We have lost two of our tenants, which severely decreased our income. That postponed all remodel work. In the mean time, I have been thinking of different heating systems. One is to installed a closed loop water source heat pump that would extract the heat from the solar tank. The solar tank would be installed below the solar collector, with a capacity of about 2,000 gallons (30FT*3FT*3FT inside dimensions). The cold side of the heat pump (evaporator) is a heat exchanger that uses water from the solar tank. A mixing valve delivers a water temperature within the range of a standard heat pump, usually between 32 and 90F. The hot side is another heat exchanger, connected to the hydronic system.
The hydronic system could be smaller thanks to the higher water temp delivered by the heat pump. Baseboard heating would be adequate for such a system. The lower cost of the hydronic heaters offsets some of the cost of the heat pump. Some of the heaters, downstairs for example, could be home made using copper tubes.
The advantage of adding a heat pump is that more heat can be extracted from the solar tank. The colder water temp in the solar tank also increases the efficiency of the solar collector. The system will be able to run on solar for a longer period of time, but will also draw more electricity.
Alternatively, the most cost efficient system maybe a water source air handler type heat pump, that would re-use the air duct system in the house. This completely eliminate the cost of the hydronic system, and still give very good efficiency.
With a common rule of 600sqft/ton, we need a 4.5 to 5 ton system.
Another improvment of the heating system is to add zoning with these [ motorized thermostat controlled registers ]. The upstairs bedrooms and downstairs living room usually get overheated, so these rooms would get the thermostatic registers.
Ultimately, cost constraints will dictate the system, so my feeling is that we will probably go for a standard air-based heat pump with thermostatic dampers in strategic locations. Later, a solar heat collection system may assist the air source heat pump.
Sunday, July 31, 2011
Monday, May 16, 2011
Property layout - first draft
The following picture presents the location of the solar collector compared to the house. It also shows its South orientation. The collector is 12Ft high, 32FT long. This location is far away from trees to avoid shading. The house may produce some shading at the end of winter days, but that should be minimal. The location of the collector is also higher that the level of the house, which will further reduce shading.
Also shown are the rainwater lines to feed our toilets and laundry rooms, as well as several outdoor spigots.
Routing the hot water lines from the collector to the tank won't be easy. The current plan is to locate the tank downstairs inside a wall separating the living room from the third bedroom, on the South side of the house. The lines must run downward continuously from the collectors to the tank. The only way is to go around the house, which will make the pipe run a little longer.
Also shown are the rainwater lines to feed our toilets and laundry rooms, as well as several outdoor spigots.
Routing the hot water lines from the collector to the tank won't be easy. The current plan is to locate the tank downstairs inside a wall separating the living room from the third bedroom, on the South side of the house. The lines must run downward continuously from the collectors to the tank. The only way is to go around the house, which will make the pipe run a little longer.
Monday, April 25, 2011
Whole System Diagram (version 1)
In looking for a location for the storage tank, I realized a tank sized to my solar absorbers will need to be 1000 gallons. I have planned on 500 - 600 gallons, inside the utility room, but 1000 gallons will not fit. The tank size was determined by the rule of thumb of 2.5 gallons per square foot of absorber. This allows a good efficiency of the absorbers, while limiting the risk of overheating. Although there won't be overheating with a drainback system, I do want a tank as big as possible, to have a storage of heat for our numerous cloudy days.
I decided to choose an alternate location for the storage tank: under the deck. There should be plenty of room for a 1000+ gallon tank, and the pipe runs won't be any longer, since the tank will be between the absorber array and the house. The only part of the design that needs change, is the hot water pre-heater. The longer pipe run between the solar tank and the electric hot water tank will decrease the efficiency of the system. So I opted for a heat exchanger, located next to the electric water heater. I haven't decided yet what kind of heat exchanger.
It will be complex and pricey, which is why it will be done in two phases. I may get 4 absorbers instead of just 2 for phase 1, since phase 2 has the 8 absorbers arranged in two banks of 4.
