burnclean said:
If you have a thermal storage system and don't like to have a back up in place, do you load more often than needed and how does the system handle this? I.E. My house is calling for heat and my thermal storage is down to 140degrees, I load up my unit and burn a full load of wood. Now its 9 at night and I know I'll probably need more heat than what is left in the storage tank sometime during the night, so I put another full load of wood in the unit and let it burn. But I can't store all that heat, so what happens? Is there a aquastat on the wood boiler that will shut it down until the thermal storage can accept heat again or is there a high limit that simply shuts down the wood boiler completely until I manually relight it? What happens when you have excess heat?
Thanks for your help.
A few basic concepts with storage:
Number 1 thing to understand is that storage disconnects the btu output of your boiler from your actual load, which of course can vary from less than 10K to whatever the maximum is for your house. This allows the boiler to work at its most efficient level while still allowing for the variation in your heating load.
Number 2 thing to get a handle on is that if you have storage you heat from that rather than the boiler itself. The storage becomes the btu accumulator and distributor all in one package. The boiler is merely the heat or btu source.
Number 3 thing of great importance is that if the heat emitters in your house will only provide adequate heat at 170-180*+, the usefulness of your storage is greatly reduced. If you have a heating system designed to provide sufficient heat all the way down to 140* or less your storage will give you much longer duration between firings. (think panel rads @ 140 or radiant floor @110*)
Now...all that being said, one would seldom find himself in the predicament you described if the storage was sized to meet the house load for a predetermined amount of time. In other words, correct system and storage design would take into account that under worst case conditions you would need xx,xxx btu's per hour. If you want to fire your boiler every 12 hours you would simply multiply the load x 12 to find out how many btu's you need to store. (in many cases this will be from 1000-1500 gallons for a typical house)
Let's work it backwards using the following assumptions: you have 1000 gallons of storage, the building load is 50,000 btu/hour and the heat emitters in the house will perform adequately down to a temp of 140*. We will also assume that you can drive the storage tank up to 190* which gives us a 50* swing to work with. Using the basic btu formula we see that (1000 x 8.33 x 50 = 416,500 btu's) available from storage. Then it's just a matter of dividing that total by the assumed load of 50,000 which shows we can work from storage with no input from the boiler for a period of 8.33 hours. If we go to 1500 gallons of storage we can now draw from it for 12.5 hours using the same parameters.
Once you know those things and have developed a "feel" for your heating system/boiler you will easily be able to make the decisions you are talking about without even thinking twice about it. It becomes less a matter of the boiler and its operating controls and more a matter of properly sizing your storage and learning the fueling habits needed to accommodate changing seasons and building loads.
Sheeesh........why can't I ever give someone a simple answer.........
simple answer: yes your boiler would have a high temperature shutdown that would begin to cycle it off/on once the boiler setpoint is reached.
