Hi,I’d love some advice if possible. I have a NIBE 1255 which only has a 180liter internal tank. If running on eco, it takes too long to reheat the water after the kids baths before us adults can have a bath in the evening. The pump will give 30 minutes to the central heating and 30 mins to the DHW. If i change the ratios it can get too cold in the house. To that end I have got myself a 4 year old 250l steel unvented cylinder. This will allow me to buffer more hot water in the afternoon whilst we are not at home off the economy 10. As a bonus I can use the 5kw solar pv to save money during the day as well.
I have come up with a few plumbing schemes but the problem I have come across is the control valves. Ideally I’d like to use some central heating valves but my research has come up with the following problems.
1. How important is the WRAS certification? We do use the water to preheat the kettle and cooking in the pans. None of the central heating ones seem to have the certification.
2. Corrosion in the drinking water circuit seems to be more of a thing. Ie can’t use central heating pumps for Destratification. Would using 3 port valves be an issue on this front if not a problem for point 1.
I have links to three diagrams. They have the tanks in serial with extra plumbing to allow shifting the water from one tank to the other. I haven’t drawn in the mixer valve to the house. In order of preference I have
Setup 1.
https://ibb.co/rxGNWFT. This uses central heating three port valves to direct the water in either direction. Ie in winter hot water from the top of the nibe tank to the top of the 250l. In the summer hot water from the 250l tank could be shunted to the NIBE internal tank. Allows maintaining stratification in either direction.
Setup 2.
https://ibb.co/yqgWrkX Uses expensive solenoid wras valves to shut of pipe work not required outside of pumping. This allows efficient moving of water when heating using the NIBE. I can’t seem to find any reasonably priced motorised valves with WRAS certification.
Setup 3.
https://ibb.co/SRc0Htp No valves. Uses a hot water circulator. The problem with this is I wouldn’t be able to maintain stratification and I would end up heating warmer water at the bottom of the NIBE resulting in reduced COP.
To head off the inevitable points, I’ve left out fittings required for unvented cyclinders as I am focussing on the control side. I am also having a qualified plumber doing the install as I am not qualified.