If 2003 was the year when GM killed the electric car, then 2010 is shaping up to be the year when it is resurrected. Nissan is currently firming up plans to sell the Leaf by year's end. GM is on track to release the Volt (not an all electric but close). Tesla has had their Roadster out for a couple years now, and recently I actually spotted one on 237 while driving to work in the morning. Then there are the smaller players, like the Fisker Karma, a plug-in hybrid like the Volt but more expensive, and the Chinese manufacturer BYD that is backed by Warren Buffet. Is the electric car now about to go mainstream and solve our problems with Mideast oil, carbon generation, and pollution?
After seeing the documentary film "Who Killed the Electric Car?" in 2006, I decided to look into what it would take to get an electric car. At that time, there were exactly zero commercially available electric cars, not even at the $109,000 price of the Tesla. So the only alternative was to convert an existing ICE powered vehicle to electric. I spent about two years researching what that would take.
My first stop was Electroautomotive, a company in nearby Felton that has been doing conversions and offering conversion kits since the energy crisis of the '70's. I attended a one day workshop on conversions held by Electroautomotive in Silicon Valley. I found out that the technology for hobbist conversions basically had also changed little since the 1970's. They were recommending a 80 volt DC system with flooded lead acid batteries. My 2002 Prius has a 274 volt NiMH battery pack and AC traction system. The range for one of their conversions varied depending on the weight of the coverted vehicle. For maximum range, they were recommeding using a 10 year old Geo Metro, since the weight is under 1500 lbs, or a light weight pickup truck, also preferably 10 years old, and then filling the back with batteries. Cost would probably have run around $8K-$12K depending on batteries and components, and, of course, I would have had to do the conversion work myself, no small problem since I am by and large hopeless with tools more complicated than a screwdriver.
The problem with converting a 10 year old car to electric is ... you end up with a 10 year old car (dents, cracked plastic from aging, no airbags or antilock breaks, stained upholstery) that goes maybe 100 miles if you are lucky. I looked into converting a new car, but there were only three cars on the market that were at or under 1500 lbs - the Toyota Yaris, the Honda Fit, and the Chevy Aveo. These are tiny cars with very little room for batteries. Given the minimum amount of room, the range would probably have been less than 100 miles.
Then there are the batteries. Lead acid batteries only last around 3 years when used as traction batteries in electric cars. Even though they are cheap (maybe around $800 for a full set) and they are up to 99% recycled, they are still heavy and having to swap out the batteries every 3 years is a major inconvenience. Flooded batteries were recommended for automotive traction applications because they have the best power output, but they are notoriously fickle and require checking periodically to be sure the plates aren't drying out. Sealed batteries require less maintenance but they don't provide enough range.
While I might have been able to live with having an expensive 10 year old car, the range was the show stopper. I wanted at least 120 miles so I could comfortably drive up to San Francisco and back without recharging (not of course that I do such a drive often, but I at least wanted to be able to do it in principle). So the next thing I looked into was lithium batteries. In principle, I would have been able to get the range I wanted, but the cost would have been prohibitive, around $20,000 just for the batteries. At the time, there was only one company that was selling prismatic lithium ion batteries appropriately large enough for such applications, Thunder Sky in China. Lithium ion batteries require a different kind of charging system and are much more sensitive to overcharging and extreme draw down than lead acid batteries.
I then turned to the local Electric Autombile Association and attended one of their meetings to find out whether anyone had experience with lithium batteries. The meeting was interesting, the featured speaker described an electric motorcycle for racing in which he attempted to clinch the world land speed record for 2 wheeled vehicles (I think he succeeded in the interim). His strategy was to essentially draw down the lithium batteries so fast that they were essentially ruined after one run, then to swap them out for the next. Not a strategy that would work for my vehicle, however.
After asking around, I got some warnings about Thunder Sky batteries, that the quality was variable. Someone said they had bought a bunch and some had turned out to run down after only a few charge/discharge cycles. Left unsaid, however, was whether the battery chemistry was safe for vehicular applications. I don't know what chemistry Thunder Sky used, but the battery chemistry used for laptop and cell phone batteries is completely inappropriate for vehicular applications without lots of additional engineering. Tesla, for example, spent years designing an explosion control cabinet to contain any of the thousands of laptop battery cells they use in the Roadster from igniting the others should a cell catch on fire. If Thunder Sky used the same chemistry as used in laptop batteries, an electric car with those batteries would have been a dangerous hazard should an accident occur.
I also finally got real about my ability to do the conversion work. Realistically, even if I got a membership at Tech Shop, there was no way I would have the time nor the motiviation to pursue the project to completion. I asked around at the Electric Automobile Association whether anybody knew of a place that would do a conversion. There was a guy there who said he would do one, we took up an email correspondence but it turned up he was really interested in selling electric scooters and the correspondence was just talk. I searched the Internet a bit. The Internet search turned up one guy in LA who had been doing conversions, but he had since stopped. There were some conversions for sale in San Francisco, a Toyota Yaris if I recall correctly, but the range was under 100 miles.
In the spring of 2008, I was just about to give up in despair when A123 Systems announced their L5 modules for turning a 2004-2008 Prius into a plug-in hybrid. And that is the subject for another post.
Wednesday, February 17, 2010
Saturday, February 6, 2010
Recalculating Solar Hot Water Performance
My previous post on the carbon reduction cost performance of my solar hot water system was unduly pessimistic. I now have the December gas bill and it looks as if the reduction is about 10% for a half year of use, or an estimated 20% for a full year, which is what I had originally figured it would be. That considerably improves the carbon reduction cost performance. Here's what the new chart looks like:
As you can see, the per kg. carbon reduction cost for my high end system is really around $27 per kg rather than $67 as in the last post. For the low end thermosyphon system, the performance is even better, around $9 per kg.
Furthermore, the state of California recently announced a subsidy of up to $1500 for solar hot water systems, on top of the 30% federal tax rebate. The last two bars show the per kg carbon reduction cost for the low end thermosyphon system and my high end system taking into account the subsidy. The subsidy still doesn't make a solar hot water system competitive with a gas fired tank hot water heater, but it helps. Figuring that at gas fired tank system costs maybe $1500 installed, it would still take around 15 years of gas savings, assuming the price of gas stays constant, to make up for the difference between the $3300 subsidized, after tax rebate cost of the low end thermosyphon system. The high end system would take longer.
Of course, if you have an electric hot water heater, the savings could be considerably better, since electricity costs more per joule of energy delivered to the water.
Furthermore, the state of California recently announced a subsidy of up to $1500 for solar hot water systems, on top of the 30% federal tax rebate. The last two bars show the per kg carbon reduction cost for the low end thermosyphon system and my high end system taking into account the subsidy. The subsidy still doesn't make a solar hot water system competitive with a gas fired tank hot water heater, but it helps. Figuring that at gas fired tank system costs maybe $1500 installed, it would still take around 15 years of gas savings, assuming the price of gas stays constant, to make up for the difference between the $3300 subsidized, after tax rebate cost of the low end thermosyphon system. The high end system would take longer.
