Thermodynamics!

[Funkworks]

Let's talk about hte exciting world of heat pumps and stuff!

I'm not sure where this goes so I'll post it here.

Heat pumps now required for new homes in Washington state

New-build residences will have to install energy-efficient heat pumps starting in July as part of Washington’s ambitious efforts to curb carbon emissions.

www.canarymedia.com

Nice, in addition to making housing even more unaffordable for many (purchase price) for negligiable benefit in global CO2 emissions is there any published plans by Washington politicians on increasing the capacity of reliable 365/24/7 electricity to feed all these EV's and heat pumps? How cold does Washington state get in the winter?

 

[Funkworks]

Ok I'll say something.

Boltzmann and Gibbs did amazing stuff!

Ludwig Boltzmann - Wikipedia

en.wikipedia.org

Josiah Willard Gibbs - Wikipedia

en.wikipedia.org

 

[Greg Furtman]

Heat pumps are the most efficient way to heat/cool a home and in the long run the least expensive.

 

[Funkworks]

Heat pumps are the most efficient way to heat/cool a home and in the long run the least expensive.

Heat pumps are great. I know the basic principles but never dug into the details so this is just getting started.

I'll get there but first I want to get this out if the way.



I might try to make a clear path as to how random walks relate to heat pumps. Sounds interesting.

 

[Hobie1dog]

The biggest source of energy we have available on our planet is Geothermal, and we haven't even really utilized it anywhere. There was some activity with ground source heat pumps back in the 80's. No requirements of wind or solar geography.

 

[Funkworks]

The biggest source of energy we have available on our planet is Geothermal, and we haven't even really utilized it anywhere. There was some activity with ground source heat pumps back in the 80's. No requirements of wind or solar geography.

Well, some have.

Energy in Iceland - Wikipedia

en.wikipedia.org

 

[Hobie1dog]

Well, some have.

Energy in Iceland - Wikipedia

en.wikipedia.org

electricity production in Iceland.[4]

"The main use of geothermal energy is for space heating, with the heat being distributed to buildings through extensive district-heating systems.[2] Nearly all Icelandic homes are heated with renewable energy, with 90% of homes being via geothermal energy"

awesome There are also NO snakes there.

 

[mbeels]

Heat pumps are the most efficient way to heat/cool a home and in the long run the least expensive.

Heat pumps are great, but one significant limitation is that their efficiency (for heating in the winter) drops off significantly the colder it is outside. For very cold climates, they aren't adequate. But for mild winters, and in the "in-between" seasons, they're pretty great.

 

[Tyeeking]

Heat pumps are great, but one significant limitation is that their efficiency (for heating in the winter) drops off significantly the colder it is outside. For very cold climates, they aren't adequate. But for mild winters, and in the "in-between" seasons, they're pretty great.

I used to live in Eastern Washington and had a high efficiency heat pump and yes it was great for the shoulder seasons and in the summer for cooling but had a lot of shortcoming in the heart of winter.

The relatively small incremental amount of heat that the heat pump put out on cold winter days/nights frequently would not keep up and meant that the air handler was constantly running which produced what felt like a cool breeze. As a result some form of reliable backup heat was required and electric resistance heat while efficient gets brutally expensive.

 

[jderimig]

Heat pumps are the most efficient way to heat/cool a home and in the long run the least expensive.

The COP of a heat pump should never drop below 1. But in cold locals where that happens often heat pumps are more expensive than gas heat at current rates. In a moderate climate where winter temps are mostly above 40F then they are more economical than gas heat.

I had a house in upstate ny with a heat pump with nat gas backup when outdoor temps dropped below ~32F or so. My heating costs were substantially lower than my neighbors with gas alone. My neighbors with heat pumps with electrical resistance heat backup heat costs were substantially higher than nat gas neighbors during cold months. Over the cost of a year it probably was a wash.

Since in cold climates you need 2 heating systems in series for backup, the first cost is higher than a gas furnace alone. So yes the cost after you spend the initial capital is lower, there is a payback issue to be taken into account.

