Is this inline electric heater too many amps?

[Jeremy Harris]

60m² is fine for a single ring final, so my guess is OK (there's no limit to the number of outlets on a single ring final circuit, just an area limit).  You will need to add the studio power and lighting circuits to the earlier load estimate though.  You could probably get away with a radial power outlet circuit for the studio at 16 A, plus a 6 A lighting circuit, so that adds another 13 A + 3.96 A = 16.96 A to the total, bringing it up from 67 A to nearly 84 A, so just too high for your 80 A supply, even without a water heater (but bear in mind that I've guessed the load for the ASHP and cooker).

 

I think you need to sit down with your electrician (as he'll be the one signing this off) and discuss all the loads, both in the house and in the studio, and work out a wiring configuration that enables you to stay within the maximum demand limit.  Some electricians are a bit more forgiving than others when it comes to applying diversity to loads to check that the maximum load is within limits, although strictly speaking they should work to the letter of the regs. The flip side is that sometimes a strict interpretation might be applied, too.  You can probably help by ensuring that you know things like the ASHP maximum input power and the cooker maximum input power.  Opting for a separate oven and hob, or perhaps two ovens and hob, can increase the load a lot.  For example, we have two built in ovens plus an induction hob and the maximum peak load on the cooker circuit is 63 A, not the 40 A I assumed earlier.

 

 

 

 

[Roz]

The electrician is having a think about it, so I'll see what he says later. I have also asked the plumber for a price on an unvented cylinder. Whilst clicking links on Amazon I happened across these.... my instincts tell me it wouldn't work to have one of these with a refillable bottle of gas connected to it, and it plumbed in to the regular shower mixer... but I am not sure why. I know it would need to have a flue and that sounds a pain.

 

I was trying to avoid using gas, but I'm nervous about how much the UVC is going to come in at! Perhaps this would do for a while until we sorted something else out.

 

https://www.amazon.co.uk/dp/B07D6YW742/ref=psdc_1939510031_t3_B014GZVWLK

 

EDIT i think maybe its a safety regulations thing

Edited July 30, 2019 by Roz

[ProDave]

That is a bigger version of the instant gas water heater in our static caravan.  It worked reasonably well withing the limitation that ours is a smaller one rated at only 11KW so you don't get a fantastic shower flow, but that one claims to be 32Kw so should be plenty.

 

You trade the expense of a G3 UVC sign off, for the expense of a gas safe sign off, and having a pair of cylinders on an autonatic changeover.

 

You would need to first check with your gas safe man that particular unit is okay for permanent instalation in a building, i.e can you get the appropriate flue parts and does it meet regulations for a habitable building?

[Roz]

3 minutes ago, ProDave said:

 

You trade the expense of a G3 UVC sign off, for the expense of a gas safe sign off,

Thanks Dave I think this is good advise and perhaps not worth the hassle if I wasnt seeing it as a long term solution

[Roz]

Guyssss.... I just spoke to another electrician who said it would be fine to use the 11kw water heater ??

[Jeremy Harris]

8 minutes ago, Roz said:

Guyssss.... I just spoke to another electrician who said it would be fine to use the 11kw water heater ??

 

 

Does he know all the other loads you have in this installation, though?

 

Worth checking, as blowing the company fuse is a PITA if it happens (and makes a fair old bang).

[Roz]

4 minutes ago, JSHarris said:

 

 

Does he know all the other loads you have in this installation, though?

 

Worth checking, as blowing the company fuse is a PITA if it happens (and makes a fair old bang).

We chatted about it, talked about the ASHP and sunamp, granted he doesnt know what one is so wont know the rating on it, I'll make sure I triple check before going ahead with anything either way though and send him all the details I can if we go further with it.

[Jeremy Harris]

23 minutes ago, Roz said:

We chatted about it, talked about the ASHP and sunamp, granted he doesnt know what one is so wont know the rating on it, I'll make sure I triple check before going ahead with anything either way though and send him all the details I can if we go further with it.

