UK Load in Amps on a mains single-phase circuit

[Carl Haworth]

I have a 230 Volt single-phase circuit with a 100 Amp cutout fuse and a 100 Amp MCB switch, so the supply is rated at 23 kVA.

Only about 13% of my total energy consumption is electricity. The remaining 87% is natural gas, supplying the following appliances (kW figures are net output power):-

22 kW boiler, 3 kW fan-flued convector heater. 8 Kw cooker.

After (if?) natural gas is turned off some time in the 2030s I can have 3-phase installed (at vast cost) to give me total kVA 55.15 at 230 Volts. As you can see, this offer is tied to reducing the supply capacity per phase to 80 Amps. So a connection from one phase (and the neutral) to my existing single-phase consumer unit would be rated at 18.40 kVA, leaving (I presume) 36.60 kVA for the 3-phase, once this is balanced (how is balancing achieved in this sort of situation, by the way?).

I will also, by then, need a powerful EV charging wallbox. An 11 kW one is for 3-phase only, as would be a 22 kW electric boiler (heat pump technology is not suitable for our home). If these two appliances consume 33 kVA, the 3-phase will be used to over 80% of its capacity, but it could be arranged that the two would never be on at the same time.

The 23 kVA single-phase circuit, with capacity reduced to 18.4 kVA, will need to carry extra loads:-

Cooker (12 kW maximum, 7 kW diversity), 3 kW convector heater.

I have done calculations of the peak consumption of the circuit as it stands now. I need to be confident that these are reasonably realistic, so that I can add the extra loads to the existing ones, and calculate the much higher peak consumptions with the extra loads added. I need to know if the total is likely to be within the reduced 18.40 kVA capacity of this circuit.

If this is relevant (please see below), the additional appliances mentioned for the single-phase, and both those for the 3-phase, have power factor 1.

As regards the existing load on the single-phase circuit, if a p.f. should be applied, it should be reasonable to use 0.8.

To work out first the load on the increased-load circuit as regards the its capacity/the capacity of the cutout fuse, I need to know if I should increase the kW of the total existing load by 1/0.8, so as to include apparent as well as real current, and get a figure in kVA. Or should use the total kW. At that point I would add the extra loads of the cooker and convector heater, as kVA and kW are identical.

Calculating Amps using kVA increases the load on the existing circuit by 25% if p.f. is 0.8, so, after adding the extra proposed loads, there is unsurprisingly considerably more "headroom" left in the circuit capacity if I calculate using kW.

I suspect that kW is the correct basis to use, because apparent current passes back into the grid after passing through the circuitry of an appliance. An appliance may draw, say. 10 Amps. If its p.f. is 0.8, 2 Amps are returned to the grid instantaneously as the 10 Amps are drawn. This is why a Watt/hour meter records using the voltage times the net current used up by loads, and so reads in kWh and not kVAh.

So I suspect that the cutout fuse draws the net current (full current less apparent current).

Which should I use for my calculation: kW or kVA? If the answer is kVA, then, in view of my comments just above, where have I misunderstood things?

I've tried to find an answer to this, but can't find any focussed guidance.

Can forum members enlighten me reliably, please?

Carl

 

[pc1966]

What matters to the supply is kVA, in fact more specifically the current. Some equipment draws more as volts go up (heater, etc) some less (switching power supplies with constant load).

Any big domestic loads have generally been heating which have a PF of 1 and it is more industrial where lots of AC motors are in use that you might assume 0.8 overall. I don't know off hand what large EV chargers are but I expect they are close to 1 by design.

However, if you are looking at the post-gas situation you really REALLY need to be looking at heat pumps of some form as they typically have a COP of around 3, so use around a third of the electric compared to the heat you use. To understand why please update your electrical plans to include to cost of the electric you are proposing to use, and then allow for 3-5% inflation (or possibly more) for the next 8 years....

 

[Carl Haworth]

What matters to the supply is kVA, in fact more specifically the current. Some equipment draws more as volts go up (heater, etc) some less (switching power supplies with constant load).

Any big domestic loads have generally been heating which have a PF of 1 and it is more industrial where lots of AC motors are in use that you might assume 0.8 overall. I don't know off hand what large EV chargers are but I expect they are close to 1 by design.

However, if you are looking at the post-gas situation you really REALLY need to be looking at heat pumps of some form as they typically have a COP of around 3, so use around a third of the electric compared to the heat you use. To understand why please update your electrical plans to include to cost of the electric you are proposing to use, and then allow for 3-5% inflation (or possibly more) for the next 8 years....

I would say we have quite a lot of appliances which have electric motors, which are pretty inductive machines so have a p.f. less than 1. All but 4 of our electric lamps (bulbs and tubes) are a mixture of discharge and LED. Both these have p.f. of 05 to 0.6. So I doubt that our overall p.f. is 1. It may not be as low as 0.8, though. I deliberately erred on the pessimistic side to ensure, if apparent Amps do have to be included when calculating the likely peak load of the whole circuit (so I need to use kVA, not kW, for arrive at the Amps), that I am not under-estimating the current.

