gravity flow conversion

ALH_4

I have seen many Vitodens boilers installed at 5000 feet and above (up to approx 7500 feet) with no problems at all.

Mike Miller

gravity flow conversion

Okay guys I would like some advice. I have looked at a beautiful old house here in town. (Denver) They need to replace the old cast iron monster that has been heating this house since world war one. I have done gravity flow conversions before using a primary/ secondary loop system and an 80% Laars copper exchanger boiler. I would really like to consider offering them an opportunity to go with a more effcient system. In talking with a supply house guy I was given some conflicting information from how I am used to thinking about these systems. He recommended one primary loop coming acress the exchanger for better temperature gain coming across the exchanger. He is selling the Monitor MZ by the way. I went to Viessmann's site but they say that their mod-con is only good to five thousand feet. We are a little higher than that here. Anyway any good ideas or suggestions wuld be appreciated

tim smith

Boiler for old gravity system

Look into the Triangle tube prestige boiler. We have had nothing but good on this boiler. Doing a 5000 sft 1920s home right now as we speak. Old gravity, cast rads. Will be a great system for them.

Unknown

I Think

he is speaking of the geographical altitude, not the sq. footage of the home.

Dave

Blackoakbob

gravity conversion

Though I haven't been at that altitude since my vist to Utah in June, I am also interested in the how and what of a gravity conversion. I am looking at one now thats a coal, oil, to gas atmospheric conversion burner. I would appreciate any direction you can give. Please correct me if I'm wrong, but is the derating of equipment due to the lack of oxygen or the pressure? Thanks in advance.
Best Regards,

mars_4

derate of boilers at denver alt.

Ive had good luck with a derate factor of .68 for atmospheric boilers, such as the Larrs jv series and a derate factor of .8 for a mod con boiler. Now that is supposed to take into account the altitude as well as the 880 btu. per cft. of gas that we have up here. having said that Ive had conversations with reps of diffrent mod con boilers that tell me that there is a minimal derate factor on there equipment. Ive not had the chance to clock some of this equipment yet so I cant say for sure that that is the case but I will keep you posted when the heating season gets rolling.

Ken_40

Most mod-cons

can handle the lower O2. For sure, the Munchkin.

It's the gas valve sensors that provide the firing rate. The derating would lilkely be under 10% at 6,000 feet IMO.

Chuck Shaw? Where are you? Inform us all...

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DaveStroman2

Mike, Don't be silly. If you use a mod-con boiler, p/s pumping is a must. If you use a cast iron or copper boiler, you must protect from condensation. Either way, you will probably use 2 pumps. I have seen copper boiler distroyed in just a few years from being rotted from the inside out due to too cool return water temps. There are so many mod-con boilers available here in the Denver area that will all work fine. Talk to the heating Dept at Dahl, Ferguson, or HVAC. They can help you design a system. Or just call me, I will give you some direction and you can even come to see one of the jobs I have done.

Dave Stroman, Denver

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Boilerpro_5

Not true, Dave

Pressure drop through a gravity conversion system is very very low so very little pump energy is required. While many modcons need very large pumps to keep water moving due to very restrictive or long passages, or both, many modcons do not have these restrictions. Dunkirk and Triangle Tube both talk of non P/S piping arrangements. Running these boilers with a high temp increase through the heat exchanger will allow you to pick up additional efficiency because return temps will stay lower with the same system output. There are still minimum flow rates on most boilers, but there's a large amount of room to work
here. The mimimum flow rate on the TT Prestige 110 is 3.9 GPM when the boiler is at full fire. This is about a 50F delta tee across the boiler. When looking at the boiler pressure drop and the supplied pump curve, this leaves about 15 ft of available head from the pump to drive the system. If you design closer to the European system delta tee standard (around 35F temp drop/rise), you'd need about 6.5 GPM through the boiler. The factory pump still has about 12 ft of head to power the system.
In my mind, the optimum setup for a gravity conversion would be to use a modcon with straight through piping, balance the flow through the radiators so you are running about 35F to 40F delta tee through the system (to leave a little room for unknowns) at design and just let 'er rip. Since most gravity conversion I have worked with (and some steam to water conversions) only need about 150F average water temp at design in the radiators and much more importantly about 115F on a typical winter day, you'll see about 132F return temps at design, and about 105F return temps on the typical day. Makes for pretty efficient use of the condensing abilities of a modcon. Oh course, from what I understand, the Viessman 200 will adjust flow rates through the boiler compensating form load and firing rates,to gain even better efficiency.

Boilerpro

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DaveStroman2

I guess I am used to the very restrictive HX in many of the boilers I have used. Also, I usually use the smallest circ I can get for the gravity portion of the system since that part will practical still flow by gravity. I have seen systems where you could turn off the pump once you get a gravity flow going. Sometimes I even do boiler protection by cycling the system pump based on the boiler return temp. Set the aquastat on the boiler return to 140 and let it cycle the system pump. This lets the boiler and boiler pump run continously when there is a call for heat. Not the most high tech way of doing it, but it works. And certainly not the way if you are also doing DHW heating as you do not want gravity flow at all. I use the Taco 2 way I controls now.

Dave Stroman, Denver

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Boilerpro_5

Interesting about the Gravity flow

and turning off the pump once it is established. Some here have talked about piping boilers P/S to a gravity system loop and letting it run by gravity like you said. I have a one pipe gravity system that this may be the trick if and when the new owners replace the old boiler. I did too well of a job tuning the old boiler up....it's running in the low to mid 80's% on my testor and their bills are pretty reasonable, so they're in no hurry to change it out. Alas, one of the disadvantages of having a combustion analyzer!

Boilerpro

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