Automation is an awesome thing

I initially installed my Attack DP35 Profi gassifier a couple of seasons ago, leaving my oil boiler for backup. Since I was not home during the day, I would have to overheat my home in the evening to hopefully get through the night, then let the oil boiler warm things in the morning, let the house cool through the day then repeat the process. This year I have added storage which helped, but until I automated things I had no idea how simple burning with solid fuel could be. My documentation is still a bit rough, so keep watching and I'll try to post as available to aid in understanding my system, which is fairly complex due to the number of heat loads, and admittedly because I an an engineer! The addition of storage helped, but I was finding it difficult to manage and had to spend a lot of time adjusting things as heat loads changed, etc. After a lot of research on what's available out there, I settled on a Vesta system from Vermont Energy Control Systems as my solution. (http://www.vecs.org). I now can light a fire and virtually ignore it until my system alerts me to add more wood, while gaining the best efficiency possible. I am using far less wood than I did without the controller and my house stays a constant temperature. I am using opposing circulators for charge/discharge of my storage, under control of the Vesta. What sets this apart from other systems I've looked at is the ability to add variable speed control to the circs under PID control. This enables me to not only control the charge cycle, but ensures that I don't starve the system, allowing the return temp to go too low, or keep the space heating zones from having sufficient energy (hydronic), or trying to heat the tank when there just isn't enough heat, causing destratification of the tank. I have learned that stratification is hugely important for efficiency and longevity of storage. The variable speed allows me to maintain an ideal delta T during tank charging, ensuring good stratificaiton and an efficient charge cycle. I typically see a delta T from the top of the tank to the bottom in the 50-60F range, with a dleta T at the FPX on the tank side in about the same range. By maintaining stratification, I am always drawing water from the bottom of the tank that is far colder than the top, improving the heat transfer function of the FPX. For the first time ever, I was able to load the boiler for a final burn last night, then go to bed, confident that the controller would do a good job of managing the heat and it was awesome! I am now truly, fossil free! The Vesta system made this very simple, as I was able to use all my existing hardware, including relays, etc. The built in PID functions coupled with the variable speed capability were essential and definitely make this a more hands off operation. One feature I really liked, but didn't fully appreciate until tuning my system, is the data logging and graphing. It makes it very simple to evaluate system performance and diagnose problems. It's very cool to see how your storage tank charge function behaves. In my case, I can watch each zone in the tank increase in temperature and was able to tune it so that each zone became fully charged before the next, maintaining excellent stratification. Programming is straight forward too - you don't need to be a computer geek to understand it. For anyone out there wanting a more automated system, I highly recommend this system.

It is a slow process, but awesome when you get there. When I think of all the time I will save, it was worth it. It's a great showpiece for my geek friends too! I am still in the process of pulling my stuff together and the rule set needs some cleanup, but it's pretty close. To save hardware, I am using just one Nimbus controller with a relay to switch between my charge and discharge circs. I use PID to charge, but just a set of three discrete settings controlled by rules for discharge. At some point I will write a PID rule for that as well, but it's not that pressing. I'll probably get a little more time on the existing setup first. In order for my rule set to make much sense, you'll need to see the system drawing. My electrical schematic is hand drawn, but it is essential in understanding the rules as well. My wood boiler and oil boiler are connected with relays, enabling the system to work if I need to take the Vesta offline for any reason. It's a little weird the way it's setup, but I did it to simplify the hardware and reduce the number of relays. It does make the rules a little more complex. The oil boiler is an Energy Kinetics System 2000 which has its own controller. Rather than bypass it entirely, I have made it part of the overall setup. It provides my basic heat demand signal by responding to the thermostats. I chose this method, as I have setback thermostats and it is really nice to have the system behave the same as oil - hit the button or reprogram the thermostat and it doesn't matter what the heat source is. The basic design approach provides the ability to enable or disable any part of the system. Thermostat override, oil boiler disable, etc. I'll post more later. If you have any specific questions let me know. My system consists of the oil boiler, DHW storage, 800 gal unpressurized bulk storage, wood boiler, and Vesta controller with lots of sensors, relays, etc. I have been experimenting some over the past couple of days, so my storage profile isn't that pretty. I'll see if I can find a good one and post the graph. It is very cool to see each layer of the tank kick in as the heat moves down further into the tank. Because the Nimbus allows me to slow the circ to an appropriate speed for good delta T, the flow is slower and that enhances stratification. All in all, I am very excited about how well the design performs. Adding zones will be a trivial exercise at this point.

