Newbie doing research

[bowhuntah]

Hi everyone. I'm new here and I'm researching what direction to go for my new construction project. My fiancee and I are going to build a 2000sf timber frame. We want to install a wood boiler as our primary heat source with a propane or electric boiler backup. I plan on having thermal storage in this system (size tbd). The basement/garage will be radiant as will the first floor. The second floor will be conventional baseboard. The heat is the easy part but I have a lot of questions about DHW and how to incorporate it into a system if at all. From what I have read, thermal storage is just for heat correct? If I want to heat the DHW with wood I will still need an indirect tank connected to the wood boiler and gas boiler? Another thought I had was to have wood boiler for heat only and a combi gas boiler/on demand water heater for backup heat. The DHW would be heated by the only the gas boiler. Another option is wood for heat, gas boiler backup heat and gas on demand for DHW. Thoughts, suggestion, HELP!

 

[ewdudley]

Welcome.

Here's a link to get you started:

https://www.google.com/url?sa=t&rct...wCom1J17zcRPmh1hg&sig2=opeQ_5AlRgZDGXZa_Ny8_A

The whole document is good, but have a look at the "System using large 'repurposed' propane tank, along with small buffer tank" page.

The author, Seigenthaler, seems to prefer pumped heat exchanger solutions for DHW, but you should consider substituting a "reverse indirect" buffer/DHW heater tank for the buffer tank shown in the drawing. You can build one or pick up something like the ErgoMax:

http://www.ergomax.com/New-Tanks.htm

 

[jebatty]

Exciting project. Wish you both well. Given energy uncertainties and environmental impacts, looking to sustainable wood supplies for space heating is a wise choice. Major consideration and construction design to allow for siting to take advantage of both active and passive solar also is very important. Our 1956 single story + full lower level walkout house (3000 sq ft total) looks to the SW over a lake. We heat with a single wood stove in the living room and a little supplemental electric in the lower level. The 40' front has about 30' of R8 window glass (U-0.12). Passive solar gain through the windows from the low angle fall, winter, and spring sun, both direct and indirect from reflection off the lake ice, will heat the house during sunny periods, even with outside temps in the -20F and lower ranges. Due to wide eaves, the summer sun is blocked. And then we have an open site with 6.9kw PV, grid tied, and that supplies 9,000 kwh/yr of electricity, which meets 75+% of our annual kwh electric demand. Due to net metering credits, PV covers our entire annual electric bill.

The wood comes from our land and electricity from "our" sun. Result: near carbon net zero house and $0 energy cost. With a water well and gravity septic system, we have $0 cost for other utilities. Can you imagine never paying any utilities? Priceless.

 

[maple1]

You can heat your DHW from the thermal storage all year round - if you really want to. It will require a fire every week or so in the summer. I have an ordinary 80 gallon electric hot water tank, I heat it from storage with a flat plate HX - that I think is quite a common setup. But having the electric hot water tank there also makes burning wood all year for DHW a questionable exercise, since it only costs us about $25/mo to heat it electrically. I did it with wood last summer, didn't the summer before, and don't know yet about next summer. Some go out of their way to incorporate year-round DHW heating into their setup, and I am likely one of those - but when all is said & done, it isn't much of a money saver, and unless your storage is really well insulated, it will add a bit of extra heat to the house in the summer. Money savings would be even less if compared to using a heat pump water heater. I don't think I would go with any type of on-demand setup.

You can also install a basic sidearm heater setup to heat an exisiting DHW tank, quite economically. It's a very simple solution. But the sidearm arrangement does not work well at all when trying to keep the DHW hot when you're not burning every day for heat. That's what I started with - and ended up adding a FPHX & small DHW circ to get satisfactory mileage out of the storage tanks.

An even simpler thing to think about to help with DHW heating is to insulate your storage tanks with an enclosure/boxed type of build, and before you finish boxing it in & dumping the insulation in - lay out a couple of rolls of 3/4" pex around & across the top of the tanks that your DHW feed runs through before it gets to your DHW heating device. That will at least do a lot of pre-heating - and likely do most of the heating of it when you are burning for heat during intermittent DHW use. I did that too. It will create a bit of a difference in pressure at the taps, hot vs. cold - but it's not an issue for us.

