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SOLAR WATER HEATING INTHE CANADIAN CLIMATE
GRAEME DOYLE
A THESIS SUBMITTED IN PARTIAL FULFILMENTFOR THE REQUIREMENTS FOR THE DEGREE OF
BACHELOR OF APPLIED SCIENCE
FACULTY ADVISOR:PROFESSOR J.S.WALLACEUNIVERSITY OF TORONTO
DEPARTMENT OF MECHANICAL AND INDUSTRIAL ENGINEERINGMARCH,2007
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I
ABSTRACT
This project aimed to complete two goals: document a methodology for designing a
large scale Solar Water Heating (SWH) system. and study the economic feasibility
these systems in the Canadian climate. The complete design proposal for the
installation of a SWH system in an existing TDSB school building was developed. An
economic analysis was performed on the designed system in order to gain insight into
the economics of SWH systems. The system was analyzed at different values of energy
cost inflation rates, debt ratios, and availability of subsidies. A sensitivity analysis was
performed on the initial costs. The financial feasibility of the SWH system was found to
increase with the availability of a subsidy, increasing energy cost inflation rate, and
decreasing debt ratio. A specific case was examined where the addition of the SWH
system allowed a summer boiler to be undersized, resulting in savings for the SWH
project and a boosted financial feasibility.
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II
Acknowledgements
I would like to thank
Professor J. S. Wallace for his insight and guidance;
Mr. Eric Steen and the TDSB for their time and support;
and
Kristina and Finn for their love and care.
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III
TABLE OF CONTENTS
1. LIST OF SYMBOLS ________________________________________ IV
1. LIST OF FIGURES_________________________________________VII
2. PROJECT OVERVIEW _______________________________________ 1
3. INTRODUCTION TO SOLAR WATER HEATING SYSTEMS _______________ 3
4. DESIGN METHODOLOGY_____________________________________ 5
4.1. OVERVIEW _____________________________________________________ 5
4.2. SITE SELECTION_________________________________________________ 5
4.3. PERFORMANCE ESTIMATION ________________________________________ 7
4.4. COST ESTIMATION ______________________________________________ 12
5. DESIGN RESULTS ________________________________________ 15
5.1. OVERVIEW ____________________________________________________ 15
5.2. SITE SELECTION________________________________________________ 15
5.3. SYSTEM DESIGN________________________________________________ 16
5.4. COMPONENT DESIGN ____________________________________________ 19
5.5. PERFORMANCE RESULTS _________________________________________ 23
6. FINANCIAL FEASIBILITY ____________________________________ 24
6.1. EVALUATION METHODOLOGY_______________________________________ 24
6.2. ECONOMIC ANALYSIS ____________________________________________ 27
6.3. SENSITIVITY ANALYSIS ___________________________________________ 28
6.4. DISCUSSION___________________________________________________ 28
7. CONCLUSION ___________________________________________ 31
8. REFERENCES ___________________________________________ 32
9. APPENDIX A:PERFORMANCE ESTIMATION DETAILS ________________ 33
10. APPENDIX B:SYSTEM DRAWINGS_____________________________ 38
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IV
1. LIST OF SYMBOLS
AT, total storage tank surface area [m]
Cs, storage capacity ratio [L/m2]
Ca, antifreeze heat capacity [J/kgC]
d, pipe diameter [m]
FR, collector heat removal factor
, solar fraction, friction factor
g, acceleration due to gravity [m/s2]
Hd/H, the fraction of diffuse radiation to total radiation
Ho, monthly average extraterrestrial solar irradiation [W/m2]
HH, monthly average solar irradiation on a horizontal surface [W/m2]
HT, monthly average solar irradiation on a tilted surface [W/m2]
h, average number of hours of bright sunlight [hours/year]
hf, friction head loss [m]
hs, static head [m]
IT, solar irradiation on a tilted surface [W/m2]
ITc, critical level of solar irradiation on a tilted surface [W/m2]
KT, average clearness index
L, longitude [degrees]
L, heating load [MJ], length of pipe [m]
, solar loop mass flow rate [kg/s]
N, number of days in a particular month [days]
P, pumping power [W]
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V
Q, volume flow rate [m3/s]
Qu, solar energy gain [MJ]
rt,n, the ratio of hourly total to daily total radiation at noon
rd,n, the ratio of hourly total to daily diffuse radiation at noon
Rb. the ratio of beam radiation on the tilted surface to that on a horizontal surface
Rb,n. the ratio of beam radiation on the tilted surface to that on a horizontal surface atsolar noon
Red, Reynolds number for duct flow
R. the ratio of radiation on the tilted surface to that on a horizontal surface
Rn, the ratio for the hour centred at noon of radiation on the tilted surface to that on ahorizontal surface for an average day of the month
Rs, ratio of the standard storage heat capacity per unit collector area of 350 [kJ/m2C]
Ti, collector fluid inlet temperature [C]
Ta, ambient temperature [C]
To, collector fluid outlet temperature [C]
Tm, minimum useful temperature [C]
UL, collector functional heat loss coefficient
V, fluid velocity [m/s]
Xc, dimensionless critical radiation level
, collector slope [degrees]
, Solar Declination [degrees]
, collector azimuth [degrees]
T, change in fluid temperature as it passes through solar array [C]
t, total number of seconds in a month [seconds]
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VI
, pipe roughness [m]
HX, heat exchanger effectiveness
, utilizability
, pump efficiency
, latitude [degrees]
, ground reflectivity
(), collector functional transmittance absorbptance product
, dynamic viscosity [Pa s]
s, Sunset Hour Angle
n, Solar noon Hour Angle
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VII
1. LIST OF FIGURES
Figure 1: Collector efficiency vs. T ________________________________________ 4
Figure 2: System input parameters used in the performance estimation model _______ 9
Figure 3: Pre-tax initial cost sensitivity _____________________________________ 13
Figure 4: Initial, Annual, and Period cost estimation __________________________ 14
Figure 5: Simplified schematic diagram for the service hot water system __________ 16
Figure 6: Closed and open collector loop designs ____________________________ 17
Figure 7: System design schematic _______________________________________ 18
Figure 8: Characteristics of selected solar collectors __________________________ 19
Figure 9: Results of comparison analysis, total array size = 70 [m2] ______________ 19
Figure 10: Fraction of the heating load supplied by solar energy _________________ 23
Figure 11: Case 1 standard initial cost, 100% debt ratio ______________________ 27
Figure 12: Case 2 standard initial cost, 50% debt ratio _______________________ 27
Figure 13: Case 3 standard initial cost, 0% debt ratio ________________________ 27
Figure 14: Undersize boiler replacement, $30,000 savings in year 0, 100% debt ratio 27
Figure 15: Best case scenario low initial costs, 0% debt ratio __________________ 28
Figure 16: Worst case scenario high initial costs, 100% debt ratio ______________ 28
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1
2. PROJECT OVERVIEW
Solar energy, though it is the source of all energy on Earth, is not what is considered
a conventional energy resource. The technology needed to exploit its undepletable
energy has been available for centuries, but does not exist in the mainstream of human
energy technologies. As a result, there is much less knowledge and experience in
dealing with the technology needed to tap the suns power. The intent of this project is
twofold: to document a methodology for designing a large scale solar water heating
system. and to study the economic feasibility these systems in the Canadian climate.
