Monoflow Continuous Circulation System

Re: Monoflow Continuous Circulation System

PostBy: steamup On: Fri Oct 28, 2011 10:08 am

It should be similar.

Pumping a gravity flow piping system is not a problem. Keep in mind that all of the radiators are piped in parallel. If the orginal plumber did a good job, they will also be fairly self balancing.

The radiator hand valves in a gravity hot water system usually have a hold drilled in the valve plug to allow a trickle of flow, so the radiator doesn't go stone cold and stop gravity flow.

Minor tweaking of rooms may be necessary for comfort. Patience will be a virtue.
steamup
 
Stoker Coal Boiler: Axeman-Anderson AA-130, Keystoker K-6
Hand Fed Coal Boiler: HS Tarm 502 Wood/Coal/Oil
Coal Size/Type: pea, buck, rice

Re: Monoflow Continuous Circulation System

PostBy: kstills On: Fri Oct 28, 2011 10:43 am

steamup wrote:It should be similar.

Pumping a gravity flow piping system is not a problem. Keep in mind that all of the radiators are piped in parallel. If the orginal plumber did a good job, they will also be fairly self balancing.

The radiator hand valves in a gravity hot water system usually have a hold drilled in the valve plug to allow a trickle of flow, so the radiator doesn't go stone cold and stop gravity flow.

Minor tweaking of rooms may be necessary for comfort. Patience will be a virtue.



Good to know that for later :)

Thanks, I'm going to be busy this weekend turning knobs it seems. :D
kstills
 
Stoker Coal Boiler: WL 110
Stove/Furnace Make: Leisure Line

Re: Monoflow Continuous Circulation System

PostBy: Sting On: Fri Oct 28, 2011 11:00 am

I cannot believe anyone actually reads this crap I write
Image
Sting
 
Other Heating: BurnHAM=NG-gas


Re: Monoflow Continuous Circulation System

PostBy: kstills On: Fri Oct 28, 2011 11:04 am

Sting wrote:I cannot believe anyone actually reads this crap I write
Image



Lol. :)

I had a bad few moments thinking about thermal shock today, so I was doing some research here. This post addresses most of the issues that I would have had, if it were in fact a problem. The boiler design apparently isn't one where I have to worry too much about that, however the response time of the boiler due to the amount of water in the system has not been optimized.

The writeup you gave makes a lot of sense and I'm anxious to try it out.

Snow in SE PA tomorrow. :shock:
kstills
 
Stoker Coal Boiler: WL 110
Stove/Furnace Make: Leisure Line

Re: Monoflow Continuous Circulation System

PostBy: cabinover On: Fri Oct 28, 2011 5:36 pm

Sting wrote:I cannot believe anyone actually reads this crap I write
Image


We don't, we simply love to gawk at yer avatar. :P
cabinover
 
Stoker Coal Boiler: Hybrid Axeman Anderson 130
Baseburners & Antiques: Sparkle #12
Coal Size/Type: Pea, Buckwheat, Nut
Other Heating: LP Hot air. WA TX for coal use.

Re: Monoflow Continuous Circulation System

PostBy: Sting On: Fri Oct 28, 2011 7:03 pm

understood
Sting
 
Other Heating: BurnHAM=NG-gas

Re: Monoflow Continuous Circulation System

PostBy: kstills On: Fri Oct 28, 2011 8:12 pm

Here's a problem.

I only have one circulator pump, and it's also the dump zone circulator.

It might be a bit difficult calibrating the flow rate so that I don't go over the high limit, and with the valve already constricted that might be a problem.
kstills
 
Stoker Coal Boiler: WL 110
Stove/Furnace Make: Leisure Line

Re: Monoflow Continuous Circulation System

PostBy: Rob R. On: Fri Oct 28, 2011 8:37 pm

Exactly what are you trying to correct?
Rob R.
 
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Other Heating: Dad's 1953 EFM Highboy

Re: Monoflow Continuous Circulation System

PostBy: Sting On: Fri Oct 28, 2011 10:24 pm

kstills wrote:Here's a problem.

I only have one circulator pump, and it's also the dump zone circulator.

It might be a bit difficult calibrating the flow rate so that I don't go over the high limit, and with the valve already constricted that might be a problem.


DO NOT just read one or two paragraphs of my drivel

and then assume you know how to balance your system or mine or his

One key point you need to keep in mind is the flow that your balancing has to equal both the engine ( your boiler ) and the load - or at least that's the target you want to get to.

