Mini Store - Heat Geek / Newark Cylinders for ASHP

[Beelbeebub]

56 minutes ago, dpmiller said:

 

not everywhere. Mains gas is still quite a new thing in NI and going from a vented tank/ oil boiler/ Willis combo is a steep learning curve for many...

To be fair,.we.had some tenant who moved from a coal fire in each room and immersion to a combi and they struggled with how little they had to do. 

 

At one point they were having issues and it turned out they were leaving it off and turning it on each time they wanted hot water! They complained it was too inconvenient to walk from the bathroom to kitchen to turn the boiler on to wash their hands! 😁 It took a while to impress upon them that they just needed to leave it on and not touch it at all. 

 

 

[JamesPa]

2 hours ago, Beelbeebub said:

For better or worse, the combi is the yardstick. 

 

I don't think people really need actually infinite hot water. They just want to not have to think about it. 

 

They also want the space a big cylinder takes up for other things. 

 

Right now the relatively big cylinder specified by manufacturers and installers is a bit of a barrier. Both in cost and size. 

 

The HG system is a good attempt at making the installation a bit lower friction. 

 

As long as the hot water delivery is good enough - ie the times where the customer has a tepid shower or has to wait 20mins for the cylinder to recharge are very few, then it's a great idea. 

 

A 9kw instantaneous water heater (variable power controlled to just top up the temp if too low) afterwards would extend the hot water delivery time and not fall foul of g3 regs. 

And I think that's the point.  In many cases it's good enough.  Nobody is claiming it's a universal solution and I think we have established that there isn't and won't be one.  

[JamesPa]

54 minutes ago, Beelbeebub said:

To be fair,.we.had some tenant who moved from a coal fire in each room and immersion to a combi and they struggled with how little they had to do. 

 

At one point they were having issues and it turned out they were leaving it off and turning it on each time they wanted hot water! They complained it was too inconvenient to walk from the bathroom to kitchen to turn the boiler on to wash their hands! 😁 It took a while to impress upon them that they just needed to leave it on and not touch it at all. 

 

 

That's hilarious.  Perhaps you need to fit placebo controls

[SimC]

I would be interested for thoughts on using one of these to convert from a vented hot water cylinder fed by a system boiler via a 3-port diverter valve to a hot water system under mains water pressure.

 

Presumably it avoids the full G3 requirements as the hot water coil must contain less than 15 litres volume within the pressurised circuit from non-return valve to closed hot water taps. Does the G3 requirement for a pressure/temperature relief valve and associated drainage then go away?

 

I already run the boiler at around 50C flow temp for heating, then turn up to around 70C on 1 day per week to heat the full tank for bath day. The remaining 6 days use an Eddi plus immersion for night/solar hot water heating of just the top half of the tank which is sufficent for showers and washing up. Presumably with the MiniStore the boiler flow temp would not need to be so high, and the 15 kW boiler would be able to provide enough top up to be able to fill a bath. The current hot water cylinder is approx 1100 H x 475 D, the same as the Tall MiniStore.

 

Just trying to think outside the box with immersion backup possible by using a Willis heater connected between the heat source flow and return connections to the MiniStore. The existing boiler system is already vented with expansion up to the loft header tank.

[JohnMo]

8 hours ago, SimC said:

I would be interested for thoughts on using one of these to convert from a vented hot water cylinder fed by a system boiler via a 3-port diverter valve to a hot water system under mains water pressure.

 

Presumably it avoids the full G3 requirements as the hot water coil must contain less than 15 litres volume within the pressurised circuit from non-return valve to closed hot water taps. Does the G3 requirement for a pressure/temperature relief valve and associated drainage then go away?

 

I already run the boiler at around 50C flow temp for heating, then turn up to around 70C on 1 day per week to heat the full tank for bath day. The remaining 6 days use an Eddi plus immersion for night/solar hot water heating of just the top half of the tank which is sufficent for showers and washing up. Presumably with the MiniStore the boiler flow temp would not need to be so high, and the 15 kW boiler would be able to provide enough top up to be able to fill a bath. The current hot water cylinder is approx 1100 H x 475 D, the same as the Tall MiniStore.

 

Just trying to think outside the box with immersion backup possible by using a Willis heater connected between the heat source flow and return connections to the MiniStore. The existing boiler system is already vented with expansion up to the loft header tank.

No G3 requirements for these cylinders.

 

But if you have room for a cylinder use a cylinder. If there is an issue doing the drain side of things for an unvented cylinder, look at a harlequin cylinder, they also require no G3. Or go full UVC but specify a heat pump cylinder, store at lower temperature your boiler will condense throughout the full heating cycle due to the big coil.