This project will consider the installation of Solar Water Heating (SWH) systems in
existing buildings. It aims to develop a complete design proposal for the installation of a
retrofit SWH system for a large building. The project will be conducted on a real building
in the Toronto area. The Toronto District School Board (TDSB) has graciously agreed to
supply the author with all necessary data on a school in order to complete the design
proposal. The TDSB has requested that the schools name or location not be disclosed
in this report for confidentiality reasons. Upon completion of the project, the TDSB will
be presented with a copy of this design proposal.
Although performed as a case study on a particular building application, the results
of the project will be generalized such that they will give an indication of the economics
of these systems. This project will serve to document the design process for developing
a technically and economically feasible solar water heating system.
Chapter 4 gives an introduction to Solar Water Heating technology. The goal of
this passage is to familiarize the reader with the two main solar collector technologies,
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Glazed Flat Panel collectors and Evacuated Tube collectors. A brief discussion about
the operating efficiency of these technologies concludes that discussion.
Chapter 5 discusses the design methodology used throughout this project. A
rationale used to select the building is described, and a description of the parameters
used in the performance estimation model is given. Readers who would like more detail
about the performance estimation calculations are referred to Appendix A. The chapter
closes with the presentation of the cost estimate and a sensitivity analysis of its
assumptions.
Chapter 6 describes the final design of the SWH system. A qualitative and
quantitative report of the aspects of the overall system design as well as the individual
component design proceeds, followed by a presentation of the final performance model
results.
Chapter 7 analyzes the financial feasibility of the project. An explanation of the
evaluation methodology is followed by the results of the economic and sensitivity
analyses. Finally the findings and implications these results are discussed.
Chapter 8 concludes the report and formalizes its findings.
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3. INTRODUCTION TO SOLAR WATER HEATING SYSTEMS
A glazed flat panel collector consists of a shallow rectangular box with a flat black
plate behind a glass cover. The plate is attached to a series of parallel tubes through
which a heat transfer fluid passes.As the liquid circulates through the system, it absorbs
energy from sunlight falling on the collectors and heats up. The heated liquid then
enters a heat exchanger or is added directly to the conventional system. The heated
water flows to a storage tank that is connected to the conventional service water heating
system. Glazed flat panel solar collectors are insulated behind the absorber plate, but
nonetheless, they are much less efficient in cold weather than in warm, though they can
still generate a net energy gain during the winter. These systems are best suited to
applications that require medium to high temperatures (1 p. 8).
Evacuated tube collectors absorb solar energy in much the same manner that
glazed panels do. An evacuated tube collector contains several individual glass tubes,
each containing an absorber plate bonded to a heat pipe and suspended in a vacuum.
The heat pipe transfers the heat to a condenser through the top of the tube. The
condensers are clamped to heat exchange blocks in a well-insulated manifold. The
collector plate absorbs radiation and transfers it to the condenser as heat. The heat
transfer fluid passes through the manifold, collects the heat from the condensers and
transfers it to a heat exchanger in a hot water tank. Cold weather and high water
temperatures have little effect on evacuated tube collectors, since the collectors are so
well insulated. However, they absorb less energy than glazed collectors because curved
glass sheath offers a lower transmittance factor than glazed collectors. These systems
are best suited to applications that require high to very high temperatures (1 p. 11).
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In general, collector conversion efficiency, the fraction of impinging solar energy that
can be converted into useful energy, is a function of the difference between fluid inlet
temperature and the ambient temperature, T. Glazed flat panel collectors start their
efficiency curve higher when there is a smaller temperature difference, but loose their
efficiency very quickly whenT is larger. Evacuated tube collectors start their efficiency
curve lower but maintain that efficiency better as T gets larger. This behavior is
summarized in
Figure 1.
Figure 1: Collector efficiency vs. T
Collector
Efficienc
Evacuated Panel
Glazed Panel
T, Difference between collector inlet temp and ambient temp
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The first criterion identified was a large service hot water demand during the
summer months. A high summer service hot water load is beneficial to the economics of
a solar heating project because it allows for the design of a larger system that can be
utilized during the summer when the load is at its lowest. During the summer months
the only demands on the service hot water system come from domestic hot water use
(kitchens and showers are the largest uses) and from pool heating. Therefore, schools
with pools, showers, and kitchens were identified as key candidates.
The second criterion identified as essential for a solar heating system was the
technical and economic feasibility of integrating the system into the existing heating
system. The heating system should also be of a type which can be easily interfaced with
a solar water heating system. For example, a heating system consisting of distributed
gas-fired or electric unit heaters would require a major renovation to the heating system
and would likely cause the project to be economically infeasible. It is desirable to select
a building with a heating system which would require very little modification in the
installation of a solar heating system. If the existing heating system is reaching the end
of its useful lifecycle and is in need of replacement, savings can be generated for the
SWH design by allowing the replacement heating system to be downsized.
The third criterion was identified as the availability of rooftop mounting space with
adequate structural support. Solar heating systems require a large rooftop area with an
unobstructed southerly exposure for mounting the solar collectors. The ability of the
structural roof elements to accept a heavy load is also a key consideration, requiring the
approval of a structural engineer prior to installation. The rooftop mounting area should
also be close to the mechanical room where the service hot water equipment is kept in
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order to minimize the amount of exposed solar loop piping which would add to the
systems heat loss. Adequate space in the mechanical room is required for the
installation of the large solar thermal storage tank. Depending on the design this may
range from a very large volume of space to no space at all, as in the case where no
solar thermal storage tank is designed.
