Boiler Piping

[rreihart]

I don't want to try to re-invent the wheel so can anyone with similar setups offer input?

My existing system is an oil boiler with indirect DHW, cast iron base board zones, and radiant zones. Tekmar controls are used to fire the boiler, run circulators and mix temperature for the radiant zones. I'm adding a BioMax 60 and hot water storage to the system.

The following diagram shows my initial attempt at how I think this should look. A brief description would be as follows:

When wood boiler fires, wood pump is on. If no call for heat, 3-way directs to storage.
When there's a call for heat, if storage temp > primary loop temp then storage pump on.
If storage temp < primary loop, then 3-way directs to primary.
If boiler temp drops, then oil boiler fires for heat to primary loop.
Oil would only supply to primary, not to wood boiler or storage.

Does this logic sound correct? Does the piping layout allow this? Suggestions?

Thanks, Rob.

 

[Eric Johnson]

I'll have to look this over in more detail, Rob, and let you know if I come up with any intelligent observations. I see your thread on the same topic on The Wall. If you can get any takers over there, you'll get lots of good advice, but they tend to pick and choose their victims on that website, so you might have to try two or three different approaches before anybody bites.

I do have one question that spring immediately to mind:

What are you doing to protect against low temp return water corrosion? I don't see any consideration for that on your drawing, though I realize that a lot of details are excluded for the sake of clarity. But it's an important part of piping a gasifier.

And one observation: My gas-fired boiler is at the heart of my system by necessity, since that's where all four zones originate and I can't think of a better way to distribute heat into the house than with my existing equipment. So I pipe directly into the gas boiler and let all the controls and circulators do their thing. But I do "decommision" it when I'm running the wood side for a few reasons. First, I don't need a backup, since the wood boiler produces enough heat 24/7 if you keep wood in it. Which I do--religiously. Secondly, because of the way my system is piped, I risk losing a lot of heat up the gas boiler stack if I don't block it off. And you obviously need to disconnect the power and shut off the gas before you do that.

From your diagram and description, I gather that hot water from your BioMax doesn't make its way into the oil boiler, so that's not an issue, but if your piping strategy evolves into something different for whatever reason (I know mine has), it's one thing to bear in mind.

Why don't you tell us more about the BioMax, Rob? Start a new thread to keep this one on track. We got lotsa room down here in the Boiler Room.

EDIT: The diagram looks good to me, except that I'm not sure about your tank piping arrangement. That's a pressurized tank, right? In which case, shouldn't the supply water from the BioMax be going into the top of the tank, with the return back to the boiler coming from the bottom? I don't have any experience with pressurized storage tanks, and I barely know what I'm talking about with heat exchangers, but it seems to me that your priority should be to return the coolest water from the tank back to the BioMax and dumping the hottest water into the top, where it can be distributed to the zones immediately as soon as there's a call for heat.

 

[Nofossil]

I have a virtually identical installation. Here's a link that explains what I did and how it works:

http://www.nofossil.org/heating.html

The big difference is that my storage tank is not pressurized. I'd assume thermal stratification in the tank (in fact, I'd try to maximize it). Plan your inlet and outlet locations accordingly.

Hope this helps...

 

[rreihart]

I've learned a lot from searching and reading on The Wall. Last fall I replaced our oil boiler, totally replaced the piping to our baseboard zones (had been a monoflo tee system that didn't work well in some areas), and installed under floor radiant in a 5-room addition. Much of what I was able to learn came from reading threads there. I had talked to a number of local heating contractors and I really felt that they were no where near the level of those posting on The Wall. That's one of the big reasons that I went at it on my own. I do have a strong sense, however that its not always homeowner friendly.

Low temp return water? I know its needed but I'm not showing anything because I'm not sure what to do yet. Most thermostatic mixing valves that I've seen are too small. I'm piping with 1 1/4" steel so I don't want to install a 1" mixing valve and restrict my flow. I think you addressed this in your EKO Has Landed thread and I liked your setup. I don't see an option on my control to run a pump based on return temp. I even asked Zenon about this and he said the control does not do this. I thought our controls were the same, but maybe they're not. The manual definitely does not show this, but the manual is not very thorough.

