Electric costs running an air conditioner

[Abe]

I am selling a lot of air conditioners at the moment, from 5Kw to 10Kw. The customer always asks, " How much does it cost in electricity"

I say, " around 12 to 15 pence an hour"

I need to know for sure if this is correct, how much does it cost or how do I work it out?

Maybe, someone has a formula

[frank]

It's quite simple Ayb. Take the running amps and convert into kw (voltage x amps / 1000). Then take the hours that the unit will be running (hours per day x days per week x weeks per year). this will give you kwH/year. When you have this figure multiply it by the cost of electricity (currently UK @5.5P per kwH- or thereabouts) and this will give you the cost of electricity per year.

Obviously, it can only be used as a guide because we cannot tell if the unit is correctly sized and if the load is constant (sunny days and not so sunny days). An over-sized system will have more starts and less running time and an undersized system will be constantly running etc. - which all affect the running time and amp draw.

As an example:

Running amps = 5.8
Voltage = 250
kw = 1.45
Hours per day = 6 (allowing for off cycles)
Days per week = 5
Weeks per year = 23 (cooling season)

so : 1.45 * 6 * 5 * 23 = 1000.5kwH

1000.5 * 5.5 = 5502.75 / 100 = £55.27 per year

Don't quote it as fact because you can be sure they will come back after the first year and say - Hey, it cost more than you said


Frank

[Abe]

Thanks Frank............

I met one customer this evening, he had a visitor from abroad who "frightened" him about the high costs of running an air conditioner in his country. So he says, were you fibbing to me about it costing 10 to 15 pence per hour per unit, I installed two 5kw wall mounts.

I told him I would check and report tomorrow. So he will have an honest reply tomorrow, presuming I can work it out!!

Cheers

[Argus]

I was often asked about the anticipated running costs of an a/c system, usually small splits, that can be notoriously difficult to assess.

I agree with the methodology described, but the real figure will depend on a number of variables that you need to plug into the quation and can be significant taken on annual running costs:

Power factor. This is the actual power consumed by an inductive load and is what the end user pays on his bill on top of the theoretical wattage. Most a/c hermetic compressors vary from 0.85 (average) to 0.95 (quite good). Some manufacturers tell you what it is, some don't - some of the figures raise an eyebrow....

Losses: Capacity losses due to variance in ambient or working load. Electrical losses, Dirty filters, etc. Refrigerant under or overcharge…….

Also, many machines designed for human comfort in the far east are rated and sold at T1 condition for cooling and then applied at something close to T2 in the UK. These will return a significant reduction on capacity. 5% or so is often quoted, the reality is often higher.

These machines make up the vast bulk of kit sold in this country, due to evaporators designed to maximise moisture removal, they also boast significant sensible heat ratios, anywhere from .65 to .85. This means that a large quantity of energy expended and paid for goes down the condensate drain - not always desirable in our climate. Manufacturers are notoriously coy about this one, too!

Finally there is the customer. How many part-hours a day is the system going to run ? We could assume 60% of a 10 hour day?
Given the unpredictable continental offshore climate here, it is difficult to come up with a seasonal average that you can transpose from one year to the next.

The ill-fated EC Energy Labelling Directive attempts to put a leveller on this by assessing a running load over 500 hours as part of their energy benchmark, but even they shied away from seasonal efficiencies.

[frank]

Marc

Last time I looked it was slightly more than 5.8p per kwh - maybe I'm getting ripped off

As I said though - we can only guess what the running costs are going to be and I agree about the dirty filters etc. Actual running cost will eventually be known and there is nothing like hindsight. One summers costs will be quite different to the next - etc, etc.

Frank

[Andy]

Hi Frank
in N.Ireland we pay anything up to 8.5p, I would consider 6.5p good, with 4.5p available only for off peak.
Regards. Andy