 

The Sunamp (if it's an electric one) is the same rating as an immersion heater, so draws about 13 A nominally.  The ASHP demand will depend on the model, for an inverter controlled one it will be somewhere around 10 A typically, maybe a bit less if it's a small one.  The cooker demand is the highest load, after the water heater.

 

No matter how I do the maximum demand calculations I can't get the result to comply with BS7671 Chapter 3, section 311.1, for either an 80 A or 100 A rated supply, if you have that 11 kW water heater.  Might be worth mentioning compliance with this section of the regs to the electrician, as it has been known for the total demand to be overlooked before now (I've done it myself, just by not thinking about it...).  This is almost the most optimistic set of load estimates I can come up with, and assumes that you only have a 32 A cooker max load (40 A would perhaps be more common):

 

1 off ring final circuit rated at 32 A (house) =  10 A + 50% of (32 A - 10 A)  = 21 A

 

1 off radial power circuit rated at 16 A (studio) = 10 A + 50% of (16 A - 6 A) = 13 A

 

2 off lighting circuits rated at 6 A, (one in house, one in studio) = 2 x 6 A x 66% = 7.92 A

 

1 off Sunamp circuit  at 16 A,  (3 kW heating element, no diversity) = 13 A

 

1 off ASHP circuit rated at 16 A (need to check this, and need power rating of ASHP, no diversity) =  10 A (could be a little less)

 

1 off electric water heater rated at 60 A (48 A appliance load, no diversity) = 48 A

 

1 off cooker circuit rated at 32 A (assumes no socket on cooker outlet) = 10 A + (30% x 22 A) = 16.6 A

 

The sum of all the above, allowing for diversity, comes to = 129.52 A

 

This is way over the 80 A supply limit, and also way over a 100 A supply limit too.

 

There's a fairly strong possibility that the main fuse will get very hot if run at this sort of overload.  It may not actually blow, unless the overload is sustained for a fairly long period, but the possibility is there that it will. 

 

It's also possible that I've made an error in the diversity and maximum demand calculations above. Perhaps one of the electricians here might like to check the maximum demand and diversity calcs above to see if I have ( @ProDave, @Onoff ? ).

 

 

 

[ProDave]

52 minutes ago, JSHarris said:

 

 

Does he know all the other loads you have in this installation, though?

 

Worth checking, as blowing the company fuse is a PITA if it happens (and makes a fair old bang).

If it blows once they will ask all sorts of awkward questions and then replace it.

 

If it blows again they are likely going to ask even more awkward questions and want to see evidence of some changes before they will replace it.

[Roz]

OK so... I went back to our electrician who fitted our outdoor socket and he also says he doesnt have an issue with the shower (he's got our full plans for the house too), however, he said if we go for an immersion tank then we would save ourselves about £100 because of cabling and labour.

 

Although, we'd then pay £350 plus extra costs of the tank (an extra £1-200 compared to instant heater) so we end up paying more. And an immersion tank takes up more space and *could* run out of water. 

 

Also the whole point in getting a sunamp in the main house was because we didnt think we had space for an immersion tank and now  we might be putting one in the workshop again... ?

 

I dont know what to decide. It feels simpler to go with the instant water heater... but also seems against some good advice!

 

EDITED because I got the saving wrong

Edited July 31, 2019 by Roz

[Jeremy Harris]

46 minutes ago, Roz said:

OK so... I went back to our electrician who fitted our outdoor socket and he also says he doesnt have an issue with the shower (he's got our full plans for the house too), however, he said if we go for an immersion tank then we would save ourselves about £100 because of cabling and labour.

 

Although, we'd then pay £350 plus extra costs of the tank (an extra £1-200 compared to instant heater) so we end up paying more. And an immersion tank takes up more space and *could* run out of water. 

 

Also the whole point in getting a sunamp in the main house was because we didnt think we had space for an immersion tank and now  we might be putting one in the workshop again... ?

 

I dont know what to decide. It feels simpler to go with the instant water heater... but also seems against some good advice!

