Any other Memco users?

Joecool85, Where are you in central Maine? I too am in central-eastern Maine (Bangor area) I had a Memco wood boiler for 10 yrs. and just replaced with an Eko 40 this year. The Memco is a well built boiler, but not the most efficient boiler out there. You will get 5-7hrs burn depending what type of wood you are burning. You would definitely benefit from storage. I have a fare amount of experience with the Memco if you want to pm me. I have helped install three of them.

With pine you will be more like 2-3 hrs. If your heart is set on the Memco call Melvin Manufacturing in Jay, Me. They still have the parts and can send you an original owners manual. It has some very good piping layouts to give you an idea how you would do an install. You can get a motorized damper, but I never used one. I ran mine closed up and it burned very clean. They like wood, lots of it! An older Tarm from the same era is more efficient, but I understand the price is right for the Memco. I ran one for ten yrs because the price was right and I have my own wood. Start out with the Memco and upgrade when you can afford. They weigh close to 1,000 lbs.

Howdy, My first unit was a Memco. it puts out plenty of heat but it burns a ton of wood. I heat roughly 2200 sq ft not the best insulated and the ole memco would blow us outta the house because at the time my dump zone was my heating zones. A tank would really help with that issue. That said, I rarely got more then 4 hours burn time. If yours come with the shaker grates , you may want to consider running coal, unless you have your own wood lot... I think if you invest in an accumulator (thermal storage) tank, it will be well worth the investment... There is a fellow on this web site that sells them. His prices for the 820 gallon tank are very fair IMHO. http://www.americansolartechnics.com/ Ironically he is in Maine too...hope that helps... oh BTW, they do come with a self regulating damper that keeps the water temp surprising close to set point...

No experience with a Memco, but I may have a manual kicking around the house if you dont have one.

Any reason you want to go with the heat exchanger. The Memco is a pressurized boiler, why add the expense and eff. loss of a heat exchanger. And like everyone has stated they are very well made and work well but do like the wood.

He is right, the flat plate makes no sense. You would only do that if you had an outdoor unpressurized boiler. Get a manual and study some piping diagrams from various sources and it will make more sense to you. By the way, pressurized storage rocks!

joecool85 said:

BRL said:

Any reason you want to go with the heat exchanger. The Memco is a pressurized boiler, why add the expense and eff. loss of a heat exchanger. And like everyone has stated they are very well made and work well but do like the wood.

Click to expand...

I don't like the idea of tying it into my system when it is going to be 30' away from the house in a shed.

I suppose if someone convinced me that it is safe and showed me how to plumb it, I'd consider it.

This is what I'd be tying into:

Oil fired boiler, two zones (3/4" pipe each, supply/return on boiler is 1 1/4") each zone has a pump that only kicks on when heat is called for. DHW has it's own coil.

Click to expand...

As long as you do the plumbing right, the only downside of having the boiler in a shed away from the house is that you have to deal with the increased head resistance of the longer pipe run...

Is the DHW coil in the existing fossil boiler? If so, that will mean that you'll either need to do a series type hookup and run through the fossil boiler with the wood boiler output, or (probably better) get the DHW off the fossil boiler and make it a third zone with a sidearm or flat plate HX going into a storage tank...

Gooserider

joecool85 said:

Gooserider said:

joecool85 said:

BRL said:

Any reason you want to go with the heat exchanger. The Memco is a pressurized boiler, why add the expense and eff. loss of a heat exchanger. And like everyone has stated they are very well made and work well but do like the wood.

Click to expand...

I don't like the idea of tying it into my system when it is going to be 30' away from the house in a shed.

I suppose if someone convinced me that it is safe and showed me how to plumb it, I'd consider it.

This is what I'd be tying into:

Oil fired boiler, two zones (3/4" pipe each, supply/return on boiler is 1 1/4") each zone has a pump that only kicks on when heat is called for. DHW has it's own coil.

Click to expand...

As long as you do the plumbing right, the only downside of having the boiler in a shed away from the house is that you have to deal with the increased head resistance of the longer pipe run...

Is the DHW coil in the existing fossil boiler? If so, that will mean that you'll either need to do a series type hookup and run through the fossil boiler with the wood boiler output, or (probably better) get the DHW off the fossil boiler and make it a third zone with a sidearm or flat plate HX going into a storage tank...

Gooserider

Click to expand...

I'm not worried about the head loss, I have a pump all picked out to run from the boiler. The plan was to have it run 24/7, if I pipe it direct into the system would I need to do that?

