variable speed circulators

Gary Usa

since the fast increase in variable speed circulators i have often wondered how to get round a problem if the system ever got a restriction or blockage ,on a low water content boiler as time goes by and scale forms it would cause the pump to go slower and slower.

it was just an interesting thought and how maybe manufacturers may of got round this problem,my only thought was if sensors were put around the system back into a central module that could control the speed in a far more accurate way and may be able to sense a problem sooner than later

mmmmmm just got thinking that was all,what do you think guys,

all the best

gary uk

Tom Anderson

As a buildup of restrictions occur, or rather increased resistance, this will have no effect of pump speed... it will reduce pump gpm capacity at the increased pump head forces the pump to ride the curve, just as it does with constant speed pumps.

Most (commercial) variable speed pumps are controlled by a piping pressure sensor located near remote terminal units, sensing pressure between the supply and return mains. Pump speed ramps up when pressure setpoint drops; increases when pressure rises. Some vari speed drives are available with built in pressure sensors.

This is actually standard operating procedure for commercial systems. Most variable speed drive (VSD) manufacturers are readily capable of accepting an input signal directly from an external presure controller.. no seperate control system (DDC) needed. Prices of VSD's are very attractive these days. Even small horsepower systems (1 HP) for residential apartment systems are cost effective. I have seen these coming in at US $800., icluding pressure sensors, installed, including contractor overhead and profit.

As a rough rule of thumb, VSD pumping will reduce annual pump energy by 50%. At 75% speed, pump energy is cut by about 50%.

Fractional horsepower pumps: VSD's are available, and are more common in euro systems, but I have no firsthand experience and am not sure if such small critters are ready for "prime time".

Hope this helps.

Art Pittaway

Hello Gary..!

If a hydronic heating system is "building up" anything, the problem is not in the circulator or controls. It's a leak, or bad piping that is admitting the minerals into the system. Fix the system and fill it once...period. Steam is another story, then it's a quality of fill water issue, softened, filtered, etc.