Sizing Manifold and Other Questions

[OH_Varmntr]

Howdy folks,
It's been awhile since I last posted, but I recently fell into a deal on a 400 gallon SS tank that I couldn't pass up, and it's thrown me back into this.

Short explanation of what I've got and where I'm trying to go. I'm afraid this will be long winded so please bear with me.

-Central Boiler 6048 outside wood burner with a single Taco 009 circulator. 90' run of 1" ThermoPex buried 48" deep to the house.
-Once inside it goes through a series-loop of HXs. The first is a 6-plate 5x12 BPHX for my DWH. Second is a 100MBTU WAHX mounted in an air handler to heat my first floor. I have used this single WAHX to heat my whole house (2 floors minus the basement) of ~2200sqft for a few years now. It's a really poor setup, I know. I have another 100MBTU WAHX that I have installed in the attic of my 2 story home that will heat my upstairs now that I have installed ductwork for it.

I'm looking to install the storage tank in my garage. I was planning on buying another FPHX (size unknown at this time) and mount it low in my basement to maximize thermosyphoning to the storage. It would have a minimum of 8' static head pressure from the tank. I have performed a heat loss calculation for the house and it came out at 62,000 BTU, but I believe it to be a bit conservative. Knowing that, I'd like to know how big of a FPHX I would need for this?

With the storage tank on the garage floor, the circulators I would like to use for my zones would each have 8' of static head as well. One of the circuits is the FPHX for my hot water and the other is for the WAHX for my 1st floor air hander. Both of these zones are entirely below the water level of the storage tank, and are very short runs so I was going to purchase ECM pumps for these circuits like the Taco Bumble Bee and set them on Delta T mode.

The last zone is for my 100MBTU WAHX in the attic. It is rated for 91.3MBTU at a Delta T of 20 at 10GPM with 1400cfm of air movement according to the spec sheet. If I've correctly interpreted what I've read, I can subtract static head from the gross head of the circulator outlet in order to get actual circulator head, plus other circuit restrictions. So if my storage tank is on the floor of my garage, the static head of the pump being 8' and the gross head of the circulator is at 25.5 feet, then the actual head the circulator would need to overcome is 17.5'? If this is correct, I would plan on raising the storage tank off the floor of the garage, which should really help with circulator selection and save some energy.

Now, I'd like to run my circulators off of a manifold if I can get away with building one. If I can get 10gpm to each WAHX that's 20gpm right there. I'm not sure what my FPHX will flow as I can't find any spec sheets on it. It's a 5x12 6-plate with 3/4" fittings. Either way, with both WAHXs running at the same time, it's nearly the limit of what I've read 1.5" copper will flow at 4ft/sec velocity. I've thought about interlocking the zones so only certain ones can run together but I'd rather not limit the capabilities of heating my house. So bumping up to 2" copper for the circulator and return manifolds sounds unscientifically accurate for me. It's just a bit more expensive. What size manifold can I get away with building?

Quite frankly, I've done a lot of reading and calculating over the past few days and I believe I've overloaded myself with it. If these questions are fairly simple to calculate, links to resources would be greatly appreciated. Thanks again for the help!

 

[Bob Rohr]

it sounds like you are running and open, non-pressurized system? Find some good reading in this tech journal about piping that type of system.
I'm concerned about that 1" pex from the wood burner, that will be the road block in the amount of BTUs that you can get into the system. Sounds like 180' of pex plus fittings and HX pressure drops?

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10_0.pdf

 

[OH_Varmntr]

Thank you for that link. There's a ton of info in there! Should be everything I need.

Yes, the system is open, non-pressurized. The piping to and from the HX will be 180' total of 1" PEX. The HX will be mounted below the woodburner in the basement. There are four 90* elbows. I can size the HX large enough to reduce the drop across it.

 

[Bob Rohr]

I doubt you will get much more than 7- 8 GPM through that 180" loop with the 009. Here is the Syzer result at 7.5 GPM. Notice the pressure drop per 100 feet, double that for your loop counting ells. You still have the pressure drop through the various HXers to consider.

You might pipe right into a buffer tank, like page 29, then take load from that. So the boiler just pumps through the tube and tank, keeping the pressure drop as low.

A larger pump could give you more gpm, but pressure drop increases as you try to shove more flow. Ideally 4 fps is the maximum velocity you want, the 7.5 GPM flow rate in 1" pex is right at 4 feet per second.

 

[OH_Varmntr]

Thanks Bob! I'd thought of plumbing the tank buffer style, but then I'd have to decrease my overall system temps keep my water from boiling at the top of the zone for my attic HX when the circulator turns off. At 190* system temp it would boil over, but at 180* it won't.

That's part of the reason I wanted them separate so I could elevate the tank in the garage, but for the simplicity of it I'll circulate through the tank. Has there been use of altitude valves in the wood-heating industry to keep two unequal height tanks at their proper levels? Just curious.