Now that we know what heat pumps are and how they work,
it’s time to talk a little more about their future.
If you’ve not seen the first video,
well you definitely should fix that before watching this one
as there will be a lot of stuff we talk about here that assumes prior knowledge.
I’ll summon a card.
Bippity Boppity Card!
Great!
A link is below, and probably in a pinned comment, too.
You ever heard about those?
They’re neat.
I want to start with a clarification of sorts.
Heat pumps definitely are the future of home heating,
at least if I can help it,
but they’re also not new.
And some people hate them!
It seems for every person who thinks heat pumps are
wicked neat-o closest-thing-to-free-energy-out-there devices
(that’s me)
there’s another who hates theirs with a passion.
Allow me to submit that you don’t hate your heat pump,
you hate your thermostat.
See, as we learned, as the outdoor temperature approaches freezing
it gets harder for air source heat pumps to work.
A smaller temperature difference between the source of heat
and the evaporator absorbing it causes the efficiency of heat pumps to drop
and eventually their output as well.
Unfortunately, it is under these precise conditions that demand for heat goes up.
It’s kind of a bummer.
So, most systems with heat pumps have some sort of backup heat source,
be it electric resistive heat
(often this is called the heat strips, though I prefer to think of it as a giant hair dryer)
or a fuel-fired furnace might be utilized.
The trouble is, until quite recently the thermostats controlling these systems
would just run the heat pump as hard it could until the output wasn’t enough to maintain the set point.
Only then would they switch to the auxiliary heat.
That meant that air coming out of your heat vents
would get milder to the point it was barely heat at all
before the thermostat gave up and switched heat sources.
That is undoubtedly annoying,
and if you’ve lived with a heating system that behaves like this
I can see why you wouldn’t like it.
But it doesn’t have to be that way, and it’s not the fault of the heat pump.
Instead of trying to run the heat pump until it just isn’t enough anymore,
a more thoughtful thermostat could handle things more thoughtfully.
If the heating system can determine its current coefficient of performance,
it can determine whether it makes sense to run the heat pump in the first place.
You could even program at which COP it should switch to auxiliary heat.
That would allow you to prioritize comfort, energy costs, or emissions.
Now, if your backup heat is electric,
any COP greater than 1 will benefit you from a cost and emissions perspective
and that’s largely why these systems will use the heat pump as long as they possibly can.
It’s saving you money! You ungr....
But you could still use this to force the backup heat on
before you notice the output falling if that’s what you really wanted.
If you have natural gas or some other fuel as your backup heat,
you could choose to input the COP that is your break-even point on cost.
Now, here in the Chicago area, we have pretty cheap electricity and pretty cheap gas.
By my calculations you need a COP of about 4 in order for a heat pump to beat the cost of gas here.
That’s certainly achievable on many winter days with a heat pump,
and certainly in the fall and early spring.
But many times it isn’t,
and if you had a thermostat which was aware of the current COP
and could switch to auxiliary heat based on it,
well, you’d be able to optimize for heating cost.
Just compare your costs of energy sources,
figure out what the COP break-even point is,
and set your system up accordingly.
This is actually a legitimate use for smart thermostats.
Even if the heating system can’t determine its own COP
(which many simpler systems can’t),
that can be reasonably predicted based upon outdoor temperatures and system specs.
A thermostat that can determine outdoor conditions can use this to its advantage,
and knowing the outdoor humidity can even help it determine how often it needs to defrost the outside unit.
Of course, this can be done locally with a temperature and humidity sensor,
but if your thermostat were aware of the current energy mix on the grid in your area,
it could also help reduce emissions by bending the COP changeover depending on what’s advantageous.
Ideally we’d have some sort of pricing structure
where the cost of each energy source was related to its emissions,
but that’s getting deeper than this video needs to go.
Oh, and speaking of defrosts.
If you have a simpler heat pump system, you might be very aware of when that happens
because the outdoor unit makes a tremendous racket.
