Heat pumps and home electrical capacity

[HSTEd]

If gas boilers really do get replaced en masse with heat pumps, a lot of people are going to get annoyed if they have 60A service supplies to their houses, as many do!

 

[Bletchleyite]

If gas boilers really do get replaced en masse with heat pumps, a lot of people are going to get annoyed if they have 60A service supplies to their houses, as many do!

In what way? Heat pumps use very little electricity, that's kind of the point - they're basically like running a fridge or air conditioner in reverse. The thing that'll annoy me about heat pumps is the noise.

60A is plenty to heat a house using resistance heating, let alone heat pumps.

 

[AM9]

In what way? Heat pumps use very little electricity, that's kind of the point - they're basically like running a fridge or air conditioner in reverse. The thing that'll annoy me about heat pumps is the noise.

60A is plenty to heat a house using resistance heating, let alone heat pumps.

Yes, the average heat pump is about 300% efficient compared to resistive heatin (which is 100% efficient). So a 1KW heat pump will produce about 3KW of heat, therefore an average house which has a 24KW gas boiler gets about 22.5KW of heat from it. That same amount of heat can be provided by a 7.6KW heat pump, - almost doable on a single 32A ring circuit. As most modern installations have a 100A supply, no change would be required when the gas boiler is replaced by a heat pump.
Even the few houses that have 60A connections would be able to have over 20KW heating, - and that is a continuous value for a fairly large house. If a shower or a large cooker is switched on, the heating system will be able to shed some load in order to provide the necessary diversity. In real terms, a house with those sorts of demand needs to have a supply that meets late 20th century standards, let alone 21st century capability.

 

[Bletchleyite]

From https://www.railforums.co.uk/thread...rail-travel-demand.208377/page-2#post-4741182

Yes, the average heat pump is about 300% efficient compared to resistive heatin (which is 100% efficient). So a 1KW heat pump will produce about 3KW of heat, therefore an average house which has a 24KW gas boiler gets about 22.5KW of heat from it. That same amount of heat can be provided by a 7.6KW heat pump, - almost doable on a single 32A ring circuit. As most modern installations have a 100A supply, no change would be required when the gas boiler is replaced by a heat pump.

Even the few houses that have 60A connections would be able to have over 20KW heating, - and that is a continuous value for a fairly large house. If a shower or a large cooker is switched on, the heating system will be able to shed some load in order to provide the necessary diversity. In real terms, a house with those sorts of demand needs to have a supply that meets late 20th century standards, let alone 21st century capability.

It's also worth taking into account that the power used on most other household devices is now tiny. For instance, all the lights on in my house (mostly LED, two CFLs) comes to about 60W, as distinct from about 600W before. An LED TV uses next to nothing compared with even a smaller CRT. With a heat pump, you wouldn't have electric fires all over the place (not that people really do these days anyway). So you're pretty much left with the cooker, the washing machine, the dishwasher, the kettle and the toaster, and as you say it's not exactly rocket science (!) to have a heat pump shut itself off for a short period if these were all in use. I suppose you might have an electric shower, but heat pumps lend themselves to heating insulated tanks slowly, so you'd probably have a shower pump or an unvented cylinder instead.

So really, it's nothing massive, and a 60A connection would be fine.

 

[AM9]

From https://www.railforums.co.uk/thread...rail-travel-demand.208377/page-2#post-4741182



It's also worth taking into account that the power used on most other household devices is now tiny. For instance, all the lights on in my house (mostly LED, two CFLs) comes to about 60W, as distinct from about 600W before. An LED TV uses next to nothing compared with even a smaller CRT. With a heat pump, you wouldn't have electric fires all over the place (not that people really do these days anyway). So you're pretty much left with the cooker, the washing machine, the dishwasher, the kettle and the toaster, and as you say it's not exactly rocket science (!) to have a heat pump shut itself off for a short period if these were all in use. I suppose you might have an electric shower, but heat pumps lend themselves to heating insulated tanks slowly, so you'd probably have a shower pump or an unvented cylinder instead.

So really, it's nothing massive, and a 60A connection would be fine.

I think that we will be used to all domestic electrical load being managed automatically with major load items negotiating their power at lower priority when appropriate. It's been happening in commercial and industrial installations for decades to avoid peak load costs.

 

[Meerkat]

They are going to have to make heat pumps a lot quieter before they can be widespread in most uk residential areas!

 

[Bletchleyite]

They are going to have to make heat pumps a lot quieter before they can be widespread in most uk residential areas!

Yes, true, that's the main issue with them, aircon units similarly make a racket!