Next will be a bill of material.
I decided to choose an alternate location for the storage tank: under the deck. There should be plenty of room for a 1000+ gallon tank, and the pipe runs won't be any longer, since the tank will be between the absorber array and the house. The only part of the design that needs change, is the hot water pre-heater. The longer pipe run between the solar tank and the electric hot water tank will decrease the efficiency of the system. So I opted for a heat exchanger, located next to the electric water heater. I haven't decided yet what kind of heat exchanger.
It will be complex and pricey, which is why it will be done in two phases. I may get 4 absorbers instead of just 2 for phase 1, since phase 2 has the 8 absorbers arranged in two banks of 4.
Next will be a bill of material.
Friday, April 22, 2011
Phase 1 Design
Phase 1 will provide hot water pre-heating, and two bedrooms with hydronic radiators. It will use two 8' * 12' solar panels using the Sunraysolar absorber plates. I compared the cost per sqft of each absorber plate model, and the 8*12 are the cheapest, so we will have to find a way to implement them.
Because they will be in front of the house, the solar absorbers will be set horizontally, with two header pipes, one above and one below, to connect the absorbers headers. Each header pipe will be 24FT long, 1.5" diameter.
I am not sure this configuration will work. I am concern with air being trapped in the horizontal risers as water raises in the vertical headers. One solution would be to not add horizontal headers, but without them the absorbers won't completely drain, so these headers are required. I am hoping the tilt of the absorbers will be enough to allow a complete fill. At this time a filling/draining test is the only way to tell.
Thermostatic valves are set on each hydronic radiator. This removes the need to add thermostats, zone valves and other expense and complexity. This is the way hydronic heating is used in France.
Here is the block diagram for phase 1:
Bill of Material:
Total = $2025.36 so far (still many items TBD)
Because they will be in front of the house, the solar absorbers will be set horizontally, with two header pipes, one above and one below, to connect the absorbers headers. Each header pipe will be 24FT long, 1.5" diameter.
I am not sure this configuration will work. I am concern with air being trapped in the horizontal risers as water raises in the vertical headers. One solution would be to not add horizontal headers, but without them the absorbers won't completely drain, so these headers are required. I am hoping the tilt of the absorbers will be enough to allow a complete fill. At this time a filling/draining test is the only way to tell.
Thermostatic valves are set on each hydronic radiator. This removes the need to add thermostats, zone valves and other expense and complexity. This is the way hydronic heating is used in France.
Here is the block diagram for phase 1:
Bill of Material:
- Absober plates (8*12) = $428.43 * 2 = $856.86
- Material for absorbers (Plywood)= TBD
- Material for absorbers (4x4 posts) = TBD
- Hydronic radiators SD70160G = $525.35 * 2 = $1050.7
- Thermostatic valves = $58.90 * 2 = $117.80
- Hydronic pump = TBD
- Solar circulating pump = TBD
- Pump Controller = TBD
- Heat exchanger (300FT pipe) = TBD
- Various piping = TBD
- Tank material (2X4) = TBD
- Tank material (plywood) = TBD
- Tank material (insulation) = TBD
- Tank material (miscellaneous) = TBD
Total = $2025.36 so far (still many items TBD)
Thursday, April 21, 2011
Heat Distribution
Heat distribution is important when using solar heated water. The heat distribution system must be able to use a low water temperature, the lower the better, so that most of the solar heat can be extracted for the tank, leaving the water close to ambient, and improving the efficiency of the collectors.
I have looked at radiant floors, baseboards, and hydronic radiators. I have summed up the pros and cons of each in the table below:
Radiant Floors:
Hydronic basebords:
Hydronic Radiators:
Based on this table, the choice is hydronic radiators.
Heating needs for our house are between 25 and 50 BTUh/sqft. Aiming at the high end, we will need a total of 3000sqft * 50BTUh/sqft = 150,000 BTUh.