If that’s a reason you don’t like heat pumps,
you should know that this is also not a necessary thing by any means.
A lot of domestic HVAC stuff
is controlled with little to no brains, if you will.
Often the thermostat is literally the only thing in control of the outside unit,
and simpler systems will just slam the reversing valve while the compressor is still running.
And that’s what’s causing that racket.
If instead the compressor were stopped before it reversed,
allowing pressures to equalize,
it would be much less noticeable.
That’s how this mini-split heat pump does it,
and to my mind that’s obviously better.
I also can’t see how changing the direction while the compressor runs isn’t somewhat rough on it,
but apparently it’s not so bad because lots of systems do this very thing.
Anyway, the point here is the little annoyances you may have
with your heat pump system are probably nothing to do with it being a heat pump.
Instead it’s simply bad design.
Or a case of misaligned priorities.
In my opinion, air conditioning systems like the one I just installed
that have no reversing capabilities
should not exist.
There is no reason this device cannot provide low-emissions heating
other than a few components are missing from it which made it slightly cheaper to build.
This is a case of “but sometimes!” thinking
leading to the embrace of less flexible systems for virtually no reason.
And it’s dumb.
Yes, in my climate there are many days where an air-source heat pump would leave me in the cold.
And that’s a terrifying prospect - I completely get it!
Nearly everyone around me has natural gas or occasionally propane heating
because in the deepest depths of the winter you frankly need it.
But since nearly everyone around me also has central air conditioning for our sweltering hot summers,
they already have a heat pump,
but it can only go one way because as of now
few people see the point of redundant heating systems
when you have cheap natural gas anyway.
But since whenever the COP of a heat pump exceeds 2.5
we can heat our homes with less fuel burned and ultimately lower emissions,
why would we not want to make the air conditioner reversible
for the many days of the year when that’s absolutely possible?
Well, frankly, the biggest barrier right now
is direct cost to the consumer.
As I said, in my area unless you can get to a COP of 4
it’s just not cost effective to run a heat pump over burning natural gas.
And since there are many, many days in the winter where that COP is a lofty goal,
even if running the heat pump is more climate friendly
it may not be more wallet friendly.
The added cost of a heat pump may never make financial sense in my area,
no matter how small the added cost might be.
At least, so long as externalities remain free to energy providers.
[various alarm sounds] Ope, too deep alert!
And that is why they’re not standard equipment around here.
Yet.
But it should be noted that the financial practicality of a heat pump
will depend entirely on your cost of heating fuel.
If it’s not natural gas,
or even if it is but it’s more expensive for you,
that math will be different.
Now, if I were king, I’d proclaim that every central air conditioning system sold
must be reversible.
It’s equipment with a 10 to 20 year service life,
and who knows what the availability and cost of heating fuel will be in 2041?
Plus, we keep making strides in system efficiency
and air-source heat pumps are becoming viable in colder and colder climates.
In fact, I just read a piece on their use in Alaska!
It can absolutely be done even up there.
But if you really want a heat pump to work in the coldest of the cold
using the least amount of energy,
you gotta go underground.
Look down.
See that?
It’s the ground!
Turn around.
There’s a human sku -
sorry.
Thinking of something else.
You know how we have water pipes going every which way underground
and even in the dead of winter they don’t freeze
(usually)?
Well, that’s because the Earth is warm.
Dig just a few feet below the surface and you’ll find the frost line.
Below this imaginary line the ground doesn’t freeze.
Where that line is changes depending on where you are,
but it’s there!
Management was just really bad about marking it when they built the place.
Since heat pumps are great at extracting and concentrating heat energy
from relatively cool places,
and since there’s a place right below our feet that doesn’t get cold enough to freeze water
no matter how cold it is outside,
if we could just get the heat energy from that place to the evaporator of a heat pump,
we could get more than enough heat to warm our homes
no matter what time of year it is.
And wouldn’t ya know it,
this is a thing we know how to do!