So I still need to know whether I should calculate current from kVA (assuming a general p.f. of under 1) or kWh, when doing arithmetic acrobatics to arrive at the likely peak consumption.

As regards your comments about central heating

Our system needs, particularly in cold weather, a water temperature of around 80. Our gas boiler easily achieves this. We have relations who have installed a very recent, and enormous, ground-source heat pump system. They have 7 acres, so masses of space for the ground loop. Unfortunately, without 3-phase electricity (they are deep in the country), although they have a 23 kVA single-phase supply (as we do), they were not able to fit a heat pump powerful enough (with an even bigger ground loop) to raise the c.h. water temperature to above 60, at best. This matters less to them than it would would to us, where we do not want to ruin a lovely garden by installing a ground loop. Their property is a big barn conversion, so they were abele to install underfloor heating throughout.

Underfloor heating is out of the question in our 50+ year old house, and we do not want the huge radiators which are necessary with water temperatures of 60 at best.

In fact, with an air-source heat pump we would be lucky to get 50 degrees, is seems. Air-source would be our only heat pump option, and is certainly not suitable. Ground-source is much more reliable in heat energy output, but you have to have the SPACE for it, and masses of disruption to install it.

So an electric boiler is our only realistic option, and we need 3-phase to run it. That is horribly expensive to install (though a lot less than a not-powerful-enough heat pump), and to configure so it also supplies our 1-phase circuits, and the running cost is eye-watering. However, if it's the only way to guarantee the radiator and DHW temperatures that we need (DHW can be heated direly by electricity of course - you do not have to run a cylinder heat exchanger for it), so be it.

 

[plugsandsparks]

Check out the latest heat pumps from Stiebel. I am wrestling with one at the moment that uses "Hot Gas recovery" - Its an extra heat exchanger around the main compressor. The temps coming off this beast are so high >100 degrees C that i am having some issues with over temp on the DHW tank and pumps !!
This is a GSHP but the concept is no different in ASHP.
I was quite frankly (and i am a cynic) amazed at where these sort of temp were coming from in heat pump tech but i can assure you they are real and makes electric heating for either DHW or CH largely redundant (albeit high initial outlay)

 

[snowhead]

Natural gas is NOT being turned off in the 2030's.
Sometime by or in the 30's the gas supply will have 20% Hydrogen mixed with it as most current appliances will work O.K .
Later, maybe 40's or 50's the whole network is likely to be 100% hydrogen, but that will require repiping of some of the network and modifying or replacing some appliances.

Trying to plan for something even in 10 years time is pointless.
Too much can change and new developments could have come online.

It may even be that they've managed to roll out the current gen 2 "Smart meters" into close to 100% households, but I would put too much hope on that happening.

 

[Carl Haworth]

Check out the latest heat pumps from Stiebel. I am wrestling with one at the moment that uses "Hot Gas recovery" - Its an extra heat exchanger around the main compressor. The temps coming off this beast are so high >100 degrees C that i am having some issues with over temp on the DHW tank and pumps !!
This is a GSHP but the concept is no different in ASHP.
I was quite frankly (and i am a cynic) amazed at where these sort of temp were coming from in heat pump tech but i can assure you they are real and makes electric heating for either DHW or CH largely redundant (albeit high initial outlay)

Thanks. That's very interesting. The Stiebel design sounds like waste heat recovery - along the lines of what happens in a condensing combustion boiler exhaust (and when you take your foot off the loud pedal on a car with "regenerative braking"!). "Every little (or lot?) helps".

I can't help wondering, though, if the major contributor to the terrific performance of the heat pump system that you are installing is to the volume of the heat energy source (the ground). If you have a ground loop with a really huge surface area, the water arriving at the first heat exchanger contains more heat energy per litre than water from a loop with a smaller surface area. The temperature rise of the water from start to finish may be little different, but that's not the key issue. If you have a heat pump powerful enough to condense the heat energy out of a sufficiently large volume of water, the temperature of the gas in the vapour compression circuit will be higher than in a smaller/less powerful system, and so on. Waste heat recovery from the motor will make the pump effectively more powerful than its rating, but probably assists efficiency rather than making a large contribution to it.

Please do correct me if my above assumption is wrong.

The difficulty that my sister and co encountered when their system was being designed was the insufficient spare capacity in their 23 kVA single-phase electrical supply to drive a gshp which could have been much larger (they had built on a big plant room for it), and could have processed much larger volumes of water, compressing a much larger volume of gas in the VC circuit to a much higher pressure so as to transfer much more heat energy to the house loop. They would have been happy to pay more for a sufficiently powerful system, but could not improve on 23 kVA owing to the absence out in the country of a 3-phase supply from a nearby substation. As I have discovered, although the reality of 3-phase is a bit of a damp squib, in our case (and theirs, had it been available), it would increase a total kVA of 23 to 55.15 (to 69 if our DNO could be persuaded to leave us with a 100 A limit per phase!).

