Low Power Factor at Elem School

I have a client with a large 4 yr old elementary School that is getting killed for low power factor. This surprises me because the only inductive motors are in HVAC equipment, and all lighting is fluorescent with high pf electronic ballasts. However, there are lots of computer equipment.

The HVAC system consists of many heat pumps and ventilation air units. There is no central chiller or water pumps anywhere. The largest motor in the school is probably 5-10 hp.

Details from one month's bill: consumption 108288 kwh demand metered 242 kw demand measured 321 kw Somehow the difference in metered and measured demand related to power factor.

Any thoughts how to determine the power factor from the given info. The utility claims measured demand = the metered demand * 0.85 / (actual pf). This gives actual pf = 0.56 NO WAY Another thought, Measured Demand is S, metered demand is P, this gives pf=0.75

Any thoughts why the power factor could be low? Any thought how to fix it. I am very hesitant to throw capacitors at the problems due to harmonic concerns and switching controls needed when going on / off backup generator.

Reply to
milo
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Reply to
John Gilmer

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To answer this we will need the following: A copy of the Tariff and the billing history. There are plenty of oddball tariffs with unusual ways to calculate bills. With a high load of computer power supplies, the customer may be basically paying a penalty for harmonics. If this is the case, power factor correction caps will not help.

Charles Perry P.E.

Reply to
Charles Perry

The HVAC system consists of many heat pumps and ventilation air units. There is no central chiller or water pumps anywhere. The largest motor in the school is probably 5-10 hp.

Details from one month's bill: consumption 108288 kwh demand metered 242 kw demand measured 321 kw Somehow the difference in metered and measured demand related to power factor.

Any thoughts how to determine the power factor from the given info. The utility claims measured demand = the metered demand * 0.85 / (actual pf). This gives actual pf = 0.56 NO WAY Another thought, Measured Demand is S, metered demand is P, this gives pf=0.75

Any thoughts why the power factor could be low? Any thought how to fix it. I am very hesitant to throw capacitors at the problems due to harmonic concerns and switching controls needed when going on / off backup generator.

Milo

In order to measure power factor, you need a kW and kVA reading. Power factor would not cause a difference between metered and measured demand, if both are in kW.

How was the demand measured? Did you use the same "window" (ie. 15 minute, 30 minute, etc)? If you measure the same way the meter does, you should get the same result, regardless of power factor.

Ben Miller

Reply to
Ben Miller

The HVAC system consists of many heat pumps and ventilation air units. There is no central chiller or water pumps anywhere. The largest motor in the school is probably 5-10 hp.

Details from one month's bill: consumption 108288 kwh demand metered 242 kw demand measured 321 kw Somehow the difference in metered and measured demand related to power factor.

Any thoughts how to determine the power factor from the given info. The utility claims measured demand = the metered demand * 0.85 / (actual pf). This gives actual pf = 0.56 NO WAY Another thought, Measured Demand is S, metered demand is P, this gives pf=0.75

Any thoughts why the power factor could be low? Any thought how to fix it. I am very hesitant to throw capacitors at the problems due to harmonic concerns and switching controls needed when going on / off backup generator.

I always start the investigation this way.

When was the power company meter last checked/ calibrated? They are not often wrong but it does happen. Ask for a new meter. Can not hurt. What was the last electrical project and when was it done. Does it corespond to any change in the electrical bill? How is the electricity being used? Big jump in the morning? Are the phases balanced? Do they have an energy man system to prevent all of the compressors turning on at the same time? How long has this been going on? What is the age of the building? How was the wireing done? Shared neutrals on the branch circuits? What size are the neutrals? Got any step down transformers? Are they connected correctly and giving the proper voltage? I had a brand new electrical distribution system installed in a building and the taps were set wrong for the incomming voltage. No one ever checked until the problems started.

Acquire an recording meter, RPM, Durants, BMI, and do at least 24 hours as close to the mains as possible. Check the readings against what you all ready have from the Power CO. Rentals are available, though it helps to have set one up a time or two. You might consider paying some one to come out and take the readings.