Ground-source or geothermal heat pumps
scavenge heat from the ground below the frost line.
There are two main ways to do this,
and both involve using an intermediary fluid to transfer heat energy.
And yes, some newer ideas don’t use an intermediary fluid but
we’re not talking about them today.
Instead of an outside unit like this with a large fan-driven,
refrigerant-to-air heat exchanger,
these systems will have a refrigerant-to-liquid heat exchanger.
There’s no law saying evaporators have to look like this, after all.
Inside your home the equipment doesn’t look too much different
from a normal furnace or air handler,
but the compressor (and sometimes there’s more than one)
as well as both heat exchangers are all right here.
And to those worried about noise from the compressors, don’t worry -
there’s plenty of sound deadening.
Engineers are smart!
What’s special about these system is where they're getting their heat from.
A long, closed loop of piping filled with a mixture of water and antifreeze
is pumped in a circuit out of the home and underground
where the liquid will absorb heat from the earth before being brought back inside.
This now warmed liquid is fed to the heat exchanger
which will absorb and concentrate that heat with the help of our friend the refrigeration cycle.
The refrigerant is then squeezed into the condenser and that heat is released into the air
and ultimately the living space.
The benefit of doing this is that no matter what the air temperature is outside,
the temperature of the fluid returning from the ground loop
will be a near-constant 50 degrees Fahrenheit or about 10 Celsius.
That temperature allows a heat pump to run at peak performance and efficiency,
delivering a nearly constant, near-maximum COP at full output no matter what.
Right now you can expect it to always meet or exceed a COP of 4,
and that will undoubtedly improve as technology advances.
And that’s obviously a huge deal!
A home with a geothermal heat pump needs significantly less energy to heat
than any other heating technology available today
(unless you count home design itself and want to bring up the passive house but that’s a topic for another time).
Even with an entirely fossil-fuel powered electrical infrastructure,
emissions are drastically reduced when using a ground-source heat pump.
Remember, exceed 2.5 and you’re getting more energy out of burning natural gas in a power plant
and sending its energy the zippy-zappy way
than natural gas itself contains.
That’s astonishing and yet completely possible.
Also important is that methane, the main component of natural gas,
is a potent greenhouse gas,
and the infrastructure we use to transport it to homes across the country is notoriously leaky.
Not requiring that infrastructure in the first place provides its own emissions reduction.
What’s more, the much lower energy requirement of homes with geothermal heat pumps
opens up many more opportunities,
particularly when it comes to renewable and locally-generated sources of power.
Oh, and of course, these systems are entirely reversible.
In the summer months, well below the frost line
the Earth stays colder than the air outside!
So in cooling mode, the system simply puts heat back into the Earth.
It’s actually almost poetic.
That heat ends up simply being borrowed in the winter monts and returned in the summer.
And being able to transfer it into a cool liquid means no matter how hot it is outside,
the system will run at peak performance.
Neat.
So what’s the catch?
Eleven words.
The upfront cost and disruptive nature of the ground loop installation.
That second part’s getting better,
but unless you happen to be lucky and have access to some natural body of water
like a pond that’s deep and large enough to use as your heat source
(which is another way to go about it, by the way)
there will have to be a network of piping installed under the ground
to collect and transport its energy.
For a long time,
this meant excavating a large area around a home
down to several feet (think about a meter-ish) below the frost line.
Then you’d go all loopy with a bunch of piping, and cover it back up.
Hopefully you remembered to put the ends of that pipe somewhere useful.
But that’s really disruptive and requires a large area of lawn or similar open space.
I mean, if you’re building a new house somewhere and have room please just do it.
It’s the perfect time.
Oh, and one interesting idea that’s taking hold is community ground loops.
A bunch of homes in a new development can be hooked up to a large,
shared ground loop that’s piped into each home.
They each have their own heat pumps extracting energy from the fluid,
but the geothermal equipment is shared,
maximizing its potential and lowering the cost-per-user.