I agree that the hp concept is the same irrespective of the heat energy source, but ground temperatures even only a metre below the surface are far more stable over the changing seasons than air temperatures.

I fear that there risk being lots of very unhappy people, used to the water temperatures and power delivery capacities of combustion boilers, who will have fallen for the ashp sales pitch which will soon start circulating vigorously on the back of the government subsidy for installing this variant of hp technology.

 

[plugsandsparks]

Yes, you on the right lines. This is a 59KW GSHP, brine is the medium circulating in the ground loop. The difference in temperature brine in/out maybe only a degree or two, but all it needs to do is turn the Fgas inside the GSHP from liquid to gas so it can run through the heat exchanger and give up its heat and turn back to liquid. Admittedly the unit has a large compressor to push the Fgas around the heat exchanger and normally heat pumps are more efficient in heat mode than cooling mode as the heat generated by the compressor easily provides some extra heat transfer into the Fgas too aid liquid to gas transition. What Stiebel have done is more formalise this heat recovery into direct hot water to aid both DHW and CH and breaks the temp barrier that normally makes heat pumps most efficient at 35 degrees. The system i am working on is set to 50 degrees fixed value direct to buffer tanks which then heat the house, hot water tank, swimming pool and warm air heat exchanger for the swimming pool air handling unit, so it has alot to do and raising the temps available means i dont need electric immersion for Legionnaires and provides hot water at a high temp for mixing further down the line. As mentioned the issue i was wrestling with was because the hot water tank rose to 74 degrees which is too much for bog standard pumps.

 

[Carl Haworth]

Natural gas is NOT being turned off in the 2030's.
Sometime by or in the 30's the gas supply will have 20% Hydrogen mixed with it as most current appliances will work O.K .
Later, maybe 40's or 50's the whole network is likely to be 100% hydrogen, but that will require repiping of some of the network and modifying or replacing some appliances.

Trying to plan for something even in 10 years time is pointless.
Too much can change and new developments could have come online.

It may even be that they've managed to roll out the current gen 2 "Smart meters" into close to 100% households, but I would put too much hope on that happening.

You are right about planning so far in advance. I just want to see how the land lies IF methane is turned off.

I don't see how a gen 2 Smart meter would allow me to view and record current consumption peaks. Am I wrong?

You're not the first person to tell me that the big NG turn-off won't happen. My wife took the same line as soon as reports started appearing threatening this, and Boris did not help by assuring all the "worried well" that they would not be forced to change their gas boiler, but simply would not be able to buy a replacement after (I think) 2035.

Which? has joined the the chorus of reassurers with (unsurprisingly) their version of the Boris message.

None of the reassurers suggests up to when (after 2035) it will remain possible to run a gas boiler. However, as you say, probably (no more than that), first a mixture of H2 and NG will replace 100% methane/ethane, then, IF there is enough of it (a big if, I suspect), pure H2 - after changing the grid trunk pipelines with new ones made of a steel which does not react terminally to green H2. Oo, er!

For various reasons, the above seems a question more of if than when, so one can't be categoric about combustible gas for boilers if you look beyond 2035 (and if that is a reliable date!).

I hadn't swallowed the doom scenario hook, line and sinker, but I would prefer to find a way around our own dependence on NG, because it has become a political, as well as an environmental, weapon.

At the moment, dumping NG and switching to electricity doesn't solve this problem in the UK because its generation here is so dependent on NG. R-R's electricity generation project could much reduce that dependence. But even there, I can't help wondering if it is wise to proliferate nuclear reactors - on safety/military defence grounds. Also, they need planning permission to be built, and there is likely to be resistance in areas where there are the sort of worries I have just mentioned.

Dare I suggest that our bottom line for generating electricity might, in the end, have to be to switch back to coal (we've still got oodles of that filthy stuff)? It needn't be so filthy now, but it's the very opposite of green.

 

[Carl Haworth]

Yes, you on the right lines. This is a 59KW GSHP, brine is the medium circulating in the ground loop. The difference in temperature brine in/out maybe only a degree or two, but all it needs to do is turn the Fgas inside the GSHP from liquid to gas so it can run through the heat exchanger and give up its heat and turn back to liquid. Admittedly the unit has a large compressor to push the Fgas around the heat exchanger and normally heat pumps are more efficient in heat mode than cooling mode as the heat generated by the compressor easily provides some extra heat transfer into the Fgas too aid liquid to gas transition. What Stiebel have done is more formalise this heat recovery into direct hot water to aid both DHW and CH and breaks the temp barrier that normally makes heat pumps most efficient at 35 degrees. The system i am working on is set to 50 degrees fixed value direct to buffer tanks which then heat the house, hot water tank, swimming pool and warm air heat exchanger for the swimming pool air handling unit, so it has alot to do and raising the temps available means i dont need electric immersion for Legionnaires and provides hot water at a high temp for mixing further down the line. As mentioned the issue i was wrestling with was because the hot water tank rose to 74 degrees which is too much for bog standard pumps.