Of course, if you have an electric hot water heater, the savings could be considerably better, since electricity costs more per joule of energy delivered to the water.
Thursday, February 4, 2010
Update on Spark Plugs
You'll recall in this post, I described how the high performance Pulsestar spark plugs from Enerpulse blew out the ignition coil on my 2002 Prius. I sent in the coil and the plugs to Enerpulse and requested they make good on their guarantee that their plugs would not harm your engine by reimbursing me for the cost of the plugs and the repair. To my surprise, I received a very nice letter from Enerpulse apologizing for the damage and a check reimbursing me for the cost of the repairs and the plugs.
It seems that some instances of their older plugs occasionally had a problem with resistance growing over time, and if the resistance becomes high enough, it causes the plug to wear down fast and eventually misfire, which can then cause damage to the coil. This explains the rapid deterioration in mileage and performance I was seeing over the summer, followed by the catastrophic failure.
They also offered a 10% discount on their new G3 version of the Pulstar plugs. These have improved lifetime and better performance. I am tempted, since the torque and pickup on the 2002 Prius is terrible, but after one bad experience with the product I am not sure whether it makes sense to try it again. I still have a set of their original plugs in my 2008 Prius, so far, they seem to be performing fine.
It seems that some instances of their older plugs occasionally had a problem with resistance growing over time, and if the resistance becomes high enough, it causes the plug to wear down fast and eventually misfire, which can then cause damage to the coil. This explains the rapid deterioration in mileage and performance I was seeing over the summer, followed by the catastrophic failure.
They also offered a 10% discount on their new G3 version of the Pulstar plugs. These have improved lifetime and better performance. I am tempted, since the torque and pickup on the 2002 Prius is terrible, but after one bad experience with the product I am not sure whether it makes sense to try it again. I still have a set of their original plugs in my 2008 Prius, so far, they seem to be performing fine.
Wednesday, January 13, 2010
Solar Hot Water Part VII: Retrospective
This post is about "lessons learned" in the process of building our solar hot water system, discussing problems and some speculations about what might help to solve them.
As mentioned in the last post, a minor problem with using the system is that the gas-fired tank tends to cool off when the gas is turned off in the summer. In the long run, we plan to get rid of the gas-fired tank backup and put in a modulating on-demand electric hot water heater. My original plan was to couple the second heat exchanger in the tank with a geothermal heat pump or high efficiency gas boiler, but neither of these options is ideal. Geothermal heat pumps won't put out more than 140F and you need the heat transfer fluid substantially hotter to get good heating when the water flow is heavy, like when you are doing laundry and taking a shower at the same time. A gas boiler wouldn't allow the tank to derive optimal heating from the sun. If the thermostat is set at 120F (recommended for domestic hot water), then the gas boiler will come on when the water drops below that temperature and the solar collector won't come on. Same is true for solar tanks with a backup electric heater coil inside the tank. The solar tank can't preheat the water. An on-demand electric hot water heater should allow the solar tank to heat up as hot as the sun can get it, and just add enough energy to bring the domestic hot water up to 120F in the winter. In addition, we can add some solar PV to our roof to offset the electricity used to run the on-demand heater. That should make our domestic hot water supply completely carbon neutral.
Aside from the aformentioned problem with an installer that did not know what he was doing, the primary problem with the system, though, is price. It is simply very expensive for the amount of carbon reduction achieved. Below is a graph comparing the cost per kilogram of eliminated carbon to two other alternatives: the same system but with a glass-lined tank instead of a stainless steel tank, and a cheaper thermosyphon system which a friend who lives in the same town had installed:
I used the estimated figure on gas eliminated from the Performance blog and included the federal tax rebate of 30% off installed system cost. I did not include the cost of the closet modifications for the thermosyphon system, because the storage tank is integrated into the collector so no change would have been needed in the closet. Note that the estimate here on cost per kilo carbon removed for our solar hot water system is too low, it does not include the winter when the solar thermal collector is contributing little.
Our system has a cost per kilo approximately that of the new refrigerator and I think it is for the same reason. I exchanged email with a friend who was surprised by the high price per kilo carbon reduction achieved for the refrigerator (which you can also see here). Normally replacing a fridge that is 10 or more years old by a new one is a fairly cost effective. I'm not sure how old the fridge was since it was there when we moved into the house, but on reflection, I think I know what the problem was. The new fridge was exactly the same model as the old, except updated with energy saving features. In our kitchen, the fridge is built-in, so we either had to get the same model or spend money on getting the space modified to take a different model. But the original fridge and now the new one are both high end models, and therefore very expensive. It is a Lexus fridge, even though, we would have been happy with something a little less high end. Similarly, the solar hot water system is a high end system, and the cost reflects it.
That explains why the carbon reduction cost for our system is about three times as much as for the thermosyphon system, but it doesn't explain why even the thermosyphon system is expensive, at almost $20 per kilo carbon removed. At that price, even with the subsidy, it is not an affordable option for most homeowners. A high end gas-fired tank costs around $700 new, and a low end gas on-demand hot water heater costs about the same. An on-demand gas hot water heater can also result in substantial carbon reduction, though it won't be possible to completely eliminate carbon of course (it would for an electric on-demand heater though, by offsetting with solar PV). The thermosyphon system is around 10x the cost for an on-demand gas system, and our indirect solar system is more than 20x. Prior the WWII, many houses in California had solar hot water systems, and today, there are cities in China where solar provides hot water for over 90% of the homes. Why is solar hot water so expensive, the energy from the sun is free, it should be cheaper in the long run for a solar hot water system?
Well, one problem is that natural gas (or, as I prefer to call it fossil gas) is just too cheap and likely to stay that way. Fossil gas releases only half the amount of carbon per therm of energy generated from coal, and something like a third less than oil so in some quarters it rates as a "clean" fuel. In addition, recent discoveries of gas deposits in shale across wide swaths of the Northeast and Mid Atlantic states promise that fossil gas will stay cheap for some time to come. On the one hand, that's good news because if fossil gas becomes cheaper than coal, switching electricity generation to fossil gas from coal in states like Illinois where most of the electricity is generated by coal could result in substantial greenhouse gas reductions. On the other hand, unlike solar and wind, fossil gas is still putting fossil carbon into the atmosphere. So to the extent that cheap fossil gas prolongs our dependence on energy technologies that dump fossil carbon into the atmosphere, it is doing us a disservice.
The other problem is that the technology itself is actually quite expensive and difficult to integrate into an existing building. It requires extensive plumbing on your roof and a backup system. Integrating with the most common type of backup system requires fussy yearly action to turn the pilot off and on, and results in suboptimal performance when the gas is off in the summer. Adding a backup system that works better costs more money. Compare this with grid tie solar PV, the kind most homeowners get these days, where the backup comes from the grid and so there is really no periodic maintenance needed or any kind of additional hardware. While solar PV requires structures on the roof (and, indeed, can result in roof leaks if not properly installed) and high voltage DC lines which are not trivial to get right, there is not as much dependence on the exact configuration of the existing structure except for proper solar exposure. A solar hot water system is more like the traditional off grid solar PV system, where the homeowner must install a large bank of batteries to store electricity for times when the sun isn't shining. Non-grid tie systems usually cost double or more what grid tie systems do, and the batteries also require monitoring and occasional replacement.
