Duane Oxley
Moon Unit
It’s been a while since I’ve posted an update about our heat exchange systems. And Eric just asked me on another thread about them, so I thought I'd post some info here...
I’ve been pretty occupied with R&D related to making them as simple and streamlined as possible and at the same time, getting maximum heat out of them. It’s an ongoing process, so it’s not easy, in terms of knowing when to stop and enjoy the accomplishment, post updates, etc. But now is a good time, I think.
This update is mainly about the Xcel design. Even so, posting about the Nemesis, in order to give some background is in order:
Both the Xcel and Nemesis come under a patent that I filed about a year ago now, in July. What makes them patentable is the unique approach to pre- heating the water, which, instead of sending the water through bypass loops to and from exchangers and then to the tank (or, from the tank, through loops and back), turns the tank itself into an exchanger, by routing heated airflow through the tank, via several parallel tubes, much like a shell and tube exchanger. This makes the transfer of heat much more direct and much more efficient. With the Nemesis design, the "spent" or "unspent" (depending upon whether it's previously used in the engine exhaust exchanger or not, respectively) is blended into the blower exhaust prior to both being routed through the exchanger- tank. For the Xcel, only blower exhaust is routed through the tank. On the Nemesis, there is a second automatic diverter that controls airflow through the exchanger-tank.
It's important to note here that these systems are not choked down in the least, in terms of blower exhaust porting. In fact, they're actually over- sized, using 3" square tube as the exhaust plumbing. This is crucial, because back pressure on the exhaust of the engine is crucial. Kohler allows 40 " W.C. on their engines. When they tested the Nemesis, they were surprised (and very pleased) to find that we had 7", regardless of whether the system was in engine exhaust bypass or not, and regardless of whether it was in blower exhaust bypass or not..
The design worked well on the first Nemesis (which had a 25 Kohler and 4005 Tuthill blower), until, during the colder winter months, we noticed a drop in temperature, from a previous at the wand output of 203 degrees, to about 175 degrees. That drop wasn’t acceptable with the goals I had set, so, I went back to R&D to make the system more efficient.
In the research that followed, I determined to change the water tank (“exchanger- tank”, actually) material, from stainless steel, to something that conducts heat better. The Xcels use aluminum, because aluminum conducts heat much more efficiently than steel. And in order to prevent corrosion problems, I researched aluminum anodizing, found a company that specializes in doing anodizing, and had the tanks hard- anodized to prevent corrosion.
Also, I developed a more efficient exhaust exchanger, via a way to spread the exhaust better across all of the tubes, providing a more uniform heat dispersion, which resulted in higher efficiency. That alone resulted in a 15- degree gain in output temperature at the previous testing level of 600 PSI, through a #6 jet equivalent, at 100 ft.
So, we built two Xcel systems and delivered them in March and they’re out cleaning every day in a company that specializes in apartments. (These systems are numbers 5 and 6 for the company, so this is a very good "test" for them.) On the delivery start- up / demo, they delivered about 180 degrees at the wand, using a Kohler 20 and a Tuthill 3006 as heat sources. But the report back from the owners is that as the work day began, they developed even more heat. (To quote the owner, “Man that thing gets hot! It’s definitely hotter than my Bruin.”) And keep in mind that the wands being used have (2) #3 jets in them, not smaller jets, to slow the flow and boost the heat.
As I said, the Xcel, unlike the Nemesis, does not route the engine exhaust through the exchanger-tank. The engine exhaust comes into the air stream after the exchanger-tank and just before the system muffler. And the exhaust out the front of the system is pretty hot, even after moving through the exchanger-tank. This indicates that, if I wanted to, I could make this system even hotter than it currently is… but I don’t want it to compete with the Nemesis. (I’ve said for some time now that the goal for the Xcel is for it to produce heat similar to a Little Giant #3 heater, which it does.)
The Xcel is basically the HX version of the "Predator" (propane) systems we make. Like them, it has no recovery tank, but instead uses a continuous pump- out approach. They're direct- coupled and very small, foot- print- wise, at 20" wide and 58" long, for the complete system.
