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Heating - Solar water heater - Aquaculture / Canada
Case study assignment
You have been hired by a government agency to prepare a prefeasibility study for a potential solar water heating system at a fish hatchery in British Columbia, Canada. This hatchery raises salmon fry until they are large enough to transfer to a grow-out pen in the ocean. To ensure that the fish receive enough oxygen and to remove waste products, fresh well water is constantly pumped into the fish rearing tanks. This large volume of water must be heated to accelerate the growth of the fish fry. Like many fish hatcheries in British Columbia, the site is remote and the heating fuel is propane, delivered by truck. Since propane a relatively expensive fuel, solar water heating may be cost-effective in reducing operating costs at the hatchery. The government agency would like to know whether a solar water heating system is financially viable.
Site information
The hatchery is located close to Comox, on Vancouver Island, British Columbia. Fresh water flows into the facility at an average rate of 700 litres per minute at a temperature varying from 6 ºC in spring to 8.5 ºC in fall. The incoming water must be heated to 12.7 ºC to promote growth of the fish fry.
Due to the age of the boiler/heat exchanger system used to heat the hatchery water, the overall heater efficiency is 50%. Another heat exchanger recovers about 65% of the heat from the outlet flow of the hatchery and transfers it to the incoming fresh water. As a result, you can assume that the solar system will require only 25 to 35% of the number of solar collectors normally installed if this heat recovery system did not exist.
Some storage will be needed to store the solar heated water through the night. The cost of polyethylene storage tanks is approximately $0.36 per litre. Since the fresh water can be heated directly in the solar collectors, there is no need for a heat exchanger.
You have considered the hatchery site and decided that the only space available for solar collectors is the south-facing roof of the hatchery building, located 40 m from the mechanical room. The roof has an open area of 335 m2 and a 3 in 12 pitch; you estimate that 20% of the available roof space should be reserved for pipes and walking space. To avoid the risk of freezing the pipes and collectors, the solar system can only operate for 7.5 months per year. Assume all piping for the solar loop is 63 mm (2½ inch) PVC.
Financial information
The system would be purchased by the government agency out of a budget for the hatchery. The agency uses a discount rate of 9%. The system is expected to last 20 years. Costs of propane have risen sharply recently, and over the past year have risen from about $0.25/L to $0.45/L. Inflation is estimated at 2.2%. To be conservative, assume that fuel prices will rise at the same rate as inflation. The current price of electricity is $0.05/kWh. Also, for this type of system there is a 25% government incentive of total initial costs.
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 1996 Natural Resources Canada, in conjunction with the Department of Fisheries and Oceans, initiated a project to test solar water heating for fish hatcheries. Two sites were selected, one in Guelph, Ontario, and the other on Vancouver Island, at Fanny Bay, British Columbia (BC). The objective was to demonstrate, under real conditions, the operation and performance of solar water heating for aquaculture.
Extensive monitoring instrumentation was installed to measure the performance of the solar heating system. The results proved that solar water heating can significantly reduce the high water heating costs and greenhouse gas emissions of the facility.
System description
In August 1997, Taylor Munro Energy Systems installed a 266 m² (2,880 ft²) solar heating system at the Rosewall Creek Fish Hatchery in Fanny Bay, BC. The system works by circulating the hatchery water through solar collectors mounted on the building roofs. The heated water from the solar collectors is returned to two insulated tanks to allow collected energy to be stored overnight. The solar system was designed to raise the temperature of the 7 ºC ground water to 14.5 ºC, but if desired, it can raise the temperature to as high as 18 ºC. An automatic mixing valve is used to ensure the fish are not exposed to any temperature fluctuations.
The solar heater has cut energy consumption of the boiler/heat exchanger by approximately 25%, and will pay for itself in energy savings within six years. Ultra-violet inhibitors in the solar collectors help ensure an expected life of 20 years. The system uses sixty 1.2 m x 3.7 m FAFCO unglazed flat plate collectors mounted on the south facing low-slope hatchery roof.
Lessons learned
The big picture
Low temperature solar water heating is often the most cost-effective application for solar water heating since inexpensive unglazed collectors can be used. Agricultural and commercial applications which use large volumes of heated water present the best opportunities. In some cases, it may be possible for customers to purchase solar energy as it is delivered (under an Energy Service Contract), rather than make an outright purchase of equipment.
Photo
Fish hatchery - Solar water heater, British Columbia, Canada
References
Case study assignment
You have been hired by a government agency to prepare a prefeasibility study for a potential solar water heating system at a fish hatchery in British Columbia, Canada. This hatchery raises salmon fry until they are large enough to transfer to a grow-out pen in the ocean. To ensure that the fish receive enough oxygen and to remove waste products, fresh well water is constantly pumped into the fish rearing tanks. This large volume of water must be heated to accelerate the growth of the fish fry. Like many fish hatcheries in British Columbia, the site is remote and the heating fuel is propane, delivered by truck. Since propane a relatively expensive fuel, solar water heating may be cost-effective in reducing operating costs at the hatchery. The government agency would like to know whether a solar water heating system is financially viable.
