pump sizing for hydronic baseboard system

Robert Jordan

Apart from sizing the pump and long loop length .... How about the heat loss in the room/building? I dare say the building envelope isn't tight and properly insulated, which is properly installed spray foam or dense pack cellulose. Fiberglass just doesn't work. Keeping the heat in goes a long way towards reducing pipe sizes, euipment size and keeping people comfortable.

j moore

pump sizing for hydronic baseboard system

I have a jvs 225,000 btu dual stage boiler and one of my zones will not get up to heat. The bypass loop is plumbed with 1 1/4" copper and driven with ups15-58fc pump. A zone pump pulls off the bypass loop also with a ups15-58fc on 1" copper and pumps into 1" manifold serving six zones of various lengths on 3/4" heat pex, all running in parallel, controlled by individual zone valves and returning to bypass manifold. Each zone is in loop configuration with baseboard in series.

The zone with the most trouble heating is the one with the most pipe and fittings as follows: 240' of 3/4" pipe, 28' feet of baseboard and (48) 90's. The shortest and least restrictive zone heats just fine and has 110' of pipe, 15' of baseboard and (26) 90's. The other 4 zones average 145' feet of pipe, 24' of baseboard and (37) 90's.

Some people have suggested that both pumps are undersized and the zone pump in particular is causing insufficient flow to the problem zone especially when other less restrictive zones are open.

Can someone help me determine proper pump sizes?

Thanks,

j moore

GW

so you have 154' of bb, so about 92,000 btu, so lets say 10 gpm for easy math. the killer is the long run, you may want to round off to 400' developed (taking 90's into acount). I vote for 40' hd at 10gpm. Wow, that's off the charts.... try a 26-99; you need much more fire power

Gary



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GW

does the troubled zone work when it's the only zone calling? That's a pretty long loop.

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j moore

pump size

Gary,

The bad zone has been deficient even when it is the only zone calling for many hours at a time. It has been difficult to evaluate performance with fluctuating outdoor temperatures. The bad zone thus far is struggling to maintain 68 F and 64 F in the two bedrooms it serves with stat set at 75 F and outdoor temps at around 0 F. This evening the home will experience -20 F. The other zones (with similar heat calc attributes and ratios of baseboard to cubic feet of heated space) have performed substantially better.

A well informed product rep has also suggested a 26-99 for the zone pump. However, as the GC, I would like to be careful on this issue before I suggest a "solution" to the licensed master plumber who installed the system. One tech also suggested that the other pump (driving the bypass loop) should be sized at rate of 1 GPM PER 10K BTU of input which would require a pump with 22.5 gpm against head pressure of the bypass loop. The 15-58 (as you likely know) maxes at 17.5 gpm at 0 head. However the temp increase from boiler inlet to outlet has seemed satisfactory (in the +20 F range)

Your response thus far has been very helpful and greatly appreciated. This home site could have nights reaching -30 F to -40 F, so any further insightful suggestions are welcome.

Thanks,
j m.

GW

pumps

yes, I see your point, you don't want to step on the guys toes, but we've all been there (there may be a perfect person out there somewhere). with today's informatioon highway, it's not too uncommon where I have homeowners popping questions on me that realy open my eyes and keep me on my toes. You shouldn't feel bad about mentioning that you 'had some time to spare, did some looking on the internet, and wondered if the pump should be bigger'. If he gets offended by that, it would be pretty sad.

This is a prefect situation for a variable speed pump like Wilo. Looks like the Wilo Stratos needs to be installed. I recommend you get a hold of the rep Mark Hunt and see if there's a way to make this problem go away without too many people's feelings getting hurt. Bottom line is the pump is just to small. The pump will cost someone some money, but the way it is now will lead to unhappy home owners.

I have to admit i didn't understand the way you described the 'by=pass' piping, but the fact of the matter is the zone pump is too small. And likely the bypass pump could be set to its lowest speed (pretty easy to dial in just by taking temp readings).

Gary

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Unknown

The boiler pump is big enough

The boiler pump gets sized to boiler OUTPUT, not boiler INPUT. You'll be fine there.

It's that long loop....

What is the temperature difference on just that long loop?

Noel

j moore

temp delta

Boiler output maxes at 190 F and cycles as low as 170 F. Measuring with infared thermometer I have observed approximate (without rigorous scientific method) return temps ranging from 135 F to 159 F on that zone.

Unknown

with that amount of baseboard

you should see less than a ten degree F. drop on that loop. when you're pumping it fast enough...

Noel

Lil-Roc

Pipe Size

Sounds like piping undersized. 225k btu 10 degree TD= 45gpm with 2" primary loop. Heat carry capactity of 1" copper @8 gpm & 20 degree TD 80K BTU, 1 1/4 copper is 14gpm with 140K BTU's. go over your piping.

Unknown

I agree with Gary & Noel,

Your primary pump seems ok, the prob sounds like the secondary,,, it`s gotta be able to get there.

Jed_2

Bottleneck!

"A zone pump pulls off the bypass loop also with a ups15-58fc on 1" copper and pumps into 1" manifold serving six zones of various lengths on 3/4" heat pex, all running in parallel, controlled by individual zone valves and returning to bypass manifold. Each zone is in loop configuration with baseboard in series."

1" copper pipe will not handle the combined flow requirements of those 6 3/4" zones. Yes the circ is too small, also. But, I take issue with the suggestion that a commercial Wilo Stratos is the answer. A UP64-99 probably is called for because of the "ups&downs" of your loops. Heck, that 240' circuit has that much equivalent length in just the 90's. I'd suggest a DPV (differential bypass valve) in this case. Yes, it isn't electrically efficient as far as the circ's operation (I forget the correct term for that), but the Grundfos isn't that big a circ. Is there an "Echo"(sp) available? The manifold should have been at least 1¼"!

Jed