DIY Thermal Store

[sirocosm]

Happy New Year!

This post is for anyone interested in researching options for a DIY thermal store.

Parts list:
£430 300l standard Telford buffer, comes with dual stat, TPRV, 3kW electric immersion
£145 Nordic Tec Ba-23-40 165kW plate exchanger with insulation
£52 FS-05 flow switch 22mm compression
2 x £50 for Grunfos Alpha 2 pumps used from eBay.

Pipe and fittings.

The Telford tank is stainless, and has two 22mm connections at the top on the side, one 1/2" at the very top, two 22mm on the side at the bottom, two stat pockets towards the bottom, a TPRV, and a spot for an immersion heater which is included with the tank. It would have been nice to be able to fit a top and bottom thermometer, and to have one or two connections half way up. Other than that, it seems pretty nice, and is reasonably well insulated, with a modern looking white cover.

The boiler is controlled by the cylinder stat, and the radiators are all controlled by TRVs, with the smart pump supplying more flow when more are open. There is no house stat.

The 165kW plate exchanger works well with the tank stat set to 60C in winter, although we don't have such a great pressure (2.2bar) or flow rate (10 liters/minute) so YMMV. We no longer run out of hot water, although our previous vented cylinder was much smaller at 120 liters. The boiler no longer cycles constantly when the heating is on.

Control wise it is very simple, just a simple cylinder stat controlling the boiler, although it should work well with smart TRVs as each rad is essentially its own zone. It is very easy to control the temperature in each room.

Attached is the system layout.

 

[UtopianRob]

Hi Sirocosm,

Nice Diagram - Thanks!

Could you tell me more about the Smart Pump? e.g. gve an example of what you mean please?

I've got a wood stove backboiler > heat store setup and I need to fit a simple CH radiator circuit pump and controller for just 3 room rads (plus one in bathroom).

SO I think I could really use a smart pumping approach..e.g....during demand, modulating flow rate or actually triggering short on/off cycles when return temp or back pressure indicate TRVs are all closed.... Is that what you mean by 'Smart Pump'?

Any help appreciated!

Cheers

Rob

 

[sirocosm]

I use Grundfos Alpha 2. Sometimes they are called variable speed or modulating pumps. They are not on/off, but rather they continuously ramp up/down depending on the resistance from the TRVs. You set them for a fixed pressure, and when TRVs open up, they pump more. They go down to a few watts when all the TRVs close. The other nice thing about the modulating pump/TRV systems is that it is always on, you don't need a room thermostat, so the rads are not constantly cycling between cold and hot. They get up to the temperature required to keep the room warm and stay there.

 

[Alwhit]

Hi. Resurrecting this thread to ask how you got on with this project? I’m about to do the same. I had planned on a Gledhill Torrent but at £1300 I decided a diy approach was worth a shot and could avoid the over-complicated circuits that Gledhill have. Any tips?

I’d planned to use the same PHE that gledhill use as there are plenty on eBay, and found a suitable flow switch. I intend to copy the connection heights for various from the gledhill spec sheet. Just running a solid fuel stove with no standard boiler.

 

[sirocosm]

The store is working well and has been trouble free. I chose the Nordic Tec 165kw exchanger because it is fairly large, and we didn't want to run the tank too hot, 60-65C. I had read reports that the Gledhill needs to be run considerable hotter than that to get decent hot water output. The Nortic Tec 165kw has .92 square meters exchange area, but I am not sure how that compares to the Gledhill.

The good thing about building it yourself is you can use commonly available parts, and if something goes wrong you can repair it yourself, and you can change it if you need to. For example if the exchanger turns out to be too small, you could just add another one in series. You could also add another tank if you want more buffer with the solid fuel.

For tips, make sure you add valves to isolate the HW exchanger and the rads for maintenance, draining the tank is expensive because it takes a lot of inhibitor. Don't put valves in the stove circuit though, you don't want someone accidentally turning those off. I also put in a lot of temperature gauge pockets in the pipework so I could monitor temperatures. Be sure to install a filter.

We hooked up the electric immersion heater for backup in case the boiler dies, but so far I have never used it.

 

[Alwhit]

Brilliant, thanks. I’ve got a 170L megaflo cylinder to convert. It’s as tall as I can go so may well put another buffer in if I need it. Great tips on the other bits, thanks. I’ll go for a Nordic tec too then I think.

The immersion on ours will be divert from our PV panels so should easily get it to temp in summer.