 

EDITED because I got the saving wrong

 

As far as the electrical work is concerned, the Sunamp is near-identical to fitting a tank with an immersion.  The only difference is that a FCU, fused at 3A, has to be connected in parallel with the feed that supplies the heating element, so that there's a fused low current supply for the Sunamp control box.  That's about 15 minutes work and less than £10 in materials, so nowhere near £100.

 

I still cannot see how the installation can be made compliant with the regs with an 11 kW instant water heater.  If your electrician is prepared to ignore the regs and sign off the installation with this fitted, then I'd be inclined to make sure he knows that you will hold him responsible if there are any future overheating or other problems relating to the potentially overloaded incoming supply.

[Roz]

20 minutes ago, JSHarris said:

 

As far as the electrical work is concerned, the Sunamp is near-identical to fitting a tank with an immersion.  The only difference is that a FCU, fused at 3A, has to be connected in parallel with the feed that supplies the heating element, so that there's a fused low current supply for the Sunamp control box.  That's about 15 minutes work and less than £10 in materials, so nowhere near £100.

 

I still cannot see how the installation can be made compliant with the regs with an 11 kW instant water heater.  If your electrician is prepared to ignore the regs and sign off the installation with this fitted, then I'd be inclined to make sure he knows that you will hold him responsible if there are any future overheating or other problems relating to the potentially overloaded incoming supply.

Thanks Jeremy - I think I confused things by talking about the Sunamp, as the quote wasnt related to that as the sunamp is going in the main house. I just meant we were trying to avoid immersion heaters taking up space on the property in general, which was what led us down the path of the sunamp, and now we might end up with an immersion heater anyway 

 

That probably didnt clear anything up... sorry I'm a rambler

 

If it helps the attached are our electrical plans... we are probably going to reduce the number of downlights by a fair amount but used this to get quotes.

 

How difficult would it be to bury an insulated pipe between house and studio (about 6m) to just use hot water from the sunamp in the house?  We could get the sunamp early and put it in the studio until we are ready to move it (or leave it there). I think you (or someone on buildhub) might have even suggested this to me when we were talking about just having an ASHP and immersion heater. 

[Jeremy Harris]

Changes to the lighting have near-zero impact on the overall maximum demand, as a 6 A lighting circuit can run nearly 1,400 W of lighting, which is way more than most houses need (the total lighting demand for our 130m² house, with all internal lights turned on, is about 300 W).

 

Running a 6m length of insulated pipe should be fairly easy, and not too costly, especially if it's just a single insulated pipe.  Perhaps cheapest to just insulated a length of 22mm plastic pipe yourselves, rather than buy the pre-insulated stuff.  This isn't hard to do, I slid insulation over a length of around 4m of 25mm MDPE outside pipe, taped it up then slid it inside a duct to protect the insulation.

 

 

[PeterW]

As this is only running a single shower or tap, I’d be inclined to do as @JSHarris says and install a pipe between the two buildings. 

 

I would go 15mm as that will reduce the flow a little but make the hot water to the workshop a bit quicker to run through. 

 

15mm Hep2O with 25mm of nitrile insulation on it will fit inside a 110mm drainpipe easily and also allow you to chuck something like CAT5 I’m there too rather than the same duct as your power so will help with WiFi or alarms etc. 

 

Would expect the whole lot should be change of £100 for the bits and a days digging. Will need to be ideally below 350mm for frost reasons. 

[Roz]

Thanks both. Maybe this is the best of both worlds as keeps things simple, and doesnt waste space. Just a bit more effort.

 

This seems off topic but is a question emerging from potentially locking in the sunamp earlier than planned, why can't high temperature heat pumps do domestic hot water directly? As in, not using a tank, or a sunamp. Is it because of flow rate?

 

 

Edited July 31, 2019 by Roz

[PeterW]

1 minute ago, Roz said:

This seems off topic but is a question emerging from potentially locking in the sunamp earlier than planned, why can't high temperature heat pumps do domestic hot water directly? As in, not using a tank, or a sunamp. Is it because of flow rate?

