Circulator Pumps

Several threads have asked questions about circulator pumps. I've decided to start a thread about circulator pumps. The most common closed hydronic loop system circulator pumps is the so called wet rotor lubricated pump. The rotor part of the motor is submerged in the pumped fluid and the impeller shaft is water lubricated. This means the seal, usually ceramic or graphite, depends on a film of water molecules for resisting wear. Some have replaceable rotors in the form of a cartridge. There are four large manufactures; Armstrong, B & G, Grundfos and Taco. All have a wide selection of pump sizes and single, multiple or variable speeds. There is interchangeability between brands because they all use a common flange mount size. Links to the product data are:

Armstrong Pumps
http://www.armstrongpumps.com/Data/pdfb ... ochure.pdf

Bell & Gosset
http://www.bellgossett.com/literature/files/4.pdf

Grundfos
http://www.us.grundfos.com/Web/Download ... TL-008.pdf

Taco
http://www.taco-hvac.com/en/products/Mo ... d_id=10671

Some have a preference of one brand over another. For me is just a choice of availability and price. Some offer internal check valves or flanges with isolation valves. This reduces installation time but increases pump price. It's important to select the correct pump for the needed flow rate. All manufactures publish pump curves. Your selection should be such that you are operating in the middle third of the pump curve. B&G has a simple design selection guide at:

http://www.bellgossett.com/homeowners/B ... -Guide.asp

The type of water being pumped and its oxygen content determines the pump casting material. Closed hydronic systems use cast iron. Open non-pressurized systems or potable water applications should use bronze or stainless pumps. These are more expensive.

All the wet rotor pumps are relatively inexpensive and they are used in many different ways to solve water flow problems. Heat zoning and primary-secondary pumps are two common uses.

The engineer in me needs to tell you that these pumps are really inefficient. They use split phase permanent capacitor run motors and have lousy starting torque. Only about 30% of the electrical energy gets imparted to the rotor as mechanical work. That said they are an economical reliable choice for residential applications. I use them myself in zoning and primary-secondary piping.

Edit: I looked up the efficiency number it's 16.9%. Much less than the 30% I stated above from my memory.

thanks!

I just realized I can bookmark the good threads for later use. This one just made my bookmark!!!

I See some pumps have 3 speeds.What circumstances require a 3 speed pump

To put it bluntly, when the person doesn't know how to select a pump using engineering principles, and uses the speed selection to cover his butt. I can think of very few applications in hydronic heating where a multi-speed circulator is an advantage. Variable speed pumps on the other hand are very useful. In injection type designs you mix hot boiler water with radiator return water to get a lower water temperature. The variable speed pump does the mixing by injecting more or less hot water conrtolled by the motor speed. In these designs the water always flows through the radiation and the water temperature is varied depending on the heating load.

Yanche wrote:The engineer in me needs to tell you that these pumps are really inefficient. They use split phase permanent capacitor run motors and have lousy starting torque. Only about 30% of the electrical energy gets imparted to the rotor as mechanical work. That said they are an economical reliable choice for residential applications. I use them myself in zoning and primary-secondary piping.

Is there a more efficient and better performing --but presumably higher price--alternative available/

Very informative! How do you know if you over sized the circulator? I can see if its under sized you won't push water through your radiators so you won't get any heat.

Your closed loop hydronic system pump is over-sized when you can hear water flowing in the pipes.

Yanche wrote:Your closed loop hydronic system pump is over-sized when you can hear water flowing in the pipes.

I never knew that. I thought that meant you had air in the system?

Well, air in the system will also make noise, especially right after the initial water fill. But after the air has been bled and the air separator has removed the dissolved gases in the water, if it still makes noise the circulator pump is over-sized.

