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Heating - Solar air heater - Institutional / Canada (Cold Lake Airport)
Case study assignment
A Canadian military base located north of Edmonton, Alberta is interested in using renewable energy to reduce natural gas consumption at its facilities. Engineering staff at the base asked you to assess the feasibility of installing a solar air heating (SAH) system to offset a portion of the ventilation air heating demand for an existing sewage treatment plant.
Site information
The military base is located near the town of Cold Lake in the Province of Alberta, about 280 km north-east of Edmonton. The sewage treatment plant was built 10 years ago and uses a natural gas-fired heating section in a rooftop air-handling unit for all space heating. The heating system's seasonal efficiency is 75%. The minimum allowable delivered air temperature is 18°C and the maximum is 30°C. The floor area of the building is approximately 320 m². The building is insulated; walls have an RSI value of 2.6 and the roof has an RSI value of 2.1. The south-facing wall of the building has an area of approximately 240 m² available for solar collectors and is not shaded at any time. The base has requested that black coloured collectors be used to optimize performance. Assume that this is a "commercial" building for the purpose of this analysis.
The plant requires high rates of ventilation to maintain acceptable indoor air quality. Based on previous experience with the building, ventilation air heating is required from around the middle of September to the middle of May. The design flow rate of outdoor air required is 17,000 m³/h. This flow rate is required 24 hours per day, 7 days per week. The engineering calculations have shown that buoyancy forces will be sufficient to move air through the collectors and to the intake of the existing air handling unit (i.e. a new fan will not be required).
Financial information
The base has the option to purchase the system or have it installed as part of an energy performance contract. You are asked to investigate the purchase option. In this scenario the Department of National Defence would pay for the system outright.
The SAH system collector is expected to cost about $110/m2 (not including installation). The installed equipment is expected to have a service life of 30 years with an annual maintenance cost of $400/yr.
The current cost of natural gas for the base is approximately $0.25/m³. The fuel cost escalation rate is uncertain but on average is expected to be 4.5% per year. The inflation rate is expected to be uniform at approximately 2.5% per year. The discount rate used for the analysis should be 9%.
The project is eligible for a federal government incentive which can provide an incentive of 25% of the purchase and installation costs of the system, up to a maximum refund of $80,000, for qualifying systems.
Prepare a RETScreen study, including a greenhouse gas emission reduction analysis, to determine the feasibility of the project. Document 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
A Canadian military base located near Cold Lake, Alberta (about 280 km north-east of Edmonton) recently initiated an energy conservation program to reduce fuel costs. As part of this program, a solar air heating (SAH) system was installed on a sewage treatment facility to reduce the natural gas consumption of the building's heating system. The sewage treatment plant was built 10 years ago and requires ventilation air 24 hours a day, 7 days a week to maintain acceptable indoor air quality. In the northern Alberta climate, the SAH system is expected to operate 7 to 8 months of the year.
This is the first SAH system installed at the Cold Lake base and the first for the Department of National Defence. With the assistance of Natural Resources Canada's Federal Buildings Initiative (FBI), the base decided to pursue an energy performance contract with an energy services company to finance a series of energy conservation measures, including this project. Under this contract, the system was installed in July 2002 and has been operating reliably since then.
System description
The solar air heating system preheats outdoor air that is required for ventilation. This reduces the heating demand for the conventional natural gas-fired heating section in the existing rooftop air-handling unit. The SAH system cladding is installed on the south facing building wall. The solar heated outdoor air rises through the collectors to a plenum at roof level. From the plenum, the air is ducted to the intake of an existing air handler where it is further conditioned (if required) and supplied to the building through the existing supply ductwork. Modulating dampers were included in the design to balance the temperature of the air during warmer weather. During summer months, when the outdoor air does not require heating, the SAH system is bypassed.
The total collector area is 140 m², which covers approximately 60% of the south facing wall of the building. The design flow rate for the system is 17,000 m³/h.
Lessons learned
This solar air heating project has demonstrated that renewable energy can be cost effective in addition to being environmentally appropriate. SAH applications in colder climates with a good solar resource that require high rates of outdoor air for ventilation are particularly attractive.
Photo
Sewage Treatment Plant Solar Air Heater, Cold Lake, Alberta, Canada
Références
Case study assignment
A Canadian military base located north of Edmonton, Alberta is interested in using renewable energy to reduce natural gas consumption at its facilities. Engineering staff at the base asked you to assess the feasibility of installing a solar air heating (SAH) system to offset a portion of the ventilation air heating demand for an existing sewage treatment plant.
Site information
The military base is located near the town of Cold Lake in the Province of Alberta, about 280 km north-east of Edmonton. The sewage treatment plant was built 10 years ago and uses a natural gas-fired heating section in a rooftop air-handling unit for all space heating. The heating system's seasonal efficiency is 75%. The minimum allowable delivered air temperature is 18°C and the maximum is 30°C. The floor area of the building is approximately 320 m². The building is insulated; walls have an RSI value of 2.6 and the roof has an RSI value of 2.1. The south-facing wall of the building has an area of approximately 240 m² available for solar collectors and is not shaded at any time. The base has requested that black coloured collectors be used to optimize performance. Assume that this is a "commercial" building for the purpose of this analysis.