 

[velvetfoot]

I'm no expert, but why not radiant in the upstairs, since the house isn't built yet? And, do you really need radiant heat in the basement? Are you going to just use it once in a while? Chances are it won't be super-finished since you'll be putting a wood boiler, big tank and maybe some wood storage down there and you only have 1000 ft2 to play with? The concrete slab would probably like constant heat.

Just thinking out loud. Wish I was building a new house from scratch.

 

[pbvermont]

I would not do the baseboard on the second floor. Use true radiant emitters, like panel radiators. Building new, you have the option to do it right, do it once. Plan for circulating lowest temp. water you can. Radiant floors are best for that. As you can see, there are a multitude of strategies for DHW. Crunch numbers and plan carefully. Get help with design and control strategies.
Contact Tom at solartechnics in ME for your heat storage solutions.
Plumbing can be a special challenge in timberframes. Needs very careful advance design. If using insulated panels for cladding house, you will have a super-insulated envelope. Your heat loads should be very small. Air exchange?
Again: careful planning.
Good luck.

 

[maple1]

To expand a bit on the above - if you do go with normal baseboard, put lots of it in. Like maybe twice what a design spec might spec. There are also types of baseboard that give more heat from water that isn't as hot as typical baseboard specs. Slant Fin makes a type - forget now the model of it. You could likely get a good part of the way to the performance of panel rads without near the cost - but if you can afford panel rads (ones I saw were pretty pricey), they would work the best. Might also consider re-purposing some old-fashion type cast iron rads, if they will fit with your decor. The whole point of this stuff is it makes better use of water that isn't as hot as typical baseboard would need, so you get more (a lot more in some cases) mileage out of your storage tanks. My house starts to lose temps in the 130-140 supply range (depending on the day) - some guys with good radiant heat (in-floor, panel rads..) can run storage down to 90-100 before they need to light up.

 

[jebatty]

Ditto comments on radiant panels, etc. The best friend of a wood boiler with storage is the ability to use low temp water, and baseboard makes that more difficult. I can use water down as low as 100F and still heat the radiant floor in my shop.

 

[velvetfoot]

I can use water down as low as 100F and still heat the radiant floor in my shop.

But if you're doing that, it's not enough for dhw.

 

[maple1]

But if you're doing that, it's not enough for dhw.

True - sort of. Depends on how long you would be going between burns. If I charge my 80 gallon DHW tank up to 150 when the fire is going, it will go a couple or three days without needing charged again - with the pex preheat thing. (Except for laundry days). So in that respect your DHW tank also contributes to your storage room.

 

[Rearscreen]

My general experience: I built my own Post & Beam by myself and installed my radiant heat by myself. Used a Buderus boiler, ran one loop up into a cement vertical slab inches from my Mansfield then back down to capture heat and get it into the hydronic. That design could have been improved upon. I put pex/al/pex in the basement slab. I wouldn't do that again. The slab sucked up the fuel then when it did get warm it felt like a sauna. The wood mass above alone heated the basement sufficently. I had a unique way of laying the pipe in the engineered joists which worked very well. Radiant is great, time consuming to install. If your Post & Beam is going to use curtainwall panels, be aware that in the mind of ants, it's one huge ant farm!

 

[bowhuntah]

Thanks! Lots of good info for me to digest. I like the idea and looks of the radiant panels. Those I will definitely use on the second floor. There will only be one zone upstairs for 2 bedrooms and a bath. The PDF from ewdudley is great and answered some of my questions. So this is what I'm thinking now. For heat I would use a wood boiler and a backup propane mod/con both plumbed into a pressurized thermal storage tank (size tbd). Radiant in floor heat for the first floor living space (possibly warmboard) and radiant panels in the basement/garage and second floor. For DHW I would use a heat exchanger out of the storage tank inline with an electric tankless heater. Does this make sense?

 

[maple1]

Have you fully investigated the electric tankless heater yet? They use a huge amount of panel capacity - which may or may not be an issue.

Also, I have an electric boiler for backup - when it's running (rarely - usually only one day a winter, none this winter), it only does the loads & does not heat storage. Some of the backup concerns would likely come down to how much you would expect to use it.

 

[bowhuntah]

Have you fully investigated the electric tankless heater yet? They use a huge amount of panel capacity - which may or may not be an issue.