Since I run my equipment with a variable input - well your mileage may vary - but you can do this with one pump. Just think it thru.
Sting
 
Other Heating: BurnHAM=NG-gas

Re: Monoflow Continuous Circulation System

PostBy: kstills On: Sat Oct 29, 2011 8:20 am

markviii wrote:Exactly what are you trying to correct?


Let me give you the full history, than we can discuss the best possible course of action. :)

My house was built in 1929, thereabouts (interestingly, it looks like it was going to be part of a very large development, the 'Wynn James Estates', but the depression hit and only 5 of the planned homes ended up being built). It's a structural brick home, with a framed second story. There are 26! windows in a house with a 32x24' footprint, but they have aluminum storms on them which means I have zero drafts. At some point, insulation was blown into the upper floor and the attic, so the home is reasonably well insulated for it's age.

I've replaced my old GE oil burner with a new LL 110K dual fuel boiler. The GE, which apparently was a 'Cadillac' boiler for it's time, looks to have been installed sometime in the 1950's. It also appears to have been tied into an existing two pipe gravity feed system, origins unknown. The mains in the basement are 2 inch, with 3/4 inch feeds and returns to the radiators, of which there are ten, 5 per floor. Frankly, were it not for the price of oil, the old system worked extremely well, was very reliable and could probably have kept running (with maintanence) until I died.

However, oil prices being what they are, I've converted over to coal. I've tied into the old system using 1 inch black iron for my feed and return, but using the bulk of the old mains to send the hot water up to the radiators. The issue this is presenting is that there is soooo much water that needs to be heated that the cycle times on the new boiler are pretty long. In oil mode, at 165k btu (approx), it took ~1 hour, 45 minutes for the circulator to start running without shutdown, it coal mode 9at 110kbtu) that extends out to 2 hours. The delta on the feed and return is as high as 100degrees, depending on how long it's been since the call for heat has gone out.

I learned a new term this week; 'thermal shock'. So in trying to figure out how to prevent that, I came across this thread. Sting's explanation on how to balance the system seems to solve two issues that I might have, that of dumping too much cold water into the system, and running the entire system more efficiently. So right now, I'm trying to work through the details on how to best accomplish that, starting with a system that only has one circulator hooked up. Running with the feed valve too far open allows too much of a delta to develop on supply and return. Running with it to restricted could potentially, I say potentially, not allow the dump zone to clear the heat from the boiler in time to keep the fire going in the grate.

Now, here's the second issue. For the record, I'm sure that these are resolvable, but it's fun to work through them (at least for me).

For some reason (probably because the damn aquastat display is upside down....that's not something someone can fix?) my low limit was set at 130f (HL-180f). I didn't notice this as a problem until this week. However, I did do some charting of burn times (I timed it from cirulator off, until the LL tripped the circulator again, then the circulator run time) at this temp to determine how long it would take for the system to come up to full circulation. The numbers were pretty linear, and I'll be I have a pretty straight line graph, but they were all done between the temperatures of 100f (low side with return) to 135f (max temp the boiler hit before the blending of the return water started dropping the temp). This was charted with all the valves on the supply and return wide open, and the boiler on max burn. All the radiators in the system came up to temp, not evenly, but by the time the 2 hours was up every radiator had warmed up and was putting out heat.

So last nite I changed my LL to 155f. Than, to start to balance the system, I restricted flow on the supply side of the boiler. In concept, for keeping the return blended better, this was working very well. I could run the system with the circulator going full out for hours at a time. The house came up to temperature, but very unevenly. In fact, I had two dead radiators (one of them being the bathroom, of course). In fact, al the radiators that were getting the most heat were in rooms I would need it the least.

I was able to close valves and start to re-direct flow to the radiators that were not getting heat, so this isn't a long term problem. However, I was surprised by the cycle time that the boiler had at the higher temperature settings (much longer than 2 hours) and how much less responsive the system was overall (heat concentrating in a few radiators).

So, that's what I'm doing. One question, based on limited testing so far, would be is it uncommon for different output temperatures to have a dramatic effect on how the heat gets distributed into the system? I've turned my HL to 165 and my LL to 145 to run some experiments today, but atm I'm changing too many variables at once without having enough knowledge of what might be happening. It could be that the restriction of the supply is causing the flow to favor a few radiartors over the others? Or it could be the water temp?

I understand, both for condensing and DHW, I want to run the temperature on the boiler higher. But if condensing is not an issue because of the solid fuel (thermal shock is apparently not an issue either, however better safe than sorry) would it be ok to run the boiler at say, 150HL and 130LL?

