Sample Household Energy Budget
WHY AUDIT ENERGY?
Anytime you want to check how well you are using energy you first have to know how much you are using over what time. There is no escaping this stage.
Of course if you are a householder, all you will have to do is look at your monthly electricity bill and there you will have it in the energy charge. Even large industries can do this. If you are satisfied with that there is no need to go further.
However, if you want to know which of your household appliances or factory processes or unit operations are wasting energy, then you have to monitor their use.
The simplest audit is to walk through and use the rated power of the items of interest. [The rated power is the power the manufacturer indicates on the specifications tab, usually near the power cord.] Multiply it by the time it is used and you will get the energy consumed.
Power is measured in watt, symbol W. 1000 W make a kilowatt, symbol kW. Time is measured in seconds, symbol s, or hours, symbol h. kW and h are used for billing purposes as follows:
Energy = Power × time
or, in the units, .
kWh = kW × h.
In the model UCC30S refrigerator above, if the rated input is used 24 hours a day, then the energy used is
(130 W ÷ 1000) × 24 h = 0.13 kW × 24 h = 3.12 kWh.
But suppose your appliance does not tell you how many W or kW it uses, then look for the voltage, symbol V, and the current or amperage, symbol A. The power or wattage in W is the product of the voltage in V and the current in A.
Power or wattage = voltage × current or amperage
or, in the units, W = V × A
For example, at the back of your fridge you see 120 V and 2 A. Multiplying,
120 V × 2 A = 240 W.
Next, convert the watts to kilowatts by dividing by 1000. This gives us 240 W ÷ 1000 = 0.24 kW.
If the fridge uses all this power 24 hours per day, then the energy consumed is 0.24 kW × 24 h = 5.76 kWh. At the current GPL household tariff of $53.78 per kWh, this is $310 per day or $9,300 per month.
But in reality, things are not so simple.
MORE ACCURATE AUDIT
The basis of this is that you want to know your actual energy use in a shorter time frame and for individual appliances in your household or industry. The example of the fridge in the walkthrough audit was not actual, it was a prognosis, the accuracy of which depends on a lot of things, e.g.:
1 Although the fridge is on all the time, the thermostat may detect that the desired temperature has been attained and automatically switch off the compressor. You use almost no energy here.
2 Automatic defrosting also has an energy cost.
3 If your fridge is new, it should be most efficient and use energy according to the Energy Star rating that is usually provided. But if your fridge is old, it can use more energy.
4 Whenever the fridge switches on, the compressor motor briefly draws much more electricity. 1600 W start-up power has been measured for a 130 W fridge for 9 seconds. This is the main reason it is hard to run a fridge on small solar panel installations.
To capture all these variations without guessing we would have to monitor the energy used by the fridge. You might even discover trends you did not know. One manager of a large company discovered that some employees were using equipment when he thought everybody had gone home.
COSTS ( all $ are Guyana$. US$1 = $210)
A simple walk through audit will not cost anything more than travelling expenses if you are a pensioner with less than 1 000 W of energy appliances. In such a case even the travelling expenses could be waived at our discretion.
Otherwise, the charge is normally 1$ per watt or VA of appliances you have. The sample household above has 4 630 W so one should expect to pay $4,630 for a walk-through analysis + $5,000 per man hour of getting the figures off the appliances and getting information of their usage. If the client provides all the information required according to our brochure, there is only the analysis charge and no man-hour charge.
Industries will be charged $1,000 per kVA (measured or on the average light bill) or $1000 per kVA of installed electric equipment + $1 per W of thermal equipment for an analysis + $5,000 per man hour of getting the figures off the appliances and getting information of their usage. This is the same rate as for the household in the example above except for the load factor.
These charges are for first-time audits only, and would include training of qualified staff to carry out energy audits. Subsequent audits by Think Engine ESCo should cost no more than 20% of the first-time audit if there has been no significant rearrangement of the system since the previous audit.
Monitoring has charges attached that depend on the meters and lengths of time.
The Clients are then advised on the way forward, viz.,
When investments are necessary to achieve the recommended economy, the possibilities and the return on the investment can be calculated --> the finance column on the energy management page.