How are evaporators sized?

[sluggish]

I know manufacturers base it upon number of taps. "Good for up to 50", or "good for 50-150 taps". Is this based on evaporation rate at a consistent heavy boil? Is it based on how much sap will run, on average, for a specific number of trees per day? Per week? Is a unit for 50 taps good for say 10gph? I don't get how it works.

Reason I am inquiring is that I plan to modify my current setup or build an evaporator for next year and I am curious about what size to go with. I was thinking that a 10-15 gph rate would be about right for me, I have 64 taps this year, will add a few more next year, but cannot get to over 100 where I am as I just don't have the trees.

I also currently have most trees fed into 5/16 tubing, gravity fed to collection barrels below. I would consider switching to 3/16 if it will get me more sap, as others have suggested, due to natural vacuum or something like that. May seem like an unrelated question, but if it affects the quantity of sap that I get, I need to build an appropriate sized evaporator.

Currently I am giving sap away to neighbours, and have dumped at least 3-400 gallons this year alone, as my current setup can only do about 3 gph.

Some input would be greatly appreciated. Keep in mind, this is a hobby for me, not a business. Investing in an RO system is not in any future plans. Wood is free and plentiful for me so I have no problem boiling from raw sap to syrup.

Thanks.

[motowbrowne]

Yes, having your taps on vacuum will greatly increase how much sap you will get. If you're going to use 3/16 tubing, how much vacuum you will achieve is dependant on how much elevation change you have from the taps to the collection point. If you've got 20' or more, you can pretty much count on double the amount of sap per tap on vacuum compared to buckets. If you've got more drop, you'll get more sap, up to about 40' of drop.

Once you know how many taps you have on buckets and on vacuum, you need to figure out what a normal run is for your location. A good rule of thumb is one gallon per tap, but it may be slightly different. Use your experience so far to help with this part.

Next we need to know how many hours you want to boil for. If you have a good run at 1 gallon per tap and want to boil for 6 hours per day we'll divide 64/6 and get 10.66. That number is how many j gallons per hour your rig needs to be able to cook to keep up with the sap you'll be collecting. Personally, I think oversized is better than undersized, so I'd be looking at something around 15-20 gph.

Good luck.

[sluggish]

I have about 40 feet at the top trees that I tap, with lines running down to the lowest ones, which would be about at the tank level where storage will be. Would 3/16 really make that much difference over the 5/16 line. Or is that figure of potentially doubling sap quantity based against buckets?

I would be able to do a 12 hour boil, I just don't want to do it every day. Maybe I need to think about bigger storage and focus my efforts to a unit that will evaporate closer to 20gph. I wonder how possible it is to get that out of an 18" x 60" evaporator. Guess I will find out. I plan to go with forced air into the unit, fully insulated and fire bricked, and a home made pre heater unit as well.

[maple flats]

With 3/16 tubing all taps at 20' or more above the outlet tank will have 20" or more of vacuum, those below that mark, have less but still have vacuum. 3/16 will generate natural vacuum because the sap does not pass the gasses in the line, whereas in 5/16 it is not the case. In the larger tubing the sap falls under the gasses and it it then hard to generate any vacuum, but with enough taps it can happen. In 3/16 it happens as soon as the trees flow enough to have a column of sap/gas/sap/gas etc. The current specs on 3/16 installation call for 25-30 or even 35 taps on a 3/16 line, thus with your current tap count you will want 2 lines of 3/16. Where you now collect, is it practical and possible to move the tank to even lower ground? If yes, it will give you more vacuum on those lower trees.
For evaporator sizing I'd suggest you make a 2' x 5 or even 6' unit, even if it is all flat pan. As a basic unit a 2x6 should give you about 18 gph evaporation. Then you could enhance it in the future with forced draft, pre-heater and a hood, each of which will gain more evaporation.
An 18x60 can get 18 GPH but not as a flat pan, you would need flues to add more heat exchange surface to get that.

[motowbrowne]

I have about 40 feet at the top trees that I tap, with lines running down to the lowest ones, which would be about at the tank level where storage will be. Would 3/16 really make that much difference over the 5/16 line. Or is that figure of potentially doubling sap quantity based against buckets?

I would be able to do a 12 hour boil, I just don't want to do it every day. Maybe I need to think about bigger storage and focus my efforts to a unit that will evaporate closer to 20gph. I wonder how possible it is to get that out of an 18" x 60" evaporator. Guess I will find out. I plan to go with forced air into the unit, fully insulated and fire bricked, and a home made pre heater unit as well.

Yes, 3/16 will make a huge difference. 5/16 with no vacuum and buckets are basically the same in my experience.