Next summer, I'm planning on ripping out the old 2 inch mains and going with 1 inch for the supply and return. By then, I'll have read Sting's books so that I can design the system as efficiently as possible. So this is a situation that I'm facing for just this winter.

But it's my new toy, and it's a puzzle, so it's fun to talk about. :)
kstills
 
Stoker Coal Boiler: WL 110
Stove/Furnace Make: Leisure Line

Re: Monoflow Continuous Circulation System

PostBy: kstills On: Sat Oct 29, 2011 8:48 am

Sting wrote:
kstills wrote:Here's a problem.

I only have one circulator pump, and it's also the dump zone circulator.

It might be a bit difficult calibrating the flow rate so that I don't go over the high limit, and with the valve already constricted that might be a problem.


DO NOT just read one or two paragraphs of my drivel

and then assume you know how to balance your system or mine or his

.


:)


My comment was not a presumption of omniscience, it was an acknowlegement of uncertainty. If the DZ takes too long to clear the boiler temp back to the LL setpoint, the fire in the grate might go out. I have no idea how long that might take, but it presents an interesting challenge.
kstills
 
Stoker Coal Boiler: WL 110
Stove/Furnace Make: Leisure Line

Re: Monoflow Continuous Circulation System

PostBy: Rob R. On: Sat Oct 29, 2011 8:53 am

How about a new thread to discuss this and some pictures of your boiler piping?
Rob R.
 
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Other Heating: Dad's 1953 EFM Highboy

Re: Monoflow Continuous Circulation System

PostBy: kstills On: Sat Oct 29, 2011 9:15 am

markviii wrote:How about a new thread to discuss this and some pictures of your boiler piping?



Hehe, well, I'm not going to re-type all that.

Maybe a mod could switch that post out into a new thread?

As for pics, the best I could do is stick diagrams (no digi). :P
kstills
 
Stoker Coal Boiler: WL 110
Stove/Furnace Make: Leisure Line

Re: Monoflow Continuous Circulation System

PostBy: Rob R. On: Sat Oct 29, 2011 9:37 am

ok, start with some good reading on gravity systems: http://www.heatinghelp.com/article/332/ ... eating-FAQ

The good stuff is towards the end, when he talks about converting the system to forced circulation. It is important to note that the system was designed around a certain delta between the supply and return...most likely 20 degrees. Ideally you would have installed a bypass on the near-boiler piping to make this possible.
Rob R.
 
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Other Heating: Dad's 1953 EFM Highboy

Re: Monoflow Continuous Circulation System

PostBy: Rob R. On: Sat Oct 29, 2011 9:43 am

From:
http://www.heatinghelp.com/article/332/
This link is broken, either the page no longer exists or there is some other issue like a typo.
... eating-FAQ

Q: When is it a good time to convert a gravity hot water system to forced circulation?
A: Usually, when the gravity system slows down because of the corrosion which has taken place over the years. Those little nooks and crannies in the pipe slow the flow and stop the heat. The natural response is to raise the temperature to make the water circulate more quickly. But you can only push the temperature so far before you begin to ask for trouble. That's when it's time to convert the system to forced circulation.

Q: What does this involve?
A: You have to add a circulator and (usually) close the system to atmosphere. You'll also have to make some changes to the near-boiler piping.

Q: What changes?
A: The old boiler probably has two outlets and two inlets because the idea in those days was to get the greatest possible gravity-induced flow of water through the boiler. The more holes, the better the circulation. That piping looked like this.

When you add the new circulator, you won't need to use such big pipes coming and going out of the boiler. In fact, you'll want to reduce the size of your near-boiler piping to give the circulator something to "push" against.

Q: Why does the circulator need something to "push" against?
A: So it won't kick itself off on its internal overload protector. A circulator does its maximum work when there's little or no resistance to flow. In a gravity system, the large pipes can't offer much resistance.

Q: Will I still need those double inlets and outlets at the boiler?
A: No, and that's another reason you should rework the near-boiler piping. With two inlets and two outlets the pumped flow might short-circuit around the boiler without moving out into the system.

Q: Suppose I don't want to repipe the boiler?
A: You may have to use two circulators - one on each supply line.

Q: How will I know what size pipe to use on the new boiler?
A: A good rule of thumb is to take the largest pipe, divide it in half and then drop one size from that. That becomes the size of your new near-boiler piping. For instance, let's say the largest pipe is 2-1/2" (if there are two inlets and outlets, you only have to consider one of them). Divide that in half and to get 1-1/4". Now drop down one size to 1" and that's what you'll use all around your new boiler.

