Problem: residential hydronic design with variable speed circulator

[alternety]

I have a new residential hydronic system with 16 zones. Design calculations show max requirements of 12.2 GPM at 10.8' head. The contractor installed a Grundfos UP26-96 F/VS. External control to hold pressure across pump/manifold constant across varying loads.

The pump is too noisy to live with. Grundfos is looking at the issue but too slowly - it is winter and we need to get the pump resolved and system purged again to add antifreeze. The house is not insulated. I am becoming seriously concerned and things are just dragging on.

The contractor does not really have any experience with small variable speed systems and has not found an expert to talk to.

The idea was to use a variable speed pump and not a pressure bypass valve across the manifolds in order to save energy and keep down flow noises through a bypass. I have been unable to find any information on the actual power consumption of the Grundfos pump within the variable speed range. The pump is rated at 205 watts.

In researching things I see references that say this type of motor does not really save much energy as speed is reduced, but no hard information. There also questions of how low it can go. From the Grundfos web site - The motor is a 2 pole asynchronous squirrel-cage
PSC (permanent split capacitor). I have been looking for a PM DC powered pump figuring wider control range, and higher efficiency, but no luck.

I am also concerned if this pump/system and the potentially small flow with only one small zone (e.g., a bathroom) calling for heat is even workable. I just do not know enough to reach a rational conclusion.

I have looked at pump curves but I just don't understand well enough what it means to the system. The Grundfos has a fairly steep curve which makes me think it is less suited for throttling down to low flows. A Taco 0010 comes close but a bit short of the maximum specified conditions. The Taco 0012 is more than enough and, like the 0010, it has a shallow curve. It is also available as variable speed according to the Taco site.

The Grundfos curve is on page 41 in this PDF

http://www.us.grundfos.com/web/Down...978351F88256C4E006EA652/$File/L-UP-PG-001.pdf

The Taco curves are here -

http://www.taco-hvac.com/products.html?view=AllFileList&current_category=18&selected_infotype=5

Ok, background done. Here is what I think I need to know and fairly desparately need the information.

Does it make sense in terms of energy savings, and will it work, to use a variable speed AC pump in this system?

If it makes sense, which pump?

If a bypass is the way to go, which pump?

Any other thoughts that can help me with the problem are also greatly appreciated.

 

[imok2]

Alternety, As you say when you are dealing with a turn down situation where more then half of all zones are off then you would want the pump with a flatter curve and less turbulance in the pump. I believe the Taco pump mod# 0012 would be a better choice. Hopefully some others will give you more advice. Good luck

 

[stanlsimon]

It sounds like you have one big pump that feeds 16 zones. Each zone has a motorized valve, right?

To throttle back a centrifugal pump does not hurt the pump, provided you don't dead head the pump completely. The wattage of the pump will go down as you throttle down the flow, just the opposite as you might think.

To modulate the speed of the motor there are relatively inexpensive devices similar to light dimmers that will clip the sine wave and give you a reasonable amount of control. The motor is to small to justify using a VFD although that is possible. To go to a DC motor they will hit you with restocking charges to bring back the AC motor.

Given the large number of zones statistically the probability of having only one zone calling for heat is reduced. If however you have one small zone that leads the others in heat demand, maybe you could provide a small electric heater in that room.

Sincerely,
slsimon

 

[alternety]

I replaced the pump with a slightly smaller one without the speed control. It appeared that the major noise was caused by the pump using a simple TRIAC for control. We had a second of the original pumps on site. Swapping the controller on the same pump changed the noise level. It never got quiet enough.

If I could have found a DC version, I would not have had to pay a restocking fee. But I could not find such a pump.

I had to add a bypass to the loop, which is what I had been tryng to avoid. It does indeed make noticible noise when only a small amount of floor is calling for heat.

Once I get the house finished and move in I would like to look at adding a controller to the existing pump motor. But the simple control you mentioned would probably do the same thing as the original in terms of noise. And I really do not know if the motor will live through other approaches. Given thier cost I will be reluctant to try.