Kabola heating systems

[sunchaser]

The WHY question I understand. If it were my decision (and it is not) I'd remove all previous heat exchanger hose and the heat exchanger of unknown capacity or reliability. Then I'd add a $100 or so plate heat exchanger, installed neatly per the book including insuring proper aqua stat control circuitry.

My small plate heat exchanger supplies many more BTUs than the boiler so when cruising it is the heat source of choice.

 

[twistedtree]

The WHY question I understand. If it were my decision (and it is not) I'd remove all previous heat exchanger hose and the heat exchanger of unknown capacity or reliability. Then I'd add a $100 or so plate heat exchanger, installed neatly per the book including insuring proper aqua stat control circuitry.

My small plate heat exchanger supplies many more BTUs than the boiler so when cruising it is the heat source of choice.

You wouldn't have details on your $100 heat exchanger, would you? I recently speced one for my boat build and the best I could do was in the $500s. That's probably driven by different requirements, but I'm curious if I missed something.

 

[markrkrebs]

I would hesitate to do that. I'd think you'd be putting your engine at risk of a leak in the hydronic system dumping the coolant out of your engine. I've experienced two serious leaks in the hydronic system, either which if undetected while running would have starved the main engine for coolant. I think a heat exchanger is the way to go keeping the engine and hydronic systems separate.

ITR the manufacturer of Hurricane systems sells a very efficient flat plate heat exchanger. Find it on page 22 of the catalog. There's a similar one on Ebay right now Alfa 3" x 8" 20 Flat Plate Heat Exchanger 3/4" MPT BL14-20D 180,000 BTU Stainless.

Thx. & good idea. Bought it.

 

[Island Cessna]

You wouldn't have details on your $100 heat exchanger, would you? I recently speced one for my boat build and the best I could do was in the $500s. That's probably driven by different requirements, but I'm curious if I missed something.

Those small stainless steel plate heat exchangers are amazingly efficient. In industrial use a unit the size of a suitcase replaces a shell and tube exchanger you can’t fit in a pickup truck!
They don’t do some difficult fluids well, but you have antifreeze/water on both sides, so no worries there.
They are designed for industrial applications where higher pressure drop can be accommodated, so I would either do the pressure drop calculations (can be complicated) or just upsize the exchanger since they are so cheap. The calculated, or arbitrary upsize could be how you end up with a $500 unit.

 

[sunchaser]

You wouldn't have details on your $100 heat exchanger, would you? I recently speced one for my boat build and the best I could do was in the $500s. That's probably driven by different requirements, but I'm curious if I missed something.

My plate exchanger seems similar if not identical to those linked in post 24 (thanks to PB). 14 years ago the ITR I have was about $100, or close to the Amazon price in #24. Since I can't get near our boat (parked in BC) I can't get the brand and size data. Our connections are 3/4" so with your larger unit likely more than we paid.

BTW, on our engines we have plate exchangers utilizing engine coolant to heat and cool engine oil. Marvelous in comparison to raw water cooled units.

 

[Delfin]

On my new (old) boat, the engine heat has been plumbed OUT of the Kabola hot water circuit. There's a heat exchanger nearby the Kabula that pulls waste heat out of the engine circuit but it goes nowhere; a short hose just connects heat-x outlet and inlet. My thought is to plumb it back in, in series with the boiler intake. I think that works if (a) boiler fires up (only) when its output temp drops and (b) circ pump is activated by demand from any remote thermostat. Is that how it works? (...hope so.) In my scheme, when cabin heat is called for, the circ pump starts and, since the boiler cold water inlet is now preheated by the engine, the boiler will run less often, if at all.

My experience is that the answer depends on what voltage your Kabola operates on. Initially, mine was 24 vdc, then had to be converted to 240 vac since the DC boards don't last with the voltage variations on a boat. When the controls were 24 vdc, the boiler would fire to maintain temperature in the water jacket. Once converted to 240 vac, it fires only when a zone calls for heat. I prefer the latter. If I understand your current setup, plumbing the heat exchanger back in series certainly makes sense, regardless of how the controller works, since engine heat does the work when underway, for free. If no zone is calling for heat, the circ pump isn't going to run, so you would rely on convection circulation, which I believe will work. In fact, stopping convection circulation prompted me to install electric ball valves in front of each zone loop which open when that zone calls for heat, which is what I did when installing warm floors in greenhouses. Without that positive shut off, hot water would always be slowly circulating.

