Measuring payoff for installation of the system simply involves collecting annual data on propane use. Consider that there is always a base use of propane used for the drying of clothes, and we do operate a wood stove during cold periods. This year has provided a lot of sunny days, which has helped in propane savings.
Domestic hot water use has remained constant, as our home has three full-time residents. One factor in savings on DHW use is that clothes washing and dishwasher running is generally done in the early afternoon, when the DHW tank is fully heated and has time to recover with solar collection. Showering is generally done during the early morning, but the well insulated tank is still hot from the day before.
Propane usage for the year (Jan 1 - Dec 31) is somewhat dependent on when the tank is filled. I have tried to be consistent on fill times not only to avoid skewing the data, but to take advantage of filling at lower pricer periods. I just did my annual October "top off" of the tank to take advantage of the lower pre-winter prices.
All that being said, here are the figures:
2007 propane usage - 1390 gallons, average price was $1.81, total cost $2728
2008 propane usage - 1180 gallons, average price was $2.11, total cost $2763
2009 propane usage - 892 gallons, average price was $1.69, total cost $1578
The system as installed in the summer of 2008. So, thoerectically savings for that year should have only been half of that this year. The numbers bear that out.
Gallons usage is the main factor in calculating gain. Cost ($) savings is kind of a mixed blessing. Lower propane cost does save me real dollars, but lengthens how long it takes to achieve a payback.
Saturday, October 10, 2009
Saturday, February 21, 2009
Exploring Possibilities for Savings
The boiler system is presently configured to start at 6AM, and heat up the DHW tank and provide heat to the floors. It shuts down at 7PM
On sunny days, the collectors begin heating water at 9AM, and by 10:30, the DHW tank is usually up to temp. On week days, I shower at 4:30 AM, and there is still ample hot water in the 80 gallon tank. My wife showers at 6:30, so I have the boiler start at 6AM to make sure she does not run out of hot water. There is still a lot of residual heat left in the tank, even after my shower, all resulting in less propane usage needed. So, there is probably not much savings available (let alone the risk of having my wife running out of hot water) with changes to the DHW system.
What may help with propane savings, is to not let the boiler bring the in-floor heating system up to temp until 10:30, so that the solar collection system has a chance to heat up the capacity tank.
On sunny days, the collectors begin heating water at 9AM, and by 10:30, the DHW tank is usually up to temp. On week days, I shower at 4:30 AM, and there is still ample hot water in the 80 gallon tank. My wife showers at 6:30, so I have the boiler start at 6AM to make sure she does not run out of hot water. There is still a lot of residual heat left in the tank, even after my shower, all resulting in less propane usage needed. So, there is probably not much savings available (let alone the risk of having my wife running out of hot water) with changes to the DHW system.
What may help with propane savings, is to not let the boiler bring the in-floor heating system up to temp until 10:30, so that the solar collection system has a chance to heat up the capacity tank.
System Saving Money and Pay-Off Projections
The $2000 Federal tax credit this year is the first obvious benefit, and I look forward to future tax credits (30% up to $2000) when I install additional vacuum tube arrays.
But, in the long term, saving on the cost of propane was the goal. My average usage for propane 2005 to 2007 was 1150 gallons. I installed the collection system last summer. My usage for 2008 dropped to 1180 gallons, and the system only began saving me propane the last half of the year. Winter temps have not been exceptional.
More accurate data will take time to produce, but it is not overly optimistic to expect my propane usage to drop to 700 gallons per year. A savings of 450 at $2 a gallon is $900. After tax credit cost of the system was $10,000 dollars, so I am still over a 10 year pay-off.
Installation of an additional 30 tube array should only cost (after tax credit) about $2400, and should further reduce propane usage by at least 200 gallons, shortening the pay-off to below the 10 year mark.
But, in the long term, saving on the cost of propane was the goal. My average usage for propane 2005 to 2007 was 1150 gallons. I installed the collection system last summer. My usage for 2008 dropped to 1180 gallons, and the system only began saving me propane the last half of the year. Winter temps have not been exceptional.
More accurate data will take time to produce, but it is not overly optimistic to expect my propane usage to drop to 700 gallons per year. A savings of 450 at $2 a gallon is $900. After tax credit cost of the system was $10,000 dollars, so I am still over a 10 year pay-off.
Installation of an additional 30 tube array should only cost (after tax credit) about $2400, and should further reduce propane usage by at least 200 gallons, shortening the pay-off to below the 10 year mark.
Tuesday, December 16, 2008
Winter Brings Highest Gains
Because I installed the collectors at an inclination to maximize gain at winter sun angles, my daily gains are at their highest on these clear sunny December days. Temperatures (daytime) have been hovering in the low 20's, so there is plenty of capacity in my heating system to put the solar gain.
A second 30 tube bank would be great right now, but even with the high angle of my collectors lowering the summer gain and the shading of the trees, I may have excess summer capacity. I will begin measuring the daily BTU gains calculated by my Vitotronic controller and post the results.
It is 12 noon. I am running dishwashers and the washing machine. The collector is putting out 130 degrees, all going to my DHW tank. It is keeping the DHW tank hot enough to supply 125 degree water to the tap, and supressing the boiler from firing. When the DHW use is over, in about 40 minutes, the DHW tank will quickly heat up to max temp (140 degrees). Then heat will be diverted to the heating storage tank.