All very interesting.

I take it that the over-high water temperature affects the loop heating the buffer tanks, so this loop is at well over that temp. 74 degrees may be enough for radiators, unless they are sized for a lower temperature, but possibly too hot underfoot for underfloor loops (and might cook floor coverings)?

I don't understand about the buffer tanks. Are they to even out the normal ups and downs of the water temperature in ch etc loops?

My sister's system, as far as I understand its details, uses the water heated by the heat exchanger powered by the gas temperature in the VC circuit of the heat pump directly for the underfloor loops and the coil in the DHW tank. The temperature of this water being only around 60 degrees in her installation means that the unvented cylinder has to have two immersion heaters (one at the bottom, plus one to heat up water at the top, to top up during high electricity cost periods.

The need for direct electrical heating here meant, to her disappointment, that the whole house just missed the top energy band on its EPC.

Are the pumps that you refer to circulating pumps for the heat exchangers supplied by the buffer tanks (house loop/s etc)? If so, I'm surprised that they are not suitable for 74 degrees. I must be missing something, because the 25 year old Grundfoss pump which sends the water heated by our gas boiler round the CH. and DHW loops has to stand up to 82 degrees (when we have the boiler temp at max in cold weather). This 3-speed standard CH pump still works quietly, and well. What's different about the pumps which have been causing your problems?

Obviously, provided the water in the DHW heating loop is well over the cut-out temp of the cylinder thermostat, the stored DHW will achieve the set temperature. Certainly we have no trouble keeping our DHW at 60 degrees when the loop temperature is over 80. The loop just heats the DHW faster when it is around this level than in seasons when the loop is at more like 70 degrees (but there is then less work for the loop water to do to achieve a cylinder temp of around 60, so there's probably not much difference between the two loop temperatures and the seasons to which they relate and the recovery speed of the DHW temp).

What can you do about the water temp in the buffer tanks, if it is too high? Is the ground loop too big (it may be very difficult now to shorten)? Can the speed of the heat pump be regulated? If neither of those solutions is possible/satisfactory, can you change the heat pump for one suitably less powerful?

MOVING ON

Although my wife won't hear of digging up even the lawn of our back garden, I'm very interested by your findings as regards the performance of a Stiebel gshp (or, presumably, ashp?) system which uses waste heat from the pump compartment to boost the temp of the loop heating the buffer tanks (or, presumably, the CH and DHW loops direct).

I don't know the make of hp in my sister's system, but it may predate the design improvement that you highlight. The system itself was designed and supplied by Ice Energy. Their contribution was apparently very impressive (not just the sales pitch!), but many problems were encountered owing to mismatch between the initial bland assurances of their builder, and the ignorance, which was revealed later, of his plumber. This was all sorted out satisfactorily in the end, but Ice Energy had to come several times to "hold the plumber's hand".

I believe that Ice Energy gave a 10-year warranty on the design and components, so the fact that this apparently very competent and helpful firm has subsequently ceased trading must be a potential worry for my sister , and is disquieting news for people looking for an honest and competent system designer/components supplier I wonder if, as can happen, an over-generous warranty policy plus too many post-installation problems. made it impossible for IE to continue trading profitably.

Your reports and comments mean that I would be interested to know approximate surface area of the pit which would have to be dug to over a metre deep to accommodate a ground loop for a gshp powerful enough for our own home. Our "heat only" gas boiler provides the heat energy for radiator and DHW heating. It is rated at 28 kW. The manufacturer claims 80% efficiency (it's a fan-flued non-condensing boiler), but independent sources suggest more like 76%. So the maximum heat output is probably around 22 kW. A local "engineer" who services this boiler (when it needs it, which is not often) considers that it is over-sized, but our experience in very cold weather is that it is about right. It may be a bit over-powerful, but that is preferable to having one which won't get the radiators hot enough in very cold weather!

Assuming that about 22 kW is the heat energy requirement of our home (ch and DHW), can you give me an ideal of the length and width of the pit that would be needed for a gshp ground loop connected to the type of motor-heat-recovery hp that you have told me about?

We are in the Trent valley, about 20 miles north of Newark. We are on flattish ground, about 75 metres above sea level. Our subsoil is clay, and we have an obviously variable, but usually quite high, ground-water table. So I would say that our ground is good, maybe very good, for heat pickup during most seasons by a gshp ground loop.

