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I am doing a bunch of mechanical room energy audits/physical plant reviews, and am seeing a whole lot of copper fin tube boilers (pick a brand) with multiple (as many as 4) stages. These appliances, in some cases, have 4 gas valves, but only two combustion zone pressurization fans. When only one burner is lit, the combustion efficiency is bad (excess air, cooling flue gas, high CO etc). That causes me concern, because most of these boilers spend most of their time on low burn, which doesn't look efficient on the combustion side.
The other thing that causes me concern is the basic design. You have a 2 pass copper fin tube heat exchanger, and regardless of which burner section (1 vs 4, or 4 vs 1) you set up as the lead burner, as the fluid passes through the combustion zone, it immediately flows through an unheated zone, giving up heat to the flue that was paid for.
Ideally, the burner compartments should be divided between the front and the back of the boiler, not left to right, or right to left. This way, the burners could be staged such that no unheated surfaces would see internal heat, nor lose heat to an unfired section.
As usual, in most cases, the appliances are grossly oversized, and this does cause issues with short cycling, and that short cycling is causing the staging controls to compound the problem of system inefficiency. Programming the controls to allow the full burner tray to come on during a call for heat increases the combustion efficiency, but compounds the short cycling inefficiency. (driving a tack with a sledge hammer)
Other than the obvious (replacement with a good mod con boiler) what can a person do with these beasts to make them more efficient (short of complete re-design from scratch on the manufacturers side)?
Tuning them is a given, but it seems to be a bandaid on a bleeding artery type of fix.
Thoughts and comments welcome. (including manufacturers)
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.