Author Topic: Heat pump efficiency: How much extra is efficiency worth?  (Read 4176 times)

ChpBstrd

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Heat pump efficiency: How much extra is efficiency worth?
« on: May 16, 2022, 01:51:27 PM »
Need some help from the brain trust!

My central heat pump went out and I've been quoted the following numbers on a replacement 2.5 ton unit:

SEER 14.25: $9,450
SEER 16.5: $11,250
SEER 18.5: $12,580

I found https://hvacdirect.com/seer-efficiency-savings-calculator.html and using my 0.12/kwh cost of electricity it seems to be a wash. The difference in price will be roughly the difference in lifetime energy costs. That leads me to think the cheapest model might be the best choice.

Do any of you have another calculation method or site? Which option would you pick?

Syonyk

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #1 on: May 16, 2022, 02:50:14 PM »
Get the most efficient.  Power costs are likely to be heading up in a hurry with inflation and energy costs, so "using less energy to thermally manage a house" will be worth more than the current value, in a lot of likely futures.  It would also mean that you need less solar to power it, etc.

ChpBstrd

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #2 on: May 16, 2022, 03:44:26 PM »
An additional detail:

We have chronic humidity problems and must run a portable dehumidifier that seems to eat as much electricity as the HVAC itself. I have read that 2 speed compressors and 2 speed air handler fans do a much better job of removing humidity from the air compared to our current 1 speed unit. Only the most expensive option includes a 2 speed compressor. However all options include a 2 speed air handler. The salesman's opinion is that having a 2 speed air handler will obtain ~75% of the humidity reducing benefit, and a 2 speed compressor the remaining ~25%.

I've also read that having a 2 stage compressor will extend the life of the unit, but the salesman wasn't so sure. The warranties for these machines are longer in any case.

Syonyk

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #3 on: May 16, 2022, 03:58:19 PM »
For $3000 difference between the low end and high end, with the energy savings, and "more ways to use it efficiently," including low speed air circulation and dehumidification, seems... likely that the money is well spent.

At some point, the SEER jump is also simply being "less stupid with defrost cycles."  Lower efficiency units have a configurable timer for when they reverse and defrost the outdoor unit below freezing - mine can reverse every 30, 60, or 90 minutes.  Frosted or not, it'll stop, reverse the valves, and heat the outdoor unit with the house heat, even if it's not the slightest bit frosted.  I set it to 90 minutes, and then run into the problem on foggy days in which it's just a ball of ice, and won't defrost until the timer hits.  A higher efficiency unit will do pressure drop math through the unit to determine when it needs to defrost - so, for us, that would mean it mostly never defrosts, but would defrost frequently on those few foggy days we have.

Given all the uncertainty in energy going forward, using less of it if you've got the money to do so (and I assume the $3k delta is an academic interest for optimization, not a make or break deal for your budget) seems very useful, and will compound if you're installing solar at some point.

ChpBstrd

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #4 on: May 16, 2022, 06:20:48 PM »
The reason I pause is that every one of the following utility calculators produce an annual savings number somewhere between $67 and $120 at my cost for electricity.

https://learnmetrics.com/seer-savings-calculator/
https://hvacdirect.com/seer-efficiency-savings-calculator.html
https://www.ushvacwarehouse.com/seer-calculator/

At that rate, it is unlikely the savings will ever cover the increased cost for the unit. I.e. the payback period exceeds 20 years, and that's not not even including discounting.

Syonyk

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #5 on: May 16, 2022, 06:56:39 PM »
Sure, but if the higher cost unit will eliminate the dehumidifier operation substantially, you've got power savings there, and if you're planning on solar and can go with a smaller system, there are savings there, etc.  If power costs go up (as seems likely), that savings value will improve over time.

Or your savings will be less because people on this forum don't tend to set things to 72F year round and ignore it.

My fairly strong opinion is that a more efficient, longer lived (if the warranty is longer, the manufacturer expects it to last longer, almost always) unit is almost certainly worth the money, either directly or indirectly.  I remain slightly annoyed we have a low efficiency, single speed, quite dumb heat pump - I didn't ask the right questions when we had the house put in and ended up with this one, which doesn't make sense to replace, but neither would I install something like it if this failed.  I'd either get a higher efficiency inverter drive unit, or just cut over to mini splits.

Anyway, someone else can take a stab one way or the other, I've had my say.

Gone Fishing

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #6 on: May 16, 2022, 07:26:36 PM »
How big is your house?  How well insulated?  If it is smallish and well insulated, a ductless unit may be more cost effective.

ChpBstrd

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #7 on: May 16, 2022, 08:10:12 PM »
How big is your house?  How well insulated?  If it is smallish and well insulated, a ductless unit may be more cost effective.
1300sf, all double pane windows, 8" cellulose in ceiling, no insulation in walls except for maybe 300sf of the house, un-insulated crawl space, 8' ceilings.

I thought about ductless; it would be cheaper, introduce redundancy, and having 2-small units in the house would allow me to dehumidify by running just one at a time on cool damp days. However, the floor plan doesn't have any good spots where the units would distribute air well and wouldn't look weird.

My parents, in a 1000sf house, had their central AC go out a decade ago and they never fixed it because a $350 12k BTU window unit meets their needs. They still use the gas furnace portion of their old HVAC unit. It worked out well for them because they've almost skipped a HVAC replacement cycle and their electric bill still isn't too bad. Not an option for me, but I have to admire their win at the game of cheap bastardom.

Abe

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #8 on: May 16, 2022, 08:38:36 PM »
I think the middle one will be the best balance of a hedge against increasing energy costs vs current costs. From my reading on this topic, there’s a plateau in cost vs efficiency around 16-17 SEER.

However the quote for your a 14.5 seer 2.5 ton unit is substantially higher than a 4 ton 16 seer unit I received in the fall. Is this the best of several quotes?

ChpBstrd

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #9 on: May 16, 2022, 08:53:53 PM »
However the quote for your a 14.5 seer 2.5 ton unit is substantially higher than a 4 ton 16 seer unit I received in the fall. Is this the best of several quotes?

The quote includes all equipment, lineset, electrical "whip", plastic pad, overflow tray and sensors, smart thermostat, installation, and 10-12y warranty. I will be shopping around. The feedback I'm receiving from the first couple of contractors I talked to is that equipment, particularly air handlers, are in short supply and a wait list is forming. Perhaps with inflation and all, last fall would have been the ideal time to get an HVAC unit.

The salesman I talked with today quoted me on Trane models, and talked somewhat disparagingly about "lower end" brands like Amanda, Westinghouse, etc, saying that getting 10 years out of such equipment is all one can expect. What brand did you have installed and how much did it cost? Was the level of work similar to what I'll have done?

Paper Chaser

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #10 on: May 17, 2022, 03:26:18 AM »
How big is your house?  How well insulated?  If it is smallish and well insulated, a ductless unit may be more cost effective.
1300sf, all double pane windows, 8" cellulose in ceiling, no insulation in walls except for maybe 300sf of the house, un-insulated crawl space, 8' ceilings.

With just R28 in the ceiling, and little or no insulation everywhere else, you're under-insulated pretty much everywhere, which is likely contributing to your humidity issue. And a house with no insulation in the walls is almost certainly not air sealed very well either. You're basically paying to condition the outdoors, and be uncomfortable at the same time currently.

Which climate zone are you in?