I thought about running through the oil boiler but I definitely don't want the oil heating the BioMax or the tank, so I came up with this arrangement.

As far as the tank goes, that was just my first idea. I think you're right though about dumping in the top and pulling out the bottom. That sounds like the right way to go.

Got to go. Soccer game.

Thanks, Rob.

 

[Eric Johnson]

You post on The Wall at your own risk, because you have to realize that most of those guys don't appreciate the competition. But there are some really great guys who seem to really enjoy helping people. You know who I'm talking about, so I won't list them. I'm blown away by those install pics. You're right about just learning through lurking.

I thought I knew how the controller was supposed to control the pump, but I'm not sure it does what I expected. Instead of kicking off when the return water exceeds 140, I think it runs through the entire cycle now, which I think is ok, but probably unnecessary above 140. The controller does shut the pump off at the end of the cycle, however. Here's a pic of how mine is piped. The two return lines are flow controlled, as is the recirc.

 

[rreihart]

OK guys, these are probably simple basic questions, but help me out with a couple things.

Nofossil, do you heat the storage tank with the oil boiler? What is the function of the motorized valve on the wood boiler bypass? Also could you clarify "I’d assume thermal stratification in the tank". Is this the idea that the top of the tank will be hotter and the bottom cooler? After thinking about it a little, I definitely agree with Eric's suggestions for inlet and outlet.

Eric, when you say "the two return lines are flow controlled", do you mean you have flow check valves to prevent reverse flow in the wrong direction? If so, what brand and type did you use? I'm certainly no expert, but I think I've read that spring types are preferred over swing.

Thanks for the input. Rob

 

[Nofossil]

OK guys, these are probably simple basic questions, but help me out with a couple things.

Nofossil, do you heat the storage tank with the oil boiler?

Only if I have extra heat left in the oil boiler when I'm done heating everything else. The primary purpose of the storage tank is to store heat from the wood boiler so I can keep the house temperatures constant without having a fire going all the time. In the summer, it stores heat from the solar panels to heat my hot water.

What is the function of the motorized valve on the wood boiler bypass?

That's a simple alternative to Eric's recirculator pump. My homebrew controller opens that valve as needed to allow a portion of the water to recirculate through the wood boiler, increasing the inlet and outlet temperatures.

Also could you clarify "I’d assume thermal stratification in the tank". Is this the idea that the top of the tank will be hotter and the bottom cooler? After thinking about it a little, I definitely agree with Eric's suggestions for inlet and outlet.

Yes - the top will tend to be hotter - sometimes much hotter. This is not a bad thing - I exploit it.

Eric, when you say "the two return lines are flow controlled", do you mean you have flow check valves to prevent reverse flow in the wrong direction? If so, what brand and type did you use? I'm certainly no expert, but I think I've read that spring types are preferred over swing.

Thanks for the input. Rob

I'll second the bad opinion on swing valves. I ended up using Taco pumps with the integral check valves. Works for me so far.

 

[Eric Johnson]

These days I try to get pumps with integral flow checks. Taco and Grundfos both make them. They're like little strainers, though, so they tend to collect any little beads of solder and other crap that might be lurking around in your piping. So make sure you have isolation valves or flanges around the pumps so that you can inspect them periodically, especially any installed on vertical runs. Ebay is a good place to shop for pumps; you pay about half what you would retail for a new one, but no warranty, I suspect.

I also have a few old cast-iron flow checks on my system. And they work as well. The nice thing about them is that they can double as bleeders and you can disable the flow check by opening a screw lever at the top. I've used both swing and spring-loaded check valves, but I don't trust 'em.

I have an aquastat at the return on the EKO that shuts both circulator pumps (the main pump and the one for the greenhouse) off when the return water temp goes below 160. This keeps the overall boiler temp in the 170 range, which is where it likes to stay. The stat at the top is for overheat protection. When the boiler supply temp hits 200, it kicks on the greenhouse loop to dissipate heat. So far, that hasn't happened (that I'm aware of).

