Design phase for new house. Opinions?

[Paul Norris]

Greetings all. I'm currently in the process of designing a heating system for a house I'm going to be building in Missouri. I could really use a thumbs up from those with some experience.

Essentially I will be using a Tarm/EKO/Other Boiler in the 100,000 btu/hr range to do double duty on DHW and radiant heating for a 1550 ft^2 house. I'm not a hvac person, but I am an engineer. In that vein, I think the most reliable solution would be to borrow someone else's design.

http://www.radiantcompany.com/images/clsdwood.jpg

This diagram seems to have the cleanest basic layout for what I'm trying to do. Does anyone see any pitfalls in this setup?

Many thanks in advance,
-Paul Norris

 

[Eric Johnson]

Welcome to the Boiler Room, Paul. I think you'll be able to get all the help and information you need right here.

Reading and understand piping diagrams is not my strong suit, but I don't understand the two flat plate heat exchangers. It looks to me like you're using your domestic water supply for hot water storage, which I don't think makes a lot of sense, at least not the way it's set up in the diagram. Since the wood-fired boiler and your house radiant both presumably operate under the same pressure, I don't see the sense in isolating them from each other with heat exchangers. Why not just run a zone over to your DHW tank and put a heat exchanger there, and pipe everything else direct? If you have a big enough tank (how big is that one, anyway?) you can set it up to recover heat from the DHW tank as well as store it.

Everything else looks fine to me.

Do you plan on having a backup source of heat in addition to the wood gasifier?

 

[Nofossil]

Welcome to the forum and to the boiler room, Paul. Nice to have another engineer here. I'll look over your design, and in the meantime you can look at mine and steal whatever makes sense - link is in my signature below.

I'll echo Eric's points. Also, it's more common to have pumps mounted low and pushing cold water through a boiler rather than pulling from the hot side. Many reasons.

I think you'll need a pump on the radiant loop as well if you plumb it as shown.

If the tank is to provide heat storage, I'd suggest that it be as large as you have room for, and put a smaller domestic hot water tank near and above it with a sidearm heat exchanger. That would allow you to ditch both the flat plate heat exchangers and get by with two pumps: One for the boiler and one for the radiant loop.

 

[Paul Norris]

Nofossil, Eric,

Thanks for the quick reply. I appreciate the info. I was thinking about using a tank in the 200-300gal range initially. It seems like 500-800 is more the butter zone based on past posts on this list. At the present time, there is only my wife and myself. After the house is built, then we'll be expanding the family.
With only 2 people (and several small ones for at least the 4-6 year time period) and a small area to heat, I was hoping to get by with one firing in the morning for showers and use the residual heat for the radiant at night. Storing in a large water heater seemed like a good idea at the time. Having no experience though, I can't say if that is feasible or not yet.
Would it be better to replace the HX near the boiler with a 3 way mixing valve then, or just plumb straight in and out? I've read it's best to keep the inlet temp to the boiler in the 140-150 range for efficiency.
I see the missing pump now in the radiant loop as well. Good eye.

 

[Eric Johnson]

You want to keep your return water temps above 140 as much as possible to protect the boiler from low return water temp corrosion. Most people use a mixing valve; I use a circulator.

Hydronic heating systems are usually pressurized to around 15 psi, which is what most boilers run at. So as I mentioned earlier, I would treat the hot water heater (or storage tank) as one of your zones and put the sole heat exchanger there, and then pipe the rest of it direct. I don't see a problem with using a big hot water heater or indirect tank for storage, since you have a relatively small heat load in a relatively mild climate. I know from experience that just 40 gallons makes a difference.

One advantage of a sidearm heat exchanger is it heats the domestic water through gravity, so you don't need a pump on the fresh water side. But if you're using a big tank for storage and DHW, then a flat plate might make more sense, since you'll probably want the faster response time that a flat plate will provide. But then you'll need a bronze circulator on the domestic water side.

It sounds to me like you're planning to use the wood gasifier as your sole heat source. I think that's not a bad approach, but your insurance company may have different ideas. They (or the bank) will probably want some kind of fossil fuel appliance in your house for backup. Just one more thing to check out.

I'm sure you'll get a lot more piping ideas and suggestions tonight.

