazed window insulates better but results in a lower solar gain. When the walls are poorly insulated, heat will escape through the wall even if the window is well insulated.
Results
In 1995 a couple planning an early retirement approached home designer Roger Algie to prepare a design for a new cottage. The building, which would eventually become their year-round residence, would be on a wooded site on the shore of Lake of Bays, near the village of Dorset, Ontario, Canada. The couple's son was a professional engineer in the window business and he advised them to do more than the minimum if the cottage was truly to become a permanent residence.
The couple listened to the advice and built a house to R-2000 standards. The house has mechanical ventilation and double layers of gypsum board built into the walls to dampen the daily temperature swings that are part of a passive solar design approach.
One question that arose during design was the whether standard double-glazed insulated glazing units (IGUs) in a wood frame should be upgraded to either high performance IGUs (with argon fill, a low-e coating and an insulated fibreglass frame) or triple-glazed "superwindows" (with double argon fill, double low-e layers, and high quality wood frame).
The couple chose the high performance double-glaze IGUs. The house has now been operating satisfactorily for about 4 years.
System description
The window and door IGUs installed in the house are double-glazed with low-e, argon fill, and an insulating spacer. The operable windows are vinyl sliders with a U-value of 1.96 W/(m²-ºC) and a SHGC (solar heat gain coefficient) of 0.41. The fixed windows are fibreglass frame picture windows with a U-value of 1.85 W/(m²-ºC) and a SHGC of 0.63. There are three 1.8 m fibreglass glazed sliding doors with a U-value of 1.59 W/(m²-ºC) and a SHGC of 0.31.
Lessons learned
- Both systems produced much better returns on investment than leaving one's money in the bank, or even some mutual funds.
- The difference in IRR for the two proposals is not so large that the choice of one system over the other will be made on price alone. The purchaser must still assign a financial value to occupant comfort.
- Superwindows will always save more energy than high performance double glazed systems, but the savings from energy alone will generally not justify their additional expense. Again, the value the user accords to comfort will determine their choice. In this case, the user felt that adequate comfort was available from the high-efficiency double-glazed windows.
The big picture
In the final analysis, the windows for the cottage were selected based on availability, comfort, and perceived long-term value. The chosen windows have performed well and deliver good value for their cost.
In the winter of 2000 monitoring equipment was used to assess the ability of the house to gain and store solar heat. The results of the monitoring show that a building with the right windows, good insulation and proper thermal mass can very nearly heat itself such that pipes do not freeze over the winter, even if not designed to be freeze resistant and not specially tuned for passive solar gain. This demonstrates an additional value for high performance windows: maintenance requirements for seasonal buildings can be significantly reduced with appropriate design and materials.
Photo
Cottage on a Wooded Site, on the Shore of Lake of Bays, Ontario, Canada
References
- Pope, Stephen, "Personal communication," Stephen F. Pope Architect, 2000.
- Thwaites, Stephen, "Personal communication," Thermotech Windows Ltd., 2000.