BTW, I see you've got hot rod on your case over on the Wall. What a great guy. When I found out that he has an EKO, that pretty much made up my mind for me. That's the first pic I've seen of his tank. Interesting--a pressurized, mixed tank with no insulation. Great information in a couple of sentences, if anybody's interested.

http://forums.invision.net/Thread.cfm?CFApp=2l.&Thread_ID=50586&mc=4

 

[rreihart]

I updated my drawing to show better flow through the storage tank, and to show a possible return protection. Based off of Nofossil's example, I'm showing a zone valve between the supply and return piping. I think this location will protect both boilers when they are running. Would an aquastat be used to open and close this zone valve? Is it better to use a zone valve or a pump? I see its done both ways. Why one over the other?

 

[Eric Johnson]

I considered replacing my four zone pumps with one big pump and four zone valves, but I was told that pumps are more responsive than zone valves. But that's room heat, so it's probably a different story. The traditional way to do what you're trying to do is with a mixing valve, allowing you to split up and control the flow. I'm not sure that you would get flow in the right place with a simple zone valve, but assuming that it would work, I would activate it with an aquastat located in or on the return line of one of the boilers--probably the BioMax. It's only an issue with the oil boiler when it's firing. Without flame in the firebox, the return water temp is irrelevant. So if you're not expecting to fire the oil side very much, I wouldn't worry about it. However it's set up now is probably sufficient. So as long as you can isolate the wood side when you're firing the oil boiler a lot--say when you go on vacation, then it shouldn't be an issue.

 

[Nofossil]

I updated my drawing to show better flow through the storage tank, and to show a possible return protection. Based off of Nofossil's example, I'm showing a zone valve between the supply and return piping. I think this location will protect both boilers when they are running. Would an aquastat be used to open and close this zone valve? Is it better to use a zone valve or a pump? I see its done both ways. Why one over the other?

I'm with Eric - pumps are more responsive, and the cost is similar. The only reason for zone valves is that Taco came out with zone valves that use essentially no energy to keep open, whereas having several pumps going at once sucks some watts - a big deal if you want to be able to run off of batteries during power failures.

You could use an aquastat - I went 'over the top' and used temperature sensors and my own homebrew controller. I have a discussion of the control logic at http://www.nofossil.org/boilersw.html.

 

[rreihart]

When I saw Eric's boiler piping photo I liked the idea of using a pump. Then I consider the fact that I currently use 6 pumps, (1-primary loop, 2- baseboard zones, 1-DHW, 1-radiant zones, and 1-inject mix temp) and I'll add 3 more (oil boiler, wood boiler, and tank). So I'm just wondering if I'm going overboard with all the pumps. At first I didn't really consider power usage since it seems pretty minimal. Now I'm a little more interested as I think about what I can do during power outages. I suppose one more pump can't add that and for low water return it can't see that much action. I should probably look harder for a 1 1/4 NPT mixing valve.

By the way Nofossil, that's a very interesting chart.

Another question. For indoor boilers, is there any concern about combustion air? Does the boiler pull enough air that you would find drafts?

 

[Eric Johnson]

Mine is out in the barn in a cinderblock room with doors on either end. I have an air vent coming from outside, for safety reasons. The vent is only 4 inches in diameter (it's an alumunim dryer vent) and I probably get a fair amount of air intrusion from the doors, which have insulation but because of my abysmal carpentry skills, are not mounted very well. But the boiler runs fine with the doors closed. My point, then, is that seems to get plenty of air. So I doubt that you'd have a problem, but nofossil is certainly more qualified to answer that, as I believe his is in his house.

The only pump I'd like to have working during a power outage would be the main system pump, which gets hot water from the wood side directly into my gas boiler. I'd open the flow control valves and let gravity heat the house (old ci rads and large-diamter pipe). That, and the blower on the boiler.