The BTUh value of hydronic radiators is calculated for a water temperature at 180°F. The solar system will be set at 140°F maximum. At a water temperature of 130°F, the derating is already 0.5, which sets the BTUh rating at between 50 and 100 BTUh/sqft.
The whole house will need between 150,000 and 300,000 BTUh.
Our bedrooms are between 120 and 160 sqft. A good choice to stay within the 50 - 100 BTUh/sqft range, and fit all bedrooms is the Myson SD70160G, at 13,000 BTUh, and $525.35.
The biggest rooms are the living rooms, upstairs and downstairs, at 33,000 sqft. Each will use 2 SD70160G, for 26,000 BTUh. Since each room has a wood stove, it is conceivable to put only one radiator in these rooms, and use the wood stoves for supplemental heat during the Winter. The system will be initially designed with two radiators in each of these rooms.
The bathrooms, stairwell and laundry rooms will use a smaller radiator, such as Myson SD6060G, at 4300BTUh and $200. There are three bathrooms, and two laundry rooms.
The total amount of BTUh is: ( 13,000 * 11 ) + ( 4300 * 6 ) = 170,000 BTUh
Because the hallways and other dead spaces are not heated, we fall on the low side of the required range. This is OK, since the solar array is not supposed to provide enough heat through the year. During December and January, supplemental heat from the wood stove will be needed. An additional heat source may also be added to the hydronic system (wood pellet boiler or heat pump).
Next step is to design the system for phase 1, which will heat our hot water and two bedrooms, using two solar panels. If everything goes well, the system will be scaled up to the whole house, and 8 solar panels.
I have looked at radiant floors, baseboards, and hydronic radiators. I have summed up the pros and cons of each in the table below:
Radiant Floors:
- PROs
Wide heating area than can use low water temperature.
The floors will be replaced, we can choose what we prefer. - CONS
Very costly solution, labor intensive.
The floor is an insulator, which offsets the advantage of a wider heating area.
Some of the heat will be drawn into the concrete slab. - Estimated Cost > $10k
Hydronic basebords:
- PROs
Cheapest solution
Heater directly in contact with the air (more efficient). - CONs
Not enough heating area, which will increase the water temperature needed to heat the room. - Estimated Cost = $4k
Hydronic Radiators:
- PROs
Can be scaled up, to account for lower water temp.
Heater directly in contact with the air.
Can use a thermostatic valve, which greatly simplifies system design. - CONs
Somewhat expensive. - Estimated Cost = $6k
Based on this table, the choice is hydronic radiators.
Heating needs for our house are between 25 and 50 BTUh/sqft. Aiming at the high end, we will need a total of 3000sqft * 50BTUh/sqft = 150,000 BTUh.
The BTUh value of hydronic radiators is calculated for a water temperature at 180°F. The solar system will be set at 140°F maximum. At a water temperature of 130°F, the derating is already 0.5, which sets the BTUh rating at between 50 and 100 BTUh/sqft.
The whole house will need between 150,000 and 300,000 BTUh.
Our bedrooms are between 120 and 160 sqft. A good choice to stay within the 50 - 100 BTUh/sqft range, and fit all bedrooms is the Myson SD70160G, at 13,000 BTUh, and $525.35.
The biggest rooms are the living rooms, upstairs and downstairs, at 33,000 sqft. Each will use 2 SD70160G, for 26,000 BTUh. Since each room has a wood stove, it is conceivable to put only one radiator in these rooms, and use the wood stoves for supplemental heat during the Winter. The system will be initially designed with two radiators in each of these rooms.
The bathrooms, stairwell and laundry rooms will use a smaller radiator, such as Myson SD6060G, at 4300BTUh and $200. There are three bathrooms, and two laundry rooms.
