What is the real story around heat pumps?

[Zucca]

Did not have time to read all the pages...

Once you understand the physics behind the heat pump you can't go wrong.

This is what I did in my home in USA:
1) I replaced my 50gal gas water heater in my garage with an 65gal electric heat pump water heater [HPWH].
2) I installed 14KW solar panels using the unused gas chimney to bring the HV solar cables down in the garage. (YES there is a metal ground shield around them... everything is safe)
3) I installed my Victron inverters (16KW peak) and MPPTs few meters away from the HPWH.

In winter the Victron devices are heating up the air and the HPWH is happy.
In summer the HPWH is cooling the air and the Victorn devices are happy.

I am now in the process to install 4 Temp sensors from my Cerbo GX so I can log all the in-out temperatures and see how much the two systems are helping each other.

WIN-WIN!

[pcprogrammer]

The bigger ones, say over 5kW claimed output, are better (more reliable) with a 3 phase compressor.

Is there a difference in life expectancy and reliability between tri phase and single phase models?

For what I have seen of the De Dietrich models there is no difference in price between them. Don't know about other brands.

Unless you have a bargain basement heat pump, why would three or single phase power make any difference? They are all inverter driven these days. Is this single vs 3 phase issue related to old heat pumps? I can definitely see a three phase induction motor giving better results.

That was what I was thinking too. We have a single phase installation but could change over to 3 phase at extra expense if it would be beneficial. Looks like it won't be needed.

[Siwastaja]

Is there a difference in life expectancy and reliability between tri phase and single phase models?

No. I think it is now impossible to buy line frequency on/off models. All are inverter machines, so there is no difference in the compressor motor, inverter power stage or drive logic. In both cases, incoming mains is just rectified. Assuming wye connection, three-phase inverter machine needs to work with internally higher DC voltage than the single phase equivalent, and single phase requires more DC bus capacitance to deal with more ripple, but such details are meaningless to normal end user.

[Siwastaja]

Which Chinese unit do you have?

Amitime which I think is the second largest heatpump producer (after Gree). These large Chinese companies know how to get the basics quite right, they are not super sophisticated designs but then again a heatpump doesn't need to be. Whenever there are technological innovations that actually improve COP or performance (like inverter drive or EVI), first premium brands use them, then a few years later all the cheap ones adapt them too and make a big deal about it in their marketing, and then a few years later again it's just standard stuff and everybody forgets to even mention such technical details.

Funnily enough, as a designer myself, I can see a lot of potential for quite significant cost savings in my Amitime unit. A cabinet full of stuff like Windows CE computer, separate wifi-RS232 module, total of four RS485 buses, and massive control cards with 20 relays out of 2 are actually used is something I would not expect from the market's cheapest product. They clearly can afford it, but they could also easily shave off another $50-100 from their manufacturing costs.

You can clearly see air-to-water heatpumps are still quite niche compared to the ubiquitous air-to-air units which are better optimized for mass market.

[JohanH]

Pretty much every heat pump now, even with a single phase input, will be using a three phase compressor because they will use an brushless or induction motor and inverter to drive that motor.  That will probably be immune to losing a phase (will likely cause the unit to shut off though if it has any monitoring of the AC line.)

The ground source heatpump that I have, Nibe F1255-6, does have a three phase connection, but only one phase is used for the BLDC motor, which has its own motor driver (three phase 20 - 120 Hz). The second phase is used for control circuitry and pumps and the third only for electrical resistive heaters. You could run this model from a single phase. The resistive heaters are wired to all phases in this installation, but because they are almost never used, there is almost never any load on the third phase. Current load in this weather (outdoor 0°C): compressor is running on 600 W on one phase (right now motor speed 44 Hz), pumps on second phase 40 W and the third phase 0 W. The larger models of Nibe use induction motors with regular inverters and they might be differently wired. I've heard about some issues with some older heatpumps breaking when losing a phase. That could theoretically be protected with an external phase protection relay.

[m k]

That's is situation with air source heat pumps from this morning:
Outside temp 2°C, humidity about 60%, clear sky, no rain, no clouds, no fog.

Pictures taken 3-4 minutes after defrost cycle completion.