 

[Nofossil]

When I saw Eric's boiler piping photo I liked the idea of using a pump. Then I consider the fact that I currently use 6 pumps, (1-primary loop, 2- baseboard zones, 1-DHW, 1-radiant zones, and 1-inject mix temp) and I'll add 3 more (oil boiler, wood boiler, and tank). So I'm just wondering if I'm going overboard with all the pumps. At first I didn't really consider power usage since it seems pretty minimal. Now I'm a little more interested as I think about what I can do during power outages. I suppose one more pump can't add that and for low water return it can't see that much action. I should probably look harder for a 1 1/4 NPT mixing valve.

By the way Nofossil, that's a very interesting chart.

Another question. For indoor boilers, is there any concern about combustion air? Does the boiler pull enough air that you would find drafts?

My recirc valve is 3/4", and it seems to flow plenty. Actually, it's much less than 3/4", since Honeywell designs these things with a 1/4" orifice. I modified it to a 5/16" orifice, but that's as big as you can go in that style valve. It provides plenty of recirculation flow in my installation. You can see it above and to the left of the wood boiler in this picture.

I almost went nuts looking for a 1 1/4" mixing valve before I gave up. In hindsight, there's other things I should have gone nuts over instead.

I think it's a good idea to provide outside air for the boiler if at all possible. There's no downside that I can see other than the mechanics of doing it. We did it for my brother's system, and I'm planning on doing it for mine this year.

 

[Eric Johnson]

I read somewhere that you want to undersize four-way mixing valves so they don't "hunt." So 1.25-inch piping would call for a 1" valve. Honeywell makes a nice one for less than $100. You can buy a control head for another $40 or so. Not sure if you'd use a four-way or a three-way mixing valve for low temp return water protection. I was checking out using one to keep my cast iron radiators at an even temp, which is something they do a lot of in Europe. In a way, it acts as hot water storage to some extent, since you're stashing heat continually into your system. And they say it keeps your house at a more even temp. Maybe next upgrade cycle.

 

[rreihart]

Set me straight on this. If I put a 1" 3-way mixing valve in my return line, isn't that creating a bottleneck and basically sizing my entire loop to 1"? Also, I've been looking at thermostatic mixing valves (for example: Honeywell AM102-1 Thermostatic mixing valve 1" NPT 100-145 F range) which I think would be set to maintain a temperature without any motorized head. Is there any reason not to use this type of product? My reason for not going this route was that 1 1/4 was hard to find, and I saw you guys doing it other ways.

I can see where using a smaller size in each of you situations where you're not restricting the main return. Your valve (Nofossil) and pump (Eric) is on more of a bypass line.

 

[Eric Johnson]

I don't know the physics of it, but I've been advised several times by heating professionals (on The Wall and elsewhere) to do that, and apparently it's not a big deal. On my flat plate heat exchanger, for example, the vendor suggested a 3/4-inch model over a one-incher, even though my piping was all one-inch. They said the head loss would be insignificant, and it was a better hx. So I bought the 3/4, forced all my flow through it, and it worked fine. I was probing The Wall for advice on a four-way mixing valve for one of my 1.25-inch lines, and somebody told me about downsizing the valve. So that's the information I'm going on. If I understood this stuff better, I wouldn't be posting so much.

You might pose the question over there and see what they say. I'm sure somebody can explain it clearly, and I'd like to hear it. Ask them about valve size and valve hunting (means it never settles down).

On the other hand, you are correct. My 1.5-inch recirc line reduces to 1" when it hits the pump flange. But it doesn't matter, since both return lines are not affected and the 1" opening is more than sufficient to keep the return up to temp. I understand pumps and aquastats a lot better than I understand mixing valves, so that's why I piped mine the way I did. I'm sure a mixing valve is more efficient--but I can feel and hear the pump working, which I like.

 

[Nofossil]

Being an engineer, I put together a spreadsheet that calculated all the flow losses for all of the valves, pipe sections, and fittings in a vain attempt to understand why it matters - I had been told by a plumber to use 1 1/4" copper for the supply and return lines. I'm pretty convinced that it's a waste. The only reason I can see is that it reduces the velocity of the water, so velocity related phenomena would be reduced as well. For instance, you might get more even flow into a set of tees. Otherwise, a waste of copper as far as I can tell. 8gpm at a 20 degree difference is 80,000 BTU/hr. A small pump can push 8gpm through a 1/2" pipe with no problem.