But if you want to add a ground loop to an existing homesite
it kinda sucks and sometimes isn't possible.
However, a more recent and exciting development
is the use of vertical drilling to go deeper rather than broader.
Using equipment similar to that which is used to dig a well for drinking water,
a borehole can be dug hundreds of feet below the soil,
and a rather simple bit of piping down and then back up can be run to extract that earthy warmth.
This is much less disruptive and easier to accomplish in areas with denser housing and little greenspace.
Dandelion energy is one company installing such systems.
Now, these aren’t cheap.
Their own website admits that this is gonna cost about as much as a small car,
and depending on how your energy is priced you may never recoup that investment.
But regardless of where you are it will reduce greenhouse emissions,
and hopefully energy starts getting priced to reflect that
[alarm sounds return] oh sorry goin’ too deep again…
What Dandelion and companies like it are doing is really important
for making geothermal heat pumps more approachable.
Simply negating the need to tear up an entire yard
is a huge step in the right direction for getting the reluctant onboard.
But it’s by no means a one-size-fits-all solution.
Unless you have the rights to dig that far down
and there’s nothing below you that could be a problem
like abandoned mines, subway tunnels, etc…
well you can’t do it.
And what about in like, ya know,
cities?
How’s a large apartment building gonna get all the heat it needs from a borehole?
Well, it can’t.
District heating, though, may be an indirect way to provide
geothermally derived heat to large urban spaces.
District heating is unfortunately not that common in the US
which is a giant shame.
Basically it’s a network of underground insulated pipes
bringing really hot water into buildings that is then fed through radiators to heat them.
One of the more clever ways to heat that water
is with the waste heat of conventional power stations,
and many countries have been doing this for decades.
It annoys me greatly that this hasn’t been normal practice everywhere since power plants have been a thing,
especially since water-loop systems for heating buildings are by no means a recent development.
But anyway, that practice can be used to provide heat
to urban centers without requiring combustion of fuels onsite
or the immense electrical supply which would be needed with resistive heating alone.
What you use to heat the water, then, is arbitrary.
It could be a large geothermal station running massive heat pumps.
Or you could even drill deep enough to get heat directly from the magma kilometers below us,
if you’re feeling adventurous.
This is all stuff that’s being researched right now,
and as usual there’s pros and cons to every one of these.
What gives?
Well Ellen, there are no easy answers.
But this video was about heat pumps.
While geothermal heat pumps may not exactly…
work in the concrete jungles of New York City,
air-source heat pumps certainly can.
And maybe they won’t make sense to use on really cold days,
but really cold days are only some of the days of winter.
We really gotta stop this whole
“Only Solutions Which Cover Every Single Possible Contingency are Feasible” nonsense
and start using what we can when we can.
That’s kind of my whole point with the
“every air conditioner should be reversible” thing.
It’s unreasonable to me to limit their potential just because some days heat pumps can’t work.
We have the technology, so... so use it when possible!
Oh yeah. Here’s a really dumb thing.
Electric cars, which nearly universally have air conditioning,
are only just now starting to make that reversible.
Cabin heat is by far the largest non-locomotive energy use in an EV,
and is a large part of why range drops in the winter.
It has always been the case that a heat pump would help a lot with that,
at least on milder days,
and yet even some brand new EV models on sale do not offer them.
Instead, resistive heat is your only option.
I don’t know if there’s some trick to ruggedizing reversing valves for road use,
or maybe there’s something else that makes it harder for cars, but c’mon!
Heat pumps need to be standard in EVs.
Figure it out!
And if you can get a COP of 2 when it’s zero degrees out, fantastic.
But ya know what’s real neat?
We’re beginning to put heat pumps in more places to do more things
besides just heat and cool our living spaces!
Fundamentally, heat pumps are just heat energy relocators and concentrators.
If there’s a place where we need a lot of heat,
we can sometimes take it from another and often with side-benefits as well.