Since technology is what Silicon Valley is all about, you would think a budding entrepreneur would be studying this problem for the next great startup, but, as far as I can tell, there are no startups looking at how to reduce the cost on solar hot water. The economics seem pretty simple to me: get the cost down around where the payback time (sorry, unfortunately that's what most people look at) is around 3-5 years. Say, maybe the installed cost is 2x an on-demand gas heater, and you don't need a half inch gas main installed for it. Anybody up for the challenge?
As mentioned in the last post, a minor problem with using the system is that the gas-fired tank tends to cool off when the gas is turned off in the summer. In the long run, we plan to get rid of the gas-fired tank backup and put in a modulating on-demand electric hot water heater. My original plan was to couple the second heat exchanger in the tank with a geothermal heat pump or high efficiency gas boiler, but neither of these options is ideal. Geothermal heat pumps won't put out more than 140F and you need the heat transfer fluid substantially hotter to get good heating when the water flow is heavy, like when you are doing laundry and taking a shower at the same time. A gas boiler wouldn't allow the tank to derive optimal heating from the sun. If the thermostat is set at 120F (recommended for domestic hot water), then the gas boiler will come on when the water drops below that temperature and the solar collector won't come on. Same is true for solar tanks with a backup electric heater coil inside the tank. The solar tank can't preheat the water. An on-demand electric hot water heater should allow the solar tank to heat up as hot as the sun can get it, and just add enough energy to bring the domestic hot water up to 120F in the winter. In addition, we can add some solar PV to our roof to offset the electricity used to run the on-demand heater. That should make our domestic hot water supply completely carbon neutral.
Aside from the aformentioned problem with an installer that did not know what he was doing, the primary problem with the system, though, is price. It is simply very expensive for the amount of carbon reduction achieved. Below is a graph comparing the cost per kilogram of eliminated carbon to two other alternatives: the same system but with a glass-lined tank instead of a stainless steel tank, and a cheaper thermosyphon system which a friend who lives in the same town had installed:
Our system has a cost per kilo approximately that of the new refrigerator and I think it is for the same reason. I exchanged email with a friend who was surprised by the high price per kilo carbon reduction achieved for the refrigerator (which you can also see here). Normally replacing a fridge that is 10 or more years old by a new one is a fairly cost effective. I'm not sure how old the fridge was since it was there when we moved into the house, but on reflection, I think I know what the problem was. The new fridge was exactly the same model as the old, except updated with energy saving features. In our kitchen, the fridge is built-in, so we either had to get the same model or spend money on getting the space modified to take a different model. But the original fridge and now the new one are both high end models, and therefore very expensive. It is a Lexus fridge, even though, we would have been happy with something a little less high end. Similarly, the solar hot water system is a high end system, and the cost reflects it.
That explains why the carbon reduction cost for our system is about three times as much as for the thermosyphon system, but it doesn't explain why even the thermosyphon system is expensive, at almost $20 per kilo carbon removed. At that price, even with the subsidy, it is not an affordable option for most homeowners. A high end gas-fired tank costs around $700 new, and a low end gas on-demand hot water heater costs about the same. An on-demand gas hot water heater can also result in substantial carbon reduction, though it won't be possible to completely eliminate carbon of course (it would for an electric on-demand heater though, by offsetting with solar PV). The thermosyphon system is around 10x the cost for an on-demand gas system, and our indirect solar system is more than 20x. Prior the WWII, many houses in California had solar hot water systems, and today, there are cities in China where solar provides hot water for over 90% of the homes. Why is solar hot water so expensive, the energy from the sun is free, it should be cheaper in the long run for a solar hot water system?
Well, one problem is that natural gas (or, as I prefer to call it fossil gas) is just too cheap and likely to stay that way. Fossil gas releases only half the amount of carbon per therm of energy generated from coal, and something like a third less than oil so in some quarters it rates as a "clean" fuel. In addition, recent discoveries of gas deposits in shale across wide swaths of the Northeast and Mid Atlantic states promise that fossil gas will stay cheap for some time to come. On the one hand, that's good news because if fossil gas becomes cheaper than coal, switching electricity generation to fossil gas from coal in states like Illinois where most of the electricity is generated by coal could result in substantial greenhouse gas reductions. On the other hand, unlike solar and wind, fossil gas is still putting fossil carbon into the atmosphere. So to the extent that cheap fossil gas prolongs our dependence on energy technologies that dump fossil carbon into the atmosphere, it is doing us a disservice.
The other problem is that the technology itself is actually quite expensive and difficult to integrate into an existing building. It requires extensive plumbing on your roof and a backup system. Integrating with the most common type of backup system requires fussy yearly action to turn the pilot off and on, and results in suboptimal performance when the gas is off in the summer. Adding a backup system that works better costs more money. Compare this with grid tie solar PV, the kind most homeowners get these days, where the backup comes from the grid and so there is really no periodic maintenance needed or any kind of additional hardware. While solar PV requires structures on the roof (and, indeed, can result in roof leaks if not properly installed) and high voltage DC lines which are not trivial to get right, there is not as much dependence on the exact configuration of the existing structure except for proper solar exposure. A solar hot water system is more like the traditional off grid solar PV system, where the homeowner must install a large bank of batteries to store electricity for times when the sun isn't shining. Non-grid tie systems usually cost double or more what grid tie systems do, and the batteries also require monitoring and occasional replacement.
Since technology is what Silicon Valley is all about, you would think a budding entrepreneur would be studying this problem for the next great startup, but, as far as I can tell, there are no startups looking at how to reduce the cost on solar hot water. The economics seem pretty simple to me: get the cost down around where the payback time (sorry, unfortunately that's what most people look at) is around 3-5 years. Say, maybe the installed cost is 2x an on-demand gas heater, and you don't need a half inch gas main installed for it. Anybody up for the challenge?
Saturday, January 9, 2010
Solar Hot Water Part VI: Performance
Last summer after the system came up, I turned off the gas hot water heater. The gas hot water heater has a pilot and pilots are just about the most energy wasting thing around. I was seeing temperatures on the solar tank of around 150F-160F in July, and it never rains in summer in California (like the old song says) so I figured we were good without the backup.
The results were mixed. Most of the time, we had plenty of hot water with the temperature being fine. With the shower on the top setting, it was not as hot as with the gas heater on (when you really need to turn the setting down to make it tolerable), but it was adequate for a nice hot shower after a long bike ride. Sometimes, though, the water was just lukewarm. This seemed to happen most often when we didn't use hot water for a number of days (like we showered at the gym) or when we went away for vacation. A couple times we had cloudy weather and the tank temperature dropped to 130F, which is I would have expected, but it didn't affect the domestic hot water temperature unless we didn't use much hot water.
The problem is that the gas-fired tank cools down if the hot water is not used for a couple days. Since there is a lot of water in the gas-fired tank, it takes a while for the hot water in the solar tank to draw through, even though the solar water is really hot. By and large, this wasn't much of a problem; it being summer, an occasional lukewarm shower wasn't an issue. I kept the gas-fired tank off until the end of October then relit it. At that point, the temperature in the solar tank was getting down below 130F.
