consider vsd's for domestic water systems..

[charlie tuna]

the results of a recent survey suprised me concerning the installation of vsd's to maintain system pressure on a domestic water system. it might be something other contractors may want to inform their customers about. we have converted some smaller buildings in the past and gathered data information on power consumption savings.
we just completed monitoring a larger building of 55 stories and the payback period is less than fouteen months. the present setup is 1-25hp and 2-50hp supplying the upper floors and 2-30hp supplying the lower floors. with data loggers we projected the total power to be over a half million kilowatt hours of consumption per year. drive manufacturers say the savings are 2/3.. our experiance is about 45 per cent. the drive installation cost would be returned in less than fourteen months. the system pressure would be maintained by pump speed. the smaller buildings have ressulted in pumps running about 52 cycles and increase to 55 or 56 cycles during water demand. at 52 cycles the horsepower consummed by the motor was near 50 per cent. during this study on the 55 story building their power rates increased from .068 to .076 cents per kilowatt hour due to fuel surcharges -- this alone reflected an additional cost of nearly $5,000. per year to operate the domestic water system. this may allow some contractors an idea or two!!!

 

[raa]

Re: consider vsd's for domestic water systems..

I have a hot water recirc system with a pretty straightforward setup, a 2h.p. 480 pump but have always had errosion problems, I had a frequency drive controller speced for the pump but when I try to "dial" it down the motor overheats and the controller senses it and shuts down. I see your topic and was curious to know if you might have some input. This is a resort hotel with a number of two story structures over about 10 acres. Thanks, raa

 

[bphgravity]

Re: consider vsd's for domestic water systems..

I have designed several VFD and PLC controlled pump systems that have been nothing but a great success. For agricultural irrigation purposes, nothing can match the flexibility and demand control. The two particular issues is no demand and full demand. These two areas present control and motor stress. Ramping cordination is key to working out these issues. More time and effort was spent on the design and control setup than the entire installation. just more fod for thought.

 

[charlie tuna]

Re: consider vsd's for domestic water systems..

there is a minumum speed the pumps can run or the water will turn to steam inside the impeller. this installation i'm doing has the pumps running at full speed against pressure regulating valves with a recirc line. the new setup will have the prv's removed and system pressure will be sensed at the highest floor served and transmitted back to the vsd via the building's management system in the form of a 0-10 volt signal. on lower buildings we have used signals on the pump's discharge line and it worked great. due this building being 747 feet high we are trying to keep any lag time to a minimum.. in recent trade magazines there are growing concerns about rising energy costs due to fuel cost increases and necessary costs for power plant expansions by the year 2005... any building operating cooling towers without vsd's have missed the boat by this time... depending on the location--the payback can be close to a year!!!! we have set data recorders on feeders before and after and know the advantages. they need to be programmed correctly, too many are not!!!!

 

[jerod]

Re: consider vsd's for domestic water systems..

charlie, what type of transducer are you using and where is it physically?