As for dhw, for right now I am going to let the oil take care of it, but I do plan on using an electric hot water heater as a tank so in the winter I can use the wood for dhw and in the summer I can use electricity.

The Memco only has a 50 gallon jacket, would 30 gallons of pressurized storage help at all? I have an old water heater available - tank is great, but the coils are bad...

Eventually I wouldn't mind adding 200-500 gallons of pressurized storage but I really don't have the money for it right now.

Click to expand...

Head loss can be a critical issue - especially in terms of running the right size pipes... If you do a search, you will find many tales of woe from people that undersized their lines because they didn't run the math on pipe sizing, and followed the bad advice from local OWB dealers - and as a result had a big boiler out in the yard that either couldn't get enough heat to their house at all, or were forced to use an oversized and power hungry pump in order to do it - I can't recommend strongly enough that you look up the Taco technical paper on pump sizing mentioned in the "tidbits" sticky and go through the math in it to make sure you are actually picking the right size pipe and pumps - remember that the underground lines are normally the most expensive part of the project aside from the boiler itself, and are one of the hardest parts to change if you get them wrong...

One of the things that I do strongly recommend is putting a couple of empty 3/4-1" conduits in the trench along with the lines, as this gives you the ability to run various low voltage and or power lines to / from the boiler site for more flexibility (put in TWO conduits, as you can't put low voltage and power in the same one...)

There are many folks that do run the boiler pump 24/7, but I feel this can often be a bit of a waste of energy - it can be argued that it is better to only run the boiler pump when you actually have a call for heat from the house.

Expanding the DHW system at a later time is not a bad idea, just be sure you plan the proper hookups for it, as that will save time and effort later.

30 gallons of storage will do little or no good, as it will store only a tiny amount of heat - assuming even a 60°F temp swing, 30g x 8lbs/g = 240lbs of water x 60BTU's / lb = 14.4kBTU's worth of storage - if you have a fairly typical 60kBTU/hr heat load, that works out to about 15 MINUTES worth of heating - hardly worth the effort... OTOH 500g x 8 = 4,000lbs x 60 = 240kBTU or about 4 hours worth of heat, going to 1,000 gallons doubles that to 8 hours... These are the kinds of times that make storage really worth while...

However the money to pay for it issue is always a factor, so this is another case where our usual advice is to put in the hookups to do storage for now, but wait a year or two for the money to get better before actually installing it.

Gooserider

There are two factors that go into looking at the flow of liquid through a pipe - flow velocity and flow volume. Flow volume is the GPM, or how many gallons of liquid move past a given point in a minute, Flow velocity is the speed, usually in feet per second, that a given drop of water travels through the pipe. The two figures are inter-related, for any given diameter of pipe, the flow velocity goes up as the GPMs go up. For a given flow velocity, as the pipe size increases, the GPM's increase. For a given GPM, as the pipe size increases, the flow velocity decreases. IOW, bigger pipes either move more volume at the same speed, or the same volume slower...

Another factor that comes into play, is the friction of the pipe, or how much resistance it offers to water flowing through it - this goes up dramatically as the flow velocity increases - meaning that past a certain point, the resistance goes up such that big increases in pump pressure give only minor increases in flow velocity or volume. When the flow rate gets into this range, you start getting noise from the fluid flow in the pipes and issues like water erosion on the insides of fittings and the like....

The desired flow velocity in a hydronic system is between 2 and 4 feet per second - slower doesn't do a good job of pushing any bubbles that form in the system down the pipes to where they can be eliminated, faster starts getting into the excessive energy requirements, noise, etc. problem range.

What happens if you set your Grundfos depends on the head resistance of the circuit that you are using, essentially if you figure out the "equivalent pipe length" of your circuit you can calculate a "head loss curve" for your circuit that will look very much like a pump curve, but going in the opposite direction - the head loss will be low at low flow velocities / volumes, and go up as the flow increases. If you plot that curve on the same chart as the pump curves, the flow will be what you see at the point where the two curves intersect... If you do this, you will probably see that there isn't a big increase in the flow volume between the different speeds... IOW you get a little more flow, but burn a lot more power...

