Home Air Conditioner vs. Electric Car

no doubt there has been a big change in the grid (supply and distribution) since a/c was invented. but ev's aren't the solution unless the grid keeps getting cleaner.

 

agreed, but it's mostly nat gas, is it not?

 

Electric hot water, if I move into a house that has it, I change it to nat gas or oil. Or maybe solar hot water if I ever get another shot at it.

Oil is great for hot water (really powerful and quick) but that was years ago when oil was cheap and elec was expensive, and at that time nat gas was banned due to lack of avail.

 

i look forward to it. and hope i'm alive to see it.

 

Youch! I finally got my all-electric home's total energy consumption down to a hair under 5000 kWh for the trailing 12 months, half of what it needed before my conservation upgrades started nine years ago. (Note for readers who know I have rooftop solar -- this number is gross consumption. Net after solar production is just 1200 kWh.)

The heat pump (minisplit, single zone) took only 1013 kWh of that. Though note that this is a heating dominated climate, I've needed no cooling in the eighteen months since putting a submeter on the heat pump/ac, and some supplemental electric resistance heat is not on that submeter. And we have had an unusually warm winter, the previous winter used 1400 kWh.

If you face this situation again, consider an electric heat pump water heater, especially if climate or building layout is not favorable to solar water heat. While much slower than even regular electric, let alone a combustion heater, it can save considerable energy. I switched almost two years ago, and the HPWH is the biggest factor in dropping my house's gross annual consumption from 7000 kWh down to 5000.

Even better HPWHs should be on the way to our domestic market, using higher pressure R744 refrigerant (i.e. CO2). They should be significantly more efficient, and work at colder ambient air temperatures. But the test results I have seen were from a unit imported from Japan / Oz for test purposes, not yet sold here.

 

The chart seems to ignore what plugin drivers find to be most important. Travel long distance (ok, that's less than 10% of the time for most plugin drivers), and we all want to QUICK CHARGE. Now you're talking 25kW - 100kW being pulled, just from one car. If a half dozen are at the same location ... and if there are eventually lots of QC locations in lots of areas - I could see there'd be issues. Now if/when the day comes that lots of folks are stopping to QC, the location better darn well have 30kW-40kW worth of PV overhead ... or maybe some other (battery backup?) method to not overload the grid during hot/muggy summers.
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It is possible with some HPWH to duct the chilled, waste air into the living area or HVAC system for some extra cooling during warmer weather. It will also dehumidify a damp location it is installed in.

 

Don't think Youch as you aren't comparing apples to apples, add your house energy consumption to your present gasoline usage (annual gallons x 33.7 kWh/gallon). You will be much happier, and it will be an accurate comparison.

Fascinating about the heat pump water heater.
How has that been working for you?
We are considering one of those ourselves for our new house project.

 

My HPWH is installed in the garage, and ducted outside to improve efficiency by not cooling the garage as much. The original electric WH was installed in a kitchen closet. But in my heating-dominated climate, an inside HPWH would harvest ambient heat from the home's heat system, defeating the efficiency efforts. It would also be noisy. That old WH closet was converted to an enlarged pantry.

Ducting kits are available for several other existing models, and will be required for some higher level efficiency ratings.

In cooling-dominated climates, it makes energy sense to install HPWHs inside the occupied space, offsetting some load from the main AC system. (Noise is another matter, noise levels vary considerably among models.) Even better are HPWHs that can be integrated with central heat pump HVAC systems, but the available choices are quite limited.

 

what if they plug in their EV and turn AC on at the same time?

 

Note: annual units updated --

I prefer to compare carbon to carbon. For most fossil fuel electric generation, less than half that 33.7 kWh thermal energy gets to the grid, the rest is lost in conversion. As a result, typical family homes have carbon footprints quite similar to the family car fleets. When non-residential buildings are thrown into the mix, I had understood that buildings overall have a larger carbon footprint than does transportation.

Before serious conservation, my house consumed an average of 10.6 MWh/year over a long period (1990-2006), or 11.3/year over a shorter window (1995-2000). Now it is down to 1.2/year net from the grid (or 5.0/year if I disconnect the solar). While my hydro-based utility has been nominally 'carbon neutral' for about a decade, customers on neighboring utilities are stuck with a nearby coal plant, so every MWh of hydro I free up to them does save them from buying a MWh of coal. Thus my house improvements are saving (somebody else) 7 to 9 tons of CO2 annually.

Under current household driving patterns, without fully spreadsheeting the fuel logs of three cars, I believe we are burning about 550 gallons per year, or about 5.5 tons of CO2. The BP (Before Prius) vehicle mix would have needed 750 gallons for the same driving, or 7.5 tons of CO2. Thus the Prius is saving about 2 tons annually.

In short, my house used to be responsible for a bit more carbon emissions than was my car fleet. Now, while the Prius is saving quite a bit of carbon, the home improvements are saving much more.

 

fuzzy1, please check your units.

Are you talking perhaps about 10.6 MWh/year or 10.6 kWh per day?

 

Oops. The former. Fixed it seconds before your post arrived here.

 

It has been working fairly well, but then I'm an engineer and technical geek. It has had some quirks, taking some adjustments from us and by us. And trying to find why it is not longer on the Northern Climate qualified product list, today I found that is was recalled last summer, due to defective evaporators. Inquiries have been placed.

Other models have previously been recalled, fallen off the list, sometimes reappearing after updates. This is not yet a mature market, so early adopters should be ready for some turmoil.

The current 'best model' appears to be a new version of the GE GeoSpring, placed on the list in late February, and the first to achieve a Tier 3 rating. See a press release here: Northwest utilities help bring game-changing water heating technology to region

I don't yet see what refrigerant this uses, but it does not appear to be in the upcoming R744 family.

This WH is sub-metered, and has been using a hair over 1000 kWh/year, in a two person household with significant travel absences. The submeter was on the old tank only 32 days, while prepping for the new tank, so I don't have a solid annual figure for it. My coarse extrapolation is that we would have used 2500/year on it, due to using much less hot water than the EPA test cycle used for the energy labels, and using a lower than normal setpoint. Homes with uncontrolled teenagers, users not coordinating loads, and high water setpoints, would see lower fractional savings. And Minnesnowta's cold winters will produce lower performance than Seattle's mild climate. HPWHs are more compelling in warmer climates.