A fellow boater suggested a parallel circuit, separate circulation pump and manual control switch, which seems cumbersome.

Does my scheme sound workable, or should I use the parallel circuit idea?

There may be better ways of plumbing these systems, but mine works like this: Hot water exits the boiler and passes through a circulation loop on the hot water heater, then to the heat exchanger on the engine, then to water/air exchangers in each zone. I could have installed a parallel circuit from the boiler to the exchanger and back to heat water in the water heater that bypasses the zones when the engine was running, but why bother? Easy enough to turn the hot water heater on and use 120 vac to heat water even when no zone is calling for heat, a.k.a. summertime. Seems simpler to me.

Here's another question: how does the hot water tank call for heat? Same way as a cabin heater, with some kind of demand signal to the circ pump? If so, then when on shore power, how does the water heater "choose" where to get the heat (or is it both?)

If the heater is powered by electricity, it uses a thermostat to heat the coils. You can put another thermostat on the water heater is you want to, so the boiler will fire when it calls for heat. But then you need a bypass loop from the water heater back to the boiler, and you're using a 40k Btu boiler to provide 5k Btu worth of heating. So, in summer, I just heat the water using 120 vac since after all, it is a water heater. Hope that helps.

 

[markrkrebs]

My experience is that the answer depends on what voltage your Kabola operates on. Initially, mine was 24 vdc, then had to be converted to 240 vac since the DC boards don't last with the voltage variations on a boat. When the controls were 24 vdc, the boiler would fire to maintain temperature in the water jacket. Once converted to 240 vac, it fires only when a zone calls for heat. I prefer the latter. If I understand your current setup, plumbing the heat exchanger back in series certainly makes sense, regardless of how the controller works, since engine heat does the work when underway, for free. If no zone is calling for heat, the circ pump isn't going to run, so you would rely on convection circulation, which I believe will work. In fact, stopping convection circulation prompted me to install electric ball valves in front of each zone loop which open when that zone calls for heat, which is what I did when installing warm floors in greenhouses. Without that positive shut off, hot water would always be slowly circulating.

There may be better ways of plumbing these systems, but mine works like this: Hot water exits the boiler and passes through a circulation loop on the hot water heater, then to the heat exchanger on the engine, then to water/air exchangers in each zone. I could have installed a parallel circuit from the boiler to the exchanger and back to heat water in the water heater that bypasses the zones when the engine was running, but why bother? Easy enough to turn the hot water heater on and use 120 vac to heat water even when no zone is calling for heat, a.k.a. summertime. Seems simpler to me.

If the heater is powered by electricity, it uses a thermostat to heat the coils. You can put another thermostat on the water heater is you want to, so the boiler will fire when it calls for heat. But then you need a bypass loop from the water heater back to the boiler, and you're using a 40k Btu boiler to provide 5k Btu worth of heating. So, in summer, I just heat the water using 120 vac since after all, it is a water heater. Hope that helps.

Thanks I really appreciate your reply. I think you are right and my setup should work. Considering yours it's interesting that the boiler fires on demand instead of on low temp. I guess that saves fuel when it's warm out, no zones want heat, and so why keep the boiler hot. Your plumbing seems less optimal though. Adding engine heat "downstream" of the boiler as in your setup will still make the boiler do most of the work even when the engine's running. Think if engines and boiler were at the same temp: the water would leave the boiler already hot and gain nothing from the heat exchanger. Or, maybe you have a way to turn the boiler off but still keep the circ pump enabled?

Meanwhile the problem with MY (proposed) setup is that, since the pump is inhibited by low boiler temperature, the boiler has to run first to enable the pump the first time. I need to disable the "low boiler temp circulation pump inhibit."

 

[Delfin]

Thanks I really appreciate your reply. I think you are right and my setup should work. Considering yours it's interesting that the boiler fires on demand instead of on low temp. I guess that saves fuel when it's warm out, no zones want heat, and so why keep the boiler hot. Your plumbing seems less optimal though. Adding engine heat "downstream" of the boiler as in your setup will still make the boiler do most of the work even when the engine's running. Think if engines and boiler were at the same temp: the water would leave the boiler already hot and gain nothing from the heat exchanger. Or, maybe you have a way to turn the boiler off but still keep the circ pump enabled?