If the plan is to be there for more than another couple of years, I'd probably buy the cheapest option that gets you the 2 stage hardware and warranty that you want, and then spend any savings on adding insulation and air sealing. Having nothing in most of the walls, and the crawl is inefficient, but also makes the living space less comfortable. The uninsulated walls can lead to drafts, and the uninsulated crawlspace can allow any moisture or soilgas under the home to enter your living space.

Were I in your shoes, I'd probably focus on encapsulating the crawlspace first to improve comfort, and air quality but also to try and reduce or eliminate the power sucking dehumidifier. This can be done DIY to save some cash if you're up for it (It's really just unrolling some plastic and taping all of the seams):
https://crawlspace-diy.com/

« Last Edit: May 17, 2022, 03:28:18 AM by Paper Chaser »

chemistk

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #11 on: May 17, 2022, 05:43:26 AM »
However the quote for your a 14.5 seer 2.5 ton unit is substantially higher than a 4 ton 16 seer unit I received in the fall. Is this the best of several quotes?

The quote includes all equipment, lineset, electrical "whip", plastic pad, overflow tray and sensors, smart thermostat, installation, and 10-12y warranty. I will be shopping around. The feedback I'm receiving from the first couple of contractors I talked to is that equipment, particularly air handlers, are in short supply and a wait list is forming. Perhaps with inflation and all, last fall would have been the ideal time to get an HVAC unit.

The salesman I talked with today quoted me on Trane models, and talked somewhat disparagingly about "lower end" brands like Amanda, Westinghouse, etc, saying that getting 10 years out of such equipment is all one can expect. What brand did you have installed and how much did it cost? Was the level of work similar to what I'll have done?

I'm responding both to this post and to the thread generally -

If you can, try and get a heat pump that has 2-stage operation, especially if you spend a lot of time in the shoulder seasons where you're not using the thing at full bore - it will absolutely save on the wear and tear and push its lifespan closer to the 15-20 year mark. I think the marginal improvement in efficiency over the base unit will be enough to hedge against rising electrical costs as well.

Also, if you can, make sure you push for an upgrade to a variable speed air handler (if you're getting a new air handler with the system). It greatly helps in avoiding that thermal shock when the air handler kicks on, instead going from a gentle breeze all the the way up to the desired speed.

That being said, I'm genuinely shocked that you were even able to get a quote for anything higher than a 16SEER system.

We just replaced our central heat pump last month with a 14SEER 3.5ton single -stage outdoor unit (Carrier) and a variable speed air handler + 8kW backup heat strips. Back in March when i was getting quotes, I was informed that it would be very challenging to get a higher end model right now, as most of the domestic HVAC suppliers are primarily assembling base models destined for new construction. Total cost for the exterior unit, air handler, smart thermostat, parts, labor, and removal of the old system was $9750.

My brother works in HVAC supply and he constantly tells me how 1) inventories are basically nonexistent, 2) getting a higher end system is a crapshoot right now, and 3) we're probably going to see 2-5 more across-the-board price increases before the end of the year. Not to mention, this is that time of year where people in the not-south start realizing that their air conditioning didn't make it through the winter so there tends to be a huge volume of orders between now and mid-summer.

Oh and specifically to your point about lower end models - that's 100% true (again courtesy of my brother). Their warehouse sometimes can see what a customer is replacing and the lower end brands definitely do fail more frequently around when the warranty is up. My personal perspective on it is that most people stay in a house 7-10 years, and if they replace their HVAC at some point in that span, the next homeowners are more likely to just shrug their shoulders and pull the trigger on another unit rather than try and get it serviced. 
« Last Edit: May 17, 2022, 05:46:50 AM by chemistk »

mayhem

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #12 on: May 18, 2022, 07:21:14 AM »
Hey ChpBstd a couple of thoughts, SEER is actually just the cooling efficiency. Do you live in a primarily air-conditioning locale? If you have equivalent heating/cooling seasons, you may consider looking at the HSPF of the equipment as well.

I'm not sure where you live, but your utility or efficiency utility may offer incentives or rebates for the more efficient model.

Also, is all of your electricity 12c/kWh, or does the rate increase after you use so many kWh. Sometimes called a base block, our utility offers a lower rate on the first 100kWh, and then the rate jumps to ~15c/kWh. If this is the case, you might see larger savings with the more efficient equipment than your initial calculations show.

Insulation and air-sealing tends to be the best bang for the buck in terms of $ savings. It's not glamorous, but it does make a huge difference.

ChpBstrd

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #13 on: May 18, 2022, 03:51:46 PM »
Hey ChpBstd a couple of thoughts, SEER is actually just the cooling efficiency. Do you live in a primarily air-conditioning locale? If you have equivalent heating/cooling seasons, you may consider looking at the HSPF of the equipment as well.

I'm not sure where you live, but your utility or efficiency utility may offer incentives or rebates for the more efficient model.

Also, is all of your electricity 12c/kWh, or does the rate increase after you use so many kWh. Sometimes called a base block, our utility offers a lower rate on the first 100kWh, and then the rate jumps to ~15c/kWh. If this is the case, you might see larger savings with the more efficient equipment than your initial calculations show.

Insulation and air-sealing tends to be the best bang for the buck in terms of $ savings. It's not glamorous, but it does make a huge difference.

Good point about HSPF. I was using SEER as shorthand for heat pump efficiency but I guess it's not so simple. I'm about 50/50 heating/cooling in the climate where I live.

My electricity is flat-rate.

I agree on the insulation too. Unfortunately, we'd have to tear the walls open to add any more. Stuffing fiberglass between crawlspace joists is known to cause mold and fungus problems in my damp climate but I might look into spray foam (probably costs a fortune).

Paper Chaser

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #14 on: May 18, 2022, 05:35:47 PM »
I agree on the insulation too. Unfortunately, we'd have to tear the walls open to add any more. Stuffing fiberglass between crawlspace joists is known to cause mold and fungus problems in my damp climate but I might look into spray foam (probably costs a fortune).

Both cellulose and foam can be blown/sprayed into wall cavities through small holes (usually under 2" diameter"). You still have to do drywall repair if it's done on the interior, or some sort of plug if they go through the exterior but it's much faster, cheaper, and easier than completely removing the drywall to install fiberglass batts, and you potentially get better insulating and air sealing than you would with fiberglass too. The right contractor will likely do the patching/plugging for you.
Injection foam:
https://www.youtube.com/watch?v=_dOm0a4unEw

RE crawlspace insulation: Rigid foam panels cut to fit tightly in the joist bays, and then sealed around the edges with cans of spray foam works just as well as professionally applied spray foam, and does it for way less cash. Ideally it would be polyiso foam, but XPS is probably fine too.
« Last Edit: May 18, 2022, 05:39:22 PM by Paper Chaser »

nereo

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #15 on: May 18, 2022, 06:49:15 PM »

RE crawlspace insulation: Rigid foam panels cut to fit tightly in the joist bays, and then sealed around the edges with cans of spray foam works just as well as professionally applied spray foam, and does it for way less cash. Ideally it would be polyiso foam, but XPS is probably fine too.

Agree that rigid foam panels cut and sealed (and foil faced preferably) are a great way to go, and what we did in our previous home.  However, I was a bit shocked to get closed cell foam quotes come in at slightly less than what the materials alone would be for the DIY approach (in our case it was $2/bf all in). Part of that is how much rigid foam panels and fasteners have gone up in price in the last two years.