Friday, October 24, 2008
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Sunday, October 19, 2008
Energy Savings Accumulating
The final system programming is complete. A "Heat Monitor" statement has been built for the Domestic Hot Water and Space Heating tanks. The heat energy is measured in Watts and is calculated from the temperature differential across the collector and the flow rate during the period that the pump (either one) runs.
The programmed parameters are: collector input flow temp, collector return flow temp, flow rate (set at 1 gpm - actual measured flow), and pump relay "on" time.
The wattage is a "totalized" acculation in watts. There are two seperate "statements" that totaled, represent the solar energy gathered, stored and delivered to the home.
Sunday, October 12, 2008
System Temps and Fine Tuning the System
DHW Temps: The heating of the domestic hot water (DHW) by the controller (vitosolic) is working great. I am heating the DHW to 50C. I have a tempering valve which mixes cold supply water with the hot tank water to keep the hot water from being at excessive temps. I also have a hot water circulating loop. This is a common system used to stop a long wait for hot water at a tap in large homes. The problem is that the water circulating is not tempered, but at the actual tank temp, so the water from the tap starts out at full temp (50C). Not only that, but the higher temp in the circulating loop (even though it is insulated), will result in higher heat loss. All that, plus the PEX tubing used in my house plumbing will not tolerate much higher temps, so that is why I am limiting the DHW tank to 50C.
Heat Collection: The default differential settings for circulating glycol through the collector and into the storage tanks are starting 5C (9F) and stopping 3C (5F). With these default settings, the pumps only cycle for a short time, on the average only a few minutes. The short cycle time comes from converging temperatures. As the cooler fluid from the tank being heated is pumped to the collector, the collector temp drops, and drops faster than the tank temp rises.
To lengthen the cycle time, I will raise the starting temp. I will not lower the stopping differential temp because doing so will likely result in inadequate differential for heat transfer to occur. I plan on starting with raising the starting differential to 7C. The collector temp comes up quickly when solar gain is good (from 10AM to 3PM), so time between cycles should not be much longer. I am betting that the increased length of time between cycles will be matched by an increase in the time length of the cycles.
Radiant Heat Delivery: Another important operating aspect of the system is delivery of heat to the radiant floor system header. The pump (P6 on the schematic), starts and stops on a temperature differential between the tank (S5), and the return line temp of the Low Loss Header (S6).
The tank must be at a high enough temp to match the temp that the boiler delivers to the header to provide radiant heat to the floors. This is tricky because the boiler control system modulates the header temp based on the outside temp, and a day/night settings where at night the header is ran at a lower temp than during the day.
The radiant heat storage tank temp can only be set at one temp, so I have set it's max temp at the top of the outside temp/boiler temp heating curve. So far, my collection capacity is not enough to hit the tank limit. What is available is the differential temp that the header return (P6) can be set at. I have been monitoring the header temp during operation, and it has become evident the the header temp drops when a zone calls for heat. After measuring the Low Loss Header (S8 in the schematic, not connected to the Vitosolic) and the return (S6), I have generally seen a 30 degrees F (about 16 degrees C) differential during operation. Based on this, I have set the S5/S6 differential to turn on the P6 pump to start a 16C, and turn off at 12C.
I will be monitoring the effectiveness of the new settings and posting the results in a week.
Heat Collection: The default differential settings for circulating glycol through the collector and into the storage tanks are starting 5C (9F) and stopping 3C (5F). With these default settings, the pumps only cycle for a short time, on the average only a few minutes. The short cycle time comes from converging temperatures. As the cooler fluid from the tank being heated is pumped to the collector, the collector temp drops, and drops faster than the tank temp rises.
To lengthen the cycle time, I will raise the starting temp. I will not lower the stopping differential temp because doing so will likely result in inadequate differential for heat transfer to occur. I plan on starting with raising the starting differential to 7C. The collector temp comes up quickly when solar gain is good (from 10AM to 3PM), so time between cycles should not be much longer. I am betting that the increased length of time between cycles will be matched by an increase in the time length of the cycles.
Radiant Heat Delivery: Another important operating aspect of the system is delivery of heat to the radiant floor system header. The pump (P6 on the schematic), starts and stops on a temperature differential between the tank (S5), and the return line temp of the Low Loss Header (S6).
The tank must be at a high enough temp to match the temp that the boiler delivers to the header to provide radiant heat to the floors. This is tricky because the boiler control system modulates the header temp based on the outside temp, and a day/night settings where at night the header is ran at a lower temp than during the day.
The radiant heat storage tank temp can only be set at one temp, so I have set it's max temp at the top of the outside temp/boiler temp heating curve. So far, my collection capacity is not enough to hit the tank limit. What is available is the differential temp that the header return (P6) can be set at. I have been monitoring the header temp during operation, and it has become evident the the header temp drops when a zone calls for heat. After measuring the Low Loss Header (S8 in the schematic, not connected to the Vitosolic) and the return (S6), I have generally seen a 30 degrees F (about 16 degrees C) differential during operation. Based on this, I have set the S5/S6 differential to turn on the P6 pump to start a 16C, and turn off at 12C.
I will be monitoring the effectiveness of the new settings and posting the results in a week.
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