Number crunching

double drats

 

How much heat does one move and how much is created from compression?

good call, I should have that number burned into memory by now. Remove the extra zeeeerrrrooo
It ain't a Mega Mansion, that's for sure.

 

Efficiency Category

To compare energy efficiency of appliances you must covert the energy units to a common unit usually Btu's

Here is a table to do that.
Energy conversion calculators - U.S. Energy Information Administration (EIA)

Once you know your usage and convert to Btu's you can tell which appliance or method is most efficient.

Cost Category

You can research the cost of Electricity, Gas, Fuel Oil, Water etc. in your area and then do the calculation on which energy source matched with the appliances efficiency is most cost effective for you.

Notes: Some Energy cost are seasonal, some vary dramatically depending on the area of the US you live in.
There is then the availability of the energy sources based on where you live.

Long Term Planning

In all cases the cost of a particular energy source will vary wildly over time. ( In our area there are years that Natural Gas is priced low for a cubic foot and in others years its price can escalate dramatically- same with electricity price per Kwh) . Availability can also be an issue ( in our area years ago certain industries had to temporarily close their factories during a severe cold spell so enough Natural Gas could be supplied to residential customers). This is why many people prefer Hybrid systems where they can heat with natural gas or electricity. This allows you to have some control over your cost and some option if availability is compromised.

Energy is an interesting topic and one that can require a great deal of thought and research to properly understand the best energy choices long term.

Even then outside influences that are not predictable can influence prices and availability dramatically - World unrest and the price and potential availability of heating oil- Government intervention in burning coal for electricity driving cost of electricity high- Regulations on disposing Nuclear Waste which make Nuclear Power Plants unattractive.

Predictable renewable energy sources such as Geothermal, Solar, Hydro and Wind can begin to become more attractive when you take the long term energy picture and cost for yourself into consideration

 

Here is a comparison of heating fuel prices based on the average local price as of 4/18/2022.

Even if I have to buy cord wood, the wood-burning stove is still the cheapest. Not the most convenient nor the easiest to operate though. My advantage is that I can supply my own cord wood all from my own property, but felling trees, moving and cutting, and drying are very labor-intensive. Wood pellets are also attractive, but I do have to buy them and storage becomes a problem. We don't have a natural gas line. If the heat pump can produce enough heat throughout the coldest months of winter, then for today's price, it is cheaper than the heating oil system we have now. Historically this was not the case. Low oil prise made even the most efficient heat pump too expensive. That's just for the operational cost only before adding conversion cost. However, I am not sure how the number is calculated for the heat pump. Any way to compare, the electric radiant heat is the most expensive way to heat the house for sure.

Yep, we use to live in a house in MA with the electric baseboard radiant heat for the entire house. No other source of heat other than an ornamental open fireplace. After moving in, the very first winter month's electric bill was ~$600, or a 600% jump from the non-heating season average. And that was over 30 years ago. I have no idea what would cost now to heat a whole house in NE with radiant baseboard electric heaters only.


Heating Fuel Prices | Governor's Energy Office

 

It can get even more confusing if an individual takes into account the particulates that escape from a home into the environment, like smoke, C02 etc., especially if there is solar. All fossil fuels produce some particulates that escape the home, no matter how efficient the appliances are.
With solar. after installation there can be an abundance of what is referred to as free energy. And it's kinda true that it's free of particulates while generating and costs ( kinda ) as it deletes or reduces a bill from a utility.

Than it gets even more complex when figuring in the manufacturing costs and their particulate matter releases and weighing them against the production costs and particulate matter releases for producing the other types of energy creating methods commonly available.
For example: California was able to run all it's state utilities for several hours of one day last year on 97% renewable sourced energy.
*(It was referenced in a youtube mostly about new solar and wind farms in CA).
But that stuff is not cheap to setup and keep running and the wind also requires battery storage even more so than large solar.

The estimates are not always easy to follow and the claims of efficiency are even harder to calculate.
It all depends on what's being compared to what, which usually gets washed over if not completely left out and or bashed as being the dumbest idea anyone ever had. Which I'm sure we all have heard of one or another of those.

 

That seems optimistic to me as regards the 50 year old ones.

The two currently available choices (at least in some parts of the country*) for gas furnaces are "standard" units in the 80%+ range, and "condensing" units in the 95%+ range.

They both have induced-draft heat exchangers (a small electric blower pulls air through the heat exchanger's burner tubes, gas nozzles inject into that moving air stream, the combustion happens as the air is pulled through the tubes, and the inducer blower forces the spent gases out the vent under pressure). The induced flow lets the heat exchanger be built so the combustion gas flow is the opposite direction of the warm-air flow, for good heat exchange. The coolest post-combustion gas is in the part of the heat exchanger where the coolest circulating air first enters. The circulating air gets warmer as it goes through the exchanger, but it is moving through the hotter regions of the exchanger, so the temperature difference stays high and heat gets efficiently exchanged.