One real-world application of heat pumps not-for-heating is the hybrid water heater.
OK, well I suppose that is still heating…
but consider a typical North American water heater with a 50 gallon tank.
Until recently, you had two choices:
electric or gas.
Gas is cheaper to operate, but requires venting
and also gas.
Electric is more expensive to operate,
but the device itself is little more than an oversized kettle.
Now, the benefit of storing hot water in an insulated tank like this
is that you’ve created a thermal battery.
Hybrid water heaters use a heat pump to maintain the water temperature in the tank,
or you could say… to keep the battery charged,
and it’s ultimately getting that energy from the air of the room it’s sitting in.
This not only uses a fraction of the energy that heating the water with electric heating elements does,
but provides the additional benefit of free air conditioning and dehumidification
in the area around the water heater!
To collect the energy it moves into the water it has an evaporator just like any air conditioner,
and it gets cold and wet.
This means hybrid water heaters need a drain line to deal with that condensate,
but I’d sure like a dehumidifier in my basement that effectively costs less than nothing to run.
It’s heating my water, and more cheaply than before!
Of course, in the winter this is perhaps a bummer,
but if you have gas heat like I do,
well now your water heater runs on gas!
Just, indirectly.
And if you had a geothermal heat pump, well it would get its heat from the ground
after your main heat pump first brought it to your home for you.
Anyway, it’s a hybrid water heater because these also have traditional heating elements
to deal with periods of high demand.
The heat pump is slower than good ‘ol fashioned hot sticks.
But, assuming you don’t have a showerthon going on in your house,
it can take its time reheating the water in the tank between uses
using as little as a quarter the energy of an ordinary electric heater.
The potential for heat pumps to be used in water heaters, by the way,
has made me fairly anti-tankless water heater.
It’s a myth that tankless water heaters provide you with “instant hot water” -
it still has to get through your pipes, and if you want instant hot water what you really need is a hot water recirculation system
and your plumbing to be completely redone,
or maybe you can get away with point-of-use booster heaters.
But anyway, now that I know that heat pump water heaters are a thing
I have no desire to go tankless.
Save that energy, baby!
Another really neat development, and perhaps even more so
is the heat pump clothes dryer.
Tumble dryers are a sort of guilty pleasure to me.
Oh sure, they save tons of time and space
but they also use a lot of energy and are typically vented outside,
which not only means there needs to be a vent in the first place
but also creates significant negative pressure when they run.
But what do dryers really do?
Well, they basically just tumble clothes around a drum
with hot air blowing through it which makes the clothes dry faster.
Making the air hot is the energy intensive part,
buuuuuut…
That’s right.
Heat pump it!
Heat pump clothes dryers are frankly amazing
because it’s about the perfect application for the technology.
You just need to get the inside of the dryer hotter than the outside.
Yeah, you could do that with heater coils or even with a lil’ gas furnace,
but there’s plenty of energy from the room it’s sitting in for a heat pump to take and concentrate.
And none of it gets lost - it just gets concentrated inside.
Best of all, you can then exhaust the hot, damp air that exits the drum
over the cold evaporator and not only re-collect that energy to be pumped back in
but also the moisture from the clothes.
You end up with a clothes dryer that needs much less energy to run,
doesn’t need venting,
and can be placed anywhere.
Some of them can even be plugged into a standard 120V electrical outlet!
Heat pump clothes dryers are slower than traditional vented solutions,
but they offer great flexibility and a much lower energy cost.
Even if you have a gas dryer,
eliminating the need for a vent will lower your heating and cooling demand when it runs
thanks to there no longer being a machine blowing the air you paid to heat or cool outside.
It’s really kind of a no-brainer to me.
Using a heat pump not only makes it cheaper to run
but solves real problems.
That is, if you’re willing to have your laundry take longer,
which I recognize is not feasible for everyone.
Now, there is one real downside to the proliferation of heat pumps.