Here's an example of my stratification. Somewhat better today - this is from about a week ago. I've tuned it to reduce the variation in boiler in/out. However, you can see how well the storage charge profile behaves. A little explanation. I have 4 sensors in a dip tube in my tank. The top is about 5" below the maximum water level, with the bottom about 2" off the bottom of the tank. The other two are spaced evenly, 12" from each other and the other two sensors. It's pretty amazing how sharp the stratification is which is evident when you consider where the sensors are positioned. "Storage Supply" is the FPX output to the top of the tank, while "Storage Return" is FPX bottom of tank. This graphing capability is awesome and so simple to use. Just pop in the dates, select the channels you want to graph and there it is. There is no way I could do an adequate job of tuning without this. You can also see how well the FPX tracks the output from the boiler. This tells me I have sized it correctly to get good transfer of heat - very low delta T in the less than 5 degree range. On this burn, I should have put a little more wood in to keep it from drooping at the end, or stopped the charge earlier. Because the boiler output dropped, it pulled the top of the tank down a bit while bringing the bottom up, but it's not clear that I got any net BTU gain and may not have had as much usable heat, because of the decrease in top tank temperature. I cannot imagine how I could do this level of tuning without the data logging and graphing capability of the Vesta.

Tennman said:

Great job George. My storage is not on line yet, but my understanding was to store as much energy as possible to the tanks while servicing house demand in the hope of achieving bottom temps as close as possible to the top... maximizing time between burns. I.e. burn wide open, as hot as possible. I can get my brain around the benefit of the lower delta T supply to the boiler to better pull energy from the boiler..... So I guess your saving a bunch of wood by controlling the flow rate from the top of storage so you can slow the burn down in the boiler to extend the burn AND manage the stratification??? Trying to get my head around if nothing has changed on the demand side how is the system managing the burn to reduce wood consumption. I love the internet monitoring and control capability. How difficult is the rule based language to learn? Very cool system.

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That is a common misconception and one I fell prey to early on in my experience with this technology. Like most machines, boilers are more efficient, last longer and are easier to manage if they are not driven at maximum output temperature. Maximum temperature should not be viewed as the best way to run a system. Every boiler has a rated maximum output, in BUT's. I run my boiler at maximum output, but not maximum temperature. BTU output is defined by the delta T and flow rate. Maintaining a higher output temperature with the same delta T simply puts more BTU's up your chimney. Think about it this way. The boiler has a certain rated BTU capacity, in BTU's per hour. What this equates to, is being able to draw the largest number of BTU's away from the boiler in the shortest amount of time possible. This is entirely disconnected from the actual boiler temperature, it has to do with delta T and flow - this determines how much heat you're drawing from the device. As an example, if you have a boiler running at 195 with a low flow rate that causes your return to be 175, you are still drawing the same number of BTU's as you would at an output temperature of 185 and return of 165. Well, in my case I have an output around 185 (my target temp), but return of under 155, which gives me a delta T 50% higher. With the same flow rate, that equates to an efficiency improvement of 50%, since I'm drawing half again as many BTU's in the same time period. Huge. This is where I get my savings, not by running the boiler at lower output, but by optimizing the load. When I get closer to the end of saturating storage, the temp needs to be higher, so I bump it up, but then target the same delta T. You have to keep in mind, it all depends on your system. In my case, 800 gals of storage won't last all that much longer at 185 than at 180, so there's really no point in sacrificing efficiency to blast out that higher temp, just to have to figure out what to do with what's left over - you have to dump it somewhere. With the Vesta online I can confidently have a good burn going when I go to bed, which allows me to go that much longer charging storage and not drawing from it. We've been having temps well below zero overnight and barely reaching zero during the day and I've been able to keep up with just one fire a day, so I'm happy with that.