The numbers as I've been punching them in assuming an equivalent pipe length of 120' (60' for the piping, and 60' for the equivalent fittings) suggest that you'd have about 10' of head @ 7.5gpm and a lot less at lower values - I would suggest seeing if the pump at lower speeds would still be moving more than you need, and look for the smallest pump that will move just enough volume to either give you the recommended 2fpm flow velocity, or the minimum amount of heat you need to keep you warm - remember, the smaller the pump, the less visible it will be on your electric bill - if you look at your pump for 8 hours a day, at 60 watts it does .48KWh, at 89 it does .712, so you save .23KWh a day, or just under 7KWh for a 30 day billing cycle - at $0.15/KWh, a dollar per month, etc. If you can get it down to a 30W pump, the savings get bigger, and remember that electric rates are probably not going down any time soon...

Gooserider

I assume the red and blue lines off the oil boiler at the top of the page come together somewhere outside the picture? If so, it looks like it should work fine given that you need to have some flow through the oil boiler for the DHW coil. I don't think you need two check valves though, I think the one on the return side of the wood boiler is all you need.

There is a slight potential for "ghost flow" through the wood boiler when it isn't running, but I think the oil boiler should be enough lower flow resistance for that not to be an issue. If it was, you might need to put a zone valve on the wood boiler line in order to force the flow through the oil boiler. (If you didn't need flow through the oil boiler, I'd be tempted to say put a ZV on the oil boiler as well, but...

The only issue I see is that you might get some odd flow patterns through the oil boiler depending on just how the flow rates of the wood and zone pumps combine and depending on which zones are running - you are doing sort of a weird form of primary secondary pumping, and depending on how the pumps combine could get flow through the boiler in either direction, which might have an impact on the DHW coil - It might be necessary to arrange the controls to cut off one or both zone pumps on a call for DHW heating if you don't get enough hot water flow through the boiler.

Gooserider

joecool85 said:

Gooserider said:

I assume the red and blue lines off the oil boiler at the top of the page come together somewhere outside the picture? If so, it looks like it should work fine given that you need to have some flow through the oil boiler for the DHW coil. I don't think you need two check valves though, I think the one on the return side of the wood boiler is all you need.

There is a slight potential for "ghost flow" through the wood boiler when it isn't running, but I think the oil boiler should be enough lower flow resistance for that not to be an issue. If it was, you might need to put a zone valve on the wood boiler line in order to force the flow through the oil boiler. (If you didn't need flow through the oil boiler, I'd be tempted to say put a ZV on the oil boiler as well, but...

The only issue I see is that you might get some odd flow patterns through the oil boiler depending on just how the flow rates of the wood and zone pumps combine and depending on which zones are running - you are doing sort of a weird form of primary secondary pumping, and depending on how the pumps combine could get flow through the boiler in either direction, which might have an impact on the DHW coil - It might be necessary to arrange the controls to cut off one or both zone pumps on a call for DHW heating if you don't get enough hot water flow through the boiler.

Gooserider

Click to expand...

How's that affect the dhw coil? Also, yes, the blue and red pipes at the top go to the baseboards in my house.

If you have a better plumbing layout, please feel free to share.

Click to expand...

OK - the only reason to want flow through the oil boiler at this point is because it has your DHW coil in it, so it is sort of an additional zone...

The water flow through the oil boiler (OB) is going to be a function of the difference in the flow through the two zones, and the flow through the wood boiler loop (WB).... Lets look at some cases:
1. If the zone pumps are off, all the flow goes through the OB.
2. If the flow through the zones is exactly the same as the flow through the WB, then there will be NO flow through the OB.
3. If the flow through the zones is LESS than the WB flow, then the difference will flow through the OB, going from supply to return.
4. However if the zone flow is GREATER than the WB flow, then you will see the extra return water flowing backwards through the OB where it will mix in with the supply from the WB and make a second trip through the zone loops (this will cool the water flowing through the zones as well...)

How does this affect the DHW coil?
#1 should be no problem, the coil is getting the entire output of the WB.
#2 is a definite problem, as the coil will only see whatever heat is in the boiler, so you need to kill one or both zone pumps in order to get case 1 or 3. (you might also need to look at control setups to keep the boiler from firing in this situation)
#3 is probably not a problem, depends on just what that flow is, and if it's enough to supply the DHW heat demand. Unless you have a really high demand, or the flow is real low, probably not an issue. If it is, cure is same as for #2.
#4 might be a problem depending on the temperature of that return water, and whether or not it is still hot enough to satisfy the DHW demand - again, if it is a problem, same cure as #2....

In terms of what I'd do about it for alternative piping diagrams - my first choice would be to get the DHW out of the boiler and into a 3rd zone, as I've mentioned before, and then get rid of the flow through the boiler unless it was actually firing. Given that you don't want to do that at this time, I don't see any real problems with what you have. (Which isn't to say that some of our other posters might not have other ideas and suggestions...)

