Dimplex Quantum storage heaters / Octopus Go Faster tariff

coffeehound

Here's an interesting (depending on your definition of interesting) factoid.  Dimplex state:

Most Dimplex storage heaters can fully charge within 5 hours and the automatic charge calculation may not always take a full charge . .

This is significant as it implies that anyone with properly-spec'd Quantum heaters can swap over to Octopus's Go Faster tariff (subject to it being offered to them, apparently, and them having a suitable smart meter) and still be able to take a full charge, but with much lower off-peak and on-peak unit costs.  This is a bit of a game-changer as the general assumption seems to be that NSHs require their full available off-peak time to store the maximum charge.

Since the newer Lot-20 compliant NSHs can hold onto more heat for longer, the extended interval between charges also shouldn't be an issue, provided the combination of stored charge and perhaps use of direct heaters in the off-peak hours, can meet the dwelling's space heating demand.  Perhaps other manufacturers' NSHs also can take a full charge in five hours.

Since the tariff isn't guaranteed to continue into the future, you wouldn't want to base any big decisions on it, but for households already kitted out with high-heat retention NSHs, it's worth considering for the near term

matelodave

I think you'd have to do some clever sums to ensure that you get sufficient heat stored during the charging period to satisfy the heat demand over the discharge period otherwsie you could find that you are using the boost/back-up heater on peak rate rate leccy to cover the shortfall and lot more than you'd hope.

Not saying that it cant be done but I'd suggest that it requires careful heatloss calculations rather than the "wet finger in the air" guesses than most people make if you want to avoid making a costly mistake.

The amount of charge the heater can take is direclty related to it's storgage capacity and the rating of the element so a 3kw elelemt for seven hours = 21kwh, if you only have 5 hours at cheap rate then it can only store 15kwh despite it's storaage capacity. Although if you assume that there might be some heat still stored, say 5-6kwh, it's feasible that you could top it up to 21kwh within 5 hours, but if it's been cold or you've used boost then you wont fully recharge it. I'd guess that more than a couple of days of cold weather would leave you short of stored heat, requiring peak rate boosts to keep warm

coffeehound

Thanks for your input, @matelodave.  As you say, the NSH cannot take in higher charge than its instantaneous rating allows, so I wonder if this is down to loose English usage and what it should have said is "most Quantum NSHs, in most situations, for most of the year, can achieve the required charge within 5 hours."  Poor form in a technical document if so.  I've asked Glen Dimplex tech services for clarification.

This is then the same discussion as had in another thread recently:  if the NSH is charging to 70% or less during Economy 7 hours, then that same charge could be achieved with a higher charge duty-factor during the reduced 5-hour window (i.e. being switched-on more of the time during that period).   A good thing with a modern NSH is that you tell it the hours available, and it calculates how long it needs to take power for within that window.

Honestly I think this can be treated more with the 'wet finger' approach.  The peak-time Octopus rate is comparable with single-rate tariffs, and the off-peak rate is about half that of typical Economy7 off-peak rates.  So the potential for savings is substantial.   Also Octopus do not charge exit fees, so if one really wanted to go elsewhere, it wouldn't be a problem.

As to the 19 hour interval between charges, the number of hours of required heating each day remains the same.  Perhaps from midnight to 7am there is no heating requirement at all, in which case the NSHs just hold onto their charge.  The SAP calculations, which are intended to mirror the real world, take High Heat Retention NSHs as being capable of retaining 45% of the original heat charge after a full 24 hours.

In the worst case scenario that there was not enough stored charge to last into the evening, then choosing a timing where for example the off-peak rate starts at 8.30pm gives the option to use direct electric heaters in the evening at off-peak rate.

So really for high heat retention NSHs, the potential for savings is high, and the risk of higher costs is low.  

It is the case of old-school NSHs where the decision becomes harder, as discussed in the other recent thread

coffeehound

Here's what GD say

In regards to the charging, yes our heaters can in fact charge fully within 5 hours in most occasions but this does depend on the installation, size and some environmental factors so we do still advise having the economy 7/10 supply available, especially during the winter months when the demand for heat is higher.

DebtFreeDream_2

I have a one bed house and have actually just done this and installed a Dimplex Quantum QM150 to use with the Octopus Go tariff. I’ve set it so it can only charge in the 00:30 – 04:00 time slot.

It has several timers which are pre-programmed, but you can modify them to suit your situation better, for example In all day, Out all day and then one called Timer, which is fully customisable. Each timer can have 4 periods in a day.

