Sizing Circulators and other questions

Eugene

The house in the last week (today is 11/23) seemed to have a very hard time getting warmed up. We are not yet moved into it, so I have the heat set down to about 60 F. We went into the house to do some cleaning and moved the themostats (there are 6 heating zones and 2 hot water zones) to 68F. It took probably 4 hours to get the house up to that temp.
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I have since discovered that two zone valves were malfunctioning, so the dining room and 1st floor office were not getting heat. I think I can handle the job of replacing these. The previous owner of the house said that his oil company said that the circulator is undersized. Here are some details that might help.
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1. Weil McLain furnace 181,000 BTU/hr, Water Mbh=157, Max W.P, water=30PSI

2. 8 zones, 6 for in-floor radiators (like kick panels) 2 for independent indirect hot water heaters

3. Zone valves are 3/4" honeywell V8043E

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Here's the first question...
The circulator pump I have is an B&G SLC-30 which I understand is no longer made and produces 16GPM . My supply house told me that one way to size a pump is to add up all the zones where 3/4" = a max of 3.5 GPM and get a pump that can do that. Is this a valid formula? In this case, 8zones x 3.5GPM = 28GPM which would indicate that the SLC-30 is under powered.
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Next question I asked my supply house was to find a more powerful replacement. They suggested either the B&G NBF-22 (22GPM) or the NBF-33 (37GPM). So my next question is, would 37 be "oversized?" Is there a downside to making the pump larger than it needs to be? Conversely, would a 22GPM pump be enough? I guess it could be as long as I dont have all zones running at the same time, and even then it might have a negligable effect on the heating...
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What is your advice?

Last question. I recently learned about a product by Beckett called the heat manager where it will not cycle the blower everytime heat is demanded. They claim to reduce your fuel bills by 10-20%. Any experience with this product? In theory (at least to me) it seems very logical.

Thank you very much! I live on your website now!
Eugene

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Others will know more about this, but it seems to me you have confused slow heating with slow circulation. The circulation rate doesn't make a big difference to heating rate, unless water is not circulating at all. Hydronics is is not like forced air, where you're pumping hot air directly into the air; here there is a radiator, and its heat output depends on how warm it is and not on how fast water is flowing through it. Slower circulation = larger delta-T (i.e. water cools more whil passing through the radiator), so BTU output does drop, but only slightly.

Heating the house 8F in 4 hours doesn't seem so bad to me. Hydronics is not like forced air.

Pumps don't have a fixed GPM, it depends on the head pressure. You have to use pump curves. The rule of thumb for GPM they have given you makes no sense to me. For a 20F peak delta-T, you need just under 1gpm through the boiler per 10,000BTU of peak heat load. And if you want the gpm to each zone, you need to use the heat load of that zone. And the gpm has to be determined from the pump curve using the head pressure of the zone. But if the gpm is not exactly right, no big deal, you'll just get a higher or lower delta-T.

The downside to higher circulation rates is that your pump will draw more power and also you may start hearing noise in the pipes. You want to run hydronic systems slow and steady.

The Beckett product is a kludge. The best way to get outdoor reset is to get outdoor reset. Neither this product nor outdoor reset will save you 10-20% except in special circumstances. Most people will save maybe 5%.

Einsiedler_2

current delta-t's

Best way to determine if your current pump is undersized is to advise what the current delta t is across the system & across each zone.

If you have thermometers, great. otherwise you may need to beg/borrow/steal an infrared gun, strap on thermometers, or otherwise..

If we know temp out & returning to boiler
and temps in & out of each zone,
we may be able help further..

by the boiler & a common 20F delta-T, I would think that 16gpm should suffice. But you'd need a pump that does 16gpm @ the head pressure your system requires. The NRF22 may do 22 GPM, but at little or no head. What is it's flow rate at the "knee" of the pump curve?

my 0.02 worth.
EIN

Ron Schroeder_2

Hi Chuckles,

I sort of agree with you about the Heat Manager. It seems to get most of it's benefit from creating a large high limit differential rather than from lowering the boiler temp. Since almost all boilers are over sized it does help.

Ron

Hugues

Wiring circulator

Why use a low voltage thermostat, relay and transformer instead of a high voltage thermostat to turn on a circulator?