In addition to these criteria, it is desired to select a building for which complete,
accurate, and long-term data on the energy consumption of only the service hot water
system is available. Since the energy consumption data supplied by the TDSB is in the
form of monthly natural gas or electricity consumption for the entire school, it is
desirable to select a building where the only equipment consuming natural gas is the
service hot water system.
4.3. PERFORMANCE ESTIMATION
In the component design phase, the total energy delivered by the system over its
lifetime is estimated based on the selection of design variables. Estimations fall into two
broad categories: detailed simulations and design methods. Detailed simulations utilize
computational methods to solve a large set of differential equations which describe the
thermal characteristics of the system. This type of estimation is quite detailed and
complex, so it is typically used to simulate experimental or one-of-a-kind systems.
Design methods, on the other hand, are models that correlate the results from hundreds
of detailed simulations to provide an empirical procedure for estimating the systems
performance. They were developed to allow designers to estimate a systems
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performance quickly and easily. This project employed the ,-Chart design method to
estimate the systems long-term performance.
The ,-Chart method was developed to study the long-term performance of
closed-loop solar energy systems by Klein and Beckman in 1979 (1). It combines the
strengths and weaknesses of the Utilizability () and -Chart methods to produce a
correlation that has proven to be more accurate and versatile than both those methods.
Details of the performance estimation calculations can be found in Appendix A.
The accuracy of the performance estimation depends on the accuracy of the
parameters used to define the system. The model parameters can be broken down into
three categories: design variables, system constants, and operation data. Design
variables are the main parameters that define the system. They are the variables that
are varied in the system analysis in order to find their optimum sizing. System constants
represent parameters that are either set at the beginning of the design or are
proportional to a design variable and so are not varied in the system analysis. Operation
data is required information necessary for calculations on the conditions under which
the system will be operating. Figure 2 lists the system parameters used in the
performance estimation model, and is followed by a brief description of each parameter.
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Category Input Parameter Type
Site
, latitude [degrees] System Constant
L, longitude [degrees] System Constant
Orientation
, collector azimuth [degrees] System Constant
, collector slope [degrees] System Constant
SolarCollector
Array
Solar collector type [Glazed or Evacuated] Design Variable
Solar collector characteristics (FR(), FRUL, Aperature) Design Variable
N, number of collectors [#] Design Variable
Storage
Tank
Cs, storage capacity ratio [L/m2] Design Variable
Storage tank characteristics (U-factor, surface area) System Constant
HeatExchanger
HX, heat exchanger effectiveness [%] System Constant
Ca, antifreeze heat capacity [J/kgC] System Constant
SystemEnergyBalance
Tm, minimum useful temperature [C] System Constant
, solar loop mass flow rate [kg/s] System Constant
Total pump power [W] System Constant
, pump efficiency [%] System Constant
Operation
Data
Lj, average heating load for month j [MJ] Operation Data
HH,j, average daily irradiation on a horizontal surface for month j[W/m
2]
Operation Data
Ta,j, average daily ambient temperature for month j [C] Operation Data
j, ground reflectivity for month j Operation Data
h, average number of hours of bright sunlight [hours/year] Operation Data
Figure 2: System input parameters used in the performance estimation model
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SITE
The longitude, , and latitude, L, of the site affect the relation of the sun to the site.
The official Toronto values given by Environment Canada were used (2).
ORIENTATION
The slope, , is the angle that the plane of the collector makes with the ground. This
changes the angle of solar irradiation falling in the plane of the collector. Increasing the
slope increases the amount of irradiation on the collector during the winter and
decreases it during the summer. For maximum solar gain the rule of thumb is to set the
slope equal to the latitude 10 [degrees] (3 p. 157). In order to increase winter energy
generation when the demand is high at the expense of summer capacity when the
demand is low, a slope greater than the latitude was used. A slope of 50 degrees was
selected in order to simplify the mounting procedure.
Azimuth, L, is the angle between due south and the direction that the collector is
facing. The azimuth angle is set to zero for optimum solar energy gain (3 p. 158).
SOLAR COLLECTOR ARRAY
The solar collector array is the defining component of the SWH system. Its design
involves deciding upon the main design variables: collector type, collector product
model, and array size.
For this study two collector technologies were considered: Glazed Flat Panel and
Evacuated Tube. Suitable product models for each type of panel were identified based
on cost and performance. The performance estimation model was then used to
compare the performance of each of the collector types. This analysis resulted in the
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selection of the Solarco SC-22 glazed flat panel as the collector product model. The
results of this analysis can be found in section 5.3.
The other key design variable in the solar collector array is the overall sizing of the
array. Using the performance estimation model, the number of panels needed to meet
the summer baseload was determined to be 55 panels for a total array area of 109.5
[m2].
STORAGE TANK
A thermal storage capacity ratio of 50 [L/m2] of collector area was considered for the
performance estimation. An insulated steel tank storage tank measuring 1.50 [m] in
diameter by 3.10 [m] in height with a U-factor of 0.3 [W/m2C] was selected.
HEAT EXCHANGER
An external shell and tube type heat exchanger with an effectiveness of 95% was
considered for the performance estimation.
The solar antifreeze fluid considered was a 50-50 propylene glycol / water mix with a
heat capacity of 5843 [J/kgC].
SYSTEM ENERGY BALANCE
The ,-Chart method requires the specification of a minimum temperature, Tm, that
must be surpassed for the solar fluid at the collector outlet to add energy to the system.
This minimum temperature was set as the expected return temperature of the service
hot water loop, which was estimated to be at 40 [C].
The mass flow rate of the solar loop, , was selected as the median of the range of
typical values described by Duffie and Beckman (4 p. 514). The mass flow rate used in
the performance estimation model was 1.64 [kg/s].
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The total system pump power was roughly estimated by calculating the static head
and head loss experienced by the system. The total system pumping power was
estimated to be 2096 [W], assuming a pump efficiency of 85%. Details on this
calculation can be found in Appendix A.
OPERATION DATA
The time scale of the available radiation, temperature, and load data determines the
time scale of the estimation. Monthly average data was used in the performance
estimation, and is the most common time scale available. Since climatic conditions vary
greatly from year to year, it is beneficial to use data that has been normalized over a
number of years. Climatic data was provided by Environment Canada in the form of 30
year monthly average radiation and ambient temperature data (2). Load data was
provided by the TDSB in the form of 6 year monthly average normalized natural gas
consumption data for the boiler plant (5).