Gooserider

joecool85 said:

The goal is to have it be that the oil will kick on if the boiler temp gets below 140 or 150, so the house stays warm even if the fire goes out. This is why originally I wanted to have a plate hx at the return of the oil furnace.

Click to expand...

Agreed, if the reason for the oil boiler being cold is that the wood boiler is... However if you have a situation like case 2 where the house is fine and the wood boiler is hot, there just isn't any flow going through the oil boiler, then there is no point in it firing... This is NOT a hard problem to solve - at a minimum all it can take is an open on rise aquastat located where it can sense the temperature coming from the wood side. Run the wire that controls the OB firing through that aquastat, and if the wood side is hot, the stat opens and keeps the OB from seeing the fire signal. If the wood side is cold, the stat closes, and the OB gets the call to fire. One can get fancier if desired, and have more delicate and adjustable control function (See some of the other threads here on system monitoring and control...) but this is essentially what any of them do...

Gooserider

joecool85 said:

I figured the wood boiler would be set to maintain 160-180F and the oil would be set 140160F or so. The house would draw from the oil boiler all the time, but since the wood boiler circuit runs through the oil boiler (keeping it hot while the wood is burning), everything would work.

Am I completely wrong here?

This is making my idea of using a hx sound much more appealing all the time as I know that would work since it is how OWB are plumbed.

Click to expand...

First off, you REALLY don't want to use an HX if you can avoid it! HX's cost efficiency because you can't get the same temp on the output side as you do on the input side... They use them one OWB's because OWB's are almost all non-pressurized, and most fossil based hydronic systems are, and benefit from being kept that way, so you need something to go from the non-pressurized OWB side to the pressurized house side... The other time an HX should be used is if there are different "chemistries" involved - i.e. you have part of the circuit that needs to be running glycol antifreeze for some reason, and don't want to run it in the entire system (lots of good reasons to avoid glycol...) However if possible you are FAR better off to run the entire system pressurized and ditch the HX.

Now your idea of running everything through the boiler is fine, aside from the issue of heating the unused boiler, which I would like to avoid, but you don't seem to mind, and would work as you described - but that isn't what you DREW in the picture above... What you drew has the two boilers in parallel, so the house will draw from which ever one offers the lowest resistance to flow - if the WB pump is running it will suck up all the water returned by the zone pumps and send it through the WB, and maybe some surplus will flow through the OB, and maybe it won't, depending on how the pump volumes interact - as I described...

If you DO insist on all the water flowing through the OB as you mentioned, you need to make the two boilers and the house loads all in series, so that all water flows through all the plumbing. This would definitely require you to control the WB pump to match the zone pumps or you would be pushing water through the zones any time the WB pump is running, whether they want it or not (You might even have a problem if only one zone pump was running...)

The other downside is that if the WB is out and the OB fires, you'd be circulating water through the WB and heating it up with the OB... To fix that I've added a 3-way zone valve to my drawing in order to provide a bypass loop on the WB... If the ZV1 flow is A-C everything goes through both boilers. If ZV1 is flowing A-B, the WB gets bypassed.

Note that the WB is tied in on the same side of the OB, and while I put it on the return side, it could be done anywhere in the system that was convenient....

Another option might be to tie the WB in with a pair of closely spaced tees, as I did in the second picture. This hydraulically separates the WB pump (P2) from the zone pumps, (Pn) and solves the problem of pushing unwanted flow through the zones. However it brings back a variant of the earlier problem, in that the OB will not see any flow from the WB unless one or both zone pumps is running and circulating water through the house loop... Incidentally, the close space tees approach gives much the same effect as an HX, without the efficiency hit...

Gooserider

Edit - note that P1 and M1 are not critical in this drawing, they are just the return water protection, and could take many different forms, I just put them in my generic blocks as an example...

joecool85 said:

I like #2, is this modification of my drawing decent?

Click to expand...

Yes, it's functionally the same as my #2, as long as you make sure that the actual connection point is a pair of closely spaced tees, i.e. less than 4 pipe diameters between the two tees, and at least 8 pipe diameters of straight run on each side of the pair...

Webstone makes a really slick combination fitting that has a couple of nice extra purge valves in it that can make it easier to get the air out of your lines - I have a link to a post that talks about it early in the Tidbits sticky...

Gooserider