If the pit (excluding the trench between the back of our long garage, where the pump would have to live, and the ground loop proper) is well within the area of our back lawn, my wife might reconsider her opposition to digging up our lawn. However, she also points out that (a) we may well be able to continue using gas in the from of methane/ethane, methane+H2 and even eventually H2 only, for another 20+ years, and (b) even if we felt it best to eliminate our dependence on gas sooner rather than later, the cost of an electric boiler, and the 3-phase supply to accommodate its load, would be a minnow in comparison with the cost of installing a gshp system. The running cost of the latter would be far lower than that of an electric boiler, and even that of running our present gas boiler, but it would take decades to recover from such savings the difference in installation costs.

 

[UNG]

While you are concentrating on the heating output and trying to achieve something similar to what you have now in the future you have to bear in mind a lot of the newer technologies rely on an increased level of property insulation to deliver the most effective results
I was always a bit sceptical of the passivhaus building methods until I got involved in a project that a local vet was building, he is very into the eco concept and built a new surgery to passivhaus spec with heat recovery, ASHP, solar panels and masses of insulation, the end result is very effective and costs very little to run but it does involve more cost. One of this guy's other projects was renovating his own house Low Energy Building Consultancy | Kingsleypassivhaus | Frodsham - https://www.kingsleypassivehouse.com/ it might seem a bit extreme but with the ever rising energy costs it has to be an option

 

[Carl Haworth]

While you are concentrating on the heating output and trying to achieve something similar to what you have now in the future you have to bear in mind a lot of the newer technologies rely on an increased level of property insulation to deliver the most effective results
I was always a bit sceptical of the passivhaus building methods until I got involved in a project that a local vet was building, he is very into the eco concept and built a new surgery to passivhaus spec with heat recovery, ASHP, solar panels and masses of insulation, the end result is very effective and costs very little to run but it does involve more cost. One of this guy's other projects was renovating his own house Low Energy Building Consultancy | Kingsleypassivhaus | Frodsham - https://www.kingsleypassivehouse.com/ it might seem a bit extreme but with the ever rising energy costs it has to be an option

Several vectors have been generated by my original innocent question of whether the maximum current load on a domestic circuit, in relation to the maximum amperage limit (or 80% of that) of the supply, should be calculated on from the peak use in kW (dividing Watts by the supply voltage), or, if there is reason to consider the particular installation to have a power factor of less than 1, in kVA (finding the higher amount of Amps from this in the same way).

I still don't have an answer to that question, but I have had several "non-answers" which are very interesting.

Your intervention is among these vectors.

We don't want to rebuild, or move, but we do accept that the already well-above-average performance of our 1968 house could be further improved. You imply that this should not necessarily be done only if clearly cost-effective over a reasonable term. We are prepared to look at this, although we do not see at present how this house could be made substantially more suitable for our needs, even with major disruption.

But we will look at the website whose address you have provided. Many thanks!

RE YOUR FIRST WORDS ABOVE

My original question to members of this website arose from the task I had set myself of trying realistically to assess how many extra Amps could be absorbed safely by our existing single-phase 23 kVA mains circuit.

That was with the view of trying to establish:-

What extra electrical load would be involved by replacing by electrical appliances our gas boiler, a gas convector heater in our lean-to utility room (this heater may no longer be strictly necessary due to substantial improvements to the insulation of that room post-dating the addition of the heater in 1997), and our venerable but brilliant Cannon gas cooker (with fold-way high level grille/rotisserie: 5.275 kW, but that will be the energy input figure).

Additionally I would need to take into account that an electric c.h. boiler, replicating the 22 kW output of our gas boiler, would need 3-phase current. This, according to our DNO, would reduce the kVA of the single-phase input from 23 to 18.4. Not good news!

I know our typical annual gas consumption over enough years to have a realistic estimate of it for one year.

With the well authenticated figure of 76% for the output of our gas boiler in relation to its 28 kW input, I used, as you noticed, the same rating (22 kW to be on the safe side) for a proposed electric boiler.

I have now been struck by how much greater is the annual requirement for kVA if we went "all-electric" than it shows when adding our current consumptions (in kVA for present single-phase installation to our gas consumption.

I estimated consumptions for the three appliances which would be replaced, and added these to our current single-phase consumption in kVA. I calculated the consumptions of the replacement electric appliances, with use periods and levels of power drawn to match what I estimate applies now to our mixed installation.

The total known annual consumption of gas as useful energy is around 20,000 kWh.

But I found it impossible to arrive at a figure as low as 20,000 kWh/pa for the present boiler alone with what seems to be its work pattern Modifying this pattern to produce a suitable figure (well below 20,000 because I have to include figures for the heater and cooker) have made it pretty clear that the present boiler is too powerful for our 2019-21 needs, even if was only slightly OTT when specified and fitted in 1997.

In fact, it looks as if we need only about a 15 kW boiler, or even less. Interestingly, our local service man spontaneously declared last year, when he serviced the boiler, and changed the gas valve (the only major component that this boiler has ever needed - apart from flue fans, which I can fit legally myself, that 15 kW was "quite enough for a house of this size and kind".