4.4. COST ESTIMATION
A comprehensive accounting of all the expected costs for the installation of the
system was performed in order to estimate the initial, annual, and periodic costs
associated with the project. This is presented in Figure 4.
Difficulty obtaining precise figures for worker wages, billable hours, and equipment
costs means that the cost estimation relies on assumptions made about these costs.
These assumptions present a degree of uncertainty into the cost estimation. In order to
estimate that degree of uncertainty, a range of values was used for each cost
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assumption in order to generate a high and low cost estimate. These results are
presented below.
Estimate Selected High Low
Cost $86,434 $107,271 $68,426
Difference $20,837 -$18,007
Percent 24% -21%
Figure 3: Pre-tax initial cost sensitivity
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Figure 4: Initial, Annual, and Period cost estimation
Initial Costs Unit Quantity Unit Cost Amount Source
Design and Development
Permits project 1 318$ 318$ City of Toronto Permit Fee Schedule
Approvals p-h 5 70$ 350$ Estimate
Project management p-h 25 70$ 1,750$ EstimateSWH system design p-h 18 70$ 1,225$ Estimate
Structural design p-h 6 70$ 420$ Estimate
Tenders and contracting p-h 10 70$ 700$ Estimate
Commissioning p-h 10 70$ 700$ Estimate
Construction supervision p-h 10 70$ 700$ Estimate
Sub-total : 6,163$
Equipment
Solar collectors # 55 750$ 41,250$ Quote from supplier
Collector support structure m 109.5 135$ 14,776$ RETscreen user manual
Solar storage tank L 5500 2.13$ 11,688$ RETscreen user manual
Heat Exchanger kW 66 9.50$ 624$ RETscreen user manual
Piping materials m 48 25$ 1,200$ Cost survey
Auxiliary equipment project 1 300$ 300$ Cost survey/Estimate
Circulating pump(s) W 2,096 2.9$ 6,021$ Cost survey
Controls project 1 750$ 750$ Cost survey
Antifreeze L 78 7$ 543$ Quote from supplier
Sub-total : 77,151$
Installation
Roof mounting installation p-h 15 40$ 600$ Estimate
Solar Collector installation p-h 25 40$ 1,000$ Estimate
Plumbing installation p-h 20 40$ 800$ Estimate
Electrical installation p-h 15 40$ 600$ Estimate
Sub-total : 3,000$Miscellaneous
Training p-h 4 30$ 120$ Estimate
Sub-total : 120$
Initial Costs - Sub-total : 86,434$
Initial Costs - Taxes : 12,101$
Initial Costs - Total 98,534$
Annual Costs Unit Quantity Unit Cost Amount Source
O&M
O&M labour p-h 2 30$ 60$ Estimate
Electricity kWh 5,613 0.10$ 561$ Estimate
Annual Costs - Total -$ 621$
Periodic Costs Period Unit Cost Amount Source
Replace Fittings 10 yr 300$ 300$ RETscreen user manual
Replace Antifreeze 10 yr 543$ 543$ Estimate
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5. DESIGN RESULTS
5.1. OVERVIEW
Of all the system design considerations to take into account, the most important is to
select a design that is a suitable match for the building. In the system design phase,
suitable designs are identified and compared against each other on a qualitative basis.
The best designs are then passed on to the component design phase, where the
designs are compared on a quantitative basis.
5.2. SITE SELECTION
Using the site selection criteria, a suitable building was chosen for this feasibility
study. The facility is a 2 storey structure of masonry construction without a basement.
The original building was constructed in 1958 and has received major additions on
several occasions. The heated floor area measures 11,532 square metres, but the roof
area is 9,226 square metres, indicating that the approximately 80% of the floor area is
one storey. It is equipped with a cafeteria kitchen, full-size pool with showers, and is
host to various camp activities during the summer break.
The service hot water system for the school provides all the energy for space
heating, domestic hot water, and pool heating. It consists of 2 large winter boilers and
one smaller summer boiler. All of the boilers are reaching the end of their useful life and
will need to be replaced within the next 5 years, according to a site assessment
performed by the TDSB (6). As stated earlier, if the replacement equipment can be
downsized because of the installation of a SWH system, then savings may be assigned
to the SWH system. A simplified diagram depicting the system is shown in Figure 5. For
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these systems, the service hot water system operates on a closed loop. Heat is added
to the loop by the boiler plant and is removed by heat exchangers connected to the
loads. This system layout is very favourable to the addition of a solar water heating
system.
DHW Storage Tank
Boiler Plant
Pool
Radiators
andFan Coils
Natural Gas
To School From water
main
Figure 5: Simplified schematic diagram for the service hot water system
5.3. SYSTEM DESIGN
The main design consideration when developing the overall system design is the
freeze protection strategy, especially in cold climates. The selection of freeze protection
strategy dictates whether the system will be an open or closed loop system. However, in
order to explain the different freeze protection strategies, open and closed loop systems
must first be defined.
n an open collector loop the fluid circulating in the collectors is deposited directly into
the solar storage tank, while in a closed collector loop, the loop is sealed and there is a
heat exchanger between the collector loop and the solar storage tank. The use of heat
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exchangers, which cannot perfectly convey all the heat from the hot water loop to the
load, reduces the amount of usable energy that can be drawn from the system. Figure 6
depicts the two system designs.
Figure 6: Closed and open collector loop designs
One of the main issues faced by solar water heating systems in an extreme
climate like Canadas, is the possibility of freezing temperatures. If proper precautions
are not taken to ensure that water in the collectors or exposed piping does not freeze,
serious damage to the system can result. Two design strategies have been developed
to safeguard a system from possible freeze damage. The first design strategy is called a
draindown system, where electric or pressure actuated valves drain the fluid in the
collectors and exposed piping back into a storage tank while filling the collectors with
air. This design incorporates an open collector loop solar storage tank, and so is only
suitable in systems with this design. A concern with this freeze protection strategy is the
reliability of the of the draindown valve itself. Electrically actuated valves will not protect
the system in the event of a power failure, and pressure actuated valves are susceptible
to freezing shut in cold weather.