PF correction by capacitors will not help the harmonic issue. Only isolation transformers will help there.

Get up close and freindly with the rate structure. I know of places in CA where the billing structure has 25 line ltems. Including 6 for PF at different times of the day. You need to understand the structure. I have done billing software for years. I have a 3 page check list of information that the customer must sign and complete BEFORE scheduling a visit.

This problem MIGHT boild down to the utility system not being stiff enough for the loading.

I have a customer in down town LA that has a constant PF of 40-50. Printing presses are killers. If it was not for the generated power on site some 6 meg the bills would be out of site. They are getting hit for something like 30 k a month for PF charges.

Sorry I am asking more questions than answers.

Reply to
albown

All

I don't begin to understand all the factors of the power factor thing. But what is a 4 year old elementary school doing running AC and not having a central AC system or perhaps two. The KW consumed looks OK until one factors in that the school is closed and has no reason to have the AC running more than 40 hours a week. Hopefully the facility is on 3 phase and at least 480 volts or maybe more. Has anyone checked the 3 phase balance? And is ther perhaps a monitoring system that keeps tab on the balance. Is every possible motor on 3 phase? Have you contacted the PE EE who signed off on this facility. Also what is the power bill in $$'s. Bob AZ

Reply to
RWatson767

in article snipped-for-privacy@comcast.com, milo at , wrote on 9/17/03

12:57 AM:

I have a client with a large 4 yr old elementary School that is getting killed for low power factor. This surprises me because the only inductive motors are in HVAC equipment, and all lighting is fluorescent with high pf electronic ballasts. However, there are lots of computer equipment. The HVAC system consists of many heat pumps and ventilation air units. There is no central chiller or water pumps anywhere. The largest motor in the school is probably 5-10 hp. Details from one month's bill: consumption 108288 kwh demand metered 242 kw demand measured 321 kw Somehow the difference in metered and measured demand related to power factor. Any thoughts how to determine the power factor from the given info. The utility claims measured demand = the metered demand * 0.85 / (actual pf). This gives actual pf = 0.56 NO WAY Another thought, Measured Demand is S, metered demand is P, this gives pf=0.75

Any thoughts why the power factor could be low? Any thought how to fix it. I am very hesitant to throw capacitors at the problems due to harmonic concerns and switching controls needed when going on / off backup generator. This post does not read well. How can metered demand be different from measured demand by as much as indicated? I don't even know how metered demand can differ from measured demand.

Solving problems of this nature should be the meat and potatoes of a PE in EE. What are your measurements?

Bill

Reply to
Repeating Decimal

Actually, in the east, water-to-air heat pumps are very popular in schools, libraries, and small offices. A cooling tower for summer loads keeps the coolant water where it should be, and in the winter they warm the same coolant in a boiler (gas or electric) so the efficiency of the heat pump can be used to heat the classroom.

There is also a huge growth in the use of geothermal sources to replace the cooling tower/boiler combination.

I dont know all of the pros and cons to this, but the one that does come to mind is the fact that if a heat pump quits, you only loose service to one classroom, if a chiller goes down you have a whole school to deal with.

Reply to
User 1.nospam

The above units don't make any sense for the purpose of evaluating power factor.

Is it possible that they are referring to load factor?

Reply to
Paul Hovnanian P.E.

X-No-Archive: Yes

Fluorescent lights aren't much of a issue. In a four year old comm/inst. bldg, all fluorescent ballasts are the high power factor type.

First, investigate whether the low power factor is caused by phase shift or harmonics. Former is relatively easy to correct and it is caused by motors and other inductive loads. I don't know how to correct the latter. Latter is caused mainly by office equipments, computers and its peripherals.

Does the school have a lot of computers? If so, I guess the easiest solution to bring up the average power factor is to shut off the computers at night and on weekends and holidays.

Reply to
AC/DCdude17

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