The eia’s data says 10.9 cents per kWh is the national average price per electricity. Essentially for whatever reason (regulatory capture, a mishap with a nuclear plant, onerous local regulations) you are paying 2.4 times what you ‘should’ be paying, given the power company locally should be able to buy natural gas generators and fuel for around the same price as a power company anywhere else.
5.29 (COP is EER/3.4) is what the fujitus RLS3 gets, which is the bare minimum your neighbors would be installing. There are more efficient models not listed on this chart, such as this 40 SEER model.
So the ‘high end’ estimate is actually the average and not high enough.
Anyways if you pay 2.4 times less for electricity, then a heat pump would be 65 percent as expensive as your boiler. Combine that with a solar array, and remember the other advantages of mini splits: redundancy, zoning, and air conditioning as well. Redundancy because a typical house will have 2-5 mini splits, so a failure of one is not a failure of climate control. Zoning, aka turning on just the units in the occupied rooms, can add another factor of 2 energy savings on top of the above. And you get air conditioning on the days you will need it.
the power company locally should be able to buy natural gas generators and fuel for around the same price as a power company anywhere else
I don’t think this is true. Getting natural gas into this part of the country is very expensive. We don’t have enough pipeline capacity, and voters are strongly against building more, so the marginal therm arrives on LNG tankers.
That’s an interesting electricity price chart. It seems like I’m paying typical rates for my state, and I don’t know why it’s high compared to other parts of my country. I wouldn’t say that’s “a flaw in my calculations”, since I’m calculating it for myself and I’m not planning to move, but it definitely sheds light on why mini-splits are more attractive for people in other places.
The “COP” in my chart is specifically “COP for heating the interior of a building when it’s 30°F (~0°C) outside”. I don’t think it’s true that COP under those conditions is equal to EER/3.4, because EER is not measured under those conditions. EER seems to be measured assuming a much smaller temperature difference between outside and inside. Heat pump COPs get worse and worse as the outdoor-indoor temperature difference gets larger.
There are other metrics such as HPSF meant to factor in aggregate performance. Since by choosing a fixed temperature you neglect all the days where the mini split has a huge efficiency advantage over combustion. Also you overlook the zoning. Larger houses that have extra rooms that are not always in use benefit from not heating those areas. And the solar. At your high local electric rates solar has a rapid payoff.
Hmm, well I was trying to ballpark “weighted average outdoor temperature”, specifically weighted by how much heat I’m using. Like, if outdoor temperature is only slightly cooler than what I want inside, I need relatively little heat regardless, so the efficiency of that heat isn’t all that important. My reference temperature of 30°F (~0°C) is very far from the lowest temperature we experience, it’s close to a 24-hour-average temperature during the coldest three months.
I didn’t know about HSPF, thanks for the tip! It seems to assume “climate region IV” (based on here for example), which I guess corresponds to this map which suggests that where I live (Massachusetts) is somewhat colder than climate region IV. Wiki says an electric heater is 3.41 and this says that 11.8 is about the highest HSPF out there (?), so if I divide them I get a weighted-average COP of 3.5, i.e. my initial ballpark guess was right on. But since I’m colder than “climate region IV” it would be even lower than 3.5. (To be clear, there are a bunch of things in this paragraph that I’m not sure about.)
Thanks for bringing up zoning, but we already have individually-settable radiators and do in fact keep unused rooms cold, so I don’t think that’s relevant to me personally. I’ll add a bullet point for the benefit of other readers.
I just haven’t gotten around to thinking about solar. One of these days...
Sure. For a new build in your climate zone, probably the most efficient setup is a tanked condensing natural gas water heater, ideally sorta centrally located. Then a hydronics air handler and vents that just cover the immediate area around the installation. This gives you the cost advantage of natural gas for most of the heating but you avoid the equipment cost of a second furnace. Tankless condensing is an option but in your biome there probably isn’t a sufficient advantage.
Then mini splits around the periphery for heating/cooling during most days.
You made a significant flaw in your calculations. https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a [average price of electricity].
