>Today, a Heat Pump can be like 200% efficient, so you 100W of chemical energy turns into 40W of electricity, then turns into 80W of heating from the heat pump.
This isn't true today. The absolute minimum COP is 3.1 in the US.
This isn't true today. The absolute minimum COP is 3.1 in the US.
Air source heat pumps are really good tech overall, especially because they also double up as AC in summer. However, in winter, in a head to head comparison, they only handily win in areas with mild climate, like eg. all west, or much of southern US. In the northwest or midwest, they are unlikely to beat efficient gas furnaces.
That heatpump would be for about a 300-400 sqft room.
The smallest ones are almost the most efficient ones in the range.
I’m not sure why this is, and whether it generalises to house-size ducted systems, but it’s pretty striking nonetheless because it’s the exact opposite of most heat related systems I can think of.
Thus, smaller units, more spread out, have access to more heat?
It’s fascinating to even see the huge increase in switchable units - running your 4/5 ton unit at 4 tons is much more efficient. (Usually)
If you look at a place like Minneapolis, which is normally considered a pretty cold US metro area, you do have a few months where the average temp is below zero. But you also have several more months where the temperature is cold enough to turn on the heat but well above freezing, where a heat pump is dramatically more efficient. When picking a heating system, it makes sense to consider comparative efficiency over the entire year, not just performance during the worst conditions in the middle of winter. Even in a city like Minneapolis, it's not obvious that heat pumps are less competitive over the entire year, even if their performance in January probably isn't fantastic.
I also think the practical geographic area extends further than people think. New York City definitely isn't the south, but per some random Googling, it doesn't appear to have any months where the average temperature is below freezing. Even Boston only has 2 months that barely drop below freezing. Most of the US northeast (definitely the mid-atlantic) by population arguably also falls into the range where heat pumps make sense.
At least in Canada I’d need to know that my system can handle a week of -30 or -40C in my city. Some places are even colder, for longer at a time.
I guess the only remaining concern is that winter storms cause both cold weather and trees falling onto powerlines. The latter is rare though
There are people who genuinely live in the middle of nowhere, on an otherwise uninhabited island as caretaker, deep in the forest manning a fire watch tower, Antarctic research base, that sort o thing, who do need have more options, because if they run out of options they're dead. If you're in that situation you still don't necessarily want gas heating though, a fossil fuel powered generator might make a lot of sense, maybe even more than one, because again electricity is so versatile.
It's much simpler to obtain and fuel a small generator to power meta loads like thermostats/circulators/blowers than a large generator that supplies the thermal load. Fully committing to a heat pump as your only heating would likely involve a large gas generator fed by municipal gas or at least a large buried propane tank (for capacity and temperature).
The straightforward backup heat answer is wood. It's easy to obtain and store, and the primary drawback of it requiring labor and attention isn't a big deal during an outage. Although if you don't do it regularly and make sure your stove is in good order, lighting a fire during an emergency situation might not be the best idea.
I heard about a guy who had copper piping with water flow going around his chimney (on the inside) and then through the house.
That'd be a cool system if you could switch out the heat source, electric and an indoor-safe wood stove. Just get a CO monitor!
They do require power to run (automated dampers, blower, circulators), so I have a small backup generator as per my last comment. And they've gotten a bit expensive (especially now that the US federal tax credit has gone away), but my estimated payback period is around 6 years.
You might wonder why I'm posting in a thread about heat pumps when I just got a different major heating source, but I see heat pumps and wood as two very complementary heat sources. Down the line I'm planning to add a water-to-water or air-to-water heat pump for the shoulder seasons (and summer DHW), so that I don't have to tend a fire (or burn oil) when the heating load is low. One four or five ton unit should take care of my heat loss most of the time, and I won't have to oversize the system to handle the dead of winter cold snaps.
It also depends on local prices. In Madison, WI our implied (not actual) electric grid efficiency based on prices is under 20%.
https://www.energy.gov/eere/femp/incorporate-minimum-efficie...
Source: your link.
Air source heat pumps are a lot easier, so they are the majority of installs.
I expect the national code doesn't give a minimum COP for air source because the performance changes with air temperature. The bulk of my heating cost occurs when it is 10-20 ⁰F outside, where someone located in a warmer spot might have most of their heating at 35-45 or whatever.
It didn't cost that much more to install and there isn't any equipment outside in the weather.
Can you or the GP share more about the economics of your installations?
I didn't bother with a bid the second time because the situation was the same. Air source was really coming along at this point (at least in the US), I should have pushed harder to get it.
My current home has enough land to go horizonal. There are 4 trenches, 6 feet deep, 3 feet wide and 300 feet long. The pipe loops down and back on each trench. Excavation was about $1000 (full day for a man and a machine) and another $1000 to bury them and a day of labor to lay the plastic pipe and weld it together.
Equipment was about $8,000 more than my other options (no natural gas here), but after tax breaks it was about $3000 more. I think it was worth it, even if there weren't tax breaks. I really had to push hard to get this. I had to use a general contractor on this house and he swore it wouldn't work. I made the calls and found someone to do it.
The system runs often when the highs are -20f, but I've never flipped on the backup electric resistance heat.
During the summer the A/C is so cheap it is practically free. It doesn't take much compared to heating. Cooling might have to get the house 30 degrees less than the outside air, but heating has to raise the house nearly 100 degrees f warmer than the outside air.
Ground source is always my first recommendation, but air source should be more popular than it is.
A funny note about the builder who thought ground source wouldn't work well, he also tried to talk me out of a tankless hot water heater because the well water would be too cold in the winter! I guess he didn't understand that the ground down far enough is a pretty steady temperature.
You can't rely on just comparing temperature differentials. During summer, the house receives a lot of extra heat in the form of sunlight.
It isn't my profession, but I've spent a fair amount of time tweaking building envelope and conditions in HVAC calculations to make decisions in how I build.
A delta of 30 vs 100 is not the only factor, but I'd bet in my case it is the largest factor. I still agree with your point of bringin up other factors. Even changing the direction a building faces can change the load on it.