Most laundries and drycleaning plants receive a monthly electricity bill with a total charge that appears to go up year by year.
Those who delve a little below the surface and break the invoice down into its various components will find that only half of the bill relates to the cost of electrical units consumed.
The other half takes the form of a “penalty charge” for the maximum electrical demand incurred during any half-hour period in the month.
The charge for the electrical units relates to the running costs of the power station and distribution network, of which the fuel burned by the power station is a major component.
The maximum demand relates to the size of the power station and electrical distribution system required simply to meet the maximum drain you place on the system when you switch everything on.
So, minimising the size of your electricity bill needs action in two areas—units and demand.
Most laundries use their units for the legitimate purpose of producing clean linen and it is often difficult to do much about this unless machinery is underloaded or left idling.
However, it is possible to address maximum demand charge and shrewd managers can show dramatic reductions without production penalties.
Simple checks in the switchroom
Some electricity supply companies monitor maximum demand in kilowatts (kW). There is a special meter in the switchroom which totals the power consumed in a half-hour period and lifts the maximum demand needle on the meter as consumption rises.
At the end of the half-hour, the moving needle sets back to zero leaving the maximum demand indicator stranded at high level.
It is a little like jetsam left stranded on the beach at the high tide mark. Every time there is a greater demand in a half-hour period during the week the needle will get nudged a little higher until finally it is read by the meter reader and reset to zero.
Some electricity companies measure maximum demand in a different unit—kilovolt amps (kVA). There is a subtle difference between kW and kVA because the latter incorporates a measure of the efficiency with which your equipment uses electricity. An electric fire utilises all of the power and a one bar fire will usually contribute either 1kW or 1kVA to maximum demand. An electric motor is far less efficient and 1kW of power absorbed could easily translate into 1.2 kVA of maximum demand.
The power factor for a piece of equipment is its demand in kW divided by its demand in kVA so the electric fire would have a power factor of 1.0 whereas the electric motor would have a power factor of less than 0.8.
It is possible to raise the power factor of a laundry so that it is close to unity by connecting a suitable capacitor across the input terminals. The difference between a laundry with proper correction and an uncorrected plant can represent an increase in maximum demand charge of over 30%.
Most laundries have capacitors fitted but in many instances they have not been kept in good repair and are not doing their job effectively.
It is often possible to detect malfunction in one part of the capacitor by feeling the outside of the casing—this will usually be warm except in the defective sections which will be stone cold.
Capacitor maintenance is a specialist job, especially with older type units which may be filled with hazardous oil containing PCB’s which require special disposal. Nevertheless, the first major step for a manager seeking to bring maximum demand charges under better control is to establish the power factor for the plant and to bring this up as close to unity as is economic.
Generally it will be found that installation of power factor correction equipment to raise the power factor to around 0.96 will give a two or three year payback.
If the maximum demand is metered in kW then there is no financial benefit to the laundry in installing power factor correction unless the electricity company insists on this as a condition of supply.
Major contributors to demand
All consumers of electricity contribute to maximum demand but some are much larger than others and offer considerable potential for reduction.
One major area is the air compressor which is a very neglected piece of equipment on most plants.
It is important because it usually contains a large motor running continuously that always contributes a large component of maximum demand into every half-hour period.
Unfortunately, air is invisible so in addition to supplying compressed air requirements to laundry equipment the compressor usually fuels a similar volume of leakage.
That means not only is the electrical demand of the air compressor sometimes twice what it needs to be, but also the capital tied up in the air compressor itself is twice as large as is necessary.
When an old air compressor struggles to cope, the natural response of many laundries is to buy a bigger one rather than cure the leaks so that the existing one can manage.
With the old type of reciprocating air compressor it is possible to measure the percentage of air being consumed by the leaks simply by running the compressor with all equipment turned off.
The percentage of time the compressor spends “on load” represents the percentage of the compressor output going to leakages.
Measuring leakage
Measurement of leakage with one of the modern rotary compressors is more difficult and is best carried out with an inexpensive inline flowmeter. If this exercise has not been carried out for the last 12 months then an energy manager will have rich pickings.
Laundries which still rely on medium fuel oil or heavy fuel oil for steam raising have a corresponding demand for oil tank heating to keep these viscous fluids mobile so that they atomise properly in the boiler burner.
In order to minimise the cost of oil tank heating the tanks themselves should be protected with at least 100 mm of weather-proof insulation.
Out-of-hours heating may have to rely on electric immersion heaters but most of the current to these should be obtainable at off-peak tariffs. During the day the tank should be heated via separate steam coil so that, properly managed, these units will contribute nil to maximum electrical demand.
In practice this is often not true because tanks are unprotected or the weather- proofing has not been kept in good condition and sometimes steam coils have not been repaired so that total reliance is placed on the electrical heaters.
For an uninsulated tank this could mean an 18kW electric heater running freely throughout the winter’s day chipping in 18kVA to the maximum demand. The cost of this unnecessary privilege will exceed £500/year even without taking into account the consumption of electrical units.
Great care is taken with the purchase of laundry equipment but similar care is rarely extended to office heating which frequently relies on peak electrical units.
It is not unusual to find 30kW of office heaters on a site while all that is needed is for these to be on during the busiest half hour period in the day for the maximum demand charge (usually well over £1000/year) to be incurred.
The next hidden contributor to maximum demand tends to be the ventilation fans.
Many older plants have large fans pumping hot air into the atmosphere and it is not unusual to see three or four units with 2kW motors running continuously.
It is interesting to note the sudden surge in power offtake when these are all switched on together—perhaps after a morning tea break when the place has warmed up.
It is not suggested that ventilation be dispensed with, but it is possible to design ventilation systems to use the minimum of power and to manage the periods during which ventilation is turned on to control the maximum demand contribution from this source.
Introducing cool air into a hot area of the workplace is often far more efficient than massive extraction of warm air from the roof apex. This is particularly relevant where tumble dryers are also drawing large quantities of air from the laundry and extract ventilation fans are effectively working against these.
The productive equipment in the laundry—its continuous batch washers and associated tumble dryers, washer-extractors and ironing equipment lead the list of high energy users.
Setting targets
It does not usually make sense to restrict the output of profit-generating productive equipment.
Ensure that full loads are processed wherever possible and, if the bulk of laundry output still relies on these, consider interlocking washer-extractors.
The interlock is only to prevent any two machines from running up to high speed spin simultaneously so the delay here should not be critical.
The easiest way to assess the potential for maximum demand reduction is to plot on a graph the actual demand in each of the last 12 months.
The variation between winter and summer will give a good indication of demand caused by heaters and seasonal lighting and a plant should be able to trim these out of the winter demand period (when the major bills occur) without problem.
This target can be further improved by adding on benefits from curing air leaks and managing ventilation in the summer.
Most plants should be capable of achieving 20% savings in actual maximum demand, coupled with a similar improvement from power factor correction, if this is not already correctly installed.
Future goals
Next winter is not going to be any easier because the main electricity companies are having to invest heavily in new equipment. They will want to see a return on this and find a way to minimise the investment itself.
The same applies over the next decade when electricity demand is expected to increase steadily year-on-year and there will be continuous pressure to improve generator utilisation with steady demand, rather than to put in extra capacity just to cope with the peaks from your laundry.