The eia’s data says 10.9 cents per kWh is the national average price per electricity. Essentially for whatever reason (regulatory capture, a mishap with a nuclear plant, onerous local regulations) you are paying 2.4 times what you ‘should’ be paying, given the power company locally should be able to buy natural gas generators and fuel for around the same price as a power company anywhere else.
Second, mini splits are significantly more often on the higher end than your numbers reflect. https://www.energystar.gov/products/most_efficient/central_air_conditioners_and_air_source_heat_pumps
5.29 (COP is EER/3.4) is what the fujitus RLS3 gets, which is the bare minimum your neighbors would be installing. There are more efficient models not listed on this chart, such as this 40 SEER model.
So the ‘high end’ estimate is actually the average and not high enough.
Anyways if you pay 2.4 times less for electricity, then a heat pump would be 65 percent as expensive as your boiler. Combine that with a solar array, and remember the other advantages of mini splits: redundancy, zoning, and air conditioning as well. Redundancy because a typical house will have 2-5 mini splits, so a failure of one is not a failure of climate control. Zoning, aka turning on just the units in the occupied rooms, can add another factor of 2 energy savings on top of the above. And you get air conditioning on the days you will need it.
I don’t think this is true. Getting natural gas into this part of the country is very expensive. We don’t have enough pipeline capacity, and voters are strongly against building more, so the marginal therm arrives on LNG tankers.
Thanks for your comment!
That’s an interesting electricity price chart. It seems like I’m paying typical rates for my state, and I don’t know why it’s high compared to other parts of my country. I wouldn’t say that’s “a flaw in my calculations”, since I’m calculating it for myself and I’m not planning to move, but it definitely sheds light on why mini-splits are more attractive for people in other places.
The “COP” in my chart is specifically “COP for heating the interior of a building when it’s 30°F (~0°C) outside”. I don’t think it’s true that COP under those conditions is equal to EER/3.4, because EER is not measured under those conditions. EER seems to be measured assuming a much smaller temperature difference between outside and inside. Heat pump COPs get worse and worse as the outdoor-indoor temperature difference gets larger.
There are other metrics such as HPSF meant to factor in aggregate performance. Since by choosing a fixed temperature you neglect all the days where the mini split has a huge efficiency advantage over combustion. Also you overlook the zoning. Larger houses that have extra rooms that are not always in use benefit from not heating those areas. And the solar. At your high local electric rates solar has a rapid payoff.
Hmm, well I was trying to ballpark “weighted average outdoor temperature”, specifically weighted by how much heat I’m using. Like, if outdoor temperature is only slightly cooler than what I want inside, I need relatively little heat regardless, so the efficiency of that heat isn’t all that important. My reference temperature of 30°F (~0°C) is very far from the lowest temperature we experience, it’s close to a 24-hour-average temperature during the coldest three months.
I didn’t know about HSPF, thanks for the tip! It seems to assume “climate region IV” (based on here for example), which I guess corresponds to this map which suggests that where I live (Massachusetts) is somewhat colder than climate region IV. Wiki says an electric heater is 3.41 and this says that 11.8 is about the highest HSPF out there (?), so if I divide them I get a weighted-average COP of 3.5, i.e. my initial ballpark guess was right on. But since I’m colder than “climate region IV” it would be even lower than 3.5. (To be clear, there are a bunch of things in this paragraph that I’m not sure about.)
Thanks for bringing up zoning, but we already have individually-settable radiators and do in fact keep unused rooms cold, so I don’t think that’s relevant to me personally. I’ll add a bullet point for the benefit of other readers.
I just haven’t gotten around to thinking about solar. One of these days...
Sure. For a new build in your climate zone, probably the most efficient setup is a tanked condensing natural gas water heater, ideally sorta centrally located. Then a hydronics air handler and vents that just cover the immediate area around the installation. This gives you the cost advantage of natural gas for most of the heating but you avoid the equipment cost of a second furnace. Tankless condensing is an option but in your biome there probably isn’t a sufficient advantage.
Then mini splits around the periphery for heating/cooling during most days.