"All Electric" Home with Instant Hot

[kwired]

Therms of gas are much cheaper than therms of electricity.

But a heat pump can move more heat with a therm of electricity than resistance heat can create with same therm. Likely can move more heat than created by a therm of gas in most cases as well.

 

[gadfly56]

Your efficiency at burning gas is way too high I believe. Isn't it more like 70% typically? I am looking at a Lopi Northfield gas stove and it is the most efficient one I can find and I believe is around 70%. I don't really care too much about arguing about the carbon footprint or overall efficiency of electricity running heat pumps etc,. But electricity has many advantages such as easier infrastructure in the house, no venting, split type systems also being able to do air conditioning, for those of us with solar systems being able to take advantage of our "free" electricity, etc.

If you do a quick Google on "gas furnace efficiency", you'll see (for new) between 92% and 96%. Even my bottom-of-the-line unit is 90%, according to the test the tech did.

 

[gadfly56]

But a heat pump can move more heat with a therm of electricity than resistance heat can create with same therm. Likely can move more heat than created by a therm of gas in most cases as well.

Highly unlikely, and certainly unlikely at a COP below 2.

 

[gadfly56]

Thank you for your question ... Ductless refers to "Mini Splits", which uses refrigerant lines to connect to air handlers which are mounted in each room. Conventional forced air systems us ducts to supply air to each room. This is where the most inefficiency accrues, running ducts in attics with outside air temperatures and duct connections that leak air.

The efficiency of mini splits is you only heat or cool each room, not the whole house. Manufacturers tried to compete with zoning systems which were outlawed by CEC because they didn't work, they had return air problems.

On a previous post I mention heat pumps struggle under 50 degrees, I was referring to forced air systems. Mini splits can work at a much lower outside temperature, without auxiliary heat. The only drawback is the condensing unit will go into "Defrost" mode when it senses ice buildup.

For the cost of one mini-split system that covers one room, you can put in a gas furnace that will heat your whole house.

 

[wwhitney]

Highly unlikely, and certainly unlikely at a COP below 2.

Actually, kwired statement was obviously true whenever COP was above 1.

Most likely you were responding to the implicit statement "But a heat pump can move more heat with a therm of electricity than resistance heat can create with same therm. Likely can move more heat with electricity costing the same as a therm of gas costs than created by a therm of gas in most cases as well."

That statement is also likely true but depends on the relative costs of gas and electricity. Heat pumps should be able to perform well above a COP of 2 in most residential applications.

Cheers, Wayne

 

[electrofelon]

For the cost of one mini-split system that covers one room, you can put in a gas furnace that will heat your whole house.

I don't know about that.... I think it's really hard to generalize and come up with a statement like that there are many variables.

 

[electrofelon]

If you do a quick Google on "gas furnace efficiency", you'll see (for new) between 92% and 96%. Even my bottom-of-the-line unit is 90%, according to the test the tech did.

Okay yes I concur. I was mixing up stove type heaters versus condensing type heaters.

 

[wwhitney]

For the cost of one mini-split system that covers one room, you can put in a gas furnace that will heat your whole house.

Maybe if the forced air ducting is in place already. But in that case you could put in a mini-split that supplies a high pressure air handler. Or a conventional central heat pump. Given that the heat pump supplies A/C also, I would expect it to compare not unfavorably with a gas furnace plus A/C in terms of cost and performance.

Cheers, Wayne

 

[W@ttson]

If it's not too late, the HO would be much better off and happy with a gas tankless. The water temp would be more consistent and the electric bill would be much lower. I've never encountered anyone that was happy with an electric tankless.

Not so fast! I have heard that CA is getting rid of all Natural Gas appliances. I know NY is going down that road. I have heard that CA is even outlawing small engine gasoline tools like lawn mowers and chain saws.

 

[mtnelect]

In California the morning gardeners are fighting back, they will not change to battery-power without compensation and charging stations from the state ! I will miss the sound of blowers and chain saws in the morning. The wood chippers are next !

 

[kwired]

Highly unlikely, and certainly unlikely at a COP below 2.

Which is why they sometimes put an outdoor thermostat to lock out the compressor when COP drops too low. There is no point in getting a heat pump if it will never see conditions above 1. There are places where COP will drop for cold spells but then go back to a COP that is still going to cost less to operate than if you only used your backup heat source.

 

[Little Bill]

I can just barely see the OP's topic from here!

 

[tortuga]

CA is getting rid of all Natural Gas appliances.

Thats an incorrect statement. They are only phasing it out of new construction.
California does not a have good in-state source for natural gas, lots of California's gas is imported from outside the US, and not very efficiently.

If you burn gas directly for heat, the process is typically 90-95%

A typical residential gas furnace from a house built in the 80's is probably 60% efficient, its not like everyone has the latest greatest gas furnace.

