Anti-freeze

ed broderick

Iam planning on adding a buffer tank to my small (glycol) content boiler. I have 4 Questions I need help with:
1. Brands - which are suitable for glycol? Dan's books make reference to Ergomax. Any ideas?
2. Advantages or disadvantage to tanks with DHW coil inside
or water flow outside of the tank? (Currently Iam using alternate means for DHW, so this is not an issue)
3. Proper Sizing of Tank - Existing boiler holds 10 gallons, system has 10 gallons for a total of 20. Is there a formula? Is Smaller or Larger capacity better for efficiency?
5. By adding the buffer tank, do I need to increase the size of my expansion tank?
Appreciate to all the Pro's who can help, you guys are the best form of training around. Thank you once again.

hr

Some ideas

As far a suitable for glycol. Are you are using inhibited hydronic system glycol, and plan on checking and maintaing the fluid? If so any tank rated for the temperature and pressure will work. Plain steel would work, glass lined HW storage tanks, or on the high end stainless steel tanks. The important thing is the insulation jacket. The more the better when storing heat!

Actually storing your btus in the form of heated water, you would be better off with a well insulated tank as opposed to the boiler. Rarely will you find a gas or oil fired boiler insulated on all sides with the R values that you find in a well insulated tank.

All gas fired boilers need a flue somewhere, and they all need a place for combustion air. As such there will always be standby and flue loss. Sealed combustion helps. Vent dampers help. Still no where near a tank surrounded on all sides by 2 or 3" of foam and jacketed in steel or vinyl.

If you are looking for a way to generate DHW from your heat source than an indirect tank me be a good choice. A bit more money, a little more involved to pipe and wire and hard to extract heating side temperatures with out going below your minimun dhw temperature requirement.

The size of the buffer could be calculated by using this formula. What this is doing is baseing the burner on cycle, balanced against heat extraction from the smallest zone (btu wise)

Yes you may have to increase the expansion tank size. Do this by adding additional tanks as opposed to replacing you current one. Assuming you have a bladder type tank. The expansion tank reps opr manufactures will be able to assist you with the correct size based on your system capacity, temperature, fluid type and pressures. I've never sized an expansion tank to large, if that helps

This is a formula from one of John Siegenthalers columns in PM magazine. For a 10 minute burner run time with a 5,000 BTU/ hr. load, using a 140-180 degree differental.

For a 30% glycol solution use a 479 constant and 450 for 50% glycol, as antifreeze solutions absorb less heat than pure water.

I am in the middle of a job that will both take advantage of a deep delta T, post purge the boiler, and a well insulated buffer tank. I'll keep the list posted.

This link may help you with some clever control logic.

http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,88522,00.html

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ed broderick

Buffer Tanks

Thanks for the great information. Are Superstor tanks well insulated and stainless? I will make some calls tomorrow using your advice.