My parameters in system design, since “Day 1”, have been to keep things simple. But with heat exchangers, that’s not as easy to do as with propane (or even, oil- fired). Because provisions have to be made in order to allow for the owner to do flood work with no water connected, and to be able to put the wand down while moving furniture, etc. Such things require a pump clutch, automatic temperature control, exhaust diversion, etc. And unlike propane or oil- fired systems, exchangers have two or more sources of heat, which have to be monitored and controlled independently of each other. But I’ve included all of this and still kept the system simple enough.
As an example, the exhaust diverter on the Xcel and Nemesis systems is automatic. And, at the same time, it’s simple. It uses a pneumatic air cylinder, pneumatic solenoid and the vacuum of the system for the airflow to operate them. The cylinder is spring- loaded, so that it defaults to the “OFF” diverter position if the pump clutch is turned off as a safety feature. But this approach also eliminates the need for two controls for the air cylinder. The diverter, as well as the exhaust exchanger, and the plumbing that connects them, as well as the plumbing downstream from the exhaust exchanger, is 304 stainless steel.
To say that I’m pleased with our progress with the Xcel and Nemesis designs is an understatement. The main thing now is to clean up the plumbing, work on cosmetics, etc.
Here are some pictures of the Xcels we built:
The Nemesis is still under revision. I'm taking my time with it because I want to revise it once, and leave it at that. The revision is pretty comprehensive from the first one. For instance, it's belt- driven. (This is because I'm planning to overdrive the blower for more heat, instead of choking it down to put it under constant strain as most other HX systems do.) In addition, the exhaust exchanger is vertically- mounted. This is simply a choice here that better suits the belt- drive frame. And finally, the exchanger- tank will have copper tubes, although the tank itself will continue to be stainless steel. Copper is a better heat transfer medium than aluminum, though a bit more complicated and costly to include in the system. So, it's reserved for the Nemesis systems.
The first belt- drive Nemesis frame is ready. It's getting everything else set up the way I want that's taking a bit of time... combined with getting ready for the Accelerated Atlanta Gathering here in just over a week. Once we're into September, I'll turn my focus more fully to the Nemesis again...
I’ve been pretty occupied with R&D related to making them as simple and streamlined as possible and at the same time, getting maximum heat out of them. It’s an ongoing process, so it’s not easy, in terms of knowing when to stop and enjoy the accomplishment, post updates, etc. But now is a good time, I think.
This update is mainly about the Xcel design. Even so, posting about the Nemesis, in order to give some background is in order:
Both the Xcel and Nemesis come under a patent that I filed about a year ago now, in July. What makes them patentable is the unique approach to pre- heating the water, which, instead of sending the water through bypass loops to and from exchangers and then to the tank (or, from the tank, through loops and back), turns the tank itself into an exchanger, by routing heated airflow through the tank, via several parallel tubes, much like a shell and tube exchanger. This makes the transfer of heat much more direct and much more efficient. With the Nemesis design, the "spent" or "unspent" (depending upon whether it's previously used in the engine exhaust exchanger or not, respectively) is blended into the blower exhaust prior to both being routed through the exchanger- tank. For the Xcel, only blower exhaust is routed through the tank. On the Nemesis, there is a second automatic diverter that controls airflow through the exchanger-tank.
It's important to note here that these systems are not choked down in the least, in terms of blower exhaust porting. In fact, they're actually over- sized, using 3" square tube as the exhaust plumbing. This is crucial, because back pressure on the exhaust of the engine is crucial. Kohler allows 40 " W.C. on their engines. When they tested the Nemesis, they were surprised (and very pleased) to find that we had 7", regardless of whether the system was in engine exhaust bypass or not, and regardless of whether it was in blower exhaust bypass or not..
The design worked well on the first Nemesis (which had a 25 Kohler and 4005 Tuthill blower), until, during the colder winter months, we noticed a drop in temperature, from a previous at the wand output of 203 degrees, to about 175 degrees. That drop wasn’t acceptable with the goals I had set, so, I went back to R&D to make the system more efficient.