Papa bear

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Heat pump efficiency: How much extra is efficiency worth?
« Reply #16 on: May 18, 2022, 07:15:53 PM »
To add to the polyiso vs xps foam - while polyiso gives you a higher r value/in, it is much less effective in cold climates and xps foam should be used.

https://www.greenbuildingadvisor.com/article/in-cold-climates-r-5-foam-beats-r-6


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Abe

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #17 on: May 18, 2022, 08:14:15 PM »
However the quote for your a 14.5 seer 2.5 ton unit is substantially higher than a 4 ton 16 seer unit I received in the fall. Is this the best of several quotes?

The quote includes all equipment, lineset, electrical "whip", plastic pad, overflow tray and sensors, smart thermostat, installation, and 10-12y warranty. I will be shopping around. The feedback I'm receiving from the first couple of contractors I talked to is that equipment, particularly air handlers, are in short supply and a wait list is forming. Perhaps with inflation and all, last fall would have been the ideal time to get an HVAC unit.

The salesman I talked with today quoted me on Trane models, and talked somewhat disparagingly about "lower end" brands like Amanda, Westinghouse, etc, saying that getting 10 years out of such equipment is all one can expect. What brand did you have installed and how much did it cost? Was the level of work similar to what I'll have done?

The all-inclusive price was about $7,000 for a 4-ton, 16 seer unit. I can't remember the exact model (we ended up not replacing our current unit since it was working fine after some repairs), but it was a high-end 2-stage unit. The lower-end unit was only about $1,000 cheaper (most of the cost is labor).

I think improving insulation is the better bet, especially now and based on your cost calculations.

Abe

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #18 on: May 18, 2022, 08:17:33 PM »
I agree on the insulation too. Unfortunately, we'd have to tear the walls open to add any more. Stuffing fiberglass between crawlspace joists is known to cause mold and fungus problems in my damp climate but I might look into spray foam (probably costs a fortune).

Both cellulose and foam can be blown/sprayed into wall cavities through small holes (usually under 2" diameter"). You still have to do drywall repair if it's done on the interior, or some sort of plug if they go through the exterior but it's much faster, cheaper, and easier than completely removing the drywall to install fiberglass batts, and you potentially get better insulating and air sealing than you would with fiberglass too. The right contractor will likely do the patching/plugging for you.
Injection foam:
https://www.youtube.com/watch?v=_dOm0a4unEw

RE crawlspace insulation: Rigid foam panels cut to fit tightly in the joist bays, and then sealed around the edges with cans of spray foam works just as well as professionally applied spray foam, and does it for way less cash. Ideally it would be polyiso foam, but XPS is probably fine too.

For reference, we paid $2,000 to replace the insulation in two 15x12 bedrooms that had gaps in the two exterior walls each (total length 54 ft) and to increase the attic from R-30 to R-40 (3000 sq ft attic). That included removing the old fiberglass from the walls, blow-in, patching, and repainting. Again, this was last summer.

Paper Chaser

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #19 on: May 19, 2022, 03:18:44 AM »

RE crawlspace insulation: Rigid foam panels cut to fit tightly in the joist bays, and then sealed around the edges with cans of spray foam works just as well as professionally applied spray foam, and does it for way less cash. Ideally it would be polyiso foam, but XPS is probably fine too.

Agree that rigid foam panels cut and sealed (and foil faced preferably) are a great way to go, and what we did in our previous home.  However, I was a bit shocked to get closed cell foam quotes come in at slightly less than what the materials alone would be for the DIY approach (in our case it was $2/bf all in). Part of that is how much rigid foam panels and fasteners have gone up in price in the last two years.

That's interesting. I haven't been following pricing lately. Anytime rigid foam comes up though, I always suggest searching local for sale sites like craigslist as you can often get perfectly good panels for a fraction of what they cost from a box store. That might bring the DIY cost back in line.

Paper Chaser

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #20 on: May 19, 2022, 03:27:35 AM »
To add to the polyiso vs xps foam - while polyiso gives you a higher r value/in, it is much less effective in cold climates and xps foam should be used.

https://www.greenbuildingadvisor.com/article/in-cold-climates-r-5-foam-beats-r-6

I think it's important to remember that most rigid foam is used on the exterior of buildings where it's exposed to ambient temps, so that's where discussions like the one in your link really matter.

My uninsulated crawlspace never gets below 50F (in the Midwest). A properly sealed and insulated crawl isn't going to have the foam exposed to ambient outdoor air temps, and probably stays the same temp as the interior of the home. That's the whole point of closing it up and insulating it.

We can debate which one is slightly more ideal, but really I'd expect any differences to be pretty minimal in this application, at least when compared to the current situation where there's no insulation or air sealing at all. We shouldn't let perfect be the enemy of good here. Getting some insulation in there is going to have a larger impact than the difference between whether it's polyiso or XPS

Jon Bon

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #21 on: May 19, 2022, 06:48:27 AM »
Need some help from the brain trust!

My central heat pump went out and I've been quoted the following numbers on a replacement 2.5 ton unit:

SEER 14.25: $9,450
SEER 16.5: $11,250
SEER 18.5: $12,580

I found https://hvacdirect.com/seer-efficiency-savings-calculator.html and using my 0.12/kwh cost of electricity it seems to be a wash. The difference in price will be roughly the difference in lifetime energy costs. That leads me to think the cheapest model might be the best choice.

Do any of you have another calculation method or site? Which option would you pick?

Wow ok those numbers are ridiculous. Oh and the Trane guy (most expensive) was pushing you towards that brand. He obviously has an incentive to say that.

Point of reference, six months ago I had a 14-15 seer system put into my house AND all the ductwork for a 1000sqft addition. $9100. This guy had to run new electrical, drain lines, place the drip pan ect etc and run a crap load of ducts for <$10,000.

Furthermore, first insulate, if you can blow in cellulose or fiberglass its dirt cheap and an easy DIY. you just need a friend and a big truck/trailer. Its not heavy just bulky. Ive done this to nearly every house I have owned. The $ savings is nice, but it also just makes your house more comfortable.

To be clear I own about 20 HVAC units. I really feel that lots of the push to go to heat pumps is greenwashing. Of course it depends on where you live, but  they can be just as expensive and dirty to run as a gas furnace in the right (wrong) conditions.



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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #22 on: May 20, 2022, 06:59:28 AM »
For the price of your middle of the road unit I was able to get a Trane XV20i which they advertise as having 750 stages....really it's just on a variable speed drive.  It's awesome because once your house gets to temp it will run at a very low speed that you can't even hear and will very gently blow air out the ducts so you again don't hear anything and can't even tell it's on.  I can't remember the SEER value but I believe it was 20.  That was two years ago so maybe they're more expensive lost COVID. 

It's saved a lot on heating bills and the air that comes out of the ducts is so warm it actually feels like gas heat. 

nereo

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #23 on: May 20, 2022, 07:07:09 AM »
To be clear I own about 20 HVAC units. I really feel that lots of the push to go to heat pumps is greenwashing. Of course it depends on where you live, but  they can be just as expensive and dirty to run as a gas furnace in the right (wrong) conditions.

I'm trying to imagine what conditions in the US would lead a heat-pump to be as expensive and dirty to run as a gas furnace, but I'm having trouble coming up with anything where both conditions are met.  Certainly when natural gas is cheap and in areas that electricity is very expensive the economics are closer to being equal, but 'dirty'? 
Can you give an example?

chemistk

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #24 on: May 20, 2022, 07:14:22 AM »
I think it's important to remember, generally for all housing related projects (labor & materials) but specifically for HVAC that prices can vary pretty significantly regionally. 