With my current house I chose nat gas. The reason was I did not like the heat from from heat pump, it was a "cold heat" because the condenser runs at lower temperature than a burner/heat exchanger. Also because of the low temperature heat more cfm was needed to heat the house. In some areas there was an "uncomfortable" draft when the heat pump was warming the house.

The above is what I experienced. Others may have different experience. I'd be curious to what others who actually lived with a heat pump in colder climates. I prefer not to hear opinions, theory or hearsay, I would prefer first hand experiences. Thanks.

Edit: One more addition from memory: In my heat pump house we had to set the thermostat at about 76F to be comfortable. In our current nat gas house we are comfortable at 70F. I know there are confounding factors like humidity but that is an observation thrown out there. Also curious on what others have directly experienced.

 

[Greg Furtman]

Heat pumps are great, but one significant limitation is that their efficiency (for heating in the winter) drops off significantly the colder it is outside. For very cold climates, they aren't adequate. But for mild winters, and in the "in-between" seasons, they're pretty great.

For those of us up north they have to be geothermal heat pumps. More expensive but also more efficient.

 

[Funkworks]

Don’t mind me, I’ll catch up on heat pumps later, just taking the long way.

 

[Sandy H.]

I grew up in the Atlanta region and my dad put a solar hot water system on the roof. The gas bill in the winter was $5-ish dollars, as we had a gas stove. House was warm (warmer than I prefer) and the air was moist, not dry like with gas heat.

My current house has conventional AC/gas heat for the main part of the house and I have a mini-split for the garage (i.e. heat pump). The air in the garage is slightly more humid than the main part of the house, but not quite as good as the solar hot water. It seems much more efficient in the garage as far as dollars spent vs. change in temperature.

If I had it to do over again, I would have done solar hot water when we had the AC replaced 7 years ago in the main house and I might still consider adding something moving forward. The sun is good at making stuff hot.

Sandy.

 

[Greg Furtman]

@hobie1dog , Check this out. If this works there could be geothermal everywhere.

 

[Greg Furtman]

Deleted. A copy of my above post.

 

[Greg Furtman]

Don’t mind me, I’ll catch up on heat pumps later, just taking the long way.

Ah, Brownian movement.

 

[Funkworks]

 

[jderimig]

electricity production in Iceland.[4]

"The main use of geothermal energy is for space heating, with the heat being distributed to buildings through extensive district-heating systems.[2] Nearly all Icelandic homes are heated with renewable energy, with 90% of homes being via geothermal energy"

awesome There are also NO snakes there.

And lots of blue-eyed blond people. What's not to like? (except for living on a volcano).

 

[NateB]

The COP of a heat pump should never drop below 1. But in cold locals where that happens often heat pumps are more expensive than gas heat at current rates. In a moderate climate where winter temps are mostly above 40F then they are more economical than gas heat.

I had a house in upstate ny with a heat pump with nat gas backup when outdoor temps dropped below ~32F or so. My heating costs were substantially lower than my neighbors with gas alone. My neighbors with heat pumps with electrical resistance heat backup heat costs were substantially higher than nat gas neighbors during cold months. Over the cost of a year it probably was a wash.

Since in cold climates you need 2 heating systems in series for backup, the first cost is higher than a gas furnace alone. So yes the cost after you spend the initial capital is lower, there is a payback issue to be taken into account.

With my current house I chose nat gas. The reason was I did not like the heat from from heat pump, it was a "cold heat" because the condenser runs at lower temperature than a burner/heat exchanger. Also because of the low temperature heat more cfm was needed to heat the house. In some areas there was an "uncomfortable" draft when the heat pump was warming the house.

The above is what I experienced. Others may have different experience. I'd be curious to what others who actually lived with a heat pump in colder climates. I prefer not to hear opinions, theory or hearsay, I would prefer first hand experiences. Thanks.

Edit: One more addition from memory: In my heat pump house we had to set the thermostat at about 76F to be comfortable. In our current nat gas house we are comfortable at 70F. I know there are confounding factors like humidity but that is an observation thrown out there. Also curious on what others have directly experienced.

We have had about the same experience with heating our home in Northern Indiana. The home we bought has a heat pump / AC unit with a natural gas furnace backup. The heat pump is great in the 40s, below that and it runs too much and too hard to be cost effective.

