Quantum Dimplex Night Storage Heater Won't Charge at Max Rate

Hey ​@martinwinlow,

That's a great suggestion from BPLightlog. It sounds like the dynamic charging calculations might be a bit off, which could lead the heaters to think they don't need to charge as much. If adjusting things isn't straightforward, it might be worth trying a full reset. Dimplex will probably suggest that when you reach out to them. I know it can be a hassle to get everything set up again, but when you call Dimplex, you can let them know, "Here’s my issue and here’s what I’ve tried." 

We’d really love to hear what Dimplex suggests as a solution. Many Dimplex customers on our forum are looking for help and your experience might just guide someone else who’s facing the same situation. Thanks for keeping us in the loop!.

Thanks to ​@Peter E ​@BPLightlog & ​@Firedog for the support on the thread. 

I'm still going with my original thought that the xx050xx in the number relates to the spec that says it has a 500W storage heating element. The xx100xx has a 1,000W element and so on up the range. I'm thinking that any power shown above 500W is additional, non-storage (immediate) heating. That heater is the smallest one in the range.

The reply from Dimplex will be interesting though.

Peter

I’m not sure I’d agree. The Dimplex Quantum brand has been around for quite some time, and I think the model designation has always included an indication of the nominal power output.
  

From 08_83324_0-3 QMRF Online G13 23-023.pdf

My own bog standard Dimplex QM150 allegedly delivers 1500W when it’s going full tilt. As a model designed for Economy 7, it takes 7 hours to charge up and 14 to release its maximum nominal capacity of ~21kWh. The heating element(s) tot up to about 3300W. 

It’s been normal practice for as long as I’ve noticed for electric heaters to be described by their heat output in kW - 1 bar = 1 unit:
 

I was thinking that the input rating had to do with the maximum possible power it could take under the worst conditions for circuit loading calculations. That's not the same as what it's designed to store (it has a 500W storage element) which is a lot less. My best guess. Given that the user wants to store energy during the EV discount rate then I would say that this is the important factor. 

I think we’re running into a spate of terminological inexactitude. This is my understanding:

• Input rating is the appliance’s maximum power draw, in this case 1020W. On a half-hourly usage chart, you’d expect to see bars up to 0.51kWh high for as long as the heater was charging (plus, of course, any background load).
    

  

   

• A heating element is a resistive load intended to convert electrical energy to heat. A 500W element would deliver 0.5kW of heat when connected to a 230V supply.
• Storage here refers to the bricks that are heated up by the heating elements. The current euphemism for these bricks is ‘storage cells’, of which the QM050RF has 4 x 3. Each cell is thus apparently designed to store 0.6kWh when fully charged. 12 x 0.6 = 7.2kWh.  

Thus ‘A 500W storage element’ doesn’t make much sense to me, but then I am a bear of very little brain … 

… and the desire to get the most out of of cheaper electricity overnight is just as strong whether it’s used to charge storage heaters or EV batteries.

I do agree with you. A QM150 heater (yours) will have storage heating elements of 1,500W and your chart shows that. A QM100 heater will have storage heating elements of 1,000W. A QM050RF will have 500W of storage heating elements although ​@martinwinlow’s chart is showing 717W of power consumption which I'm taking to be 500W of storage heating plus 217W of immediate (non-storage) heating (possibly) plus fan if one is fitted to the RF variant. A conversation with Dimplex may resolve that.

And you are right. 500W of storage heating doesn't make sense except for heating a very small room or as part of a much larger system with a number if such units distributed around the property of which we know very little about.

Peter E - The only (logical) problem with your comment (IMO) is that the QM50 is designed for trad Eco7 tariffs (ie 7 hours of ‘charging’ time) and 7.2kWh of storage (max) would need 7 hours at ~1kW, not 7 hours at 500W… I will ring Dimplex shortly...

I agree that you need a conversation with Dimplex. The spec sheet is quite ambiguous with regards to what it says in terms of storage and heating capability. You could interpret the 500W as the maximum rate of heat you can extract from the storage element or it could be an electrical rating. In which case I agree that 717W appears to be anomalous.

On the other hand ​@Firedog’s observation that his QM150 units taking 1,500W is entirely consistent that his 1500W rating is electrical not heating. I'm joining Noel in the group of people who are confused. Hi Noel! Room for another one?

Peter

Errr … Not quite, I think. The screenshot of my half-hourly bar chart shows that my QM150 is taking ~1.5kWh per half-hour. The power draw it thus ~3.0kW. 

The model designation gives the nominal output, so a QM050 is designed to deliver 0.5kW. To maintain this level over 14 hours would require a stock of 7.0kWh, neatly matched by the nominal storage quantity of 7.2kWh. 

To amass 7.2kWh over [Economy-] 7 hours would demand a power draw of 7200/7  = 1030W, again neatly matched by the spec’s 1020W (max) input rating.

The electrician is chiefly interested in this 1020W input rating. The heating engineer is much more concerned with the other rating, the nominal output of 500W.

Unless Martin has some configuration setting to limit the power draw, I’m inclined to suspect that only two of the three elements are actually working as he’d like them to (1020 x 2/3 = 680W, not far off the observed ~700W draw (4.217kWh / 6h = 703W).

Join the club. Discombobulation is our aim! 

Just spoke to Dimplex Technical (0344 879 3586, BTW) and they took my email address to send me an expanded explanation of the more abstract aspects of the Quantum’s specs and features as well as a form to fill in to get to the bottom of my issue.  I will report back in due course.

Meanwhile, having had a bit to do with Sunamp heat batteries (I have recently installed a Thermino Xplus 150) I have been wondering why it is that Dimplex and other night storage heater manufacturers are not yet using phase change material (PCM) technology for their heaters. I started by doing a comparison of volumetric heat energy capacity of; the sodium acetate used by Sunamp’s heat batteries, Dimplex's ‘heat cells’ and water (and threw in volumetric energy density of decent lithium ion batteries for good measure)….

Volumetric energy density of Li-Ion Battery: ~500Wh/litre 
Volumetric energy density of Water: 46Wh/litre
Volumetric energy density of PCM: ~90-140Wh/litre
Volumetric energy density of Dimplex bricks: 650Wh/litre

I quickly discovered that it isn't quite as straightforward as this. The main issue as far as PCM is concerned is dealing with the latent heat aspect of how this product works makes things a bit more complicated than water or what is essentially concrete.  But the big takeaway from my comparison was how on earth can concrete have such high energy density compared with the others? And the answer is simply because, unlike water or PCM, there is no limit (-ish) to how hot you can make them in the charging process.

You can compress water and therefore get more heat energy into it but that is less than ideal arrangement for obvious reasons and you can pick a PCM with a higher melting point I guess but not without I imagine a significant increase in the cost and complexity of controlling it all safely. But Concrete… Well you can pretty much fire as much heat at it as you like (within reason) and as a consequence this is why it has such a disproportionately bigger heat energy capacity for a given volume. Obviously, in every case, good insulation is key!