anyone use a Variable speed drive to control heating pump motor?

elfie

have a 15 hp motor used to circulate heating hot water 24/7 - anyone have experience using a VSD to reduce speed of motor to save on energy during lower demand periods?



there is a need for the motor to operate 24/7 due to size of facility and to maintain flow and balance for a mixing valve (ie. to control temp of water circulating to facility)



when its warmer and heat demand is lower, it would be nice to reduce rpms on motor and reduce electricity costs.



thanks

meplumber

Quite Often

We use VFD's quite often to control 3 phase, heating loop circulating pumps.  The best way to control the VFD is with a Delta T controller, like a 775.  It will give you either a 4-20 or 0-10 output.

elfie

VSD - ease of use

hi,

thanks for your answer



is the VSD you refer to easy to use?  one thing I have been searching for is a convenient way to program a setback feature that can be easily modified.



for some reason the industry doesnt want to make a VSD with user friendly programming controls



the facility has no overnight occupants so it is crazy to keep the motor at same speed, etc.



are you saving money on electricity and does it save on NG use?



thanks

meplumber

Cart before the horse.

No VFD can do a setback by itself. You have to have a total control package to do what you are trying to do. You would have to setback the entire building temperature for this to work. I would suggest talking to a Controls Contractor. They can provide you with a whole host of options and try and help you decide between what you need and what you can afford.



Good Luck.

elfie

rpm setback

hi,



i was interested in finding a control device that can reduce power use by the motor overnight (and i believe a timer device connected to the VSD would be needed)



i am curious to know the functionality of the VSD' s that you have seen



thanks for you comments

meplumber

night setback

The way that those systems work is as follows,



The heating circuit pump is setup to follow a Preset Delta T. The Delta T is measured across the supply and return loops fed from the pump. The controller then outputs a 4-20 or 0-10 signal to the VFD to lower or raise the pump speed. This Delta T is not easily adjustable.



The building setback is set through either a supply temperature system on the boilers and tied to a clock system, or a centralized space setpoint setback also controlled by a clock.



Simply slowing the pump down at night will do nothing to decrease the amount of heat consumed by the building. The only way to do that is to lower the target temp of the space or do the massive amount of math and setup a constant circulation system and setback the boilers accordingly, which may cause other problems depending on the boiler.



This is not an easy fix or a maintenance project. This is a time consuming project for a competent controls and or Mechanical contractor.



Simply installing a VFD on the circ pump will not do what you want it to do, even with a Delta T controller.

elfie

motor power use reduction

thanks for the comprehensive response, but i think installation in out case makes sense to be much simpler.



the VSD makes sense to reduce a motor that may be oversized for the facility



its a complex structure of pipes and the goal was to attach a VSD to a pump motor and evaluate how well system heats throughout the heating loop during lower demand periods



i suspect that reducing pump motor RPM's may not be noticeable throughout the facility.



most of the benefit should be reduced electricity use (less water circulating would seem to have some NG reduction benefits as part of the heating loop are not well controlled).



keeping a motor running 24/7 during days that reach up to 50's as occurs frequently during winter doesnt make sense (cant turn off  commercial boiler and pump for a short period of a couple days)

meplumber

I understand what you are trying to do.

I am a commercial, institutional, and industrial contractor.  I understand what you are trying to do.  I am just trying to tell you that it won't give you what you want.



Good Luck to you.

Mark Eatherton

Demand...

Demand dictates flow. If the control valves are a 2 way type of valve, the pressure differential controller makes as much or more sense than a temperature differential. Both are related, but pressure differential gives a better, clearer picture as to whats going on. Pipes can be emitters, whether we want them to be or not, which can affect delta T. It may be a gain to the envelope, but may not be necessary.



If your system uses a 3 way bypass on each emitter, then you have no choice but to use temperature differential to control the pumps speed. The pressure differential across the system will be nearly constant, regardless of the control valves position.



If you wanted to maintain a different differential (T or P) for different times, you will either need to invest in a top end EMS system that can make the changes for you, or use two different controllers, switching between them using a separate switching relay.



If you have an existing set back control logic at the POU, in either case, as loads are shed, it will be seen in either temperature or pressure differentials across the system anyway.



HTH



ME

SWEI

motor power use reduction

How big is this pump?  How many BTUs does the system move?  Any idea what kind of head it's pushing?  Oversized pumps are unfortunately common, and there is usually some benefit to be gained from properly matching the pump(s) to the load.  If the system has large pumps and was tuned using bypass valves, a static VFD implementation may be worth implementing even without active control of the pump speed.  Or not.



If the pump is small enough, an ECM-based smart circ might be simpler and cheaper than a VFD, especially if the current pump is single phase.



As Mark points out, the ultimate control strategy really does depend on the type and layout of control valves in the system.

elfie

environment controlled by both 3 way and 2 way valves

the heating environment consists of two bldgs.  one bldg has proportionally controlled valves (Johnson Controls system) and the other bldg (much older) uses 3 way valves to control flow.



10 million btu's are created per day (based on NG use); daily capacity of boiler is 60 million btu.  clearly an oversizing issue.   they should have installed two boilers to share load vs one.  no backup exists.



there is a mixing valve by the boiler that is controlled with an aquastat that changes the temp of heating water circulating based on outside temps (very very effective and simple)



i like the idea of using a device to monitor pressure as a way to control pump speed.



i simply want to install a VSD and modify rpm's of motor and see how it impacts heating to facility.  we may find that a 7.5 hp motor vs a 15 hp motor is adequate - but no one knows. a VSD would seem to be a way to assess what facility needs are (and setting a VSD to reduce motor power consumption and rpm's at night may be extremely rewarding as facility is unoccupied at night)



thanks

SWEI

loads

You've mixed a few metaphors here so help me out:



60MM BTU/day = 2.5 MM BTU/hr (is this the size of the boiler?  Is it an input or an output rate?)  Sounds from the mixing valve ODR like the boiler is probably conventional, but it may still fire at more than one rate if it's that big.



10 MM BTU/day load is interesting as far as cost goes, but doesn't tell us much about the peak load (which is what needs to be accommodated both in piping and pumping.)



This system needs a proper analysis by a competent contractor or engineer.

elfie

BTU clarification

the boiler size is 2.5 mm btu/hr; there is modulation in the burner.  the boiler is like a race horse confined to a stall.  not sure how much inefficiency there would be if its alot bigger than it needs to be.



peak load is difficult to assess.



one issue we have is a mixing valve that tends to fully open at night (ie. when temps are lower) because the aquastat does not have any setback control (an older honeywell device without a setback clock installed); the heating loop has lots of open windows, so there is likely lots of inefficiency in heating areas when then is no need.