It’s been a while since I posted much of an energy post (other than my TED anniversary post on the 1st of April (here)). So, here we go.
First, for those that don’t know, a heat pump is just what it sounds like. It “pumps” or takes heat from inside (cooling) or outside (heating) and moves it to the other side. Basically, it’s an air conditioner that can “reverse”. See wiki page. When people just say “heat pump” they generally mean an air source heat pump (outside air is the source, or sink/dump for the heat). There are also “ground loop” heat pumps that use the ground as the source or sink/dump. Ground loop heat pumps are more efficient than air source ones, but they are much more expensive, and require more room to install (there are lines that run in the ground, either horizontally or vertically, which takes space/money to install). In my case, I have an air source heat pump.
As someone that lives in the Pacific NW, I have seen a lot of discussion online, and even on TV, about how using Natural Gas at home is more efficient than using electricity for everything. This is something I have spent a fair amount of time considering, since I’m a home owner, and Northwest Natural Gas is constantly sending me flyers saying “install natural gas, and get tax breaks”.
The vast majority our power here in the PWN is generated by Hydro, Wind, and some Nuclear (in WA state) (Oregon Stats, Washington Stats). There are a couple fossil fuel plants here and there (in Oregon, it’s primarily NG generation, with very little coal. Washington has almost no fossil fuel energy production), but largely, we’re Hydro (this is further evidenced by the public opposing construction of LNG (Liquid Natural Gas) depots on the Oregon coast (link). My entire house is run on electricity with a heat pump providing heating and cooling, and I can guarantee, it uses less total energy than a gas furnace would. At best, I could switch my aux heat, water heater, and range over to gas. But I’d still be using electricity for everything else. Not to mention that, if I used gas for something, I’m stuck buying that gas from a gas company. However, by using straight electricity, I can say, put photovoltaics on my house, and suddenly become less dependent on the grid than I ever could be on gas. Even if I had some large source of methane on my property (multi-property septic system maybe?), I’d still be burning something, which would produce CO2.
In thinking about it, and looking at total BTU output, the real advantage to natural gas is in heating water (tankless water heater), or in doing rapid house heating (like, if I wanted to turn my heat down to 55 at night). Electricity can heat water, air, etc, but it generally isn’t good at big heating jobs (like tankless water heaters that take 50F water to 110F in short order). Resistive heat via electricity is 3,412btu/kwh. In the town where I live, a KWH is $0.0463. So, 1000btu’s costs me $0.00463 if I am using resistive heat (which, my home heating is primarily a heatpump, but I’ll get back to that). If I was to use natural gas, 1 ft3 is 1,028btus. A therm (100000btus (or, I guess 100ft3) costs $1.18957, so 1000btu’s for gas costs $0.0119. So, electricity is cheaper all around. And electricity here in the Willamette valley doesn’t create CO2 emissions. Add to this that my heat pump, on an average day, is 3-4x more efficient than straight resistive heat, and my cost per BTU is significantly less than natural gas. The calculations for heat pump efficiency can be found here. For the record, my heat pump is a 2.5 ton Trane XL15i . The 2.5 ton rating is due to the fact my home’s heating load is about 28,000 btu/hour.
A heat pump’s real weakness is BIG temperature changes. It’s less efficient when outside air temperature is very low (when heating the home), or very high (when cooling the home), and trying to heat the home more than a few degrees at a time, since the heater only gets to about 90F or so (meaning heating a home from 55F to 68F would take quite some time with 90F air), as opposed to a gas furnace that produces air upwards of 120F, and will always be that temp. Heat pumps aren’t going to be as warm if the outdoor temperature is 15F. However, heat pumps are still going to be more efficient than resistive heat until outdoor temperature is well below 0F, even though it won’t be able to keep up with the rate at which your home is cooling (which of course depends on your home).
The trick becomes something like hot water. My water heater is a pretty efficient tank style (Bradford White M2HE50S6DS). It’s insulation provides an R value of 20. It’s a pretty good water heater, but it’s still got hot water sitting in a tank when no one is using it. So, every day I use X amount of power keeping that water hot. Now, I haven’t figured out how to easily figure out how much power that is per day, but I’m pretty sure it’s on the order of 1-1.5KWH/day… so, 4-6 cents per day. This wouldn’t make up for the added efficiency of a tankless water heater. You could also argue a gas clothes dryer would be better… but again, the cost per BTU is HIGHER for gas here. Plus, how much gas would I use leaving pilot lights on in some stuff. Update: I did the math for a day I was out of town (May 8th, 2010), and my hot water heater used approximately 90kw that day, or about 5kw over 18 minutes. So, this works out to 5kwh * (18/60), or 1.5KWH. Or, about $0.07/day in idle power costs. I could decrease this a bit by further insulating my hot water heater, or making my garage a bit more weather tight (I have really poor garage doors at this time).
So, what about people in other parts of the country? I’d say you should do the math. I know outside my area, power can be about 3-4x the cost it is here. So, gas sounds more appealing in that case. The CO2 emissions issue is a question anywhere. Because one issue is, a natural gas fired power plant is going to be MUCH more efficient than 1000’s of households all burning natural gas individually (a power plant is going to re-burn exhaust, have the ability to do carbon scrubbing/sequestration, etc… individuals are not).
And of course, all of this doesn’t even touch on the idea that since the gulf spill (great site I just found dealing with FF’s is here), and questions about the real safety of fracking, whether we should really be looking at moving off FFs more and more rather than thinking about electricity is inefficient. No matter what, using gas or any fossil fuel is still helping perpetuate our reliance on burning fuels. Sure, I drive, and my car burns gas, but I’m not saying go off the grid. I’m saying that before you start believing that gas is a better option than electricity, do the math. At the least, look at what a split system would cost you, where you have a gas furnace, AND a heat pump. This gives you the best of both worlds, in that you can turn your heat way down at night, and during the day, your heat pump will take care of keeping your house at temp. The price difference between a gas furnace and air conditioner combo vs. a gas furnace and heat pump combo should be relatively minor, and you’ll more than make up for it in the long run (plus, there are plenty of tax rebates on heat pumps).
This is an ongoing discussion that I’m sure won’t end for quite some time, and I’m perfectly open to someone calling bullshit, or pointing out a flaw in my math. I’d love to discuss more.