A water heater; and a heat pump water heater...

[Externet]

What is the difference ?  Marketing ?

[TheVat]

Much more efficient.  Less than half the kwh/yr of a conventional electric WH.  Some of the newer ones will run on an ordinary house 120V 15A circuit.  The old WH are juice hogs, usually need a 240V and 30 A circuit.  

[Externet]

How does it work ?   The outlet is hot water.  What is the energy input ?

[iNow]

8 minutes ago, Externet said:

How does it work ? 

It’s a reverse air conditioner. 
 

 

This video goes into a bit more detail:

 

 

 

[Externet]

OK. 

 Found this, kind of shows its workings.  What really makes me scratch my head is in summer I could get cool air ducting it for the house, and hot water. Great.

How is the behavior in winter, the contraption installed on a cold basement.

[iNow]

Both videos I shared covered that. They find heat even in extreme cold 

[exchemist]

8 hours ago, iNow said:

Both videos I shared covered that. They find heat even in extreme cold 

Though the heat output drops when the temperature difference between input and output becomes large. The heat pumps I have looked at quote a minimum input temperature at which the specified output can be achieved. As I recall, something in single digit -ve Celsius temperatures.

Edited July 4 by exchemist

[Externet]

Thanks. 

For summer water inlet of 15C, a desired water outlet of 50C, in a 20C air ambient basement, may work as the 'air conditioner' heats the water with its 'outside the window' condenser and cools the dwelling with its 'inside the window' ducting the evaporator.

Sounds good for tropical climates, if use of hot water is extensive.  In other words, cooling a 'window' airconditioner condenser with water instead of air.  That is pumping the heat inside the dwelling into a water tank.

For winter, a 10C water inlet, a desired water outlet of 50C, in a 10C air ambient basement; the 'reversed air conditioner' would warm the water with its 'outside the window' condenser and cool the basement with its 'inside the window' evaporator degrading the temperature differential unless expelled out the dwelling. 

Where is the "hot air in" in the image at post #5 coming from ?  From the heating furnace in the dwelling ?   Yes,  should say "hardly and barely warm air in"  

Sounds complicated contraption for little if any performance.

For sure the industry has tested and retested this as a very profitable wallet wringer product before putting such in the market.   But for winter weather, smells not much convenient.

-Image borrowed from the web-

12 hours ago, Externet said:

What is the energy input ?

Oh ! I see it now !  The energy to heat water comes from the house furnace in winter.   But to sell the thinghy, advertises "It takes little 120VAC" instead of your power hungry standard water heater.  Yes, sure, and the furnace consumes the additional energy. 

Agree the heat pump outside units do perform well for heating a dwelling in limited cold weather

But not for an inside unit.

 

 

[Ken Fabian]

In cold weather it will be more a case of cold air going in and colder air going out at the air source side of the system - the air doesn't have to be warm or hot in human terms - with the difference in heat content between cold and colder air delivered (in water heaters) to the water in the tank.

If you install one inside in a heated space your HPHW will warm water quicker by parasitising the warmth in the air and cooling it, ie you will lose out on the space heating side. Better to put them outside or only in ventilated, unheated inside spaces. With systems suited to those temperatures.

We have one (outside) and it does work very well for (is built for) Australian conditions - we rarely get below zero temperatures where we live and it only gets that cold overnight and early morning with daytime temperatures higher. We set ours to run on a timer from about mid-morning to mid-afternoon to take advantage of solar pv on our roof as well as warmer air temperatures; it is a rare day where that draws any power from the solar batteries and rarer still that we draw power from the grid because the batteries as well as PV are too low. Small household using a smaller unit that draws about 500W for 2-3 hrs a day in warm seasons and 4-5 hours in winter.

But I'm not entirely convinced it will be better value for money compared to having enough more PV on the roof and running a regular resistance heater - the HPHW is a lot more expensive to buy and a lot depends on how long it lasts. (Still cheaper than "passive" solar hot water systems, the sort it replaced though). New solar installs tend to be signficantly larger than our older system - at less cost - and the panels can be expected to last beyond 30 years, where the HPHW probably do well to last more than 10 years. Upgrading the PV isn't as simple as adding more panels; wiring and inverter upgrades would be involved.

 

Externet, I seem to recall a thread from you about use of stored hot water to supplement home heating (?) . Probably not what you had in mind  - this is more about combining hot water and house heating using heat pump hot water that makes significantly higher temperatures and time shifting the heating load within each 24 hr period to take best advantage of when electricity prices are lowest. Also can do summer cooling. Taking advantage of heat pumps being more efficient during daytime is one of the parameters the system works with.

