Circulation pump sizing with multiple fan coils.

Dave_KC

Questions for the forum when sizing a circulation pump with multiple fan coils.

1) Since there doesn't exist a time when all fan coils will be calling for heat simultaneously, is the preference to use a worse case number of fan coils (ie the most calling for heat at the same time), or another factor?
2) For the fan coil BTUs per circuit, do you use the fan coil heating capacity specification, the manual J value for the room the fan coil is running in, or the fan coil waterflow volume?
3) Would you recommend using a Delta T of 20 or 30 for the pump calculation?

leonz

If each fan coil is heating a separate zone has its own thermostat a separate "circulator" for each zone may be needed.

If you have not done a heat loss study to size a boiler the points are kinda moot.

EBEBRATT-Ed

@Dave_KC

The mfg of the fan coil or the install manual will tell you the gpm required for each fan coil and the temp drop across the coil. Adding up the coil GPM from all coils will give you the flow needed in that circuit at design conditions.

Once you know the gpm required you can size your main pipe for the total gpm and the branches to each coil based on each coils gpm.

The you have to calculate the pump head which is probably (but not always) the fan coil with the most resistance to flow. You calculate the flow in the main including pipe and fittings at the total flow in the main. Then add that to the one fan coil that has the most resistance at it's required gpm including the coil, branch piping from the mains and any control valves pipe and fittings.

If the fan coils are oversized for the heat loss you could size the pipe only for the heat loss only. This could cause balancing issues at design conditions.

My decision would be based on how much oversized they are.

If you have a choice on which TD to run fan coils are usually 20 degrees or less to prevent blowing cold air but it's not written in stone

Dave_KC

Thank you, Ed. Just what I was looking for. I calculated based upon 5 fan coils running at the same time as well as 7 fan coils:




We're replacing the current boiler with 2 new 100K modulating boilers for redundancy. The old circulator is a UPS 40-80, running in low speed. While no complaints with heat, it just seems overkill for my calculations?

GGross

Are your fan coils piped separately from one another on a main header? You would only need calculate the largest pressure drop circuit, not added together

Dave_KC

Correct, they are piped separately on a main header. The 3.1 pressure drop is multiplied by the # of circuits in my calculations. Are you saying it only needs to be calculated for the 1 circuit?

EdTheHeaterMan

Dave_KC said:

Correct. I just calculated based upon the fan coil that is furthest from the main loop (280+30 feet). Assuming it has the greatest pressure drop.

Then why is the Head on your chart 3.1, but you added them together to come up with 17.5 or 23.7 for the total? If all you need is 3.1 ft of head for the highest pressure drop, the all the other zones (or loops) will work with 3.1 or less.

Dave_KC

Thank you. Sounds like since the circuits are in parallel, the 3.1 ft of head will suffice. Are the pump sizes ever adjusted for buffer tanks?

EdTheHeaterMan

The Pump Head is calculated based on the largest pressure drop the pump needs to overcome. If that includes the buffer tank then, Yes, the buffer tank is considered part of the work the circulator has move water through.

Here is a text book I used to teach my one day Hydronics seminar https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference Guide.pdf
The easy rule of thumb is explained on pages 7 and 8. (see attachment below)

For more information on pipe sizing and the amount of heat that can be moved through a particular pipe start at page 4

mattmia2

(but the buffer tank itself is going to be essentially 0 head compared to the pipes leading to and from it)

hot_rod

A delta P circ would be ideal for multiple liads

jumper

You may end up with circs for each coil. Especially if controls are on/off for each coil. Put a bypass farthest away from boiler or chiller whose circulator can then run continuously.

EdTheHeaterMan

jumper said:

You may end up with circs for each coil. Especially if controls are on/off for each coil. Put a bypass farthest away from boiler or chiller whose circulator can then run continuously.

?

Using one ECM pump.... Really you think he need to use separate pumps? I believe that @hot_rod has the best advise. no Bypass and a ∆P ECM will work best.

jumper

Really you think he need to use separate pumps?

Otherwise it's zone valves for on/off. Do you prefer changing solenoids or cartridges?
Bypass is to keep sufficient water flowing. That "hydraulic
independence" touted by those primary/secondary fans.

EdTheHeaterMan

I have used Zone valves on all kind of systems. I never had a problem with using them as long as the correct pump is selected. Since @Dave_KC is using a ECM pump, there is no need for a bypass, the pump will match the load based on the number of open zone valves. And as far as replacing zone valve actuators or circulator cartridges, most zone valve actuators can be changes without getting wet. But that is not a reason for my decision, Zone Valves are more efficient and less costly IMHO. Understanding all the choices and you will make better design decisions.

in this text I use to teach a Hydronics course... https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference Guide.pdf ...you can find lots of helpful information like this on page 19

So don’t oversize circulators. Use the ones in our “Rule of Thumb”
and you’ll be in good shape.

We believe the Series 100 is the best choice for zone valves because it
has a very flat performance curve. Take another look at that curve. Can
you see how the head pressure hardly rises at all as the flow slows from
say, 25 gpm to 4 gpm? The Series 100 was designed for systems with
zone valves. It has this remarkable ability to shed load without building
much pressure. Not all circulators can do this.
If you’re having problems with zone valves that whistle or bang
when they close, try a Series 100 in place of the circulator you have
in there now.
Watch how the problem disappears

The ECM pumps make the adjustment automatically. So they are actually better than the old school B&G 100

Just rambling thoughts from some old guy. This stuff worked long ago and still works today.

hot_rod

jumper said:

Really you think he need to use separate pumps?

Otherwise it's zone valves for on/off. Do you prefer changing solenoids or cartridges?
Bypass is to keep sufficient water flowing. That "hydraulic
independence" touted by those primary/secondary fans.

A bypass is a highly parasitic device intended for fixed speed circulators. With such a wide range of ECM to handle varying flow requirements and saving 50-80% power consumption, why not?

I suspect the wire to water efficiency of that series 100 is maybe 15%?

jumper

For systems with many fan coils I used pumps with steep curve so that flow doesn't vary that much. I sold coil & pump as a package. I didn't get complaints about those. I did worry about over powered main pump overwhelming coil pumps. One reason why pump salesmen fear series pumping.