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Heating - Solar air heater - Apartment building / Canada
Case study assignment
You have been hired by a government housing authority to prepare a feasibility study on their behalf. The client owns and operates a number of older high-rise apartment buildings and some of them are in need of repair due to moisture penetration of the exterior walls. The client's structural consultant has recommended that a metal rain screen be added to the affected walls to prevent further degradation of the bricks and also to provide a method of insulating the walls from the exterior side.
Apartment buildings require continuous ventilation for the corridors and common areas. Most buildings have the fresh air fan located on the roof. Heat recovery is generally not an option because of the high cost of collecting all of the exhaust ducts and bringing them to the intake.
Solar air heating (SAH) technology has improved dramatically over the past decade and it is now possible to have a maintenance-free, unglazed, all-metal solar absorber panel mounted as a rain screen. The solar rain screen can be connected at the roof level to the intake of the existing ventilation fans. The housing authority would like you to prepare a preliminary feasibility analysis of utilising a solar rain screen and determine whether the incremental costs of the solar system would have a simple payback period less than 10 years.
Site information
The twenty-four story senior citizens building, located in Windsor, Ontario, Canada, has four corner sections that require rain screens, with one of the corners facing south. The south corner is 61 m high and 5.5 m wide. The fresh air intake fans are located about 25 m from the south wall corner; there are a number of obstacles between the corner and the fans. The capacity of the fans is 23,000 m³/h of continuous fresh air. Six existing gas heaters, connected to one intake duct, heat the fresh air. The heaters are not very efficient, with an estimated seasonal burner efficiency of 67%.
The building is predominantly dark brown. It is insulated with 5 cm of rigid fibreglass having a thermal conductivity of about 0.033 W/(m-ºC).
Financial information
The housing authority has allocated a repair budget for rain screens; the incremental costs of the solar system would be funded under this budget provided that the payback is less than 10 years. For the analysis, operation & maintenance costs are not considered as the solar rain screen is the same material as conventional rain screen and there are no additional fans required. As this is a government-owned facility, corporate taxes do not apply.
The cost of gas is approximately $0.20/m³. The housing authority uses a discount rate of 7%.
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
Real project
Results
In 1993, the Ontario Ministry of Housing implemented a recladding program for several apartment buildings that had brick deterioration problems. Conserval Engineering prepared a feasibility analysis for a number of the apartment buildings to determine whether a solar air heating (SAH) system would be cost-effective and could be implemented within an acceptable payback period.
The study showed that most apartment buildings with rooftop ventilation fans requiring rain screens were suited for the installation of a solar rain screen where the metal solar cladding would provide heated air to the intake of the rooftop fresh air fans. The Windsor Senior Citizen's Complex, the tallest building in the study and the one highlighted in this example, was one of several projects that were implemented. The SAH systems, operating since 1994, show significant energy savings - roughly 210 MWh per year. The increase in the temperature of the air through the panels has been as high as 30 °C.
System description
The unglazed solar air heater installed at the Windsor Senior Citizen's building was 61 m high by 5.5 m wide with a total area of 335 m². A brown colour was selected to match the 3 non-solar corners. The system has no heat storage. Whenever solar energy is available, the heated air is collected and directed into the intake of the existing gas heated fresh air fans located on the roof. The total capacity of the fans is 23,000 m³/h, which gives a flow rate through the collector of approximately 69 m³/(h-m²).
The incremental cost for the SAH system over a conventional rain screen was approximately $29,000 and the predicted annual fuel cost savings were approximately $5,000, producing a payback of approximately 6 years.
Lessons learned
Photo
World's Tallest Air Collector Installed as Combined Solar Collector and Rain Screen for Ouellette Manor Senior Citizen's Building, Windsor, Ontario, Canada
References
Case study assignment
You have been hired by a government housing authority to prepare a feasibility study on their behalf. The client owns and operates a number of older high-rise apartment buildings and some of them are in need of repair due to moisture penetration of the exterior walls. The client's structural consultant has recommended that a metal rain screen be added to the affected walls to prevent further degradation of the bricks and also to provide a method of insulating the walls from the exterior side.
Apartment buildings require continuous ventilation for the corridors and common areas. Most buildings have the fresh air fan located on the roof. Heat recovery is generally not an option because of the high cost of collecting all of the exhaust ducts and bringing them to the intake.
