heat exchanger

DaveC

My question has to do with sizing a flat plate heat exchanger for a connection of an open outdoor furnace system to an existing closed loop system. I know how many btuh I need for the heat exchanger but what I'm not sure about is this: I sized the unit for a 30 degree delta t on the primary side. I sized the unit for a 30 degree secondary delta t. The unit is sized for full load btuh conditions. But... what will the output of the unit be if 1 zone is on (instead of 3)? Is there a calculation for the secondary output at different flow rates?
My thought is that the heat exchanger will transfer heat faster if the secondary flow decreases being as the primary side remains the same. So if I have a heat exchanger sized for 180000 btuh at a 30 degree delta t and I only have 1 zone on at 40000 btuh what will be the results on the secondary side?
P.S. The word "unit" above refers to the flat plate heat exchanger - not the outdoor furnace.

DaveC

heat exchanger

Any thoughts on this thread?

Ranger

Def'i.ni'tion

Fur"nace/n.An enclosed place in which heat is produced by the combustion of fuel,as for reducing ores or melting metals,for baking pottery,etc.;as,an iron furnace;a hot-air furnace;a glass furnace,etc.
Boil"er/n.An enclosed vessel in which water is heated and circulated,either as hot water or steam,for heating or power.

hr

I'd think

of the HX as an extension of the boiler. Really all a HX is doing is seperating two fluids. There is a bit of efficiency loss, through any exchanger, the tables and software show this.

If you only move 4 GPM through the B side the output would be 40,000 at a 20° delta t. The B side output would depend on how much you flow and the delta T. Of course you cannot get more out than you put in. Wouldn't that be nice!

Same with the boiler 130,000 output at max flow or any portion of that at lower flows.

Is this your question?

hot rod

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DaveC

Ranger

Actually the definition of boiler/furnace wasn't part of my original post, but I believe a heating vessel is considered a furnace if the heated liquid media is not pressurized (open system)<3psi. A boiler (closed system) is pressurized >3psi. At least this is what I always understood. Matt

hr

I'm not sure

exactly why those outdoor wood burners are commonly called furnaces. I've heard listings, or insurance reasons?

If you build a camp fire and suspend a kettle of water over it, have you built a furnace or a boiler?

Some of those outdoor units are just packaged, insulated versions of that example

hot rod

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DaveC

Hot Rod

Here are my parameters: 180000 btuh required at full load. I sized the exchanger at a 30 delta t an the primary and the secondary. So I need 12 gpm on the A side and 12 gpm on the B side at design conditions. Let's say that the flat plate is in series with 3 parraleled zone pumps. (you took out the oil boiler and put in it's place the flat plate). That would make 4 pumping scenarios. If all 3 pumps were on I would be at full load. If only 1 pump was on at say 3 gpm what would be the resulting B side output of the flatplate? Does this make sense? The A side would stay the same but the be side would change at partial load. My thought is that the heat transfer would improve due to the greater imbalance of flow from the A to B sides.
By the way this is not how we are hooking the system up. We are using parralel P/S. with the existing oil boiler. I was just curious about the flow/Heat transfer properties of the flatplate.

DaveC

furnace

I think it possibly does have to do with insurance/certification reasons. Correct me if I'm wrong about the furnace/boiler definition. Matt

DaveC

Hot Rod

Did you see my latest post in answer to your reply on 5/4.

Ranger

I stand corrected...

...it's just that the word "Furnace" being used in a question involving fluid medium just does'nt seem to sit quite right with me if you will....kinda like "My Buuurrnn- ham
Furnace" or my "Hot Water Heater".,See what I mean?!And I must admit I forgot about the "Vessel Under Pressure" deal.
So I once again I must state that I stand corrected,Matt.I re-learned something today.I just hope I have'nt offended "The Spelling Guy".And I am also sorry I can not formulate an intelligent opinion to your origional question.So I must bid you good day sir.