Below you can see a comparison of our gas usage for July through November in 2008 and 2009:
As you can see, the usage was reduced from July through October, but it shot up in November. That's because we had a cold snap in the beginning of December (the November bill includes a couple weeks into December) this year, and November was generally much colder than last year. One of the difficulties of using year over year comparisons of energy usage is this kind of variability due to changes in the weather, etc. In fact, the increase in November completely overwhelmed the savings for July through October. July through November 2008 was 98 therms while the same period this year was 97 therms, just one therm less, or around 1%. If you look at the period from July through October, not counting the time when space heating was generating most of our gas demand, the reduction in gas usage is around 71%.
From last summer's data, I now know we use about 1 therm a month for cooking. In 2004, I discovered that our forced air furnace had a pilot light (yeech!) and I started turning it off in summer. I can therefore use the summer gas use from 2004 through 2009 prior to installation of the solar hot water system to estimate how much gas we used for hot water heating. That gas will be completely eliminated in the summer 6 months (essentially April through September) with solar hot water. For the other 6 months, estimating usage is more difficult, because the solar acts as a preheater for the gas heater. So the amount of gas eliminated won't be the same as for the summer; on the other hand, it also won't be zero. To be conservative, we can say that it is, in fact, zero; that is, that the gas tank is responsible for all the hot water heating.
The average gas use in the summer months just for hot water heating is 6.32 therms per month. The average annual monthly use for 2004-2008 is 36.5 therms per month. Figuring 6 months of 6.32 therms reduction and 6 months of 0 therm reduction, the percent savings comes out to 8.65%. So, say, around 10% reduction since we were on the conservative side about the winter use (yes, I know this is a fudge factor but it is the best I can do with the data I have). Anyway, I think I will need some more data for at least another year before I can really say what the reduction is like. There are also some ways to collect data that require measuring the hot water heater output, which I may decide to collect in the end.
The other interesting issue is the effect of the various insulation treatments I've tried. Below is a graph showing the temperature in the morning and evening in July before I installed the radiant barrier insulation:
I didn't use any sophisticated monitoring device for recording these temperatures, I just wrote them down on paper. That's why there are so many holes in the recording, some days I forgot, others we were on vacation. In general the temperature is running around 160F
Below is a chart of the morning and evening temperatures with the tank completely covered in radiant barrier insulation:
The gap between morning and evening is slightly smaller, and the average temperature of the tank drops over the month. The dates here are getting into fall, when the days are shorter and there is less sun on the collector.
Below is a graph of the morning and evening temperatures after putting on the R-13 fiberglass batt blanket:
The temperatures now are a lot lower because the time period is into December when the sun is at the lowest point, but the gap between the morning and evening temperature has narrowed considerably.
Insulation was highly effective in reducing heat loss from the tank. The temperature drop in degrees F per hour was 0.68 for no insulation - noticeably *above* what Superstor advertises. For radiant barrier only, the drop was 0.54, average of two sets of measurements, one shown above and one taken just before the batt was installed in December. For radiant barrier plus batt, the drop was 0.23. The temperature outside the tank had little impact, the measurements in September and December for the radiant barrier insulation were close (0.57 in September and 0.52 in December). This might possibly be due to the fact that the tank closet itself has 6" of closed cell foam on the top and around 3-6" on the walls, keeping the tank enclosure toasty.
In fact, the insulation was so effective in cutting heat loss from the tank that I am now a bit worried it might overheat in the summer and cook the glycol. We shall see. I've signed up for a maintenance contract to have them come and check the glycol once a year to make sure it isn't acidic, at least for a couple years until I feel comfortable with the system. And, as a practical matter, the Schueco system is specifically designed to purge if the collector reaches stagnation temperature, to avoid cooking the glycol. So I think the system should be OK, and the extra insulation will sure help in the winter. Why can't Superstor put that extra insulation on the tank in the first place? It can't really be a question of cost. And I wonder, since it has about cut the heat loss in half, whether it would have allowed me to get by with one instead of two Schueco panels? Something for a pleasant evening of calculation in the near future.
The results were mixed. Most of the time, we had plenty of hot water with the temperature being fine. With the shower on the top setting, it was not as hot as with the gas heater on (when you really need to turn the setting down to make it tolerable), but it was adequate for a nice hot shower after a long bike ride. Sometimes, though, the water was just lukewarm. This seemed to happen most often when we didn't use hot water for a number of days (like we showered at the gym) or when we went away for vacation. A couple times we had cloudy weather and the tank temperature dropped to 130F, which is I would have expected, but it didn't affect the domestic hot water temperature unless we didn't use much hot water.
The problem is that the gas-fired tank cools down if the hot water is not used for a couple days. Since there is a lot of water in the gas-fired tank, it takes a while for the hot water in the solar tank to draw through, even though the solar water is really hot. By and large, this wasn't much of a problem; it being summer, an occasional lukewarm shower wasn't an issue. I kept the gas-fired tank off until the end of October then relit it. At that point, the temperature in the solar tank was getting down below 130F.
Below you can see a comparison of our gas usage for July through November in 2008 and 2009:
From last summer's data, I now know we use about 1 therm a month for cooking. In 2004, I discovered that our forced air furnace had a pilot light (yeech!) and I started turning it off in summer. I can therefore use the summer gas use from 2004 through 2009 prior to installation of the solar hot water system to estimate how much gas we used for hot water heating. That gas will be completely eliminated in the summer 6 months (essentially April through September) with solar hot water. For the other 6 months, estimating usage is more difficult, because the solar acts as a preheater for the gas heater. So the amount of gas eliminated won't be the same as for the summer; on the other hand, it also won't be zero. To be conservative, we can say that it is, in fact, zero; that is, that the gas tank is responsible for all the hot water heating.
The average gas use in the summer months just for hot water heating is 6.32 therms per month. The average annual monthly use for 2004-2008 is 36.5 therms per month. Figuring 6 months of 6.32 therms reduction and 6 months of 0 therm reduction, the percent savings comes out to 8.65%. So, say, around 10% reduction since we were on the conservative side about the winter use (yes, I know this is a fudge factor but it is the best I can do with the data I have). Anyway, I think I will need some more data for at least another year before I can really say what the reduction is like. There are also some ways to collect data that require measuring the hot water heater output, which I may decide to collect in the end.
The other interesting issue is the effect of the various insulation treatments I've tried. Below is a graph showing the temperature in the morning and evening in July before I installed the radiant barrier insulation:
Below is a chart of the morning and evening temperatures with the tank completely covered in radiant barrier insulation:
The gap between morning and evening is slightly smaller, and the average temperature of the tank drops over the month. The dates here are getting into fall, when the days are shorter and there is less sun on the collector.
