Well, part way, we have a Wallbox EVSE. A VW ID.4 lead sled is on order and the black forest elves are tinkering away on it as I write. In Order Locked limbo awaiting on the boat state.
So, in this post, I want to write a bit above EVSE shopping, and evolving plans to de-carbon Dismal Manor which currently has gas hot air heat and gas hot water.
- 2021-08-06 Original
Electric Vehicle Charging
Electric vehicle charging is similar in concept to charging phone and laptop batteries. The path is about the same. And the architecture is about the same. Starting with your utility’s customer supply transformer, there is
- the feed from the utility transformer to the meter,
- your electric meter,
- the feed from the meter to your panel, and
- from your panel to a charge point for your vehicle.
In North America, we call the charge point equipment Electric Vehicle Supply Equipment. It has the following jobs.
- Ground fault and arc fault protection of the load and feeder from the home load center supplying the EVSE.
- Earthing the vehicle for safety while charging
- Communicating with the vehicle about the capability of the electrical supply. What voltage is available? What current flow is available?
- Providing a safe and convenient means of connecting the vehicle and the electrical supply.
- Making it difficult to connect yourself to the electrical supply.
In North America, EVSE and vehicle manufactures design the vehicle charging interface to meet the requirements of Society of Automotive Engineers Specification J1772 which covers electrical matters in a manner to be in compliance with the North American electrical code, charging session management protocols, demand management communications protocols, and the requirements for the plug and receptacle used to make the charging connection.
There are several regional plugs in use and Tesla, by being first, did its own thing.
The Vehicle is in Charge
Oh, that’s a horrible pun! But I think I’ll keep it.
The battery charger is actually part of the vehicle’s power electronics. Each vehicle has AC to DC conversion and a DC charger. By putting all of the charging electronics in the vehicle, the charge point supply equipment is kept simple and reusable and the charge point need not have any knowledge of how the vehicle’s battery is charged.
Modern vehicles allow you to set up the charge using the vehicles information and entertainment system or a smart phone application. These let you specify when to complete charging, the desired final level of charge, and if the vehicle is to be heated or cooled in anticipation of the day’s use.
A Notional Charger
Each vehicle design has its unique partitioning of functions so we’ll consider a functional partitioning of the charging process.
Notional is a neat word. It means fanciful. It’s short for we don’t know what’s inside so we’ll make up something plausible.
The vehicle and EVSE chat to determine the current available to charge the battery. The vehicle Level 2 charger is rated at 11 KW. The EVSE supply circuit is rated at 40 Amps or about 9.8 KW so the vehicle must draw 40 amps or less.
The home charging process starting with AC power requires conversion of AC to bulk DC at some voltage. The bulk DC is cleaned up and perhaps converted to a different, potentially changing voltage for use in the charging process. Charging starts at a constant current to bring battery voltage up to temperature corrected total voltage based on the cell chemistry. Once at temperature corrected voltage, the charge continues at constant voltage until the finishing current is reached. The finishing procedure continues at constant current until the final voltage is reached.
The finishing procedure brings each cell up to a similar state of charge and equalizes cell voltages across the battery. It is also supposed to remove any dendrites forming on the anodes.
When the battery is being charged by a DC fast charger, the VW ID.4 finishing procedure begins when the battery reaches 80% charge. The finishing procedure is needed only every now and again so, VW recommends that you charge to 80 percent for the normal weekly orbit and fully charge when planning a trip. While on your trip, VW recommends charging to 80% while traveling and a full charge over night.
There’s a Protocol for That!
The vehicle and the CD fast charge point chat using a protocol to determine the power available, and the voltage and current available. Fortunately, there is only one so we don’t have to invent C3P0 (Star Wars Protocol Droid) just yet. IEC 63110 is world-wide standard for communication between charge points and electric vehicles to control charging. This protocol covers the technical niceties of arranging for appropriate electricity to be supplied in the proper amounts. The standard covers function, protocol states and state transitions, and the protocol data units and data formatting used to do the actual signalling down to which order the bits are sent. The details of the protocol are beyond the scope of this article.
There’s a second protocol, Open Charge Point Protocol that is used to manage commercial chargers, client authentication, client payment collection, etc. Commercial charge points use this protocol to contact your charging service, get your payment particulars, and submit billing and receive payment from your service. In the US, Electrify America is the best of these.
Charging process phases
Notionally, you can think of the charging process as having three phases, current control, voltage control, and finishing charge. The starting current control phase limits charging current while bringing the battery voltage up to the level needed for the for the constant voltage varying current mid-charge procedure. The mid-charge proceeds at a fixed terminal voltage until the battery is charged as indicated by reaching a fully charged current target value. The charge reverts to current control until the battery reaches the target terminal voltage.
Typical EV charging battle rhythm
VW recommends the following routine.
