Issue #113
May-June 2011

Visit Home Energy

Table of Contents

Belkin Conserve Insight Plug-in Meter

What is Sub-Metering?

How Efficient is Your Air Conditioner?

Ten Energy Saving Tips

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Belkin Conserve Insight Plug-in Meter
Belkin recently introduced the Conserve Insight Energy Cost Monitor which is now available in our Energy Monitor Store at Home Energy It is a low cost plug-in meter for single 120 volt loads that uses a six foot cord to connect the display.

This feature allows you to monitor appliance loads without having to get on your hands and knees to read the display, such as with your refrigerator. Simply plug the meter into the wall, plug the appliance into the meter and place the display on a nearby table or counter top where it will be easy to read.

The display shows power consumption in watts, energy cost in dollars and the CO2 carbon footprint of the appliance. Energy cost uses an average kilowatt-hour cost for the U.S. or you can enter the actual rate from your bill. As a low cost unit, only flat rates can be input. If you have a tiered or time of use rate, you'll have to estimate the flat rate equivalent.

The CO2 footprint is also adjustable to reflect different levels of carbon emissions produced by the various utilities around the country. You'll need to check with your local utility to get their best estimate of this value in terms of CO2 lbs. per kilowatt-hour.

After 45 minutes of measurement, the unit will project cost and carbon footprint for an entire year. This is handy when measuring loads that cycle on and off like refrigerators or laptop computers.

Watts do not project forward. They are displayed in real time down to a resolution of 1/2 watt. Kilowatt-hours, however, are not displayed. They can be estimated by dividing the electric rate into the cost projection.

If you are just getting interested in energy monitoring, or need a 120 volt appliance monitor to sub-meter 120 volt loads for your whole house energy monitor system the Belkin Conserve Insight Energy Cost Monitor may be a good fit for you. Priced at under $30, its hard to go wrong on this one.

What is Sub-Metering?

Sub-metering refers to the measurement of electricity used by an appliance, circuit, or sub-panel performed while the total load on the parent panel is also being measured. This technique provides an accurate measurement of the amount of power used by the appliance, the energy consumed and the percent of total load it represents.

Knowing the individual load of each appliance and the amount of energy it uses provides the detail needed to make good decisions about how to conserve energy without sacrificing service. Use the Power Panel Profiler to help you organize this information and track your energy cost reduction strategy.

In the home, sub-metering 120 volt plug loads is best accomplished with a plug-in meter such as the Kill-A-Watt or the Belkin Conserve Insight discussed above. However, not all 120 volt loads are plug accessible. Consider an array of recessed lights or a dishwasher or microwave that are hardwired into the wall.

Plus, 240 volt loads are the biggest challenge to measure accurately. These include at a minimum in most homes the central air conditioner, clothes dryer, oven/range and electric hot water heater. The dryer uses a plug that is different from the range and the hot water heater and central air are hardwired. For this reason there are no residential 240 volt plug-in meters to our knowledge.

To work around these hurdles we must go directly to the circuit breaker panel. Total load measurement for the home should continue while sub-metering. Using our home energy monitor, we connect the extra current transformers (CT's) to the load side of the circuit breaker that serves the appliance we want to measure. 120 volt loads will use a single CT connected around the black wire exiting the circuit breaker. 240 volt loads will require 2 CT's. One goes on the black wire and one on the red wire exiting a 2-pole breaker.

Record and monitor electrical usage on each appliance for a week, or a month for more accuracy, to determine the amount of energy used. When you are satisfied that you have a realistic picture of that appliance's energy profile, move the CT's to another appliance and repeat the process. Record results in the Power Panel Profiler as you move forward.

As an alternative to this process, you may want to consider a circuit level energy monitor such as the eMonitor. These systems track individual circuits on an ongoing basis. However, this capability will bump up the cost of a home energy monitoring system significantly.

The average size of your electric bill should be the determining factor. If you want to recover your energy monitoring investment within two years don't spend more than twice your monthly electric bill on a system. Good results can be achieved with lower cost systems provided the extra steps are taken to gather the detail needed to make good energy saving decisions.

How Efficient is Your Air Conditioner?