Looks can be misleading.

The structure is what it is because air is not dense enough that lesser surface area would be enough.
Actual operation happens between refrigerant and inner wall of the pipe.
So the machine doesn't know that there is frost, generally it only knows that compression is fine or not.

Condenser/evaporator can be insufficient when general operation changes from the normal sufficient operation.
It can still be fine with visually not so fine looks.

Evaporator was fully clogged, no air passes at all. And fan operates at very high speed.

In this situations heat pump works with COP slightly under 1. Heat dissipated in compressor are transferred to inside unit. Power needed for fan is lost.

Do you know defrosting periods between different humidity levels?

Here air-to-air machine is now using 400W and easily maintaining +21C indoors when outdoors is +1C and humidity being >95%.
Some visible frost has accumulated but operation of the machine is stable and unchanged.

When humidity goes up the efficiency of radiation process goes down but it also becomes more powerful per square.
If pump ignores that it may overuse the situation.
But changing 0C water to 0C ice is equal to 80C temp difference of liquid, so having sort of ice on top of the surface is not a straight forward thing.

[coppice]

Which Chinese unit do you have?

Amitime which I think is the second largest heatpump producer (after Gree). These large Chinese companies know how to get the basics quite right, they are not super sophisticated designs but then again a heatpump doesn't need to be. Whenever there are technological innovations that actually improve COP or performance (like inverter drive or EVI), first premium brands use them, then a few years later all the cheap ones adapt them too and make a big deal about it in their marketing, and then a few years later again it's just standard stuff and everybody forgets to even mention such technical details.

I don't know where Amitime are in the rankings, but I think they are quite small compared to Gree, Midea and Haier. The big guys have the volume to finance the R&D to both performance improve and cost reduce their designs. An overly complex design is is something of a red flag. Midea is a big brand name, but they also make heat pumps that carry other big names, like Toshiba and Carrier. Haier products carry various names, but I think they are names they own.

You can clearly see air-to-water heatpumps are still quite niche compared to the ubiquitous air-to-air units which are better optimized for mass market.

I think that is compartmentalised. Until recently the main market for air-to-water heat pumps was big commercial systems, and I think those should be quite mature. Consumer heat pumps have been mainly air-to-air heat, and mostly cooling only. That market has been highly optimised. The growing market for reverse cycle and heat only models is gradually getting those optimised, too.

[m k]

Here air-to-air machine is now using 400W and easily maintaining +21C indoors when outdoors is +1C and humidity being >95%.
Some visible frost has accumulated but operation of the machine is stable and unchanged.

I left and upped the target temp 1C, came back few hours later and indoor temp was heading to 22.5C and machine used 1770W.
Dropped the target down 1C, no real operational change and room temp kept rising.
After an hour or so later indoor temp is near 23C and machine is using 1100W, outdoor temp being a bit above zero and humidity over 95%.
After few minutes of defrosting indoor temp meter says 22.5C and next cycle start using 960W, bit later it's 1200W.
Now indoor temp is 22C, pump is chilling and using 236W, outdoor temp is probably under zero and humidity around 90%.

Few log things.
We have 3 different m3 styles, thrown, piled and solid.
Our last piled qubes were 80EUR, first more mixed and later more pine.
Here dry piled m3 of birch is said to have 1700kWh and pine 80% of that.

Once we chopped an oak and a maple, not big.
Those were very difficult to burn, oak practically didn't burn by its own.
Maple was burning but needed a hot base.

I also had free wood once.
We collected what harvester left behind, the area was some hundred meters aside and wet.
Collected trunks were chopped with a guillotine style cutter with a claw for splitting, nice thing but can't do too thick trunks.
Putting in a bent trunk can also be a bit bad for nearby flesh.
For me chopped logs were too long so I had to still cut them afterwards, the pile was also there, in the woods, so some hauling was necessary.
Just for the sake of it I estimated how much the big pile would have been cost if sold, it was over 100EUR/m3 a long ago, at least a double now.
Most of the time was used for collecting trunks, it took many days even when tractor collected small piles to big pile, but good exercise anyway.
I'd say that free can be pretty relative.