 

[Funkworks]

Ah, Brownian movement.

Well, just a 2D random walk of 1 particle among other similar ones. Brownian motion is normally shown as a big particle being tossed by many smaller ones, like this:



And here's someone explaining Brownian motion:



But I don't think Brownian motion leads to heat pumps so I'd leave it at that for now.

 

[cls]

Also because of the low temperature heat more cfm was needed to heat the house. In some areas there was an "uncomfortable" draft when the heat pump was warming the house.

Good point. Had that experience with one of the new fangled high efficiency furnace 25 years ago. Damn blower ran frequently and for long times pushing out lukewarm air. Also it wanted to move too many CFM for the house's original ducts, so it was noisy too. Frankly I think I should have sued the installer.

Anyway, very happy with a new new high efficiency furnace AC unit in a different house (2 years ago)

 

[mbeels]

For those of us up north they have to be geothermal heat pumps. More expensive but also more efficient.

Good point, there is a near limitless reservoir of heat buried below the surface.

 

[Peartree]

We have had about the same experience with heating our home in Northern Indiana. The home we bought has a heat pump / AC unit with a natural gas furnace backup. The heat pump is great in the 40s, below that and it runs too much and too hard to be cost effective.

Ditto my experience in Ohio. I had an apartment in college with a heat pump and resistance heat backup. In the winter I never felt warm even though the thermostat said that I should be. The only way to feel warm was to force the resistance heat to run, and that was too expensive to do very often. Over the years, I have known several folks who saved money by switching from a heat pump to natural gas. The biggest factor is often the relative prices of natural gas or propane versus the price of electricity. During those periods when people were saving money switching to gas, it was because gas was (and often is) relatively cheap and electricity was (and often is) relatively expensive. When my wife and I purchased our first home, it had all electric, baseboard resistance heat. By our second or third year there, I installed a fireplace insert and my father-in-law and I worked all summer, every summer, to cut enough firewood to heat most of the house with our basement fireplace. When we moved in, the electric budget from the power company was $500 per month. But, by burning wood, heating only about half our house, getting a lower electric rate by installing a demand switchable water heater, and running the swimming pool circulating/filtration pump on a 50% duty cycle instead of 100%, we cut our monthly bills to under $300 (all figures in 1990 dollars).

Short answer, I don't like heat pumps and electric heat is way more expensive.

 

[Tyeeking]

Ditto my experience in Ohio. I had an apartment in college with a heat pump and resistance heat backup. In the winter I never felt warm even though the thermostat said that I should be. The only way to feel warm was to force the resistance heat to run, and that was too expensive to do very often. Over the years, I have known several folks who saved money by switching from a heat pump to natural gas. The biggest factor is often the relative prices of natural gas or propane versus the price of electricity. During those periods when people were saving money switching to gas, it was because gas was (and often is) relatively cheap and electricity was (and often is) relatively expensive. When my wife and I purchased our first home, it had all electric, baseboard resistance heat. By our second or third year there, I installed a fireplace insert and my father-in-law and I worked all summer, every summer, to cut enough firewood to heat most of the house with our basement fireplace. When we moved in, the electric budget from the power company was $500 per month. But, by burning wood, heating only about half our house, getting a lower electric rate by installing a demand switchable water heater, and running the swimming pool circulating/filtration pump on a 50% duty cycle instead of 100%, we cut our monthly bills to under $300 (all figures in 1990 dollars).

Short answer, I don't like heat pumps and electric heat is way more expensive.

From a comfort standpoint it’s really hard to beat a wood stove. It’s a radiant heat that soaks into everything.

When I lived in Eastern Washington once temps dropped below 40 (about 4 months of the year) it was off with the heat pump and stoke the wood stove.

 

[Blast it Tom!]

Heat pumps are the most efficient way to heat/cool a home and in the long run the least expensive.

That graph is in dollars, and I think for now that the cost of natural gas has been artificially driven up by market forces & increased regulations. I know my commodity cost for natural gas has gone up by 350% in the last two years for no apparent reason other than the two mentioned, I have gas stove, heat, clothes dryer and water heater and seldom paid more than $100/month here in Western PA. Until this winter, I suspect THAT will change.