So we'll try to find someone qualified in energy assessment to produce a heat requirement for our home before I do much more work on my forecast.

 

[plugsandsparks]

The hot gas recovery is currently piped just to DHW cct. The tank temp of 74 is measured half way down the tank. The pump that failed is used to circulate around the DHW circuit. Even when the tank is not calling for heat the hot gas recovery is so strong it conducts through the pipework. As mentioned its an issue that is ongoing.

You asked a question re-KVA loads etc etc . I cannot work out what you are trying to work out but FWIW.

Take your heat loss for the house, add a portion of your DHW demand, based on heat exchanger capacity and usage / now many people are in the house, this will give a base demand in KW, lets say its 24KW.
If you use a heat pump at 50 degrees, check the COP for the heat pump at 50 degrees against various environmental conditions, so lets say use a COP of 3. Divide your 24KW by 3, this gives 8KW, lets say PF is 0.9, then your KVA for your heat pump is 8 divided by 0.9 = 8.9KVA Nett. If using a TP supply then this will draw approx 15A. If on a single phased supply it will be approx 40A.

Now of course you need to find a specific heat pump that has a small excess above your worst case heat demand of 24KW, this could be a 30KW heat pump, whatever it is you can proportion the above figures accordingly or simply choose the heat pump and look at the manufacturers data for max current draw .

The ground loops were designed by the manufacturer so again you need to talk to them.

Heat pumps can be quite simple and output direct to radiators or UFH, you can use mixers to ensure the temp around the rads or UFH are to the designed temp, e.g. 40 degrees for UFH and 50 for rads.

Buffer tanks are used in more complicated systems when the demand can be very variable and it stops the heat pump cycling on low demand and can give a more immediate response to sudden high demand

 

[Carl Haworth]

The hot gas recovery is currently piped just to DHW cct. The tank temp of 74 is measured half way down the tank. The pump that failed is used to circulate around the DHW circuit. Even when the tank is not calling for heat the hot gas recovery is so strong it conducts through the pipework. As mentioned its an issue that is ongoing.

You asked a question re-KVA loads etc etc . I cannot work out what you are trying to work out but FWIW.

Take your heat loss for the house, add a portion of your DHW demand, based on heat exchanger capacity and usage / now many people are in the house, this will give a base demand in KW, lets say its 24KW.
If you use a heat pump at 50 degrees, check the COP for the heat pump at 50 degrees against various environmental conditions, so lets say use a COP of 3. Divide your 24KW by 3, this gives 8KW, lets say PF is 0.9, then your KVA for your heat pump is 8 divided by 0.9 = 8.9KVA Nett. If using a TP supply then this will draw approx 15A. If on a single phased supply it will be approx 40A.

Now of course you need to find a specific heat pump that has a small excess above your worst case heat demand of 24KW, this could be a 30KW heat pump, whatever it is you can proportion the above figures accordingly or simply choose the heat pump and look at the manufacturers data for max current draw .

The ground loops were designed by the manufacturer so again you need to talk to them.

Heat pumps can be quite simple and output direct to radiators or UFH, you can use mixers to ensure the temp around the rads or UFH are to the designed temp, e.g. 40 degrees for UFH and 50 for rads.

Buffer tanks are used in more complicated systems when the demand can be very variable and it stops the heat pump cycling on low demand and can give a more immediate response to sudden high demand

My original question posted on this website is ("is" because it hasn't been answered! yet!):-

I need to be able to compare the present peak load of my single-phase circuits with the capacity of the supply (80 Amps. at 80% of the maximum supply capacity of 100 Amps), in order to see how much "headroom" there is for additional single-phase appliances needed if we change our fuel from the present combination of electricity and gas to electricity only.

I know what my present load is in kWh per year, so I can divide that figure by 365 and then 24 in order to find the load per hour. From this, I can estimate likely peak loads.

However, should I be calculating the load in Amperes obtained from the consumption recorded by the domestic meter, if the installation operates, which seems very likely, at a power factor of less than 1? If I need to take p.f. into account I must calculate the load as kVA (real current plus apparent current), and find the Amps from that figure.

For example, if my annual consumption is 4,500 kWh, at p.f. 0.8 the consumption of real plus apparent current is 4,500/0.8, which is 5,625kVA.

The current for 4,500 kWh at 230 Volts over 1 hour (divide by 230 x 365 x 24 and multiply by 1,000) is 2.233 Ah.

For 5,625kVA it is 2.79 Ah.

If I quadruple the mean Amps to estimate peak instantaneous current, we have 9.32 Amps where the base unit of power is the kW. and 11.166 Amps where it is the kVA

This difference between 9.32 and 11 66 Amps is immaterial on my present consumption.

