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Meter Messenger #121 -EV Impact on Home Energy
October 17, 2012

Issue #121
September-October 2012

Visit Home Energy

Table of Contents

EV Impact on Home Energy

What are Current Transformers?

Power Over Ethernet LED's

Ten Energy Saving Tips

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EV Impact on Home Energy

Plug-in electric vehicles (EV's), if they catch hold in the market, will have a significant impact on how we use power in our homes. The reason being that charging stations will become the largest power user in the home when they are on.

Today the Nissan Leaf, Chevy Volt, Tesla Roadster, Toyota Prius Plug-in Hybrid are some of the EV's currently available on the market. Sales are still weak as compared to gasoline powered vehicles for reasons of the weak economy, the lack of public charging stations and higher cost. If these challenges can be overcome and EV's go mainstream, charging strategies will become paramount in managing the additional load on the grid.

An EV can be fully charged in about eight hours using a 120 volt connection. If a 240 volt connection is used, referred to as a Level 2 charger, that time can be cut in half. However, cutting the time in half will double the power demand during the four hour charging period.

Utilities are worried about the impact this will have if EV deployment becomes widespread. If fifty percent of your neighborhood drives av EV, consider the electrical load on the local substation when everyone plugs into their charger after getting home from work. If left unchecked, brownouts could become common.

Smart Grid programs are being developed that will use time-of-use rates to encourage customers to delay EV charging until off-peak periods, say after 10:00 PM. Another approach is to draw power remaining from EV batteries to serve the grid during peak periods such as 4:00 to 8:00 PM and return it to the vehicle during off-peak periods.

In either case, the electronic intelligence will be complex. Some of this intelligence will reside in the EV, some in the charger and some with the utility. The customer should also have the ability to override this intelligence if the need arises but must realize they will be billed at a higher rate to exercise the privilege.

If you have an EV, or are considering one in the future, we recommend a reliable energy monitor that can measure your total energy as well as that drawn by your EV charger. This way you will have an on-going record of when it was on and, over time, come to know exactly what it cost to "fuel" your EV.

What are Current Transformers?

Current transformers, more commonly referred to as CT's, are used to measure the amount of current flowing through a conductor. They are simply small coils that wrap around a wire. As the current flows through the wire it induces an electromagnetic field which can be sensed by the CT's coil. Since this field is induced by the current it is called inductance.

CT's convert this inductance into a small current that, along with voltage measurement, allow energy monitors to calculate power and energy readings. When utility rates are entered into the energy monitor cost information is readily available, as well.

A CT must be used for each circuit that is to be measured. If a whole house energy monitor is used the CT's are only placed around the feeders to the main service panel. Multi-point and circuit level monitors also measure at the service entrance but have additional CT's placed on specific circuits. These CT's are placed around the conductor wire on the load side of the appropriate circuit breaker. If measuring 240 volt loads, two CT's are required - one for each hot leg of the circuit.

If using a circuit level monitor, it is possible to double up single phase loads by routing conductors from adjacent circuit breakers through the same CT. The result is a measurement of the load on both circuits. This works well for lightly loaded circuits and reduces the cost of having to purchase a CT for every single circuit in the building.

CT's come in two categories: solid and split core. Solid core CT's look like a small doughnut which must have the conductor threaded through the center hole. The advantage is lower cost but installation requires the wire to be removed and reinstalled for each circuit breaker.

Split core CT's are hinged and can be opened to clamp around the conductor without having to remove it from the breaker. They are a must for measuring whole house loads since the measurement point on the line side of the main breaker remains hot.

The size of a CT is rated by the maximum amperage it can measure. The safest rule of thumb is to size CT's to match the circuit breaker rating for the circuit being measured. It is generally OK to undersize by 20 to 30 percent because circuits generally run well below rated capacity. In other words, a 15 amp CT will work just fine on a 20 amp circuit. On the other hand, if a CT is significantly over-sized, accuracy suffers.

When planning an energy monitor installation it is very important to determine the size and quantity of CT's to be deployed. First, decide what you want to measure. Next, make a list of the circuits in your breaker panel noting what size they are and what circuits they serve. Our Power Panel Profiler is a great tool to help you organize this information.

When you know the number and the size of each circuit to be measured you can narrow your product selection and determine your cost. Our energy monitor store provides a wide selection of systems from which to choose.

Power Over Ethernet LED's

Power over Ethernet (PoE) technology now has the capability to power light emitting diode (LED) bulbs directly. Current PoE nodes support a maximun of 25.5 watts per port. Cisco's new Universal PoE technology bumps that up to 60 watts. Most LED's operate on less than 20 watts. This means you will be able to power LED lighting directly from Ethernet cable (Cat 5 or Cat 6) reducing the cost of unnecessary electrical wiring.

Since the LED lights are part of an Ethernet network they become easier to measure, monitor and control because each fixture can be treated as an endpoint on that network. Photo sensors on the network can brighten or dim LED's based upon changing conditions of ambient daylight. Occupancy sensors can be used illuminate an area as a person walks down a hallway or enters into a room. One company is developing a device that integrates the motion and ambient lighting sensors directly into the bulb.

As an electronic device, LED's can also act as a a network signal repeater that can transmit signals over a wireless network or through power line transfer using the home's electrical system. A new technology under development, called Visible Light Communications, will transmit data using the actual light from LED bulbs stationed as nodes on a wireless network.

The LED bulbs of today are giving way to a whole new level of high efficiency lighting technology and communication tomorrow.

Ten Energy Saving Tips

1. If you use a heat pump with supplemental power strips, step your programmable thermostat settings in two degree increments when warming the house from overnight setbacks. A step of three degrees or more will usually trigger auxiliary heat to come on. Auxiliary heat strips do not to have to run long to negate all the energy savings gained from lowering the thermostat the night before.

2. Be sure to check for leaks and good insulation coverage on duct work in your attic, crawl space or basement. If water pipes reside near duct work in unconditioned space, you may want to add an electric heating tape to those pipes to prevent freezing. Insulating duct work will lower the temperature of any unconditioned space it travels through during the winter months.

3. If you use natural gas, propane or fuel oil for heat, it is a good idea to install a carbon-monoxide detector in your home to alert you of a combustion or ventilation problem with your furnace as we move into the heating season.

4. Consider upgrading your holiday lighting to LED's this year. The pin-point light is bright and uses only a fraction of the energy conventional lighting consumes.

5. Connect laptop chargers, cell phone chargers and any other peripheral charger to the power strip. Equipment does not need to be charged 24/7 to keep batteries at or near 100%. Chargers continue to draw power, even if the device being charged is disconnected.

6. Be sure to keep drapes open on south facing windows as we move into the cooler months. The lower sun angle will add passive solar heat to the room lowering furnace run time.

7. Consider solar powered sidewalk lighting - especially now that the days are much shorter. Solar outdoor lighting requires no wires and there is no energy cost.

8. If your home has hydronically fed radiators place a heat reflector between the radiator and the wall to direct more heat into the room.

9. Consider a laptop as a replacement for your desktop next time you upgrade. Besides being very portable they use less energy.

10. Check for drafts, worn weatherstripping and gaps under exterior doors throughout the winter season. Seal those gaps as soon as possible to lower discomfort from the cold and a high electric bill.

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