Bob wrote:

Yanche wrote:The engineer in me needs to tell you that these pumps are really inefficient. They use split phase permanent capacitor run motors and have lousy starting torque. Only about 30% of the electrical energy gets imparted to the rotor as mechanical work. That said they are an economical reliable choice for residential applications. I use them myself in zoning and primary-secondary piping.Edit: efficiency is 16.9%, see edited post above

Is there a more efficient and better performing --but presumably higher price--alternative available/

The overall efficiency of a circulator is the sum of the centrifugal pump efficiency and the motor efficiency. Pumps with small diameter impellers have lower efficiencies. Large pumps, much larger than those used in residential application, also have diffuser vanes that are missing in residential sized pumps. These vanes improve pump efficiency. So for residential applications we are stuck with the low end of the centrifugal pump efficiency.

The electric pump motor is another story. Fractional HP circulator pumps are available with standard non-integral motors. Unfortunately most are sold with split phase electrical motors, the lowest efficiency of all motors. Some are available with special order motors. The Taco Series 110-120 is one such example. See:

http://www.taco-hvac.com/en/products/In ... d_id=15552

You would want to specify a capacitor start, capacitor run induction motor for highest efficiency. I have no idea what the relative cost would be.

This is all an academic exercise because the amount of electricity saved with a special order pump would likely be small compared to it's purchase price. The electronically speed controlled wet rotor circulator pump might have high efficiency. With proper electronics the normally split phase motor can be made to operate like a capacitor start, capacitor run motor. I'll leave that evaluation to another student of circulator pump efficiencies.

Edit: I looked up the efficiency of a large circulator pump, Taco TA Series Model 0538, efficiencies are 45 to 63% depending on operating point. 63% at 200 gal/min & 75 ft of head. Just what's needed to get that Outdoor Furnace Water through the 1/2 inch underground PEX.

Yanche wrote:Well, air in the system will also make noise, especially right after the initial water fill. But after the air has been bled and the air separator has removed the dissolved gases in the water, if it still makes noise the circulator pump is over-sized.

interesting. Thanks for the insight! I learned me sometin' knew today!

Yanche, any idea just how much you would have to oversize a pump to have it make noise?? Seems to me you would really have to have a lot of friction from undersized piping for the amount of flow before you would create noise.. noise is after all just a form of energy.

All the achedemics aside,, the pumps and motors are amazingly good at what they do for the electricity they burn, Used to be the only pump available was the B&G 100, the 'Red Pump' everyone used them, it was the only one... it had a lousy unreliable coupling between the motor and the 'oil box' that also leaked and made a mess. I have many unpleasant memories of repairing these pumps.
The along came the Taco 007 and it's equivalents... they have ONE moving part, water lubricated, and run on the same electicity as a light bulb.. about 100 watts... amazing.. and now available for about $70-80... install it and forget it.

Sizing, firguring out flow rates, the 'head' and all that stuff that requires formulas and measurements.. is right in Yanche's department... I'm more like a caveman when it comes to this... if something isn't happening the way I want it to.. I just get a BIGGER HAMMER.. not the right approach, I know..


Greg L

Desired flow velocity in closed loop hydronic system is 2 - 4 ft/sec. Two ft/sec. or greater is required to entrain air bubbles in a vertical pipe with downward flow. The goal is to get the bubbles to the air separator. Above 4 ft/sec. you get noise.

The head loss created by the piping increases as the 1.75th power of the flow rate. So double the flow rate and you increase the head loss by a factor of about 3.4. So using an grossly over-sized pump will make water flow noise plus use much more electric power to operate it. I'll try to work out a specific example for Greg's undersized piping question.

Yanche,
The outside boiler dealer where I purchased my pex al pex only sells 2 pumps. The Wilo Star S 16 FX 3spd and the Wilo Star 30F. He did not ask me very much about what kind of install I was doing but wants to sell me the larger pump. Can you tell me anything about the two. Also where should I go to get the proper calculations done. Would a email to taco help? Thanks Brian

I'm not familiar with the brand. But a Google search turned up the specifications. See:

http://www.wilo-na.com/cps/rde/xbcr/na- ... D-0609.pdf

Tell me more about what you are trying to do and what you are planning to buy.