The main difference is what happens to the water. As the furnace reacts methane (CH₄) with O₂ from the air, it makes a bunch of carbon dioxide and water (in a perfect world, CH₄ + 2O₂ ⇒ CO₂ + 2H₂O, though what really happens is not quite that pretty). The water comes into existence as vapor, holding its latent heat of vaporization.

In the 80%-ish furnaces, that heat is left behind in the vent gas so the water stays vapor all the way out. These use standard metal appliance venting out the roof or up a chimney. Because the water stays vapor all the way out, it doesn't rust the furnace components or vent piping.

In the 95%-ish furnaces, enough heat is extracted to condense the water vapor before it leaves the furnace, capturing that latent heat of vaporization that would otherwise be lost. They have to be made with rust-resistant heat exchangers, and have rustproof PVC vent piping, often right out the side of a house. The condensed water goes into a drain.

My previous furnace, vintage 1981, used natural-draft burners. There was no inducer blower, just long burner tubes at the base of the heat exchanger, making big lazy flames in the draft supplied by the chimney. This flow could only be up, so in an upflow furnace design, the heat exchange was less efficient. The incoming cool air got warmed most right away, as it entered the bottom of the heat exchanger where the flame was hottest, and then the warming air followed the cooling gas up the path of the exchanger, with the temperature difference getting smaller and smaller and the heat exchange tapering off.

I'm pretty sure my old one had a nameplate rating of about 82,000 BTU/hr in for 60,000 BTU/hr out, or about 73% efficiency at best, and even that neglected cycling losses, like all the heat sent up the chimney during the first minute or so before the circulating blower would start.

* It seems like around 2013 there was some talk about phasing out the 80% option for new installations in northern parts of the country. But my neighbor seems to have put one in this year, so it must still be an option around me.

 

The last time we had very high heating oil prices (circa 2008) I even thought about replacing our old wood-burning stove with a coal-burning stove. Back then the cost of a bag of anthracite coal with higher BTU contents was cheaper than a wood pellet in a bag. They could be stored outside unlike wood pellets. With a large enough hopper, it can be set to automatic operation for an entire day without adding new fuel, unlike the conventional wood-burning stove. It was an attractive option economically back then, but I did not want to add another fossil fuel burner to my house. So the idea was abandoned.

Ideally, if I can start from scratch and design and build a house to live in, then I would consider only passive solar heating in the earth-sheltered house. Trombe wall behind the south-facing solar gain should capture, store, and distribute enough heat to warm the entire house even in cold winter in New England with minimal use of another source of heat if designed correctly. And, it would be far less complex to construct and maintain and far more cost-effective than say geothermal solar heating system.

 

These numbers are thermal efficiencies; how much of the heat energy from the fuel is used to supply heat from the appliance. Resistive electric and NG can only reach 100% because they are being consumed to make heat. As said, heat pumps are moving heat around, so can exceed that 100% limit. A 200% system is using 1 btu of electricity to supply 2 btu of heat.

That's going to vary with how much heat is available on the cold side for moving.

 

@ChapmanF
The one thing I'll add about the old furnace (almost identical to your old one), is the cold air returns with is the part with the filters that need to be changes all the time. Another thing is that the heat exchanger is not a direct route up as it too bends around a bit inside the furnace before it's exhausted out the chimney.

When I talked with a HAVC service tech many ( 10? ) years ago and mentioned that I shut off my pilot in the summer, he mentioned "but what about the condensation"? I didn't know any better, but it still didn't stop me from shutting off the always on pilot in my 1960's furnace when the furnace would not run for several months, If there is any deterioration from condensation inside the furnace during summer, it was only to the thermocouple that sits inside the pilots flame, which tells the electrical system in the furnace that the pilot is still burning. And I doubt that would be effected either when the both gas and electric to the furnace are turned off in the summer months. And that is an easy part to find and install, even for an old antique like mine. The regulator as is the combination fan and limiter control is getting harder to find for my model, but they are still around at some places too.

 

My Dream House construction would be in an area with a natural geothermal source that had the opposite temp of the natural occurring ambient temps that used the most energy to heat or cool per year. Like a cool spring in the desert or a hot spring in our northern wastelands..
And who's the lucky son of a gun that finds a location like that?

 

Sounds more like a sales pitch to me unless it's comparing and electric water heater to an electric water heater / heat pump combo, like in fuzzy1 post above, Or it's just theoretical efficiency. Sorry.

It sure does depend on how much is moved and how much is created.

 

"An Air Source Heat Pump (ASHP) typically produces about 3kW thermal energy for every 1kW of electrical power consumed, providing an effective “efficiency” of 300%. It is thermodynamically impossible to have more than 100% efficiency, as this indicates that more energy is being generated than is being put in. As a reason, the performance is displayed as a Coefficient of Performance (COP) instead of efficiency. The case above would be represented as having a COP of 3.

It appears that more energy is being provided than is consumed because the only “valuable” input energy is electricity used to run the compressor and circulating pumps. The rest of the energy transferred from a heat source that would otherwise not be utilized (such as the ground, ambient air, or a river) is not considered an energy input."
Heat Pump Efficiency: Equation & Formula | Linquip

Saying 300% isn't correct phrasing, but it isn't wrong in terms of fuel uses to heat a living space or water. COP values aren't like engine oil viscosity labels; they directly relate to the heating efficiency of the system. Now, the COP rating of a system does depend on the local climate, which is a major difference from thermal efficiency. Which is why there is also seasonal COP ratings.