In talking with my brother, he said that in some sections of their distribution network, the all-in cost for the system we purchased that I mentioned above would be closer to the $8k mark, and that's with it being installed by an authorized Carrier representative.

If ChpBstrd shopped around (and I would have assumed he did), then I'd expect those Trane prices to be typical if not a little on the high end of the area.

Now, on the other hand, you are generally going to pay a premium to have a system installed by an authorized retailer vs. having a local HVAC handyman install. The upside to the local guy is that you're usually getting the materials at or near cost. the downside is that you probably won't be getting an installation warranty and it's more difficult to assess whether the job was done properly - and scheduling id going to be more of a crapshoot if he's busy with other jobs.

For the price of your middle of the road unit I was able to get a Trane XV20i which they advertise as having 750 stages....really it's just on a variable speed drive.  It's awesome because once your house gets to temp it will run at a very low speed that you can't even hear and will very gently blow air out the ducts so you again don't hear anything and can't even tell it's on.  I can't remember the SEER value but I believe it was 20.  That was two years ago so maybe they're more expensive lost COVID. 

It's saved a lot on heating bills and the air that comes out of the ducts is so warm it actually feels like gas heat. 

Unfortunately, just like the housing and car markets, it's almost impossible to compare prices from 3 years ago to now. Moreover, these new higher costs (and much more limited product selection) are probably here to stay.

chemistk

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #25 on: May 20, 2022, 07:19:49 AM »
To be clear I own about 20 HVAC units. I really feel that lots of the push to go to heat pumps is greenwashing. Of course it depends on where you live, but  they can be just as expensive and dirty to run as a gas furnace in the right (wrong) conditions.

I'm trying to imagine what conditions in the US would lead a heat-pump to be as expensive and dirty to run as a gas furnace, but I'm having trouble coming up with anything where both conditions are met.  Certainly when natural gas is cheap and in areas that electricity is very expensive the economics are closer to being equal, but 'dirty'? 
Can you give an example?

Just piling on here, I think even when the COP is only near 2, unless your area is exclusively burning coal for power generation, heat pumps are still cleaner from a 'best use of energy' perspective.

Not to mention, fueled residential heat will always carry more risk for poor health effects than heat pumps. Even when they're well-vented and [properly sealed, you're still running a higher risk for CO and slow natural gas leaks directly into the air supply of the home. Plus all the minor losses of natural gas at all the connections en route to your furnace, I'd say that it's pretty much impossible to claim that they're cleaner than heat pumps.

big_owl

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #26 on: May 20, 2022, 08:00:51 AM »
My understanding is that when you consider the source of your electricity and not just the 300% efficiency of your heat pump, then yes, a high efficiency gas furnace and a heat pump actually have similar efficiencies.  Plus in my experience gas furnaces have the potential to last a lot longer. 

That said, where I live I need A/C anyway so it makes sense just to get a heat pump as well so I only have once piece of hardware to maintain.  Not to mention I'm in the boons and don't have natural gas anyhow.  Especially now that the new ones give off heat that feels like warm gas.  My 17yr old unit felt like it was blowing cold air out and never had you feeling warm

Jon Bon

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #27 on: May 20, 2022, 09:08:11 AM »
To be clear I own about 20 HVAC units. I really feel that lots of the push to go to heat pumps is greenwashing. Of course it depends on where you live, but  they can be just as expensive and dirty to run as a gas furnace in the right (wrong) conditions.

I'm trying to imagine what conditions in the US would lead a heat-pump to be as expensive and dirty to run as a gas furnace, but I'm having trouble coming up with anything where both conditions are met.  Certainly when natural gas is cheap and in areas that electricity is very expensive the economics are closer to being equal, but 'dirty'? 
Can you give an example?

Well I think we all agree that in certain conditions a heat pump just turns into a massive space heater right? The heat strips come on and then it is consuming more than any other appliance. The heat strips on my unit are a double 50 amp breaker, the largest in my box.

So if you live in climate zone 4 or below I think heat pumps are fantastic. The heat strips barely run and heat pumps do their job pretty well.

Now where I live we are mostly on coal *checks notes* nope mainly natural gas I was way off! I think my argument is less persuasive with using gas rather than coal. But I still think the below is true.

How is it more efficient to (wastefully) convert natural gas to electricity, then ship it to me, to convert it back into heat? Would it not be easier to ship me the raw material (gas) and then have me convert it directly to heat in my furnace?

Note: I am not at all a geothermal/electrical engineer, or whatever smart people run our power grid. Convince me otherwise but I don't see how a giant ass space heater is better than a furnace.

chemistk

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #28 on: May 20, 2022, 09:44:17 AM »
To be clear I own about 20 HVAC units. I really feel that lots of the push to go to heat pumps is greenwashing. Of course it depends on where you live, but  they can be just as expensive and dirty to run as a gas furnace in the right (wrong) conditions.

I'm trying to imagine what conditions in the US would lead a heat-pump to be as expensive and dirty to run as a gas furnace, but I'm having trouble coming up with anything where both conditions are met.  Certainly when natural gas is cheap and in areas that electricity is very expensive the economics are closer to being equal, but 'dirty'? 
Can you give an example?




Well I think we all agree that in certain conditions a heat pump just turns into a massive space heater right? The heat strips come on and then it is consuming more than any other appliance. The heat strips on my unit are a double 50 amp breaker, the largest in my box.

So if you live in climate zone 4 or below I think heat pumps are fantastic. The heat strips barely run and heat pumps do their job pretty well.

Now where I live we are mostly on coal *checks notes* nope mainly natural gas I was way off! I think my argument is less persuasive with using gas rather than coal. But I still think the below is true.

How is it more efficient to (wastefully) convert natural gas to electricity, then ship it to me, to convert it back into heat? Would it not be easier to ship me the raw material (gas) and then have me convert it directly to heat in my furnace?

Note: I am not at all a geothermal/electrical engineer, or whatever smart people run our power grid. Convince me otherwise but I don't see how a giant ass space heater is better than a furnace.

Very rough calculations:

1 cubic foot of natural gas contains ~171mJ of energy, also equivalent to roughly 47.5kWh (this may not be completely accurate, and it probably varies regionally, but the exact number is functionally irrelevant - the rest of the calculations can be adjusted for whatever is input).

A 2015 estimate put the average performance of a natural gas powered electricity plant at about 56% (https://www.forbes.com/sites/judeclemente/2016/04/10/u-s-natural-gas-electricity-efficiency-continues-to-improve/?sh=739c44fd35a4)

This means (using the number above), every cubic foot of CNG burned at a plant produces about 26.6kWh of electricity.

Your gas furnace is probably about 92% efficient, and assuming you have no leaks, for every cubic foot of natural gas you buy, your furnace can turn that into the equivalent of ~43.7kWh of heat.

A lower end central heat pump in a moderate climate has a COP of about 2.5 on a good day. Many heat pumps are edging toward 3, and some even closer to 5 (less in colder climates). Sticking with 2.5-3, that essentially means that for every kWh of electricity that's consumed by the pump, it ideally is producing 2.5-3kWh of equivalent heat.

Ignoring minor transmission losses supposing your electricity is coming from a natural gas fired plant, every cubic foot of natural gas that is consumed by the plant is converted into the equivalent of 66.5kWh (COP 2.5) - 79.8kWh (COP 3) of heat.

Or in other words, it's more efficient for the natural gas plant to burn the stuff if you have an air-source heat pump than if your gas furnace does so. On a good day, almost twice as efficient.

Now maybe you're thinking "but what about the days where it's too cold and the COP drops to 1 (aka the heat strips are on)"?

