Bramco Posted February 28, 2022 Share Posted February 28, 2022 Hi, I'm sure I read a post some time ago about companies that do bespoke DHW tanks. I think we might need one... We will have solar PV with diversion and need a tank with 2 immersions, so that we can divert into the middle immersion first and then when that has taken all it can to an immersion in the bottom of the tank. If I look at the direct tanks with 2 immersions, they are all configured like this. We intend to try and manage with Solar PV diversion and cheap rate electricity for the UFH and DHW but may need to install an ASHP in the future. The ASHP tanks all seem to have the bottom immersion above the coil for the ASHP and some have them at least halfway up the tank which would be useless for the diversion scenario above. None of the cylinder suppliers seem to cater for what we need. I'm sure I've read somewhere on here about a companies that can do bespoke cylinders but I can't find the thread. Any help/pointers, much appreciated. Simon Link to comment Share on other sites More sharing options...
ProDave Posted February 28, 2022 Share Posted February 28, 2022 Telford will do what you want. Talk to Trevor at Cylinders 2 Go 1 Link to comment Share on other sites More sharing options...
dpmiller Posted February 28, 2022 Share Posted February 28, 2022 as will World Heat. 1 Link to comment Share on other sites More sharing options...
Bramco Posted February 28, 2022 Author Share Posted February 28, 2022 Thanks @ProDave@dpmiller I think I've found one as standard though - Worcester Bosch indirect - but only on the larger tanks - 250l and 300l. See image below. The only issue might be the coil - does the coil need to be longer/have a greater surface area for ASHPs over standard boilers? Simon Link to comment Share on other sites More sharing options...
dpmiller Posted February 28, 2022 Share Posted February 28, 2022 what's the spec of the coil? ASHP ones do tend to be bigger I'd be surprised if WB aren't adding a premium to the price too... Link to comment Share on other sites More sharing options...
Bramco Posted February 28, 2022 Author Share Posted February 28, 2022 1 hour ago, dpmiller said: I'd be surprised if WB aren't adding a premium to the price too... More than likely.... 1 hour ago, dpmiller said: what's the spec of the coil? ASHP ones do tend to be bigger On the 300l tank it is 0.86 surface area, capacity 4.75l and 21kW Not sure what an ASHP one would be. But the WB solar cylinder which has 2 coils, has an identical coil for solar. Simon Link to comment Share on other sites More sharing options...
dpmiller Posted February 28, 2022 Share Posted February 28, 2022 my WH cylinder has coils which are 3m2 and 42kW... Link to comment Share on other sites More sharing options...
Bramco Posted February 28, 2022 Author Share Posted February 28, 2022 1 hour ago, dpmiller said: my WH cylinder has coils which are 3m2 and 42kW... Which I guess is fine if you have a large gas boiler. But the ASHP we were looking at installing if the experiment of doing things just on off peak electricity would only be 7kW. This is about the same as the 2 immersions, so wouldn't heat the water up any faster. Also, if I've done the sums right, heating 300l up from 20C to 45C would require about 8.75kWs, so would be done in 1.5 hours with 6kW of immersion heaters (or Willis heaters). Even to get to 65C would only take 2.5 hours. Which given the tank it will normally be at about 45 to 50 means that the recharge time won't be ridiculous. Time will tell though, we'll measure the heck out of things when they are installed and adapt our strategy from there. Having said all that and thinking about things as I type, I wonder what on earth 42kW means in terms of the cylinder coil? I'm assuming it means it can deliver 'up to' 42kW depending on the temperature difference and the ability of any boiler/heat source to deliver that amount of heat. Simon Link to comment Share on other sites More sharing options...
dpmiller Posted February 28, 2022 Share Posted February 28, 2022 remember that with an ASHP you're working with less differential between coil and tank contents which pushes the requirement for a bigger transfer area Link to comment Share on other sites More sharing options...
Bramco Posted March 2, 2022 Author Share Posted March 2, 2022 On 28/02/2022 at 17:02, dpmiller said: remember that with an ASHP you're working with less differential between coil and tank contents which pushes the requirement for a bigger transfer area Yes, a bit more digging and it looks as though the WB wouldn't really have enough surface area on the coil. I found a site somewhere that said 0.2m2 per kWh which might be useful for anyone else thinking about this. Newark have an interesting page on their site -> https://newarkcylinders.co.uk/solar-hp-cylinders.html which says the same as you and specs their HP coil at 3.42m2 which is more like some others we've looked at. They will also do the dual immersion heaters that we need. So we'll investigate prices with them. Simon Link to comment Share on other sites More sharing options...
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