The total amount of BTUh is: ( 13,000 * 11 ) + ( 4300 * 6 ) = 170,000 BTUh
Because the hallways and other dead spaces are not heated, we fall on the low side of the required range. This is OK, since the solar array is not supposed to provide enough heat through the year. During December and January, supplemental heat from the wood stove will be needed. An additional heat source may also be added to the hydronic system (wood pellet boiler or heat pump).
Next step is to design the system for phase 1, which will heat our hot water and two bedrooms, using two solar panels. If everything goes well, the system will be scaled up to the whole house, and 8 solar panels.
Wednesday, March 23, 2011
Buget cuts and military expenses
Today I'll do some comparison between the proposed GOP 2011 budget cuts, and the military expenditures of the last 10 years. The GOP proposed budget cuts are based on yearly budget, so when they say $30M (millions) cut on the first item on the list, Flood Control and Coastal Emergencies, that is for 1 year.
To put things in perspective, I calculated how long it took our military in Afghanistan and Iraq to spend the same amount of money. $30M is 2 hours of war. In this case, the GOP is basically proposing to cut the Flood Control and Coastal Emergencies funds for one year, in order to pay back just 2 hours of war.
There are a total of 70 items. Here are the one that saddened me the most:
Anyway, here is the full list, enjoy!
1. Flood Control and Coastal Emergencies: 30 M$ = 2 Hours
2. Energy Efficiency and Renewable Energy: 899 M$ = 3 Days
3. Electricity Delivery and Energy Reliability: 49 M$ = 3 Hours
4. Nuclear Energy: 169 M$ = 10 Hours
5. Fossil Energy Research: 31 M$ = 2 Hours
6. Clean Coal Technology: 18 M$ = 2 Hours
7. Strategic Petroleum Reserve: 15 M$ = 53 Minutes
8. Energy Information Administration: 34 M$ = 3 Hours
9. Office of Science: 1100 M$ = 3 Days
10. Power Marketing Administrations: 52 M$ = 4 Hours
11. Department of Treasury: 268 M$ = 16 Hours
12. Internal Revenue Service: 593 M$ = 2 Days
13. Treasury Forfeiture Fund: 338 M$ = 20 Hours
14. GSA Federal Buildings Fund: 1700 M$ = 5 Days
15. ONDCP: 69 M$ = 5 Hours
16. International Trade Administration: 93 $M = 6 Hours
17. Economic Development Assistance: 16 M$ = 57 Minutes
18. Minority Business Development Agency: 2 M$ = 8 Minutes
19. National Institute of Standards and Technology: 186M$=11Hours
20. NOAA: 336 M$ = 20 Hours
21. National Drug Intelligence Center: 11 M$ = 39 Minutes
22. Law Enforcement Wireless Communications: 52 M$ = 4 Hours
23. US Marshals Service: 10 M$ = 36 Minutes
24. FBI: 74 M$ = 5 Hours
25. State and Local Law Enforcement Assistance: 256 M$ = 16 Hours
26. Juvenile Justice: 2.3 M$ = 9 Minutes
27. COPS: 600 M$ = 2 Days
28. NASA: 379 M$ = 23 Hours
29. NSF: 139 M$ = 9 Hours
30. Legal Services Corporation: 75 M$ = 5 Hours
31. EPA: 1600 M$ = 4 Days
32. Food Safety and Inspection Services: 53 M$ = 4 Hours