 

[AM9]

Maybe there's a market for ground to air heat pumps in some circumstances, or even a local water loop that premises can tap into. The concept of shared soakaways have been in modern developments for decades.
When the cost of CO2 generation starts to rise, and a market for suitable replacements grows, there's plenty of experience in heat transfer and management to provide solutions. Just look how the pace of EV development has increased as the inevitable CO2 restrictions approach.
I think that serious insulation of domestic property may also become more of a requirement than a 'nice to have'.

 

[Bletchleyite]

I think that serious insulation of domestic property may also become more of a requirement than a 'nice to have'.

I'd certainly agree on that one. The "Passivhaus" standard is where we should be looking - that includes things like thick outside insulation (that is why most Swiss buildings are rendered and you don't see bare brick like you do here), triple glazing[1] and heat recovery ventilation systems[2]. Do it well and there isn't much of a cost penalty for heating with simple resistive heating.

It can be difficult to incorporate that into existing properties, so perhaps some demolition will be needed? A good, environmentally beneficial job creation exercise?

[1] This is now mainstream. My parents are having some rotten old wooden windows replaced with uPVC, and they're going for triple because it barely costs more these days.

[2] Basically, instead of having the windows open all the time you have an extractor fan and inward vent based system, and a heat exchanger between the two so much of the heat going out gets put back in again (or if you like vice versa in summer). My friend has one in his flat, they cost a couple of hundred quid plus the ducting, and while they use similar principles to aircon aren't quite as power hungry so do gain overall.

 

[xotGD]

Heat pumps are all well and good in new well insulated houses. But in old housing stock they don't have the 'umph' (technical term!) to deliver enough heat quickly enough. Folks are going to get mighty annoyed if their gas boilers are ripped out and replaced with something inferior.

Convertingthe gas grid to hydrogen is the other way to decarbonise domestic heating. Expensive, yes, but technically doable and less disruptive for the consumer.

 

[edwin_m]

Many people are going to need their supplies upgrading to fit a reasonably fast electric car charger, which is going to be far more demanding than a heat pump.

 

[HSTEd]

~7kW for a heat pump is only the start.

Then you have to add in an electric car charger, an electric oven.... and then someone puts the kettle on......

It's not hard to get above 60A/~16kW.

 

[Bletchleyite]

You needn't have a fast charger for your car at home, 13A will do, home charging is overnight (when conveniently you aren't using a lot else).

 

[BRX]

[2] Basically, instead of having the windows open all the time you have an extractor fan and inward vent based system, and a heat exchanger between the two so much of the heat going out gets put back in again (or if you like vice versa in summer). My friend has one in his flat, they cost a couple of hundred quid plus the ducting, and while they use similar principles to aircon aren't quite as power hungry so do gain overall.

I think that in general they rely just on a heat exchanger and don't involve a heat pump, so in that sense they aren't really similar to aircon. Essentialy the only energy input they need is for the fans to move the air.

 

[HSTEd]

You needn't have a fast charger for your car at home, 13A will do, home charging is overnight (when conveniently you aren't using a lot else).

13A is unlikely to be sufficient for long range electric cars.
People will expect to be able to fully recharge their car overnight.

They will want 10kW or more of charging power.

 

[AM9]

~7kW for a heat pump is only the start.

Then you have to add in an electric car charger, an electric oven.... and then someone puts the kettle on......

It's not hard to get above 60A/~16kW.

You lets look at those assumptions:

"Then you have to add in an electric car charger," as @Bletchleyite says, for a normal user, a 3KW charger will do. For a heavy user, a 7KW charger will suffice *​

"an electric oven" that would be another 3-4KW *​

"someone puts the kettle on" another 2.2KW *​

* As is almost certain to happen, higher power domestic electrical devices will be operating in a co-operative environment where a priority system will manage their access to power. Taking those three examples that you've given, the kettle would be regarded as a high priority device and have no restrictions on its 2-5minute bursts of use.
The cooker, usually wired to a 40A circuit might use more than 3-4 KW for short periods, - except for big feasts like Christmas etc., but the oven, and probably the hob elements (or electronic drives) will be operating under thermostatic control, so their aggregate draw will bwe well under maximum.
So that leaves the space heating and the car charger. The heating will of course be modulating on and off once the set temperature is neared and the car charger will oblige by disconnecting for short periods to give the other devices what they need when they need it.
Mostly, the car charger will have as much power as it wants overnight, unless the residents want a breakfast the size of a Christmas dinner every morning.
One other thing, the recommendation for electrical wiring is to replace it every 25-30 years. Of course, not everybody does that but 50 years really is an unusually long time to not have any improvement around the consumer unit when a pair of 16mm tails would need to be replaced. I haven't seen 10mm tails in a domestic installation since the early '70s. 80mm tails have been the minimum for 40+ years and I believe that 25mm is now the only standard. For cable the other side of the company fuse, that's the DNO's problem.
Those investing in a EV and needing a non-CO2 creating heating system will need to invest in a couple of short tails for their new consumer unit. Big expense?