But if I want to increase the load on this circuit by adding new appliances with a total load of 16.250 kW and p.f. 1, I have to add (16,250/230) Amps:. That gives 70.652 Amps as a possible extra peak load.

Adding this to:-

9.32 Amps, where the base unit for the existing consumption is the kW, gives a total instantaneous load of (9.32 + 70.65) 79.97 Amps, which is within 80% of the maximum capacity of the 100 Amp maximum supply.

But adding it to:-

11.166 Amps. where the base unit for the existing consumption is the kVA because the installation is estimated to operate at power factor 0.8, and because current loads have to include apparent as well as real current. This gives a total instantaneous load of (11.166 + 70,65 Amps) 81.82 Amp, which exceeds 80% of the capacity of the 100 Amp maximum supply.

So it makes what can be a very significant difference to establishing what peak current can be added to an existing installation if the current load on the supply has be calculated including apparent current, where the current installation operates at a power factor of less than 1, compared with assuming that the p.f of the installation is 1, where kW and kVA have the same value.

SIZE OF PIT FOR THE GROUND CIRCUIT OF A GIVEN GSHP

What firm do you suggest that I contact?

You are right that I need to establish the heat energy requirement for our house. 22 kW was calculated by the firm that installed the present boiler in 1997, converted gravity DHW heating to pumped, and modernised and slightly extended the original twin single pipe circuits by putting some radiators onto two-pipe.

This house had had cavity wall insulation injected by its previous owner in 1972 (I have the certificate). The U value of the cavity walls was already much better than average due to the use of lightweight (aerated) blocks for the inner leaf of these walls, and for internal partition walls.

Loft insulation was vestigial. We upgraded most of the windows to double glazing before 1997. But, since then, we have had much better high-performance Upvc double glazing installed throughout and have greatly improved the loft insulation to a standard where it has a performance similar to that of 300 mm mineral fibre blanket laid on the top of the upstairs ceilings.

In 1998 we added large and well insulated porch, giving us a direct route to the forward section of the garage, and separated the back section of the garage from the boiler/utility room, which opens into it, by a very substantial double-skinned-with-cavity partition (this created a workshop/utility extension room, leaving a large garage forward of it)

The very large flat roof area covering porch, garage, workshop and the main utility room was re-roofed in 1998 using insulated boarding.

Between 1997 and 2004 I completed the modernisation of the radiator circuits which had been started in 1997.,but left as "hybrid pipework".

So the heat requirement of the house should be considerably lower now than the 22 kW which was calculated (rather generously, I suspect) in 1997.

We had our boiler serviced last October. The service man (who, as usual, is always looking for the opportunity to change an "old" boiler") commented that he thought our existing boiler far too powerful for our house (as far as he knew anything about it!). He considered that we should not need more than about 15 kW.

He may be right, and the requirement is probably a lot lower than 22 now, but this needs establishing against a full U-value calculation for the house.

I intend either to do this calculation myself, or get it done by an energy assessor.

 

[James]

You should not be trying to calculate maximum demand by dividing daily consumption by 24 or any other period like a month or year.

for example if you have a 70A constant draw from a heat pump, a shower whilst boiling the kettle or cooking dinner could blow the main fuse even though your daily average will be well below the maximum available supply.

 

[Carl Haworth]

You should not be trying to calculate maximum demand by dividing daily consumption by 24 or any other period like a month or year.

for example if you have a 70A constant draw from a heat pump, a shower whilst boiling the kettle or cooking dinner could blow the main fuse even though your daily average will be well below the maximum available supply.

Thanks!

I do realise this. I gave notional peak consumptions to highlight the issue raised by my original question posted on this website, which has not been answered (yet).

I will probably eventually monitor consumption over at least a year, using a current monitor which plots a graph, and whose output can be connected to my PC. The monitor will probably have to be re-set after its maximum run time, but I think that I will end up with a series of graphs stored on my PC, each for a period of well under a year. and which, even if they are not absolutely contiguous at the joins, should tell me what I need to know

If you know of a neater and quicker way of doing this, do please tell me.

Can you also answer my kW/kVA question?

 

[Avo Mk8]

I'm not able to answer your question I'm afraid, but have a comment or two:

You mention assuming a PF of 0.8 in your calculations.
I think it's most unlikely the PF would be as low as 0.8. Reports on the interweb (therefore must be true ) suggest a typical UK domestic figure for a household of around 0.95.

For a modest outlay you could purchase a meter to find the current position (sorry!) - just an example below:
(there are many cheap direct reading displays, but most seem to have a current transformer that is a rigid toroid, so cannot be placed on incoming tail - maybe through design!)