Site information
The hatchery is located close to Comox, on Vancouver Island, British Columbia. Fresh water flows into the facility at an average rate of 700 litres per minute at a temperature varying from 6 ºC in spring to 8.5 ºC in fall. The incoming water must be heated to 12.7 ºC to promote growth of the fish fry.
Due to the age of the boiler/heat exchanger system used to heat the hatchery water, the overall heater efficiency is 50%. Another heat exchanger recovers about 65% of the heat from the outlet flow of the hatchery and transfers it to the incoming fresh water. As a result, you can assume that the solar system will require only 25 to 35% of the number of solar collectors normally installed if this heat recovery system did not exist.
Some storage will be needed to store the solar heated water through the night. The cost of polyethylene storage tanks is approximately $0.36 per litre. Since the fresh water can be heated directly in the solar collectors, there is no need for a heat exchanger.
You have considered the hatchery site and decided that the only space available for solar collectors is the south-facing roof of the hatchery building, located 40 m from the mechanical room. The roof has an open area of 335 m2 and a 3 in 12 pitch; you estimate that 20% of the available roof space should be reserved for pipes and walking space. To avoid the risk of freezing the pipes and collectors, the solar system can only operate for 7.5 months per year. Assume all piping for the solar loop is 63 mm (2½ inch) PVC.
Financial information
The system would be purchased by the government agency out of a budget for the hatchery. The agency uses a discount rate of 9%. The system is expected to last 20 years. Costs of propane have risen sharply recently, and over the past year have risen from about $0.25/L to $0.45/L. Inflation is estimated at 2.2%. To be conservative, assume that fuel prices will rise at the same rate as inflation. The current price of electricity is $0.05/kWh. Also, for this type of system there is a 25% government incentive of total initial costs.
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 pumping power per unit of collector area has been set to 2 W/m². The "low flow" design of this system uses lower than typical flow rates; this results in low pump power requirements.
- Piping and solar tank losses are low since the required water temperatures are low and the water is not stored for long periods before use.
- Losses due to snow and dirt are low since 1) the system operates outside of the season when snow might fall and 2) the rainy climate keeps the collectors clean.
- The time allotted for solar water heating (SWH) system design and construction supervision are higher due to the large size of this project.
- The solar loop piping materials and the solar loop installation costs are higher as the pipe running between the 2 buildings had to be buried in a trench; and due to the precise mixing of heated and unheated water required to obtain the desired temperature required non-standard piping and plumbing.
- The collector installation costs are low as omitting the racking structure simplifies installation.
- The sensitivity of the salmon fry to water temperature necessitated a precise but expensive mixing valve assembly.
- A relatively conservative approach has been used to estimate the cost of propane: the current price and the price of a year earlier have been averaged, to give $0.35/L.
- Solar energy equipment is exempt from the 7% provincial sales tax in British Columbia.
Real project
Results
In 1996 Natural Resources Canada, in conjunction with the Department of Fisheries and Oceans, initiated a project to test solar water heating for fish hatcheries. Two sites were selected, one in Guelph, Ontario, and the other on Vancouver Island, at Fanny Bay, British Columbia (BC). The objective was to demonstrate, under real conditions, the operation and performance of solar water heating for aquaculture.
Extensive monitoring instrumentation was installed to measure the performance of the solar heating system. The results proved that solar water heating can significantly reduce the high water heating costs and greenhouse gas emissions of the facility.
System description
In August 1997, Taylor Munro Energy Systems installed a 266 m² (2,880 ft²) solar heating system at the Rosewall Creek Fish Hatchery in Fanny Bay, BC. The system works by circulating the hatchery water through solar collectors mounted on the building roofs. The heated water from the solar collectors is returned to two insulated tanks to allow collected energy to be stored overnight. The solar system was designed to raise the temperature of the 7 ºC ground water to 14.5 ºC, but if desired, it can raise the temperature to as high as 18 ºC. An automatic mixing valve is used to ensure the fish are not exposed to any temperature fluctuations.
The solar heater has cut energy consumption of the boiler/heat exchanger by approximately 25%, and will pay for itself in energy savings within six years. Ultra-violet inhibitors in the solar collectors help ensure an expected life of 20 years. The system uses sixty 1.2 m x 3.7 m FAFCO unglazed flat plate collectors mounted on the south facing low-slope hatchery roof.
Lessons learned
- A "low-flow" design using small pipes and pumps reduced capital and operating costs making the system more cost-effective.
- Using existing building roofs eliminates the need for collector racking thus significantly lowering the project cost.
- PVC tanks work well for zero-pressure applications and are much less expensive than other materials.
The big picture
Low temperature solar water heating is often the most cost-effective application for solar water heating since inexpensive unglazed collectors can be used. Agricultural and commercial applications which use large volumes of heated water present the best opportunities. In some cases, it may be possible for customers to purchase solar energy as it is delivered (under an Energy Service Contract), rather than make an outright purchase of equipment.
Photo
Fish hatchery - Solar water heater, British Columbia, Canada
References
- Enermodal Engineering Ltd., Solar Water Heating at Rosewall Creek Salmon Hatchery, October 1997.
- Thwaites, Joe, "Personal communication," Taylor Munro Energy Systems Inc., 2000.