What it does is use these timers to evaluate how much of a charge it’s going to need to provide the required heat for the next day. For example, I can see on a day I set it to Out all Day, it used a lot less electricity than on a day I set the timer to In all day.

It's early days, but my house is now nice warm despite the autumn chill, I'm looking forward to how things will work out in the winter.

I think modern storage heaters get a bad press, but modern storage heaters will store energy from whatever time of the day or night you want it to, and from any source like solar. The original Economy7 tariff is probably on its way out, but is being replaced by smart time flexible tariffs that are focused on EVs. It would be great to see a storage heater automatically interact with Octopus’s Agile tariff, like some EV chargers do.

I can also run the QM150 like those Fischer heaters, which are sort of meant to run 24/7 in the back ground. The difference is the Quantum will use the cheap 14Kw of heat it's stored before drawing any peak rate electricity.

coffeehound

Thanks for your post, @DebtFreeDream_2 , it’s very helpful to get real-world experience from owners. 

I did ask GD if they planned to offer integration with Octopus for their cloud control platform, but they said there were no plans at present. Hopefully that will be the future where setting the correct timings is automated. 

Swipe

I'm surprised you have your storage heaters on already but please keep us updated as winter approaches.

JohnSwift10

Swipe said:

I'm surprised you have your storage heaters on already but please keep us updated as winter approaches.

My wife wanted to put the heating on today as she felt cold.
The temperature in the lounge was 19.3 deg C

DebtFreeDream_2

I thought I’d report back as now it’s getting proper cold, the Quantum heater is being put under test. What I have realised is that I will need to add another smaller Quantum heater to my kitchen area (a QM050RF) as the QM150RF is slightly under powered for the open plan kitchen/living room area I’m trying to get it to heat. This isn’t a reflection on the heater, more me trying to save the cost of two heaters.

Anyway, the QM150 is trying to heat a space larger than it is rated for, and 4 hours is nowhere near enough time for it to charge fully overnight to do this. When it was 0 degrees C outside, it needed 6 hours of charging to just keep the room at 19oC for 14 hours, which it did, and I think was actually pretty impressive. It took a lot of timer manipulation to get it to do that though.

It does try to dynamically work out how much of a charge it thinks it’s going to need for the next day, which is one way it saves you money, however in my case this isn’t working out because the room temperature sensor is located somewhere akin to a cold spot, and coupled with the fact the room is too big for it, seems to confuse it and it doesn’t charge enough. I’ve tried every official way to make it charge more, like setting “Additional Charge” to +4 hours, or modifying the “Heat Demand Offset” to plus or minus 50% and giving it up to 12 hours to charge. I even replaced the room temperature sensor. I raised a ticket with Dimplex, not heard back after two weeks though.

Finally though, I’ve turned Slave Mode on, which removes the “cleverness” and just makes it charge for a 100% of the off peak time you set, or until it’s full. It takes it about 7-8 hours to go from 10% to 100%, but any unused heat is stored well, and will naturally reduce the next night’s charge period. This method seems to work much better than it trying to work out what it needs. The laws of thermodynamics take over, and they’re usually right. This all assumes you want it to prioritise it heating your home effectively, and it goes back to working like an old skool storage heater, except it’s massively better at retaining the heat and controlling when it released via the timers and thermostat. Seems like the best of both worlds to me.

I’d also like to add that you can set it to automatically supplement the stored heat with the heater element that runs from off peak electricity. If the stored heat drops below about 50%, it will use this heater element automatically to bring the temperature of the air coming out of the grill to something high enough to heat the room. I think this is one reason why a lot of people complain that their electricity bills have gone up massively. You can turn this off though, but leave it on for the boost function.   

I think the lesson I’ve learnt here is to over spec the heaters I need. Maybe if I had Installed two QM150RF heaters, I could charge them to 50% in 4 hours, and I would get all the heat I would need. I’m not sure though, because when the core is below 50%, the heat it pushes out is at a lower temperature, it works best when the core is above 50%.

EDIT: March 2022
Ok so I found a massive source of cold air in my kitchen area from the service riser that goes all the way up to the loft, and from the wall cavity being exposed under the kitchen worksurfaces. Since blocking these off, my kitchen/living room area is noticeably warmer, and the single QM150RF with 5 hours of charge between 00:30 - 04:30 and 17:00 - 18:00 is keeping down stairs warm at a fairly steady 18-21oC throughout most of the day, and completely warm at 21oC from 5pm - 11pm in the evening. I now plan on getting another QM070RF and putting it on the landing upstairs to help even the heating out. I'm also looking at solar too, it would be great to partially charge the storage heaters from solar during the day for when I get home from work.