I came across it here https://www.volts.wtf/p/heat-pumps-with-thermal-batteries (an interview - a bit of reading to get to the grit)

The company's site - https://www.harvest-thermal.com/product#tank

Quote

Combine a high-performance heat pump water heater with some thermal storage and some really, really good controls, and you can run that heat pump whenever makes the most sense for the grid, whenever it's most efficient and whenever's going to save the most money. Store that heat in the thermal battery.

This isn't for off-grid although elements of it probably could be.

For interseasonal heat storage it seems to me that borehole type ground source heat pumps offer the best option, but need costs to come down, especially the drilling costs.

Edited July 4 by Ken Fabian

[Externet]

11 hours ago, Ken Fabian said:

I seem to recall a thread from you about use of stored hot water to supplement home heating (?)

Hi and thanks.   

Yes, I may have posted a contraption of 1200W solar panels heating a 20 litres water container indoors to boiling! temperature and releasing its heat also after sunset. (lasts to about midnight).  I use it only in winter.     

Posted also a spiral length of black PVC pipe on the roof feeding the standard electric water heater inlet with pre-heated water for a much less energy consumption in summer.

And a photovoltaic roof solar system heats and supplies all the house all year from the surplus grid-tied generated. My electrical bill has been $0.0 the last 37 months and the system paid for itself last month.

[sethoflagos]

On 7/4/2024 at 3:33 AM, iNow said:

It’s a reverse air conditioner.

Aren't air-conditioners, heat pumps and refrigerators all fundamentally the same thing from a basic physics standpoint? 

The differences seem only to be on PoV focus: which bit connects to ambient and whether the desired product comes from the heat source (cooling) or heat sink (heating)

On 7/4/2024 at 4:27 AM, iNow said:

Both videos I shared covered that. They find heat even in extreme cold 

 

On 7/4/2024 at 1:16 PM, exchemist said:

Though the heat output drops when the temperature difference between input and output becomes large. The heat pumps I have looked at quote a minimum input temperature at which the specified output can be achieved. As I recall, something in single digit -ve Celsius temperatures.

Perhaps not relevant to a domestic application, but industrially it is common practice to 'daisy chain' refrigeration cycles. For instance a methane cycle can extract heat at -175 ⁰C  exhausting to the cold end of an ethylene cycle at -100 ⁰C which in turn exhausts to the cold end of a propane cycle at -15 ⁰C which exhausts to ambient.

This temperature can be (and often is) extended with say a cryogenic nitrogen cycle at the cold end.

While the final exhaust is simply regarded as 'waste heat', each additional cycle of the chain significantly reduces overall efficiency. But what if we added additional high temperature cycles to the upper end? Domestic heating has been already discussed, and this recovers not just the thermal energy extracted in the low temperature cycles, but also the electrical energy consumed in compression. This turns around the economic balance appreciably since the thermal exhaust now has value comparable to that of combustion heating, and easily beats electrical resistance heating.

Water/steam heat pump cycles could achieve temperatures of ~550 ⁰C before metallurgy becomes a real issue, and low cost thermal energy at these temperatures could substitute at an industrial scale for fossil fuels in globally important endothermic reactions like nitrogen fixation, catalytic cracking, drying, etc. etc. but perhaps that's a topic for a different thread.

The key point is that if value is created from both ends of a refigeration cycle, then the economics is drastically improved. 

On 7/5/2024 at 12:47 AM, Ken Fabian said:

But I'm not entirely convinced it will be better value for money compared to having enough more PV on the roof and running a regular resistance heater - the HPHW is a lot more expensive to buy and a lot depends on how long it lasts.

Scale it up to provide hot water/space heating for a group of apartment blocks or similar densely populated area, then the challenge is less economic, more political (in certain less community oriented jurisdictions).

Edited July 6 by sethoflagos
typo

[iNow]

1 hour ago, sethoflagos said:

Aren't air-conditioners, heat pumps and refrigerators all fundamentally the same thing

Yes. I was mentioning direction when using the word reverse. Trying to help the OP visualize.

Air conditioners tend to remove heat from inside air and exhaust that heat outdoors. The heat pump water heaters tend to remove heat from outside air and exhaust that heat into the water being warmed. 

It oversimplified, but I thought might lead to a clearer picture since the nature of the OPs confusion was unclear to me.