Hot Water Loop Supply
Solar Collector
Collector
Loop Pump
Hot Water Loop
Return
Hot Water
Loop
Storage
Hot Water Loop
Supply
Solar Collector
Collector
Loop Pump
Hot Water Loop
Return
Solar Collector
and Hot Water
Loop Storage
Closed Collector Loop Design Open Collector Loop Design
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The second freeze protection design strategy uses a fluid with a very low freezing
point (antifreeze) as the collector fluid. This eliminates all risk of freeze damage in the
system, but due to the high cost of antifreeze, a closed collector loop with a heat
exchanger must be used. This again puts a constraint on the system design and
reduces the efficiency of the system, as described above.
The existing service hot water system in the school is a closed loop design which
serves the various loads through heat exchangers. This system is very easily modified
to incorporate a solar water heater loop in a boiler preheating configuration. This design
is beneficial because small temperature increases generated by the SWH loop can
reduce the fuel consumed by the boiler substantially. A closed collector loop design was
selected in order to facilitate the use of antifreeze as the collector fluid. The expense of
reduced performance and extra cost is justified, because in the Canadian climate robust
freeze protection is a must. This design was chosen because it offers the most reliable
and simple freeze protection. A diagram of the system design is shown in Figure 7.
Pool
Radiatorsand
Fan Coils
Natural Gas
To School
From watermain
BoilerPlant
DHWStorage
Tank
HX
Solar Collector
Hot WaterLoop
StorageTank
HX
Figure 7: System design schematic
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5.4. COMPONENT DESIGN
SOLAR COLLECTOR ARRAY
The solar collector array is the defining component of the SWH system. Its design is
the single most influential aspect of the system performance, both thermally and
economically. The design of the solar collector array involves deciding upon the main
design variables: collector type, collector model, and array size.
For this study two collector technologies were considered: Glazed Flat Panel and
Evacuated Tube. Suitable product models for each type of panel were identified based
on cost and performance. The selected panel models are manufactured by Solarco
Manufacturing Inc., a Toronto area company. Local sourcing reduces the expense
incurred when transporting the panels from their supplier. The performance estimation
model was used to compare the performance of each of the collector types. The results
of this analysis are given below.
Collector Type Model FR() FRUL Aperature [m2 /panel] Cost [$/panel]
Glazed SC-22 0.79 3.25 1.99 $ 750
Evacuated VCR-16 0.47 1.05 0.80 $ 900
Figure 8: Characteristics of selected solar collectors
Collector Number of Panels Total System Cost Energy Gain [MJ/year]
Tm = 40C Tm = 70C Tm = 100CSC-22 (Glazed) 35 $ 59,235 141,661 84,545 38,906VCR-16 (Evacuated) 87 $ 118,826 106,599 81,957 58,426
Figure 9: Results of comparison analysis, total array size = 70 [m2]
The results of this analysis provide an insight into the operation of the two collector
technologies. At lower minimum useful temperatures (Tm) the glazed collector is more
effective at collecting energy, while at higher temperature the evacuated collector is
more effective. This result agrees with the general collector efficiency graph shown in
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Figure 1. Since the SWH system in this project is serving as a boiler preheater, high
temperatures are not required, so the benefits of the evacuated collector are lost. Also,
for the same area an evacuated collector array would cost nearly twice as much as a
glazed collector array, so the Solarco SC-22 glazed flat panel collector was selected for
use in this project.
The other key design variable in the solar collector array is the overall sizing of
the array. The number of panels and size of the array proportionally affect the amount of
energy generated by the system. The methodology for sizing the solar collector array is
to provide enough energy to just meet the summer baseload. Sizing the system for the
baseload demand is a good strategy to ensure that the system is never underutilized.
Also, a system which generates large amounts of unused energy during the summer
poses a danger to itself as it needs to vent the excess energy in a suitable fashion. If
pressure relief valves malfunction and the system heats up too quickly the pressure in
the solar loop can build up and cause a catastrophic failure, damaging the system and
endangering building occupants. Using the performance estimation model, the number
of panels needed to meet the summer baseload was determined to be 55 panels for a
total array area of 109.5 [m2].
THERMAL STORAGE
Thermal storage in SWH affects system performance in two ways. Firstly, it allows
solar energy to be saved for use at night or during periods of prolonged cloudiness.
Secondly, it increases the efficiency of the system by allowing the solar loop to dump its
energy even when the load is small. The storage tank was sized mainly considering
cost, constraining the selection within the acceptable range of storage capacity ratios
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described by Duffie and Beckman (4 p. 540). A thermal storage capacity ratio of 50
[L/m2] of collector area was selected, yielding a total storage tank capacity of 5500 [L].
The size of an individual thermal storage tank is limited by the size of the door to the
boiler room. Fortunately, the boiler room of the selected school has a double door
opening to outside which could facilitate a maximum tank diameter of approximately 1 to
1.5 [m]. A storage tank measuring 1.50 [m] in diameter by 3.10 [m] in height was
selected. In terms of the storage tank construction, an insulated steel tank with a U-
factor of 0.3 [W/m2C] was selected. Steel tank construction was favoured over
fibreglass design due to the need for pressurization in the service hot water loop.
HEAT EXCHANGER
The closed collector loop design necessitates the use of a heat exchanger to
transfer heat from the solar antifreeze fluid to the service hot water fluid. In order to
achieve a high heat exchanger effectiveness, an external shell and tube type heat
exchanger has been selected. This requires pumps on both the solar fluid and service
fluid sides to circulate the fluids through the heat exchanger, which increases the
parasitic losses. The extra expense in equipment and operational costs is justified by
the increased ability to extract useful heat from the solar fluid. The external heat
exchanger configuration also facilitates easy maintenance and repair.
A 50-50 propylene glycol / water mix was selected for the solar antifreeze fluid due
to its low toxicity and effectiveness as a heat transfer fluid and antifreeze. The low
toxicity of propylene glycol is important in order to avoid the need for a double walled
heat exchanger. Double walls are often required as a safety measure in case of leaks,
helping ensure that the antifreeze does not mix with the potable water supply (6 p. 416).
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It is to be expected that the existing domestic hot water heat exchanger is double
walled, since the service hot water loop likely contains bacterial inhibitor chemicals.
However, due to the age and condition of the existing equipment, it was decided to err
on the side of caution and select a non-toxic antifreeze fluid.
CONTROL SYSTEM
On/off operation of a fixed flow rate collector pump is the most widely used pump
and system control configuration (7 p. 101). Power switching controllers employ simple
electromechanical relays which are cheap, reliable, and familiar to installers. This
simple control scheme is possible because more complicated control points such as the
boiler control already have installed control mechanisms which react to the temperature
of the service hot water loop, irrespective of the SWH system.