 

[BrownianHeatingTech]

Okay, a few things:

Piping diameter is related to flow restriction due to friction losses, not absolute flow levels. You can shove an awful huge amount of water through a 3/4" orifice, if you get enough pressure. The maximum level is called "choked flow." You'll never be anywhere near that.

So, what you're actually dealing with is the friction loss due to the velocity of the water. The smaller the pipe, the faster the water, and the more frictional loss, which means bigger pumps to overcome it. Running water through many feet of small pipe would be a problem. Shoving it through a very short length of small pipe (eg, a mixing valve, or the inlet and outlet pipes on a heat exchanger) is not a big deal.

A thermostatic mixing valve is the way to go for return temp protection, as far as simplicity. An electronic system will be more serviceable... it can be easily bypassed, when needed, by disconnecting a wire or throwing a switch, and can be adjusted for "fine-tuning" by turning a screw in the aquastat. The aquastat would go on the shared return pipe (since you're installing it, anyway, and you have a radiant loop, there's no reason not to protect the oil boiler).

The current system, however, won't achieve it, as you're only going to get a small amout of flow through the bypass connection, since the water will be more likely to just head on up to the primary loop. You need a three-way zone valve in place of the tee next to the current valve, so it can direct water either up or left, depending on the aquastat's signal. When shopping for zone valves, look for the "cv" number, which relates to the flow restriction - higher means better flow.

The pumps for each boiler should be moved to the return side of the boiler. Pumps should pump "into" the hydraulic load. In the case of heating zones, that means pumping away from the heat source, towards the zone. In the case of boilers on their own loop, that means pumping towards the boiler, since that's the major load the pump is dealing with.

If your heating zones have their own circulators, it's a very good bet that you don't need the primary loop pump, at all. But you'd need to draw up the system you have, before I could say for certain.

Joe
Brownian Heating Technology

 

[Eric Johnson]

Thanks, Joe. Really informative post that cleared up a few things in my muddled brain. And welcome to the new Boiler Room.

I bought a 1-inch three-way zone valve for my system. Honeywell makes a nice valve as does Taco. The Honeywells net out at about $100 for the valve body and the motor head, but if you order online, make sure you talk to someone who understands what you are looking for, since Honeywell's two-way and three-way zones have basically the same part number for some reason. On my first attempt, I received the two-way zone. The Taco lists at $160 and I couldn't find anyone who would discount it. I hear the Taco is a fine piece of equipment, but my HW works just fine.

 

[BrownianHeatingTech]

Thanks, Joe. Really informative post that cleared up a few things in my muddled brain. And welcome to the new Boiler Room.

Thanks.

I bought a 1-inch three-way zone valve for my system. Honeywell makes a nice valve as does Taco. The Honeywells net out at about $100 for the valve body and the motor head, but if you order online, make sure you talk to someone who understands what you are looking for, since Honeywell's two-way and three-way zones have basically the same part number for some reason. On my first attempt, I received the two-way zone. The Taco lists at $160 and I couldn't find anyone who would discount it. I hear the Taco is a fine piece of equipment, but my HW works just fine.

Taco is a nice valve, but they don't have an extensive product line, and their units tend to be more restrictive to flow, and draw a lot more electrical power, when compared to the Honeywell or Erie valves. The exception is Taco's Electronic Ball Valve line, which has decent flow characteristics, and draws very little power. But there isn't a 3-way EBV available. Personally, I use Erie most.

Joe

 

[rreihart]

Thanks for the info Joe. Sorry I didn't reply sooner, I'm struggling to find time to sort everything out. I've been rethinking my drawing, but have not come up with a plan I really like. Last night it struck me that I have the return from the buffer tank dumping directly into the wood boiler, no low temp protection. I'm also still trying to sort out controls. I used some fairly pricey controls last year and I really don't want to spend a lot more again. And I'm still trying to get my hands on a storage vessel.

 

[EricV]

The Termover valve that came with my Tarm is a 1 1/4" unit.