 

[ISeeDeadBTUs]

Welcome aboard. I'm not sure if this will be your house, or a clients. In any event. I am neither an engineer, nor any good at plumbing. But I would rethink the sole-fuel source thing. Most of us here get at least moderately excited about heating our residences and our hot water with an 'almost-free' fuel. But I have oil backup. And a not-quite-finished backup generator. It's great to save operating expenses. But the WAF takes a serious nosedive when due to unforeseen circumstances, she has to wait a couple of hours before you can get the house warmed back up AND she can't hop in the 'cuzzi and warm up until the house comes back on line. Yes, it sucks shelling out the extra bucks for the backups. But don't kid yerself. . .WAV costs $$, one way or another

Jimbo

 

[Nofossil]

Nofossil, Eric,

Thanks for the quick reply. I appreciate the info. I was thinking about using a tank in the 200-300gal range initially. It seems like 500-800 is more the butter zone based on past posts on this list. At the present time, there is only my wife and myself. After the house is built, then we'll be expanding the family.
With only 2 people (and several small ones for at least the 4-6 year time period) and a small area to heat, I was hoping to get by with one firing in the morning for showers and use the residual heat for the radiant at night. Storing in a large water heater seemed like a good idea at the time. Having no experience though, I can't say if that is feasible or not yet.
Would it be better to replace the HX near the boiler with a 3 way mixing valve then, or just plumb straight in and out? I've read it's best to keep the inlet temp to the boiler in the 140-150 range for efficiency.
I see the missing pump now in the radiant loop as well. Good eye.

I know that it's a new house, but it would be worth doing a heat load study to help size everything. Two+ people typically use around 60,000 BTU/day in hot water. Add the house heat load and you can start figuring out the range of sizes that make sense for heat storage. At a minimum you'd probably want enough storage to carry you for a day in the cold season. That way, you can build one fire per day and still expect the house to be comfortable until it's convenient to build the next. Beyond that, a larger tank allows you to skip days when it's not so cold. I was able to skip three days in the last week, for instance.

Mounting the DHW tank above and near the storage tank allows thermosiphoning to work at its best. Truly great if you ever add solar for summer hot water.

 

[Paul Norris]

ISeeDeadBTUs,
I've considered the single source heating issue. Like I said I'm still in the design phase. And, yes the design is not for a client, it is a personal setup. The entire house is a fairly unconventional design (partially earth-bermed, ICF, passive solar) and my overriding goals are more about long term sustainability. I suppose that an Oil or LP boiler could be added later if needed for comfort, but currently I'm trying to size the "wood side" so that it can be run by itself long term if needs be.

Nofossil,
I'm drawing up your idea for the main loop with two tanks now. I like that much better in concept. When I've got it done, I'll post again to see if this jives with what you're suggesting.
Also, I'd never heard that 60,000 per person number before. That might change things a bit. I've sized the house's BTU/hr loss on paper, but I haven't figured exact tank size needed yet and that dhw figure makes me think again. Everything being done at this point is mutable.

Thanks again to all.

 

[Paul Norris]

Something more like this?

 

[Nofossil]

60,000 BTU per day is a family of four, not per person unless you take a lot of showers.

What are the green star symbols?

I have a block diagram of my system posted on the sticky thread that talks about primary/secondary loop plumbing. If I were doing yours, I'd mak a couple of changes to your latest block diagram:

1) The sidearm should be in series with the boiler outlet.
2) I'd have a circ for the storage just like the circ for the boiler
3) I'd have a zone valve that bypassed the storage circ so that the boiler can pump around the storage circ when it needs to heat the tank
4) I'd have a zone valve for the radiant zone. Maybe not needed, but I'd want to be able to shut it off when I'm heating the tank.
5) I'd have a zone valve for the return line that's parallel to your radiant zone I actually don't have a return line as such, but it might be good to have a path to allow flow when there's no demand. I use the tank instead.

If you look at my diagram, you'll see how that works. I don't have the sidearm or a radiant zone, but your radiant zone (with its circ and mixing valve) could take the place of my baseboard zones.In that case, I'd draw it with top-to-bottom flow. Looks like your radiant pump is pointing the other way.

 

[wdc1160]

I like the setup changes you have made.
Are 1 of the pumps firing the wrong way?? Assuming I know what the pump symbol?
If those green suckers are shutoff valves-- are u going to have modes of operation where water travels through some circuits in reverse?
Is there are method to extract water out of therm storage for space heat with out going back through boiler?