a piping question

R. Kalia

I am a homeowner and I am not planning to do the work described below myself, but the skill of contractors varies widely, as you know, so I want to educate myself on this subject.

Our house has two zones. One uses 2" and 3" pipes to radiators (converted gravity system) and is driven by a B&G series100 (0gpm at 8ft, 37gpm at 0ft). The other has long streches of 3/4" copper pipe to baseboards and is driven by a smaller pump with higher head, NRF22 (0gpm at 15ft, 22gpm at 0ft).

Monitoring the thermostats' usage tells me that the two zones call for heat about the same amount each day. In other words, they don't really need to be separate zones any more than any given room or rooms in anyone's house needs to be a separate zone.

I'd like to ask the contractor who will install a condensing boiler to hook both zones up to a single pump; that way I can have it circulate constantly and have a single thermostat turn the boiler on/off but not the pump.

However, I don't understand the science of circulation pumping and am worried that maybe flow to the higher-head (thinner-pipe) zone will be inadequate or some other unexpected change will occur. I know the heating rate is not strongly dependent on flow rate, but....

So my question is, how can I figure out why the original pump choices were made, whether they are good choices, and what the choice would be if we used a single pump. How can I measure the head in a single zone? How can I measure the flow rate from the current pumps? (Summer is a good time to do this.) Our house heats up slowly...I'd like to know if the flow is adequate or if we should use a bigger pump for the high volume former-gravity zone. What happens if a low-head zone and higher-head zone are connected in parallel to the same pump? What are the tricks for connecting them so the flow rates come out reasonable in both zones without having 2 pumps? Is there a book where this stuff is explained in detail?

PS I know I can leave the 2 pumps as is, and have them both wired to run all the time. That would cost a little bit more in power, maybe, but not a big deal. I would still like to figure out the hydronic principles involved and find the most elegant solution.

Mr Takagi

Similar situation

I too am only a HO, but your situation sounds a lot like my house. I have an old converted gravity system with cast iron radiators, but the dining room has been changed over to 16ft of baseboard at some point. The baseboard is piped in with the rest of the house on one zone with a B&G 100 circulator and I have never noticed that room being any hotter or cooler than the rest of the house. This may not be the "correct way", but that's what I got with the house and it seems to work. I too am looking at a condensing boiler to replace mine- the guys here on the wall are a real help in researching your options.

R. Kalia

I think I found most of the answers I need at

http://www.pmengineer.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2732,116233,00.html
and
http://www.pmengineer.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2732,106650,00.html

What I'm getting from here is that since 2" pipe and 3/4" pipe have an R value (hydraulic resistance) that differ by about a factor of 100 on a per foot basis, and the pipe lengths in the two zones are roughly the same, it is VERY difficult to connect the two systems in parallel to the same pipe and get sufficient flow through the 3/4" pipe zone. This is not based on a detailed calculation but just some rough estimates.

Am I right in a general sense?

S Ebels

In a word

Yes

You have two very different types of piping there and mixing them on one pump would not be a "good thing". Widely different "head" requirements.

DaveGateway

Beware of loosing zones

I don't agree that most zones in a home all have the same heat requirements, especially on different floors. Most people, including myself will try to split a house into more zones. With different piping flows, rads and BB in your home, you might find constant circ will expose which zone actually puts out more overall heat and notice temp differences, requiring TRV's, flow valves, or going back to switching circs on and off.

MikeB34

remember daniel-san

Water take path of least resistance. With 2 drastically different pipe sizes, more flow would naturally go to the 2-3" pipe over the 3/4". This is probably why you have 2 pumps, to ensure adequate flow throught he 3/4" pipe.

I would leave em both in place.

Good luck. Mike

Mike Kraft_2

Joe makes a good point.

Cast iron radiation will hold the heat and radiate heat after circulation is off(thermal mass).Where as CU finned HWBB will cool down faster.Putting all emitters on the same pump will leave you with hot and cold areas.

Using constant circulation as a stradegy with a condensing boiler is great.Adding TRV's(thermostatic radiator valves)to the iron rads will allow specific control in each room.Danfoss offers a TRV for HWBB also.Your curve can be adjusted to the room that offers the least amount of BTU's that the emitters will allow on design day.If the water temperature is not cool enough to take advantage of the condenser you may want to add another mixing device to reset its temperature.This will allow the higher mass emitters to make the boiler condense.Typically cast iron rads are way over sized to rooms do to many factors.Insulation,window upgrades and original oversizing do to the era of installation.

If you do take this route be sure to allow for a device called a Pressure differential bypass valve(PDBV).This will not allow the pump to dead head do to a drop in the pressure.This of course would be a result of TRV's closing.

cheese

R. Kalia

TRV for HWBB?

> Danfoss offers a TRV for HWBB also.


Thanks for the detailed reply. I have never been able to find such a valve. I have studied the Danfoss web page but there's nothing obvious. Can you guide me to this calve? many thanks,

Wayco Wayne_2

I recently did

a job where we took out the gravity piping and ran Multicore tubing instead. It freed up the head room in the basement so the HO could put in a rec room. It also was constant circulation off a manifold so he could balance the flow between radiators. In the future he could even run thermostats and wire them to zone valves on the manifold, (telestats) I'll see if I can find a picture of this job. His heating bill went way down after we were done. WW

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Mike Kraft_2

Chuck

Cut and paste.This is an add on to the RA2000 series.

http://www.danfossheating.com/catalog/heating/heatcoolvalves/kovm.htm

cheese

R. Kalia

Oh, 3-way mixing valves driven by external signals. I thought it was TRVs.

Constantin

Yet another neat Propress/Munchkin installation.

Kudos on the installation, a neat, easy-to-follow job.

The use of black steel pipe for the gas supply instead of CSST is a nice touch also.

If there is one thing I would improve, it's the electrical wiring. Unlike pipes, the stuff does not have a tendency to stay straight. The loose wires have a way of visually distracting...

Don Walsh

Wayco Wayne

Has the ProPress paid for itself yet? Grumpy

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Wayco Wayne_2

Not yet!

But it's a lot to pay back. In the Summer we don't do as much boiler piping as we are an HVAC company. In the winter though we were mowing down some jobs. It cuts labor time way down. By the Way we did go back and neaten up the wiring since that picture was taken. I should have taken another picture for display purposes. WW.

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