- Charge to full for delivery. Or not. How many times have you taken delivery of a vehicle with only a gallon or two of gas in the tank?
- Using the vehicle for local travel, discharge the battery to 10%-20% capacity.
- Charge the vehicle to 80% capacity.
- Repeat steps 2 and 3 for local driving (trips less than 100 miles).
- For longer day trips, 200 miles or so, charge fully and drive the trip on one charge.
- For trips greater than 200 miles, charge fully for departure and plan to charge following the 80-20 rule en route.
Pick a bingo charge remaining at which level you will go directly to a DC fast charger and recharge. The distance off the route or the charger spacing on the route determines the bingo charge level. In many areas, 10% leaves enough margin to drive gently to the charge point.
The road trip protocol is very similar to the weekly routine protocol. Charge fully to set out. Discharge to 10%-20%. Charge to 80% and drive the next leg. The 80%-20% numbers run about 2 hours at highway speeds which is a recommended point at which to take a break for a stretch, loo calls for you and pets, pet show and tell, etc while the car is charging. In about 30 minutes, the car is ready for the next leg.
The Granny Cable
Most EV deliveries include a “granny cable” to AC charge the vehicle from a 110 V outlet. The granny cable lets you maintain charge for local travel when visiting relatives, etc. so you can get to the DC fast charger at some point.
Can your utility charge your vehicle?
Yes easily. The vehicle charging is roughly equivalent to running a large residential heat pump on a cold night. Your utility knows how to do that. And it is easier on the utility. Your air con, unless it is new, does what is called a locked rotor start. The juice goes on and the motor sucks down a huge amount of current to get the compressor moving and bring it to speed. Modern inverter air con does a soft start easing the the compressor up to speed without drama and provides power to run it at part load if needed.
Your EV behaves like an inverter driven air con. The on board charger starts the charge gently to bring the cells up to charging voltage. As the cells charge, the current tapers off. At about 80% charge, the charger begins its finishing protocol designed to top off the cells and bring them to design individual cell voltage.
Utility implications of electric vehicles
So, what happens when you and the 5 neighbors sharing your transformer all put their vehicles on to charge? The total demand can exceed the capacity of the local transformer causing it to overheat or to blow a fuse.
So, you and your neighbors may have to take turns. Think alternate side of the street charging. Even house numbers charge on even days and odd numbers on odd.
Remember 80-20. Charging is likely a once or twice a week thing in practice. No need to fill up every night. So not a problem until all those F-150 Lightnings start showing up in 2022.
Or Dominion can put in a bigger transformer. But that’s as bad as it will get. Dominion has to be planning for migration of home heating to cold climate heat pumps. Aren’t they? That will drive residential upgrading. As we will see, residential heating and cooling is the killer app! With heating loads being 3 or so times cooling loads.
Dominion can upgrade customer supply transformers only so many times before overloading the retail branch supply transformer that supplies 13.2 KV power to your street. And this can ripple some distance up through the distribution.
Hawaii provides an example in the opposite direction. Because fuel was expensive and power was expensive, and solar panels came with 20 years of power, everybody put in solar panels. The utility quickly found its customer supply transformers overloaded during afternoon peak sun so the permitting process had to be expanded to upgrade the customer supply transformers as needed. Customer operating permits would be delayed until the utility could survey the transformer and replace it if needed.
Will there be enough generation?
Supply of EV charging power is easily within the capabilities of the utility’s generation? In general, yes. Your utility will encourage you to charge your vehicle in the evening or over night in what are off-peak hours. If you have time of use metering, they will charge you top dollar to charge during the summer afternoon peak or the early morning winter peak.
The utility planning process in cooperation with the utility’s regional transmission operator’s planning process ensures that utilities have adequate plant designs to meet anticipated load. PJM (Pennsylvania, New Jersey, and Maryland) tries to optimize the generation mix across the region’s utilities to minimize air pollution and CO2 production while meeting economic constraints. The PJM integrated resource plan makes specific recommendations for each member utility.
In addition, Dominion does economic forecasting and demand forecasting to plan equipment upgrades and additions. The utility prepares its Integrated Resource Plan using a 15 year planning horizon, revises the plan yearly, and purchases equipment with a 40 year service life. Dominion tends to wait until their is a solid business case for responding to customer clamoring for the latest thing. For example, recent planning and orders are adding utility solar and off-shore wind to the Dominion generation fleet. But it is only recently that the business case has been there.
In recent years, Dominion has changed strategy from gas turbine combined cycle generation to utility scale solar generation plus utility scale marine wind generation. Both forms of generation now have lower levelized costs (purchase, fuel, and maintenance) than the gas turbine plus steam turbine plants formerly favored. But Dominion is still being conservative regarding over-night base load. They will likely always have some nuclear generation and combined cycle generation in the mix in case the weather doesn’t cooperate with the solar and wind units.