 

Flow rate on a heat pump is really low - 3-6 litres per minute at most - and they also only increase the temperature by a small amount each time. You would need a heat pump the size of a combi boiler (24kw upward) to try and do anything like a combi and that could be north of £12-15k plus a 3 phase supply...

[Roz]

3 minutes ago, PeterW said:

 

Flow rate on a heat pump is really low - 3-6 litres per minute at most - and they also only increase the temperature by a small amount each time. You would need a heat pump the size of a combi boiler (24kw upward) to try and do anything like a combi and that could be north of £12-15k plus a 3 phase supply...

Ah haha thanks! I can stop wondering now.

[Roz]

Thanks everyone for your help. Now thinking of just ordering the sunamp from bublshop (are they the only off the shelf shop?), brings up some questions I've had lurking in my mind for a while.

 

When going through the sunamp recommended installer down here, they mentioned that we could get a high temperature heat pump that heats at 62 degrees, and that they are talking to sunamp about whether they will update their controller software to allow the sunamp to charge a couple of degrees less than it does at the moment. I saw one of these heat pumps on ebay but wasnt ready to commit to the idea, but if I see one again, is this a legitimate thing? Can sunamp actually just update their software? It's not about the actual material not changing state until the exact temperature?

 

He said we could get everything now and if sunamp update their software we can just update it in the future to make them work. 

 

My second question is, is the mains electricity charged sunamp the same as the one that can be charged by a heat pump?  

 

p.s. sorry this is segwaying a bit, but I didnt want to mess up other threads

Edited August 1, 2019 by Roz

[Jeremy Harris]

9 minutes ago, Roz said:

Thanks everyone for your help. Now thinking of just ordering the sunamp from bublshop (are they the only off the shelf shop?), brings up some questions I've had lurking in my mind for a while.

 

When going through the sunamp recommended installer down here, they mentioned that we could get a high temperature heat pump that heats at 62 degrees, and that they are talking to sunamp about whether they will update their controller software to allow the sunamp to charge a couple of degrees less than it does at the moment. I saw one of these heat pumps on ebay but wasnt ready to commit to the idea, but if I see one again, is this a legitimate thing? Can sunamp actually just update their software? It's not about the actual material not changing state until the exact temperature?

 

He said we could get everything now and if sunamp update their software we can just update it in the future to make them work. 

 

My second question is, is the mains electricity charged sunamp the same as the one that can be charged by a heat pump?  

 

p.s. sorry this is segwaying a bit, but I didnt want to mess up other threads

 

 

Unfortunately the issue with charging the hot water Sunamp from a heat pump has little to do with the controller or its software, it's a fundamental physical issue with the phase change material that it uses to store heat.  This has a transition temperature of 58°C, but needs to be uniformly heated to about 65° (or a bit more) in order to ensure all the solid has melted to liquid.  I suspect that your electrician probably doesn't understand how the Sunamp works, which isn't surprising, as it is a novel product.

 

The electrically heated Sunamp is much the same as the hot water heated one, it differs by having an electric heating element in the base, in addition to the heating heat exchanger.  This has two effects; it allows the PCM material to be directly heated, much like an immersion heater heats a hot water cylinder, and it allows both heat exchangers to be plumbed together in parallel, which increases the instantaneous heating power a bit.

[Roz]

20 minutes ago, JSHarris said:

 

 

Unfortunately the issue with charging the hot water Sunamp from a heat pump has little to do with the controller or its software, it's a fundamental physical issue with the phase change material that it uses to store heat.  This has a transition temperature of 58°C, but needs to be uniformly heated to about 65° (or a bit more) in order to ensure all the solid has melted to liquid.  I suspect that your electrician probably doesn't understand how the Sunamp works, which isn't surprising, as it is a novel product.

 

The electrically heated Sunamp is much the same as the hot water heated one, it differs by having an electric heating element in the base, in addition to the heating heat exchanger.  This has two effects; it allows the PCM material to be directly heated, much like an immersion heater heats a hot water cylinder, and it allows both heat exchangers to be plumbed together in parallel, which increases the instantaneous heating power a bit.