13A is unlikely to be sufficient for long range electric cars.
People will expect to be able to fully recharge their car overnight.

They will want 10kW or more of charging power.

So if you are a road warrior wanting 80KWH per day, giving about 200+ miles every day, you will need to make some investment in your electrical installation. That is hardly the average driver though, - indeed it would be ridiculous to assume otherwise.

Many people are going to need their supplies upgrading to fit a reasonably fast electric car charger, which is going to be far more demanding than a heat pump.

A single 6-7KW (i.e. 32A protected circuit) circuit for a charger is likely to satisfy over 80% of user's needs.

 

[HSTEd]

As is almost certain to happen, higher power domestic electrical devices will be operating in a co-operative environment where a priority system will manage their access to power.

And there will be ten different interoperability standards and noone will support anyone elses, and there will probably have to be electrical work to put a meter in place to measure how much headroom is left!

One other thing, the recommendation for electrical wiring is to replace it every 25-30 years. Of course, not everybody does that but 50 years really is an unusually long time to not have any improvement around the consumer unit when a pair of 16mm tails would need to be replaced. I haven't seen 10mm tails in a domestic installation since the early '70s.

Currently I appear to have a pre nationalisation cutout.

They are replacing it cause I am moving my electricity meter outside, but since they will be using the same cable from the street I shall have to see how big the fuse on the new cutout is.

 

[apk55]

The substation at the end of the road could be a problem as well as the cables from it. Typically they are rated for an average household load of about 3KW continuous and probably 9KW peak (average through the estate), particularly in areas where gas is available for heating.
If you start putting on high contious loads for long periods (eg car chargers and heat pumps) the the substation and some of the cables in the ground will overheat and fail. Replacing several million substations will not be cheap and will take many years.

 

[AM9]

And there will be ten different interoperability standards and noone will support anyone elses, and there will probably have to be electrical work to put a meter in place to measure how much headroom is left!



Currently I appear to have a pre nationalisation cutout.

They are replacing it cause I am moving my electricity meter outside, but since they will be using the same cable from the street I shall have to see how big the fuse on the new cutout is.

Your installation is hardly typical. Of course there will be some that need more work, - but out of 30m residences?

The substation at the end of the road could be a problem as well as the cables from it. Typically they are rated for an average household load of about 3KW continuous and probably 9KW peak (average through the estate), particularly in areas where gas is available for heating.
If you start putting on high contious loads for long periods (eg car chargers and heat pumps) the the substation and some of the cables in the ground will overheat and fail. Replacing several million substations will not be cheap and will take many years.

Yes of course, and that will be part of the change. Comparing what we have now with what it might be at some point in the future just shows that work needs doing, not that it can't be done so let's keep burning hydrocarbons.

 

[HSTEd]

Your installation is hardly typical. Of course there will be some that need more work, - but out of 30m residences?

My understanding is that most of the terrace houses around me are in a similar condition.

 

[AM9]

And there will be ten different interoperability standards and noone will support anyone elses, and there will probably have to be electrical work to put a meter in place to measure how much headroom is left!



Currently I appear to have a pre nationalisation cutout.

They are replacing it cause I am moving my electricity meter outside, but since they will be using the same cable from the street I shall have to see how big the fuse on the new cutout is.

That will require a bit of leadership on the part of governments in their programme of meeting their carbon neutral targets. The EU will probably set the standard for much of the 230v/50Hz world*, despite wailing of the 'take back control' enthusiasts.
* Yes I know that the voltage and frequency doesn't need to be the same for it to work everywhere, but at the moment the powers in the US seem to be in denial of climate change..

My understanding is that most of the terrace houses around me are in a similar condition.

That's still a minority. The alternative is 'it's too difficult so we'll do nothing'. We might as well open up the coal mines again.

 

[HSTEd]

That will require a bit of leadership on the part of governments in their programme of meeting their carbon neutral targets. The EU will probably set the standard for much of the 230v/50Hz world*, despite wailing of the 'take back control' enthusiasts.

Really we should abuse the voltage tolerances to drive the voltage as high as we can.
For example setting the negative tolerance on the 230V supply to 0%.

230V -0%, +10% for example.

That's still a minority. The alternative is 'it's too difficult so we'll do nothing'. We might as well open up the coal mines again.

The average age of the housing stock isr ather large.
There will be many many millions of housings that will need new service connections.

 

[AM9]

Really we should abuse the voltage tolerances to drive the voltage as high as we can.
For example setting the negative tolerance on the 230V supply to 0%.