[JEH]

I know HeatGeek intend their mini-store to be used with ASHPs but like @JohnMo I'd be very interested in using one to replace my old vented cylinder and gravity fed hot water. I have a new system boiler (Vitodens 100W) but an old cylinder, and I think the mini-store has a load of advantages - not least avoiding the G3 mandatory inspections every year? As I see it, the mini-store is not much different to another radiator zone. Adam at HeatGeek did a test to see if his ASHP could keep a shower going with this tank and it was pretty good but a gas boiler would have no trouble doing that. It would be more efficient to keep a smaller amount of hot water at a temperature close to what we need for a shower - with the boiler condensing at all times when reheating it. There would be less heat loss from a smaller, cooler body of water than a conventional 250L tank at 65°. No chance of Legionella. No immersion heater required, so I can stuff the airing cupboard with insulation that would normally trip the usual thermal cutout. No scorching hot water left in pipes from the tank every time a tap is used. And potable pressurised hot water.

I can't quite get my head around the whole thing but I reckon a mini-store could effectively turn any system boiler into something like a more efficient and capable combi with a giant preheat capacity? Would HeatGeek consider installing such a thing and what would it involve?

[sharpener]

On 27/10/2024 at 00:15, JEH said:

not least avoiding the G3 mandatory inspections every year

 

AFAICS it is an urban myth that you need to pay someone to do this. The annual servicing intstructions are in the UVC manual and the little that needs doing you can do yourself: clean the strainer, check the pressurisation and test all the controls and the two relief valves.

[PhilT]

On 27/10/2024 at 00:15, JEH said:

I know HeatGeek intend their mini-store to be used with ASHPs but like @JohnMo I'd be very interested in using one to replace my old vented cylinder and gravity fed hot water.

 

I can't quite get my head around the whole thing but I reckon a mini-store could effectively turn any system boiler into something like a more efficient and capable combi with a giant preheat capacity? Would HeatGeek consider installing such a thing and what would it involve?

I would also very much like to get rid of ghastly tank in loft. I have a heat pump but the 2nd video in the original post specifically refers to a gas boiler application at 09:00

[JamesPa]

On 27/10/2024 at 00:15, JEH said:

I know HeatGeek intend their mini-store to be used with ASHPs but like @JohnMo I'd be very interested in using one to replace my old vented cylinder and gravity fed hot water. I have a new system boiler (Vitodens 100W) but an old cylinder, and I think the mini-store has a load of advantages - not least avoiding the G3 mandatory inspections every year? As I see it, the mini-store is not much different to another radiator zone. Adam at HeatGeek did a test to see if his ASHP could keep a shower going with this tank and it was pretty good but a gas boiler would have no trouble doing that. It would be more efficient to keep a smaller amount of hot water at a temperature close to what we need for a shower - with the boiler condensing at all times when reheating it. There would be less heat loss from a smaller, cooler body of water than a conventional 250L tank at 65°. No chance of Legionella. No immersion heater required, so I can stuff the airing cupboard with insulation that would normally trip the usual thermal cutout. No scorching hot water left in pipes from the tank every time a tap is used. And potable pressurised hot water.

I can't quite get my head around the whole thing but I reckon a mini-store could effectively turn any system boiler into something like a more efficient and capable combi with a giant preheat capacity? Would HeatGeek consider installing such a thing and what would it involve?

So far as I can see its going to work with a gas boiler, as would a conventional thermal store (which also doesn't need G3).  

 

The reason UVCs are preferred for ASHPs over thermal stores are that, for any given stored water temperature/volume combination, you will get much more DHW from a UVC.  With an ASHP you want to keep the flow temperature (and thus the stored water temperature) low, so a UVC is the obvious way to go.  Gas boilers are typically run at a higher FT (although in fact also perform better if run at FT of 55 or less), so a thermal store becomes a more realistic possibility.

 

In performance terms the Heat geek mini cylinder is a bit 'in between'.  Because it has a large coil the temp difference between the stored water and the output DHW is less (so you get more DHW than with a typical thermal store that has a smaller coil).  Furthermore there is no temperature difference between flow and 'stored' water, because the 'stored' water is actual water from the central heating system.  Yet more it is designed to be used with real time re-heat (so again you get more DHW than with a thermal store).  None of this is enough to make its yield of DHW equal to a UVC of the same size run at the same temperature (unless the DHW is run off slowly) but it still gives a better DHW yield than a conventional thermal store for the window of parameters it is designed to work in.

 

Dont assume however that its a drop in replacement for an existing cylinder, you may have to play with the system controls a bit.

Edited October 28 by JamesPa