The control system operates by measuring the difference between the collector
inlet temperature and the collector outlet temperature, T. The system collects solar
energy by turning the pump on whenever T reaches a preset amount, Ton. The
controller turns the pump off whenever T drops to another preset amount, Toff. The
value ofToff is typically 0.5 1 C and the value ofTon typically 4 6 timesToff (7 p.
102). Selection of these constants is important in order to reduce the frequency of
cycling that the will system experiences, which increases the parasitic losses incurred
by the pump.
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5.5. PERFORMANCE RESULTS
The final system design was evaluated using the performance estimation model.
The resulting energy gains represent the performance of the system in a typical year.
The annual net solar energy delivered by the system was estimated to be 241,459 [MJ],
displacing 10,835 [m3] of natural gas. Parasitic pumping losses consumed 5,613 [kWh]
of electrical energy. Therefore the system generated 11.95 times more energy than it
consumed. The overall fraction of the total heating load supplied by the SWH system
was 2.69%, while the monthly solar fraction during July and August was 100%. Figure
10 charts the solar fraction as well as the total solar energy gain in [MJ].
Figure 10: Fraction of the heating load supplied by solar energy
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Energy Gain 9,024 14,300 22,017 25,719 28,919 29,430 28,658 27,615 28,863 20,680 5,775 2,853
Solar Fraction 0.0058 0.0105 0.0178 0.0370 0.0728 0.3296 1.0000 1.0000 0.1998 0.0379 0.0060 0.0019
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
S
olarFraction
En
ergyGain[MJ]
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6. FINANCIAL FEASIBILITY
6.1. EVALUATION METHODOLOGY
The economics of the project depend on several key financial factors: the availability
of a government subsidy, the energy cost escalation rate, the debt ratio and interest
rate, and the discount rate. The following section will describe the selection of those
factors as well as the economic indicators that will be used to evaluate the project.
GOVERNMENT SUBSIDY
Solar water heating installations are generally characterized by high initial costs and
low operating costs. Thus the basic economic problem is one of comparing an initial
known cost with estimated future operating costs. Reducing the initial cost can
substantially benefit the economics of a project, especially if debt is taken on for
financing. Many governments offer subsidies to renewable energy installation projects
to help offset costs and give the emerging technology a boost. The Government of
Ontario currently offers a rebate on the provincial sales tax for residential SWH
systems, however, a building such as the school considered in this project would not
qualify. Since 1998, the Canadian Federal Government has offered substantial rebates
through its Renewable Energy Deployment Initiative (REDI) program. The program
provides a refund of 25 percent of the purchase and installation costs of qualifying
renewable energy systems, to a maximum refund of $80,000 per installation (8). On
January 19th
, 2007 Prime Minister Stephen Harper announced the cancellation of the
REDI program, and beginning of the the ecoENERGY program that will replace it. The
ecoENERGY for Renewable Heat program, will provide $36 million over four years to
increase the adoption of clean renewable thermal technologies for water heating and
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space heating and cooling (9). However, there has been no information made public
about the details of this program. For the purposes of this project, the assumption will
be made that the two programs are equivalent in their rebates. In order to gain insight
into the effect of government subsidies on the economics of SWH projects, the project
will be evaluated with and without this subsidy.
ENERGY COST INFLATION RATE
The energy cost inflation rate is that rate at which the price of energy is expected to
increase in the future. Selecting a suitable rate is difficult given the high degree of price
volatility that the energy market experiences. The methodology used in this analysis
was to use both the historic data and future projections. The historic 25 year overall rate
of increase in US natural gas prices was estimated at 43%, based on records from the
Energy Information Administration (EIA) (10). However, forecasts by the EIA predict that
natural gas prices will have declined by -0.7% by the year 2030 (11). Both figures have
discounted increases due to general inflation. Since it is likely that the true energy cost
inflation rate will fall within this range, the project will be evaluated at 0%, 20%, and 40%
overall 25 year energy cost inflation rates. This rate will be applied on top of a flat
general inflation rate of 2.0% based on current Canadian trends (12).
DEBT RATIO AND INTEREST RATE
The debt ratio is the percentage of the initial costs that were borrowed to finance the
project. This ratio changes the project economics because with increasing debt ratio
there will be increasing interest paid. The project will be evaluated at debt ratios of
100%, 50%, and 0% in order to examine its effect. The interest rate paid on debt was
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selected at 6.0%, based roughly on the current (March 2007) prime rates for long term
closed loans (13).
DISCOUNT RATE
The discount rate represents an investors minimum acceptable rate of return on
investment, or in other words, the rate of return that would be earned had the money be
put into an alternate investment. The discount rate was selected at 4.0%, roughly based
on the current rate on long term government bonds in Canada (13).
ECONOMIC INDICATORS
Net Present Value (NPV) is defined as the present value of a series of cash flows,
evaluated at the discount rate. It is an indication of the profitability of an investment
minus the opportunity cost of an alternative investment returning at the discount rate (14
p. 152).
Simple Payback (SPB) is the amount of time it takes to recover the initial costs, not
taking into account the time value of money. It is simply the initial costs divided by the
income generated per year. It is a highly popular indicator due to its lack of dependence
on variables such as discount and interest rates, however, it is suggested not to rely
completely on this indicator since the timing of cash flows and duration of the project are
ignored (14 p. 155).
Discounted Payback (DPB), similar to simple payback, is the amount of time it takes
to recover the initial costs of a project. The discounted payback, however, takes into
consideration the time value of money. It is considered a more realistic indicator than
simple payback (4 p. 467).
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6.2. ECONOMIC ANALYSIS
The economic analysis of the project was evaluated at differing values of three key
factors: the availability of a government subsidy, the energy cost escalation rate, and
the debt ratio. The project was evaluated over an expected lifetime of 25 years. The
results of these evaluations are given below.