I like round numbers so suppose there are 180 days out of the year you're using heat from a system with a COP of 3 under reasonable conditions. I'd bet that there will be less than 20 total days (factoring in nightly lows) where the COP is at 1 because you're using the heat strips. And then suppose you're at about 75% average efficiency otherwise (I'm making this up, but you need to account for edge-temps, time the system takes to defrost, etc.).

So your average COP for the entire heating season is going to be about 2.1 in this scenario. That means for all the gas the power plant burns in a heating season, you'll be seeing an average of 55.9 kWh of heat per day from your heat pump AND backup strips. That's a considerably more efficient use of natural gas.

Better yet, natural gas plants are getting more efficient, renewables are a thing, hydro and nuclear say "Hi!" and coal is on the outs. So reality is that in 2022, you're going to be even better off efficiency wise with a heat pump.

Now clearly the underlying issue is that natural gas is still fundamentally less expensive, but that's for now and I'd bet that in the next decade or two as fossil fuels decline, residential natural gas will be not nearly as cheap compared to electricity.

ETA, this guy is one of my favorites to have on in the background. He lives in the Chicago area, and I based the above though exercise off this video of his. It's worth watching all his videos on heat pumps:

https://www.youtube.com/watch?v=MFEHFsO-XSI&ab_channel=TechnologyConnections
« Last Edit: May 20, 2022, 09:48:27 AM by chemistk »

Jon Bon

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #29 on: May 20, 2022, 09:57:32 AM »
To be clear I own about 20 HVAC units. I really feel that lots of the push to go to heat pumps is greenwashing. Of course it depends on where you live, but  they can be just as expensive and dirty to run as a gas furnace in the right (wrong) conditions.

I'm trying to imagine what conditions in the US would lead a heat-pump to be as expensive and dirty to run as a gas furnace, but I'm having trouble coming up with anything where both conditions are met.  Certainly when natural gas is cheap and in areas that electricity is very expensive the economics are closer to being equal, but 'dirty'? 
Can you give an example?




Well I think we all agree that in certain conditions a heat pump just turns into a massive space heater right? The heat strips come on and then it is consuming more than any other appliance. The heat strips on my unit are a double 50 amp breaker, the largest in my box.

So if you live in climate zone 4 or below I think heat pumps are fantastic. The heat strips barely run and heat pumps do their job pretty well.

Now where I live we are mostly on coal *checks notes* nope mainly natural gas I was way off! I think my argument is less persuasive with using gas rather than coal. But I still think the below is true.

How is it more efficient to (wastefully) convert natural gas to electricity, then ship it to me, to convert it back into heat? Would it not be easier to ship me the raw material (gas) and then have me convert it directly to heat in my furnace?

Note: I am not at all a geothermal/electrical engineer, or whatever smart people run our power grid. Convince me otherwise but I don't see how a giant ass space heater is better than a furnace.

Very rough calculations:

1 cubic foot of natural gas contains ~171mJ of energy, also equivalent to roughly 47.5kWh (this may not be completely accurate, and it probably varies regionally, but the exact number is functionally irrelevant - the rest of the calculations can be adjusted for whatever is input).

A 2015 estimate put the average performance of a natural gas powered electricity plant at about 56% (https://www.forbes.com/sites/judeclemente/2016/04/10/u-s-natural-gas-electricity-efficiency-continues-to-improve/?sh=739c44fd35a4)

This means (using the number above), every cubic foot of CNG burned at a plant produces about 26.6kWh of electricity.

Your gas furnace is probably about 92% efficient, and assuming you have no leaks, for every cubic foot of natural gas you buy, your furnace can turn that into the equivalent of ~43.7kWh of heat.

A lower end central heat pump in a moderate climate has a COP of about 2.5 on a good day. Many heat pumps are edging toward 3, and some even closer to 5 (less in colder climates). Sticking with 2.5-3, that essentially means that for every kWh of electricity that's consumed by the pump, it ideally is producing 2.5-3kWh of equivalent heat.

Ignoring minor transmission losses supposing your electricity is coming from a natural gas fired plant, every cubic foot of natural gas that is consumed by the plant is converted into the equivalent of 66.5kWh (COP 2.5) - 79.8kWh (COP 3) of heat.

Or in other words, it's more efficient for the natural gas plant to burn the stuff if you have an air-source heat pump than if your gas furnace does so. On a good day, almost twice as efficient.

Now maybe you're thinking "but what about the days where it's too cold and the COP drops to 1 (aka the heat strips are on)"?

I like round numbers so suppose there are 180 days out of the year you're using heat from a system with a COP of 3 under reasonable conditions. I'd bet that there will be less than 20 total days (factoring in nightly lows) where the COP is at 1 because you're using the heat strips. And then suppose you're at about 75% average efficiency otherwise (I'm making this up, but you need to account for edge-temps, time the system takes to defrost, etc.).

So your average COP for the entire heating season is going to be about 2.1 in this scenario. That means for all the gas the power plant burns in a heating season, you'll be seeing an average of 55.9 kWh of heat per day from your heat pump AND backup strips. That's a considerably more efficient use of natural gas.

Better yet, natural gas plants are getting more efficient, renewables are a thing, hydro and nuclear say "Hi!" and coal is on the outs. So reality is that in 2022, you're going to be even better off efficiency wise with a heat pump.

Now clearly the underlying issue is that natural gas is still fundamentally less expensive, but that's for now and I'd bet that in the next decade or two as fossil fuels decline, residential natural gas will be not nearly as cheap compared to electricity.

ETA, this guy is one of my favorites to have on in the background. He lives in the Chicago area, and I based the above though exercise off this video of his. It's worth watching all his videos on heat pumps:

https://www.youtube.com/watch?v=MFEHFsO-XSI&ab_channel=TechnologyConnections

Awesome response thank you.

I appreciate the math rather than just talking points about how my heat pump/solar panels/tesla is saving the planet! I think I follow your math Ill get into it and I'll check out your youtube guy as well.

For sure having a HP with renewable is the magic bullet so to speak. Unfortunately we are a long way off from that.






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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #30 on: May 20, 2022, 10:09:16 AM »
I appreciate the discussion from all sides - it's always good to challenge assumptions.
FWIW my state (climate zone 6A) has been pushing heat-pumps hard, and (IMO) for good reason - the overwhelming majority of homes are heated by #6 heating oil.  Expensive to operate, expensive to transport, and fairly dirty overall.  A minority of households even have gas service to their address.

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #31 on: May 20, 2022, 10:56:59 AM »
To be clear I own about 20 HVAC units. I really feel that lots of the push to go to heat pumps is greenwashing. Of course it depends on where you live, but  they can be just as expensive and dirty to run as a gas furnace in the right (wrong) conditions.

I'm trying to imagine what conditions in the US would lead a heat-pump to be as expensive and dirty to run as a gas furnace, but I'm having trouble coming up with anything where both conditions are met.  Certainly when natural gas is cheap and in areas that electricity is very expensive the economics are closer to being equal, but 'dirty'? 
Can you give an example?




Well I think we all agree that in certain conditions a heat pump just turns into a massive space heater right? The heat strips come on and then it is consuming more than any other appliance. The heat strips on my unit are a double 50 amp breaker, the largest in my box.

So if you live in climate zone 4 or below I think heat pumps are fantastic. The heat strips barely run and heat pumps do their job pretty well.

Now where I live we are mostly on coal *checks notes* nope mainly natural gas I was way off! I think my argument is less persuasive with using gas rather than coal. But I still think the below is true.