The plant requires high rates of ventilation to maintain acceptable indoor air quality. Based on previous experience with the building, ventilation air heating is required from around the middle of September to the middle of May. The design flow rate of outdoor air required is 17,000 m³/h. This flow rate is required 24 hours per day, 7 days per week. The engineering calculations have shown that buoyancy forces will be sufficient to move air through the collectors and to the intake of the existing air handling unit (i.e. a new fan will not be required).
Financial information
The base has the option to purchase the system or have it installed as part of an energy performance contract. You are asked to investigate the purchase option. In this scenario the Department of National Defence would pay for the system outright.
The SAH system collector is expected to cost about $110/m2 (not including installation). The installed equipment is expected to have a service life of 30 years with an annual maintenance cost of $400/yr.
The current cost of natural gas for the base is approximately $0.25/m³. The fuel cost escalation rate is uncertain but on average is expected to be 4.5% per year. The inflation rate is expected to be uniform at approximately 2.5% per year. The discount rate used for the analysis should be 9%.
The project is eligible for a federal government incentive which can provide an incentive of 25% of the purchase and installation costs of the system, up to a maximum refund of $80,000, for qualifying systems.
Prepare a RETScreen study, including a greenhouse gas emission reduction analysis, to determine the feasibility of the project. Document 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 building type is defined as "commercial" as opposed to "industrial" for two reasons: a.) The calculation should not include destratification savings because the solar air heating (SAH) system is ducted to an existing air handler and no additional destratification measures (e.g. fabric ducts) are implemented; and b.) the sewage treatment plant requires a constant design flow of outdoor air. For the "industrial" building type however, the "design airflow rate" implies a mix of indoor and outdoor air that varies depending on SAH system outlet temperature.
- The design objective selected for the solar collectors was "standard operation" since the intent was to design the system to provide a balance between maximizing renewable energy collected and maximizing efficiency.
- The "building temperature stratification" input is set to zero because savings from destratification should not be included in this analysis. This is because the SAH system is ducted to an existing air handler and no additional destratification measures (e.g. fabric ducts) are implemented.
- No incremental fan power is required since buoyancy is sufficient to overcome frictional losses through the collectors and the added ductwork.
- A relatively low cost of $500 was included for the feasibility study because the RETScreen analysis should be sufficient to determine the feasibility of this project and can be completed quickly. Also, a full feasibility study is not required since there has been ample experience with similar systems and solar air heating for ventilation air is a well-developed technology.
- A relatively high transportation cost of $2,000 was included to allow for delivery of the equipment to the remote location.
- There are no credits for cladding material/labour since the existing cladding was less than 10 years old and in very good condition.
- The costs for fans and ducting materials and labour are relatively low since only ductwork was required (i.e. no additional fans were necessary).
- There are no credits for fan and duct material/labour since there were no changes needed to be made to this equipment in the base case scenario.
- It is not necessary to define the base case electricity system for the greenhouse gas analysis as the base case heating system fuel type is natural gas (i.e. not electricity), and also due to the fact that the incremental fan power is equal to zero, so there is no additional electricity required in the proposed case heating system.
Results
A Canadian military base located near Cold Lake, Alberta (about 280 km north-east of Edmonton) recently initiated an energy conservation program to reduce fuel costs. As part of this program, a solar air heating (SAH) system was installed on a sewage treatment facility to reduce the natural gas consumption of the building's heating system. The sewage treatment plant was built 10 years ago and requires ventilation air 24 hours a day, 7 days a week to maintain acceptable indoor air quality. In the northern Alberta climate, the SAH system is expected to operate 7 to 8 months of the year.
This is the first SAH system installed at the Cold Lake base and the first for the Department of National Defence. With the assistance of Natural Resources Canada's Federal Buildings Initiative (FBI), the base decided to pursue an energy performance contract with an energy services company to finance a series of energy conservation measures, including this project. Under this contract, the system was installed in July 2002 and has been operating reliably since then.
System description
The solar air heating system preheats outdoor air that is required for ventilation. This reduces the heating demand for the conventional natural gas-fired heating section in the existing rooftop air-handling unit. The SAH system cladding is installed on the south facing building wall. The solar heated outdoor air rises through the collectors to a plenum at roof level. From the plenum, the air is ducted to the intake of an existing air handler where it is further conditioned (if required) and supplied to the building through the existing supply ductwork. Modulating dampers were included in the design to balance the temperature of the air during warmer weather. During summer months, when the outdoor air does not require heating, the SAH system is bypassed.
The total collector area is 140 m², which covers approximately 60% of the south facing wall of the building. The design flow rate for the system is 17,000 m³/h.
Lessons learned
- This is the first SAH system for the Department of National Defence.
- The system has operated reliably since it was installed.
- The application of the SAH system at a sewage treatment facility is appropriate since high outdoor air rates are required to maintain acceptable indoor air quality.
- The northern location of the installation results in a relatively large ventilation heating demand that is well suited to be met by the SAH system.
This solar air heating project has demonstrated that renewable energy can be cost effective in addition to being environmentally appropriate. SAH applications in colder climates with a good solar resource that require high rates of outdoor air for ventilation are particularly attractive.
Photo
Sewage Treatment Plant Solar Air Heater, Cold Lake, Alberta, Canada
Références
- Jones, Rowland, "Personal communication," Conserval Engineering Inc., 2002.
- Northcott, Rod, "Personal communication," 4 Wing Military Base, Department of National Defence, 2002.
- Pelton, Michael, "Personal communication," Enermodal Engineering Ltd., 2002.