Meanwhile the problem with MY (proposed) setup is that, since the pump is inhibited by low boiler temperature, the boiler has to run first to enable the pump the first time. I need to disable the "low boiler temp circulation pump inhibit."

I dug out the plumbing schematic I did up for the system and I misspoke. The heat exchanger on the CAT is last in line.

As I mentioned, when I switched over to 240 vac after the 24 vdc board went toes up, I questioned why the new circuitry only fired the boiler on demand. Most of the big systems I installed in greenhouses kept the water jacket temperature at set point all the time, as my Kabola used to do. However, in practice because the water volume is so small, firing on demand doesn't add much time to get hot water to the exchangers.

Curious, but what is the voltage your unit operates on, and how old is it? Never encountered the "low boiler temp circulation pump inhibit".

 

[sunchaser]

Meanwhile the problem with MY (proposed) setup is that, since the pump is inhibited by low boiler temperature, the boiler has to run first to enable the pump the first time. I need to disable the "low boiler temp circulation pump inhibit."

On our ITR system the aqua stat on the plate heat exchanger controls the on off for the hydronic circulating pump with boiler switch off. Opening and closing the on engine coolant loop valves to the now "hot" plate heat exchanger is essentially the hydronic system on/off with boiler switch off.

 

[twistedtree]

Thanks I really appreciate your reply. I think you are right and my setup should work. Considering yours it's interesting that the boiler fires on demand instead of on low temp. I guess that saves fuel when it's warm out, no zones want heat, and so why keep the boiler hot. Your plumbing seems less optimal though. Adding engine heat "downstream" of the boiler as in your setup will still make the boiler do most of the work even when the engine's running. Think if engines and boiler were at the same temp: the water would leave the boiler already hot and gain nothing from the heat exchanger. Or, maybe you have a way to turn the boiler off but still keep the circ pump enabled?

Meanwhile the problem with MY (proposed) setup is that, since the pump is inhibited by low boiler temperature, the boiler has to run first to enable the pump the first time. I need to disable the "low boiler temp circulation pump inhibit."

Re the boiler firing based on call-for-heat vs boiler temp, both approaches are pretty common, and many boiler controls can be set to operate either way. Delfin's obviously got changed as part of the retrofit. For a boat, I prefer firing on call-for-heat. Maintaining boiler temp seems more common in home units, especially when it's also used to heat domestic hot water. The idea is to avoid the longer heat-up time if you let the boiler temp drop.

 

[twistedtree]

Curious, but what is the voltage your unit operates on, and how old is it? Never encountered the "low boiler temp circulation pump inhibit".

That's another parameter that I've seen programmable in different boiler controllers. I think the idea is that with the circulator off, you can get an initial slug of water heated up faster. If you run the circulator, then you have to heat the whole system's volume of water.


Lots of systems also have lockouts on fans so they don't start blowing until the water is up to temp. Rather than blowing cold air while you wait for the temp to come up, you only start blowing once it will actually be hot air rather than cold.

 

[markrkrebs]

I dug out the plumbing schematic I did up for the system and I misspoke. The heat exchanger on the CAT is last in line.

As I mentioned, when I switched over to 240 vac after the 24 vdc board went toes up, I questioned why the new circuitry only fired the boiler on demand. Most of the big systems I installed in greenhouses kept the water jacket temperature at set point all the time, as my Kabola used to do. However, in practice because the water volume is so small, firing on demand doesn't add much time to get hot water to the exchangers.

Curious, but what is the voltage your unit operates on, and how old is it? Never encountered the "low boiler temp circulation pump inhibit".

Yah, firing on demand is better, I agree. Mine's 24V. By circ pump inhibit, I'm just using a term that makes sense to me. In the Kabola manual I find (section 5, Operating the boiler) reference to pumpstop thermostat: that's what I'm talking about. Thanks again.

 

[markrkrebs]

That's tricky, and excellent. That way you can just shut the boiler off underway.