Adding a boiler or two to a single zone monoflo system, simplest setup?

[Dune]

Present situation: Oil fired boiler, online, unused, homemade wood fired boiler, in parralel, suppling heat.
Plan: install WVO fired diesel gensett for cogen and utilize existing baseboard system to distribute heat, using wood boiler as supplement. Eventualy I plan to intergrate a second cogen, burning wood gas.
Originaly I had planned to install the diesel genset in parralel to the existing boilers and run the engine coolant through the heat loop, with a small modine in the garage to dump ecxess heat. My brother who is a master plumber and hydronic/steam heat expert informed me that this was not a good idea, and that I should use a heat exchanger. Since I am making the system so much more involved and complex anyway, and the return on my investment should be much greater now, I am considering a primary/secondary style, with storage.
My questions to you are; 1. Is it true that I cannot run engine coolant in my baseboard system or nontoxic antifreeze in my engine?( I really don't want an antifreezed heating system any way)
2. What is the best primary/secondary loop design considering I will eventualy have four boilers online? The original Weil- Mclean will never be run by me.
3. How do I calculate how many gallons of storage is nessasary?
4. Is storage nessasary or even advisable? I will only be running the Co-gen system when I have free WVO, otherwise the wood boiler will heat the house.
5. Is there such a thing as too large a heat exchanger? I have a heat exhanger that I know is much larger than needed to cool the diesel engine. I will have to bush the ports down and also throttle the flow with a ball valve. My brother thinks a should use a propely sized H.E., but I don't see why it would matter.
Any and all comments/suggestions greatly apreciated. Thankyou.

 

[Nofossil]

This seems like a good example of a system that's complex enough to make primary/secondary the approach of choice. Give each heat source and load loop a circulator that provides the desired flow and temperature delta - multi-speed circs make it a lot easier to tune.

I'd use a standard automotive thermostat in the diesel to maintain coolant at the design temp. I'd also agree with using a flat plate HX between the diesel and the hydronics.

Storage helps if you ever have a situation where the most efficient heat output is greater than the heat load. Storage is sized by calculating your BTU load during the period of time you'd like to heat from storage - typically 12 to 24 hours, though there are installations that have higher and lower capacities. You also need to know 'Delta T' - the operating temperature range for storage - the difference between the maximum easily achieved storage temp and the lowest useful storage temp.

Size in gallons = btu load for period / 8.3 / deltaT

 

[ssupercoolss]

now thats some heavy duty thinkin right there. however, things to keep in mind are, 1. antifreeze is actually good at disapating heat, like better than water, thats 1 reason we use it in our cars. i think the antifreeze may not be as effiecient as plain water. 2. a leak in this system will have your house smelling like my shop. 3. a leak in this system could destroy your expnsive diesel engine, with out the proper cut off switches.

 

[Gooserider]

now thats some heavy duty thinkin right there. however, things to keep in mind are, 1. antifreeze is actually good at disapating heat, like better than water, thats 1 reason we use it in our cars. i think the antifreeze may not be as effiecient as plain water. 2. a leak in this system will have your house smelling like my shop. 3. a leak in this system could destroy your expnsive diesel engine, with out the proper cut off switches.

Not quite FB... Antifreeze is actually LESS effective as a heat transfer fluid than plain water. If you look at the stuff on designing a hydronic system you will even see that some of the design factors are different because of this. The primary reason we use it in cars is in the name - it keeps engine blocks from freezing solid and getting damaged in the winter. As an added advantage, it slightly raises the boiling temperature of the coolant, which gives an added margin of boilover protection to engines in hot climates, and allows a slightly higher normal operating temperature...

In answer to the OP, you definitely don't want to be running automotive antifreeze in your house system. I'm not sure what restictions might be on running hydronic antifreeze through an engine, and I can't think of any real reason to object to running the same water through both if water is an option from a freeze standpoint - however I might be missing something. Nonetheless, it probably wouldn't be a bad idea to do some isolation with a heat exchanger. IMHO Heat exchanger sizing is a function of how many btu's / hr you need to exchange, and the temperature differential. Seems to me like it would be hard to oversize an exchanger, although it is easy enough to undersize one. The only problem with a larger than minimum exchanger is that you might suck too much heat out of the source and cool it below optimum operating temps, which is why NoFossil was suggesting an automotive thermostat on the engine and the use of variable speed circs in order to throttle the heat flow.

Gooserider

 

[Dune]

Thankyou for your thoughtfull replies. As I begin the installation this ummer, I am sure I will have more questions. I hope to be running the meter backwards by December.