Zoning with a circulator and the high voltage thermostat opens and closes the circuit. To me it's much simpler then using a 24v transformer to power a thermostat, then the thermostat trips a 24v to 120 v relay to turn on a circulator? You save on the transformer and relay with using a dirt cheap electric baseboard thermostat that is rated at 1500W plus usage for a 100W circulator.

I'm new to this, so please show me the path.

Thank you.
Hugues

Tim Doran

Do the math

The correct way to approach this is the measure up the connected load on each circuit. So how many feet of baseboard are you trying to drive? I would typically also do a heat loss on the space(s) to make sure that the load and the application concure but in your case I would work from the radiation. Once you know the btu's required you can convert them to gpm. GPM = btu /(delta T x 500) is close enough in your case unless the system has glycol.

Add the total gpm for all of the circuits and this is what you need for flow. Now you must figure the head or resistence. You should figure all of the pipe and fitting loss for each circuit as well as the pressure drop through things like your zone valves. The worst case circuit will basically determine the ft/hd that the circulator must overcome.

You now have the two basic pieces of information required to properly select a circulator, flow and pressure drop.


Tim D.

Einsiedler_2

SPDT

by using 24V t'stat thru relay, you have an extra set of relay contacts for other use - such as triggering call for heat to boiler.

thats one advantage.

EIN

Eugene

the math

Tim Doran seems to have proposed an accurate way to go *if* I was building the system from scratch because I cannot even begin to estimate the fittings or the length of radiators/pipes nor do I have any way to calculate BTU in your equation. I am also not sure what number to put in for delta-T.

On the other hand, it seems that EIN's proposed method is readily measurable. Place a thermometer on the supply and return side of any zone, measure the difference. This is something I can do!

But, what is an appropriate delta-T? is 20F the right number? If so, then I should easily be able to tell if my current circ pump is adequate or not (delta-t<20F=pump ok, delta-t>20=pump not ok)...Actually, it seems to me the best way is to run all 8 zones simultaneously, then measure each zone delta-T. If all are in 20F (or whatever the right number should be) then I'm ok.

As for this busines of "head" I will try to get my supply house to fax me the "curves" for these pumps, but it is still not clear to me how to determine how much "head" I have. Since my pipes are in the walls, I do not see how I could figure this out. Also, the house is heated on 4 floors so each floor could be significantly different. Any suggestions?

thanks
Eugene

Plumbob

You are right that the advice you are being given is not easy to implement. You asked a question and so people are answering it. But is the question worth asking? My advice is, don't "solve" a problem you don't have. It seems your system is working quite well.

If you want to "solve" it, one apparently wasteful but actually cost-effective way is to buy a bigger pump and put it in yourself. Pumps are fairly cheap, especially on ebay. See if it makes any difference (I bet it won't). See if you start hearing turbulence noise. If it doesn't work, throw it out and put your current pump back. Three-speed pumps are especially good for this; they are about the same price as single-speed pumps and give you three speeds to try. I bought a Grundfos 15-58 three-speed on ebay for $70; unfortunately, that pump isn't big enough for your purposes.

Einsiedler_2

Determining Headloss

Static Pressure = 17 psi+ (4 stories)

Head Pressure = Velocity Head + Pressure Head
Velocity Head = Velocity (ft/sec) Squared /Divided by 64.4
Pressure Head = P-Static(psi) * 144 / divided by Density of fluid (use 60)

So with a few assumptions..

Systems should not exceed 7ft/sec. so we'll use 6ft/sec.
6.0~squared, divided by 64.4 = 0.559 (Velocity Head)

Pressure head = Static Pressure * 144 / divided by Density (60)
17*144/60 = 40.80

Total Head = .559+40.8 = 41.35 Feet.

seems high doesnt it.. mind that this is based on 7 ft/sec. your sys is prob closer to 4ft pper sec, but that wont change the head much.

get a pump that will do 16gpm @ 44ft hd.
install pressure gauge on both side of pump (inlet & outlet)
and measure pressure differential (psi), multiply by 2.1 & whalla, thats the true system head, that pump is seeing. Cross reference to pump curve & the actual flowrate will be revealed.

EIN

Eugene

I gotcha

I understand. Only reason I thought I had a problem is because the fuel company that services the unit said I should install a "bigger" circulator. At the time I was even more ignorant of all this stuff than I am now and did not know what questions to ask as to why. But now it seems a sensible thing would be to ask them.