Thanks Jeremy. This was actually the sunamp recommended installer (that charges £600) who said this.... I do think they are quite new to sunamp too but still. He said he was waiting on sunamp to confirm whether they would/could.

 

So you can't buy the electrically heated sunamp and then connect it to an ASHP later (this is what the installer suggested)? Can you connect it to solar pv later?

Edited August 1, 2019 by Roz

[Jeremy Harris]

18 minutes ago, Roz said:

Thanks Jeremy. This was actually the sunamp recommended installer (that charges £600) who said this.... I do think they are quite new to sunamp too but still.

 

So you can't buy the electrically heated sunamp and then connect it to an ASHP later (this is what the installer suggested)? Can you connect it to solar pv later?

 

That doesn't bode well, if a Sunamp installer doesn't understand the fundamental principles of the product.  It was something I picked up very early in the short, on the 'phone, "training" session I had with Sunamp, along with another related factor, which is that a part of the storage capacity of the Sunamp comes from the temperature at which the liquid phase change material is held, which is well above the phase transition temperature.

 

In theory you should be able to buy and install an electrically heated Sunamp and then change it to a hot water heated one later, as the electrically heated unit will have the water heating heat exchanger fitted.  The controller may need changing, but I suspect not, as the electrically heated version has both a power relay to switch the heating element on and off and a smaller relay that can provide a call for heat signal to a boiler.  I've not looked at this in detail, but from the wiring manual, and from a look at the way the controller is internally wired, it seems possible to just connect the heating heat exchanger to the flow and return from a boiler and then use the dry contacts in the secondary relay to turn the boiler on and off as required. 

 

The only word of caution I'd express is that Sunamp have made several changes to their controller specification and configuration, so the above is based on what's actually in our controller (which is around 3 months old) and may or may not be what's available now.  Having said that, I can't see any reason why a relay couldn't be connected to the heating output connections, together with a changeover switch, so that the Sunamp could then be used either with electric heating or with heating from a boiler, assuming that the input heat exchanger is plumbed to the boiler flow and return.  In all probability the small signalling relay that's in our controller will be in all the new controllers, though, as I get the feeling that Sunamp have been trying to standardise on them a bit.

[Roz]

5 minutes ago, JSHarris said:

 

That doesn't bode well, if a Sunamp installer doesn't understand the fundamental principles of the product.  It was something I picked up very early in the short, on the 'phone, "training" session I had with Sunamp, along with another related factor, which is that a part of the storage capacity of the Sunamp comes from the temperature at which the liquid phase change material is held.

 

In theory you should be able to buy and install an electrically heated Sunamp and then change it to a hot water heated one later, as the electrically heated unit will have the water heating heat exchanger fitted.  The controller may need changing, but I suspect not, as the electrically heated version has both a power relay to switch the heating element on and off and a smaller relay that can provide a call for heat signal to a boiler.  I've not looked at this in detail, but from the wiring manual, and from a look at the way the controller is internally wired, it seems possible to just connect the heating heat exchanger to the flow and return from a boiler and then use the dry contacts in the secondary relay to turn the boiler on and off as required. 

 

The only word of caution I'd express is that Sunamp have made several changes to their controller specification and configuration, so the above is based on what's actually in our controller (which is around 3 months old) and may or may not be what's available now.  Having said that, I can't see any reason why a relay couldn't be connected to the heating output connections, together with a changeover switch, so that the Sunamp could then be used either with electric heating or with heating from a boiler, assuming that the input heat exchanger is plumbed to the boiler flow and return.  In all probability the small signalling relay that's in our controller will be in all the new controllers, though, as I get the feeling that Sunamp have been trying to standardise on them a bit.

Yes, he said he was waiting on sunamp to confirm whether they would/could do it but it was his understanding that it would be fine.

 

So is this the one I want to be able to electrically charge it? http://www.bublshop.co.uk/sunamp-uniq-e-hw-hot-water-store-heat-pump-pv-model/p2038

 

OK thats interesting. It's actually less likely that we'll get a high temperature heat pump (that is high enough for the sunamp) than it is that we will get solar electricity panels in the future. But it would be OK to connect solar panels at a later date too? 