Energy CostInflation Rate
No Subsidy With Subsidy
NPV SPB DPB NPV SPB DPB
0% -$44,573 25.22 Never -$14,768 18.92 Never
20% -$36,848 25.22 Never -$7,043 18.92 Never
40% -$28,127 25.22 Never $1,678 18.92 21
Figure 11: Case 1 standard initial cost, 100% debt ratio
Energy CostInflation Rate
No Subsidy With Subsidy
NPV SPB DPB NPV SPB DPB
0% -$33,741 25.22 Never -$6,644 18.92 21
20% -$26,016 25.22 Never $1,081 18.92 18
40% -$17,296 25.22 23 $9,801 18.92 16
Figure 12: Case 2 standard initial cost, 50% debt ratio
Energy CostInflation Rate
No Subsidy With Subsidy
NPV SPB DPB NPV SPB DPB
0% -$22,909 25.22 21 $1,480 18.92 1720% -$15,184 25.22 20 $9,205 18.92 16
40% -$6,464 25.22 18 $17,925 18.92 15
Figure 13: Case 3 standard initial cost, 0% debt ratio
Energy CostInflation Rate
No Subsidy With Subsidy
NPV SPB DPB NPV SPB DPB
0% -$9,321 17.76 Never $20,494 11.46 N/A
20% -$1,596 17.76 23 $28,219 11.46 N/A
40% $7,124 17.76 18 $36,939 11.46 N/A
Figure 14: Undersize boiler replacement, $30,000 savings in year 0, 100% debt ratio
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6.3. SENSITIVITY ANALYSIS
The range of initial costs given in Figure 3 was used to perform a sensitivity analysis
on the cost estimation. The best case scenario (low cost estimation, 0% debt ratio) and
the worst case scenario (high cost estimation, 100% debt ratio) are presented below.
Energy CostInflation Rate
No Subsidy With Subsidy
NPV SPB DPB NPV SPB DPB
0% -$1,806 19.77 17 $17,307 14.82 14
20% $5,919 19.77 16 $25,033 14.82 13
40% $14,640 19.77 15 $33,753 14.82 12
Figure 15: Best case scenario low initial costs, 0% debt ratio
Energy CostInflation Rate
No Subsidy With Subsidy
NPV SPB DPB NPV SPB DPB
0% -$73,873 31.42 Never -$36,743 23.57 Never
20% -$66,148 31.42 Never -$29,018 23.57 Never
40% -$57,427 31.42 Never -$20,297 23.57 Never
Figure 16: Worst case scenario high initial costs, 100% debt ratio
6.4. DISCUSSION
The results of the economic analysis presented above gives an insight into the
economics of SWH systems. As was expected, financial feasibility increased with the
availability of a subsidy, increasing energy cost inflation rate, and decreasing debt ratio.
The most obvious trend in the economic analysis was the benefit of a government
subsidy towards the economics of the project. Under standard initial costing, no case
had a positive NPV without the aid of the subsidy. However, with the subsidy, all three
cases had the possibility of returning a positive NPV. The best case scenario (low initial
cost, 0% debt ratio) had a positive NPV without subsidy, indicating that if initial costs
could be lowered then financial feasibility without subsidy might be reached.
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The energy cost inflation rate had a strong effect on the financial feasibility of the
project. Under a rate of 0%, only Case 3 with subsidy and the Best case scenario with
subsidy had a positive NPV. This indicates that if fuel costs remain stable at current
relative costs for the next 25 years as predicted by the EIA (11), solar water heating
may never become economically feasible without government subsidies, even with
reduced initial costs.
Increasing the amount of debt taken on in order to finance the project drastically
reduced the financial feasibility of the project. The worst case scenario (high initial cost,
100% debt ratio) had no chance of generating a positive NPV, even with high energy
cost inflation rates. It is ideal to finance the initial cost of a SHW system with cash to
avoid paying any interest charges, however, this is not an option for most organizations.
Simple payback periods depended only on initial costs and the availability of a
subsidy. The simple payback periods ranged from 31.42 years (high initial cost, no
subsidy) to 11.46 years (Undersize boiler replacement, $30,000 savings in year 0 with
subsidy). Under standard initial costs and with subsidy the SPB was 18.92 years.
Discounted payback periods ranged from never paying back to 12 years (low initial cost,
with subsidy, energy cost inflation 40%). The average DPB for standard initial costs with
subsidy was 16 years and without subsidy was 20.5 years, not including scenarios that
never reached payback. Even the best payback scenario yielded a payback much
longer than the TDSB is willing to consider, which is typically 8 years.
In the case where the replacement summer boiler was undersized, a credit of
$30,000 was applied in year 0. This improved the economics significantly, surpassing
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even the best case scenario. However, a positive NPV was still only reached with the
availability of a government subsidy, or a high energy inflation rate.
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7. CONCLUSION
The financial feasibility of a SWH project was found to be highly dependant on initial
costs, energy cost inflation rates, and debt ratios. This study found that under the right
conditions, such as utilizing an available subsidy, a high energy cost inflation rate, or a
low debt ratio, the installation of a SWH system could have a positive net present value,
indicating that the investment would a good one. However, many of the results of the
scenarios analyzed in this study found that under unfavourable conditions, such as the
opposite of those mentioned above, the system caused a net economic loss.
A specific case was examined where the addition of the SWH system allowed a
summer boiler to be undersized, resulting in savings for the SWH project and a boosted
financial feasibility. More research should be done into finding such niche applications
that maintain an acceptable level of comfort for the buildings occupants, but allow the
SWH system to fit into construction budgets.
The economic analysis indicated that if fuel costs remain stable at current relative
costs for the next 25 years as predicted by the EIA (11), large solar water heating
systems may never become economically feasible without government subsidies, even
with reduced initial costs.
Currently solar water heating systems seem to be poised right on the line between
profits and losses. It is up to the design team to create a system that is cost effective,
yet robust enough to provide free solar energy to its building for years to come.
