Flow of hot water (faster vs slower)

mixer440

What's better: Water circulating fast with the circulator turning off part of the time?

or>>

Water circulating slower with the circulator on almost all of the time?

Grundfos 1542 vs 2664

Steamhead

What kind of system

are we talking about here, Mike?

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mixer440

Sorry to be vague. I'm just curious. I don't want to complicate things either. Let's say you had a loop of hot water and when you used the 2664 you got heat with no other complications (forget about noise...etc). The circulator runs for awhile then turns off. The waters moving the btus pretty fast.

On the other hand, you try a 1542 in the same exact circuit and notice that the pump is running almost all the time, and you still get heat---probably a little slower.

So. Ignoring design and problems, which would be:
----more efficient considering cost and heating?
----and maybe more important, can a 1542 run all the time?

Does that even make sense?

Gary Fereday

Gary Fereday

I love ? if ?'s

if the piping is insulated, you can answer you own ?'s. which one uses the least amperage over time. Just look on the pumps rating. If it not insulated, the longer hotter temp has to be constantly replaced, along the pipe's length. That could be costly. And one more thing, a constantly running motor cost less to run than one stopping and starting a lot. Any electric motor is a short circuit upon start up. that is and can be expensive. So pay your money and take your chance. Good luck! (either motor is not a big drag on the power meter anyway) jmho bigugh

Frank_3

By any chance is the boiler running more frequently when using the slower pump?

Theoretically, at least, the slower pump will produce a greater temperature drop, so the return water temperature will be cooler, which should make the boiler fire more often. That'd only be noticeable, though, if the difference in temperature drop between the fast and slow pump was significant.

The only other thing I can think of is that you're probably not doing this on a design day (zero degrees outside in my part of the country). The slower pump and lower return temperature could be a problem if the room needs a lot more btuH on a design day compared to the day you were trying the two pumps out.

My 2 cents.

hr

Pumps

The 26-64 is a 180 watts while the 15-42 is around 85 watts The new 15-58 super brute is 89 watts on speed 3. This may be the best bang for your electrical bucks. It all depends on how much you need to move against how much resistence. Run the numbers! Or guess if you want

All wet rotor pumps are terribly inefficient, electrically speaking. If you run them on the knee of the curve maybe 20- 30% An 85 watt pump moving 10 gpm (of water)at 10 feet of head is running about 21.5% efficient. Run them down curve and they really look bad! Say you only need 3 GPM and you use that same 85 watts. Ouch! lots of sloshing going on without much energy being transfered for the same amount of electricty consumed! Pick a better pump, maybe a 25 watt version!

Breaks me up when I see a wall covered with a dozen or so same sized pumps moving a 150,000 BTU/hr. load. Probably not one running at it's best efficiency. How could they be. But it looks impressive, and wins contests. 12- 85 watt pumps = 1020 watts. May as well use that 1 KW to heat a room with electric baseboard at 100% efficiency! Just kidding!

You will notice a movement in the pump industry going back to open frame air cooled motors, on small circs (B&G PL series and some Armstrongs) Claims are about a 40% increase in efficiency by getting the motor out of the drag imposed by the fluid in a wet rotor pump!

Noise has been my complaint, however with these pumps. I want my radiant systems as quiet as possible. What to do what to do! Always a trade off.

hot rod

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hvacfreak

I feel your type of heat distribution would determine this. Cast iron radiators vs copper fin tube- fin tube will need higher velocity , cast will be slower to heat regardless of velocity. Just my opinion I could be wrong.
- JACK

bluenose_10

10 is 10

If you only need 10 gpm @ design temp. and the 15-42 gives it to you, why would you put on a bigger pump.I've had 15-42 run 24/7 during heating season ( 7 months)for numerous years, with no problems.Like you've heard already your not talking about big numbers on power, probably less than somebody drying a load of clothes in an electric clothes dryer. But that's just my two Canadian cents

Duncan_2

Let's see...

For an indirect water heater, higher temperature, faster flow would be better: quicker recovery.

For a space heating system, lower temperatures, constant circulation would be better. Less temperature swings, more comfort.

Slower circulation and lower temperatures need to be within reason. Delta t and gpm deliver the heat. That's what makes reset and thermostatic radiator valve so nifty.

Sure a 1542 can run constantly, as long as it's not pumping against a dead end.

Grundfos 1542 almost always, on residential. 2664 on long loops with high head.

Roger Litman

Very slow water

If you circulate the water very slowly, you may find that the last radiation in the loop will not get hot as you have pulled the heat from the water with the first part of the loop. That is why the baseboard is rated differently at 4gpm rather than 1 gpm. At those numbers with using the recommended maximum length( about 80 feet commonly) there is not a lot of difference. There is a generally better comfort level with a more continous circulation which can be achieved with either using your baseboard at 300BTU and keeping you boiler at lower temperatures(my favorite) or by using outdoor reset.

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scrook

slower circulation...

the water'd move slower and the delta t would be greater but less volume of the cooler water would return to the boiler vs more of the 'less cooled' water so the heat removed from the boiler would be the same in the end and it would fire about as often for about as long in either case.

Frank_3

I stand corrected. I never thought about that or bothered to do the math, but you're right. The temperature of the boiler's water mass decreases at about the same rate.

You learn something new every day.

That being the case, I'd still stick with the higher flow rate.

Duncan_2

Efficiency

System efficiency is higher in systems with lower operating temperatures. Less parasitic and standby losses. In these systems, the pump will run constantly or nearly constantly. It may cost a little more up front for a dynamic control, or condensing equipment, but in the long run, comfort and savings will be greater.

Too much on/off hammers equipment to death, too, like the difference in a car's longevity and repair record contrasting city stop and go driving vs. freeway cruising. It's just less wear on the equipment.