Reducing Home CO2 creation
While the big electrical equipment companies were learning how to make competitive wind and solar generation, the major international HVAC suppliers were learning how to make heat transfer based HVAC that outperforms on-site furnaces and boilers for space heating and domestic water heating. Modern machines have performance coefficients of 2 to 5 depending on ambient temperature. That means that $1 given to the utility moves a minimum of $2 heat on a design basis cold night and $5 of heat under milder conditions.
One machine to heat and cool?
With the advent of variable speed compressor and fan drives, it is possible to size heat pumps for both summer cooling and winter heating using variable refrigerant flow technology. Dismal Manor, being small, needs about 7 KW of cooling (2 tons or 24,000 BTU/Hr to use archaic units). In shoulder season heating service, the machine maintains temperature down to about 40 F or 4 C. Our indoor temperature is about 22 C so the machine is breaking even against an 18 C differential. Not bad for 2006 Lennox Elite 16 equipment.
The heat conduction equation
The heat conduction equation is linear in temperature differential. The machine now at Dismal Manor can heat the house against a 18 C temperature differential between inside and outside. Here, the design basis winter temperature is -20 C. So on the coldest day, the heat pumps would need to balance out a 42C differential plus some extra muscle to cover convective losses (it gets windy here). So a ROM estimate is that we need 16.3 KW of heating.
Here in North America, we reckon heating in BTU/Hr and cooling in tons of ice per day or (12,000 BUT/hr). So my 2 ton machine covers about 1/3 of our design basis cold day needs. So I need about 72,000 BTU per hour on the design basis day. Duct leakage in the legacy system wastes about 1/3 of input so maybe 48,000 BTU/hr of capacity with a ductless split system. This ROM analysis is consistent with the gas furnace sizing.
Looking at the Mitsubishi North America catalog, the car charger has an electrical load demand similar to that of a 45,000 BTU per hour inverter drive cold climate heat pump compressor. The catalog recommends a 50 Amp branch circuit or 40 Amp maximum load. This is the same rating as the EVSE circuit. It is likely that 2 of these units would be installed in an older home characterized by high air infiltration and limited wall insulation.
Implications for the utility
The Department of Energy and national building and electrical codes are directing the home building industry toward use of cold climate heat pumps for home heating. I expect we will see HVAC manufacturers phasing out gas furnaces over the decade and that high efficiency heat pumps will become the norm for space heating throughout the country.
The adoption of electric vehicles and the adoption of heat pump home heating will drive utility upgrading of the retail distribution. Electric vehicle demand and heating demand can be comparable but heating demand is a every night thing while car charging is likely a once or twice a week thing.
Efficient Electric Hot Water
In Rhode Island, the house I rented had an electric hot water heater. Each month, we used about 400 KWH heating water. In RI, the water heater had its own meter and was billed differently. Water heaters typically draw 5 KW. This makes them about 1/2 an EV charger in mid-charge.
Hybrid water heaters
The DOE and the water heater industry are encouraging the use of hybrid water heaters using a heat pump plus resistance heaters packaged in the tank footprint for residential sue. These devices are a significant improvement over pure resistance heaters but are an interim solution. Given the short life time of fiberglass lined tanks (8 years), I would be reluctant to buy one. There’s a big price premium and the payback is real but water heater leaks are no fun. We currently have a Rennai gas demand heater here. It’s a 100,000 BTU/Hr beast the size of a suitcase.
Split Heat Pumps
Japanese manufacturers moved the compressor outside, harvest heat from the ambient air rather than conditioned space, and by clever choice of refrigerant, have eliminated the resistance heaters.
The Japanese now have split heat pump hot water heating. An outdoor compressor brings heat in to warm water in a storage tank similar to that in electric heaters except the clever Japanese use stainless steel for the tank. Using CO2 as a refrigerant, they easily provide toasty hot water for washing and hydronic heating. Split unit hot water heat pumps using CO2 refrigerant are just now being introduced to the US.
CO2 refrigerant is in widespread use in supermarket refrigeration where it offers multiple advantages. CO2 systems allow large supermarkets to zone cooling in cases with shelf cooling and bin cooling staged. Heat recovery allows heat to be transferred to other areas of the store where it is needed.
High performance cold heat pumps are more efficient than condensing boilers and have coefficient of performance similar to VRF air to air heat pumps. $1 of electricity in delivers $5 of heated water in mild weather. In small residential installations, the refrigerant to water heat exchanger and storage tank are combined into a single unit.
Power requirements are modest, a 15 Amp 240 volt two pole circuit in North America. This is about 1/3 to 1/6th the demand of home heating. I don’t foresee hot water heating service being a utility design driver.
Return on investment is 5 years but is sensitive to usage and climate. This is mature technology on the market in Japan for over 10 years.
You must be logged in to post a comment.