How is it more efficient to (wastefully) convert natural gas to electricity, then ship it to me, to convert it back into heat? Would it not be easier to ship me the raw material (gas) and then have me convert it directly to heat in my furnace?

Note: I am not at all a geothermal/electrical engineer, or whatever smart people run our power grid. Convince me otherwise but I don't see how a giant ass space heater is better than a furnace.

Very rough calculations:

1 cubic foot of natural gas contains ~171mJ of energy, also equivalent to roughly 47.5kWh (this may not be completely accurate, and it probably varies regionally, but the exact number is functionally irrelevant - the rest of the calculations can be adjusted for whatever is input).

A 2015 estimate put the average performance of a natural gas powered electricity plant at about 56% (https://www.forbes.com/sites/judeclemente/2016/04/10/u-s-natural-gas-electricity-efficiency-continues-to-improve/?sh=739c44fd35a4)

This means (using the number above), every cubic foot of CNG burned at a plant produces about 26.6kWh of electricity.

Your gas furnace is probably about 92% efficient, and assuming you have no leaks, for every cubic foot of natural gas you buy, your furnace can turn that into the equivalent of ~43.7kWh of heat.

A lower end central heat pump in a moderate climate has a COP of about 2.5 on a good day. Many heat pumps are edging toward 3, and some even closer to 5 (less in colder climates). Sticking with 2.5-3, that essentially means that for every kWh of electricity that's consumed by the pump, it ideally is producing 2.5-3kWh of equivalent heat.

Ignoring minor transmission losses supposing your electricity is coming from a natural gas fired plant, every cubic foot of natural gas that is consumed by the plant is converted into the equivalent of 66.5kWh (COP 2.5) - 79.8kWh (COP 3) of heat.

Or in other words, it's more efficient for the natural gas plant to burn the stuff if you have an air-source heat pump than if your gas furnace does so. On a good day, almost twice as efficient.

Now maybe you're thinking "but what about the days where it's too cold and the COP drops to 1 (aka the heat strips are on)"?

I like round numbers so suppose there are 180 days out of the year you're using heat from a system with a COP of 3 under reasonable conditions. I'd bet that there will be less than 20 total days (factoring in nightly lows) where the COP is at 1 because you're using the heat strips. And then suppose you're at about 75% average efficiency otherwise (I'm making this up, but you need to account for edge-temps, time the system takes to defrost, etc.).

So your average COP for the entire heating season is going to be about 2.1 in this scenario. That means for all the gas the power plant burns in a heating season, you'll be seeing an average of 55.9 kWh of heat per day from your heat pump AND backup strips. That's a considerably more efficient use of natural gas.

Better yet, natural gas plants are getting more efficient, renewables are a thing, hydro and nuclear say "Hi!" and coal is on the outs. So reality is that in 2022, you're going to be even better off efficiency wise with a heat pump.

Now clearly the underlying issue is that natural gas is still fundamentally less expensive, but that's for now and I'd bet that in the next decade or two as fossil fuels decline, residential natural gas will be not nearly as cheap compared to electricity.

ETA, this guy is one of my favorites to have on in the background. He lives in the Chicago area, and I based the above though exercise off this video of his. It's worth watching all his videos on heat pumps:

https://www.youtube.com/watch?v=MFEHFsO-XSI&ab_channel=TechnologyConnections

Excellent math.  Thank you for sharing!

I'll also add one of the key reasons that heat-pumps are pushed so much, and I would consider it more than "greenwashing".

Actually doing something about climate change is about a lot more than putting up a few solar panels, buying some EV's, and singing kumbaya around the campfire.  It involves getting to zero emissions from fossil fuels.  That's nada, zilch, or zero.  You can add a few layers of nuance when talking about things like cows and cement, but that's really the story.  While the overall emissions of heat pumps today will vary based on what the electric grid is doing, there is a very real reason to convert anything powered directly with fossil fuel's to an electric version. 

ChpBstrd

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #32 on: May 20, 2022, 11:21:32 AM »
I also appreciate the math. It makes sense when you think about how basic a home gas furnace is. They aren't much more than space heaters with external ducts. Compare even a 95% furnace to a modern gas turbine. It's like comparing a lawnmower engine to a modern car engine. The furnace is built to be cheap. The turbine is engineered to be efficient.

https://www.ge.com/gas-power/resources/education/what-is-a-gas-turbine

For sure having a HP with renewable is the magic bullet so to speak. Unfortunately we are a long way off from that.

Actually I'm having this configuration installed this year. I'll cover 80% of my power bill, which includes heating and cooling from my HP, with solar panels and net metering. I plan to get rid of my account with the natural gas company and switch my remaining two gas appliances (stove and dryer). I never used much gas but getting rid of the gas bill and its base charges will allow my solar project to have a rate of return over 7%. And that ROI number is based on the silly assumption today's electricity and gas prices will stay the same forever. And I already live in a place with dirt-cheap electricity - plenty of hydro and NG resources nearby - so as long as solar equipment remains cheap it's a matter of time before more people switch. 

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #33 on: May 20, 2022, 11:54:12 AM »
To be clear I own about 20 HVAC units. I really feel that lots of the push to go to heat pumps is greenwashing. Of course it depends on where you live, but  they can be just as expensive and dirty to run as a gas furnace in the right (wrong) conditions.

I'm trying to imagine what conditions in the US would lead a heat-pump to be as expensive and dirty to run as a gas furnace, but I'm having trouble coming up with anything where both conditions are met.  Certainly when natural gas is cheap and in areas that electricity is very expensive the economics are closer to being equal, but 'dirty'? 
Can you give an example?




Well I think we all agree that in certain conditions a heat pump just turns into a massive space heater right? The heat strips come on and then it is consuming more than any other appliance. The heat strips on my unit are a double 50 amp breaker, the largest in my box.

So if you live in climate zone 4 or below I think heat pumps are fantastic. The heat strips barely run and heat pumps do their job pretty well.

Now where I live we are mostly on coal *checks notes* nope mainly natural gas I was way off! I think my argument is less persuasive with using gas rather than coal. But I still think the below is true.

How is it more efficient to (wastefully) convert natural gas to electricity, then ship it to me, to convert it back into heat? Would it not be easier to ship me the raw material (gas) and then have me convert it directly to heat in my furnace?

Note: I am not at all a geothermal/electrical engineer, or whatever smart people run our power grid. Convince me otherwise but I don't see how a giant ass space heater is better than a furnace.

Very rough calculations:

1 cubic foot of natural gas contains ~171mJ of energy, also equivalent to roughly 47.5kWh (this may not be completely accurate, and it probably varies regionally, but the exact number is functionally irrelevant - the rest of the calculations can be adjusted for whatever is input).

A 2015 estimate put the average performance of a natural gas powered electricity plant at about 56% (https://www.forbes.com/sites/judeclemente/2016/04/10/u-s-natural-gas-electricity-efficiency-continues-to-improve/?sh=739c44fd35a4)

This means (using the number above), every cubic foot of CNG burned at a plant produces about 26.6kWh of electricity.

Your gas furnace is probably about 92% efficient, and assuming you have no leaks, for every cubic foot of natural gas you buy, your furnace can turn that into the equivalent of ~43.7kWh of heat.

A lower end central heat pump in a moderate climate has a COP of about 2.5 on a good day. Many heat pumps are edging toward 3, and some even closer to 5 (less in colder climates). Sticking with 2.5-3, that essentially means that for every kWh of electricity that's consumed by the pump, it ideally is producing 2.5-3kWh of equivalent heat.

