New boiler engineering help

heidleml

Hello,

I have a customer in a 1730's home on the Chesapeake Bay. They currently have a two pipe steam system.

A healthy home is very important to them (they are currently having the house abated of lead). They also do not want any combustion to be occurring within the home. These seem to be non-negotiables.

They are going to have new radiators made for the house to match the existing. They also want to put a new condensing boiler in a separate building about 50' from the house.

I can handle taking out the existing piping and re piping for hot water, etc. I have heard and seen buffer tanks online and that they are preferred in some situations. Not sure if this would be the case.

We will need to get two pipes over from the new building in a trench. Should I just go with close tees in the boiler house and a high head pump to get out to the main house? Should I go with 2" pipe to reduce friction? Should I come right off the boiler and run to a buffer tank inside the house?

I know you all live and breath this stuff and I would be super appreciative for some guidance. Thank you.

Jamie Hall

Fifty feet isn't a long enough run to worry much about head loss — I'd size the pipes for the load pretty much as usual. As to head, just keep in mind elevation just as you usually would; if the boiler house isn't much below or above the load, that's not a factor anyway.

Insulate those lines separately, and then insulate the dickens out of the whole assembly. Check depth of burial with the local building department.

Otherwise the whole thing is not that different from any other mod/con installation — just with a longer than usual distance from the boiler to the manifolds…

Others will comment…

bburd

If the new radiators will match the existing ones, they will have less heating capacity on hot water than they did on steam. The first step should be a heat loss calculation for sizing purposes; you may want to oversize the radiators to take advantage of the efficiency of the condensing boiler at lower supply water temperatures. This will also account for energy efficiency upgrades since original construction, such as insulation and double glazing.

What is the total heating load and design water temperature difference? From these you can calculate the required flow rate to size the underground piping and main pump.

How will you zone and control the system inside the house?

How will domestic hot water be heated?

Jamie Hall

Oh and one other thing. Don't let them skimp on the boiler house. It must be well insulated and tight, with dedicated makeup air for the boiler and exhaust. And plenty of room to work around the boiler!

Mad Dog_2

Steamhead is In Maryland. Mad Dog

delcrossv

Alternatively, keep the 2 pipe steam, drip the supplies and returns into a condensate tank and pump it back to the boiler house.

No need to worry about resizing rads and the rest.

HVACNUT

I would keep the hydraulic separation in the boiler room, and trench the secondary circuit to the main house basement, or wherever it's coming in. Then zone circuits, if any from there.

Sleeve everything underground, and run extra control wiring. Isolation valves everywhere. Purge valves where needed.

The manual will state the pump needed for the boiler, and the piping design. The fifty foot horizontal run isn't an issue, as long as the manual is followed.

Injection pumping is another way to go.

Are we allowed to know why no combustion in the main house? Heavy oxygen?

Jamie Hall

May I make one other suggestion, @heidleml ? Get a very thorough and very complete performance contract with them, preferably cost plus pricing with an agreed mechanism for change orders…

(I'd keep the steam, too — but that's not going to fly if they want a mod/con)

hot_rod

This isa common way to pipe underground. You see this a lot in district systems in Europe. The tube size depends on the BTU load

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GroundUp

The Insulpex that Hot Rod shows above is about the best option for something like this. Any sort of conduit or corrugated type of chase WILL have water intrusion at some point or another, and become a big problem. As far as sizing, all piping and circulator(s) need to be sized per the heat load. What is the heat loss of the space and design supply water temp? What will be used for domestic water heating? These remote type of systems are not uncommon and I've got quite a few of them under my belt. Some utilize a cold start arrangement with control wiring buried alongside the piping in a conduit, others are a hot start with a constant circ underground.

EBEBRATT-Ed

Primary secondary with the tees or LLH in the boiler house. Pipe size to the house depends on the flow needed.

The only reason to use a buffer tank is if the smallest zone will short cycle the boiler. What about DHW?

HPWH or electric HWH or an indirect tank in the house?

@Jamie Hall

Elevation shouldn't matter with a closed loop……Unless it is hundreds of feet to affect pressure rating of equipment?????

Kaos

Air to water heat pumps are pretty cheap nowadays and newer ones can do decently hot water.

For a costumer that doesn't want to burn fuel, I think it would be an easy sell.

Bonus, no outdoor hut, no underground piping.

You do have to do your homework on heat loss and emitter sizing. A good helping of floor heat in addition to the rads also helps.

heidleml

Thank you for all of the replies!

For the comments about heat loss etc., I just had a first consultation with the homeowner. There are 8 radiators in the house and the Historic Trust is making him remove the modern windows and put back single pane to keep the history.

I intend to do the calculations on this after I have a concept.

I will most definitely use an application specific product for the tubing underground-seems like this could be a point where contractors could get “creative”. Any specific product links? I think I saw something by uponor and rehau was in the picture from Hot Rod.

I like the idea of an indirect in the main house. They are also interested in a HPWH.

Again thanks for all of the responses.

Jamie Hall

Bravo for the Historic Trust. Now if they can find a carpenter who can do the historic windows correctly, you will find they are almost as good as the latest and greatest for the vinyl clad folks.

However. You might enquire — on your client's behalf — if the Trust will accept removable inner storm windows. I know the National Park Service does for National Historic properties. If your Trust does, they are a superb approach to really tightening up historic windows, and the combination has equal or better performance than all but the very top line triple pane affairs. If you need more information, send me a PM.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1821016#Comment_1821016

If you want to be really creative use an A2WHP instead of a boiler. It could do heating, cooling, and DHW via those underground pipes. I fired a Viessmann VitoCal unit today. I had to look at the fan to see if it was running it is so quiet. I hope to run 1.5- 2 COP in heating mode.

A load calc and radiator assessment would be needed. You want to run 120F or lower to use a HP effectively.

Some killer rebates and incentives if you search www.dsireusa.org

Yes Uponor and Rehau have that sealed underground pex. As well as a few of the outdoor wood boiler companies. @GroundUp knows of the best brands for the $$.

A primer on air to water systems

https://idronics.caleffi.com/magazine/27-air-water-heat-pump-systems

GroundUp

Uponor does not make a sealed underground PEX system. They have a corrugated and wrapped system, but it's pretty susceptible to damage and water intrusion.

Rehau Insulpex, Central Boiler Thermopex/Rovanco Rhinoflex (same thing, different name- both utilize Rehau PEX inside), and Urecon Logstor are the only 4 products on the market that eliminate the possibility of inadvertent damage and groundwater infiltration due to their high density closed cell foam construction. The Logstor is all metric and the so-called 1-1/4" version of Thermopex is also metric so fittings can be a little funky to source, but the others are standard nominal PEX sizes. As far as I know, the Insulpex is the only one that will go larger than 1-1/4" nominal in SAE size PEX

hot_rod

I thought the Uponor EcoFlex was the pioneer of underground systems? I have seen 3” size used on snowmelt systems

https://www.uponor.com/en-us/commercial-solutions/ecoflex?k_cca=uponor_search_intent&gad_source=1&gbraid=0AAAAACoxdJm2fFWkyMtVgEQL9qWosb5TH&gclid=EAIaIQobChMI58-6kZbriQMVgCRECB1W8g7OEAAYASAAEgIwW_D_BwE