Also, I have an electric boiler for backup - when it's running (rarely - usually only one day a winter, none this winter), it only does the loads & does not heat storage. Some of the backup concerns would likely come down to how much you would expect to use it.

I've researched them a little. I did notice that they do take up a lot of panel space. I should have said electric or propane tankless and electric or propane backup. Right now I'm just trying to figure out the basic setup.

 

[velvetfoot]

I'm not sure you want to charge that entire big storage tank with propane, do you?

 

[bowhuntah]

I'm not sure you want to charge that entire big storage tank with propane, do you?

I'm not sure what you mean. Remember, I'm a newbie.

 

[maple1]

I'm not sure what you mean. Remember, I'm a newbie.

Think he was referring to this:

For heat I would use a wood boiler and a backup propane mod/con both plumbed into a pressurized thermal storage tank (size tbd)

That sort of implies you would also heat storage with the backup - but might not be what you meant. While everything is actually all tied together, you'd usually not want to heat storage with your backup when your backup is going. My electric boiler is like that, via check valves. But having said that, my setup also short-cycles badly on backup, so I have on my radar to remove one of my check valve flappers when the opportunity presents, and drill a small hole in it so it will let a little bit of storage flow into the backup loop. My situation is partly because my backup electric boiler is oversized for what it does - but I think even with a more properly sized one there would still be some short cycling, when only one or two zones are heating.

 

[bowhuntah]

Think he was referring to this:

For heat I would use a wood boiler and a backup propane mod/con both plumbed into a pressurized thermal storage tank (size tbd)

That sort of implies you would also heat storage with the backup - but might not be what you meant. While everything is actually all tied together, you'd usually not want to heat storage with your backup when your backup is going. My electric boiler is like that, via check valves. But having said that, my setup also short-cycles badly on backup, so I have on my radar to remove one of my check valve flappers when the opportunity presents, and drill a small hole in it so it will let a little bit of storage flow into the backup loop. My situation is partly because my backup electric boiler is oversized for what it does - but I think even with a more properly sized one there would still be some short cycling, when only one or two zones are heating.

Ahh I see! That's how it's drawn in the PDF so I assumed that was how it's done. So the backup boiler is plumbed directly to the manifolds?

 

[velvetfoot]

there would still be some short cycling

But would that matter, with an electric boiler? Are there stages on the electric boiler?

 

[ewdudley]

Ahh I see! That's how it's drawn in the PDF so I assumed that was how it's done. So the backup boiler is plumbed directly to the manifolds?

In the slides linked-to above see the drawing "wood gasification boiler with pressurized storage" (page 95, it looks like). The backup boiler is connected directly to storage, but the return to the boiler draws from a point high up on the tank. This provides a smaller buffer for the backup boiler that is enough to prevent short-cycling, but since it provides heat to the top of the main storage tank the rest of the system works the same independently of what the heat source is.

 

[bowhuntah]

In researching backup options I came across combination propane boiler/on demand water heaters. Would there be any issue using one of these with a wood boiler and are there any issues with these units in general?

 

[maple1]

But would that matter, with an electric boiler? Are there stages on the electric boiler?

Maybe not. It has stages, 4 of them, one for each element. So they each turn on, a few moments apart, until all 4 are heating, then they reverse & each drops out until none are heating. Then it's not too long before they do it again. I just don't like all that action happening all the time - although with the size of the boiler, I likely can't avoid it. Don't think there are any settings on it to restrict it to just using an element or two either.

 

[JP11]

Seems like a very expensive backup system. If it were me.. I'd put that money into different things. I'd go with a automatic standby generator. Then electric heat for the backup of wood. OR, a nice wood stove and hearth in the basement for emergency heating if the power was out.

You're in Maine. I'm around the Auburn/Lewiston area if you want to see how some of this stuff integrates. I applaud your planning ahead of time.

JP

 

[bowhuntah]

Seems like a very expensive backup system. If it were me.. I'd put that money into different things. I'd go with a automatic standby generator. Then electric heat for the backup of wood. OR, a nice wood stove and hearth in the basement for emergency heating if the power was out.

You're in Maine. I'm around the Auburn/Lewiston area if you want to see how some of this stuff integrates. I applaud your planning ahead of time.

JP

JP, I'd love to see how the systems integrate. I'm not too far away in Windham. Send me a PM with your contact info. Thanks!