Below is a graph of the morning and evening temperatures after putting on the R-13 fiberglass batt blanket:
Insulation was highly effective in reducing heat loss from the tank. The temperature drop in degrees F per hour was 0.68 for no insulation - noticeably *above* what Superstor advertises. For radiant barrier only, the drop was 0.54, average of two sets of measurements, one shown above and one taken just before the batt was installed in December. For radiant barrier plus batt, the drop was 0.23. The temperature outside the tank had little impact, the measurements in September and December for the radiant barrier insulation were close (0.57 in September and 0.52 in December). This might possibly be due to the fact that the tank closet itself has 6" of closed cell foam on the top and around 3-6" on the walls, keeping the tank enclosure toasty.
In fact, the insulation was so effective in cutting heat loss from the tank that I am now a bit worried it might overheat in the summer and cook the glycol. We shall see. I've signed up for a maintenance contract to have them come and check the glycol once a year to make sure it isn't acidic, at least for a couple years until I feel comfortable with the system. And, as a practical matter, the Schueco system is specifically designed to purge if the collector reaches stagnation temperature, to avoid cooking the glycol. So I think the system should be OK, and the extra insulation will sure help in the winter. Why can't Superstor put that extra insulation on the tank in the first place? It can't really be a question of cost. And I wonder, since it has about cut the heat loss in half, whether it would have allowed me to get by with one instead of two Schueco panels? Something for a pleasant evening of calculation in the near future.
Wednesday, December 30, 2009
Solar Hot Water Part V: Insulation
A much underappreciated part of making a solar hot water system efficient is properly insulating it to reduce parasitic losses. There are two aspects to this:
The contractor did a fine job on the pipes carrying the heat transfer fluid outside leading from the solar collector to the inside of the house. This is a particularly crucial area, because if the air temperature is low during the day the losses in this section can be really high. But for the pipes on the inside, if you take a look at my previous post on installation (which you'll find here), you can see that the contractor sort of insulated the pipes on the inside. The black rubber you see around the pipes in some of the pictures is pipe insulation. The contractor did an OK job with most of the pipes except around the gas fired hot water heater. The pressure relief valve pipe and the hot water pipe leading into the house were not insulated and radiating heat. Also, at places where the pipes had a bend, the black rubber pipe insulation stopped and left small areas of copper exposed that could radiate heat. Getting pipe insulation right takes a lot of time and effort, something most contractors don't want to do (otherwise they would have to charge you for it).
So I spent some time doing the pipe insulation myself. I installed the black rubber insulation around all the pipes which the contractor forgot, and sprayed some high temperature foam insulation around the pipe corners, and around the connections between the pumping station and the feed-in lines. Here's a picture of how the pipes look in the ground floor gas-fired hot water heater closet:
The blobs of pink matter you see hanging down from the pipes where a corner is are the high temperature foam. Note that this is not the standard polyurethane foam that you can get for insulation at the hardware store, this is foam which is rated for installing, for example, between floors in apartment buildings to help retard the progress of a fire. It won't stop a fire, since it is organic and will ultimately burn, but it is rated to a much higher temperature than the standard, white polyurethane foam that's used for sealing around doors and windows. It's available at Home Depot, and the important distinguishing factor is, as you can see, that it is pink. I used high temperature foam because the temperatures around the pump station (which you can't see here) and around the furnace flue which leads up through the closet can get pretty high, maybe around 180F, which might cause the normal foam to get soft, if not melt. Finally, the white blobs you see are tags indicating what each of the pipes do (sorry, the picture is a little out of focus because the shutter was open for a long time and my camera doesn't have image stabilization).
The second aspect is the tank. The Superstor comes with 1.5" of closed cell foam insulation, and they claim that it loses around 0.5F per hour (as we will see in a later post, this is optimistic at best). To my mind, that is simply not enough insulation. My Hot Springs hot tub has around 6" of closed cell foam, and it loses maybe 2F overnight if I turn the temperature down to 80F after having it up around 102F, and that is outside where the ambient temperature in winter is a lot lower than inside the house. I think the reason they don't add more insulation to the Superstor is that it would make the tank's diameter bigger, and, of course it would make the tank even more expensive (the Superstor is pretty expensive as is).
My first plan was to spray the tank with closed cell foam before the contractor installed it, but a quick check with the city building inspector indicated that they would probably not approve the project if the tank was coated with closed cell foam. I then came up with the idea to take radiant barrier insulation made from aluminum foil and plastic bubble wrap and make a form the size of the tank, then spray it with closed cell foam to make a kind of jacket. So I tried that (sorry, no pictures) but the result was too rigid once it had dried and I couldn't get it into the narrow space between the tank and the wall.
Since I had some radiant barrier left, I decided to wrap both tanks in radiant barrier insulation as a start. I did this work in summer right after they installed the system, and the solar tank was radiating heat strongly, a bad sign. I did the wrapping in two phases, first the left side then the more complicated right side around all the connections. Here's a picture of what the Superstor looks like when it is completely wrapped in radiant barrier insulation:
One issue was what kind of tape to use. Standard duct tape probably won't work because the glue will melt from the high temperatures in summer. I first tried an aluminum tape from 3M that is specifically for furnace flues and other high temperature applications. It wasn't ideal, it was stiff and didn't adhere unless you really pressed it, also, it had sharp edges, but it sort of worked, although some places that weren't pressed hard enough came loose. I then found a similar tape from Nashua which sticks a lot better and doesn't require strong pressing to bind.
After I finished the radiant barrier job, I discovered that a new line of high temperature duct tape had been introduced on the market. I used some that on the R-13 fiberglass blanket which I wrapped around both tanks on top of the radiant barrier. You can see that on the bottom of the picture above of the gas fired tank. Here's what the Superstor looks like nicely clothed in its new fiberglass blanket:
The gray stripes around the tank are where I taped together the R-13 batts.
One question that might come up is: why not used one of the premade vinyl insulation jackets that are commercially available? I thought about this, but there are a number of problems. First, I couldn't get a jacket big enough for the Superstor. It is 60" tall, much larger than a standard 40 gallon gas or electric domestic hot water heater. Second, they only provide something like R-7 of insulation. I now have R-13 with maybe R-7 or so of radiant barrier. Finally, vinyl is not a good material to have around the house, especially around hot areas where chemicals can outgas. I looked around for a jacket that didn't have a vinyl skin but could not find any.
In the next post, I'll talk a bit about how the system is performing, and provide some data about how well my insulating treatments have worked.
- Properly insulating the pipes carrying the hot water and the heat transfer fluid from the solar collector.
- Ensuring that the solar tank and any backup storage (the gas fired tank in my case) are sufficiently insulated to reduce loss during water storage.
The contractor did a fine job on the pipes carrying the heat transfer fluid outside leading from the solar collector to the inside of the house. This is a particularly crucial area, because if the air temperature is low during the day the losses in this section can be really high. But for the pipes on the inside, if you take a look at my previous post on installation (which you'll find here), you can see that the contractor sort of insulated the pipes on the inside. The black rubber you see around the pipes in some of the pictures is pipe insulation. The contractor did an OK job with most of the pipes except around the gas fired hot water heater. The pressure relief valve pipe and the hot water pipe leading into the house were not insulated and radiating heat. Also, at places where the pipes had a bend, the black rubber pipe insulation stopped and left small areas of copper exposed that could radiate heat. Getting pipe insulation right takes a lot of time and effort, something most contractors don't want to do (otherwise they would have to charge you for it).