In the research that followed, I determined to change the water tank (“exchanger- tank”, actually) material, from stainless steel, to something that conducts heat better. The Xcels use aluminum, because aluminum conducts heat much more efficiently than steel. And in order to prevent corrosion problems, I researched aluminum anodizing, found a company that specializes in doing anodizing, and had the tanks hard- anodized to prevent corrosion.
Also, I developed a more efficient exhaust exchanger, via a way to spread the exhaust better across all of the tubes, providing a more uniform heat dispersion, which resulted in higher efficiency. That alone resulted in a 15- degree gain in output temperature at the previous testing level of 600 PSI, through a #6 jet equivalent, at 100 ft.
So, we built two Xcel systems and delivered them in March and they’re out cleaning every day in a company that specializes in apartments. (These systems are numbers 5 and 6 for the company, so this is a very good "test" for them.) On the delivery start- up / demo, they delivered about 180 degrees at the wand, using a Kohler 20 and a Tuthill 3006 as heat sources. But the report back from the owners is that as the work day began, they developed even more heat. (To quote the owner, “Man that thing gets hot! It’s definitely hotter than my Bruin.”) And keep in mind that the wands being used have (2) #3 jets in them, not smaller jets, to slow the flow and boost the heat.
As I said, the Xcel, unlike the Nemesis, does not route the engine exhaust through the exchanger-tank. The engine exhaust comes into the air stream after the exchanger-tank and just before the system muffler. And the exhaust out the front of the system is pretty hot, even after moving through the exchanger-tank. This indicates that, if I wanted to, I could make this system even hotter than it currently is… but I don’t want it to compete with the Nemesis. (I’ve said for some time now that the goal for the Xcel is for it to produce heat similar to a Little Giant #3 heater, which it does.)
The Xcel is basically the HX version of the "Predator" (propane) systems we make. Like them, it has no recovery tank, but instead uses a continuous pump- out approach. They're direct- coupled and very small, foot- print- wise, at 20" wide and 58" long, for the complete system.
My parameters in system design, since “Day 1”, have been to keep things simple. But with heat exchangers, that’s not as easy to do as with propane (or even, oil- fired). Because provisions have to be made in order to allow for the owner to do flood work with no water connected, and to be able to put the wand down while moving furniture, etc. Such things require a pump clutch, automatic temperature control, exhaust diversion, etc. And unlike propane or oil- fired systems, exchangers have two or more sources of heat, which have to be monitored and controlled independently of each other. But I’ve included all of this and still kept the system simple enough.
As an example, the exhaust diverter on the Xcel and Nemesis systems is automatic. And, at the same time, it’s simple. It uses a pneumatic air cylinder, pneumatic solenoid and the vacuum of the system for the airflow to operate them. The cylinder is spring- loaded, so that it defaults to the “OFF” diverter position if the pump clutch is turned off as a safety feature. But this approach also eliminates the need for two controls for the air cylinder. The diverter, as well as the exhaust exchanger, and the plumbing that connects them, as well as the plumbing downstream from the exhaust exchanger, is 304 stainless steel.
To say that I’m pleased with our progress with the Xcel and Nemesis designs is an understatement. The main thing now is to clean up the plumbing, work on cosmetics, etc.
Here are some pictures of the Xcels we built:
The Nemesis is still under revision. I'm taking my time with it because I want to revise it once, and leave it at that. The revision is pretty comprehensive from the first one. For instance, it's belt- driven. (This is because I'm planning to overdrive the blower for more heat, instead of choking it down to put it under constant strain as most other HX systems do.) In addition, the exhaust exchanger is vertically- mounted. This is simply a choice here that better suits the belt- drive frame. And finally, the exchanger- tank will have copper tubes, although the tank itself will continue to be stainless steel. Copper is a better heat transfer medium than aluminum, though a bit more complicated and costly to include in the system. So, it's reserved for the Nemesis systems.
The first belt- drive Nemesis frame is ready. It's getting everything else set up the way I want that's taking a bit of time... combined with getting ready for the Accelerated Atlanta Gathering here in just over a week. Once we're into September, I'll turn my focus more fully to the Nemesis again...