To make them, we need refrigerants.
And refrigerants have created a Whack-A-Mole of engineering challenges.
When we first ventured down the path of refrigeration,
we were using gaseous ammonia as a refrigerant.
It was actually a fantastic refrigerant,
but it was very toxic and leaks were very dangerous to human life.
That was the problem that Thomas Midgely Junior solved with the creation of Freon.
Freon was the first non-toxic non-flammable refrigerant,
and we were thrilled to have it!
Of course, decades later we realized the ozone layer was disappearing
and we figured out that CFCs like Freon were the culprit.
So, replacement refrigerants were developed like our friend R-134a.
These HFCs don’t harm the ozone layer,
but they are ridiculously potent greenhouse gases.
This here is over 1,400 times better at trapping heat in the atmosphere
than carbon dioxide.
Great!
Even though in an ideal world it will never leave the refrigerant loop,
eventually refrigeration systems develop leaks.
If you ever bought one of these to recharge your A/C, that’s why.
So these HFCs are being phased out for newer refrigerants like
2,3,3,3-Tetrafluoropropene
also known as R-1234yf.
This refrigerant has a global warming potential of less than 1,
so as far as we can tell it’s harmless.
Currently, these new refrigerants are rather expensive.
And the reason is patently obvious.
It’s patents.
These next-gen refrigerants are protected by patents
and their owners are absodidily OK with exploiting that and hard.
Now, that was once the case for this fella.
But those patents have expired and that’s why Walmart can sell it in these cans for less than $5.
In some states, anyway.
Perhaps my most radical thought I’ll put forth here
is that patents on things like,
oh I don’t know,
climate-friendly refrigerants that we really need to make a lot more of and fast
should be invalidated.
Maybe we ought to consider some classes of things unpatentable
and instead encourage their development through some sort of prize system
or just develop them publicly from the start
I don’t know just spitballin’ here.
I just think it’s not great that R-1234yf costs 10 times as much as the chemical it’s replacing
because we need that!
Then again, there is another option.
Carbon dioxide can actually be used as a refrigerant,
although when you do that it prefers you call it R-744.
It’s more polite.
Now if you’re wondering,
“Well if that’s possible why haven’t we just been doing that from the start?”
I’ll tell ya!
The working pressures you need to make carbon dioxide a refrigerant are...
quite high.
Think 1,000+ PSI.
That means the refrigeration equipment needs to be much more robust in order to handle it,
making it more expensive.
More traditional synthetic refrigerants...
that sounds wrong but, yes
don’t need such high pressures and so refrigeration systems using them are just easier to build.
So right now it’s pick your poison.
Cheap system, expensive gas…
or cheap gas but expensive system.
But anyway, we’ve talked about all I wanted to talk about heat pumps.
For now, anyway.
I fully expect them to find their way into more and more places,
and I’m sure we’ll address many of their flaws as time goes on.
And if we can make an air-source heat pump operate with a COP of 4 in arctic temps,
well golly gee that’d just be neat-o!
I hope we can do it.
But one thing is for sure about the future.
I’m pumped for it.
♫ geothermally smooth jazz ♫
I wanna -
[incessant coughing]
And if you had a thermostat which was aware of its current ... bleugh.
Hoo hoo hoo hoo I skipped a word!
What was that in the script?
Aware of the current COP…
yeah that was just an error and I f.. I s.. I.. I made it!
Turn around. There’s a human sk .. sorry.
[evil laughter]
Even with an entirely fossil-fuel powered electrical infrastru…
that’s a lot of big words in this one.
Now the benefits of storing hot water in an insulated tank like this is that… the benefit!
Aehehehe!
A bore hole can be dug hundreds of feet below the soil,
and rather than
[rude raspberry]
So, are we pumped?
Are we pumping up the jam?
You know, somebody probably has that job at the Smuckers factory.
And then when the jars get put on pallets?
Those folks always end with jam-packed days.