 

Lots of people. My last two homes have been like that.
When the ambient temp outside is 100 in the summer, our GSHP is drawing in 55 degree temps.
When ambient temps hit 30 below (F) our GSHP is drawing 55 degree temps.

The condensers then warm our house as much as needed.
In six MN winters we have yet to run our resistance coils as back-up heat. It just hasn’t been needed.

So if designing a house from scratch, this is quite easy to do for many people.

 

Except that geothermal HP would cost $$$ far more than a passive solar earth-sheltered house. I know a guy who built his earth-sheltered 100% off-grid house for less than a regular construction house.

 

I used to do that too. I suspect the condensation is a red herring in that context.

I don't think the pilot by itself makes enough heat to keep a whole HX, vent system, and chimney from seeing condensation ... and at the same time, that burning pilot is making water vapor 24✕7.

I did have to consider condensation when I replaced the furnace. That left the water heater as the only appliance using the chimney, but a 30,000 BTU/hr water heater isn't enough to prevent condensation in the original size of masonry flue, so I needed a properly-sized flue liner added so there wouldn't be moisture damage done to the chimney.

 

That's fantastic! I am also betting it wasn't built in Minnesota or another northern climate.
We looked into both earth sheltered and passive homes before building our net-zero home.

The earth sheltered homes have issues in our climate zone, and the passive-haus requirements were super expensive.
We preferred a simple, comfortable home that only came in about 10-15% above a built-to-code (aka minimum legal) house.

We use the concept of passive solar quite a bit. On sunny days during the winter, our heat pump doesn't need to run until about 11 or midnight.

Passive solar and earth homes work great for some, but each region and buyer/designer has their own needs. This leads to many paths to reach efficiency.

 

Just curious, why was your climate zone have an issue with building an earth-sheltered home, and what would make it super expensive?

I can see that each building site has different requirements and issues to deal with, but I can't think of a generalized reason that would exclude the northern climate from building an earth-sheltered home. In fact, most of the earth-sheltered homes I have read about on the internet are in the northern climates, and most of them seem to cost far less than a conventional home of similar build and size.

Here are some examples. Out of 5 in the list, 2 were built in Maine, 1 in NH, 1 in upstate NY, and 1 in TN.
DIY Earth Sheltered Homes- Thehomesteadingboards.com

I do see an advantage of the geothermal HP with conventional house construction in the southern climate where AC is a necessity. But if heating is the primary need for energy, then there is nothing cheaper than passive solar design, I would think.

 

There is little reason for anyone to switch from other fuels to electric resistance heat (apart from cooking).

But my region has a huge installed base of electric resistance heat, a legacy from the old days of very cheap and abundant hydropower, and frequent lack of natural gas service. The idea now is to get more of these homes to convert to heat pumps for space and water heat. Clothes dryers should eventually move that way too, but that is still an immature product market.

Very crudely (neglecting fans and circulating pumps and control overhead), about 1 unit of heat comes from the compressor itself, equal to the amount of electricity consumed to run it. And 2 or 3 additional units of heat get soaked up through the evaporator from the ambient source (air / ground / water), and get compressed / pumped up to the condenser, for a total of 3 or 4 heats expelled at the output. An ideal heat pump is the same as a Sterling-cycle heat engine, but run in reverse to convert mechanical energy into heat output.

As a previous respondent already point out, heat pump "efficiency" is common vernacular for COP (coefficient of performance) or EF (energy factor), which is the ratio of total heat output to electric-only energy input. The heat input taken from the local ambient is considered "free", and left out of the equation.

Heat pumps get their best ratings with narrow input to output temperature differences (actually, ratios of absolute temperatures, i.e. numbers expressed on Kelvin or Rankine scales, not Celsius or Fahrenheit), and performance falls as those temperature differences increase.

The theoretical heat pump performance limit is just the inverse of the Sterling-cycle heat engine efficiency limit. For a 0°C outdoor ambient (273K) to 20°C (293K) indoor temperature rise, this works out to (293) / (293-273) = 14.7. For someone wanting a warmer indoor temperature of 25°C (298K) with outdoor ambient of -40°C (233K), the theoretical COP limit is (298)/(298-233) = 4.65, much lower but still a huge improvement over electric resistance.

A ground source system with 10°C ground might be capped at COP = 29.

No commercial products are yet getting close to these theoretical limits. Note also that commercial air-source product ratings are defined for a weighted average seasonal temperature profile, not for just for a single temperature condition.

The coldest climate zones still need some alternate heat source for their coldest nights that no available heat pump products can handle. And for overall equipment cost reasons, most installations in less-cold zones still use other supplemental heat to avoid buying expensive cold-climate heat pump capacity that would be used only very rarely. But the temperature points at which heat pumps can affordably be sole heat sources keep getting pushed ever lower.