If your largest size happens to be two-inch, pipe your new boiler in 3/4". It will look odd, and it might make you feel uncomfortable, but it'll work. Different systems call for different piping techniques. One size doesn't fit all and a gravity conversion is definitely different from a brand-new, forced-circulation job.

Q: How do I size the circulator for a conversion job?
A: It's real easy with these jobs. You're looking for high flow at a relatively low head pressure. A good choice is a circulator similar to Bell & Gossett's Series 100.

Your goal is to move a lot of water around the system as quickly as possible against very little resistance to flow. This type of circulator does just that.

Q: Can't I use a small, water-lubricated circulator instead?
A: These are fine circulators for most modern, forced-circulation systems, but not the best choice here. You don't need to generate much head pressure on these conversion jobs because the pipes are enormous and the resistance to flow is almost nonexistent. Using a small, high-speed, wet-rotor circulator is a poor choice on a gravity conversion because it will do the exact opposite of what you're trying to accomplish.

Q: I'm not sure I understand the difference between flow and head pressure. Can you explain it?
A: Sure! Flow is the "train" on which heat travels. Flow "delivers the goods" to the radiators. Head is resistance to flow and it's important, too, but only in relation to flow.

Q: Well, then what determines the head pressure?
A: In general, the size of the pipes. The smaller the pipes, the greater the required pump head, and vice versa. Since gravity systems have very large pipes, there's no need for a high-head circulator. What you need is high flow.

Q: Where is the best place to install the circulator?
A: It's always best to put it on the supply side of the boiler, pumping away from the compression tank. Piped this way, the circulator will add its pressure to the system's fill pressure and make it easier to get the air out. The system will also run more quietly.

Q: Do I have to use a bypass around the boiler on these jobs?
A: Most boiler manufacturers recommend that you install a bypass around their new boilers when you use them on a gravity system. Here's what that bypass piping looks like.

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Q: What's the reason for the bypass?
A: It's there to protect the boiler against condensation and thermal shock.

Q: What's thermal shock?
A: Thermal shock is what happens to hot metal when you hit it with relatively cold return water. If you take a glass plate out of the oven and run cold water over it, it will break, won't it? That's thermal shock.

Q: How does the bypass piping help prevent this?
A: The boiler bypass allows the majority of the return water to bypass around the boiler while just a small portion of that water flows through the boiler, picking up the necessary heat.

Q: You said something about condensation. What's that all about?
A: If the return water temperature is too cool, the combustion gasses can reach their dew point and turn into a liquid inside the boiler. That liquid is very corrosive to metal. It can damage or destroy a boiler in no time at all. By using the bypass, you're mixing hot supply water into the relatively cold return water and raising the boiler water temperature to a point where the gasses can't condense inside the boiler.

Q: Does the bypass serve any other purpose?
A: It allows the boiler to come up to high-limit temperature and shut off. Without the bypass, the large volume of water moving through the boiler often keeps the temperature low and prevent the boiler from reaching high-limit. This does a good job of increasing the fuel bill.

Q: Is there another way to pipe the replacement boiler without using the bypass?
A: You can use primary/secondary pumping techniques.

Q: What's primary/secondary pumping?
A: It's a way of treating the flow through the system and the flow through the boiler as two separate things.

Q: Is there an advantage to this?
A: There is because some boilers require a minimum flow to operate at their maximum potential. This flow may not be the same as the flow you need in the system. If you use a bypass line, someone may adjust it after you've left. This can cause problems with both the boiler and the system.

Q: How do I pipe for primary/secondary flow?
A: Tie the existing supply and return lines together to form a system loop. Then, use two standard tees, set no further than a foot apart, and attach the new boiler to the loop. Like this.

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The primary pump serves the system, while the secondary pump takes care of the boiler. You meet the flow needs of both in a very simple way. The not-more-than-twelve-inch spacing between the tees allows the pumps to operate independently. When the secondary pump is off, there will be no flow through the boiler if you keep the spacing within that 12" limit.

Q: Why is that important?
A: By controlling the flow through the boiler, you're taking charge of the stand-by losses of the system. If the burner is off and the boiler pump is stopped, you will have minimal loss to the flue.

Q: How do I control a primary/secondary system such as this?
A: You can have both pumps and the burner come on at the same time. Or better yet, you can run the system pump (the primary) on an outdoor-air reset control, and cycle the boiler pump (the secondary) and the burner to meet the temperature needs of the building on any given day. This is the ideal way to manage an old gravity hot-water system.
Rob R.
 
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Other Heating: Dad's 1953 EFM Highboy