Solar air heating (SAH) technology has improved dramatically over the past decade and it is now possible to have a maintenance-free, unglazed, all-metal solar absorber panel mounted as a rain screen. The solar rain screen can be connected at the roof level to the intake of the existing ventilation fans. The housing authority would like you to prepare a preliminary feasibility analysis of utilising a solar rain screen and determine whether the incremental costs of the solar system would have a simple payback period less than 10 years.
Site information
The twenty-four story senior citizens building, located in Windsor, Ontario, Canada, has four corner sections that require rain screens, with one of the corners facing south. The south corner is 61 m high and 5.5 m wide. The fresh air intake fans are located about 25 m from the south wall corner; there are a number of obstacles between the corner and the fans. The capacity of the fans is 23,000 m³/h of continuous fresh air. Six existing gas heaters, connected to one intake duct, heat the fresh air. The heaters are not very efficient, with an estimated seasonal burner efficiency of 67%.
The building is predominantly dark brown. It is insulated with 5 cm of rigid fibreglass having a thermal conductivity of about 0.033 W/(m-ºC).
Financial information
The housing authority has allocated a repair budget for rain screens; the incremental costs of the solar system would be funded under this budget provided that the payback is less than 10 years. For the analysis, operation & maintenance costs are not considered as the solar rain screen is the same material as conventional rain screen and there are no additional fans required. As this is a government-owned facility, corporate taxes do not apply.
The cost of gas is approximately $0.20/m³. The housing authority uses a discount rate of 7%.
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 "High temperature rise" design objective has been selected, there are 3 reasons for this choice. First, it is financially preferable - the project has a higher return and a shorter payback period with the larger collector. This reflects the high cost of the ducting, which is fixed regardless of the size of the collector. Second, the whole corner wall needed to be clad in a rain screen, and the client did not wish to clad part of the wall in solar rain screen and the rest in conventional rain screen. Third, residential building operators typically prefer a high average air temperature rise to high efficiency operation.
- There are no development costs in excess of those for a conventional rain screen.
- No canopy was used in this installation.
- Since no additional fan was necessary, balance of equipment costs are solely for ducting. The ducts for this building were particularly expensive due to the long run of duct, the obstacles between the solar collector and the intake fans, and the use of insulated ducts, necessitated by the winds prevalent at the top of the 24 story building.
Real project
Results
In 1993, the Ontario Ministry of Housing implemented a recladding program for several apartment buildings that had brick deterioration problems. Conserval Engineering prepared a feasibility analysis for a number of the apartment buildings to determine whether a solar air heating (SAH) system would be cost-effective and could be implemented within an acceptable payback period.
The study showed that most apartment buildings with rooftop ventilation fans requiring rain screens were suited for the installation of a solar rain screen where the metal solar cladding would provide heated air to the intake of the rooftop fresh air fans. The Windsor Senior Citizen's Complex, the tallest building in the study and the one highlighted in this example, was one of several projects that were implemented. The SAH systems, operating since 1994, show significant energy savings - roughly 210 MWh per year. The increase in the temperature of the air through the panels has been as high as 30 °C.
System description
The unglazed solar air heater installed at the Windsor Senior Citizen's building was 61 m high by 5.5 m wide with a total area of 335 m². A brown colour was selected to match the 3 non-solar corners. The system has no heat storage. Whenever solar energy is available, the heated air is collected and directed into the intake of the existing gas heated fresh air fans located on the roof. The total capacity of the fans is 23,000 m³/h, which gives a flow rate through the collector of approximately 69 m³/(h-m²).
The incremental cost for the SAH system over a conventional rain screen was approximately $29,000 and the predicted annual fuel cost savings were approximately $5,000, producing a payback of approximately 6 years.
Lessons learned
- SAH system should be considered whenever a metal rain screen or wall repair work is required: the incremental cost of the solar project is normally justified.
- The cost of connecting the solar collector to the existing fans can be significant and the ideal situation is, therefore, to have the fans located as close to the south wall as possible.
- Whenever ventilation fans require replacing, solar air preheating should also be considered.
Photo
World's Tallest Air Collector Installed as Combined Solar Collector and Rain Screen for Ouellette Manor Senior Citizen's Building, Windsor, Ontario, Canada
References
- Nikiforov, Vladimir, "Personal communication," Conserval Engineering Inc., 2000.
