why is temp stratification better in layers and not the whole tank hot as possible one would think if tank was all 180 vers top 180 middle 170 and bottom 155 it would hold more btu's I don't know? help
The goal most times when batch burning a wood boiler with storage is to charge the tank top to bottom at what point the boiler is out of wood and goes out at what point you are then coasting on the tank for the next number of hours maybe a day or more depending on the size of the tank and the heat load. If the tank is not over pumped during the pull off ie. just pump what is needed for the load and return as cold as possible the tank still remains quite hot at the top and the colder statification line moves up thru the tank. If the tank remains well stratified the hot water at the top is more "usable" than if the tank was mixed and ended up with a lukewarm mixture. This can be most helpful for someone using a baseboard fintube heaters that typically transfer best with hotter water or if you are charging an indirect domestic hot water tank. Following is a link to a 5 minute power point video showing a typical burn cycle for someone batch burning a boiler with a loading unit pump and utilizing a storage tank. It is a visual that demonstrates how stratification works.
sorry guys I have an old system from 2003 its a non pres system called sst usind 2 coils in a rubber bladder I send picts today sorry markwhy is temp stratification better in layers and not the whole tank hot as possible one would think if tank was all 180 vers top 180 middle 170 and bottom 155 it would hold more btu's I don't know? help
thanks a lot for the infro I must think on it a wile my srorage is no psi with 2 coils for heating up the tank and 1 for taking out the heat I think it called the sst typeOur storage is 1046 imp gallons with the tank laying horizontal . So from bottom to top its height is 54 " . On charging ,the bottom temperature can achieve a maximum temperature of 185 F but more typical would be 180 F , with the top temperature maximum of 195 F. As the storage cools it stratifies at consistent differential of 20 degrees , between the top and the bottom .
In this system the boiler and storage share the same water ,but only with static pressure ( open to atmosphere expansion tank on the floor above ). There are two copper coils inside the storage one for dhw and the second for heat ,these coils are 8" from the top of the tank extending the storage's total 110" of length for good heat transfer. The charging pipe from the boiler enters the tank at the top from one end, 36" from the charging pipe there is a baffle that the coils rest on this baffle extends down into the storage 16" . If the storage temperature is low when you start to recharge this 36" space plus the remaining top 8" heat very quickly giving you a readily available heat or dhw . This setup eliminates the need to have the boilers output switched from storage to the house if the storage temperature is low , and secondly no water has to be circulated an outside the storage for dhw or house heat loads . Though storage is horizontal this set up allows for good stratification .
For the short time I've been on "Hearth " this system is definitely not typical ! But has worked with no problems for over 30 years .
To get a huge delta T like this requires a lot of thought (and likely a radiant slab), but it's by far the most effective way to use storage.
True, but in many cases slowing down the rate of circulation creates hotter and cooler areas in the structure. Not good for a long baseboard loop, for instance. I've toyed with the idea of introducing a charge of hot water from storage into a baseboard system, then recirculating it at relatively high speed until it's cooled down, then returning it to the bottom of storage. That would only work if you had plenty of excess baseboard output capacity, but would maximize stratification.Swapping out ones 'conventional' circulator for a new Alpha or Bumblebee can alleviate a lot of that thought burden. 'Bigger Delta T For Dummies'. Yours truly included.
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