circulator pump energy calculations

ginahoy

I need help estimating the energy required for a 1/8 hp circulator pump that supplies hot water to a forced air fan coil. I don't know the pump model # but I checked the specs of some common brands and none include a power curve, only flow rate vs. pressure drop.



Is there a way to estimate a pump's power consumption (watts) based on the flow rate and pressure drop? For this application, I estimate the circulation loop will have a total drop of about 20 feet of head at flow rate of 4 gpm.



(note: edited by op for clarity)

Gordy

pump energy

A taco 0014 will deliver 4 gpm at 20' of head.

The 0014 is 1.55 amps.



1.55 amps x 115 volts = 178.25 watts this could vary depending on voltage delivered my house has 120 volts.



If the pump runs for 5 hours a day.



178.25 watts x 5 hours = 891.25 watts per day.



891.25 watts / 1000 watts = .89 KWH



If your electric is 10 cents a KWH then.



.89 KWH x .10 cents = 9 cents a day.



The circ will require the proper sized circuit to delivered the power required for the circ.





Gordy

ginahoy

need more than namplate VA rating

Thanks for your reply. I should have mentioned I'm an electrical engineer, so I understand how to do energy calculations based on nameplate amp rating. However, this is of little use for my needs since actual current draw varies with head pressure and flow rate. I need a bit more precision. Moreover, volt-amps is only part of the picture, as it doesn't consider the pump's power factor (watts = VA * PF), and we know that all pumps have a PF of less than 1.0, often substantially less.



The pump in question is built into the Rinnai 37AHB hydronic air handler. Unfortunately, Rinnai's literature doesn't disclose the pump's brand / model. Perhaps someone can ID the brand from the attached photo? It doesn't appear to be a Taco. What I do know is from the air handler specs:1/8 hp "wet rotor" type, 115VAC, and it's pumping potable water.



Surprisingly, none of the pump specs I've reviewed include power curves (watts-gpm). I'm guessing this is because historically, in a typical boiler application, pump energy tends to be trivial compared to the system's overall energy budget. However, when the source is a tankless water heater, the pressure drop is substantially higher due to small bore of the heat exchanger tubing. This means that pump energy represents a relatively larger share of annual heating costs when comparing a dhw-supplied hydronic fan coil with other heat options.



I thought there may be a way to estimate the energy draw based on the operating point of 4 gpm at 20 ft of head. This should be possible since the efficiency (work vs. heat) for pumps of this class should be similar. Othewise I'll see if Rinnai will disclose the pump make/model so I can lean on the pump manufacturer to provide a power curve.



click image to enlarge:

Gordy

Contact

http://www.heatinghelp.com/forum/profile/2302090/Steve-Thompson-WILO



I'm sure Steve can help you out.



Gordy

ginahoy

got the answer I was looking for

I learned from Rinnai that the air handler in question uses a modified Taco 009. I just spoke with an applications engineer at Taco. Referring to an (unpublished) pump power curve, he said this model consumes from 140 to 160 watts, depending on the operating point. In this case, around 145 watts. Too bad they make it so hard to find this out.



David Butler

Gordy

Interesting

To know Dave,

 Thanks for finding out, and sharing. So basically power consumption varies 20 watts from rated amps on the 009 depending where on the circulator curve you are.



 Did they indicate if other taco 00 series have similar variations?



Gordy

ginahoy

circulator pump energy calculations

I didn't ask, but you'll always see a variation in power consumption across the operating range of any pump (or fan motor). The question is how much, and the shape of the curve. I would expect all of Taco's 00 series 1/8 hp motors have a similar range. Larger pumps would likely have a wider range. The nameplate amperage is a starting point for estimating the power at low head pressures.



BTW, I was unable to find out the power factor, but given the nameplate amp rating for this motor, it must be very high, like over 90%.



I deal with HVAC blower fans and their power curves vary dramatically across their operating range, and the shape of the curve depends largely on whether the motor is PSC technology, or the newer more efficient ECM type. ECM means electronically commutated motor, also known as a brushless DC motor, and PSC means permanent-split capacitor.



Small circulator motors are undoubtedly PSC, which means they'll slow down (and draw less current) as the force against which the motor is working is increased, in this case, the head pressure of the fluid. Note that even though the power drops at lower flow rates, the efficiency (watts per gallon pumped) will drop even more.



An ECM is typically configured to maintain constant torque, or constant RPM (accomplished by an internal microprocessor), so power consumption actually goes up as the opposing force increases, until the motor reaches the stall point.

Gordan

ECM technology is not wholly foreign to the hydronic crowd. :-)

Small circulator motors are not undoubtedly PSC; Laing/ITT, Wilo, and Grundfos have for years marketed ECM circulators, and Taco is due to join them soon.

ginahoy

circulator pump energy calculations

in the 1/8 hp size??



edit: I stand corrected. I just reviewed Grundfos' ALPHA series literature. Nice. What I meant to, or should have said was that the circulator in question is obviously PSC. Obvious to me from the pump curve.

Gordan

That's tricky

As most of these circulators are variable output. But yes, Grundfos' Magna range and Wilo's Stratos range have models that straddle 1/8 hp. (E.g. Stratos 1.25 x 3-25.)