overpumping?

Matt_21

for a new customer last year. the boiler is a vitodens with a low loss header. on the system side, the customer insisted on circulators for each zone. there are 7 zones of baseboard. each zone has a taco 003.
each zone was designed at 1gpm and about .62 ft of head. the taco 003 at .62 ft of head is putting out about 5 gpm.
there haven't been any problems with heating all winter. we had gone for a service call one time and the homeowner wanted to turn on all zones at once to make sure everything would work when it got into the single digits. once everything was on, the supply & return temps dropped and after an hour, the supply temp was only at 132* and the return was at 85*. we had the boiler maxed out at 167*.
i'm wondering if we are overpumping and should throttle down the flows to each zone. also, am i correct in assuming with the low loss header, we are only taking a percentage of the boiler supply water so it's going to take longer to increase the water supply temp.

Brad White_9

Yes, over-pumping

The 003's, small as they are, are performing toward the right side of their curve and as you suggest, probably dishing out about 5 GPM, practically full open.

Loss of temperature control is the first casualty and you are seeing it. A lot of "playing catch" within the LLH. I would not say it would take longer to come to temperature so much as you are running away from temperature control. The boiler will over-fire to try to keep up. You may get there but at a cost.

The smallest Vito LLH has a maximum flow rate of 17.5 GPM on the system side and you would be about twice that. Balancing valves are key.

You can throttle the return ball valves (not the circulator suction/isolation valves thank you), for the short term to test and see.

Long term I would install 1/2" or even 3/8" bona-fide balancing valves. I like Macon (they do have a 3/8" size, perfect for these micro-flows) but Tour and Andersson, Oventropp (MEPCO is the US version), Armstrong, are all good. Look for a good number of turns open to closed. Macon has ten, Oventropp/MEPCO has seven, T&A has four. All good.

Matt_21

brad thanks

for your help. if i install the balancing valves and open all zones at once, i assume it will still take a while for all zones to reach setpoint due to the low loss header. the owner had a WM cast iron boiler at his previous residence and would crank open the zones and watch the temp come up quick. i tried to explain this system works differently but he doesn't want to believe me.

Brad White_9

Matt,

If each circuit is properly balanced (flow to heat loss), the time it takes to warm up will be a function of your radiator sizing at the operating point. Remember that it is all BTU's in to BTU's out and it takes a given temperature water to get that output from the radiation.

In the case you have now, over-pumping is diluting your water temperature in the LLH so the radiation cannot perform correctly.

Your primary side runs in the 5-6 GPM range while your secondary circuits in total should amount to about 7 GPM if correctly balanced.

Right now you are running five times that, potentially, on the radiation side. Amazing it works as well as it does...


Agreed, the Vitodens has a lot of us "thinking differently". I am at the ground level of that myself. Fascinating. But we have to educate our customers to think differently also. That is the key.

Once you get things balanced and the customers sees the diffeerence, they too shall come to believe.

Keep me posted.

Brad

Joe Mattiello_2

vitodens is a low mass boiler isn't it?

Perhaps the system volume is higher then the boilers capacity to keep up with demand. You might require a storage tank to store heated water, which does take away from the boilers efficiency but in this case it may improve efficiency as opposed to realizing degradation of overall performance.
Joe Mattiello
Technical Support Technician
Tel. 401-942-8000 X 484
Fax. 401-942-2360
1160 Cranston St
Cranston, RI 02920
joemat@taco-hvac.com

Matt_21

the low loss header

prevents this problem from happening.