Supposedly my furnace is 93% efficient. If that's a true thermodynamic efficiency, I'm not sure any refrigeration-cycle based unit like a heat pump could actually beat that. Carnot diagrams, that sort of thing. But I could be wrong...

 

[mbeels]

Supposedly my furnace is 93% efficient. If that's a true thermodynamic efficiency, I'm not sure any refrigeration-cycle based unit like a heat pump could actually beat that. Carnot diagrams, that sort of thing. But I could be wrong...

I believe (I also could be wrong) that the difference is your furnace may be 93% efficient in turning the fuel that you purchase into heat for your house. A heat pump uses a smaller amount of fuel to move heat from somewhere else outside your home, into your home. In that case the source of heat is "free", it's just there, outside, or in the ground. You still need energy to run the heat pump, but one unit of heat pump energy is potentially capable of moving more than one unit of heat.

But as for comfort, I agree with the above, wood stoves are really hard to beat!

Edit: That's why refrigerators and heat pumps use "Coefficient of Performance" as an efficiency metric, otherwise the numbers would be >100%.

 

[bjphoenix]

I would like to have a new heat pump and a new A/C system to go along with it. Our house is 35 years old, my service company told me that the electric heater is original to the house and the A/C is probably about 25 years old. Natural gas is not available in our neighborhood. They both work well, the service company said they could easily keep the heater running for a long time but one leak in the A/C and it is doomed to replacement. Our winter electric bills are about twice what we were paying for natural gas at our previous house. We have thought about replacing our system but we probably won't live here long enough to get our money back, but otoh we might not be lucky enough to go that whole time without the A/C breaking.

My sister in law just got a new heat pump system, the company that installed it told me how much it should save per month over electric heat and I calculated that it would take about 15 years for the heat pump to pay for itself over electric heat. I don't understand the comments about "cold heat", her system blows hot air out of the vents when running the compressor.

I studied thermodynamics in college but that was too long ago for me to be able to draw the graphs of the heat cycle. I remember the instructor saying that we could even use water as a refrigerant if all of the hardware was built to not corrode.

 

[jderimig]

I don't understand the comments about "cold heat", her system blows hot air out of the vents when running the compressor.

In my experience the condenser pressure (which determines the temperature of air) depends on the outside temperature. The colder it is outside the less heat gets 'collected' by the evaporator outside which lowers the pressure at the condenser. The colder it is outside the cooler the exhaust air and the longer the system needs to run to pump that heat into the interior.

 

[bjphoenix]

In my experience the condenser pressure (which determines the temperature of air) depends on the outside temperature. The colder it is outside the less heat gets 'collected' by the evaporator outside which lowers the pressure at the condenser. The colder it is outside the cooler the exhaust air and the longer the system needs to run to pump that heat into the interior.

What is the crossover temperature at which the thermodynamic cycle isn't working well? I will try to go by sometime when it is that cold and check it out.

 

[jderimig]

What is the crossover temperature at which the thermodynamic cycle isn't working well? I will try to go by sometime when it is that cold and check it out.

From basic thermodynamics the COP ideal (Carnot cycle limit) is:
COPheating = Th / (Th - Tc) Where Th = absolute Temp of hot side, Tc = absolute Temp of cold side (outside)
COP is roughly how much heat you are pumping in divided by how much energy input (to the compressor). So as the delta T between inside and outside increases the COP drops pretty quickly. You will always get as much heat energy as you are putting into the compressor. The electrical energy input to the heat pump is generally no where near the amount to heat your house on its own so you need a minimum COP to be able to maintain the inside temperature. That minimum COP depends on the size of the heat pump and how lossy your house is. So that crossover temperature will vary. If you have a tight house, the heat pump could be still effective as low as 25F. If you have leaky windows and poor insulation it could be as high as 40F.

Now all heat pumps have backup, usually resistance heaters. So if you check when its cold outside and feel hot air coming out, it might be you are feeling the electric heater kicking in.