preheater question

[KReinisch]

Can you just set a homemade copper preheater over the flue pan without a hood and still preheat enough. I don't like the idea of a hood but want to preheat a little.

Thank You!

[Pibster]

You would warm the sap slightly but I doubt it would be worthwhile. You would still need drip trays under the pipes. The hood helps force the steam around the copper pipes and greatly increases the sap temperature. My preheater normally heats the cold sap to around 170 degrees.

[maple flats]

Don't fight a hood. They help get a faster boil even without a pre-heater. Then a pre-heater can do lots more. A preheater without a hood will do very little. When you make or get a hood, set it up with cables and pulleys to lift it for cleaning. The hood needs a condensate gutter around the inside to carry off the water that collects as well as what drips off a pre heater.
My last pre heater brought cold concentrate up to between 180-190 once the boil got going full speed. I'm just building a new one trying to get that up even better before next season. You not only want a hood, but you want a damper in the hood stack to control the steam better.

[KReinisch]

You getting rid of your old hood?

[maple flats]

I sold my old homemade one to the guy who bought my old set of pans shortly before I went to pick up my new ones.

[KReinisch]

There is a hood on craigslist for a decent price. Its a bit bigger that my 3x8 but I was thinking of suspending in about 4 foot over pans. Will that still work?

[wiam]

Hood needs to be pretty tight on the pan to be very effective with a preheater.

[maple flats]

If you really don't want a hood (however I can't see the reason) you might want to make one like Johnny Cuervo made years ago. Search out the post where he describes how he made it.
While Johnny Cuervo has not been active recently on the trader, his post and pictures on his preheater was great. It used the stack, but was fully adjustable for temperature. by the use of springs to get more or less contact with the hot stack.
Lately I think Johnny has been designing maple equipment and a friend produces it. They have been at the Verona Winter Conf. selling tap pullers and other items.

[pdr]

Preheating makes common sense, of course. Any studies on just how much it improves boiling efficiency?

[jrgagne99]

If I remember correctly, of the total energy required to boil 1 gallon that starts at 40F, 25% is needed just to bring it from 40F to 212F. So i think the upper limit on efficiency improvement is 25%. A steam-away can give you 75% or more, due to the agitation of the hot sap bath. Think of a stagnant jacuzzi vs. a bubbly jacuzzi. The bubbly one has a lot more steam coming off. A pre-heater is a lot like a stagnant jacuzzi with the cover over it. No steam can escape. Steam-away is the way to go.

[cncaboose]

Don't let these guys convince you that the pre-heater is worthless without a hood. I have one made using 4 parallel baseboard fin tube pipes. Does it heat the sap as much as the hood set up? Nope. Does it make a noticeable difference? Yes. I spent $100 on it 7 years ago and I know that it has paid for itself several times over in saved firewood with virtually no maintenance. Key points: you must have drain trays under the tubes to catch the condensation and run it off outside the evaporator; you really need to have it set up with a drain valve so you can drain it on sub-freezing nights, unless you have a heated sugarhouse. I really like hearing, seeing, and smelling my sap boil, so no hood for me.

[KReinisch]

Do you have any pictures of that pre heater. I have had thoughts of building one. Thank You!

[Pibster]

If I remember correctly, of the total energy required to boil 1 gallon that starts at 40F, 25% is needed just to bring it from 40F to 212F. So i think the upper limit on efficiency improvement is 25%. A steam-away can give you 75% or more, due to the agitation of the hot sap bath. Think of a stagnant jacuzzi vs. a bubbly jacuzzi. The bubbly one has a lot more steam coming off. A pre-heater is a lot like a stagnant jacuzzi with the cover over it. No steam can escape. Steam-away is the way to go.
I see that you made your own steamaway, was it difficult to build? I would have a steamaway in a heartbeat if they weren't so expensive. There is another thread started a couple of weeks ago on plans to build a steamaway but nothing really posted yet.

[cncaboose]

I can't seem to get my photos into the post. If you send me an email at cncaboose@gmail.com I'll email you some photos. Ian

[TimJ]

Preheating makes common sense, of course. Any studies on just how much it improves boiling efficiency?

I'm pretty sure the most referenced study shows 15% efficiency gain with a preheater and hood.

http://www.fs.fed.us/ne/newtown_square/publications/research_papers/pdfs/scanned/OCR/ne_rp388.pdf

https://www.uvm.edu/~uvmaple/sappreheaters.pdf

[TimJ]

Don't let these guys convince you that the pre-heater is worthless without a hood. I have one made using 4 parallel baseboard fin tube pipes. Does it heat the sap as much as the hood set up? Nope. Does it make a noticeable difference? Yes. I spent $100 on it 7 years ago and I know that it has paid for itself several times over in saved firewood with virtually no maintenance. Key points: you must have drain trays under the tubes to catch the condensation and run it off outside the evaporator; you really need to have it set up with a drain valve so you can drain it on sub-freezing nights, unless you have a heated sugarhouse. I really like hearing, seeing, and smelling my sap boil, so no hood for me.

what is the temperature of the sap coming out of your non-hooded preheater?

[MISugarDaddy]

On my previous 4' drop flue evaporator I made a 7 tube preheater out of 3/4" copper that I operated without a hood and it would heat 32 degree sap to 105 degrees.
Gary

[cncaboose]

Temp of preheated sap for me varies a LOT, depending on sap temp going into the preheater and the sap flow rate.