To answer the other question, The Vesta language is based on common terminology used in the HVAC industry, so if that's where you come from it's simple. In my case, I have a software background, so I constantly fought it. Once I followed the manufacturer's suggestions, everything fell into place. That's another great thing about the Vesta, the support. The guy who designed the system and wrote the software, etc. is readily accessible and loves this stuff. He will do whatever it takes to help you get your system working perfectly. I know, I've been a pain in his ... side and he's been there 24/7. Gotta go, just got a message that I need to feed the boiler. Man, this is easy now!!

maple1 said:

Not sure I read right - are you saying you up your delta-T from 20 to 30 while maintaining the same flow?

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ewdudley said:

Boiler efficiency depends on three things: flue gas temperature, flue gas excess oxygen, and completeness of combustion. Unless your new gizmo affects these factors in the right direction in a measurable way then you've done nothing verifiable to improve efficiency.

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True, but I was talking about heat transfer efficiency, which is what heats your house. I can have the most efficient fire in the world, but if I'm not able to translate that into a warm cozy house it's not of much value.

maple1 said:

Not sure I read right - are you saying you up your delta-T from 20 to 30 while maintaining the same flow?

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There's a piece missing here. I use a FPX to transfer heat to/from storage. The flow is constant on the boiler side of the FPX. By varying the flow on the storage side, I'm able to control the boiler delta T. That's where the variable speed control comes in. I do not have enough heat load in the rest of my system to maintain a delta T higher than 20, so the boiler will go into rest mode. If I can run a hot fire consistently, I get good combustion efficiency and I can draw more heat from the system in the same period of time, improving overall system efficiency, which has dramatically improved fuel consumption. A higher delta T translates into lower flue temps and less heat up the chimney.

If I had a way to measure all those, I am confident that I could present the efficiency improvement in those terms. The simplest way I have to measure the efficiency at a system level is what I mentioned in my last post. I don't yet have thermocouples for combustion or flue temp, so I am reliant on a dial gauge magnetically attached to the back of the flue thimble on the boiler. Nice flat surface, so it's not too bad, but given the resolution and accuracy, not much good for anything but relative changes. The delta T change I made caused a 50 degree drop in flue temperature on that gauge. I find it far more useful to look at overall system efficiency than to focus on a single function, such as combustion efficiency.

ewdudley said:

Heat transfer efficiency depends on four things: rate of combustion, flue gas temperature, flue gas excess oxygen, and completeness of combustion. Unless your new gizmo affects these factors in the right direction in a measurable way then you've done nothing verifiable to improve heat transfer efficiency.

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By the way, your four factors only relate to generating BTU's, they have nothing to do with transferring those BTU's to do anything useful.

Yup, it's called conservation of energy. Regardless of how many BTU's I'm able to generate, my goal is to heat my house. The more of those bad boys that end up there the better. I look forward to the day when I have sensors to gather the data required to evaluate and control combustion efficiency, since controlling that is still a highly manual task with compromises in combustion quality, overall heat output and the life of the boiler. I burn a mix, since my firewood comes from maintaining my lot. Poplar, pine, white birch, oak, red cedar and buckthorn are the most common. I generally start my fire with softwood, since as you point out, it burns quick and hot, establishing a bed of coals, then I focus more on hardwood, but still use a mix. This does complicate combustion also. I've already spent way more on this system than I ever imagined, so the additional instrumentation will just have to wait.

Dudley, if all you want to do is criticize, I suggest you opt out of this thread. Keep in mind that not everyone has the instrumentation to conduct the measurements you suggest. However, there are other ways of evaluating efficiency in their absence, which is all I currently have to work with. I suspect that making changes to flow rates etc. is something you've done, it's just that you're able to relate those back to combustion to verify their effectiveness. Not all of us have that capability. If you look back to my previous post you'll see that I did just that - my change in delta T related directly to a 50 degree reduction in flue temperature. I don't have a thermocouple in the gas stream yet, so I don't refer to it as flue gas temperature, since I am measuring the outside of the pipe. It's all relative. We work with the tools we have.

Yes, I should have phrased that as heat transfer improvement. I have insufficient sensor information to calculate an exact percentage increase in efficiency, but the fact that my flue temperature reduced by 50 degrees and my delta T increased by 50%, it is obvious that it was an improvement. Clearly from a system perspective, it's not 50%. What I can tell you is that I am using the same amount of wood for a burn, but burn for a shorter period of time and transfer more net heat into storage with a lower flue temp. The only point I am trying to make is that there are many ways to measure performance improvements and they are all related. Some are more empirical than others