So I spent some time doing the pipe insulation myself. I installed the black rubber insulation around all the pipes which the contractor forgot, and sprayed some high temperature foam insulation around the pipe corners, and around the connections between the pumping station and the feed-in lines. Here's a picture of how the pipes look in the ground floor gas-fired hot water heater closet:
The blobs of pink matter you see hanging down from the pipes where a corner is are the high temperature foam. Note that this is not the standard polyurethane foam that you can get for insulation at the hardware store, this is foam which is rated for installing, for example, between floors in apartment buildings to help retard the progress of a fire. It won't stop a fire, since it is organic and will ultimately burn, but it is rated to a much higher temperature than the standard, white polyurethane foam that's used for sealing around doors and windows. It's available at Home Depot, and the important distinguishing factor is, as you can see, that it is pink. I used high temperature foam because the temperatures around the pump station (which you can't see here) and around the furnace flue which leads up through the closet can get pretty high, maybe around 180F, which might cause the normal foam to get soft, if not melt. Finally, the white blobs you see are tags indicating what each of the pipes do (sorry, the picture is a little out of focus because the shutter was open for a long time and my camera doesn't have image stabilization).
The second aspect is the tank. The Superstor comes with 1.5" of closed cell foam insulation, and they claim that it loses around 0.5F per hour (as we will see in a later post, this is optimistic at best). To my mind, that is simply not enough insulation. My Hot Springs hot tub has around 6" of closed cell foam, and it loses maybe 2F overnight if I turn the temperature down to 80F after having it up around 102F, and that is outside where the ambient temperature in winter is a lot lower than inside the house. I think the reason they don't add more insulation to the Superstor is that it would make the tank's diameter bigger, and, of course it would make the tank even more expensive (the Superstor is pretty expensive as is).
My first plan was to spray the tank with closed cell foam before the contractor installed it, but a quick check with the city building inspector indicated that they would probably not approve the project if the tank was coated with closed cell foam. I then came up with the idea to take radiant barrier insulation made from aluminum foil and plastic bubble wrap and make a form the size of the tank, then spray it with closed cell foam to make a kind of jacket. So I tried that (sorry, no pictures) but the result was too rigid once it had dried and I couldn't get it into the narrow space between the tank and the wall.
Since I had some radiant barrier left, I decided to wrap both tanks in radiant barrier insulation as a start. I did this work in summer right after they installed the system, and the solar tank was radiating heat strongly, a bad sign. I did the wrapping in two phases, first the left side then the more complicated right side around all the connections. Here's a picture of what the Superstor looks like when it is completely wrapped in radiant barrier insulation:
One issue was what kind of tape to use. Standard duct tape probably won't work because the glue will melt from the high temperatures in summer. I first tried an aluminum tape from 3M that is specifically for furnace flues and other high temperature applications. It wasn't ideal, it was stiff and didn't adhere unless you really pressed it, also, it had sharp edges, but it sort of worked, although some places that weren't pressed hard enough came loose. I then found a similar tape from Nashua which sticks a lot better and doesn't require strong pressing to bind.
After I finished the radiant barrier job, I discovered that a new line of high temperature duct tape had been introduced on the market. I used some that on the R-13 fiberglass blanket which I wrapped around both tanks on top of the radiant barrier. You can see that on the bottom of the picture above of the gas fired tank. Here's what the Superstor looks like nicely clothed in its new fiberglass blanket:
One question that might come up is: why not used one of the premade vinyl insulation jackets that are commercially available? I thought about this, but there are a number of problems. First, I couldn't get a jacket big enough for the Superstor. It is 60" tall, much larger than a standard 40 gallon gas or electric domestic hot water heater. Second, they only provide something like R-7 of insulation. I now have R-13 with maybe R-7 or so of radiant barrier. Finally, vinyl is not a good material to have around the house, especially around hot areas where chemicals can outgas. I looked around for a jacket that didn't have a vinyl skin but could not find any.
In the next post, I'll talk a bit about how the system is performing, and provide some data about how well my insulating treatments have worked.
Wednesday, December 23, 2009
Solar Hot Water IV: The Installation Experience
Chris and Justin from Sunwater Solar came by and had a look at our house. We decided to put the collectors on the east side since the west side is occupied by the solar PV. The east side gets sun primarily in the morning, but since the solar PV is higher value in the afternoon (about 3x the tariff other times), having it on the west side is a better deal. So it made sense to keep the remaining space on the west side, about enough for another 3 PV panels, for solar PV if we decide to add some in the future.
Then came the question of where to put the tank. We initially considered putting it in a small house next to the sauna, or maybe next to the fireplace pod that sticks out from the house, but ultimately we decided to repurpose the cold air return for the forced air heating. We had the forced air heating taken out a couple years ago and put in hydronic floor heating, so we didn't need the space any more. It is on the second floor in the hallway. The space consisted of a plenium with a large grate on the front, which led into the downstairs furnace room. When we had the hydronic furnace installed in the furnace room, the plenium was blocked off from downstairs. As we discovered when we opened up the space and removed the plenium, the flue from the furnace and the gas fired hot water heater in the downstairs mechanical room ran up the middle. We had a bit of work to do on the space.
Point to note when planning a solar hot water system: be sure to include enough time and money for upgrading the space where you plan to put the tank and the pump station if you are not going to use your existing tank.
Sunwater doesn't do the kind of drywall and carpentry work needed to modify the space, so we asked a friend of ours who is a contractor, Tim Hmelar (check out his new business, Purple Coupon) to do it. Tim is the most reliable contractor I know, his work always comes in on time and at or under budget. Together with Tim's brother Frank, who sometimes helps him on jobs, we decided to put a door in the side of the space and a hatch where the grate for the cold air return was located. The pump station then could be installed in the upper space on the inside of the hatch, with the tank below it. Just under the hatchway, we decided to put a platform on which someone could sit while servicing the pump station.
Because the flue ran up the middle of the space, Tim and Frank had to move it to the back. You can see the new location before the platform was installed:
The black pipe is the vent from the bathroom, which is on the wall immediately to the right of the flue.
Here's a view of the bottom where a plywood floor was installed to support the tank:
One issue we ran up against was what to put on the inside walls. By code, if there was any loose wiring, we needed to have some kind of protection in place to keep someone from accidentally grabbing the wires. But the amount of space in the closet was pretty tight, especially since I wanted to wrap the tanks in additional insulation. The normal thickness of drywall is 1/2" but it turns out you can also get 1/4" drywall, which is what we ended up using. This gave us another 1/2" of space. In addition to that, Tim put 6" of closed cell foam insulation on the roof and at least 3" on the walls of the closet, to reduce the amount of heat transfer into the house in the summer, when the tank can get up to 175F.
The downstairs gas heater tank looks pretty normal as you can see from this picture:
The insulating blanket isn't doing much good since it is not tight against the tank, and, by the way, the outer skin is vinyl, which is quite unhealthy. But we were were going to change all that.