230V -0%, +10% for example.

That's the tolerance of the connected devices. The UK supply typically 240V rarely drops below 230v.

 

[GRALISTAIR]

They are going to have to make heat pumps a lot quieter before they can be widespread in most uk residential areas!

Yes, true, that's the main issue with them, aircon units similarly make a racket!

When I eventually retire back to the UK I will be used to it. I sleep with aircon on - absolutely needed in Georgia, USA.

 

[edwin_m]

You lets look at those assumptions:

"Then you have to add in an electric car charger," as @Bletchleyite says, for a normal user, a 3KW charger will do. For a heavy user, a 7KW charger will suffice *​

"an electric oven" that would be another 3-4KW *​

"someone puts the kettle on" another 2.2KW *​

* As is almost certain to happen, higher power domestic electrical devices will be operating in a co-operative environment where a priority system will manage their access to power. Taking those three examples that you've given, the kettle would be regarded as a high priority device and have no restrictions on its 2-5minute bursts of use.
The cooker, usually wired to a 40A circuit might use more than 3-4 KW for short periods, - except for big feasts like Christmas etc., but the oven, and probably the hob elements (or electronic drives) will be operating under thermostatic control, so their aggregate draw will bwe well under maximum.
So that leaves the space heating and the car charger. The heating will of course be modulating on and off once the set temperature is neared and the car charger will oblige by disconnecting for short periods to give the other devices what they need when they need it.

A single 6-7KW (i.e. 32A protected circuit) circuit for a charger is likely to satisfy over 80% of user's needs.

I suspect an electric hob would have to be a priority device - trying to keep something simmering and not boiling over will be infuriating if the hob randomly switches off part way through.

The other problem is legacy devices, which wouldn't have the capability to load-shed. We have two fairly hefty power showers and I think we're over nominal capacity if they're both in use, but the electrician said it would be OK and so far nothing has tripped out so far. Getting a car charger might also involve getting a heat pump and replacing the showers with hot feed.

 

[apk55]

I suspect an electric hob would have to be a priority device - trying to keep something simmering and not boiling over will be infuriating if the hob randomly switches off part way through.

The other problem is legacy devices, which wouldn't have the capability to load-shed. We have two fairly hefty power showers and I think we're over nominal capacity if they're both in use, but the electrician said it would be OK and so far nothing has tripped out so far. Getting a car charger might also involve getting a heat pump and replacing the showers with hot feed.

Fuses and MCBs can normally withstand small overloads for short periods. A typical domestic MCB will only trip at 1.4 to 1.6 times the rated current and this is after a delay depending on the severity of the overload. It will only trip instantly if the overload is 4 times the rated current. This is done to ensure reliable operation at the rated current as the actual current limit which is done thermally falls with increasing temperature.

 

[AM9]

Fuses and MCBs can normally withstand small overloads for short periods. A typical domestic MCB will only trip at 1.4 to 1.6 times the rated current and this is after a delay depending on the severity of the overload. It will only trip instantly if the overload is 4 times the rated current. This is done to ensure reliable operation at the rated current as the actual current limit which is done thermally falls with increasing temperature.

Yes, there are three ratings of MCBs where the delay varies, type B,C&D. The B is the normal type for domestic loads, the others are there for loads with long start-ups where current are higher than normal running levels, e.g. lift and hoist motors.

 

[Bobdogs]

Heat pumps are all well and good but what use are they to tower block, maisonette and those who do not have a garden.

 

[edwin_m]

I think we're talking air source heat pumps here. Essentially an air conditioner that can run backwards.

 

[AM9]

Heat pumps are all well and good but what use are they to tower block, maisonette and those who do not have a garden.

Remember that gas boilers, along with gas cookers, will be banned from new built houses from 2025, (if the Government sticks to its own ruling). That means buildings will be designed to accommodate other non-CO2 creating heating and cooking solutions. If they don't, they won't get approval from planners or building control.
So there will be appropriate provision for heat extraction or sinking (they are likely to be offered with heat pump heating and cooling). Add to that the reduction in allowed heat loss from the building itself, the issue of heat pumps is likely to be just another thing for builders to design in.
With the trimming of the market for new gas appliances, manfacturers are likely to turn to other heating solutions and that will pave the way for the administration to incrementally discourage the perpetual use of gas in the replacement of old systems. Ultimately, price adjustments in the cost of gas, like other hydrocarbon fuels (petrol/diesel) will be used to flush out the majority of remaining users. So expect the same sort of reaction that there was to the banning of tungsten lightbulbs.Like the stockpiled lightbulbs, the number of working boilers will steadily tend to zero.