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8. REFERENCES
1. Andren, L.Solar Installations: Practical Applications for the Built Environment. London : The Cromwell
Press, 2003.2. A General Design Method for Closed-Loop Solar Energy Systems. Klein, S. A. and Beckman, W. A.1979, Solar Energy, Vol. 22, pp. 269-282.3. Environment Canada. Canadian Climate Normals 1971-2000 (Toronto, Ontario). National ClimateData and Information Archive. [Online] http://climate.weatheroffice.ec.gc.ca/.4. Morehouse, J.Optimum System Design Techniques. [ed.] G. Lf. Active Solar Systems. Cambridge :The MIT Press, 1993, pp. 152-180.5. Duffie, J. A and Beckman, W. A. Solar Engineering of Thermal Processes. Hoboken : John Wiley &Sons, 2006.6. Toronto District School Board. Internal Records.7. Karaki, S. Space Heating: System Concepts and Design. [ed.] G. Lf. Active Solar Systems.Cambridge : The MIT Press, 1993, pp. 411-463.8. Bryon Winn, C. Controls in Active Solar Energy Systems. [ed.] G. Lf. Active Solar Systems.Cambridge : The MIT Press, 1993, pp. 81-149.9. Natural Resources Canada. Renewable Energy Deployment Initiative (REDI). Natural ResourcesCanada web site. [Online] Mar 2007. http://www2.nrcan.gc.ca/es/erb/erb/english/View.asp?x=692.10. . ecoENERGY Efficiency Initiative. Natural Resources Canada web site. [Online]http://www2.nrcan.gc.ca/es/erb/erb/english/View.asp?x=698.11. Energy Information Administration. U.S. Natural Gas Prices. EIA web site. [Online]http://tonto.eia.doe.gov/dnav/ng/hist/n3020us3A.htm.12. . Forecasts and Analysis of Energy Data - Natural Gas Prices AEO. EIA web site. [Online]http://www.eia.doe.gov/oiaf/forecasting.html.13. Statistics Canada. Latest Release from the Consumer Price Index. Statistics Canada web site.[Online] http://www.statcan.ca/english/Subjects/Cpi/cpi-en.htm.14. Bank of Canada. Rates and Statistics. Bank of Canada web site. [Online]http://www.bankofcanada.ca/en/rates/index.html.15. Szonyi, A. J., et al. Principles of Engineering Economic Analysis. Toronto : Wall & Emerson, Inc.,
2003.16. Klein, S. A. Design Methods for Active Solar Systems. [ed.] G. Lf. Active Solar Systems.Cambridge : The MIT Press, 1993, pp. 39-76.17. White, F. M.Fluid Mechanics. New York : McGraw-Hill, 2003.18. City of Toronto. Building Permit Fee Schedule. City of Toronto web site. [Online] 2007.http://www.toronto.ca/building/fee_schedule.htm.19. RETScreen International. RETScreen Software Online User Manual, Solar Water Heating ProjectModel. RETScreen International web site. [Online] 2005. www.retscreen.net.
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9. APPENDIX A:PERFORMANCE ESTIMATION DETAILS
,-CHART CALCULATION DETAILS
The concept of Utilizability was first discussed by Whillier in 1953 in his Ph.D.
dissertation at MIT (15). Utilizability, , is defined as the fraction of incident solar
irradiation in the plane of the collector that can be extracted as useful heat. The monthly
average utilizability is defined by the following equation (4 p. 700)
T Tc
Days Hours T
I I
I N
where IT is the solar irradiation in the plane of the collector and ITc is the critical level of
solar irradiation that just exceeds the amount needed to counter the energy lost to the
environment from the collector surface. At any intensity of radiation below this critical
level the system will experience a net energy loss and will not circulate the collector
fluid. ITc is defined by the following equation (4 p. 697)
aR L mTc
R
F U (T T )I
F
Tm is the minimum useful temperature; aT is the monthly average ambient temperature;
RF is the collector heat removal factor; is the effective product of the cover
transmittance and the collector plate absorptance; LU is the collector overall energy loss
coefficient. is a correction factor to introduce the monthly average
transmittance-absorptance product.
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As can be seen from the above equations, Utilizability is a function of climatic conditions
such as ambient temperature, collector fluid inlet temperature, and irradiation level, as
well as energy transfer characteristics of the chosen collector.
Due to the transient nature of these climatic conditions, however, the monthly
average utilizability, , cannot be approximated by substituting monthly average
climatic data into the equations above. Instead, it must be approximated through a
dimensionless correlation. cXIs the dimensionless critical radiation level, defined by (4
p. 700)
aR L mTc
c
T ot,n n R t,n n
F U T TIX
r R H F r R K H
The monthly average utilizability is calculated by the following correlation (4 p. 701)
2n
c cR
exp a b X cXR
2
T T
2
T T
2
T T
a 2.943 9.271K 4.031K
b 4.345 8.853K 3.602K
c 0.170 0.3061K 2.936K
The ,-Chart variables are then calculated as such (4 p. 704)
Tc RA F H NY
L
c R LA F U 100 tX'L
The solar fraction can then be solved for numerically from (4 p. 707)
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rd,n, the ratio of hourly total to daily diffuse radiation at noon (4 p. 83)
n sd,n
ss s
cos cosr
24sin cos
180
Rn, the ratio for the hour centred at noon of radiation on the tilted surface to that on a
horizontal surface for an average day of the month (4 p. 129)
d,n d d,n dTn b,n g
t,n t,nn
r H r HI 1 cos 1 cosR 1 R
I r H r H 2 2
Hd/H , the fraction of diffuse radiation to total radiation (4 p. 80)
s T
2 3dT T T
for 81.4 and 0.3 K 0.8
H1.391 3.56K 4.189K 2.137K
H
s T
2 3dT T T
for 81.4 and 0.3 K 0.8
H1.311 3.022K 3.427K 1.821K
H
Rb . the ratio of beam radiation on the tilted surface to that on a horizontal surface (4 p.
104)
s s
b
s s
cos cos sin ' ' sin sin180
Rcos cos sin sin sin
180
1
s 1
cos tan tan' min
cos tan tan
Rb,n. the ratio of beam radiation on the tilted surface to that on a horizontal surface at
solar noon (4 p. 25)
b,n
cosR
cos
R. the ratio of radiation on the tilted surface to that on a horizontal surface (4 p. 103)
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d dTb g
H HH 1 cos 1 cosR 1 R
H H H 2 2
PUMPING POWER CALCULATION DETAILS
The first step is to calculate the pipe flow Reynolds number from (16 p. 353)
d
4QRe
d
If Red > 2300 then the flow is turbulent. Use the following equation to calculate the
friction factor (16 p. 366)
1.11
.5
tur d
1 6.91.8log
Re 3.7d
Now calculate the head loss using (16 p. 352)
2LVh
d2g
The required pumping power is then (16 p. 751)
s fgQ h hP
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10. APPENDIX B:SYSTEM DRAWINGS
Boiler #1
SolarCollectorArray
HX
Boiler #2
SummerBoiler
Supply Service Hot Water
ExpansionChamber
Natural Gas
Filter
DrainageVessel
PressureRelief Valve
ModulatingControl
Return Service Hot Water