The guy Sunwater sent to do the installation was an older tradesman, quite pleasant to talk with, but I began to have some suspicions about his competence almost immediately. One day I came home from work after the tank had been installed, and found that he had connected the feed lines from the collector to the top heat exchanger instead of the bottom. Now, heat rises, so this configuration would have caused the tank to stratify with the incoming cold water line injecting cold water on the bottom and the hot water on the top, where the water outlet for the domestic hot water is. I called him up and made him change the plumbing.
In the picture below, you can see the bottom of the fully installed Superstor tank, where most of the interesting stuff is happening (there's some on the top too but not as much):
The two lines in the back with the black foam around them are the feed lines from the collector, going through the correct lower heat exchanger. The corrugated line is the pressure overflow from the tank, the line it is connected to is the pressure overflow coming down from the expansion tank and pump station in the upper chamber above the platform. The line entering the tank is the cold water input from the house and ultimately the main. The other line in the elbow on the right side is the hot water running to the gas hot water tank downstairs, you can't see the pipe running down from the top of the tank where the hot water outlet is because it is behind the door frame. There is also another pipe running across behind the cold water input, connected to the pan, that's also an overflow pipe to the drain. In the back is the furnace and gas hot water heater flue.
Below you can see the internals of the pump station in the upper chamber before the cover was put on:
The brass colored cylinder is the pump, three gauges on the front provide information about the temperature (to and from collector) and pressure in the feedlines. The feedlines coming from the collector through the outer wall of the house are on the top. The blue wire is the power cord (110v, 15 amp, we also had Tim install a plug for it). Here's what the pump station looks like when the cover is on:
And here you can see the white expansion tank:
The grey wire in the background is the sensor cable from the collector, the corrugated line is the pressure overflow from the expansion tank to the pipe going to the drain downstairs, and of course the ubiquitous flue.
Since the solar hot water acts as a preheater for the gas heated tank downstairs, it needed to be plumbed into the gas tank. Here's a picture of what that now looks like:
The grey knob you see in the middle is the mixing valve. It is where the hot water from the tank is mixed with cold water to keep the domestic hot water below 120F. Above that temperature, scalding is possible. As for the rest, the grey steel line on the left is the pressure overflow, the horizontal line with the red lever on the bottom is the hot line from upstairs, feeding into where the cold line would normally go (for preheating), the horizontal line on the top is the cold going to the tank upstairs. The grey knob is where the domestic hot water comes out of the gas tank. In the back on the right is a feed line for the hydronic boiler, from the cold line, and a cold line that goes into the tank, with the red lever now in the off position. Switching the front red lever to off and the back to on causes the solar tank to be cut out of the loop. Unfortunately, there is no way to switch the gas tank out of the loop (more on this in a later post).
Charging the collector feedlines with the heat transfer fluid requires a very specific pressure adjustment to match the height difference between the collector and the expansion tank, and also any air in the feedlines must be purged or the bubbles will cause a lock and prevent pumping. After the installer charged it up the first time, the tank didn't seem to be getting any heat. It turned out that the pump wasn't on because he had forgotten to turn on the power switch! He came and fixed that, but then the pumps were really loud and there still didn't seem to be any heat getting into the tank. So he came back again: he had forgotten to bleed the air out and so the lines were locked. When I checked the pressure after he finished, it turned out he had way overpressurized the lines, as if there were 10 vertical feet or so between the collector and the expansion tank instead of the 2-3 feet there is. By this time I had had enough of this guy. When I discovered that the unions on the tank and in the pumping station were leaking hot glycol (and copiously at that), I called Justin and told him I wanted somebody who knew what they were doing put on the project.
Justin was very accommodating and worked with me to get the problems fixed (also, I didn't send him his last payment until he did, just to make sure). But it took another month before we could get the unions properly fixed. Justin sent one of his best guys over, and he first re-soldered the unions on the tank. But he couldn't get the pump station unions tight. It turns out they have a kind of pressure coupling which seals when tightened, but when overtightened, leaks. So he had to send his very best guy to come and cut through the pressure couplings. One slip and they would have had to reinstall the entire feedline set from the collector again (or, at least, a substantial part of it)! But thankfully he managed to cut just precisely right and they reinstalled the pressure couplings. Both sets of unions now looked solid.
Despite the fact that we had such problems with the installation, I don't hold it against Justin, and I would still recommend Sunwater. As it turns out, the installer had only been working for Sunwater for a few months, whereas the other two guys had been working with Justin for years. I've been in this situation myself: you hire someone with a great resume and they turn out to be a dud (or, even worse, they falsified the resume and don't know the basics of the job). So I didn't hold it against him. Justin really tried to get the system properly fixed, and ultimately did fix it to my satisfaction. However, this does point up a problem with the whole area of residential green energy and energy efficiency remodeling: many contractors and/or the people working for them don't have a clue. So they often do things, especially when it comes to insulation or weatherizing, that are ineffective or, in this case, downright harmful.
Point to note when planning a solar hot water system:be sure you understand how the system is supposed to work and what is needed in terms of insulation to make it efficient, and make sure the contractor does the work necessary to ensure it works properly.
Note to President Obama: "Cash for Caukers" won't work if the caukers don't know how to wield a cauking gun so they can properly insulate. Most people in construction in the US are in the business because they can't do any other work. Unlike Europe, where trades require a substantial amount of technical training, and where the trades have over the last 10 years upgraded their members' training through in service education to address energy conservation and green energy equipment installation, the assumption in the US seems to be that anybody can do this work without any training. If this kind of attitude goes into "Cash for Caukers" the resulting weatherization is not going to save energy, it will be a colossal waste of money. I'd recommend to the Congress if they want to do "Cash for Caukers" that they should budget enough that any contractor who plans to participate must take a 6 month course in energy efficiency building so they understand what they are doing. And - just to be on the safe side and avoid fraud - have people trained to inspect the job periodically the way building inspectors do, since most inspectors don't have the training to spot improperly installed green energy devices or ineffective insulation either.
Then came the question of where to put the tank. We initially considered putting it in a small house next to the sauna, or maybe next to the fireplace pod that sticks out from the house, but ultimately we decided to repurpose the cold air return for the forced air heating. We had the forced air heating taken out a couple years ago and put in hydronic floor heating, so we didn't need the space any more. It is on the second floor in the hallway. The space consisted of a plenium with a large grate on the front, which led into the downstairs furnace room. When we had the hydronic furnace installed in the furnace room, the plenium was blocked off from downstairs. As we discovered when we opened up the space and removed the plenium, the flue from the furnace and the gas fired hot water heater in the downstairs mechanical room ran up the middle. We had a bit of work to do on the space.
Point to note when planning a solar hot water system: be sure to include enough time and money for upgrading the space where you plan to put the tank and the pump station if you are not going to use your existing tank.
Sunwater doesn't do the kind of drywall and carpentry work needed to modify the space, so we asked a friend of ours who is a contractor, Tim Hmelar (check out his new business, Purple Coupon) to do it. Tim is the most reliable contractor I know, his work always comes in on time and at or under budget. Together with Tim's brother Frank, who sometimes helps him on jobs, we decided to put a door in the side of the space and a hatch where the grate for the cold air return was located. The pump station then could be installed in the upper space on the inside of the hatch, with the tank below it. Just under the hatchway, we decided to put a platform on which someone could sit while servicing the pump station.