If you burn that gas to produce electricity, not so much. The EIA says that the US generating fleet is not quite 40% efficient turning fossil fuels into electricity. So, for 100 units of thermal energy, you get (generously) 40 units of electricity out. The distribution losses are about 9%, so now we are down to 37.4 unit of energy delivered to the heat pump. To be as efficient as direct heating, the heat pump can't operate at a COP below (90/37.4) or 2.4. And please, no nattering about how we can just increase the efficiency of the grid. We're talking about today. So, if you are in a climate zone with many more heating degree days than cooling, the barrier is a COP of 2.4.

I dont see the distribution losses of the gas infrastructure to the homes in that calculation.
I know on the east coast has older iron pipes that are less efficient than the electric grid.
I say just assume distribution losses of both systems to be about equal.

 

[kwired]

Thats an incorrect statement. They are only phasing it out of new construction.
California does not a have good in-state source for natural gas, lots of California's gas is imported from outside the US, and not very efficiently.

A typical residential gas furnace from a house built in the 80's is probably 60% efficient, its not like everyone has the latest greatest gas furnace.

I dont see the distribution losses of the gas infrastructure to the homes in that calculation.
I know on the east coast has older iron pipes that are less efficient than the electric grid.
I say just assume distribution losses of both systems to be about equal.

That might be true in places that don't get all that cold. Around here is somewhat rare to find one that old. If you do chances are it has a bad heat exchanger and is a CO hazard but occupants don't know it. Heat exchanger gone bad is a main reason majority of them have been replaced to begin with.

 

[gadfly56]

Actually, kwired statement was obviously true whenever COP was above 1.

Most likely you were responding to the implicit statement "But a heat pump can move more heat with a therm of electricity than resistance heat can create with same therm. Likely can move more heat with electricity costing the same as a therm of gas costs than created by a therm of gas in most cases as well."

That statement is also likely true but depends on the relative costs of gas and electricity. Heat pumps should be able to perform well above a COP of 2 in most residential applications.

Cheers, Wayne

You are confusing the issue. The issue is what does one therm of gas deliver at the furnace vs what does one therm of gas deliver as electricity? Converting that therm of gas to electricity gets you about 38% of the energy value at the heat pump. That's why you need a COP of ~2.4 or over to break even.

 

[wwhitney]

You are confusing the issue.

I read "a therm of electricity" to mean 29.3 kWhs. If you read it as "the kWhs you'd get from burning a therm of gas in a modern generating plant" then that would explains some of the confusion.

The issue is what does one therm of gas deliver at the furnace vs what does one therm of gas deliver as electricity?
Converting that therm of gas to electricity gets you about 38% of the energy value at the heat pump. That's why you need a COP of ~2.4 or over to break even.

Agree on the 2.4 calculation being approximately correct. Disagree on the earlier "unlikely" statement. COP of 2.4 or above is typically the case.

Cheers, Wayne

 

[gadfly56]

Thats an incorrect statement. They are only phasing it out of new construction.
California does not a have good in-state source for natural gas, lots of California's gas is imported from outside the US, and not very efficiently.

A typical residential gas furnace from a house built in the 80's is probably 60% efficient, its not like everyone has the latest greatest gas furnace.

I dont see the distribution losses of the gas infrastructure to the homes in that calculation.
I know on the east coast has older iron pipes that are less efficient than the electric grid.
I say just assume distribution losses of both systems to be about equal.

That would not be the correct approach. You have to take the electricity losses into account in this analysis because you are converting one form of energy into another, and efficiency is important.

 

[wwhitney]

The upshot of this residential electric vs natural gas discussion is:

- For new installations, the operating costs are roughly a wash. Roughly meaning within a factor of sqrt(2) or so (70% to 140%). Obviously this is going to depend on local energy prices and will change over time.

- There are a lot of advantages of not burning gas in your home, I won't go into them all now.

So if the upfront costs (haven't checked) and operating costs are truly equivalent, then electricity is a clear winner. If gas is cheaper, then depending on how much cheaper and how much you value the benefits of electricity, there's an incentive to go with gas.

And the greater energy density of natural gas is a clear winner for certain applications, like tankless water heaters. Maybe that's the only typical residential case?

Cheers, Wayne

 

[retirede]

That would not be the correct approach. You have to take the electricity losses into account in this analysis because you are converting one form of energy into another, and efficiency is important.

Ultimately, the homeowner only cares about $ required to heat the home. In colder climates, gas almost always wins, except for geothermal heat pumps when the utility provides a subsidized electric rate.

 

[kwired]

Ultimately, the homeowner only cares about $ required to heat the home. In colder climates, gas almost always wins, except for geothermal heat pumps when the utility provides a subsidized electric rate.

geothermal is usually pretty inexpensive to operate (compared to other options) but often rather expensive to install. Ductwork, the unit itself are same or similar as many other options to install, but you also need wells, ground loops, etc. unless you are in a location where you have an abundant supply of water that is not too difficult or costly to set up to circulate through your system.