[sluggish]

Thanks for the great info. I can get the storage tank about 4-5 feet lower than it's current position, but then I will have to pump it back up to get to the shack. Or I could simply not use the lower ones on the line and use buckets for those few trees. I have all summer to map out a plan of attack as to how I run my lines next year.

Now to decide what to do with this 1500 feet of 5/16 tubing.

[Cody]

CDL has a t 3/16-3/16 to 5/16 for the drop line, thats what we did.Used all our 5/16 line for drops then you have a wider range of spiles.

[MISugarDaddy]

The general rule of thumb with a flat pan is 2 gallons of evaporation for every square foot of surface area. That is the optimum evaporation you are likely to get with a hot fire on a flat pan.
Gary

[lyford]

pretty sure the expected rate is closer to 1 g/hr

[sluggish]

So all this info makes sense to me, and is helpful, but the question remains. How do manufacturers determine the size of the unit. There must be some kind of standard that they go by as to determining how many taps a unit is rated for. Do they base it on a standard boiling day of 8 hrs at approximately 1 gallon of sap per tap per day? There must be some sort of basic formula and then the end user ultimately determines what is suitable for them.

For example, Assume 2 neighbours(Bill and Frank) each have 50 taps. If Bill likes to boil for 12 hour periods each day and Frank likes to boil only 6 hrs a day every second day, they would obviously need different sized evaporators if they want to start and end their season on the same day. In this case, Frank would need a much larger evaporator to keep up with sap flow since he is boiling less frequent, even though they have the same number of taps and assume the same sap quantities. This all makes sense in my mind but maybe I'm not explaining it properly(that happens a lot), so I am curious as to what the criteria is for manufacturers to give their evaporators a rating. Anybody know?

[wiam]

Not sure what manufacturers use for tap capacity. I would look more at evaporation capacity. And do the rest of the calculations myself.

[Big_Eddy]

So all this info makes sense to me, and is helpful, but the question remains. How do manufacturers determine the size of the unit. There must be some kind of standard that they go by as to determining how many taps a unit is rated for. Do they base it on a standard boiling day of 8 hrs at approximately 1 gallon of sap per tap per day? There must be some sort of basic formula and then the end user ultimately determines what is suitable for them.

For example, Assume 2 neighbours(Bill and Frank) each have 50 taps. If Bill likes to boil for 12 hour periods each day and Frank likes to boil only 6 hrs a day every second day, they would obviously need different sized evaporators if they want to start and end their season on the same day. In this case, Frank would need a much larger evaporator to keep up with sap flow since he is boiling less frequent, even though they have the same number of taps and assume the same sap quantities. This all makes sense in my mind but maybe I'm not explaining it properly(that happens a lot), so I am curious as to what the criteria is for manufacturers to give their evaporators a rating. Anybody know?

Years ago, the Atkinson's catalogue listed a sizing calculation in it.

It went something like

8 hour boiling day including 1 hour for startup and shutdown = 7 hours boiling time.
At 1 gpm / sq ft for average firing, this 2x4 flat pan evaporator is rated at an average of 8 GPH, or 56 gallons a day.
With an average yield of 1 gallon per tap per day, this evaporator is suitable for ~50 taps.


Reality is you need to do your own calculating based on whether you plan to boil every day or once or twice a week, whether your trees are on pipeline or buckets, and how many hours in a row you want to boil.

I don't think there is any standard used by manufacturers, but I would expect their assumptions for evaporation rates and hours per day are both towards the higher end of the spectrum.

There are a number of previous threads on selecting the "best" evaporator size for you. Hunt through the archives a bit if you're unsure what size would best suit you.

[Big_Eddy]

From their 2004 catalogue 14259

[sluggish]

These is the answer I was looking for on that label. Was just curios how they based their sizing, regardless of whether they overrate it to make the sale. Thanks Big Eddy

[jeugster]

Anyone know the expected gal/hour at a high vacuum?

[motowbrowne]

Anyone know the expected gal/hour at a high vacuum?

What do you mean?

Are you talking about how much sap you get from your woods when the trees are on high vacuum?

[jeugster]

Yeah, that's what I meant. How much sap does your system need capacity to handle with the expected sap flow.

In other words what GPH do size your capital equipment to handle when using high vacuum collection.

[motowbrowne]

Yeah, that's what I meant. How much sap does your system need capacity to handle with the expected sap flow.

In other words what GPH do size your capital equipment to handle when using high vacuum collection.

I think that depends on a few factors. Mostly, how much of your time is available for processing sap. Running high vacuum, you'd better figure on being able to handle 2 gallons per tap in a day. If you can process sap every day then you could get away with that much or maybe 25% more storage. More is better. If you can't cook every day, you'd better have lots more.

After that, it's just about sizing your cooker and or RO to deal with how much sap you've got in the time you have available.