Ignoring minor transmission losses supposing your electricity is coming from a natural gas fired plant, every cubic foot of natural gas that is consumed by the plant is converted into the equivalent of 66.5kWh (COP 2.5) - 79.8kWh (COP 3) of heat.

Or in other words, it's more efficient for the natural gas plant to burn the stuff if you have an air-source heat pump than if your gas furnace does so. On a good day, almost twice as efficient.

Now maybe you're thinking "but what about the days where it's too cold and the COP drops to 1 (aka the heat strips are on)"?

I like round numbers so suppose there are 180 days out of the year you're using heat from a system with a COP of 3 under reasonable conditions. I'd bet that there will be less than 20 total days (factoring in nightly lows) where the COP is at 1 because you're using the heat strips. And then suppose you're at about 75% average efficiency otherwise (I'm making this up, but you need to account for edge-temps, time the system takes to defrost, etc.).

So your average COP for the entire heating season is going to be about 2.1 in this scenario. That means for all the gas the power plant burns in a heating season, you'll be seeing an average of 55.9 kWh of heat per day from your heat pump AND backup strips. That's a considerably more efficient use of natural gas.

Better yet, natural gas plants are getting more efficient, renewables are a thing, hydro and nuclear say "Hi!" and coal is on the outs. So reality is that in 2022, you're going to be even better off efficiency wise with a heat pump.

Now clearly the underlying issue is that natural gas is still fundamentally less expensive, but that's for now and I'd bet that in the next decade or two as fossil fuels decline, residential natural gas will be not nearly as cheap compared to electricity.

ETA, this guy is one of my favorites to have on in the background. He lives in the Chicago area, and I based the above though exercise off this video of his. It's worth watching all his videos on heat pumps:

https://www.youtube.com/watch?v=MFEHFsO-XSI&ab_channel=TechnologyConnections

Transmission losses can be as high as 10%, fwiw. 

NorCal

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #34 on: May 20, 2022, 12:12:45 PM »
To be clear I own about 20 HVAC units. I really feel that lots of the push to go to heat pumps is greenwashing. Of course it depends on where you live, but  they can be just as expensive and dirty to run as a gas furnace in the right (wrong) conditions.

I'm trying to imagine what conditions in the US would lead a heat-pump to be as expensive and dirty to run as a gas furnace, but I'm having trouble coming up with anything where both conditions are met.  Certainly when natural gas is cheap and in areas that electricity is very expensive the economics are closer to being equal, but 'dirty'? 
Can you give an example?




Well I think we all agree that in certain conditions a heat pump just turns into a massive space heater right? The heat strips come on and then it is consuming more than any other appliance. The heat strips on my unit are a double 50 amp breaker, the largest in my box.

So if you live in climate zone 4 or below I think heat pumps are fantastic. The heat strips barely run and heat pumps do their job pretty well.

Now where I live we are mostly on coal *checks notes* nope mainly natural gas I was way off! I think my argument is less persuasive with using gas rather than coal. But I still think the below is true.

How is it more efficient to (wastefully) convert natural gas to electricity, then ship it to me, to convert it back into heat? Would it not be easier to ship me the raw material (gas) and then have me convert it directly to heat in my furnace?

Note: I am not at all a geothermal/electrical engineer, or whatever smart people run our power grid. Convince me otherwise but I don't see how a giant ass space heater is better than a furnace.

Very rough calculations:

1 cubic foot of natural gas contains ~171mJ of energy, also equivalent to roughly 47.5kWh (this may not be completely accurate, and it probably varies regionally, but the exact number is functionally irrelevant - the rest of the calculations can be adjusted for whatever is input).

A 2015 estimate put the average performance of a natural gas powered electricity plant at about 56% (https://www.forbes.com/sites/judeclemente/2016/04/10/u-s-natural-gas-electricity-efficiency-continues-to-improve/?sh=739c44fd35a4)

This means (using the number above), every cubic foot of CNG burned at a plant produces about 26.6kWh of electricity.

Your gas furnace is probably about 92% efficient, and assuming you have no leaks, for every cubic foot of natural gas you buy, your furnace can turn that into the equivalent of ~43.7kWh of heat.

A lower end central heat pump in a moderate climate has a COP of about 2.5 on a good day. Many heat pumps are edging toward 3, and some even closer to 5 (less in colder climates). Sticking with 2.5-3, that essentially means that for every kWh of electricity that's consumed by the pump, it ideally is producing 2.5-3kWh of equivalent heat.

Ignoring minor transmission losses supposing your electricity is coming from a natural gas fired plant, every cubic foot of natural gas that is consumed by the plant is converted into the equivalent of 66.5kWh (COP 2.5) - 79.8kWh (COP 3) of heat.

Or in other words, it's more efficient for the natural gas plant to burn the stuff if you have an air-source heat pump than if your gas furnace does so. On a good day, almost twice as efficient.

Now maybe you're thinking "but what about the days where it's too cold and the COP drops to 1 (aka the heat strips are on)"?

I like round numbers so suppose there are 180 days out of the year you're using heat from a system with a COP of 3 under reasonable conditions. I'd bet that there will be less than 20 total days (factoring in nightly lows) where the COP is at 1 because you're using the heat strips. And then suppose you're at about 75% average efficiency otherwise (I'm making this up, but you need to account for edge-temps, time the system takes to defrost, etc.).

So your average COP for the entire heating season is going to be about 2.1 in this scenario. That means for all the gas the power plant burns in a heating season, you'll be seeing an average of 55.9 kWh of heat per day from your heat pump AND backup strips. That's a considerably more efficient use of natural gas.

Better yet, natural gas plants are getting more efficient, renewables are a thing, hydro and nuclear say "Hi!" and coal is on the outs. So reality is that in 2022, you're going to be even better off efficiency wise with a heat pump.

Now clearly the underlying issue is that natural gas is still fundamentally less expensive, but that's for now and I'd bet that in the next decade or two as fossil fuels decline, residential natural gas will be not nearly as cheap compared to electricity.

ETA, this guy is one of my favorites to have on in the background. He lives in the Chicago area, and I based the above though exercise off this video of his. It's worth watching all his videos on heat pumps:

https://www.youtube.com/watch?v=MFEHFsO-XSI&ab_channel=TechnologyConnections

As a minor nitpick, you should probably handicap your furnace efficiency numbers a bit.  The efficiency ratings are as-new numbers, but they decline in efficiency with wear and usage.

I just had my unit serviced and measured.  It's 10 years old and still in excellent condition.  It was 92% efficient when new, but it was measured at 86% today.  Assuming a furnace lasts for 20-30 years, the average efficiency over its lifespan is probably in the mid 80's.

chemistk

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #35 on: May 20, 2022, 04:00:49 PM »
@NorCal @big_owl Both great points.

The numbers typically work in favor of a heat pump so long as it can maintain a real world COP of at least 2.5, and so long as your utility isn't all coal.

Also important again to note that efficiency in consumption of a fuel source has nothing to do with price, which for now is still very much in favor or natural gas. But we're nearly there with heat pumps being effectively better in all of the most common setups.

The end efficiency of the system depends on a wide, wide range of factors that are very difficult to generalize.

Another factor brought up earlier in the thread is that even the best heat pumps will have replacement windows that hit sooner than furnaces. 10-15 years on a system vs longer on a furnace is still a big expense to consider, but like I said before I think we're going to see those costs reconcile in the future to the point that heat pumps will indeed be universally cheaper.

