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This page gives the details on the performance of Kevin's $1K solar water heating system. Plots and comments on performance are provided for each month from May through October of 2009.
Monthly Performance Plots
Performance for May 21 through June 19 of 2009.
The system is achieving a somewhat lower solar fraction than my system -- we think that this is due to the following:
The collector area per gallon of hot water demand is lower than my system. Kevin's family hot water use is about 57 gallons per day and his collector area is 45 sqft of collector area. This compares to our roughly 24 gallons per day and an effective 40 sqft of collector.
The ground water temperature in Kevin's area is very low -- about 43F, so there is more heating to do.
In order to get better summer performance, Kevin has changed the tilt to a more horizontal angle. The performance graph shows the before and after, and the tilt change definitely improves performance.
Some additional observations from Kevin on performance:
* tank temp gain on sunny days is 8 to 13 C
* Cloudy days don't gain much if anything, especially with hot
water demand at the same time (May 31 is a good example).
* Tank temp during periods of no hot water use is stable,
indicating minimal heat losses from the tank. See night of May
22/23, where the only drop was in the morning after a shower. I
added my insulation scraps to the sides and top of the tank
today for even more insulation, so there is a minimum of 3" of foam.
* Our family uses a lot of hot water! Tank temp drops fast with
hot water use. I was disappointed with this at first, but this
is exactly what I want - ready exchange of heat from the tank
into the water flowing through. Incoming water is at 6C, so the
exchanger is transferring a lot of heat during those 12 minute
showers that I timed.
* The stagnation test yesterday at 12:30 PM on a sunny day had a
peak temp of 76C (I saw 81C on the Steca between the 5 minute
datalogging readings).
Overall, I am happy with my system. I realized beforehand that my hot water demand would be higher than yours, but hoped the system would do better. But still, I am getting a solar fraction of:
Incoming water temp 6C
Hot water tank set at 40C
Temp rise needed: 34C
Ave tank temp these days 35C
Solar temp rise = 35 - 6 = 29C
Solar fraction = 29/34 = 85%
Kevin sent in the performance update for the month of July
From Kevin:
As promised, here is July data. The family was away for a few weeks early in the month, so I thought this would get a good test of the performance with low demand. Unfortunately, it coincided with a period of cool, cloudy weather, so my hopes of breaking the 50 C barrier weren't realized. Top tank temp was 48C. The last 2 weeks of the month were mostly hot and sunny. The tank temps average about 40C, so this is hot enough that my hot water heater hasn't come on at all since ~July 14th.
This looks better to me, so it looks like the increased tilt helped some.
Kevin sent in the performance update for the month of August.
Here is Kevin's note on the August performance:
The notable part of this month was a 7 day period when we were on vacation. This is a good illustration of what may be the maximum I can expect from the current system. The tank temp got to 53C while we were gone, in a period of sunny weather. The tank temps declined in the last few cloudy days of our absence, showing heat loss from the tank. While we were home, the tank temps were mostly between 30 and 40C, but dipped as low as 20C.This month's performance led me to start work on an additional collector panel, which will increase the collector area by ~50%. That, and some tree removal now that the sun is lower and the collectors are getting partial shade, should improve things.The data gaps were caused by low battery voltage, running the datalogger using AA cells. I have since switched to a wallwart power supply.I decided to replace our showerhead. The old one wasn't bad, at 2 USGPM, but we bought a new Waterpik multi-setting one, and I especially like the pause feature. Flows from the new one are 1.4 GPM in normal mode, 1.6 GPM in massage mode, and 0.6 GPM in pause mode. Everyone is happy with the new one. Now it's a matter of training the household to use the pause setting when we can.
Performance plot for September 2009.
Some comments on September:
Kevin
Performance plot for October of 2009. Includes effect of an added 3 by 8 ft collector on the 11th.
I commissioned my additional panel on October 11th. It's a 3' X 8' one that is very similar to my existing ones. The main changes are:
Luckily I had a blue sky day for the first day of operation, although it was unseasonably cold in early October. This was the first day the system has started, run, and stopped in below freezing conditions, and I am happy to report that there were no problems. Starting temp was -7C, getting up to -1C. I gained 11C in the tank in the 4 hours of operation until the trees in my yard shaded the collectors, which bodes well for performance. A rise of 11C would be good performance for running all day with the original collectors. I continue to be amazed at the power of the sun, even in the cool half of the year - when it was -5C out, the collector temp was +45C, giving a 50C difference!
October was not a very sunny month at all. A pre- and post-expansion comparison can be seen for October 5th performance (8 C tank temp rise) and after Oct. 11th (10 to 12C rise). There were also some stormy days that were completely flat, with no collector temp rise over the outside temp.
I am seeing that the new panel runs 2 to 4C higher in temp than the old ones, and I am thinking that this is because of the insulation I put on the sides, as well as maybe the tighter construction with the foam wiggle strips. If the new panel runs hotter before the pump turns on, this is a good thing, indicating better heat retention, but if it runs hotter when the pump is running, it may mean that the panel is less efficient at transferring heat to the tank. So I decided to do a stagnation test to check this out.
The new collector was running 3C hotter when I turned the pump off for the test, and the new one climbed to 7C hotter and stayed there. The outside air temp was +4C during the test, and the collector temps went from 44C to over 80C, which covers the temperature range that they run at when the pumps are running. The test results give me confidence that the extra insulation is effective and should result in more heat available for the circulating water to collect.
Kevin
Gary November 14, 2009