Solar Energy Systemsin the Eco-Village at the University of Manitoba

Mechanical Thesis Defense Heather King

What is the aim of this thesis?1. To discuss the types of solar collectors to be

installed at the “eco-village”.2. To determine the optimum angle and direction

these collectors should be installed at.3. To model the efficiency of the evacuated tube

collector and the flat-plate collector.4. To carry out a brief economic and

environmental analysis.

SOLAR COLLECTORS TO BE INSTALLED AT

THE“ECO-VILLAGE”

Apricus Evacuated Tube Collector

How does it work?

•Radiation is absorbed from the sun through a system of 30 evacuated tubes.

A vacuum is created between the transparent outer tube and the selectively coated inner tube.

A copper heat pipe is inserted into the inner tube. This works as a condenser.

• Liquids boil at a lower temperature when the surrounding air pressure is decreased.

• Water in the heat pipe will vaporize if the temperature of the heat pipe reaches 30°C.

• Vapor rises to the top of the heat pipe and transfers heat into the manifold fluid.

• This cooled vapor condenses and returns to the bottom as liquid.

EnerWorks Flat Plate Collector

How does it work?•Radiation strikes the glazed, flat

surface of the collector.

•Heat is transferred into the heat transfer fluid, which is then transferred into storage water through a heat exchanger.

Sunsiaray Northern Comfort

Flat-Plate Collector

• Works the same way as the EnerWorks flat-plate collector.

• Only difference is that air flows through the fluid transfer tubes, not a heat transfer solution.

How does it work?

NRG Solar Wall

•Metal cladding on the wall contains thousands of tiny perforations that let air pass through.

•Air accumulates free heat from the cladding as it passes through.

•Warmed up heat is added to the HVAC system.

How does it work?

SOLAR COLLECTOR LOCATION

Σ = Tilt Angle

Ultimate Goal: Determine the optimum tilt angle.

1. Geographic Location

2. Calculate the Incident Angle, θ

• Incident angle = the angle between the sun’s rays and the plane surface of the collector

θ = Incident Angle

•We want to optimize the tilt angle and direction.

•This can be done by setting cosθ in the following relation equal to 1 and using the solver function in Excel to optimize Σ and Φ.

cosθ = (sinA)(cosΣ) + (cosA)(sinΣ)[cos(Z-Φ)] = 1

Where:A = the angle of elevation of the sunZ = the azimuth angle of the sunΣ = the tilt angle of the planeΦ = the direction of the tilt angle

Results: Optimum Tilt Direction = 0°

Results: Optimum Tilt Angle = ???

3. Calculate the Solar Irradiance at the “Eco-Village”• In order to determine the optimum tilt angle of the

plane we must calculate the amount of solar irradiance received at the “Eco-Village”.

•This is done by using the relation:

Where: = the direct radiation received by the collector

= the solar radiation received at ground level

cosNb II

bI

NI

•Use varying values of the tilt angle, Σ, in the previous equation allows us to determine the optimum tilt angle.

Results: Optimum Tilt Angle = 45°- 50°

HEAT TRANSFER ANALYSIS

Apricus Evacuated Tube Collector Efficiency

• The transfer of heat through the collector is analyzed by modeling the collector as an electric circuit.

• The amount of useful energy collected by the evacuated tube collector is determined by:

• Which allows us to calculate the collector efficiency:

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Efficiency Calculator• The seven variable inputs necessary for the spreadsheet to calculate the

efficiency are:1. The temperature of the ambient air surrounding the collector, in

degrees K.2. The temperature of the heat transfer fluid entering the manifold, in degrees K.3. The mean temperature of the collector tube, in degrees K.4. The mean temperature of the heat pipe, in degrees K.5. The mass flow rate, in kg/s, of the liquid within the heat pipe.6. The velocity of the air flow over the collector, in m/s.7. The month of the year. A scroll down menu is available for the user to choose the month of the year that the preceding three parameters

were collected. Once the month of the year is known, the spreadsheet can calculate the appropriate incident radiation value received by the collector.

EnerWorks Flat-Plate Collector

•The amount of useful energy collected by the flat-plate collector is determined by:

•Which allows us to calculated the collector efficiency:

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Efficiency Calculator• The four variable inputs necessary for the spreadsheet to

calculate the efficiency are: 1. The temperature of the ambient air surrounding the

collector, in degrees K.2. The temperature of the heat transfer fluid entering the collector, in degrees K.3. The mass flow rate, in kg/s, of the heat transfer fluid

entering the collector.4. The month of the year. A scroll down menu is available for the user to choose the month of the year that the preceding three parameters were collected. Once the month of the year is known, the spreadsheet can calculate the appropriate incident radiation value received by the collector.

ECONOMIC ANALYSIS

U of M District Heating System

• The power plant runs 6 steam boilers, two of which are summer boilers.

• These two summer boilers have a max steam output of 15,000 lbs/hour.

• The boilers run at approx. 81% efficiency.

Can we replace one of the summer boilers with solar

energy?• The most steam one of the summer boilers produced in

2006 was 9879 lbs/hour.• In order to completely eliminate one of the summer boilers

from the district heating system, a system of solar collectors must be able to produce the equivalent amount of energy as the produced by the boiler.

• Using the following relation, it can be seen that a boiler emitting 9879 lbs/hour of steam is rated at approximately 332.5 kW.

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How many collectors does it take to produce 332.5 kW?

• As we do not have any data collected from the collectors to test the efficiency calculators, the stated manufacturer efficiencies will be used in the following calculations.

• Collector Efficiencies:Apricus Evacuated Tube Collector = 0.717EnerWorks Flat-Plate Collector = 0.4776 (using SRCC

data)

• The table below shows the RETScreen daily radiation values for Winnipeg Airport, in kWh/m²/d, converted to W/m².

• We will use the value for August (367.3 W/m²).

Results:

We would need to use a system of either:

1. 418 Apricus Evacuated Tube Collectors- or-

2. 560 EnerWorks Flat-Plate Collectors

What is the payback period of installing a system of solar

collectors?• Boiler operation cost

based on a natural gas price in Winnipeg

of $0.024/kWh.• CO2 reduction incentive based on a trading price of $32.40/tonne of CO2• Reduction of 64.14

tonnes of CO2 per year!

How much land is needed?

Approximately ½ a football field

Rooftop Availability

Architecture Building:

~ 1500 m²

EngineeringBuilding

~ 1000 m²

Results: A substantial amount of the district heating system can be

supplemented by solar energy.

CONCLUSIONS

Evacuated Tube or Flat-Plate?

Evacuated Tube Collectors Flat-Plate Collectors

• High accuracy (70% – 80%)• High price ($2500)• Easy to repair (replace one

or more tubes)

• Moderate accuracy (35% - 45%)

• Moderate cost ($1750)• Costly to repair (must

replace the whole collector)

• Quantity over quality decision.• In the long run, evacuated tube collectors are the

recommended choice.

Should solar collectors be installed?• Yes, solar collectors should be installed.

• The payback period is less than the life span of the collectors, creating a profit for the university and a large reduction in carbon dioxide emissions.

• More research should be carried out to further examine the potential of installing solar collectors on the rooftops of campus buildings.

QUESTIONS?