33. Farm Service Agency: 201 M$ = 12 Hours
34. Agriculture Research: 246 M$ = 15 Hours
35. Natural Resource Conservation Service: 46 M$ = 3 Hours
36. Rural Development Programs: 237 M$ = 14 Hours
37. WIC: 758 M$ = 2 Days
38. International Food Aid grants: 544 M$ = 2 Days
39. FDA: 220 M$ = 13 Hours
40. Land and Water Conservation Fund: 348 M$ = 21 Hours
41. National Archives and Record Service: 20 M$ = 2 Hours
42. DOE Loan Guarantee Authority: 1400 M$ = 4 Days
43. EPA ENERGY STAR: 7. 4 M$ = 26 Minutes
44. EPA GHG Reporting Registry: 9 M$ = 32 Minutes
45. USGS: 27 M$ = 2 Hours
46. EPA Cap and Trade Technical Assistance: 5 M$ = 18 Minutes
47. EPA State and Local Air Quality Management: 25 M$ = 2 Hours
48. Fish and Wildlife Service: 72 M$ = 5 Hours
49. Smithsonian: 7. 3 M$ = 26 Minutes
50. National Park Service: 51 M$ = 4 Hours
51. Clean Water State Revolving Fund: 700 M$ = 2 Days
52. Drinking Water State Revolving Fund: 250 M$ = 15 Hours
53. EPA Brownfields: 48 M$ = 3 Hours
54. Forest Service: 38 M$ = 3 Hours
55. National Endowment for the Arts: 6 M$ = 22 Minutes
56. National Endowment for the Humanities: 6 M$ = 22 Minutes
57. Job Training Programs: 2000 M$ = 5 Days
58. Community Health Centers: 1300 M$ = 4 Days
59. Maternal and Child Health Block Grants: 210 M$ = 13 Hours
60. Family Planning: 327 M$ = 20 Hours
61. Poison Control Centers: 27 M$ = 2 Hours
62. CDC: 755 M$ = 2 Days
63. NIH: 1000 M$ = 3 Days
64. Substance Abuse and Mental Health Services: 96 M$ = 6 Hours
65. LIHEAP Contingency fund: 400 M$ = 24 Hours
66. Community Services Block Grant: 405 M$ = 24 Hours
67. High Speed Rail: 1000 $M = l3 Days
68. FAA Next Gen: 234 M$ = 14 Hours
69. Amtrak: 224 M$ = 14 Hours
70. HUD Community Development Fund: 530 M$ = 2 Days
To put things in perspective, I calculated how long it took our military in Afghanistan and Iraq to spend the same amount of money. $30M is 2 hours of war. In this case, the GOP is basically proposing to cut the Flood Control and Coastal Emergencies funds for one year, in order to pay back just 2 hours of war.
There are a total of 70 items. Here are the one that saddened me the most:
- Economic Development Assistance = 57 minutes of war. Great choice in a time of recession.
- National Drug Intelligence Center = 39 minutes of war. We don't have a drug problem in this country ...
- Juvenile Justice = 9 minutes of war. Just 9 minutes of war!
- NSF = 9 hours. Science has never served this country.
- Food Safety and Inspection Services = 4 hours of war. Haw we never had food contaminations in this country.
- WIC = 2 days of war. Wicked! If you can't raise a kid on your own, don't have one...
- Family planning = 20 hours of war ... and you can't use birth control either! That goes well with the item above!
- Substance Abuse and Mental Health Services = 6 hours of war. We REALLY don't have a drug problem in this country.
Anyway, here is the full list, enjoy!