PEACEFAIR 100A Multi-function Meter Voltage Current Power Factor Frequency Energy Tester physical parameters(1*Meter+ 1*open type CT) : Amazon.co.uk: DIY & Tools

PEACEFAIR 100A Multi-function Meter Voltage Current Power Factor Frequency Energy Tester physical parameters(1*Meter+ 1*open type CT) : Amazon.co.uk: DIY & Tools

www.amazon.co.uk

AC Digital Multimeter Ammeter Voltmeter 80-260V Current Transformer LCD Display | eBay

Excellent Visual Experience - The LCD HD display screen, combined with the backlight function, makes it easy to read the displayed data, giving you an excellent visual experience. Monitor AC circuits more comprehensively!

www.ebay.co.uk

If you have a smart meter, depending on the model, you may find sequencing through the displays shows not only the usual kWh, but kVArh as well, in which case you could work out PF from that.

 

[Carl Haworth]

I'm not able to answer your question I'm afraid, but have a comment or two:

You mention assuming a PF of 0.8 in your calculations.
I think it's most unlikely the PF would be as low as 0.8. Reports on the interweb (therefore must be true ) suggest a typical UK domestic figure for a household of around 0.95.

For a modest outlay you could purchase a meter to find the current position (sorry!) - just an example below:
(there are many cheap direct reading displays, but most seem to have a current transformer that is a rigid toroid, so cannot be placed on incoming tail - maybe through design!)

PEACEFAIR 100A Multi-function Meter Voltage Current Power Factor Frequency Energy Tester physical parameters(1*Meter+ 1*open type CT) : Amazon.co.uk: DIY & Tools

PEACEFAIR 100A Multi-function Meter Voltage Current Power Factor Frequency Energy Tester physical parameters(1*Meter+ 1*open type CT) : Amazon.co.uk: DIY & Tools

www.amazon.co.uk

AC Digital Multimeter Ammeter Voltmeter 80-260V Current Transformer LCD Display | eBay

Excellent Visual Experience - The LCD HD display screen, combined with the backlight function, makes it easy to read the displayed data, giving you an excellent visual experience. Monitor AC circuits more comprehensively!

www.ebay.co.uk

If you have a smart meter, depending on the model, you may find sequencing through the displays shows not only the usual kWh, but kVArh as well, in which case you could work out PF from that.

Thanks!

I am puzzled that it is proving so difficult to establish whether the current load on a circuit, hence on its cut-out fuse, is the full current drawn (real plus apparent current) or the net current (real current only).

However, your suggestion of 0.95 p.f. for a typical domestic installation is not only less pessimistic than my 0.80, but may be more realistic. If the latter, it makes it less critically important to know whether I should be working in kW or kVA!

I will ask Octopus Energy about the Smart meter that they say they want me to agree to have. I would normally resist this to the wire (sorry!), because I fear large and disruptive implications (eg, meter position, and so on) for an installation like ours. I suppose(!) that we wouldn't have to meet the cost of replacing the supply over a distance of around 8 metres under our drive in order to bring it to a new, external meter box, but we would be left with a load of fall-out as regards "making good".

It would be crazy to get involved in this unless we were installing 3-phase at the same time. And we're certainly not ready to make a decision on this at the moment. In any case, if our DNO means what they say, our supply amperage would be reduced to 80 Amps per phase, rather than the present 100 Amps of our single-phase, so we'd be obliged to have whatever form of electrically powered heating we might decide on (when we are ready!) on 3-phase. New large loads would be needed for the single phase, which would be at (safe level) 80% of 80% the present capacity (64 Amps).

CURRENT MONITOR

Many thanks for the links, which I will follow.

I'm already investigating a monitor: Omega OM-DCEV. This uses two clamps on the phase wire:-

https://uk.farnell.com/omega/om-dvcv/data-logger-ac-voltage-current/dp/3410288?gclid=EAIaIQobChMIrJaL9uTP9QIV2MLVCh22wQyYEAQYAiABEgIMBfD_BwE&mckv=_dc|pcrid|565467377247|plid||kword||match||slid||product|3410288|pgrid|125527087130|ptaid|pla-301834726710|&CMP=KNC-GUK-GEN-SHOPPING-SMART-EDMIUMROAS-Test821&gross_price=true#anchorTechnicalDOCS

Do you have any knowledge of this monitor?

I've emailed Omega (whose price is £265 (they are - or appear to be! - the manufacturer) to try to establish points such as:

- Will it record total current or only p.f. current?

_ With a PSU replacing its AAA batteries, has it enough memory to log current over a year, or will it have to removed at intervals (what intervals?) to transfer the data collected to date to my PC, and then be replaced and re-started.

I'm hoping for an answer! (I'm sure you know the feeling!)

Best wishes,

Carl





.

 

[plugsandsparks]

Fuse responds to the VA load, real and apparent

 

[Carl Haworth]

Fuse responds to the VA load, real and apparent

 

[Carl Haworth]

Thanks very much - as I feared!

However, AVO 8 MKO (hope i've got that right) considers that 0.95 is a more realistic p.f. for a domestic installation than 0.60, so the difference between the two narrows considerably!

Whew!