Air conditioning system efficiency is measured with the Seasonal Energy Efficiency Rating or SEER. This rating compares the total Btu (British Thermal Unit) output for a cooling season to the total watt-hour input. It is used to measure the efficiency of central air conditioner or heat pump systems as they cycle on and off throughout the cooling season. Mathematically the SEER rating is calculated by dividing the total Btu output by the total watt-hours used during the season.

A second rating called Energy Efficiency Rating or EER also represents a ratio of Btu output to watt-hour input for central air conditioners and heat pumps. It differs from the SEER in that it is measured only with the unit powered on, not cycled on and off. SEER ratings will always be higher for a given piece of equipment than EER ratings by 12 to 15%. Thus, the SEER rating is used as the industry standard.

What is a good SEER rating? The lowest SEER rating for central air systems produced in The U.S. today is 13. Energy Star rated homes require a minimum SEER of 14. Residential units can have a SEER as high as 20 but come at a pricey premium. These high SEER systems often operate with much higher refrigeration pressures which can increase maintenance costs.

How much can I save by replacing my current central air conditioner with a higher SEER rating? A quick way to estimate savings is to compare SEER ratings. For example, if you find your current air conditioning system is rated at 10 SEER (check the manual to find out) and you would like to replace it with a 14 SEER unit simple divide 10 into 14 and subtract the result from one. In this case it would be 1 - (10/14) = 28.6%. In other words upgrading from a 10 to 14 SEER unit would save you nearly 30% in cooling costs.

If you have a heat pump, this savings would also apply to that portion of your heat load that is produced by the heat pump. However, it would not apply to the energy used by the supplemental heating strips.

Keep in mind that the 28.6% savings generated is only on your cooling and heat pump compressor cost, not your entire electric bill. To determine how much energy is being used by your air conditioning system refer to the sub-metering strategy discussed above. For additional tips on determining air conditioner efficiency check out our Central Air Conditioner Systems page or visit the SEER comparison page.

Ten Energy Saving Tips

1. Now that the hot weather is upon us, double checking the cooling values on your programmable thermostat. Can you bump the temperature up a degree or two when you are home without causing too much discomfort? How about 3-4 degrees when you are away? Be sure to activate hold settings or vacation mode when you are traveling for more than a day.

2. If you have a pool, how many hours per day do you run your pump? If you use regular chemicals or a salt system 8-10 hours should be adequate provided you keep up with algeacide treatments. If you use a UV system, the pump will need to remain on most all of the time. If contemplating a pool purchase for your home keep this operating cost statistic in the back of your mind when choosing a purification system.

3. Afternoon sun through westerly facing windows can add a lot of heat load to your central air system. Pull drapes on those windows during these hot summer afternoons to reduce AC run time.

4. If you are planning to build a house this year, locate outdoor AC condenser units on the north side of the house to keep them in the shade (south side if in the southern hemisphere). Air conditioner efficiency can drop by as much as ten percent when condensers operate in the heat of direct sunlight.

5. If your home already has the outdoor AC condenser unit is installed in a hot, sunny area consider planting shrubs in the vicinity to provide shade to increase condenser efficiency.

6. Keep a watch for bathroom or range hood fans that get left on inadvertently. A small 50 CFM bath fan can expel the entire conditioned air content of a 2500 square foot home in less than 8 hours leaving that much more work for your AC system to replenish.

7. If planning for window replacements be sure to consider those with good Low-E glass ratings. The amount of heat gain they can shield your cooling system from is significant.

8. Old air conditioning system struggling to keep you cool? Consider a heat pump as a replacement if you live in a moderate climate. Heat pumps deliver up to 3 times the heating or cooling output per unit of energy input for outside temperatures above 40 degrees F. Below that temperature, efficiency drops off quickly and soon requires supplemental heating to maintain comfort which is expensive.

9. If using alternative energy such as solar keep receptors clean and free from shadows by trimming trees and shrubs in the vicinity. The same is true for wind. Be sure smooth, steady air flow is reaching the rotor at all times. Disturbed air flow to the turbine rotor has the same effect as placing a solar panel in the shade.

10. Check your attic insulation for holes or gaps. R-30 batts are an absolute minimum. The best option is to have insulation blown at least foot thick across your entire attic.

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