1. Flood Control and Coastal Emergencies: 30 M$ = 2 Hours
2. Energy Efficiency and Renewable Energy: 899 M$ = 3 Days
3. Electricity Delivery and Energy Reliability: 49 M$ = 3 Hours
4. Nuclear Energy: 169 M$ = 10 Hours
5. Fossil Energy Research: 31 M$ = 2 Hours
6. Clean Coal Technology: 18 M$ = 2 Hours
7. Strategic Petroleum Reserve: 15 M$ = 53 Minutes
8. Energy Information Administration: 34 M$ = 3 Hours
9. Office of Science: 1100 M$ = 3 Days
10. Power Marketing Administrations: 52 M$ = 4 Hours
11. Department of Treasury: 268 M$ = 16 Hours
12. Internal Revenue Service: 593 M$ = 2 Days
13. Treasury Forfeiture Fund: 338 M$ = 20 Hours
14. GSA Federal Buildings Fund: 1700 M$ = 5 Days
15. ONDCP: 69 M$ = 5 Hours
16. International Trade Administration: 93 $M = 6 Hours
17. Economic Development Assistance: 16 M$ = 57 Minutes
18. Minority Business Development Agency: 2 M$ = 8 Minutes
19. National Institute of Standards and Technology: 186M$=11Hours
20. NOAA: 336 M$ = 20 Hours
21. National Drug Intelligence Center: 11 M$ = 39 Minutes
22. Law Enforcement Wireless Communications: 52 M$ = 4 Hours
23. US Marshals Service: 10 M$ = 36 Minutes
24. FBI: 74 M$ = 5 Hours
25. State and Local Law Enforcement Assistance: 256 M$ = 16 Hours
26. Juvenile Justice: 2.3 M$ = 9 Minutes
27. COPS: 600 M$ = 2 Days
28. NASA: 379 M$ = 23 Hours
29. NSF: 139 M$ = 9 Hours
30. Legal Services Corporation: 75 M$ = 5 Hours
31. EPA: 1600 M$ = 4 Days
32. Food Safety and Inspection Services: 53 M$ = 4 Hours
33. Farm Service Agency: 201 M$ = 12 Hours
34. Agriculture Research: 246 M$ = 15 Hours
35. Natural Resource Conservation Service: 46 M$ = 3 Hours
36. Rural Development Programs: 237 M$ = 14 Hours
37. WIC: 758 M$ = 2 Days
38. International Food Aid grants: 544 M$ = 2 Days
39. FDA: 220 M$ = 13 Hours
40. Land and Water Conservation Fund: 348 M$ = 21 Hours
41. National Archives and Record Service: 20 M$ = 2 Hours
42. DOE Loan Guarantee Authority: 1400 M$ = 4 Days
43. EPA ENERGY STAR: 7. 4 M$ = 26 Minutes
44. EPA GHG Reporting Registry: 9 M$ = 32 Minutes
45. USGS: 27 M$ = 2 Hours
46. EPA Cap and Trade Technical Assistance: 5 M$ = 18 Minutes
47. EPA State and Local Air Quality Management: 25 M$ = 2 Hours
48. Fish and Wildlife Service: 72 M$ = 5 Hours
49. Smithsonian: 7. 3 M$ = 26 Minutes
50. National Park Service: 51 M$ = 4 Hours
51. Clean Water State Revolving Fund: 700 M$ = 2 Days
52. Drinking Water State Revolving Fund: 250 M$ = 15 Hours
53. EPA Brownfields: 48 M$ = 3 Hours
54. Forest Service: 38 M$ = 3 Hours
55. National Endowment for the Arts: 6 M$ = 22 Minutes
56. National Endowment for the Humanities: 6 M$ = 22 Minutes
57. Job Training Programs: 2000 M$ = 5 Days
58. Community Health Centers: 1300 M$ = 4 Days
59. Maternal and Child Health Block Grants: 210 M$ = 13 Hours
60. Family Planning: 327 M$ = 20 Hours
61. Poison Control Centers: 27 M$ = 2 Hours
62. CDC: 755 M$ = 2 Days
63. NIH: 1000 M$ = 3 Days
64. Substance Abuse and Mental Health Services: 96 M$ = 6 Hours
65. LIHEAP Contingency fund: 400 M$ = 24 Hours
66. Community Services Block Grant: 405 M$ = 24 Hours
67. High Speed Rail: 1000 $M = l3 Days
68. FAA Next Gen: 234 M$ = 14 Hours
69. Amtrak: 224 M$ = 14 Hours
70. HUD Community Development Fund: 530 M$ = 2 Days
Tuesday, March 1, 2011
Estimated solar fraction
Using monthly insolation data, sun angle and collector tilt, it is possible to estimate how much of our home energy needs (based on utility bills) will be provided by the solar system.
The first important data is the solar energy falling on each horizontal square foot, daily average, for each month, in KWh/day/sqft (click on the table or graphic to bring full screen):
Check my earlier post for references on this data.