 

[Nickfromwales]

Hi @Roz

Reading through this screamed STOP! with the uber-complex electric inline heaters etc / CU upgrade / faff / more faff / crap flow rate etc, and begs for a hot feed to be taken from the ( already going to be there any way, wink wink ) SA unit in the house. 

I’d put a hot return circuit in too, timed or switched on with occupancy. A really well insulated pipe run would have negligible heat losses ( some on here say that would be excessive, I say not ) so pursue the hot feed from the house route with both hands. 

As @PeterW says, run a 110mm pipe and terminate it above DPC level both ends so water cannot get in and fill it. Buy a coil of 15mm Hep2o and a cool of 10mm Hep2o and run those two inside one piece of 25mm wall 22mm internal diameter pipe insulation and tape both along the seam, and around the pipe ( mummify it ). To clarify, the 15 and 10mm pipes sit tight together inside the same single piece of insulation. 72mm total outside diameter, and you’ll still have room for a cat6, a 5-core flex for signal ( switch for the hot return ) and an uninsulated cold 15mm Hep2o pipe too. 

Trench / duct / pipe pull can be done in a day. Back fill the trench after you’ve tested the plumbing for leaks, but tbh with continuous runs from house to studio you’d have to have done something very wrong to have any issues. 

Beef the SA unit up to a size 12, you’d need a size 9 minimum anyway, and it only adds £300 to upsize ), go onto Octopus Energy, get 5p / p / kWh from 00:30 to 04:30 and heat the size 12 unit once a day. Cheaper than burning natural gas, no maintenance/ inspection, and will massively reduce fatigue on the boiler. 

You could actually just go for a heat only / system boiler, and use that to top up, but I’d not do that if it were me. I’d keep both heat exchangers in the SA for DHW to max the flow rate out as you’ll then have a few outlets requiring DHW from the one SA unit. 

Sorted. 

 

[Jeremy Harris]

The model we have is the eHW, but the 9 kWh version, which is OK for just the two of us.  I suspect the tiny little 3 kWh version won't be anywhere near big enough for you, as it's really only suitable for supplying a low usage requirement, like just hot water to taps and basins.  It won't be able to deliver enough hot water for a shower or bath (might just manage one quick shower before it runs out).

 

Contrary to what @Nickfromwales says, we've found that the 9 kWh version is plenty big enough for the two of us, with enough spare hot water to allow an evening bath as well as two morning showers.  As a rule of thumb I've found that a single shower takes about 3 kWh worth of hot water, a bath much the same (unless it's a large bath), so for normal use of two showers a day the 9 kWh version is about 50% over-sized.  Given that it can be charged from the mains in about 3 hours this seems to be an adequate margin to me.

[Nickfromwales]

A size 9 unit ( ~10.5kW actual ) lends itself to managing your DHW water use and deciding how / when you have to boost it with grid. 

My proposal to go to a size 12 unit ( ~14kWh actual ) will have much more space to store energy, allow for the drain from the HRC, and guarantee that you’ll be fine to charge once a day from low rate electricity ( allowing you to downscale the size of your intended PV array too ). At 5p/ unit with Octopus, plus the ( iirc ) 5.2p export tariff ( available now ) this would work out the best bang for your buck. 

 

PV won’t cut it all year round, but grid is constant ( at least as long as the supplier is in business ) but consumer deals for buying electric should get better with EVs becoming more popular ( or even mandatory ) and suppliers having to lend themselves to more sensible ( dare I say ‘consumer friendly’ tariffs. 

 

Having additional headroom in the capacity of the SA also means more energy can be harvested in times of plenty, for use when maybe the PV output the following day is poor. £300 well spent imho, as you’re paying for the smaller unit and installation anyway.

 

When given this option a lot of people are going for it. Cheaper than lithium storage and a much longer lifespan / near zero service & repair, so economics wise, for dumping excess PV or load-shifting,  a good option afaic.