The other reason I thought he might have been right (again as a novice) is that the previous owner of the house needed space heaters in certain areas. That got me to thinkin that perhaps something of the system was underpowered. The furnace says 181,000 btu/hr and the house is about 5200 square feet (basement is additional sqft, perhaps 500 or so). I have no other information about "R factor" or heat loss or anything. I do know the windows are terrible and that will be one of the first improvements I will make.

I do appreciate all the input (even the esoteric and mathematical!) because I am learning great stuff!

Eugene

Joe_47

pumps

Do your self a favor... Stay away from B&G, go with Grundfos. Thier UPS15-58f is a three speed pump which could work in many applications. more reliable and consistant

Ron Schroeder_2

Hi Ein,

Don't forget that in a closed system, static head DOES NOT add to the pumping head.

Ron

Ron Schroeder_2

> I understand. Only reason I thought I had a

> problem is because the fuel company that services

> the unit said I should install a "bigger"

> circulator. At the time I was even more ignorant

> of all this stuff than I am now and did not know

> what questions to ask as to why. But now it

> seems a sensible thing would be to ask them.

> The other reason I thought he might have been

> right (again as a novice) is that the previous

> owner of the house needed space heaters in

> certain areas. That got me to thinkin that

> perhaps something of the system was underpowered.

> The furnace says 181,000 btu/hr and the house is

> about 5200 square feet (basement is additional

> sqft, perhaps 500 or so). I have no other

> information about "R factor" or heat loss or

> anything. I do know the windows are terrible and

> that will be one of the first improvements I will

> make.

>

> I do appreciate all the input (even

> the esoteric and mathematical!) because I am

> learning great stuff!

>

> Eugene



The cold areas could be under sized radiant, out of balance flow, airbound or some other problem other than a too small circ.

Ron Schroeder_2

The cold areas could be under sized radiant, out of balance flow, airbound or some other problem other than a too small circ.

Also, if you must replace the pump, I would lean toward 2 pumps with 4 zones on each. Going from only one zone valve open to all 8 at the same time is a very big move on the pump curve for the pump to handle.

Ron

Einsiedler_2

stand corrected.

I stand corrected.

So what is the viscous friction then I ask?
and how does one calulate it if piping/fittings unknown (hidden in walls)..

How about ball parking by taking the building width (ft), length(ft) & height (ft) - add them up & divide by 10.

I'd bet this is close..

EIN

hr

If you do upsize

to a high head circ, with that many zone valves you will want to add a pressure activated bypass valve. this will assure that if only one ZV is open you will not get noise, velocity, and possible leak by on the closed valves.

The delta t of a system changes. A cold house or zone will start with a larger delta t. As the zone nears it's setpoint that delta t could drop to only a few degrees. The load drives the delta t.

Take a look at these two pump curves. Suppose you had a system requiring 6 gpm at 21 ft of head. Which pump would you chose, and why.

One of these pumps will offer tighter flow under varying head conditions.

As the others mentioned pick a circ that matches your systems need based on the closest calc you can arrive at. Plenty of small pump choices out there these days

hot rod

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Plumbob

(a) While people here tend to be very knowledgeable, the field of hydronics has many people with little knowledge but a strong profit motive. "Not enough heat? let's sell him a bigger pump AND a bigger boiler!" After all, no homeowner can fight the logic that if something is not doing the job, a bigger one will be an improvement. But hydronics is a too complex for that kind of thinking. Fuel company people are some of the worst.

(b) If some rooms are cold (which you didn't say before), you DO have a problem. but a bigger pump probably won't solve it.

PS I'm a homewner. One of the first things I did when I moved into a house with hydronic heat is buy a bigger pump for one zone. I thought this would help it heat faster. It didn't do squat, of course, and it made so much noise upstairs that I got rid of it.

Now just because it happened to me doesn't mean it'll happen to you, but be forewarned. It took me six months on this site to learn enough that I was able to make intelligent decisions. And of the local contractors I talked to, 8 out of 10 were incompetent, so it was essential that I learn to make my own decisions.

Ron Schroeder_2

The Bell and Gossett rule of thumb is to imagine how you would run the pipes, measure that distance and multiply by 1.5 for the elbows. Of course, you also need to know the pipe size. 1/2 inch pipe should be 1.5 GPM, 3/4" should be 4 GPM and 1" should be 8 GPM. At those flows, the head will be about 4 feet for each 100 equivilent feet of pipe. For a zoned system, use the longest run.

Ron