Sun angle, calculated for the 1rst day of each month, graphical representation, followed by monthly data:
Next we need to calculate the collector sun angle. The ideal collector sun angle is 90°. The graphic shows how the collector sun angle is calculated (example shows June data), and the following table, each monthly value, for a 70° tilt.
Formula is:
Collector Sunangle = 180° - Tilt - Sunangle
The data from the table shows that maximum efficiency (collector sun angle = 90°) is achieve during the winter months, which is the reason of the 70° tilt.
Next, the ratio between horizontal area and collector area is needed to estimate the energy per collector sqft. This ratio is C/A, as represented on the graphic.
Area Ratio = sin(Collector sunangle) / sin(Sunangle)
Here too, the high tilt angle favors the winter months.
From these data, we can calculate the KWh/day per collector sqft:
KWH/day/collector sqft = KWh/day/horizontal sqft * Area ratio.
It is interesting to see how much the variation in monthly insolation is reduced by choosing the right tilt angle (compare the table above to the first table).
Finally, the solar fraction per month, for a 400sqft collector at 48% efficiency (60% from commercial flat plates data, and 80% for the "DIY factor"):
The yearly solar fraction is estimated at 96%.
The same calculation with a 600sqft collector, yields a 100% solar fraction, while a 275sqft yields a 90% solar fraction.
The difference in solar fraction between 350sqft and 400sqft, is only 1%. The December solar fraction goes from 67% (400sqft) to 58% (350sqft).
It seems that the best size is anywhere between 350 and 400sqft.
Final data is the needed collector area per month. This data could be useful if I want to occult part of the collector to avoid overheating. I will try to use a drainback system, but even with drainback, the empty collector exposed to the sun will wear faster than a shaded collector.
Also the 100 or so sqft needed during summer are for hot water needs, so this data is helpful in dimensioning the hot water system alone.
The first important data is the solar energy falling on each horizontal square foot, daily average, for each month, in KWh/day/sqft (click on the table or graphic to bring full screen):
Check my earlier post for references on this data.
Sun angle, calculated for the 1rst day of each month, graphical representation, followed by monthly data:
Next we need to calculate the collector sun angle. The ideal collector sun angle is 90°. The graphic shows how the collector sun angle is calculated (example shows June data), and the following table, each monthly value, for a 70° tilt.
Formula is:
Collector Sunangle = 180° - Tilt - Sunangle
The data from the table shows that maximum efficiency (collector sun angle = 90°) is achieve during the winter months, which is the reason of the 70° tilt.
Next, the ratio between horizontal area and collector area is needed to estimate the energy per collector sqft. This ratio is C/A, as represented on the graphic.
Area Ratio = sin(Collector sunangle) / sin(Sunangle)
Here too, the high tilt angle favors the winter months.
From these data, we can calculate the KWh/day per collector sqft:
KWH/day/collector sqft = KWh/day/horizontal sqft * Area ratio.
It is interesting to see how much the variation in monthly insolation is reduced by choosing the right tilt angle (compare the table above to the first table).
Finally, the solar fraction per month, for a 400sqft collector at 48% efficiency (60% from commercial flat plates data, and 80% for the "DIY factor"):
The yearly solar fraction is estimated at 96%.
The same calculation with a 600sqft collector, yields a 100% solar fraction, while a 275sqft yields a 90% solar fraction.
The difference in solar fraction between 350sqft and 400sqft, is only 1%. The December solar fraction goes from 67% (400sqft) to 58% (350sqft).
It seems that the best size is anywhere between 350 and 400sqft.
Final data is the needed collector area per month. This data could be useful if I want to occult part of the collector to avoid overheating. I will try to use a drainback system, but even with drainback, the empty collector exposed to the sun will wear faster than a shaded collector.
Also the 100 or so sqft needed during summer are for hot water needs, so this data is helpful in dimensioning the hot water system alone.
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