Because the flue ran up the middle of the space, Tim and Frank had to move it to the back. You can see the new location before the platform was installed:
The black pipe is the vent from the bathroom, which is on the wall immediately to the right of the flue.
Here's a view of the bottom where a plywood floor was installed to support the tank:
One issue we ran up against was what to put on the inside walls. By code, if there was any loose wiring, we needed to have some kind of protection in place to keep someone from accidentally grabbing the wires. But the amount of space in the closet was pretty tight, especially since I wanted to wrap the tanks in additional insulation. The normal thickness of drywall is 1/2" but it turns out you can also get 1/4" drywall, which is what we ended up using. This gave us another 1/2" of space. In addition to that, Tim put 6" of closed cell foam insulation on the roof and at least 3" on the walls of the closet, to reduce the amount of heat transfer into the house in the summer, when the tank can get up to 175F.
The downstairs gas heater tank looks pretty normal as you can see from this picture:
The guy Sunwater sent to do the installation was an older tradesman, quite pleasant to talk with, but I began to have some suspicions about his competence almost immediately. One day I came home from work after the tank had been installed, and found that he had connected the feed lines from the collector to the top heat exchanger instead of the bottom. Now, heat rises, so this configuration would have caused the tank to stratify with the incoming cold water line injecting cold water on the bottom and the hot water on the top, where the water outlet for the domestic hot water is. I called him up and made him change the plumbing.
In the picture below, you can see the bottom of the fully installed Superstor tank, where most of the interesting stuff is happening (there's some on the top too but not as much):
The two lines in the back with the black foam around them are the feed lines from the collector, going through the correct lower heat exchanger. The corrugated line is the pressure overflow from the tank, the line it is connected to is the pressure overflow coming down from the expansion tank and pump station in the upper chamber above the platform. The line entering the tank is the cold water input from the house and ultimately the main. The other line in the elbow on the right side is the hot water running to the gas hot water tank downstairs, you can't see the pipe running down from the top of the tank where the hot water outlet is because it is behind the door frame. There is also another pipe running across behind the cold water input, connected to the pan, that's also an overflow pipe to the drain. In the back is the furnace and gas hot water heater flue.
Below you can see the internals of the pump station in the upper chamber before the cover was put on:
The brass colored cylinder is the pump, three gauges on the front provide information about the temperature (to and from collector) and pressure in the feedlines. The feedlines coming from the collector through the outer wall of the house are on the top. The blue wire is the power cord (110v, 15 amp, we also had Tim install a plug for it). Here's what the pump station looks like when the cover is on:
And here you can see the white expansion tank:
The grey wire in the background is the sensor cable from the collector, the corrugated line is the pressure overflow from the expansion tank to the pipe going to the drain downstairs, and of course the ubiquitous flue.
Since the solar hot water acts as a preheater for the gas heated tank downstairs, it needed to be plumbed into the gas tank. Here's a picture of what that now looks like:
The grey knob you see in the middle is the mixing valve. It is where the hot water from the tank is mixed with cold water to keep the domestic hot water below 120F. Above that temperature, scalding is possible. As for the rest, the grey steel line on the left is the pressure overflow, the horizontal line with the red lever on the bottom is the hot line from upstairs, feeding into where the cold line would normally go (for preheating), the horizontal line on the top is the cold going to the tank upstairs. The grey knob is where the domestic hot water comes out of the gas tank. In the back on the right is a feed line for the hydronic boiler, from the cold line, and a cold line that goes into the tank, with the red lever now in the off position. Switching the front red lever to off and the back to on causes the solar tank to be cut out of the loop. Unfortunately, there is no way to switch the gas tank out of the loop (more on this in a later post).
Charging the collector feedlines with the heat transfer fluid requires a very specific pressure adjustment to match the height difference between the collector and the expansion tank, and also any air in the feedlines must be purged or the bubbles will cause a lock and prevent pumping. After the installer charged it up the first time, the tank didn't seem to be getting any heat. It turned out that the pump wasn't on because he had forgotten to turn on the power switch! He came and fixed that, but then the pumps were really loud and there still didn't seem to be any heat getting into the tank. So he came back again: he had forgotten to bleed the air out and so the lines were locked. When I checked the pressure after he finished, it turned out he had way overpressurized the lines, as if there were 10 vertical feet or so between the collector and the expansion tank instead of the 2-3 feet there is. By this time I had had enough of this guy. When I discovered that the unions on the tank and in the pumping station were leaking hot glycol (and copiously at that), I called Justin and told him I wanted somebody who knew what they were doing put on the project.
Justin was very accommodating and worked with me to get the problems fixed (also, I didn't send him his last payment until he did, just to make sure). But it took another month before we could get the unions properly fixed. Justin sent one of his best guys over, and he first re-soldered the unions on the tank. But he couldn't get the pump station unions tight. It turns out they have a kind of pressure coupling which seals when tightened, but when overtightened, leaks. So he had to send his very best guy to come and cut through the pressure couplings. One slip and they would have had to reinstall the entire feedline set from the collector again (or, at least, a substantial part of it)! But thankfully he managed to cut just precisely right and they reinstalled the pressure couplings. Both sets of unions now looked solid.
Despite the fact that we had such problems with the installation, I don't hold it against Justin, and I would still recommend Sunwater. As it turns out, the installer had only been working for Sunwater for a few months, whereas the other two guys had been working with Justin for years. I've been in this situation myself: you hire someone with a great resume and they turn out to be a dud (or, even worse, they falsified the resume and don't know the basics of the job). So I didn't hold it against him. Justin really tried to get the system properly fixed, and ultimately did fix it to my satisfaction. However, this does point up a problem with the whole area of residential green energy and energy efficiency remodeling: many contractors and/or the people working for them don't have a clue. So they often do things, especially when it comes to insulation or weatherizing, that are ineffective or, in this case, downright harmful.
Point to note when planning a solar hot water system:be sure you understand how the system is supposed to work and what is needed in terms of insulation to make it efficient, and make sure the contractor does the work necessary to ensure it works properly.
Note to President Obama: "Cash for Caukers" won't work if the caukers don't know how to wield a cauking gun so they can properly insulate. Most people in construction in the US are in the business because they can't do any other work. Unlike Europe, where trades require a substantial amount of technical training, and where the trades have over the last 10 years upgraded their members' training through in service education to address energy conservation and green energy equipment installation, the assumption in the US seems to be that anybody can do this work without any training. If this kind of attitude goes into "Cash for Caukers" the resulting weatherization is not going to save energy, it will be a colossal waste of money. I'd recommend to the Congress if they want to do "Cash for Caukers" that they should budget enough that any contractor who plans to participate must take a 6 month course in energy efficiency building so they understand what they are doing. And - just to be on the safe side and avoid fraud - have people trained to inspect the job periodically the way building inspectors do, since most inspectors don't have the training to spot improperly installed green energy devices or ineffective insulation either.
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