Coverting from gravity hot water

Paul Fredricks_3

We are looking at a gravity hot water conversion. The current system has 3 - 3" zone valves on it. The idea is to install the new boiler with circulators and flow checks. Do we have to keep the flow checks 3"? I'm thinking we can drop down to 1 1/4" since we are now pumping the water through the system.

Any thoughts?

Robert O'Brien

Sounds like a plan

Watch out for orifices in upstairs rads,although if you zone the floors separately that won't be a  issue.1 1/4" flow valves will do the trick. New boiler or just a repipe?

Paul Fredricks_3

.

New boiler. I would sure think that would be fine, but there are some opinions that there won't be enough flow or it won't heat properly...or something like that. Can't see why there'd be an issue.

Robert O'Brien

I got the formula

I got the one size less than half existing pipe size formula from one of Dan's books,only did a handful but all work just fine!

Paul Fredricks_3

Thanks

I'll have to look through my books and see if I have that one.

Paul Fredricks_3

Found IT!

It's in the "How Come" book. Thanks Bob.

Paul Fredricks_3

Hey Dan!

Look what I found inside.

Tim McElwain

Paul are you going with

a Mod/Con on the gravity system?  If so they work out great, I commissioned one of the first ones done many years ago when the Munchkin first came out. Everyone was a little nervous about doing it but with outdoor reset and the typical volume of water coming back to the boiler at an already lower temp it has worked out great. We replaced an old coal which had been converted to a Roberts Gordon up-shot conversion burner which never really heated the house. In fact they had three gas space heaters in the house so they could keep warm. After the Munchkin space heaters gone and better yet a 42% reduction in gas usage.

Robert O'Brien

Gravity oil to Vitodens

The savings is huge,did this in Dec 2010,recouped the investment already

Paul Fredricks_3

Tim

This is an oil job.

icesailor

Conversions:

I would zone it into the three circuits/zo0ne valves you already have to solve any flow problems and add a 4 way mixer with ODR.

That way, if there are orifi upstairs, it should solve itself.

Paul Fredricks_3

More info

The system has 2 - 3" zone valves, but only one thermostat. The valves must be there to stop the flow when the tstat satisfies. It can't be zoned well because it's 2 stories and one valve does the left side of the house, the other the right.

In discussing this job more, we will probably combine the "zones", use a single 0010 w/ flow check to serve both, and use primary/secondary for the boiler connection. That will keep the boiler temp up and give a steady flow to the system. Not sure if reset is in the package or not, but we'll set the high limit down to 160°.

With primary/secondary, do we have to match the ciculators? Or is a 007 on the boiler and a 0010 on the system OK? 

kcopp

a 0010 is...

way too big. A Grundfos 15-58 on LOW speed is prob. your best bet. You are trying to mimic the gravity flow. Formula is... 1/2 the pipe size then drop down 1 more after that.... so if its 3" it would be 1.25" pipe.

Mark Eatherton

Mix and matching pumps is OK, but...

If you do go in there with a non condensing boiler, I'd strongly recommend that you put an ESBE anti condensing valve to keep the new boiler like new...



If you go with a modcon, you have nothing to worry about, other than free oxides, and Caleffi has a new magnetic device to save your bacon there.



If theres money in the budget, the ultimate would be to put TRV's at a but the reference radiator, and drop a WILO ECO Stratos variable speed pump on the main. Full modulation throughout...



ME

Paul Fredricks_3

.

Then why use a circulator at all? Dan's book recommends a circulator like a B&G 100 series. There's a good amount of flow in those, though I can't seem to find a pump curve anywhere.

SWEI

B&G Series 100 curve

Is very similar to that of a 0010.  Xylem has re-arranged the site and somehow managed to make it even harder to find information - here's a snip from the catalog.



This curve is a perfect fit for a short boiler loop on a 399k, but I haven't found a whole lot of other applications recently.  A smart circ and TRVs would be my choice here as well.

Paul Fredricks_3

agreed

but the money isn't there. The oil boiler has an output of 180 MBH. Is the 0010 overkill? Would a 007, at 2/3 the flow rate of the 0010, be a better bet? The only thing I worry about is flow since this splits into two loops.

I appreciate the help guys. Haven't even seen a gravity system in a long time, much less done a conversion.

SWEI

Got a number

for system head?  Even a SWAG?

Paul Fredricks_3

No

I haven't seen the job, but given it's 3" mains the head has to be pretty low.

MikeyB

Conversion

Paul, I believe Steamhead and Gordo have done quite a few of this type of conversion job, and had some really nice pics of them as well, primary/secondary w/existing 4" mains (if my memory serves me right)  w/an Indirect as well, real nice work.

Steamhead

Paul, the first thing to do

after the heat loss is done and the boiler is sized, is to do a radiation count. You will use this to size the circulator, from this chart:



http://www.heatinghelp.com/article/343/Circulators/238/Sizing-Circulators-for-Hot-Water-Heating-Systems



This is pretty much the same thing as the older method of using a B&G 100/Taco 110 and downsizing the piping, as described above. That method was the best we could do before these small wet-rotor circs came out. But the newer circs use less electricity, have fewer moving parts and don't need oiling.



If you're doing a primary-secondary setup, you would size the system secondary circ from this chart. The primary and the boiler secondary (if used) circs would be sized in the more-usual manner.



The key factor here is that you don't want to over-pump this system. If you do, the water will move too fast and short-circuit thru the rads, reducing their heat output.



Depending on the manufacturer, the boiler may require some sort of inlet temperature regulation. Taco has a couple solutions that look good, and include outdoor reset as well as a boiler return sensor: the 4-way I-valve and the variable-speed injection circ. Icesailor has had good results with the I-valve and I hope to try the VSI/ODR circ soon.

Paul Fredricks_3

Thank you, Mr Head.

Good info. The job is on delay till next month, so it will give me some time for the engineering.

TonyS

Reverse returns

One option we use is to reverse the returns, cut the return at the first t closest to the boiler and plug it, go to the back of the return and cut in a t or weld on a threadolet and run 1 1/4 back to the boiler. Then you have a reverse return system, this works well especially if the house has had some non gravity modifications done, such as a new kitchen or bath with baseboard, this will usually solve these problems.

If no such modifications have been made, we have been piping directly through the exchanger on our Prestiges and keeping the pump on low with continuous and this has been working out really well.

Steamhead

That snowman was probably about 40% efficient

according to one of my Dead Men's Books, so any modern boiler would have been more efficient!