Circulator engineering 201

GW

Did I get it right or the supplier dude?

<A HREF="http://www.heatinghelp.com/getListed.cfm?id=368&Step=30">To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"</A>

GW

Circulator engineering 201

I have this job coming up where I'm going to residentialize a 16 unit apartment complex. After a recent dilemma with my local supplier, I waited 3 days to finally get a motor for a Taco 1600 series circ. Now, in the same building, I’ll be replacing the 5 GPM boiler with two smaller boilers, Tekmar the deal, and I’d like to install two smaller pumps instead of the 1610 beast that’s there now (we’ll save the motor for another building). I can't deal with waiting for "non-shelf" parts.

Anyways, here's my question. I once was taught if you have one circ right after the other, you double the flow. If they're side by side, then come back together, you double the head. Did I get this right? I was at my local vendor today and the sales guy was saying it was the other way around.

Because I rambled on a similar post just a few minutes ago, I will install pressure taps so I can see the pressure drop on whatever it is I install. Just for good diagnostic politeness.

Thanks for the help

Gary


To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

gerry gill

i think its the other way

around.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Brad White_9

Series versus Parallel

Gary, sorry, you have it just backwards.

They supplier is correct. I hate that too!

When you have two circulators in series (the same ones, let's not mix and match) you double the head but get the same flow. The first one moves X gpm at the differential it would normally give. The second takes the same flow (cannot create what it does not receive) and adds it's differential pressure yet again.

If you have two in parallel you double the flow.

This last statement is in very rough terms and there are certain dependencies. For example if you run only one, your flow is "X". If the second one comes on (intermittently) the flow will not be "2X" because the pressure drop due to increased flow will rise by approximately the square of the flow. Your operating point will ride the curve (balancing what flow can be created against what new head resistance has also been created...). And this head versus flow business is an exponential function too...

For example, say you run one circulator at 5 GPM and it produces or works against 5 feet of head. Turn on your second circulator with the idea of doubling the flow. You may get only 8 GPM as a balance point because the head has increased from 5 feet to over 12 feet. The system curve will dictate your actual balance point, so this is just an idea of what can happen.

Now, you can select two circulators in parallel to get the flow you want, but two existing circulators in parallel will not double their output against the same system.

Your pressure tap approach is the best thing going, you can then see for yourself what the real story is!

Hope this helps-

Brad

GW

Thanks

I got it now and I totally understand you're thinking on the performance. I'll be "cramming" more water so the resistance (head of course) will rise accordingly.

This may be stretching the norm here, but would it be crazy to have a second pump on a set point control? I'm really not trying to build a freak here, but the way this building is set up presently is this: once the temp drops to 65 or whatever outside, a setpoint kicks on the 1610 Taco (the boiler is bumping limit 24/7/365, which will be addressed once the new boilers go in with Tekmar). That's all great BUT all the apartments have zone valves, and i know when it's mild out probalby 1/2 the apartments aren't calling for heat.

I can't imagine this is a great engineering accomplishment as far as overworking the 1610 goes. If ALL 16 units happen not to be calling for heat, there are by-passes at the end of the two main run-outs, so we're not dead-heading, but never the less I think my idea has some merit, what ya think?

gary

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Brad White_9

Flow Versus Capacity Output

Gary,

The relationship of flow to output is rather uneven. You can drop your flow by 50% and still get roughly 90 percent of your output. (All you have done is dropped your average water temperature by ten degrees if you are running a 20 degree Delta-T).

If you are running 180-160, your AWT is 170. Cut the flow in half to a theoretical 180-140 and your AWT drops to 160. Your outputs will be down but not as much as your flow would say.

Put it another way- say you ARE running 180-140 water normally and want more capacity. You double your flow and quadruple your pressure drop... and add about ten percent to your heat output. Oh boy.

So from what I am reading, you want to keep adding flow to meet demand...

With that many zone valves, I might think of a circulator with a VFD sized for the entire flow and run it off differential pressure. Very smooth. Save the DP valves should the VFD fail or go into bypass.

Nice way to control the building. Best bet for modulating capacity is to reset the temperature anyway. Not mess with flow.

Hope that helps!

Brad

ALH_4

pump

The first step is to plot a system curve, which will probably include a few assumed values because it is an existing system. What do you mean by a 5 gpm boiler?

Whether series pumps will double the head or parallel pumps will double the flow depends on whether or not you get to size the pipe, fittings, etc. If you have control over the piping, you can control the system curve to some extent. In your case, you have to track the system curve someone else gave you.

-Andrew

GW

5 gpm

5 gallons of oil, sorry about that. So 700,000 BTU input, so in theory I'd like to move 56 GPM or so. Actually, I just ran a heat loss and I'm going to install two 1.7 gph boilers (yes, I'm downsizing, or shall i say "right sizing"). with my smaller boilers I'll want to move about 35 or 36 GPM.

The boiler is in the middle of the building. It's about 180 feet each way. Two story building, maybe 12 feet vert from boiler pump to second floor BB. What do you think for head?

If it's too wacky to tandem the pumps, I could install two smaller pumps, one for each side (remember the boiler is in the middle of the building). Does this make more sense than my "bringing a second pump on when temp drops to x"? I need to send 18 GPM per side and the given head I mentioned; I forgot how to plot out the total length formula.

Thanks, gary


To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

hr

What about a VS bdelta P

pump? seems like the perfect application. Check with Grundfos or Wilo. I believe they have them avsailable in large sizes.

Or add a drive to an off the shelf pump.

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

GW

head

I looked at the good ole Burnham Heating Helper. 4.2' per 100'. I'll take the 180, add the vertical, and round it off to two hundred, multiply by 2, and figure 400 feet. 4 x 4.2 = 16.8 ft/hd. 17 ft at 19 gpm---I'll go with two (one for each side of the building) Grundfos UPS26-99BFC pumps, or two Taco 0013. Thanks for the help on this, Gary

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

hr

Keep in mind the 3 speed Grundfos

in the 26-99 series. Give a bit more adjust-ability.

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

ALH_4

dT

Ah, I missed that it was oil. Can you live with a 30 degree dT? Depending on the pipe size and the configuration, if you split it in half you might do as well as to get away with a 26-64 or 26-99 on each side. This is all hot water baseboard in parallel with a zone valve at each unit? I guess it's just a personal preference, but I prefer to use two smaller pumps independently rather than one big one.

-Andrew

ALH_4

Speed

I'm too slow for this! ;-)

Weezbo

you also triple the cavitation...

i think it is better not to close couple by flange to the two pumps instead give it some space like valve 3X pipe nipple flange on both sides of full port valve...

i like your idea of spliting the system in half and using variable speed control with an injection system much better.