Syonyk

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #36 on: May 20, 2022, 05:29:08 PM »
Well I think we all agree that in certain conditions a heat pump just turns into a massive space heater right? The heat strips come on and then it is consuming more than any other appliance. The heat strips on my unit are a double 50 amp breaker, the largest in my box.

Those conditions are quite rare.  Even in colder climates.  Go look up a chart for a decent heat pump, and you'll find that the COP is >1 ("better than the heat coils") down to -15F or below, and some of the low temperature inverter drive units hold their performance rather radically colder.  The old units from the 80s or so hit that point around freezing, but newer ones are radically better - even the basic single speed compressor units.

If you have a good furnace, it's also worth considering a dual fuel system.  You use the heat pump in mild weather, and switch over to the existing furnace in the extreme cold.  Radically more efficient most of the time, and still having the power of a gas furnace in the dead of winter if it's -40 or something.

Jon Bon

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #37 on: May 22, 2022, 09:28:04 AM »
Well I think we all agree that in certain conditions a heat pump just turns into a massive space heater right? The heat strips come on and then it is consuming more than any other appliance. The heat strips on my unit are a double 50 amp breaker, the largest in my box.

Those conditions are quite rare.  Even in colder climates.  Go look up a chart for a decent heat pump, and you'll find that the COP is >1 ("better than the heat coils") down to -15F or below, and some of the low temperature inverter drive units hold their performance rather radically colder.  The old units from the 80s or so hit that point around freezing, but newer ones are radically better - even the basic single speed compressor units.

If you have a good furnace, it's also worth considering a dual fuel system.  You use the heat pump in mild weather, and switch over to the existing furnace in the extreme cold.  Radically more efficient most of the time, and still having the power of a gas furnace in the dead of winter if it's -40 or something.

Yeah I am going to push back on this one.

If the heat strips (almost) never come on, they would not install them in the unit. But they do, and they cost a fortune when they run. Furthermore the heat strips do in fact come on all the time during regular usage. Not emergency heat, but regular usage the HP goes into defrost mode and the heat stirps come on.

I learned this the hard way as my HP would go into defrost mode and push out air that was 55 degrees. What the hell? Well turns out my hvac guy did not strip the wires when he set it up. So they were not kicking on. So yes the heat strips come on during regular usage.

Secondly, I had the most expensive electric bill I have ever had in February of this year.  Some extra usage would make sense, but this was outrageous.

My usage was
Feb of 21 665 KWH
Feb of 22 1,245 KWH

Now you may say that its reasonable for a HP to take a long of energy in the winter and I agree if you were heating a whole house. However my HP is busy heating all of 400 sqft on the second floor. I have a gas furnace heating the rest of the house, it was just with the addition this is what was recommended. So even with the gas furnace heating the downstairs, and through thermodynamics partially heating the addition too I still used almost 100% more electricity yeah over year using my HP.

Its possible that something was wrong, or I left a window open for 3 days however unlikely. Its a single data point and I get that. But in my experience heating 2 rooms with a HP costs more than heating my entire house with a gas furnace. I don't like HPs and I don't think that they work partially well. We can argue over efficiency and environmental effects I think the do score points there. But my point is there are some serious negative trade offs for HP versus gas heat.






big_owl

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #38 on: May 22, 2022, 10:03:42 AM »
For me.personally the best heating option would be natural gas hydronic baseboard heating.  That's what I grew up with in Michigan and it was so luxurious compared to forced air.  And my parents' hydronic furnace is from the 1970s and hasn't had a single replacement part required in 50yrs.  Even all the control valves for the water loops are original equipment. 

Syonyk

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #39 on: May 22, 2022, 01:55:51 PM »
If the heat strips (almost) never come on, they would not install them in the unit. But they do, and they cost a fortune when they run. Furthermore the heat strips do in fact come on all the time during regular usage. Not emergency heat, but regular usage the HP goes into defrost mode and the heat stirps come on.

Defrost mode... is a pain point with heat pumps, yes, though often enough it's that the installer didn't set it up properly.  Higher end heat pumps have a far smarter defrost mode than the dumb (idiotic?) timer based ones that lower efficiency units have, and the reduction in defrost cycles is worth a couple SEER points.  It greatly irritates me that the cheaper units (of which I have one) don't have such a system.

If you've got a unit going into defrost every 30 minutes below freezing, it's not going to be nearly as efficient as one that doesn't, mostly from the backup coils.  Turn the coils off and you gain quite a bit.  I've got 10kW of my coils switched off at the panel, and the only reason I don't have the others off is that they share with the blower circuit.

Quote
Secondly, I had the most expensive electric bill I have ever had in February of this year.  Some extra usage would make sense, but this was outrageous.

My usage was
Feb of 21 665 KWH
Feb of 22 1,245 KWH

You admit that your installer was a muppet, and then use your experience with heat pumps as evidence that they're not efficient?

What was the delta on your gas use?  If the heat pump was taking more of the load than the furnace (it's hard to "just heat 400 sq ft" of a typical house, if you've got ducting), that would explain some of it.  But on some nasty cold winter months (average temps in the 15-20F range, lows below 0), we use 2000kWh on a pure electric house with a heat pump for everything.  Heating, hot water, cooking, and transportation miles.  So I'd perhaps have someone else come look at your install.

Jon Bon

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #40 on: May 23, 2022, 11:56:08 AM »
I've thought about turning off the heat strips, but then I might as well turn the unit off completely. It just makes it unbearable in defrost mode. Something I do need to do is get one of those nest thermostats. I have heard you can program so that they almost never go into emergency heat mode.

Gas usage was pretty much exactly the same 139/138 during the month. Feb of 22 was 5 degrees colder but that gas usage makes sense as the house was tighter than it was in 2021.

To me this whole discussion kind of feels like chatting with a solar installer. He tends to quote perfect conditions and perfect equipment. The real world performance is not nearly as good. But yes I would take real world numbers over projected ones every time. I am more then happy report back next winter. I even included my entire years electrical usage.

I feel like heat pumps are perfect when the overnight low never gets below 35 degrees, but I am in climate zone 6 and I get a day or 2 at or below zero every winter. Looking at my electrical bill I posted in the daily temp from my gas bill, and February was (obviously) cold!

To be completely fair it looks like the HP works fine until you hit a certain temp (25-30 degrees?), and it looks like I hit it in February. The other months were expensive but acceptable. Now its still more expensive to run than a gas furnace, but is likely better for the environment? I am thankful that I do have both types of heat available.



« Last Edit: May 23, 2022, 11:58:37 AM by Jon Bon »

nereo

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Re: Heat pump efficiency: How much extra is efficiency worth?
« Reply #41 on: May 23, 2022, 01:51:26 PM »
Monthly averages aren't terribly useful when trying to examine heating and cooling loads. Heating degree days (HDD) and cooling degree days are far more relevant, as are the number of days (or even hours) you spend below various points (e.g. below +35ºF).
As an example why, we moved within zone 6A from a home inland to one very close to the coast.  As such, our very hot and very cold days are mitigated substantially (less extremes), while the differences in the monthly mean temp is barely noticeable. We've had heat pumps in both locations but they are far more efficient here, even though we've moved a mere 40 miles from our previous location.

As to whether a personal gas furnace hooked up to the grid is more or less polluting than an electric heat pump, it likely still depends on your region's power generation portfolio. But given how quickly renewables are being added, I suspect it will continue tipping (and strongly) towards heat pumps in the years to come.