Has Heat Pump Technology Really Improved This Much?

[stem]

Just read this article published by the BBC quoting a guy at Octopus Energy with regard to recent improvements in heat pump technology who, describes installation of their Cosy 6 air source heat pumps as "little fuss" and as simple as "Combi boiler out, heat pump in". Anyone have, or come across, a heat pump that can really replace a combi boiler and generate instant hot water direct from the cold mains?

 

[bernardgreen]

From the BBC article """A major change has been the rise of new refrigerants, including R290, or propane"""

I am informed that the Environmental Protection Agency ( USA ) has banned the use of R290 in residential systems in the United States.

 

[MNW67]

Intrigued so I rang them. The (very nice and informed) rep confirmed it still needs a cylinder! "Would need to sacrifice some space". Suggested loft for most people.

 

[stem]

Not surprised really, but you would have expected Octopus Energy's 'Head of Flexibility' (whatever that means) as he was nominated for interview to at least have a basic understanding of what they are offering.

 

[MNW67]

More than a bit misleading, IMO, especially for your average consumer.

In theory, going forward, could they make a heat pump with enough juice to do instant hot water?

 

[Mike13]

More than a bit misleading, IMO, especially for your average consumer.

In theory, going forward, could they make a heat pump with enough juice to do instant hot water?

Not really, it would be much to oversized for over 95% of the year that would put it back into the unaffordable category.

 

[martygturner]

From the BBC article """A major change has been the rise of new refrigerants, including R290, or propane"""

I am informed that the Environmental Protection Agency ( USA ) has banned the use of R290 in residential systems in the United States.

You are mis-informed...currently the use of R290 is limited to 150g per appliance but will soon be upped to 500g, it is not banned.

 

[bernardgreen]

In theory, going forward, could they make a heat pump with enough juice to do instant hot water?

In theory yes but only if there was a adequate source of "pumpable " heat energy.

A reasonable flow of instant hot water requires more than 20 kW of heat from burning gas in a combi boiler.

Electric showers at 10 kW are limited to a low flow rate,

For air source heat pumps the evaporator ( outdoor heat exchanger ) would need a very large surface area. And would still be at risk of freezing up.

A flowing water ( or large lake ) sourced heat pump could be made to provide hot water but a cylinder would be needed.

For what is worth.... In the late 1970's we looked into a heat pump using flowing water in a stream as part of the heating system for the house we were building.
Two major problems ....
(1) preventing contamination of the stream if there was a leak of refrigerant
(2) designing a heat exchanger that would not become clogged with debris carried in the water,

 

[bernardgreen]

You are mis-informed...

In The United States Enviro-Safe R 290 Refrigerant is not legal for use in a Central Residential or Central Commercial Air Conditioning System. Allowable uses can be determined by reviewing the regulations by visiting the E.P.A website. In the United States the E.P.A. (Environmental Protection Agency) regulations state it is illegal to use any hydrocarbon refrigerant, and/or Enviro-Safe R290 refrigerant, in a Central Residential or Central Commercial Air Conditioning Systems.

Enviro-Safe FAQ - Refrigerant R290 Consumer Notice

I accept that the rule applies to "Central Residential" systems

 

[fixitflav]

I accept that the rule applies to "Central Residential" systems

Whatever that means. Does it mean it's banned for a group of houses (using a centralised heating system) but OK for single properties?

 

[martygturner]

Enviro-Safe FAQ - Refrigerant R290 Consumer Notice

I accept that the rule applies to "Central Residential" systems

again you should get your info from the epa rather than a commercial site selling refrigarant :

https://www.epa.gov/sites/default/files/2018-08/documents/epa_frdoc_0001-22694.pdf

 

[ScottishGasMan]

R290 is just propane. We have bulk stores of propane outside thousands of houses as it is now in the UK. The amount of propane (R290) in a domestic heat pump is tiny.

Where some of the difference will be is that in the UK a majority of domestic "heat pumps" are monoblock systems so the flammable refrigerant is contained outside. For the U.S. its much much more likely for them to have split systems where the refrigerant lines run inside the properties meaning you could have a volume of pretty high pressure propane inside your property.

It's quite common for flammable refrigerants to be used indoors in small quantities in fridges or heat pump tumble dryers, but the volume needed for central heating heat pumps is normally more than the allowed limits. So you don't see split R290 systems much at the moment.

 

[ScottishGasMan]

Just read this article published by the BBC quoting a guy at Octopus Energy with regard to recent improvements in heat pump technology who, describes installation of their Cosy 6 air source heat pumps as "little fuss" and as simple as "Combi boiler out, heat pump in". Anyone have, or come across, a heat pump that can really replace a combi boiler and generate instant hot water direct from the cold mains?

The technology for air source has improved, however basic physics has not.

To run a heat pump at similar or lower cost than a gas boiler in the U.K you need to design a heating system that will work at low temperatures. i.e. when its -3 outside I only need my radiators to be 40 degrees in order to keep my house at 20 degrees. So this would suit a heat pump nicely for running costs.

If I needed to run my radiators at 70 degrees to keep warm which is more like traditional gas heating systems then it would cost an absolute fortune to run a heat pump at those temperatures. (still cheaper than running electric heating, but much dearer than gas)

Many houses, especially older properties have radiators that are massively oversized, so its often the case that they could actually be suitable for heat pump temperatures, however the pipework needs to be assessed as they need more water flowing through them than with gas boiler systems.

Again, some properties it's not really that big an upheaval, some its pulling the lot out and starting again.

And when the person who sells you electricity is selling you electric heating I panic. Are they fitting a heat pump to a very inefficient system and being offered a cheaper rate of electricity to mitigate the running costs?

As far as a combi/heat pump, I'm sure someone somewhere is working on it, however in reality it would be incredibly difficult to do, and would not save any space as already suggested due to the size of heat pump required to run it, and I'd be certain if they did make one it would cost a lot to run.

 

[MNW67]

I have been wondering why heat pumps need such a small dT and then, on Googling, I found the answer was actually on this forum!

As far as heat pumps go. The refrigerant gas isn't particularly hot in the way a boiler is. for a 50 degree flow on a boiler, burning gas in a boiler will have a flame temp of near 2000 degrees (lower in reality dependent on air mixture) but hot all the same.

Heat pumps depending on refrigerant type, could be closer to 60-80 degrees it has to pass to the central heating water. If the water is flowing out the heat pump at 50, then the refrigerant gas entering the heat exchanger at say 60 can only drop 10 degrees before returning to the refrigerant cycle.

That doesnt mean they cant produce much heat (energy) as the refrigerant will enter the heat exchanger as a hot gas (60degree) and condense where it passes the heat to the water system, this condensing gives up a lot of heat energy (in the same proccess of latent heat that you have on a condensing boiler)

But since there is a narrow temperature between the Refrigerant Gas entering the HP heat exchangers and the condenses liguid refrigerant leaving, it means you need a high flowing supply of slightly cooler water entering the HP to keep stealing the heat.