Download
1 / 24
240 likes | 261 Views
…and how they affect overall system efficiency. Variable Speed Circulators…. What Does Variable Speed Do?. When you change circulator speed: Change flow rate by same proportion Change head produced by square of proportion
E N D
…and how they affect overall system efficiency Variable Speed Circulators…
What Does Variable Speed Do? • When you change circulator speed: • Change flow rate by same proportion • Change head produced by square of proportion • Change power required by cube of proportion (based on motor efficiency)
The 5 Goals of Variable Speed Pumping • Match pumping capacity to actual heating load • Eliminate velocity noise • Simplify installation • Use less electricity • Increase overall system efficiency
Variable Speed Applications • Zone valve jobs • Radiant jobs w/actuators • Zone pumping? Eh…
Variable Speed Pumping Methods • ΔP • Varies the speed so the pump does not exceed a certain pressure difference • ΔT • Varies the pump speed to maintain a certain temperature difference How well does each work?
Match Pump Capacity To Load • ΔP – works somewhat • Chop upper portion of pump curve • Flow is limited • But not in direct proportion to required BTUs
Match Pump Capacity To Load • ΔT – works! • BTU/hr = GPM x ΔT x 500 • With a constant ΔT, flow isadjusted only by required BTUH • Constantly adjusts speed to maintain ΔT
Simplify Installation/Eliminate Noise • ΔP – works somewhat • Max pressure determined by worst case head loss zone • Requires setup/programming • Low head loss zone may have velocity noise • Can produce higher than needed flow
Simplify Installation/Eliminate Noise • ΔT – works! • BTU/hr = GPM x ΔT x 500 • Keep ΔT constant – easy setup • Flow rate adjusts to maintain optimum ΔT • Prevents noise
Use Less Electricity • ΔP – works • ECM motors • Permanent magnet • ½ wattage of PSC • Res models use 5 – 60 watts
Warning! • ECM = permanent magnet • Wet rotor circs fail due to black iron oxide • Where will it all go? • “Learning” mode • Needs power 24/7/365 • 5w x 6,260 “off” hours
Use Less Electricity • ΔT – works! • Not quite as efficient as ECM, but still pretty good • Taco 008-VDTF uses up to 78% less electricitythan fixed speed version
But Think About It… • Most efficient motor is one that is “OFF” • Taco DeltaT’s do not require constant power • Can use standard switching relay • That’s 0 watts X 6,260 “off” hours!
36 33 Energy Consumption 137 kW kW consumed, 2,500 hour heating season Assuming 12.5 hours of operation daily 117 kW 102 kW ECM circulators draw constant 5 kW in “standby” mode to keep memory powered – for 6,260 non-heating hours annually Taco 00 VDT draws NO powerwhen off – runs off standard relay or zone valve controller
25% Savings!! WOW!!!! Dude, that’sonly $3.16 per year… Cold, Hard Facts…
What About System Efficiency? • System components • Heating plant AFUE • Control strategy • Zoning • Distribution system • Heat emitters • RFH vs. Air Heat
Market Shifts • “Mod-con” vs cast iron • Emphasis on fuel consumption • 25-50% energy savings? • Electrical consumption • BTU/kW ratio • Zone valves vs. zone circs • 6 circs @ 80W = 480W • 1 vs circ @ 60@ + 6 zone valves @ 1.44W each = <69W • >85% reduction!
Increasing System Efficiency • ΔP – works somewhat • Reduces electrical consumption, but… • Can’t guarantee optimal ΔT thru system, boiler
Increasing System Efficiency • ΔT – WORKS!! • Ensure proper ΔT • Ensure lowest possible return temp to boiler • Maximize boiler efficiency
The Scorecard Tells The Story… Delta T Delta P • Match pump capacity to load • Simplify install, Eliminate noise • Use less electricity • Increase system efficiency
